DIGITAL TIMING SYNCHRONIZATION WITH JITTER REDUCTION TECHNIQUE FOR CAP-BASED VDSL SYSTEM

Synchronization“Synchronised”redirects here.For the racehorse,see Synchronised(horse).Synchronization is the coordination of events toop-Firefighters marching in a paradeerate a system in unison.The familiar conductor of an orchestra serves to keep the orchestra in time.Systems operating with all their parts in synchrony are said to be synchronous or in sync.Today,synchronization can occur on a global basis through the GPS-enabled timekeeping systems(and sim-ilar independent systems operated by the EU and Russia). 1TransportTime-keeping and synchronization of clocks was a crit-ical problem in long-distance ocean navigation;accurate time is required in conjunction with astronomical obser-vations to determine how far East or West a vessel has traveled.The invention of an accurate marine chronome-ter revolutionized marine navigation.By the end of the 19th century,time signals in the form of a signal gun,flag, or dropping time ball,were provided at important ports so that mariners could check their chronometers for error. Synchronization was important in the operation of19thcentury railways,these being thefirst major means of transport fast enough for the differences in local time be-tween adjacent towns to be noticeable.Each line han-dled the problem by synchronizing all its stations to head-quarters as a standard railroad time.In some territories, sharing of single railroad tracks was controlled by the timetable.The need for strict timekeeping led the compa-nies to settle on one standard,and civil authorities even-tually abandoned local mean solar time in favor of that standard.2CommunicationIn electrical engineering terms,for digital logic and data transfer,a synchronous circuit requires a clock signal. However,the use of the word“clock”in this sense is dif-ferent from the typical sense of a clock as a device that keeps track of time-of-day;the clock signal simply sig-nals the start and/or end of some time period,often very minute(measured in microseconds or nanoseconds),that has an arbitrary relationship to sidereal,solar,or lunar time,or to any other system of measurement of the pas-sage of minutes,hours,and days.In a different sense,electronic systems are sometimes synchronized to make events at points far apart appear si-multaneous or near-simultaneous from a certain perspec-tive.(Albert Einstein proved in1905in hisfirst relativ-ity paper that there actually are no such things as abso-lutely simultaneous events.)Timekeeping technologies such as the GPS satellites and Network Time Protocol (NTP)provide real-time access to a close approximation to the UTC timescale and are used for many terrestrial synchronization applications of this kind. Synchronization is an important concept in the following fields:•Computer science(In computer science,especiallyparallel computing,synchronization refers to the co-ordination of simultaneous threads or processes tocomplete a task with correct runtime order and nounexpected race conditions.)•Cryptography•Multimedia•Music(Rhythm)•Neuroscience124SEE ALSO•Photography•Physics(The idea of simultaneity has many difficul-ties,both in practice and theory.)•Synthesizers•Telecommunication3Uses•Film synchronization of image and sound in sound film.•Synchronization is important infields such as digital telephony,video and digital audio where streams of sampled data are manipulated.•In electric power systems,alternator synchronization is required when multiple generators are connected to an electrical grid.•Arbiters are needed in digital electronic systems such as microprocessors to deal with asynchronous inputs.There are also electronic digital circuits called synchronizers that attempt to perform arbi-tration in one clock cycle.Synchronizers,unlike arbiters,are prone to failure.(See metastability in electronics).•Encryption systems usually require some synchro-nization mechanism to ensure that the receiving ci-pher is decoding the right bits at the right time.•Automotive transmissions contain synchronizers that bring the toothed rotating parts(gears and splined shaft)to the same rotational velocity before engaging the teeth.•Film,video,and audio applications use time code to synchronize audio and video.•Flash photography,see Flash synchronization Some systems may be only approximately synchronized, or plesiochronous.Some applications require that relative offsets between events be determined.For others,only the order of the event is important.4See also•Asynchrony•Atomic clock•Clock synchronization•Data synchronization•Double-ended synchronization•Einstein synchronization•Entrainment•File synchronization•Flywheel•Homochronous•Kuramoto model•Mutual exclusion•Neural synchronization•Phase-locked loops•Phase synchronization•Reciprocal socialization•Synchronism•Synchronization(alternating current)•Synchronization in telecommunications •Synchronization of chaos •Synchronization rights•Synchronizer•Synchronous conferencing•Time•Timing Synchronization Function(TSF)•Time transfer•Timecode•Tuning forkOrder synchronization and related topics•Rendezvous problem•Interlocking•Race condition•Concurrency control•Room synchronization•Comparison of synchronous and asynchronous sig-nallingVideo and audio engineering•Genlock•Jam sync•Word sync3 Aircraft gun engineering•Synchronization gearCompare with•Synchronicity,an alternative organizing principle tocausality conceived by Carl Jung.5References6External links•J.Domański“Mathematical synchronization of im-age and sound in an animatedfilm”47TEXT AND IMAGE SOURCES,CONTRIBUTORS,AND LICENSES 7Text and image sources,contributors,and licenses7.1Text•Synchronization 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英文资料及中文翻译6 TRANSMISSIONS OF DIGITAL DATA:INTERFACES AND MODEMS(From Introduction to Data Communications and Net Working,Behrouz Forouzan)Once we have encoder our information into a format that can be transmitted, the next step is to investigate the transmission process itself. Information-processing equipment such as PCs generate encoded signals but ordinarily require assistance to transmit those signals over a communication link. For example, a PC generates a digital signal but needs an additional device to modulate a carrier frequency before it is sent over a telephone line. How do we relay encoded data from the generating device to the next device in the process? The answer is a bundle of wires, a sort of mini communication link, called an interface.Because an interface links two devices not necessarily made by the same manufacturer, its characteristics must be defined and standards must be established. Characteristics of an interface include its mechanical specifications (how many wires are used to transport the signal); its electrical specifications (the frequency, amplitude, and phase of the expected signal); and its functional specifications (if multiple wires are used, what does each one do?). These characteristics are all described by several popular standards and are incorporated in the physical layer of the OSI model.6.1 DIGITAL DATA TRANSMISSIONOf primary concern when considering the transmission of data from one device to another is the wiring. And of primary concern when considering the wiring is the data stream. Do we send one bit at a time, or do we group bits into larger groups and, if so, how? The transmission of binary data across a link can be accomplished either in parallel mode or serial mode. In parallel mode, multiple bits are sent with each clock pulse. In serial mode, one bit is sent with each clock pulse. While there is only one way to send parallel data, there are two subclasses of serial transmission: synchronous and asynchronous (see Figure 6-1).Parallel TransmissionBinary data, consisting of 1s and 0s, may be organized into groups of n bits each. Computers produce and consume data in groups of bits much as we conceive of and use spoken language in the form of words rather than letters. By grouping, we can send data n bits at a time instead of one. This is called parallel transmission.DataParallel SerialSynchronou AsynchronFigure 6-1 Data transmissionThe mechanism for parallel transmission is a conceptually simple one: use n wires to send n bits at one time. That way each bit has its own wire, and all n bits of one group can be transmitted with each clock pulse from one device to another. Figure 6-2 shows how parallel transmission works for n=8.Typically the eight wires are bundled in a cable with a connector at each end.8 bitSender ReceiverWe need eightFigure 6-2 Parallel transmissionThe advantage of parallel transmission is speed. All else being equal, parallel transmission can increase the transfer speed by a factor of n over serial transmission. But there is a significant disadvantage:cost. Parallel transmission requires n communication lines (wires in the example) just to transmit the data stream. Because this is expensive, parallel transmission is usually limited to short distances, up to a maximum of say 25 feet.Serial TransmissionIn serial transmission one bit follows another, so we need only one communication channel rather than n to transmit data between two communicating devices .The advantage of serial over parallel transmission is that with only one communication channel, serial transmission reduces the cost of transmission over parallel by roughly a factor of n.Since communication within devices is parallel, conversion devices are required at the interface between the sender and the line (parallel-to-parallel).Serial transmission occurs in one of two ways: asynchronous or synchronous.Asynchronous TransmissionAsynchronous transmission is so named because the timing of a signal is unimportant. Instead, information is received and translated by agreed-upon patterns. As long as those patterns are followed, the receiving device can retrieve the information without regard to the rhythm in which it is sent. Patterns are based on grouping the bit stream into bytes. Each group, usually eight bits, is sent along the link as a unit. The sending system handles each group independently, relaying it to the link whenever ready, without regard to a timer.Without a synchronizing pulse, the receiver cannot use timing topredict when the next group will arrive. To alert the receiver to the arrival of a new group, therefore, an extra bit is added to the beginning of each byte. This bit, usually a 0, is called the start bit. To let the receiver know that the byte is finished, one or more additional bits are appended to the end of the byte. These bits, usually 1s, are called stop bits. By this method, each byte is increased in size to at least 10 bits, of which 8 are information and 2 or more are signals to the receiver. In addition, the transmission of each byte may then be followed by a gap of varying duration. This gap can be represented either by an idle channel or by a stream of additional stop bits.In asynchronous transmission we send one start bit (0) at the beginning and one or more stop bits (1s) at the end of each byte. There may be a gap between each byte.The start and stop bits and the gap alert the receiver to the beginning and end of each byte and allow it to synchronize with the data stream. This mechanism is called asynchronous because, at the byte level, sender and receiver do not have to be synchronized. But within each byte, the receiver must still be synchronized with the incoming bit stream. This is, some synchronization is required, but only for the duration of a single byte. The receiving device resynchronizes at the onset of each new byte. When the receiver detects a start bit, it sets a timer and begins counting bits as they come in. after n bits the receiver looks for a stop bit. As soonas it detects the stop bit, it ignores any received pulses until it detects the next start bit.Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same.The addition of stop and start bits and the insertion of gaps into the bit stream make asynchronous transmission slower than forms of transmission that can operate without the addition of control information. But it is cheap and effective, two advantages that make it an attractive choice for situations like low-speed communication. For example, the connection of a terminal to a computer is a natural application for asynchronous transmission. A user types only one character at a time, types extremely slowly in data processing terms, and leaves unpredictable gaps of time between each character. Synchronous TransmissionIn synchronous transmission, the bit stream is combined into longer “frames,” which may contain multiple bytes. Each byte, however, is introduced onto the transmission link without a gap between it and the next one. It is left to the receiver to separate the bit stream into bytes for decoding purposes. In other words, data are transmitted as an unbroken string of 1s and 0s, and the receiver separates that string into the bytes, or characters, it needs to reconstruct the information.In synchronous transmission we send bits one after another withoutstart/stop bits or gaps. It is the responsibility of the receiver to group the bits.Without gaps and start/stop bits, there is no built-in mechanism to help the receiving device adjust its bit synchronization in midstream. Timing becomes very important, therefore, because the accuracy of the received information is completely dependent on the ability of the receiving device to keep an accurate count of the bits as they come in.The advantage of synchronous transmission is speed. With no extra bits or gaps to introduce at the sending end and remove at the receiving end and, by extension, with fewer bits to move across the link, synchronous transmission is faster than asynchronous transmission is faster than asynchronous transmission. For this reason, it is more useful for high-speed applications like the transmission of data from one computer to another. Byte synchronization is accomplished in the data link layer.6.2 DTE-DCE INTERFACAt this point we must clarify two terms important to computer networking: data terminal equipment (DTE). There are usually four basic functional units involved in the communication of data: a DTE and DCE on one end and a DCE and DTE on the other end. The DTE generates the data and passes them, along with any necessary control characters, to a DCE. The DCE does the job of converting the signal to a formatappropriate to the transmission medium and introducing it onto the network link. When the signal arrives at the receiving end, this process is reversed.Data Terminal Equipment (DTE)Data terminal equipment (DTE) includes any unit that functions either as a source of or as a destination for binary digital data. At the physical layer, if can be a terminal, microcomputer, computer, printer, fax machine, or any other device that generates or consumes digital data. DTEs do not often communicate directly with one another, they generate and consume information but need an intermediary to be able to communicate. Think of a DTE as operating the way your brain does when you talk. Let’s say you have an idea that you want to communicate to a friend. Your brain creates the idea but cannot transmit that idea to your friend’s brain by itself. Unfortunately or fortunately, we are not a species of mind readers. Instead, your brain passes the idea to your vocal chords and mouth, which convert it to sound waves that can travel through the air or ov er a telephone line to your friend’s ear and from there to his or her brain, where it is converted back into information. In this model, your brain and your friend’s brain are DTEs. Your vocal chords and mouth are your DCE. His or her ear is also a DCE. The air or telephone wire is your transmission medium.A DTE is any device that is a source of or destination for binarydigital data.Data Circuit-Terminating Equipment (DCE)Data circuit-terminating equipment (DCE) includes any functional unit that transmits or receives data in the form of an analog or digital signal through a network. At the physical layer, a DCE takes data generated by a DTE, converts them to an appropriate signal, and then introduces the signal onto the telecommunication link. Commonly used DCEs at this layer include modems . In any network, a DTE generates digital data and passes it to a DCE; the DCE converts the data to a form acceptable to the transmission medium and sends the converted signal to another DCE on the network. The second DCE takes the signal off the line, converts it to a form usable by its DTE, and delivers it. To make this communication possible, both the sending and receiving DCEs must use the same encoding method, much the way that if you want to communicate to someone who understands only Japanese, you must speak Japanese. The two DTEs do not need to be coordinated with each other, but each of them must be coordinated with its own DCE and the DCEs must be coordinated so that data translation occurs without loss of integrity.A DCE is any device that transmits or receives data in the form of an analog or digital signal through a network.6 数字数据传输：接口和调制解调器（选自«数据通信与网络»，Behrouz Forouzan著）咱们将信息编码成能够传输的格式，下一步确实是探讨传输进程了。

**The Process of Performing**Performing is a multifaceted process that involves preparation, practice, and execution. Whether it is a theatrical play, a musical performance, or a dance routine, the process of performing generally follows several key stages.The first stage is preparation. This begins with understanding the material or the role one is about to perform. For actors, this means analyzing the script and delving into their character's background, motivations, and relationships. Musicians need to familiarize themselves with the score, interpreting the composer’s intentions and understanding the structure of the piece. Dancers often start by studying the choreography and grasping the emotions and themes that their movements need to convey.Next comes practice. This stage involves repeated rehearsal to refine and perfect the performance. Actors rehearse their lines, blocking, and interactions with other characters. Musicians practice their parts individually and with the ensemble, focusing on timing, intonation, and dynamics. Dancers rehearse their routines, working on their technique, synchronization with other dancers, and expressiveness.During practice, performers often face challenges and setbacks. It is common to encounter difficulties with memorization, timing, or coordination. Overcoming these challenges requires perseverance and a willingness to adapt. Feedback from directors, conductors, or choreographers plays a crucial role in guiding performers through this stage. Constructive criticism helps them identify areas for improvement and refine their skills.As the performance date approaches, performers transition into the final phase: execution. This is when all the preparation and practice culminate in front of an audience. The execution phase involves a careful balance of confidence and focus. Performers must manage their nerves and stay present in the moment, while also adhering to the timing and cues established during rehearsal.The live performance itself is an opportunity for performers to showcase their work and connect with the audience. It is often accompanied by a mix of excitement and anxiety. Performers need to stay adaptable, as live shows can be unpredictable, with potential for unexpected issues such as technical difficulties or changes in the environment.After the performance, there is typically a period of reflection and evaluation. Performers review their performance, discuss feedback, and consider what went well and what could be improved. This reflection is essential for growth and development, as it helps performers learn from each experience and prepare for future endeavors.In conclusion, the process of performing is an intricate journey that involves thorough preparation, diligent practice, and a focused execution. Each stage is crucial in shaping a successful performance, and the ability to navigate these stages effectively is key to delivering a compelling and memorable experience for both the performers and the audience.。

多比特信号跨时钟域同步电路以及方法English:Multi-bit signal cross-clock domain synchronization circuits and methods are commonly used in digital systems to ensure proper timing and data alignment between different clock domains. The main challenge in designing such circuits is to ensure reliable and robust synchronization while dealing with potential issues such as clock skew, metastability, and data corruption. One commonly used approach is to utilize synchronization elements such as flip-flops or latches along with proper clock domain crossing techniques. These techniques include two-flop synchronizers, synchronizers with handshake protocols, and self-timed synchronizers. Two-flop synchronizers are often used due to their simplicity and effectiveness in mitigating metastability issues, while protocols like the Gray code handshake can provide more robust synchronization. Additionally, self-timed synchronizers eliminate the need for a common clock signal, making them suitable for asynchronous systems. Overall, the design of multi-bit signal cross-clock domain synchronization circuits and methods requires careful consideration of timing requirements,synchronization element selection, and robustness against potential synchronization issues.中文翻译:多比特信号跨时钟域同步电路及方法通常在数字系统中广泛使用，以确保不同时钟域间的正确计时和数据对齐。

中英译文翻译英文：High Speed Digital Hybrid PLL Frequency Synthesizer译文：高速数字混合锁相环频率合成器To get the high-speed, it is necessary to prepare the precise synchronization of the complicated design.In 2001, H. G. Ryu proposed a simplified structure of the DDFS (direct digital frequency synthesizer)-driven PLL for the high switching speed [2].However, there is a problem that the speed of the whole system is limited by PLL.Y. Fouzar proposed a PLL frequency synthesizer of dual loop configuration using frequency-to-voltage converter (FVC) [3].It has a fast switching speed by the PD (phase detector), FVC using output signal of VCO and the proposed coarse tuning controller.However, H/W complexity is increased for the high switching speed.Also, it shows the fast switching characteristic only when the FVC works well.Another method is pre-tuning one which is called DH-PLL in this study [4].It has very high speed switching property, but H/W complexity and power consumption are increased due to digital look-up table (DLT) which is usually implemented by the ROM including the transfer characteristic ofVCO(voltage controlled oscillator).For this reason, this paper proposes a timing synchronization circuit for the rapid frequency synthesis and a very simple DLT replacement digital logic block instead of the complex ROM type DLT for high speed switching and low power consumption. Also, the requisite condition is solved in the proposed method. The fast switching operation at every the frequency synthesis process is verified by the computer circuit simulation.II.DH-PLL synthesizerAs shown in Fig.1, the open-loop synthesizer is a direct frequency synthesis type that VCO 要得到高运行速度,事先做好复杂设计的精确同步是必要的。

时钟同步服务方案英文Clock Synchronization Service ProposalIntroduction:In today's highly connected world, accurate and synchronized timekeeping is crucial for various domains like telecommunications, finance, transportation, and cybersecurity. Achieving precise clock synchronization across multiple devices or systems is a significant challenge that needs to be addressed. This proposal outlines a clock synchronization service that aims to provide a reliable and efficient solution to this issue.Objective:The primary objective of our clock synchronization service is to ensure that all devices and systems in a network have highly accurate and synchronized clocks. This will enable precise network coordination, event timing, scheduling, and data consistency.Service Architecture:Our clock synchronization service will be based on the Network Time Protocol (NTP), a widely used protocol for clock synchronization over the Internet. It will consist of three main components:1. Time Servers:A set of highly accurate and reliable time servers will be deployed in key areas of the network. These servers will serve as primary time references and will be responsible for generating accurate time signals. To ensure redundancy and fault tolerance, multiple time servers will be deployed in each location.2. Time Clients:All devices and systems in the network that require accurate clock synchronization will act as time clients. These time clients will periodically synchronize their clocks with the time servers using the NTP protocol. The time clients will calibrate their clocks based on the time signals received from the time servers.3. Time Monitoring and Management:A centralized management system will be established to monitor and manage the clock synchronization service. This system will keep track of the time servers and time clients, ensure the proper functioning of the service, and alert administrators in case of any issues or failures.Synchronization Algorithm:To achieve accurate clock synchronization, our service will utilize the NTP's hierarchical algorithm. This algorithm helps synchronize clocks in the network bycompensating for network delays and other sources of clock error. It will ensure that the time signals generated by the time servers are transmitted to the time clients with minimal delay and error.Security Measures:Clock synchronization is not only crucial for accurate timekeeping but also for maintaining a secure network. Our clock synchronization service will incorporate robust security measures to protect against unauthorized access and tampering. This includes authentication and encryption mechanisms to ensure that time signals are transmitted securely and only trusted time sources are used for synchronization.Benefits:Implementing our clock synchronization service will provide numerous benefits to the network and its users:1. Accurate Timekeeping: With highly synchronized clocks, all devices and systems in the network will have access to precise time information, enabling accurate event timing, synchronization, and coordination.2. Improved Efficiency: Accurate clock synchronization will enhance the efficiency of variousprocesses that rely on time-sensitive operations. This includes financial transactions, data backups, network coordination, and real-time communications.3. Enhanced Security: By utilizing secure and trusted time sources, our service will contribute to the network's overall security. Synchronized clocks are essential for secure communication protocols, digital certificates, and network forensics.4. Simplified Network Management: Our centralized management system will provide administrators with a comprehensive view of the network's clock synchronization status. This will help in identifying and resolving issues quickly, reducing maintenance efforts.Conclusion:Accurate clock synchronization is crucial for the efficient and secure operation of modern networks. Our clock synchronization service proposal aims to address this need by providing a reliable, efficient, and secure solution based on the Network Time Protocol. By implementing this service, networks can benefit from synchronized clocks, improved efficiency, enhanced security, and simplified network management.。

1.PCM原理抽样量化与编码:sampling,quantizing and coding话路:speech channel幅值: amplitude value抽样频率: sampling frequency抽样速率: sampling rate脉冲流: stream of pulses重复率: repetition rate编码过程: coding process模拟信号: analog signal传输质量: transmission quality数字通信: digital communication数字传输: digital transmission含噪声的环境: noisy environment传输路由: transmission path信噪比 :signal-to-noise ratio信号电平 :signal levels噪声功率: noise power地面系统: terrestrial system二进制传输: binary transmission反向操作: reverse operation8-位码序列: 8-digit sequence接受端: receiving terminal帧格式 :frame format同步字 :synchronization word实现这三项功能的方案 :the schemes for performing these three functions一串幅值: a series of amplitude values电话质量的话路 a speech channel of telephone quality一个8位二进制码的序列: a sequence of 8-binary digits理论上的最小抽样频率 :a minimum theoretical sampling frequency占据着300Hz到3.4kHz频率范围的话路: a voice channel occupying the range 300Hz to 3.4kHz 每个样值8-位码: 8-digits per sample value汽车点火系统的打火: the sparking of a car ignition system重复率为64kHz的脉冲流: the stream of the pulses with a repetition rate of 64kHz真实信号与噪声信号的关系: relationship of the true signal to the noise signal由卫星上接受到的信号 :the signal received from a satellite一条特定消息中的全部信息 :the complete informatian about a particular message被传信号的波形 :the shape of the transmitted signal由传输路由引入的衰减: the attenuation introduced by transmission path将抽样的幅值转换成一串脉冲的单元 :the unit that converts sampled amplitude value to a set of pulses涉及到第一路，第二路及其他各路的序列: a sequence relating to channel 1,2 and so on被称为同步字的独特码序列: a unique sequence of pulses called synchronization word地面系统 :terrestrial system脉冲的“有”或“无” : the presence or absence of the pulses高速的电子开关: a high-speed electronic switch时分多路复用器 :the time division multiplexer时分多路复用 :Time Division Multiplexer2.异步串行数据传输串行接口 serial interface显示终端 CRT terminal发送器与接收器 transmitter and receiver数据传输 data transmission数据流 data stream闲置状态 the idle state传号电平 mark level空号电位 space level起始位 start bit停止位 stop bitT秒的持续时间 duration of T seconds奇偶校检位 parity bit错误标志 error flag传输错误 transmission error下降沿 fallinf edge符号间的空格 intersymbol space接收机的定时 receiver timing本地时钟 local clock磁带 magnetic tape控制比特 control bit逻辑1电平 logical 1 level二进制数据 binary data明显的缺点 obvious disadvantage异步串行数据传输 asynchronous serial data transmission最为流行的串行接口 the most popular serial interface所传送的数据 the transmitted data发送器与接收器的时钟 the clocks at the transmitter and receiver电传机的时代 the era of teleprinter一个字符的点和划 the dots and dashs of a character符号间空格持续时间的三倍 three times the duration of intersymbol space被称为字符的比特组 the group of bits called characters由7或8个比特的信息组成的固定单元 the invariable units comprising 7 or 8 bits of information 由接收机本地产生的时钟 a clock generated locally by the receiver在字符后所收到的奇偶校检位 the received parity bit following the character起始位的下降沿 the falling edge of the start bit数据链路面向字符的特性 the character-oriented nature of the data link3.数据通信地下电缆 underground cable通信卫星 communication satellite微波设备 microwave facilities调制器与解调器 modulator and demodulator缓冲器 buffer定时信号 timing signals同步脉冲 synchronization pulses时隙 time slot移位寄存器 shift register传输媒体 transmission medium线形衰弱 linear attenuation信息安全 information security键盘 keyboard数据终端 data terminals某种类型的数据转换设备 some type of data conversion equipment视频显示终端 visual display terminal称为数据调制解调器的双向数据发送接收机 two-way data transmistter-receiver called a data modem 全双工的数据传输系统 full-duplex data trandmission system由数据处理器的运算速率所决定的速率 the rate determined by the operating speed of the data processor由接口部件来的定时信号 timing signals from the interface assembly磁心存储器 magnetic core memories线性衰减和时延特性 linear attenuation and delay characteristics传输损伤 transmission impairments语音中的冗余特性 the redundant nature of speech在数据发送器中的编码过程 coding process in the data transmitter二进制的不归零信号 binary nonreturn-to-zero signal4.互联网网络资源：network resource信息服务：information services远程终端：remote terminals互联的系统：interconnected systems命令：command电子邮件：electronic mail主机：host无线信道：wireless channels搜索工具：searching tools用户界面：user interface存取：access文本信息：textual messages协议：protocol超文本协议：hypertext protocol分布在全世界的计算机的巨大网络：gaint network of computers located all over the world主干系统：backbone system全国范围的网络：nationwild network电子会议：electronic conferences实时对话：live conversation最大的信息库the largest repository of the computers on the net网络设备资源：network facilities resources在网上的绝大多数计算机：the vast majority of the computer on the netUNIX操作系统：the UNIX operating system在因特网和你的PC机之间传送数据的方法：a way to move data between the internet and your PC 方便的搜索工具：the convenient searching tools联网的超文本协议：the network hypertext protocol5.光纤通信介绍光纤通信:optical fiber communications光源：light source波长：wavelength激光器：laser色散：dispersion传输介质：transmission medium多模光纤：multi-mode fiber长途干线：long-houl trunks单模光纤：singer-mode fiber带宽：bandwidth带宽用户：wideband subscriber纤维光学：fiber-optics商用技术：commercial technologe门限电流：threshod current光检测器：photodetector波分复用：wavelength multiplexing纤维光网络：fiber-optic network视频带宽：video bandwidth长途传输：long distance transmission中继距离：repeater spacing已装光纤的总长度：the total length of installed fiber长途通信系统：long-haul telecommunication system低衰减的石英纤维：the low-loss silica fiber衰减接近瑞利极限的光纤：fibers with losses approaching the Rayleigh limit室温下的门限电流：room temperature threshold currents较长波长区：the longer wavelength region用户接入工程：subscriber access project部件性能和可靠性的改进：improvements in component performance and reliability已安装的光纤系统的数据速率：data rates for installed fibre optic system每秒吉比特：gigabit per second range波分复用：wavelength multiplexing带宽用户环路系统：widebend subscriber loop system多纤连接器：multifibre connectors设计寿命：projected lifetime光源：light source单模光纤：single-mode fibre分布反馈式激光器：distributed-feedback laser信息容量：information capacity交换体系：switching hierarchy带宽业务：broadband services6.同步数字系列同步数字系统：synchronous digital hierarchy国际标准：international standard信号格式：signal format网络节点接口：network node interface支路信号：tributary signals数字交叉连接：digital cross-connection网络管理：network management网络维护：network maintenance网络运营者：network operators传输速率：transmission rate支路映射：tributary mapping灵活性：flexibility用户业务：subscriber services覆盖层：overlay levels制造商：manufacturer同步传输帧：synchronous transmission frame线路终端复用器：line terminal multiplexer分插复用器：add-drop multiplexer再生中继器：regenerator灵敏度：sensitivity虚容器：virtual container成帧字节：framing bytes段开销：section overhead端到端传输：end-to-end transmission误码监视：error monitoring信号处理节点：signal processing nodes净负荷：payload指针：pointer同步传输系统：synchronous transmission system覆盖nni的标准：the standard covering the NNI国际标准接口：the international standard interface直接同步复用：direct synchronous multiplexing灵活的通信联网：flexible telecommunication networking点对点的传输技术：point-to-point transmission technology先进的网络管理：advanced network management不同厂家提供的设备：the equipment supplied by different manmufacturers SDH提供的灵活性：the flexibility provided by SDH同步复用设备的运营者：operator of synchronous multiplexers电信联网：telecommunication networking支路信号：tributary signals维护能力：maintenance capabilities统一的电信网络基础结构：unified telecommunication network infrastructure 组件：building blocks终端复用器：terminal multiplexer贯通方式：through-mode fashion同步数字交叉链接：synchronous DXC可变带宽：arying bandwidth各个支路信号：individual tributary signals传输系统：transport system光载体：optical carrier二维图形：2-dimensional map传输次序：the order of transmission7.波分复用对光特性的理解：the understanding of the property of light基本重要性：the fundamental important想象今天的通信系统：to imagine the communication system of today光的高速公路：the highway of light巨量的信息：the massive amount of information采用通信新技术：to adopt new communication technology大量的视频信息：the large amounts of video information波分复用：the wave divide multiplexing只发送单个波长：to send only one wavelength传输大量的波长：to transmit a large amount of wavelength无差错传输：the error-free transmission自愈特性：the self-healing propertys直接接入光网络：to access directly to the optial network视频信息：the video information导致WDM革命的主要进展：the major advance that led to the revolution光放大器的发明：the invention of the optical amplifier下一段光纤：the next span of fiber提高所有波长信号的功率：to boost the signal power of all wavelength在光放大器方面的进展：the advances in optical amplifier增益均衡技术的发展：the development of gain equalization techniques多波长传输：the multiple-wavelength transmission无线系统的增长：the growth of various application各种各样的业务：the wide various application处理各种业务类型：to handle various types of traffic全光交叉连接：the all-optical cross-connect8.寻呼系统的发展通信手段：communication means被叫人：called person紧急通信：urgent communications移动电话网：mobile telephone network电话交换台：telephone switchboard寻呼业务：paging service电子电路：electronic circuitry无线传输：wireless transmission无线发射机：wireless transmitter个人代码：personal codes服务区：service area单向通信：one-way communication寻呼用户：paging users顾客：customer技术进步：technological progress系统的效率：efficiency of the system专用的无线网络：dedicated wireless network终端设备：terminal equipment全球覆盖：global coverage无线增益：gain of the antenna空间站：space station通信网络的运行：the operation of a communication network有线的和移动的电话网络：the wired and mobile telephone network光和声音的信号装置：optical and acoustical signaling devices本地电话交换台的接线员：the operator of a local telephone switchboard 第一代寻呼系统：the first generation of paging system利用无线传输的寻呼系统：the paging system using wireless transmission 专用的无线接收机：the dedicated radio receiver社会和经济效益：social and economic advantages电子电路的小型化：the miniaturization of electronic circuitry价格效率比：cost efficiency小型无线电接收机：the miniature radio receiver显示能力：display capability全球覆盖：global coverage空间站的天线增益：the space station antenna gain地球同步轨道卫星：geostationary orbit satellite用户终端：user terminal9.蜂窝式移动电话系统蜂窝式移动电话：cellular mobile telephone服务性能：services performance频谱：frequency spectrum频带：frequency band微处理器：microprocessor移动手机：mobile unit广播业务：broadcast servise天线：antenna子系统：subsystems移动用户：mobile subscriber服务能力：service capability利用率：utilization带宽：bandwidth单边带：single-sideband扩频：spread spectrum大规模集成电路：large scale integrated circuits蜂窝点：cellular site蜂窝交换机：cellular switch无线机架：radio cabinet呼叫处理：call processing频谱利用率：frequency spectrum utilization有限的指定频带：the limited assigend ferquency band 服务区：servise area复杂的特性和功能：complicated features and functions大规模集成电路技术：large-scale integraesd circuit technology试验性的蜂窝系统：developmental cellular system中央协调单元：central coordinating element蜂窝管理：cellular administration传统移动电话的运行限制：operational limitiation of conventional mobile telephone system 有限的服务能力：limitied service capability无线通信行业：radio communcation industry可用的无线电频谱：available radio frequency spectrum所分配的频带：the allocated frequency band移动收发信机：mobile transceiver技术上的可行性：techological feasibility严格的频谱限制：severe spectrum limitations调频广播业务：FM broadcasting services传播路径衰耗：propagration path loss多径衰耗：multipath fading电话公司地方局:telephone company zone offices10.全球移动通信系统个人通信 personal communcation通信标准 communcation standrads固定电话业务 fixed telephone services网络容量 network capability移动交换中心 mobile switching center国际漫游 international roaming宽带业务 broadband services接口转换 interface conversion频谱分配 frequency allocation模拟方式 analogue mode蜂窝通信原理 cellular communcation principe拥塞 jamming蜂窝裂变 cellular splitting基站 base station寄存器 register收费功能 billing function接入方法 access method突发脉冲传输方式 brusty transimission mode开销信息 overhead information切换算法 handover algorithms短消息服务 short message services技术规范 technical specificationtotal access communcation system 全接入的通信系统global mobile communcation system 全球移动通信系统time division multiple access 时分多址facsimile and short message services 传真和短消息服务fixed communcation networks 固定通信网络a more personalized system 更加个性化的系统the cost and quality of the link 链路的价格和质量market growth 市场的发展fixed telephone service 固定电话服务coxial cable 同轴电缆interface convision 接口转换cellular communcation priciple 蜂窝通信原则frequency reuse and cell splitting 频率复用和蜂窝裂变cochannel interference 共信道干扰theoretical spectual capability 理论上的频谱容量micro-cellular system 微蜂窝系统base station transceiver 基站收发信机subscriber register 用户寄存器burst transmission mode 突发脉冲传输模式overhead information 开销信息advanced handover algorithms 先进的切换算法facsimile and short message services 传真和短消息服务the GSM technique specications GSM技术规范说明11.电路交换和分组交换电路交换 circuit switching分组交换 packet switching报文交换 message switching子网 subnet信头 header目的地址 destination address误差控制 error control存储转发方式 store-and-forward manner突发性 bursty传输时延 transimission delay中间交换设备 intermediate switching equipment交换技术 switching technique返回信号 return signal报文处理机 message processor给定最大长度 given maximum length信息转移 information transfer随机性 random专用电路 dedicated circuit电路利用率 channel ultilizationthe capability of soring or manipulating user's data 存储和处理用户数据的能力the special signaling message 特定的信令信息a well defined block df data callde amessage 被精心定义的称为报文的数据块the information regarding the source and destination address 涉及源和目的地址的信息the computer referred to a message processor 叫做报文处理器的计算机the store-and-forward transmission technique 存储转发传输技术the dynamic allocation of bandwith 带宽的动态分配the overall transmission delay of message 报文整个的传输时延switching technique 交换技术ciruit switching 电路交换message switching 报文交换packet switching 分组交换total path of connected lines 连线的整个通路source-destination pair 源到目的地的一对communication parties 通信各方transmission unit 传输单元intial connection cost incurred in setting up the circuit 在建立电路时的起初连接成本low delay constraint required by the user 用户所需的最短时延的限制the fixed dedicateded end-to-end circuit 固定专用的端到端电路low channel ultization 低的电路利用率12.ATM异步转移模式异步转移模式 asynchronous逻辑信道 logical channel虚电路 virtual circuits虚路径 virtual paths建议 recommendation网络层network level业务与应用层 service and application虚连接 virtual connection信息高速公路 information superhigh way点播电视 video-on-demand统计复用 statistical multiplexing数字化的信息 digital information标识符 identifer协议 protocols网络节点 network node宽带网 broadband networkATM论坛 ATM forum面向未来 future-proofed图象编码 image encodeing虚拟专用网 virtual private network数据处理 data processing被叫做信元的短的分组 short packets called cells每秒几百兆比特的速率 bit rates of several hundred megabits a second独特的复用方法 unique multiplexing method任何两个终端之间的物理连接 the physical connection between any two terminals交互式的视频业务 interactive video services多媒体业务的自然载体 a nature vehicle for multimedia services运营者和用户当前和未来的要求 the current and future requirement of both perators and users 高比特率信道的交换技术 the technique for switching high bit rate channel异步转换模式 asychornous transfer mode复用和交换技术 multiplexing and switching technique所承载的传输类型 the underlying type of transmission双重标识 dual identification虚电路 virtual circuit虚路径 virtual path信元在网络节点上的转移 the transfer of cells to the network nodes每秒几百爪比特 hundreds megabits a secondI.121建议 recommendation I.121服务质量 the quality of service与实际需求成比例 in proportion to the exact requirement网络所传送的应用和业务 the applications and service transported over a network构成虚网络的能力 the ability to construct virtual networks低价高效的利用网络设施 cost-effective use of infrastructure面向未来的 future-proofed协调传送不同业务的不同网络 coordinating different networks carrying different services未来的信息高速公路的基本部件 essential components of future information superhighways统计复用 statistical multiplexing资源的最佳使用 optimum use of resources虚拟专用网 virtual private networks13.多媒体多媒体 multimedia交互环境 interactive enviornment视频压缩 video compressin高清晰度电视 high definition television数字信号处理器 digital signal processor点播业务 on-demand services视频服务器 video servers硬件、软件和应用 hardware,software and applications存储 storage彩显 colour moniter全活动图象 full motion picture视频编码器 vision encoder字节 bytemixture of hardware,software and applications 硬件、软件和应用层interactive environment 交互环境personal desk top computers 个人桌面电脑video compression 视频压缩the vision encoder 视频编码器video-on-demand interactive services 交互式视频点播业务multimedia enviroment 多媒体环境visual images 视频图象hard disk storage 硬盘存储colour monitor 彩显the standards of multimedia 多媒体标准motion pictures 活动图象consumer quality of video and audio 顾客质量的视频和音频broadcast images 广播图象high definition television 高清晰度电视coding algorithms 编码算法digital signals processor 数字信号处理器14.公用电信网公用电信网 public telecommunication network本地环路 local loop交换节点 switching node双绞线 twisted pair外部呼叫 external call端局 end office数字数据系统 digital data systems二线连接 two wire connection收费中心 toll center电路交换网 circuit-switching network电话用户 telephone subscriber数据流量 data traffic链路 link中继线 trunk半双工的 half-duplex全双工的 full-duplex中间交换节点 intermediate switching node音频电路 voice-frequency circuit汇接交换机 tandem switch拓扑 topology接点间的 internode路由 route全双工的连接 full-duplex connection集中话务量的功能 the funcion of concentrating traffic被称为汇接交换机的交换节点 the switching node called tandem switch一小部分用户 a fraction of subscribers在站和网络之间的接口 the interface between the station and the network 发送数字信号的用户 the subscriber that transmit digital signal国家网络 national network结构部件 architectural components接点间的支路 the branches between nodes树状拓扑 tree topology传输设备 transmission facilities多条音频电路 multiple voice-frequency circuits同步时分复用 synchronous TDM相邻的端局 adjacent end offices全连通性 full connectivity被分离开的子网 isolated subnetworks高效中继线 high-usage trunks路由选择的基本次序 basic order of selection主干体系网络 backbone hierarchical network连到不同端局的俩个用户 two subscribers attached todifferent office交换区 exchange area15.综合业务数字网全球通信 global communications灵活性 flexibility端到端的数字连接 end-to-end digital connectivity开放网络 open network语声编码 voice encoding综合业务数字网 integrated services digital network系统结构 infrastructure国际标准化组织International Organization for Standardization通信载体 communication carriers传输媒体 transmission medium接口设备 interface equipment带宽限制 bandwidth limitation交换设备 switching equipment语音编码 voice encoding脉码调制 pulse code modulation基本接入 basic access综合业务数字网 the integrated services digital network国际标准化组织 the International Organization for Standardization由于传输媒体导致的质量下降 degradation due to the transmission medium4kHz话路中所固有的带宽限制 bandwidth limitations inherent in a 4kHz voice channel标准化的接口 standardized ports脉（冲编）码调制 pulse code modulation数字通信 digital communicationISDN的标准和系统结构 ISDN standards and system architecture全球通信 global communication数字技术的逐步应用 progressive application of digital technology共同通信载体 public communication carriers高质量 enhanced quality大量的接口设备 substantial quantity of interface equipment在传送话音、数据、视频和其他业务上的灵活性 flexibility in the transmission of voice , data , video and other services带宽的限制 bandwidth limitations端到端的数字连接 end-to-end digital connectivity语音编码技术 voice encoding techniques基本接入信令速率 basic access signaling rate统一的接入 universal access试验性的技术 experimental technology16.电信世界的业务和未来X.25协议 X.25 protocol电视信号 television signals宽带业务 narrowband services基本接入 basic access电信业务 teleservice用户电报 telex无线电波 radio waves地面天线 ground antenna同轴的 coaxial直接广播系统 direct broadcast system端到端的时延 end-to-end delay抖动 jitter繁忙小时 peak hours芯片技术 chip technology高清晰度电视 high definition television运行也维护 operations and maintenance现有的公用网络 the existing public network传统的双向对话 classical two-way voice conversation基于X.25协议的分组交换数据网络 packet switched data network based onX.25 porotocols对网络的拥护接入 the user access to the network对网络的用户接入 the user access to the network信道速率为70 Mbit/s的电路交换业务 a circuit switched service with a channel rate of 70 Mbit/S 与业务无关的网络 the service-independent network对资源的最佳统计共享 the optimal statistical sharing of the resources电信业务 telecommunication service用户电报网 telex network文字报 messages of characters双向对话 two-way voice conversation同轴树状网络 coaxial tree network公用天线的电视网络 community antenna TV network直接广播系统 16 direct broadcast system以太网 Ethernet令牌总线网和令牌环网 token bus and token ring network全球范围的独立网络 world-wide independent networks电话网络的繁忙小时 the peak hours in the telephone network资源共享 resource pooling繁忙小时流量 23 peak hour traffic窄带业务的综合 integration of narrow-band services在语声编码和芯片技术方面的进步 the progress in speech coding and chip technology新的电信业务 a new teleservice对新业务要求的适配 adapting to new service requirements移动电话：the mobile telephone第三代移动业务：the third generation mobile service无线通信：the wireless communication手机：the handset 全球漫游：the global roaming 无线标准：the wireless standard 蜂窝点：the cell sate 峰值数据速率：the peak data rate平均吞吐量：the average throughput 下载：the download多址接入：the multiple access扩频：the spread spectrum technology时隙：the timeslot To comebine high speed mobile access with internet protocol-based service将高速移动接入与基本IP的服务结合起来To standardized future digital wireless communication对未来的数字无线通信标准化theinternet protocol –based services基于互联协议的服务the single global wireless standard但与全球无线标准to accommodation the continuing growth of voice services as well as new wireless internet services容纳语音服务的持续增长及新的无线因特网服务 the spectrum allocation flexibility频谱分配的灵活性 the international telecommunication union国际电信联盟the boundaries between communication ，information，media and entertainment在通信，信息，媒体，娱乐之间的分界线。

synchronize的几种用法Synchronize: Understanding and Exploring Its Various Uses IntroductionThe term "synchronize" refers to the act of coordinating and aligning actions or events to ensure they occur simultaneously or in a particular order. Synchronization plays a vital role in various fields, including technology, communication, music, sports, and more. In this article, we will delve into the different uses and applications of synchronization, exploring its significance and impact in our everyday lives.1. Synchronization in TechnologyIn technology, synchronization refers to the process of coordinating activities between devices, systems, or processes to ensure smooth and efficient operation. It is crucial in ensuring proper functioning and avoiding errors or inconsistencies. Here are some key areas where synchronization plays a crucial role:a. Data Synchronization: Data synchronization involves keeping multiple copies of data consistent across multiple devices or systems. Common examples include synchronizing contacts, calendar events, or files between smartphones and computers. This ensures that the latest updates are available across all devices, allowing users to access their information seamlessly.b. Network Synchronization: Network synchronization involves aligning the timing and frequency of various devices within anetwork. It is particularly important in telecommunications and data transmission, where synchronized clocks and signals ensure reliable communication and prevent data loss or corruption. Network synchronization is achieved using techniques such as Network Time Protocol (NTP) or Precision Time Protocol (PTP).c. Multimedia Synchronization: In the realm of multimedia, synchronization refers to the harmonious alignment of audio and video components. Whether it's watching a movie, streaming a video, or playing a video game, proper synchronization between audio and visual elements is crucial for an immersive experience. Any lag or delay can disrupt the viewing or gaming experience and reduce the overall quality.2. Synchronization in CommunicationEffective communication relies heavily on synchronization, ensuring that messages are transmitted, received, and understood correctly. Here are a few aspects where synchronization plays a crucial role in communication:a. Synchronized Communication Channels: In telecommunication, synchronization is crucial to ensure accurate transmission and reception of signals. Synchronized channels prevent overlap or interference between multiple users or devices sharing the same medium, such as the frequency bands in wireless communication. This enables efficient communication without data loss or distortion.b. Synchronized Speech and Body Language: In face-to-facecommunication, synchronization is essential for effective conversation. It involves synchronizing speech patterns, body language, and gestures to ensure clear and concise communication. By observing and mirroring each other's movements, individuals can establish rapport and better understand one another.c. Synchronized Communication Tools: With the advent of modern technology, various communication tools, such as video conferencing or instant messaging applications, have become commonplace. These tools rely on synchronization to provide real-time communication across different devices or locations. By synchronizing audio, video, and text messages, individuals can effectively communicate, collaborate, and share information.3. Synchronization in Music and EntertainmentMusic is an art form that heavily relies on synchronization. Musicians, bands, and orchestras use synchronization to create harmonious compositions. It ensures that different instruments or vocal performances blend seamlessly, creating a cohesive and pleasing sound. Here are a few ways synchronization is used in music:a. Beat Synchronization: In music production, especially in electronic music genres, beat synchronization is critical. It involves aligning different layers of sound, such as drum beats, basslines, and melodies, to create a rhythmically cohesive track. Synchronization ensures that these elements play in perfect unison, enhancing the overall listening experience.b. Synchronized Light Shows: In live performances, synchronization also comes into play when coordinating musical performances with visual effects, such as light shows or pyrotechnics. By synchronizing the music with lighting cues and special effects, performers can create a visually stunning and immersive experience for the audience.c. Audio-Visual Synchronization: In the film and television industry, synchronization is crucial for ensuring that sound effects, dialogue, or music are properly aligned with the on-screen action. Lip-syncing, for example, involves synchronizing the movements of actors' lips with the dialogue being spoken. A slight delay or mismatch can result in a disjointed viewing experience.4. Synchronization in SportsSports also heavily rely on synchronization, ensuring fair play, accurate timing, and smooth coordination between athletes and teams. Here are a few key areas where synchronization is vital in sports:a. Timekeeping Synchronization: Accurate timekeeping is crucial in various sports, from track and field events to team sports like basketball or soccer. Synchronized clocks and timing systems ensure precise measurements of athletes' performance, allowing for fair competition and accurate results.b. Team Synchronization: In team sports, synchronization plays a significant role in coordinating players' actions and strategies. From synchronized swimming to basketball plays, synchronizedmovements and communication facilitate effective teamwork and successful execution of game plans.c. Broadcast Synchronization: Watching sports on television or online requires synchronization between the live action and the broadcast. Broadcasters ensure synchrony between the video feed, audio commentary, and on-screen graphics to provide a seamless viewing experience for audiences worldwide.ConclusionSynchronization is a fundamental concept that finds wide applications in various fields, including technology, communication, music, and sports. Whether it's data synchronization for seamless cross-device access, communication synchronization for effective dialogues, or music synchronization for harmonious compositions, synchronization plays a crucial role in our everyday lives. Understanding and harnessing synchronization allows us to enhance efficiency, improve communication, and create more enjoyable and immersive experiences.。

CONTENTSPXI Timing and Synchronization Modules Detailed View of PXIe-6674TKey FeaturesNI-Sync Application Programming Interface (API) Platform-Based Approach to Test and Measurement PXI InstrumentationHardware ServicesPXI Timing and Synchronization Modules PXIe-6674T, PXIe-6672, PXI-6683 and PXI-6683H•Generate high-stability PXI system reference clocks and high-resolution sample clocks •Minimize skew through access to PXI-star and PXIe-Dstar chassis trigger lines •Import and export system reference clocks for synchronization between multiple chassis orexternal devices •Achieve synchronization over large distance through GPS, IEEE 1588,IRIG-B or PPS•Develop advanced timing and sync applications with NI-Sync and NI-TClk softwarePowerful, Reliable Timing and SynchronizationNI’s PXI timing and synchronization modules enable a higher level of synchronization on the PXI platform through high-stability clocks, high-precision triggering and advanced signal routing. Implementing timing and synchronization hardware can vastly improve the accuracy of measurements, provide advanced triggering schemes, and allow synchronization of multiple devices for extremely high-channel-count applications. NI’s portfolio includes both signal-based and time-based solutions to deliver the advantages of synchronization to numerous applications.Table 1. NI offers various PXI modules to meet a range of timing and synchronization requirements.*Accuracy within one year of calibration adjustment within 0 ºC and 55 ºC operating temperature rangeDetailed View of PXIe-6674TSlot Compatibility PXI Timing or Peripheral Slot PXI or PXIe Hybrid Peripheral Slot PXIe System TimingSlot PXIe System TimingSlot Oscillator Accuracy*TCXO / 3.5 ppm TCXO / 3.5 ppm TCXO / 3.5 ppm OCXO / 80 ppb DDS Clock Generation Range Not available Not available DC to 105 MHz 0.3 Hz to 1 GHzDDS Clock Generation Resolution Not availableNot available0.075 Hz2.84 µHzPXI 10MHz Backplane Clock Override ● ● ● Clock Import Capability ● ● ● Clock Export Capability● ● ● ● Time-Based Synchronization (GPS, IEEE 1588, IRIG-B, PPS)● ● PXI Trigger Access (PXI_TRIG) ● ● ● ● PXI-Star Trigger Access (PXI_STAR) ●● ● PXIe-Dstar Trigger Access (PXI_DSTARA/B/C)● Front Panel Physical Connectors SMB, RJ45SMB, RJ45SMB SMA PFI Lines on Front Panel3366Key FeaturesHigh-Stability, High-Accuracy Onboard ClockApplications requiring highly reliable and consistent clock signals require a highly stable oscillator to avoid clock inaccuracies. For an NI PXI Express chassis, the oscillator is accurate to 25 parts per million (ppm). Inserting an NI PXI timing and synchronization module into the system timing slot of the chassis enables the user to replace this backplane system reference clock using the higher accuracy oscillator of the module. The PXIe-6672 and PXI-6683 modules contain a temperature-compensated crystal oscillator (TCXO) which can achieve accuracies better than 4 ppm. The PXIe-6674T features an oven-controlled crystal oscillator (OCXO) with an accuracy of 80 parts-per-billion (ppb). Note that the PXI-6683H contains the same oscillator as the PXI-6683, but due to its hybrid connectivity is not able to override the backplane clock.Figure 1.By referencing the OCXO on the PXIe-6674T, the 10 MHz backplane clock of a PXI chassis achieves muchlower phase noise and thus more clock stability.PXI modular instruments with phased-lock loop circuits, such as high-speed digitizers and waveform generators, can take advantage of the high-precision clock of timing and synchronization modules. When locking to a high-accuracy reference clock, the instrument inherits the accuracy of the clock, achieving sample clock resolutions as low as 0.5 Hz with an OCXO-based module.Skew Reduction with Star and Differential Star LinesDue to the variation in signal path lengths between slots in a PXI chassis, skew may be introduced when sending clocks or triggers to multiple slot destinations over the PXI trigger bus. To address this, all NI PXI chassis also include trace-length-matched star trigger lines accessible from a timing and synchronization module in the system timing slot. Star trigger lines can reduce skew to a maximum of 1 ns. Additionally, PXI Express chassis include differential star trigger lines capable of minimizing slot-to-slot skew to under 150 ps.Figure 2.While every slot of the PXI backplane may access the PXI trigger bus, the star trigger lines and differential star trigger lines are only accessible through the system timing slot.Time-Based Synchronization with GPS, IEEE 1588, IRIG-B or PPSThe NI PXI-6683 and PXI-6683H timing and synchronization modules synchronize PXI and PXI Express systems through time-based technology or protocols. Time-based modules can generate triggers and clock signals at programmable future times and timestamp input events with the synchronized system time including that of real-time systems. For PXI Express systems requiring time-based synchronization with backplane clock discipline or star trigger access, the PXI-6683H can be combined with the PXIe- 6674T or PXIe-6672 to provide a full-featured synchronization solution.Advanced Routing of Clocks and TriggersUsing a PXI timing and synchronization module provides the capability of advanced routing of clock and trigger signals. Through the combination of system timing slot access and FPGA-based routing, many more source-to-destination routes become possible, allowing more flexible designs and efficient use of system resources.Table 2. The PXIe-6674T timing and synchronization module features a wide vaiety of source-to-destination routes bycombining the power of the PXI Express architecture with the signal-routing capabilities of the onboard FPGA.● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●●●●●●●NI-Sync Application Programming Interface (API)The NI-Sync driver allows configuration of system timing and synchronization through LabVIEW, C, or .NET. This includes signal-based synchronization, such as sharing triggers and clocks to be used directly, or time-based synchronization, using time protocols such as IEEE-1588, IRIG, or GPS for non-tethered systems. NI-Sync is designed for use with other NI drivers, such as NI-DAQmx, for advanced timing, high channel count, distributed or multiple-instrument applications.DestinationS o u r c ePlatform-Based Approach to Test and MeasurementWhat Is PXI?Powered by software, PXI is a rugged PC-based platform for measurement and automation systems. PXI combines PCI electrical-bus features with the modular, Eurocard packaging of CompactPCI and then adds specialized synchronization buses and key software features. PXI is both a high-performance and low-cost deployment platform for applications such as manufacturing test, military and aerospace, machine monitoring, automotive, and industrial test. Developed in 1997 and launched in 1998, PXI is an open industry standard governed by the PXI Systems Alliance (PXISA), a group of more than 70 companies chartered to promote the PXI standard, ensure interoperability, and maintain the PXI specification.Integrating the Latest Commercial TechnologyBy leveraging the latest commercial technology for our products, we can continually deliver high-performance and high-quality products to our users at a competitive price. The latest PCI Express Gen 3 switches deliver higher data throughput, the latest Intel multicore processors facilitate faster and more efficient parallel (multisite) testing, the latest FPGAs from Xilinx help to push signal processing algorithms to the edge to accelerate measurements, and the latest data converters from TI and ADI continuallyincrease the measurement range and performance of our instrumentation.PXI InstrumentationNI offers more than 600 different PXI modules ranging from DC to mmWave. Because PXI is an open industry standard, nearly 1,500 products are available from more than 70 different instrument vendors. With standard processing and control functions designated to a controller, PXI instruments need to contain only the actual instrumentation circuitry, which provides effective performance in a small footprint. Combined with a chassis and controller, PXI systems feature high-throughput data movement using PCI Express bus interfaces and sub-nanosecond synchronization with integrated timing and triggering.OscilloscopesSample at speeds up to 12.5 GS/s with 5 GHz of analog bandwidth, featuring numerous triggering modes and deep onboard memoryDigital InstrumentsPerform characterization and production test of semiconductor devices with timing sets and per channel pin parametric measurement unit (PPMU)Frequency Counters Perform counter timer tasks such as event counting and encoder position, period, pulse, and frequency measurementsPower Supplies & Loads Supply programmable DC power, with some modules including isolated channels, output disconnect functionality, and remote senseSwitches (Matrix & MUX) Feature a variety of relay types and row/column configurations to simplify wiring in automated test systemsGPIB, Serial, & Ethernet Integrate non-PXI instruments into a PXI system through various instrument control interfaces Digital MultimetersPerform voltage (up to 1000 V), current (up to 3A), resistance, inductance, capacitance, and frequency/period measurements, as well as diode testsWaveform Generators Generate standard functions including sine, square, triangle, and ramp as well as user-defined, arbitrary waveformsSource Measure Units Combine high-precision source and measure capability with high channel density, deterministic hardware sequencing, and SourceAdapt transient optimizationFlexRIO Custom Instruments & Processing Provide high-performance I/O and powerful FPGAs for applications that require more than standard instruments can offerVector Signal Transceivers Combine a vector signal generator and vector signal analyzer with FPGA-based, real-time signal processing and controlData Acquisition Modules Provide a mix of analog I/O, digital I/O, counter/timer, and trigger functionality for measuring electricalor physical phenomena©2019 National Instruments. All rights reserved. LabVIEW, National Instruments, NI, NI TestStand, and are trademarks of National Instruments. Other product and company names listed are trademarks or trade names of their respective companies. The contents of this Site could contain technical inaccuracies, typographical errors or out-of-date information. Information may be updated or changed at any time, without notice. Visit /manuals for the latest information. Hardware ServicesAll NI hardware includes a one-year warranty for basic repair coverage, and calibration in adherence to NI specifications prior to shipment. PXI Systems also include basic assembly and a functional test. NI offers additional entitlements to improve uptime and lower maintenance costs with service programs for hardware. Learn more at /services/hardware .Program Duration 3 or 5 years3 or 5 years Length of service programExtended Repair Coverage●●NI restores your device’s functionality and includes firmware updates and factory calibration.SystemConfiguration,Assembly, and Test 1 ● ●NI technicians assemble, install software in, and test your system per your custom configuration prior to shipment.Advanced Replacement 2 ●NI stocks replacement hardware that can be shipped immediately if a repair is needed.System Return MaterialAuthorization (RMA)1 ●NI accepts the delivery of fully assembled systems when performing repair services.Calibration Plan (Optional) Standard Expedited 3NI performs the requested level of calibration at the specified calibration interval for the duration of the service program.1This option is only available for PXI, CompactRIO, and CompactDAQ systems.2This option is not available for all products in all countries. Contact your local NI sales engineer to confirm availability. 3Expedited calibration only includes traceable levels.PremiumPlus Service ProgramNI can customize the offerings listed above, or offer additional entitlements such as on-site calibration, custom sparing, and life-cycle services through a PremiumPlus Service Program. Contact your NI sales representative to learn more.Technical SupportEvery NI system includes a 30-day trial for phone and e-mail support from NI engineers, which can be extended through a Software Service Program (SSP) membership. NI has more than 400 support engineers available around the globe to provide local support in more than 30 languages. Additionally, take advantage of NI’s award winning online resources and communities .。

单脉冲到正交脉冲转换电路Single pulse to quadrature pulse conversion circuits are commonly used in various applications, including communication systems, radar systems, and control systems. These circuits are designed to converta single input pulse into two output pulses that are 90 degrees outof phase with each other. This conversion is essential for many applications that require precise timing and synchronization of signals.单脉冲到正交脉冲转换电路在各种应用中经常被使用，包括通信系统、雷达系统和控制系统。

这些电路被设计用来将单个输入脉冲转换为两个输出脉冲，这两个脉冲相位差90度。

这种转换对于许多需要信号的精确定时和同步的应用是至关重要的。

There are several ways to implement a single pulse to quadrature pulse conversion circuit. One common technique is to use a combination of flip-flops, XOR gates, and delay elements. The flip-flops are used to store the incoming pulse, while the XOR gates and delay elements are used to generate the quadrature pulses. Bycarefully designing the logic gates and delay elements, it is possible to achieve the desired phase relationship between the output pulses.实现单脉冲到正交脉冲转换电路的方法有几种。

loop rate synchronizerA loop rate synchronizer is a synchronization technique used in digital communication systems to maintain a consistent data transmission rate between two devices. It is commonly used when data is transmitted over an analog medium and needs to be recovered and synchronized at the receiving end.In a loop rate synchronizer, the receiving device continuously adjusts its timing based on the timing information extracted from the received signal. The synchronization process involves two main steps: timing recovery and phase adjustment.Timing recovery involves estimating the timing of the incoming signal by detecting timing information embedded within the signal. This can be done using techniques such as matched filtering, correlation, or clock recovery algorithms. The timing error between the received signal and the local clock at the receiver is then calculated.Phase adjustment is the second step, where the receiver adjusts the phase of its local clock to align with the received signal. This can be achieved by continuously adjusting the frequency of the local clock, either by speeding it up or slowing it down, until the phase error is minimized. This process is often implemented using a phase-locked loop (PLL) or a delay-locked loop (DLL) to generate a synchronized clock signal.By continuously adjusting the timing and phase, the loop rate synchronizer ensures that the receiver maintains a consistent data transmission rate, even in the presence of timing and phase errorsin the received signal. This synchronization technique is important for reliable and accurate data communication over analog transmission channels.。

Product BrochureDigital MultimetersContentsPXI Digital Multimeters Digital Multimeter Devices Key FeaturesSoftwareSupporting Documentation Configure a Custom NI System What is PXI?PXI Instrumentation Hardware ServicesPXI Digital MultimetersPXI-4065, PXIe-4080, PXIe-4081, and PXIe-4082Software: Includes interactive soft front panel inInstrumentStudio ᵀᴹ software, API support for LabVIEW and text-based languages, shipping examples, and detailed help filesVoltage measurements up to 1,000 VDC (700 VAC)Current measurements up to 3 AResistance measurements up to 5 G ΩUp to ±500 VDC/VRMS common-mode isolation Up to 1.8 MS/s isolated, 1,000 V waveform acquisitionBuilt for Automated Test and MeasurementPXI Digital Multimeters (DMMs) range from low-cost 6½-digit devices to high-performance 7½-digit models. Some models includespecialized features such as extended measurement ranges, an isolated digitizer mode with sample rates up to 1.8 MS/s, extended calibration cycles, and basic inductance and capacitance measurements. Combined in a single instrument, these features provide a solution to the measurement challenges inherent in traditional precision instruments: limited measurement throughput and flexibility. These DMMs deliver a smarter way to tackle difficult applications in industries ranging from consumer electronics to aerospace and defense.NI’s DMM portfolio is highlighted by the PXIe-4081, the high-performance 7½-digit DMM. It provides 26 bits of resolution and high-stability,metrology-class voltage measurements that range from 10 nV to 1,000 V, current measurements that range from 1 pA to 3 A, and resistance measurements that range from 10 µΩ to 5 G Ω.FIGURE 1PXI-4065, PXIe-4081, and PXIe-4082 Digital MultimetersTable 1. NI offers PXI DMMs ranging from low-cost 6½-digit options to the high-performance 7½-digit DMM.PXI-4065PXIe-4080PXIe-4081PXIe-4082DescriptionBasic6½-Digit DMMHigh-Performance 6½-DigitDMMHigh-Performance 7½-Digit DMMHigh-Performance 6½-Digit DMMMaximum Voltage (V)3003001,000300 Maximum Current (A)3131 Maximum Sample Rate 3 kS/s 1.8 MS/s 1.8 MS/s 1.8 MS/s Basic Accuracy (10 VDC, 2-Year)90 ppm¹25 ppm12 ppm25 ppm Maximum Calibration Cycle1-year2-year2-year2-year DC and AC Voltage●●●●DC and AC Current●●●●2-Wire and 4-Wire Resistance●●●●Frequency/Period-●●●Basic Inductance/Capacitance---●¹One-year calibration specifications are shown for the PXI-4065 because it does not include a two-year calibration option.Detailed View Of PXIe-4081 7½ Digit DMMTiming and synchronization Industry-standard connectivityData streaming through PCIExpressPXI ejector handle FIGURE 2The PXIe-4081 has the functionality of a box DMM with all the feature benefits of PXI.Digital Multimeter DevicesUSB-4065, PCI-4065, and PCIe-4065Software: Includes interactive soft front panel inInstrumentStudio ᵀᴹ, API support for LabVIEW and text-based languages, shipping examples, and detailed help files Voltage measurements up to 300 V Current measurements up to 3 A2-wire and 4-wire resistance measurements up to 100 M ΩUp to ±300 VDC/VRMS common-mode isolation Up to 1.8 MS/s isolated, 300 V waveform acquisitionBuilt for Automated Test and MeasurementNI’s PC-based DMMs perform AC/DC voltage, AC/DC current, and 2- or 4-wire resistance measurements, as well as diode tests. Some models include specialized features such as extended calibration cycles and an isolated, high-voltage digitizer mode with sample rates up to 1.8 MS/s. Combined in a single instrument, these features provide a solution to the measurement challenges inherent in traditional precision instruments: limited measurement throughput and flexibility. These DMMs deliver a smarter way to tackle difficult applications in industries ranging from consumer electronics to aerospace and defense.FIGURE 3USB-4065 and PCIe-4065 Digital Multimeter DevicesTable 2. NI offers DMMs ranging from low-cost USB-powered devices to high-performance PCI-based devices.USB-4065PCI-4065PCIe-4065Description Basic 6½-Digit DMMMaximum Voltage (V)300Maximum Current (A)3Maximum Sample Rate (kS/s)3Voltage Accuracy (10 VDC, 2-Year)90 + 12 ppm Maximum Calibration Cycle 1-yearDC and AC Voltage ●DC and AC Current●2-Wire and 4-Wire Resistance ●Frequency/Period-Detailed View of USB-4065 6½-Digit DMMCompact size (7.0 in x 4.1 in x 1.3 in)Industry-standard connectivityLightweight (10 oz)Bus-powered for portabilityFIGURE 4The USB-4065 DMM has the functionality of a traditional box DMM in a lightweight form factor with USB connectivity.Key FeaturesHigh-Precision MeasurementsThe analog-to-digital converter (ADC) is the backbone of high-performance PXIe-408x DMMs. A unique combination of off-the-shelf high-speed ADC technology and a custom-designed sigma-delta converter provides the noise, linearity, and speed performance required to achieve high-speed and high-precision measurements.The PXIe-4081 uses stable onboard voltage references to provide steady performance across temperature and time. No other DMM in this price range offers this reference source and its accompanying stability, which is why the PXIe-4081 includes a two-year guaranteed accuracy of 12 ppm to further reduce the cost of test by minimizing downtime for instrument calibration. This beats the one-year accuracyspecifications of most traditional benchtop DMMs, providing you with more accurate measurements with lower cost of ownership and less downtime. The PXIe-4081 also uses advanced DMM measurement techniques such as offset compensated ohms, high-order DC noiserejection, and self-calibration to ensure accurate measurements.FIGURE 5Over a 12-hour noise and drift test of 0 VDC with each DMM set to 100 mV input range with 10 power line cycle (PLC) aperture time, the PXIe-4081 (blue) outperforms both the leading 6½-digit (light grey) and 7½-digit (dark grey) benchtop DMMs.FIGURE 6The unique combination of off-the-shelf high-speed ADC technology and a custom-designed sigma-delta converter optimizes linearity and noise for up to 7½-digitprecision and stability while offering digitizer sample rates up to 1.8 MS/s.Flexible Measurement Rate with an Isolated DigitizerTraditional DMMs are designed to provide high resolution and precision, with little regard to acquisition speed. The unique architecture of the PXIe-408x DMMs offers a continuously variable reading rate that ranges from 7 S/s to 10 kS/s, so you can choose the sample rate and resolution you need for your application.FIGURE 7PXIe-408x DMMs can acquire 36X faster than traditional benchtop DMMs, which gives you increased insight into your device under test.Traditional DMMs are designed to provide high resolution and precision, with little regard to acquisition speed. The unique architecture of the PXIe-408x DMMs offers a continuously variable reading rate that ranges from 7 S/s to 10 kS/s, so you can choose the sample rate andresolution you need for your application.FIGURE 8Depiction of the Scanning Process from the NI-SWITCH API to the DMMSynchronization and IntegrationNI PXI DMMs use the inherent timing and synchronization capabilities of the PXI platform to communicate with switches and otherinstruments within the PXI chassis. You can use switches with a DMM to expand the instrument’s measurement capability to hundreds or thousands of test points. NI DMMs “handshake” with NI switches by sending and receiving hardware-timed triggers over the PXI backplane and scanning through a list of switch connections stored in memory on board the switch module. This method of scanning removes the software overhead associated with traditional scan lists and can create a deterministic scan list for faster test execution with more repeatable timing.FIGURE 9Calibration TimelineSynchronization and IntegrationNI DMMs offer self-calibration, which is traditionally found in only the highest resolution DMMs. Self-calibration corrects for all DC gain and offset drifts within the DMM using a precision, high-stability internal voltage reference that has an outstanding temperature coefficient and time drift that account for all resistance and current source drifts. Using the self-calibration feature makes NI DMMs highly accurate and stable at any operating temperature—well outside the traditional 18 °C to 28 °C range.This operation takes less than a minute to complete and requires no external calibrator, which minimizes the maintenance burden of deployed systems. PXIe-408x DMMs have a two-year external calibration cycle thanks to the self-calibration precision circuitry thatminimizes the maintenance burden of deployed systems. Visit to learn more about NI’s calibration services.FIGURE 10LabVIEW VI Built with the NI-DMM APISoftwareSynchronization and IntegrationIn addition to the soft front panel in InstrumentStudio, the NI-DMM driver includes a best-in-class API that works with a variety ofdevelopment options such as LabVIEW, C, C#, and others. To ensure long-term interoperability of DMMs, the NI-DMM driver API is the same API used for all past and current NI DMMs. The driver also provides access to help files, documentation, and dozens of ready-to-run shipping examples you can use as a starting point for your application.NI Software-The Right Tool for the JobNI has a variety of software for engineers working on research, validation, and production test applications. Learn about our software that helps engineers perform quick ad-hoc tests, build an automated test system, automate data analysis and reporting, develop test sequences, and more.LabVIEW DIAdem TestStandAcquire data from NI and third-partyhardware and communicate usingindustry protocolsUse configurable, interactive displayelementsTake advantage of available analysisfunctionsGraphical programming environment thatengineers use to develop automatedresearch, validation, and production testsystems.Display data in multiple 2D-axissystemsPerform calculations with a simplepoint-and-click interfaceAutomate your measurement dataanalysis workflow, from import toanalysisData analytics software for measurementdata search, inspection, analysis, andautomated reporting.Call and execute tests in LabVIEW,Python, C/C++, or .NETConduct complex tasks, such asparallel testingCreate customer operator interfacesand robust tools for deployment anddebuggingTest executive software that acceleratessystem development for engineers invalidation and production.G Web FlexLogger™InstrumentStudio™Data transfer APIs for connecting tosystems written in LabVIEW, Python,or C#Pre-built objects for data display anduser inputIncluded hosting on SystemLink™CloudDevelopment software that helpsengineers create web-based userinterfaces wihtout the need for traditionalweb development skills.Interactive visualization tools formonitoring tests with drag-and-dropcharts, graphs, and controlsAbility to set alarms that monitorsingle channels or groups forunexpected behaviorNo-code data acquisition softwareengineers use to build validation andverification test applications.Customizable layouts for monitoringmultiple instruments at onceInteractively debug in tandem withcodeTDMS file export containinginstrument settings, measurements,and raw dataApplication software that simplifies setupand configuration of NI PXI hardwareTable 3. NI Digital Multimeter DocumentationDocument Type ModelGetting Started Guide NI Digital MultimetersSpecifications PXI-4065, PXIe-4080, PXIe-4081, PXIe-4082 USB-4065, PCI-4065, PCIe-4065Supporting DocumentationConfigure a Custom NI SystemNI’s online system advisors help you create a custom system based on your specific requirements. Use the advisor to choose compatible hardware, software, accessories, and services and then save your selections as configurations for easy quoting and purchasing later. Visit /advisor to learn more.What Is PXI?A Platform Approach to Test and MeasurementPowered by software, PXI is a rugged PC-based platform for measurement and automation systems. PXI combines PCI electrical-bus features with the modular, Eurocard packaging of CompactPCI and then adds specialized synchronization buses and key software features. PXI is both a high-performance and low-cost deployment platform for applications such as manufacturing test, military and aerospace, machine monitoring, automotive, and industrial test. Developed in 1997 and launched in 1998, PXI is an open industry standard governed by the PXI Systems Alliance (PXISA), a group of more than 70 companies chartered to promote the PXI standard, ensure interoperability, and maintain the PXI specification.SoftwareComputer Timing and Synchronization PXI ChassisPCI Express Gen 3 throughput up to 24 GB/s sub-nanosecond latency, P2P streaming, integrated triggeringInstrumentationPXI ModulesDC to mmWave, oscilloscope, programmable power supply, switch/MUX, DMM, VSA, VSG, VST, AWG, SMU, DAQTest Management and Code DevelopmentCode sequencing, database reporting, usermanagement, operator interface, parallelexecution, signal processing. 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外文资料翻译之邯郸勺丸创作L ED using digital tube digital display its high-brightness, indicating the advantages of intuitive intelligence is widely used in areas such as equipment and household appliances. AT89C52This article describes a single-chip microcomputer as the core, to a total of anode high-brightness LED L ED as a display composed of seven figures show that the practical design of multi-function electronic clocks, the clock shows a week, hour, minute, second, it can be switched to year, month, day showed that the whole point of music at the same time and from time to time the alarm time and other functions can also be used for electronic stopwatch.Clock circuit is the heart of the computer, which controls the rhythm of the work of the computer is through the completion of complex sequential circuits function in different directions.Clock, since it was invented that day on, people's lives has become an indispensable tool, especially in this era of efficient, the clock is in the human production and living, learning and other fields is widely. However, with the passage of time, people not only to the requirements of the clock is getting higher andhigher precision, and functional requirements for the clock more and more, the clock has not only a tool used to display time, in many practical applications It also needs to be able to achieve more other functions. Features such as alarm clock, calendar display, temperature measurement function, humidity measurements, voltage measurements, frequency measurements, have been under-voltage alarm function. Digital clocks to the people's production and life has brought great convenience, but also greatly expands the time feature the original clocks. Such as regular auto-alarm, Automatic time-ling, time process automation, from time to time broadcast, from closed-circuit automatic lights, oven timer switch, on-off power equipment, electrical and even a variety of timing is automatically enabled, all of which are based on digital clocks and watches based. It can be said that the design of the significance of multi-function Digital Clock Digital Clock is not just itself, a greater significance of the multi-function digital clock in a number of real-time control systems. In many practical applications, as long as the digital clock circuit of the programs and hardware to a certain degree of modification could be useful for real-time control system, which applied to the actual work and production to. Thus, digital clock and to expand its applications,has a very practical significance.With the development of human civilization, science and technology, there is the request of the clock continues to improve. Clock has not only seen as a tool to display the time, in many practical applications also need to be able to achieve more other functions. High-precision, multifunction, small size, low power consumption, is the development trend of the modern clock. In this trend, digital clock, multifunction clock has become the modern design of the production of research-led direction. This article is based on this design direction for the control of a single-chip core design requirements of a multi-function indicators in line with the digital clock.The design is based on the principle of single-chip technology to chip AT89C52single-chip microcomputer as the core controller, through the production of hardware and software procedures for the preparation, design to produce a multi-functional digital clock system. The clock system mainly by clock module, alarm module, the ambient temperature detection module, liquid crystal display module, control module and the keyboard signal prompted module. System is simple and clear user interface that can 4V ~ 7V DC power under normal operation. Able to accurately display time (display format hh: mm: seconds seconds, 24-hour system), maybe time to adjust at any time, with clock time settings, alarm on / off, only to make functions, where the clock to measure the ambient temperature and displayed. Hardware and software design into the guiding ideology, give full play to the single-chip features, most of the functions through software programming to achieve, the circuit is simple and clear, high system stability. At the same time, the clock system also has the power of small, low cost, and highly practical. System components as a result of less use, single-chip occupied by the I / O port not more than, the system has a certain degree of scalability.Clock design is no theory of discrete logic, programmable logic, or using full-custom silicon devices of any digital design, in order to successfully operate and reliable clock is crucial. Poor design of the clock in the limits of temperature, voltage deviation or the manufacturing process will result in the case wrong, and debugging difficult, spending a lot. In the design of FPGA / CPLD clock when several types of commonly used. Clock can be divided into the following four types: global clock, clock gating, multi-level logic clock clock and volatility. Multi-clock system to include the above-mentioned four types of any combination of the clock.No matter what methods are the real circuitclock tree can not achieve the ideal assumption that the clock, so we must be based on an ideal clock, the clock real work to build a model to analyze the circuit, so as to make the circuit performance and the practical work as expected . Clock in the actual model, we have to consider the spread of clock-tree skew, vertical jump and absolute bias and other uncertainties.To register, the clock was working along the arrival of the data terminal when it should have been stable, so as to ensure that the work along the sampling clock to the accuracy of the data, this data preparation time that we call set-up time (setup time). Data should also be working along the clock to maintain over a period of time, this period of time known as the hold time (hold time).Global clock for a design project, the global clock (or clock synchronous) is the simplest and most predictable clock. In the PLD / FPGA design of the clock the best options are: by a dedicated global clock input pins of a single master clock-driven clock design projects to each flip-flop. As long as possible should be used in the design of global clock projects. PLD / FPGA has a dedicated global clock pins, the device is directly connected to each register. Global clock to provide such a device in the shortest possible delay to the output clock.Clock-gated in many applications, the entire design of the overall use of external clock is not possible or practical. With the product of PLD logic array clock (that is, the clock is generated by the logic), to allow arbitrary function alone all trigger clock. However, when you use the array clock, the clock should be carefully analyzed the function, in order to avoid glitches.Usually constitute the array clock clock-gated. Clock gating often interface with the microprocessor, and used the address to write to control the pulse line. However, when using combination of flip-flop when the clock function, usually there is a clock-gated. If the following conditions, such as clock gating can be as reliable as global clock work: Drive the clock logic must contain only one "and" the door or a "or" gate. If any additional work in some state of logic, the competition will be the burr.A logic gate input as the actual clock, and the logic gate must be of all other input as the address or control lines, in relation to their compliance with the establishment and maintenance of clock time bound.Multi-level logic generated clock when the clock-gating logic of the combination of more than one (or more than the individual "and" doors or "or" gate), the evidence of thereliability of the design of the project has become very difficult. Even if the prototype or simulation results show that there is no static dangerous, but in fact the risk may still exist. In general, we should not use multi-level combinational logic to clock the flip-flop in the PLD design.Traveling-wave clock clock another popular use of traveling-wave circuit is the clock, that is, the output of a flip-flop used as a clock input of another flip-flop. If careful design, traveling-wave clock can be the same as the global clock to work reliably. However, the traveling-wave clock made from time to time with the calculation of the circuit becomes very complicated. Line-wave traveling-wave clock flip-flop of the chain have a greater clock time between the offset and exceed the worst case the set-up time, hold time and clock to the output circuit of the delay, allowing the system to the actual slowed down.Multi-clock system, many system requirements within the same multi-PLD clock. The most common example is the two asynchronous interfaces between microprocessors, or microprocessors and asynchronous communication channel interface. As the clock signal between the two requirements to establish and maintain a certain time, so that the above application from time to time the introduction ofadditional constraints. They also requested that some asynchronous synchronization signal.In many applications, only the synchronization of asynchronous signals is not enough, when the system of two or more non-homologous clock, the data it is difficult to establish and maintain the time to be assured that we will face the complex matter of time . The best way is to all non-homologous clock synchronization. PLD internal use of the lock loop (PLL or DLL) is a very good, but not all of PLD with a PLL, DLL, and chip PLL with most expensive, so unless there are special requirements, the general occasions PLL can not use with the PLD.At this time we need to take to enable the use of the D flip-flop-side, and the introduction of a high-frequency clock.采纳L ED 数码管的数字显示以其亮度高、显示直观等优点被广泛应用于智能仪器及家用电器等领域. 本文介绍一种以AT89C52单片机为核心,以共阳极高亮度L ED 数码管作为显示器件组成7 位数字显示的实用多功能电子时钟的设计,该时钟可显示星期、时、分、秒,也可切换为年、月、日显示,同时具有整点音乐报时及按时闹钟等功能,也可作电子秒表使用.时钟电路是计算机的心脏, 它控制着计算机的工作节奏就是通过复杂的时序电路完成份歧的指令功能的.时钟, 自从它被发明的那天起, 就成为人们生活中必不成少的一种工具, 尤其是在现在这个讲究效率的年代, 时钟更是在人类生产、生活、学习等多个领域获得广泛的应用.然而随着时间的推移, 人们不单对时钟精度的要求越来越高, 而且对时钟功能的要求也越来越多, 时钟已不单仅是一种用来显示时间的工具, 在很多实际应用中它还需要能够实现更多其它的功能.诸如闹钟功能、日历显示功能、温度丈量功能、湿度丈量功能、电压丈量功能、频率丈量功能、过欠压报警功能等.钟表的数字化给人们的生发生活带来了极年夜的方便, 而且年夜年夜地扩展了钟表原先的报时功能.诸如按时自动报警、按时自动打铃、时间法式自动控制、按时广播、自动起闭路灯、按时开关烘箱、通断动力设备、甚至各种按时电气的自动启用等, 所有这些, 都是以钟表数字化为基础的.可以说, 设计多功能数字时钟的意义已不只在于数字时钟自己, 更年夜的意义在于多功能数字时钟在许多实时控制系统中的应用.在很多实际应用中, 只要对数字时钟的法式和硬件电路加以一定的修改, 即可以获得实时控制的实用系统, 从而应用到实际工作与生产中去.因此, 研究数字时钟及扩年夜其应用, 有着非常现实的意义.随着人类科技文明的发展, 人们对时钟的要求在不竭地提高.时钟已不单仅被看成一种用来显示时间的工具, 在很多实际应用中它还需要能够实现更多其它的功能.高精度、多功能、小体积、低功耗, 是现代时钟发展的趋势.在这种趋势下, 时钟的数字化、多功能化已经成为现代时钟生产研究的主导设计方向.本文正是基于这种设计方向, 以单片机为控制核心, 设计制作一个符合指标要求的多功能数字时钟.本设计基于单片机技术原理, 以单片机芯片AT89C52作为核心控制器, 通过硬件电路的制作以及软件法式的编制, 设计制作出一个多功能数字时钟系统.该时钟系统主要由时钟模块、闹钟模块、环境温度检测模块、液晶显示模块、键盘控制模块以及信号提示模块组成.系统具有简单清晰的把持界面, 能在4V～7V直流电源下正常工作.能够准确显示时间（显示格式为时时：分分：秒秒, 24小时制）, 可随时进行时间调整, 具有闹钟时间设置、闹钟开/关、止闹功能, 能够对时钟所在的环境温度进行丈量并显示.设计以硬件软件化为指导思想, 充沛发挥单片机功能, 年夜部份功能通过软件编程来实现, 电路简单明了, 系统稳定性高.同时, 该时钟系统还具有功耗小、本钱低的特点, 具有很强的实用性.由于系统所用元器件较少, 单片机所被占用的I/O口未几, 因此系统具有一定的可扩展性.时钟设计无沦是用离散逻辑、可编程逻辑, 还是用全定制硅器件实现的任何数字设计, 为了胜利地把持, 可靠的时钟是非常关键的.设计不良的时钟在极限的温度、电压或制造工艺的偏差情况下将招致毛病的行为, 而且调试困难、花销很年夜.在设计FPGA/CPLD时通常采纳几种时钟类型.时钟可分为如下四种类型：全局时钟、门控时钟、多级逻辑时钟和摆荡式时钟.多时钟系统能够包括上述四种时钟类型的任意组合.无论采纳何种方式, 电路中真实的时钟树也无法到达假定的理想时钟, 因此我们必需依据理想时钟, 建立一个实际工作时钟模型来分析电路, 这样才可以使得电路的实际工作效果和预期的一样.在实际的时钟模型中, 我们要考虑时钟树传布中的偏斜、跳变和绝对垂直的偏差以及其它一些不确定因素.对寄存器而言, 那时钟工作沿到来时它的数据端应该已经稳定, 这样才华保证时钟工作沿采样到数据的正确性, 这段数据的预备时间我们称之为建立时间（setup time）.数据同样应该在时钟工作沿过去后坚持一段时间, 这段时间称为坚持时间（hold time）.全局时钟对一个设计项目来说, 全局时钟(或同步时钟)是最简单和最可预测的时钟.在PLD/FPGA设计中最好的时钟方案是：由专用的全局时钟输入引脚驱动的单个主时钟去钟控设计项目中的每一个触发器.只要可能就应尽量在设计项目中采纳全局时钟.PLD/FPGA都具有专门的全局时钟引脚, 它直接连到器件中的每一个寄存器.这种全局时钟提供器件中最短的时钟到输出的延时.门控时钟在许多应用中, 整个设计项目都采纳外部的全局时钟是不成能或不实际的.PLD具有乘积项逻辑阵列时钟（即时钟是由逻辑发生的）, 允许任意函数独自地钟控各个触发器.然而, 当你用阵列时钟时, 应仔细地分析时钟函数, 以防止毛刺.通经常使用阵列时钟构成门控时钟.门控时钟经常同微处置器接口有关, 用地址线去控制写脉冲.然而, 每当用组合函数钟控触发器时, 通常都存在着门控时钟.如果符合下述条件, 门控时钟可以象全局时钟一样可靠地工作：驱动时钟的逻辑必需只包括一个“与”门或一个“或”门.如果采纳任何附加逻在某些工作状态下, 会呈现竞争发生的毛刺.逻辑门的一个输入作为实际的时钟, 而该逻辑门的所有其它输入必需当做地址或控制线, 它们遵守相对时钟的建立和坚持时间的约束.多级逻辑时钟当发生门控时钟的组合逻辑超越一级(即超越单个的“与”门或“或”门)时, 证设计项目的可靠性变得很困难.即使样机或仿真结果没有显示出静态险象, 但实际上仍然可能存在着危险.通常, 我们不应该用多级组合逻辑去钟控PLD设计中的触发器.行波时钟另一种流行的时钟电路是采纳行波时钟, 即一个触发器的输出用作另一个触发器的时钟输入.如果仔细地设计, 行波时钟可以象全局时钟一样地可靠工作.然而, 行波时钟使得与电路有关的按时计算变得很复杂.行波时钟在行波链上各触发器的时钟之间发生较年夜的时间偏移, 而且会超越最坏情况下的建立时间、坚持时间和电路中时钟到输出的延时, 使系统的实际速度下降.多时钟系统许多系统要求在同一个PLD内采纳多时钟.最罕见的例子是两个异步微处置器器之间的接口, 或微处置器和异步通信通道的接口.由于两个时钟信号之间要求一定的建立和坚持时间, 所以, 上述应用引进了附加的按时约束条件.它们也会要求将某些异步信号同步化.在许多应用中只将异步信号同步化还是不够的, 当系统中有两个或两个以上非同源时钟的时候, 数据的建立和坚持时间很难获得保证, 我们将面临复杂的时间问题.最好的方法是将所有非同源时钟同步化.使用PLD内部的锁项环（PLL或DLL）是一个效果很好的方法, 但不是所有PLD都带有PLL、DLL, 而且带有PLL功能的芯片年夜多价格昂贵, 所以除非有特殊要求, 一般场所可以不使用带PLL的PLD.这时我们需要使用带使能真个D触发器, 并引入一个高频时钟.创作时间：二零二一年六月三十日。

专利名称：Synchronization of digital communication systems发明人：Thomas Dolle,Tino Konschak申请号：US09/185022申请日：19981103公开号：US06160821A公开日：20001212专利内容由知识产权出版社提供摘要：According to the present invention a system and a method for synchronising digital communication systems is proposed. Thereby a reference symbol RS consisting of a sequence of a plurality of synchronisation patterns SP and followed by data symbols, which are both modulated (13) on a RF-frequency is provided. The received reference symbol (RS) is correlated with a delayed version of itself and the correlation peak is identified giving the position and complex correlation result that can be used for the timing and frequency synchronisation of a digital communication system. According to the present invention the phase of the last and/or the first of the plurality of synchronisation patterns SP of said reference symbol RS (or a part or a multiple thereof) is phase shifted, e.g. by 180°, before the transmission step. According to the present invention therefore the effects of random contribution of adjacent data symbols of the reference symbol to a correlation calculation based on a synchronisation algorithm can be entirely eliminated. Through the inversion of the last synchronisation pattern and the reference symbol the correlation peak, which is used to determine the symbol timing, is offset inside the reference symbol. Thus, the precision of the timing error estimation is improved significantly.申请人：SONY INTERNATIONAL (EUROPE) GMBH 代理机构：Frommer Lawrence & Haug, LLP.代理人：William S. Frommer,Bruno Polito更多信息请下载全文后查看。

CONTENTSPXI Digital Pattern InstrumentsDetailed View of PXIe-6571 Digital Pattern Instrument Key FeaturesNI-Digital Pattern Application Programming Interface (API) Digital Pattern Editor Application SoftwarePlatform-Based Approach to Test and MeasurementPXI InstrumentationHardware ServicesPXI Digital Pattern Instruments PXIe-6570, PXIe-6571•Software: Includes Digital Pattern Editor for pattern development and debugging, APIsupport for LabVIEW and text-based languages, shipping examples, and detailed help files•32-channel, 100 MHz vector rate with 39.0625 ps of edge placement resolution•Digital voltage -2 V to 6 V, and PPMU force voltage -2 V to 7 V •Up to 200 Mb/s data rate and 160 MHz clock generation•Combine multiple modules to create digital subsystems with up to 512 channels •Dedicated source, capture, and history memory resources for up to eight parallel test sitesSemiconductor ATE-Class Digital on the Open PXI PlatformPXI Digital Pattern Instruments deliver ATE-class digital to the industry-standard PXI platform for testing a broad range of RF and mixed-signal integrated circuits (ICs). The NI PXI platform and NI Semiconductor Test System (STS) are an ideal platform for characterization and production test of RF and mixed-signal ICs from RF front ends and power management ICs to transceivers and Internet of Things systems on chip with built-in connectivity and sensors.The PXIe-6571 is the highlight of NI’s offering for digital production and characterization test of semiconductor devices. For basic digital signals and interfaces, consider PXI Digital I/O Modules or PXI Reconfigurable Digital I/O Modules.Table 1. PXI Digital Pattern Instruments are built for the testing of semiconductor devices.Module Width 2 slots 1 slotActive Load 24 mA 16 mAChannels32 per module256 maximum in a synchronized subsystem 512 maximum in a synchronized subsystemPin ElectronicsDigital: -2 V to +6 V, 32 mA PPMU measure voltage: -2 V to +6 V, 32 mA PPMU force voltage: -2 V to +7 V, 32 mAMaximum Vector Rate 100 MHz (10 ns minimum vector period) Maximum Data Rate 200 Mb/sMaximum Clock Generation 160 MHz**Pattern Timing31 time sets39.0625 ps edge placement resolutionDrive Formats Non-return (NR), return to low (RL), return to high (RH) (100 MHz max),surround by complement (SBC) (50 MHz max)Vector Memory Depth 128 M/ChannelOpcode Support Flow control, sequencer flags and registers, signal, source and capture, subroutineSource and Capture Engines Broadcast or site-unique Serial or parallel8 per instrumentSource and Capture Memory 256 Mbit source memory, 1 MSample capture memoryFrequency Counters 5 kHz to 200 MHz, per pinHistory RAM (8,192/N sites) -1 cyclesSCAN Support Flattened SCAN patterns, up to 128 M* Note that the PXIe-6571 requires a chassis with 82 W slot cooling capacity, such as the PXIe-1095. For more on PXI power and cooling, see this white paper.** Clock rates >133 MHz will have a non-50% duty cycle.Detailed View of PXIe-6571 Digital Pattern InstrumentKey FeaturesHardware OverviewPXI Digital Pattern Instruments have several types of vector and dynamic pattern memory and feature pin electronics. The block diagram in Figure 1 shows the instruments’ functional hardware components.Figure 1. PXI Digital Pattern Instruments offer advanced ATE memory features like history, source, and capturememory with the right levels of user abstraction.Timing and ExecutionPXI Digital Pattern Instruments burst digital data based on patterns that are made up of individual vectors. The time set includes the period of the vector in time, a drive format for the pin, and placement of the digital edges.The drive formats, or vector formats, supported by these instruments are non-return, return to low, return to high, and surround by complement. Having the ability to use all of these formats gives engineers the ability to make the most efficient digital interface with as few vectors as necessary.Figure 2. The combination of drive format and pattern value will determine what the digital waveform looks like. Each time set for a PXI Digital Pattern Instrument has a defined period, up to six drive edges, and a compare strobe. The time sets for a PXI Digital Pattern Instrument have up to six drive edges and a compare strobe to act on the formats defined above. Drive on and drive off are edges that determine when the pin drivers will enable and disable. Drive data and drive return define when the pin driver will assert a high or low level. The drive return edge is only used in return vector formats. The compare strobe specifies the time in a vector when the pin comparator determines if the pin is at a high, low, or midband voltage level based on defined thresholds.Pin ElectronicsPin electronics provide the electrical interface to the DUT and allows the engineer to drive or receive digital data and emulate the conditions of other loads and components interacting with the device.In a drive state, the pin driver of the pin electronics is engaged and forces the voltage on the pin to be low or high as determined by a 0 or 1 in the pattern. A pin driver will source or sink up to 32 mA to achieve the defined high or low value on the pin when enabled. Digital pattern instruments use 0 and 1 to represent drive pin states.Compare states are non-drive states that use the comparators of the pin electronics to assess incoming data against predefined thresholds. Comparators are included in pin electronics and have settable levels for high and low voltages that are made in context to the DUT. To represent the different non-drive states that a pin can take, L, H, X, V, E, and M are all used.Figure 3. Pin drivers and comparators within the pin electronics use defined voltage levels for drive and comparestates in the digital pattern.NI STS Integration and Digital System SynchronizationPXI Digital Pattern Instruments make up the digital test subsystem of the STS. The instruments are supported in all STS software and are calibrated using a timing calibration load board and a DC calibration load board, both from NI. The diagnostic software and calibration tools ensure high reliability and uptime of the system. It also gives a single system the ability to have many unified digital test resources.Figure 4. With PXI Digital Pattern Instruments, more test engineers can take advantage of the STS, a PXI-based,open platform semiconductor production test system. Synchronization and IntegrationPXI Digital Pattern Instruments can be synchronized together within a single PXI chassis using a PXI timing and synchronization module and the NI-Sync device driver. This synchronization can be done both within the STS and in a stand-alone PXI chassis. By synchronizing multiple instruments, a single digital subsystem can have up to 512 synchronized channels that achieve a specified edge placement accuracy performance. A unified digital subsystem can span single sites and combine match and failed conditions across multiple digital pattern instruments.Figure 5. PXI Digital Pattern Instruments can be synchronized using a PXI Timing and Synchronization module tocreate a digital subsystem of many unified channels.Digital Pattern Editor Application SoftwareThe Digital Pattern Editor is an interactive tool for importing, editing, or creating test patterns. The editor also includes tools like Shmoo plots to provide a deeper understanding of DUT performance across variation, as well as debug tools like overlaying pattern failures on a pattern or using digital scope to get an analog view of the pin data. Features like multisite and multi-instrument pattern bursting empower the engineer to expand from development into production leveraging the same workflow. All of the sheets developed in the Digital Pattern Editor can be reused by the API in LabVIEW, C, or .NET languages, as well as in the TestStand Semiconductor Module.Pattern Development and FormatA pattern file is a collection of vectors, with each vector containing time sets, labels, opcodes, pin states, and comments. The Digital Pattern Editor has development sheets for all of these items as well as debug tools for refining patterns, time sets, and specifications. A compiled, binary version of the pattern file is required to edit or burst. Engineers can compile an ASCII text pattern file format (.digipatsrc) into a binary version using the Digital Pattern Editor or a command line process. The ASCII form can be used to convert existing patterns by following the well-defined pattern file format. Design simulation and SCAN files generated by EDA tools can be cyclized and targeted to the NI format using existing customer in-house EDA workflows or third-party cyclizing tools.Figure 6. The Digital Pattern Editor is powerful development and debug software for semiconductor digital tests. The window can be configured to view development sheets and debugging tools all at the same time.History RAM Overlay Feature and History RAM ViewEngineers can view the History RAM in two ways: using the History RAM overlay feature in the pattern document and looking at the History RAM view. The History RAM overlay displays the subset of burst results that corresponds to vectors in the current pattern based on the settings specified in the History RAM and signal setup pane. The History RAM view includes the corresponding time sets, labels, opcodes, pattern names, vectors/cycles, pin data, and comments. Rebursting a pattern overwrites the data in the History RAM overlay mode and in the History RAM view.Digital ScopeTo aid engineers in debugging patterns, the digital scope tool displays a progressively updated two-dimensional plot of the actual analog levels of the digital waveform along with the expected data from the pattern.Shmoo PlotThe Shmoo tool displays a dynamically updated intensity plot of pass and fail values for a sweep of two variables. The Shmoo executes on multiple sites and engineers can switch the plot results displayed from site to site during the operation without hindering the sweep’s completion.The Shmoo can sweep up to two variables including levels, voltages, currents, edges, or specifications at a time. The Shmoo operation can execute in sweep, zigzag, progressive resolution, or edge traversal mode.Figure 7. PXI Digital Pattern Instruments and the Digital Pattern Editor give semiconductor test engineers the featuresand tools they need in characterization and production.NI-Digital Pattern Application Programming Interface (API)The NI-Digital Pattern Driver includes a best-in-class API that works with a variety of development options such as LabVIEW, C, and .NET languages. To ensure long-term interoperability of PXI Digital Pattern Instruments, the NI-Digital Pattern Driver API is the same API used for all past and current PXI Digital Pattern Instruments. The driver also provides access to help files, documentation, and ready-to-run shipping examples you can use as a starting point for your application.Platform-Based Approach to Test and MeasurementWhat Is PXI?Powered by software, PXI is a rugged PC-based platform for measurement and automation systems. PXI combines PCI electrical-bus features with the modular, Eurocard packaging of CompactPCI and then adds specialized synchronization buses and key software features. PXI is both a high-performance and low-cost deployment platform for applications such as manufacturing test, military and aerospace, machine monitoring, automotive, and industrial test. Developed in 1997 and launched in 1998, PXI is an open industry standard governed by the PXI Systems Alliance (PXISA), a group of more than 70 companies chartered to promote the PXI standard, ensure interoperability, and maintain the PXI specification.Integrating the Latest Commercial TechnologyBy leveraging the latest commercial technology for our products, we can continually deliver high-performance and high-quality products to our users at a competitive price. The latest PCI Express Gen 3 switches deliver higher data throughput, the latest Intel multicore processors facilitate faster and more efficient parallel (multisite) testing, the latest FPGAs from Xilinx help to push signal processing algorithms to the edge to accelerate measurements, and the latest data converters from TI and ADI continuallyincrease the measurement range and performance of our instrumentation.PXI InstrumentationNI offers more than 600 different PXI modules ranging from DC to mmWave. Because PXI is an open industry standard, nearly 1,500 products are available from more than 70 different instrument vendors. With standard processing and control functions designated to a controller, PXI instruments need to contain only the actual instrumentation circuitry, which provides effective performance in a small footprint. Combined with a chassis and controller, PXI systems feature high-throughput data movement using PCI Express bus interfaces and sub-nanosecond synchronization with integrated timing and triggering.OscilloscopesSample at speeds up to 12.5 GS/s with 5 GHz of analog bandwidth, featuring numerous triggering modes and deep onboard memoryDigital InstrumentsPerform characterization and production test of semiconductor devices with timing sets and per channel pin parametric measurement unit (PPMU)Frequency Counters Perform counter timer tasks such as event counting and encoder position, period, pulse, and frequency measurementsPower Supplies & Loads Supply programmable DC power, with some modules including isolated channels, output disconnect functionality, and remote senseSwitches (Matrix & MUX) Feature a variety of relay types and row/column configurations to simplify wiring in automated test systemsGPIB, Serial, & Ethernet Integrate non-PXI instruments into a PXI system through various instrument control interfaces Digital MultimetersPerform voltage (up to 1000 V), current (up to 3A), resistance, inductance, capacitance, and frequency/period measurements, as well as diode testsWaveform Generators Generate standard functions including sine, square, triangle, and ramp as well as user-defined, arbitrary waveformsSource Measure Units Combine high-precision source and measure capability with high channel density, deterministic hardware sequencing, and SourceAdapt transient optimizationFlexRIO Custom Instruments & Processing Provide high-performance I/O and powerful FPGAs for applications that require more than standard instruments can offerVector Signal Transceivers Combine a vector signal generator and vector signal analyzer with FPGA-based, real-time signal processing and controlData Acquisition Modules Provide a mix of analog I/O, digital I/O, counter/timer, and trigger functionality for measuring electricalor physical phenomena©2019 National Instruments. All rights reserved. LabVIEW, National Instruments, NI, NI TestStand, and are trademarks of National Instruments. Other product and company names listed are trademarks or trade names of their respective companies. The contents of this Site could contain technical inaccuracies, typographical errors or out-of-date information. Information may be updated or changed at any time, without notice. Visit /manuals for the latest information.10 December 2019 Page 11 | | PXI Digital Pattern Instruments Hardware ServicesAll NI hardware includes a one-year warranty for basic repair coverage, and calibration in adherence to NI specifications prior to shipment. PXI systems also include basic assembly and a functional test. NI offers additional entitlements to improve uptime and lower maintenance costs with service programs for hardware. Learn more at /services/hardware .Program Duration 1, 3, or 5 years 1, 3, or 5 years Length of service programExtended Repair Coverage ● ● NI restores your device’s functionality and includes firmware updates and factory calibration.System Configuration, Assembly, and Test 1 ● ● NI technicians assemble, install software in, and test your system per your custom configuration prior to shipment.Advanced Replacement 2 ● NI stocks replacement hardware that can be shipped immediately if a repair is needed.System Return Material Authorization (RMA)1 ● NI accepts the delivery of fully assembled systems when performing repair services.Calibration Plan (Optional)Standard Expedited 3 NI performs the requested level of calibration at the specified calibration interval for the duration of the service program. 1This option is only available for PXI, CompactRIO, and CompactDAQ systems. 2This option is not available for all products in all countries. Contact your local NI sales engineer to confirm availability. 3Expedited calibration only includes traceable levels.PremiumPlus Service Program NI can customize the offerings listed above, or offer additional entitlements such as on-site calibration, custom sparing, and life-cycle services through a PremiumPlus Service Program. Contact your NI sales representative to learn more.Technical SupportEvery NI system includes a 30-day trial for phone and e-mail support from NI engineers, which can be extended through a Software Service Program (SSP) membership. NI has more than 400 support engineers available around the globe to provide local support in more than 30 languages. Additionally, take advantage of NI’s award winning online resources and communities .。

OverviewThe National Instruments 5122 high-resolution digitizer features two 100 MS/s simultaneously sampled input channels with 14-bit resolution, 100 MHz bandwidth,and up to 256 MB of memory per channel in a compact,3U PXI or PCI module.With its high sampling rate and low-distortion front end,the NI 5122 is ideal for a wide range of applications in automotive,communications,scientific research,military/aerospace, and consumer ing National Instruments new Synchronization and Memory Core (SMC) architecture,you can easily synchronize to other analog and digital instruments to develop high-channel-count or mixed-signal test systems.Analog Input PerformanceThe NI 5122 uses 14-bit analog-to-digital converters (ADCs), low-noise variable-gain amplifiers,and a low-jitter 100 MHz timebase to deliver 75 dBc spurious-free dynamic range and 62 dB signal-to-noise ratio.The 14-bit data converters have 64 times the resolution of traditional 8-bit instruments,providing more accurate time and frequency-domain measurements.Software selectable 50 Ωor 1 MΩinput impedance,input ranges from 200 mV pp to 20 V pp,seven trigger modes,and antialias and noise filters make the NI 5122 versatile enough to meet the most demanding application requirements.The programmable DC offset feature maximizes the use of the entire 14-bits of vertical resolution.Onboard self-calibration also ensures measurement stability over the entire operating temperature range of0 to 55 °C.Deep Onboard Acquisition MemoryThe NI 5122,based on the SMC architecture,comes with either 8,32 or 256 MB of high-speed memory per channel (4,32,or 128 million 14-bit samples per channel).The NI 5122 can acquire more than 1 million triggered waveforms without software intervention in multiple-record acquisition mode,for applications such as RADAR, ultrasound,and event detection,which require short trigger rearm times.In addition,you can timestamp each triggered event with 100 ps resolution in both single-shot and multiple record acquisition modes. The NI 5122 also can stream data continuously from onboard memory to host memory for longer acquisitions and streaming to disk.The high-speed PCI bus and the scatter-gather bus mastering capabilities of the NI MITE ASIC move data to the computer at speeds up to 100 times faster than traditional instrument interfaces,thereby dramatically decreasing overall test time.TriggeringThe NI5122 digitizer has three trigger sources – analog,digital,and software pare the input signal on either channel or the external trigger channel to one or two thresholds for edge,hysteresis,or window trigger detection.Y ou can also use line-selectable video triggering for NTSC,PAL,or SECAM broadcast standards.Drive andreceive digital triggers to and from the PXI or RTSI trigger bus or the•2 channels simultaneously sampled at 14-bit resolution•100 MS/s real-time and 2.0 GS/s random interleaved sampling •100 MHz bandwidth•50 Ωor 1 MΩinput impedance, software selectable•200 mV to 20 V input range•75 dBc SFDR and 62 dB SINAD •8,32,or 256 MB of memoryper channel•Edge,window,hysteresis,video, and digital triggering with100 ps timestampingModels•NI PCI-5122•NI PXI-5122Operating Systems•Windows 2000/XP Recommended Software •LabVIEW™•LabWindows/CVI •Measurement Studio™Other Compatible Software •Visual Basic•C/C++Application Software (included)•Spectral Measurements Toolkit (32 and 256 MB/channelmodels only)Driver Software (included)•NI-SCOPENI 5122Figure 1. Graph of Dynamic Performance (FFT)NEWexternal 9-pin AUX connector.Y ou can specify the number of samples to acquire before and after a trigger event occurs.These pretrigger and posttrigger settings also apply when the module is used in multiple-record mode.Timing and SynchronizationAn advanced 100 MHz clock generator produces the low-jitter,low-phase-skew clock for the precise clocking and stable synchronization necessary for high-speed,high-resolution digitizers.Y ou can also use an external clock source,such as the NI P XI-5404,for applications that require very specific sample frequencies or you can clock directly from the device under test.Synchronize multiple instruments using the PXI backplane 10 MHz reference clock or an external reference rangingfrom 1 to 20 MHz in 1 MHz increments.Because the NI 5122 is built onhigh-channel-count applications,and build mixed-signal test systemsusing NI 5421 arbitrary waveform generators and NI 655x digitalwaveform generator/analyzers.CalibrationEvery NI 5122 is factory calibrated to verify that it meets NIST-traceable standards.The NI 5122 has an onboard calibration circuit that corrects for environmental effects on gain,offset,frequencyresponse,and timing.The NI 5122 also offers a 2-year calibration cycle,reducing your downtime.When you want to calibrate your device externally,return your NI 5122 to National Instruments or ship it to a qualified metrology lab for routine calibration.Software Every National Instruments high-speed digitizer comes with theIVI-compliant NI-SCOP E driver,which is fully compatible with NI LabVIEW,LabWindows/CVI,and Measurement Studio,as well asMicrosoft Visual C++ and Visual Basic.NI-SCOPE includes more than 50 built-in measurement and analysis functions,and an interactive SCOP E Soft Front Panel.The Spectral Measurements T oolkit gives you sophisticated frequency-domain measurements such as power in-band,multiple peak search,and 3D spectrogram,for applications such as communications,signal intelligence,and avionics.2National Instruments • Tel: (800) 433-3488•Fax: (512) 683-9300•info@ •NI PCI-51228 MB/channel............................................................778758-0132 MB/channel..........................................................778758-02256 MB/channel........................................................778758-03NI PXI-51228 MB/channel…………….......................................778756-0132 MB/channel..........................................................778756-02256 MB/channel........................................................778756-03Includes NI-5122 module,NI-SCOPE,SCOPE Soft Front Panel.The 32 and 256MB/channel models also include the Spectral Measurements Toolkit.AccessoriesRecommended PXI switch NI PXI-2593............................................................778793-01Switchable 1/10x probeSP200B......................................................................763391-019-pin DIN to BNC for AUX I/O connector Aux110..................................................................189919-0R5Related ProductsNI 5421 Arbitrary Waveform GeneratorNI PXI-5404 Clock and Frequency Generator NI 655x Digital Waveform Generator/AnalyzerBUY ONLINE!Visit /products and enter pxi5122 or pci5122Ordering Information Decimation EngineAC/DC Coupling50 Ω-1 M ΩCH 0100/40/20 MHz Filter Stage Gain and Offset Control14-Bit ADCPXI BusAC/DC Coupling50 Ω-1 M ΩCH 1EXT TRIG Clk OUT Clk IN AUXAC/DC CouplingTrigger & EventControl100/40/20 MHz Filter Stage Gain and Offset Control14-Bit ADCTiming and SynchronizationEngineRouting MatrixOnboard Memory (8, 32, or 256 MB)Onboard Memory (8, 32, or 256 MB)SMC (Synchronization and Memory Core)NI-MITE (PCI Bus Interface)PXI Trigger BusFigure 2. Hardware Block DiagramFigure 4. Spectral Measurements Toolkit 3D Spectrogram100 MHz, 100 MS/s, 14-Bit Digitizer3National Instruments • Tel: (800) 433-3488•Fax: (512) 683-9300•info@ •These specifications are valid for 0˚ to 55˚ C for PXI, and 0˚ to 45˚ C for PCI, unless otherwise stated.Acquisition SystemNumber of channels......................................... 2 simultaneously sampled Vertical resolution............................................14 bits Bandwidth 1(-3dB)............................................100 MHzBandwidth limit filters (software selectable)......20 MHz noise (2-pole Bessel)40 MHz antialias (-6dB, 6-pole Chebyshev)Maximum sample rate.....................................100 MS/s real-time, 2 GS/s random interleave sampling Onboard sample memory.................................8, 32, or 256 MB per channel (4, 16, or 128 million samples)Pre and post trigger data points 2.....................0-100% of full record length Input impedance...............................................50 Ωand 1 M Ω|| 27 pF(±2 pF), software selectableFull scale input range ......................................50 Ω: 200 m Ω, 400 mV, 1 V, 2 V, 4 V, 10 V1 M Ω: 200 mV, 400 mV, 1 V,2 V, 4 V, 10 V, 20 VVertical offset ranges.......................................±50% of full scale input rangeMaximum input overload.................................50 Ω: 7 V rms with peaks ≤10 V, 1 M Ω: peaks ≤42 V Input coupling...................................................AC, DC, GND (AC coupling on 1 M Ωonly)AC coupling cutoff frequency (-3dB)................12 HzAccuracyDC accuracy (0 V offset setting)Passband Flatness (referenced at 50 kHz)AC amplitude accuracy (50 kHz)......................50 Ω: ±0.06 dB, 1 M Ω: ±0.09 dB Channel to channel crosstalk...........................≤-100 dB at 10 MHzSpectral Characteristics (typical)Dynamic performance (50 Ωinput impedance with 10 MHz, -1 dBfs input signal)* PCI-5122Phase noise density (10 MHz input)................<-100 dBc/Hz at 100 Hz,<-120 dBc/Hz at 1 kHz,<-130 dBc/Hz at 10 kHzAcquisition ModesReal-time sample rate......................................100 MS/s to 1.526 kS/s sampling rateRandom interleave sampling (RIS)................... 2 GS/s to 200 MS/s sampling rate (repetitive signals only)Timebase SystemTimebase options.............................................Internal, PXI star, external (CLK IN)Total sample clock jitter 4.................................≤1ps rmsInternalInternal sample clock frequency .....................100 MS/s sampling rate with decimation by n where1≤n ≤65,535Timebase accuracy...........................................±25 ppm (±0.0025%)ExternalExternal sample clock sources.........................CLK IN (SMB connector), PXI starExternal sample clock range............................30 to 105 MHz. Variable with decimation by n where1≤n ≤65,535External reference clock sources.....................CLK IN (SMB connector), PXI backplane 10 MHz External reference clock range........................ 1 to 20 MHz in 1 MHz incrementsExternal clock amplitude..................................Sine wave: 0.65 V pp to 2.8 V pp (0 dBm to 13 dBm)Square wave: 0.2 V pp to 2.8 V ppExternal clock impedance................................50 Ω, AC coupledTrigger SystemModes...............................................................Edge, hysteresis, window, video, digital, immediate, software Sources.............................................................CH 0, CH 1, TRIG, PXI_Trig <0:6>, PFI <0:1>, PXI Star, Software Slope.................................................................Rising or falling Hysteresis.........................................................Fully programmableVideo trigger.....................................................Negative sync of NTSC, PAL, and SECAM standards Video trigger types...........................................Any line, specific line, specific field High-frequency reject filter..............................50 kHz software selectable Low-frequency reject filter...............................50 kHz software selectableSensitivity.........................................................CH0 and CH1: 2.5% FS up to 50 MHz increasing to 5% FS at 100 MHz;TRIG: 2.5% up to 100 MHz decreasing to 10% at 200 MHzLevel accuracy..................................................CH0, CH1 and TRIG: ±3.5% FS up to 10 MHz Time resolution.................................................100 ps with time-to-digital converter enabled Holdoff 5............................................................ 2 µto 171.79 s, software selectableExternal Trigger Channel (TRIG)Impedance........................................................1M Ω|| 22pF Range................................................................±5 V Coupling............................................................AC, DCPowerSpecificationsMultiple record acquisition (0-100% pre and post trigger data)Memory per Channel Maximum number of records8 MB 32,76832 MB 131,072256 MB 1,048,576Full scale input range 50 Ωand 1 M Ω200 mV, 400 mV, 1 V, 2V±0.65% of Input ±1.0 mV 4 V, 10 V ±0.65% of Input ±8.0 mV 20 V±0.65% of Input ±10.0 mVFull Scale Input Range 50 Ωand 1 M ΩFilters off400 mV, 1 V, 2 V, 5 V,±0.4 dB DC to 20 MHz 10 V, 20 V ±1 dB 20 MHz to 50 MHz 200 mV±0.4 dB DC to 20 MHz ±1 dB 20 MHz to 40 MHz Anti alias filter onAll ranges±1.2 dB DC to 16 MHz ±1.6 dB 16 MHz to 32 MHz*351026B -01*351026B -012004-3102-305-101-D© 2004 National Instruments Corporation. All rights reserved. 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专利名称：PROCESS AND CIRCUITRY FOR TIMING SYNCHRONIZATION发明人：HESPELT, Volker,ALBERTY, Thomas申请号：DE1988000019申请日：19880116公开号：WO88/007294P1公开日：19880922专利内容由知识产权出版社提供摘要：Process for timing synchronization in a digital data transmission receiver with a timing-error detector, to which are sent the in-phase component and quadrature component of the demodulated receiving signal from which the doubled frequency signal terms have been removed by low-pass filtering, and which acts as an input signal produced from the combination of the received signal with the output signal of the carrier oscillator. The output signal acts as a control signal uTI for the timing generator, the demodulated received signal being converted into two complex signals in the timing-error detector by means of two band-passes; said signals are coupled by a coupling circuit to form a control signal, which actuates the timing-error correction circuit; the process is characterized by the fact that the band-pass output signals are so coupled to form a second control signal uTR by means of a second coupling circuit that the two control signals uTR and uTI may be interpreted as the real part and the imaginary part of a complex actuation variable uT = uTR + juTI; also that the average A of the control signals uTR and uTI is calculated, and that finally the average value uTR, uTI thus achieved is calculated by a calculating circuit CC to achieve an actuating variable δ which controls the timing-error correction circuit TEC.申请人：HESPELT, Volker,ALBERTY, Thomas地址：Gerberstraße 33 D-7150 Backnang DE,Lichtensteinstraße 44 D-7150 Backnang DE,Danziger Straße 28 D-7150 Backnang DE国籍：DE,DE,DE代理机构：ANT NACHRICHTENTECHNIK GMBH更多信息请下载全文后查看。

On the Synchronization Techniques for Wireless OFDM SystemsBo Ai,Member,IEEE,Zhi-xing Yang,Chang-yong Pan,Jian-hua Ge,Yong Wang,Member,IEEE,and Zhen LuAbstract—The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper.The typical algorithms dealing with the symbol timing synchronization,the carrier frequency syn-chronization as well as the sampling clock synchronization are briefly introduced and analyzed.Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed,with several key issues on the synchronization for the OFDM systems discussed.Index Terms—Carrier frequency synchronization,continuous mode and burst packet mode transmission systems,OFDM, sampling clock synchronization,symbol timing synchronization.I.I NTRODUCTIONO FDM,associated with other related technologies have found its wide applications in many scientific areas due to its high spectrum efficiency,its robustness against both multi-path and pulse noises,its highly reliable transmission speed under serious channel conditions,adaptive modulation for each sub-carrier according to the channel conditions, and etc.It has become fundamental technology in the future 4G-multimedia mobile communications systems[1].Many digital transmission systems have adopted OFDM as the modulation technique such as digital video broadcasting terrestrial TV(DVB-T)[2],digital audio broadcasting(DAB), terrestrial integrated services digital broadcasting(ISDB-T), digital subscriber line(xDSL),WLAN systems based on the IEEE802.11(a)[3]or Hiperlan2,multimedia mobile access communications(MMAC),and thefixed wireless access(FW A) system in IEEE802.16.3standard.OFDM has also found its application in Cable TV systems.Technologies fundamentally based on OFDM,such as vector OFDM(V-OFDM),wide-band OFDM(W-OFDM),flash OFDM(F-OFDM)have also shown their great advantages in certain application areas.There are some disadvantages,however,appeared in the OFDM systems,for example,the large Peak-to Average Power Ratio(PAPR)as well as high sensitivity to the synchronization errors.Synchronization issues are of great importance in allManuscript received April26,2005;revised October27,2005.This work was supported in part by the National Natural Science Funds in China(Nos. 50177001,60372007,and60332030)and by the Ministry of Information Industry Foundation under Grant no.2002291.B.Ai is with the Dept.of E&E Tsinghua University,State Key Lab.on Microwave and Digital Communications,China(100084).He is also with the Engineering College of Armed Police Force,Xi’an,China(710086)(e-mail: abeffort_apple@).Z.Yang and C.Pan are with the Dept.of E&E Tsinghua University,State Key Lab.on Microwave and Digital Communications,China(100084).J.Ge and Y.Wang are with the National key Lab.of Integrated Service Net-works,Xidian Univ.,Xi’an,China(710071).Z.Lu is with the Dept.of Electronic Engineering in Shanghai Jiaotong Uni-versity,China(200052).Digital Object Identifier10.1109/TBC.2006.872990digital communications systems,especially in the OFDM systems.Synchronization errors not only cause inter-symbol interference(ISI)but also introduce inter-carrier interference (ICI)due to the loss of orthogonality among all sub-carriers. In this paper,we focus on the synchronization schemes in the OFDM systems.Fundamental theory for the synchronization is briefly described in Section II and in Section III,the symbol timing scheme and three improved methods for thefine symbol timing in frequency domain are proposed.We then conduct the analysis on the carrier frequency recovery as well as the sampling clock synchronization methods in Sections IV and V respectively.In Section VI,joint estimation of all the synchro-nization errors including timing,frequency and phase offsets is simply described.Technical forecast is made in Section VII with conclusions drawn in Section VIII.II.O VERVIEW FOR THE S YNCHRONIZATION IN OFDM S YSTEMS Synchronization is of great importance for all digital com-munication systems.OFDM systems are very sensitive to both timing and carrier frequency offset,especially,when combined with other multi-access techniques such as FDMA,TDMA,and CDMA.Therefore,synchronization is extremely crucial to the OFDM systems.A.Three Synchronization Issues in the OFDM Systems There are three major synchronization issues in the OFDM systems:a.The symbol timing synchronization,which is to deter-mine the correct symbol start position before the FFT de-modulation at the receiver end.b.The carrier frequency synchronization(i.e.,carrier fre-quency recovery technique),which is utilized to eliminate the carrier frequency offset caused by the mismatch from the local oscillators between the transmitter and the re-ceiver,nonlinear characteristic of the wireless channel as well as the Doppler shift.c.The sampling clock synchronization,which is to miti-gate the sampling clock errors due to the mismatch of the crystal oscillators.All these synchronization errors will significantly degrade system performance[4],[5].B.Synchronization Technologies in the Continuous Mode and Burst Packet Mode Transmission SystemsAccurate synchronization is indispensable to suppress the negative impact of the synchronization errors in the commu-nication systems no matter,whether it is in continuous or burst packet mode transmission systems.However,these two different modes require different synchronization schemes:0018-9316/$20.00©2006IEEEa.In the burst packet mode,synchronization ought to beestablished at any time because when data streams are ready to transmit is unknown The duration of the training symbols used for synchronization in this mode is rela-tively short and synchronization should be done within a single training symbol time for the systems such as IEEE 802.11(a)[3]and HiperLan/2to avoid the reduction of the system capacity.It is inappropriate to do averaging over many symbols or pilots because of the stringent re-quirement on synchronization time and the less number of sub-carriers.It is also important for the systems in this mode to establish the synchronization in time domain and this will greatly reduce the acquisition time since it avoids the feedback from frequency domain.b.In the continuous mode such as DAB,DVB-T[2]sys-tems,averaging method can be used to improve the es-timation accuracy because there is no stringent require-ment on the acquisition time.In this mode,large numbers of sub-carriers has been utilized and,it is appropriate to apply the cyclic prefix(CP)or pilots to these synchroniza-tion methods.III.S YMBOL T IMING S YNCHRONIZATIONWhen signals are transmitted through severe channel con-ditions of multi-path fading,pulse noise disturbance and the Doppler Shift,it is important to solve symbol timing synchro-nization problemfirst during the design process of an OFDM receiver.The symbol timing error can not only disturb the amplitude as well as the phase of the received signal,but also introduce ISI. In order to perform the FFT demodulation correctly,the symbol timing synchronization must be done to determine the starting point(i.e.FFT window)of the OFDM symbol.The cyclic prefix (CP,or Guard Interval,GIB)can be removed afterwards.The concept of the GIB wasfirst proposed by A.Peled[6],which can prevent OFDM symbols from ISI disturbance and keeps the orthogonality among all the sub-carriers.Fig.1shows the vari-ation of the signal constellation due to the symbol timing errors. Fig.1(a)and(1b)represent the symbol starting point within GIB(case1)and outside ISI-Free region(case2)respectively. It clearly shows how bad the signal constellation could be due to the symbol timing errors.Accurate and steady symbol timing synchronization can be realized through the coarse symbol timing,thefine symbol timing as well as the symbol timing control structure combined together.The coarse symbol timing synchronization isfirst executed in time domain and then,thefine symbol timing in frequency domain is done to ensure a more accurate estimation. The symbol timing control structure is utilized to coordinate the operations of the coarse and thefine symbol timing.A.The Coarse Symbol Timing Algorithms in Continuous Mode The conventional algorithms for the coarse symbol timing synchronization in time domain are MLE(Maximum Like-lihood Estimation)utilizing the cyclic prefix of the OFDM symbols.The most representative algorithm was proposed by J.J.Van de Beek[7].However,good performanceachieves(a)(b)Fig.1.(a)Constellation variation due to the symbol timing error.The total subcarriers N=2048,cyclic prefix L=128,64-QAM mapping.No carrier frequency and sampling clock offset.The normalized symbol timing offset is 36(samples)Case1.(b)Constellation variation due to the symbol timing error. The total subcarriers N=2048,cyclic prefix L=128,64-QAM mapping. No carrier frequency and sampling clock offset.The normalized symbol timing offset is36(samples)Case2.only under the AWGN channel.When the channel condition becomes severely degraded,data in GIB is badly contaminated by ISI,there will be significantfluctuation for the starting point estimated for the OFDM symbol.And suchfluctuation will have the significant influence on the carrier frequency offset as well as the sampling clock offset estimation in frequency domain.To improve the performance of ML Estimator,a novel scheme utilizing both CP and pilots to do the coarse symbol timing synchronization was proposed by ndström [8].It has better performance compared to that of[7]under the multi-path fading channel.However,the nonnegligible fluctuation still exists because of the ISI contamination on the data within GIB and the limited number of pilots used for estimation.In order to mitigate thefluctuation,T.M.Schmidlintroduced a new method making use of the training symbols in time domain,in which a timing function was defined[9]. It has better performance compared to those proposed by J.J.Van de Beek and ndström.Unfortunately,it has a“flat region”in the estimation,which,to a great extent,increases the variance of the symbol timing estimator.Some new schemes has been proposed in the literatures [10]–[13]in recent years to overcome the defects of the al-gorithms mentioned above,with the target to decrease the fluctuation of the starting point of the estimated symbol as well as to make the estimation within the ISI-Free region.The convolution characteristic of the cyclic prefix are utilized in literature[10],while,PN sequences are adopted in[11]–[13], to take the advantage of the intrinsic,fairly good correlation property of PN:Kasami sequence is utilized in[11]with the excellent correlation properties;and in[12],[13],a novel timing recovery methods for TDS-OFDM(key techniques for the Terrestrial Digital Multimedia/Television Broadcasting System,namely DMB-T proposed by Tsinghua University [14])is developed.This scheme is based on the searching and tracking on the correlation peaks of the PN sequences,which is as the GIB for each OFDM symbol.Because of the excellent correlation properties of the so-called m-sequence,the perfor-mance of these algorithms[10]–[13]outperforms those from[7]–[9]under the multi-path fading channels.B.The Fine Symbol Timing Synchronization in Continuous ModeThefine symbol timing synchronization in frequency domain is often required to guarantee the estimation accuracy.A pre-amble structure including a synchronizationfield(S-filed)and a cell-searchingfield(C-field)is proposed in literature[15]with thefine symbol timing done by using the cell identification method.In[16],a specially designed pilot symbol structure is utilized to generate afine symbol timing -puter simulations and analysis verify their good estimation per-formances but low bandwidth efficiency.The residual symbol timing error may cause the phase rotation of the sub-carriers in frequency domain.In this Section,we propose three improved algorithms to do thefine symbol timing based on the algorithm introduced by[17].Computer simulations show that these pro-posed methods have better performance compared with the al-gorithm in[17]when under serious channel conditions.In the following,we referred the algorithm in[17]as Algorithm1,and named our proposed methods as Algorithm2,Algorithm3and Algorithm4respectively.Algorithm2:(1)(2)Where,denotes the number of scattered pilots(SP),isa complex variable forthe SP inthe OFDMsymbol,is the phase deviation of the two adjacent SP’s causedby the symbol timing offsetof OFDM symbol,is thedistance between the two adjacent SP’s.,,denotestheFig.2.Performance comparison among Algorithm1,2,3,and4for thesymbol timing estimation.The total subscribers N=2048,cyclic prefixL=128,SNR=5dB,Rayleigh fading channel[2],normalized carrierfrequency offset is0.135and048respectively.integer part of symbol timing offset,useful symbol duration pe-riod and the nominal sampling frequency respectively.This al-gorithm has the same limited estimation range as that in Algo-rithm1and its estimation accuracy is influenced by the carrierfrequency offset[17].Algorithm3::Algorithm1and2perform the estimation onthe adjacent SP’s within the same OFDM symbol.In algorithm3and4,we derive the offset for thefine symbol timing from thepilots in the two consecutive OFDM symbols(Fig.2).Thatis,(3)Where,denotes the complex conjugationof,Algorithm4::The same as that in Algorithm3,SP’s of con-secutive OFDM symbols can be utilized.But the only differentfrom algorithm3is the phase characteristic of known pilots isnow givenby:(4)Lots of computer simulations validate the following conclu-sions:a.The performances of algorithms2and4outperformthat of algorithms1and3under multi-path fading channels re-spectively.This is because the phase characteristic is utilized inalgorithms2and4,while,the power characteristic is utilizedin algorithms1and3.It is well known that,power character-istic is much more sensitive to the multi-path fading channelsthan phase characteristic.b.When the normalized decimal car-rier frequency offset is less than certain value(about0.15thatof sub-carrier spacing),the performance of algorithms3and4outperform that of algorithms1and2and the best estimationresults can be obtained with Algorithm4.c.When the normal-ized decimal carrier frequency offset is larger than certain value(about0.15that of sub-carrier spacing),the performances of al-gorithms1and2outperform that of algorithms3and4and thebest estimation results can be achieved by Algorithm2.The de-tailed analysis for the effects of the carrier frequency offset onthefine symbol timing synchronization can be found in[17].Fig.3.Frequency synchronization estimator.C.The Symbol Timing Synchronization Algorithms in Burst Packet Transmission ModeThe synchronization requirements vary with the applications, therefore,we should adopt the appropriate synchronization techniques in both continuous and burst packet transmission modes respectively.As being discussed in Section II-B,it is inappropriate to do the symbol timing synchronization with pi-lots in the burst packet mode due to the stringent requirements on synchronization time.In[18],a novel scheme to do the coarse symbol timing with training symbols is proposed and, the computer simulations based on IEEE802.11(a)standard [3]illustrate that more accurate coarse symbol timing synchro-nization can be achieved by the convolution method in time domain than that by the ordinary MLE method,no matter it is in the office environment[19]or under much severe channel conditions[2].This really comes from the fully utilization of the convolution property of CP.D.Symbol Timing Synchronization Control ModelOther than the accuracy of the estimation in the symbol timing synchronization process,the robust and efficient syn-chronization control structure to ensure the system stability is also requested.A new symbol timing synchronization control model has been proposed in[10].Similar to those control models in[17],[20],it also has two synchronization states:the acquisition state and the tracking state.The difference is that the threshold and counters are utilized to perform the control process with less computational complexity than those in[17].IV.C ARRIER F REQUENCY R ECOVERY T ECHNIQUES Carrier frequency offset(CFO)caused by the Doppler shift, local oscillators mismatch between the transmitter and the re-ceiver ends,may introduce ICI and destroy the orthogonality of OFDM sub-carriers,resulting in the losses of SNR.With the insertion of the GIB in OFDM symbols,symbol timing error within a certain range will not introduce ISI and ICI.OFDM system is more sensitive to the CFO and the sampling clock offset(SCO).Regarding to higher modulation modes such as 64-QAM,tiny CFO may introduce severe degradation on the system performance[21].Carrier frequencyoffset puts an extra phase factorofin the received signal,where is the sub-carrierspacing,is the CFO normalizedby and is usu-ally divided into an integerpart,(multiple of the sub-carrier spacing,causing a shift of the sub-carrier indices),and a dec-imalpart,(less than half of the sub-carrier spacing,causes a number of impairments,including attenuation and rotation of the sub-carriers and ICI).We can divide CFO into three parts:the integer part,the coarse decimal part and thefine decimal part.CFO can usually be compensated for through the following procedures shown in Fig.3.First,a coarse symbol starting point for the FFT demod-ulation is provided by the coarse symbol timing module and then,the estimation and correction of the coarse decimal fre-quency offset in time domain is performed to minimize the ICI impact on the estimation in frequency domain,with the integerpart estimated in frequency domain to get the correct sub-car-rier index.Finally,the residual frequencyoffset,i.e.thefine decimal frequency offset is estimated.A tracking loop structure (the Acquisition and the Tracking Mode Switching module)can be exploited to coordinate the coarse decimal part,the integer part and thefine decimal part of the frequency offset.Each of them makes unique contribution to the recovery of the carrier frequency offset[50].Many literatures have discussed how to make OFDM systems less sensitive to the carrier frequency offset,for instances,per-form the windowing on the transmitted signals or use self-can-cellation schemes[22],[23].However,long prefix adopted in systems with these approaches results in low bandwidth effi-ciency.Generally,we can divide the carrier frequency recovery algorithms into three categories:a.Methods are based on training symbols or pilots[9],[24]–[33],named Data Aided(DA)method.b.Methods use of the intrinsic structure of OFDM symbols,e.g.cyclic prefix[7],[34]–[40],which is called Non DataAided(NDA)method.c.Blind approaches [41]–[43],which relies on the signal statistics and often has very high computational com-plexity,some approaches may have extra requirements on the channel statistics.A.Integer Carrier Frequency OffsetThe integer as well as the coarse decimal CFO correction can make the sub-carriers spacing offset less than half of sub-car-rier spacing in the present of more than tens of sub-carriers.Most algorithms for the integer CFO estimation [9],[29],[31],[44]–[47]nowadays have two major defects:a.Limited esti-mation range on CFO;b.Stringent requirement on the symbol timing synchronization.The earliest algorithm in this category was proposed by P.H.Moose [47]with the estimation rangelimitedwithin,that is,only 1/2that of sub-carrier spacing.P.H.Moose tried to overcome this problem by increasing thesub-carrier spacing to avoid phase offsetexceeding .How-ever,the increase of sub-carrierspacing satisfying (5)may decrease the useful OFDM symbol durationtime ,resulting in tighter requirements on the symbol timing synchronization.Besides,the increase of the sub-carrier spacing will not enlarge the range of the integer part estimation to a very largeextent.(5)T.M.Schmidl et al.,later,proposed an improved algorithm [9]with better performance under multi-path fading channel,and its estimation range was one time wider than that by P.H.Moose [47].Unfortunately,a large pre fix is still needed,for ex-ample,in DVB-T [2]systems,pre fix (2k mode)must be used.On the other hand,its estimation range is still very limited and is sensitive to the symbol timing errors.Three improved estimation algorithms are proposed in litera-ture [48]to overcome these defects.All of them use the power and phase characteristic of the known pilots,which is insensitive to the symbol timing errors and have a wider estimation rangeof integer part of CFO (i.e.,as largeas,with the total number of useful sub-carriers in one OFDM symbol).B.Coarse Decimal Carrier Frequency OffsetAs mentioned earlier,CFO estimation should follow three procedures.If the decimal part of CFO,however,can be es-timated in frequency domain,why should we carry out the coarse CFO estimation in time domain first?There are two main reasons:a.To reduce ICI caused by CFO,which lays the foundation on a more accurate CFO estimation in frequency domain;b.To estimate and compensate for the CFO all in time do-main,reducing the synchronization time,and is suitable for the systems of burst packet transmission mode.The early-proposed typical algorithm on the coarse decimal CFO estimation was from J.J.Van de Beek et al.[7]with CP characteristic exploited.T.M.Schimdl et al.,later,proposed a new algorithm named SCA [9].However,either of them has a very stringent requirement on the symbol timing.An improved algorithm,not so sensitive to the symbol timing errors was pro-posed recently in literature [49],with only(is the length of the Guard Interval)correlation window length utilized for es-timation,avoiding the data portion contaminated by the incor-rect phase information from the symbol timing errors.Computer simulations show that when the decimal part of the CFO approaches to 0.5of the sub-carrier spacing,the estimated value may,due to the multi-path fading,the phase noises as well as the discontinuity of the arctangent function,jump to the inverse polarity,as pointed out in literature [47].For example,if the decimal frequency offset in data streams is 0.498of the sub-carrier spacing,the estimate result with the typical algorithms mentioned above may be -0.467of the sub-carrier spacing.The strategy to avoid the above problem in P.H.Moose algorithm is to reduce the length of the DFT and use larger carrier spacing,degrading the overall system performance.A second-order IIR filtering can be used to solve this problem [49].C.Fine Decimal Carrier Frequency OffsetAfter correction based on the coarse decimal CFO estima-tion,the residual decimal CFO in data streams may be reduced to only 1%,and then the fine decimal CFO estimation deals with the residual CFO.The typical algorithm was also proposed by P.H.Moose [47].However,it suffered a problem of poor band-width ef ficiency.In fact,pilots embedded in the OFDM symbols can be utilized to do the fine decimal CFO.D.Carrier Frequency Offset Control ModelIt is necessary to have a control module to coordinate the operations of the integer CFO,the coarse decimal CFO and the fine decimal CFO [48].As shown in Fig.3,this module consists of two modes:the acquisition mode and the trackingmode.After the estimation on the integerpartand fine dec-imalpartin frequency domain,the counter value COUN will increase or decrease depending on whether the valueofis larger than a constant A (set by the system per-formance requirement,forexample,).The value of COUN decides whether it is in the tracking or the acquisition mode.Performance and detailed analysis on this control model is presented in [50]showing excellent performance in estima-tion,tracking and correction of CFO.E.Carrier Frequency Offset in the Burst Packet Mode There is no stringent requirement on acquisition time in the continuous systems such as DAB,DVB-T [2]and DMB-T [14],averaging method or filtering over many OFDM symbols can be adopted to increase estimation accuracy,where it is appro-priate to adopt those methods based on CP or pilots.Some lit-eratures make use of the null sub-carriers for power detection to estimate the CFO [51].However,for systems in the burst packet mode,repetitive structure is often utilized with,no differ-ence either between these null sub-carriers or the idle time be-tween neighboring blocks.Those methods,therefore,are inap-propriate in the burst packet mode.Because of the short duration time of packets,it has more stringent requirement on synchro-nization acquisition time (i.e.,acquisition done within a single OFDM symbol).Besides the requirement on estimation accu-racy,fast convergence is also needed.The accuracy of the CFO estimation in time domain,nonfeed back synchronization model are equally important to these systems and,the synchronization should be established only in time domain [13],[48].(a)(b)Fig. 4.Constellation variation due to the sampling clock offset.Total sub-carriers N=2048,cyclic prefix L=128,64-QAM modulation, normalized sampling clock offset is1ppm,after200OFDM symbols.Other factors follow DVB-T standard[2].V.S AMPLING C LOCK S YNCHRONIZATIONThe sampling clock errors are mainly from the mismatch of the crystal oscillators between the transmitter and the re-ceiver.Other factors such as multi-path fading,noise distur-bance,symbol timing estimation errors may also contribute to the sampling clock offset(SCO).The sampling clock errors will negatively influence the symbol timing synchronization.For ex-ample,assume1ppm sampling clock offset in2K mode with a GIB of512samples in DVB-T[2],the FFT window will move one sample around every400symbols.The higher the sam-pling clock offset,the more the influence on the symbol timing synchronization.Fig.4shows signal constellation variation due to the sam-pling clock offset.It is obvious that the larger the SCO,the more severe the distortion.Detailed analysis on the effects of sampling clock offset on symbol timing is presented in[52].In order to analyze the effects of SCO on the system performance in a more explicit way,SCO is divided into two parts:the sam-pling clock phase offset and the sampling clock frequency offset [17],[20],[53],[54].Effects of the sampling clock phase offset is similar to that of the symbol timing offset,leading to the signal phase distortion;while the sampling clock frequency offset in-troduces ICI.By defining Inter-Sample-Interference,effects of the sampling clock offset on system performance could be ana-lyzed deeply[55].The synchronous sampling and the asynchronous sampling are two different kinds of methods for the sampling clock syn-chronizations[56]–[58].1)Timing algorithms are usually used in the synchronoussystems to control both phase and frequency of a V oltageControl Crystal Oscillator(VCXO)[53],[59]–[61].Compared to the asynchronous digital sampling systems,it has large timingfluctuation due to high-level phasenoises.The need of the analog circuits makes it inconve-nient for the system integration[62].2)An independent oscillator is often exploited for samplingin an all-digital system.Timing algorithms are used tocontrol NCO(Numerical Control Oscillator)and then usethe NCO output to control the interpolatorfilter.BER per-formance of the asynchronous system in[54],[62]showsthat the asynchronous systems are more sensitive to CFOthan the synchronous puter simulations in[63]demonstrate that unrealistic interpolator may causecyclic tracking errors in asynchronous systems,whichnever occurs in the synchronous systems.The estimated sampling clock offset and decimal part of symbol timing error may be considered as an adjusting variable when we do sampling clock synchronization.This sampling clock adjusting variable is derived in frequency domain and then fed back to time domain to adjust digital oscillator,guar-anteeing the stability of the loop control circuit.VI.J OINT E STIMATION A LGORITHMSSome algorithms can be utilized for the joint estimation of all the synchronization errors including the symbol timing,the carrier frequency and the sampling clock offsets.Algorithms mentioned in the former sections such as[7]–[9],[47],are the typical algorithms to do the joint estimation of symbol timing and decimal CFO.The decimal CFO estimation utilizing the de-tected phase of the received frequency-domain complex data in the pilot sub-carriers or training symbols,is to be performed after the estimation of symbol timing errors.However,just as we have analyzed in Section IV-B,they all have stringent require-ment on the symbol timing synchronization.Some new joint es-timation algorithms are proposed recently[64],[65],in[64], the proposed algorithm with a weighted least squares technique generates offset estimates with minimum RMS errors.Multiple received OFDM symbols as an observation interval are utilized in[65],both of which are less sensitive to the symbol timing errors.The joint estimation and tracking of symbol timing and sam-pling clock errors are presented in[17],[53].The main problem。