扩频通信系统的介绍
摘要：本应用笔记概述了扩频技术的原理，讨论了涵盖直接序列和快速跳频的方法。相关理论方程的性能估算。以及讨论直接序列扩频（DSSS）和跳频（FHSS）这两种扩频方式。
简介
扩频技术越来越受欢迎，就连这一领域以外的电器工程师都渴望能够深入理解这一技术。很多书和网站上都有关于这方面的书，但是，很多都很难理解或描述的不够详尽。（例如，直接序列扩频技术广泛关注的是伪随机码的产生）。
下面讨论扩频技术（双关语意）。
简史
一名女演员和一名音乐家首次以书面形式描述了扩频通信技术。1941年，好莱坞女星Hedy Lamarr和钢琴家George Antheil描述一个安全的无线链路来控制鱼雷。他们获得了美国专利#2.292.387。但这一技术被遗忘了，没有在当时受到美军的重视，直到20世纪80年代它才开始活跃起来。从那时起，这一技术在有关恶劣环境中的收音机链接方面越来越受欢迎。
最典型的扩频技术应用是数据收发器包括卫星定位系统（GPS）、3G移动通信、无限局域网(符合IEEE?802.11a,IEEE 802.11b,IEEE 802.11g标准)，还有蓝牙技术也帮助了那些通讯落后和无线电通信条件有限的地方，因此，它是一种昂贵的资源。
扩频通信的原理
扩频是香农定理的典型：
C=B×log2(1+S/N) 公式（1）在公式中，C为信道容限，单位是比特/秒(bps),意指单位时间内信道中无差错传输的最大信息量。B为信号频带宽度，单位是Hz，S/N为信噪比。也就是说，C为信道允许通过的信息量，也代表了扩频的性能。带宽(B)是代价，因为频率是一个有限的资源。信噪比体现了环境条件或物理特性（如障碍、干扰器、干扰等）。
上式说明，的情况下，在无差错传输的信息速率C不变时，如果信噪比很低，则可以用足够宽的带宽来传输信号，即使信号功率密度低于噪音水平。（公式可用！）
改变公式（1）中对数的底数，2改为e，则为In=loge。
因此，
C/B=(1/ln2)×ln(1+S/N)=1.443×ln(1+S/N)公式（2）
根据MacLaurin扩展公式
ln(1+x)=x-x2/2+x3/3-x4/4+…+(-1)k+1xk/k+…:
C/B=1.443×(S/N-1/2×(S/N)2+1/3×(S/N)3-…) 公式（3）
在扩频应用中，通常S/N很低。（正如刚才提到的，信号功率密度甚至低于噪音水平。）假定噪音水平即S/N<<1，香农公式可简单表示为：
C/B≈1.443×S/N公式（4）
简化为：
C/N≈S/N 公式（5）
或者：
N/S≈B/C 公式（6）
向固定了信噪比的信道发送错误的信息，只要执行基本扩频信号的传播操作：增加传输带宽。尽管这一原则看起来很简单明确，但实现她却很复杂，主要是因为展宽基带的电子设备必须同时存在展宽和解扩的操作过程。
定义
不同的扩频技术都有一个共同之处：密钥（也称为代码或序列）依附于传输信道。以插入代码的形式准确地定义扩频技术，术语“频谱扩展”是指扩频信号的几个数量级的带宽在有密钥的传输信道中的扩展。
以传统的方式定义扩频更为精确：在射频通信系统中，将基带信号扩展为比原有信号的带宽宽得多的高频信号（如图1）。在此过程中，传输宽带信号产生的损耗，表现为噪声。扩频信号带宽与信息带宽之比称为处理增益。扩频过程的处理增益大都在10dB 到60dB 之间。
要应用扩频技术，只需在天线（接收器）之前加入相应的扩频码。相反，你可以删除一个点的扩频码（称为解扩操作）接收发射链路数据恢复。解扩过程是重新恢复原始带宽的过程。很明显，同样的代码必须在事先知道在传输通道两端的信息。（在某些情况下，在调制和解调的过程中代码应该是知道的）。
图1.扩频通信系统
传播工作带宽的影响
图2说明了信号带宽的通信链路评估
图2.扩频操作遍及一个更宽的频率带宽的信息能量
扩频调制是一种适用于如BPSK 或直接转换。传统的调制可以证明所有其他信号接收不到扩频代码将保持它们原有的信息，极没有被扩展。
解扩过程中带宽的影响
同样，解扩过程如图3。
输入的扩频码
频率
数据的处理增益
数据输入宽度 扩频调制 数据输入 能量
能量
PF 载体 输电链 扩频代码
接收链
扩频代码
数据输入
射频输出
射频输入 射频连接 相同的配置序列 数据输出
能量
数据输入宽度
数据输入 解扩调制
能量
输入的扩频码 数据的处理增益
PF 载体 频率
图3,在解扩过程中恢复的原有信号
在这里，解扩调制已经取得了正常解调操作，也表明了干扰或干扰信号在解扩传输过程中被扩展！
由于带宽的浪费抵消了传播的多用户
扩频结果直接在一个更宽的频带使用，完全对应之前的“处理增益”。 因此扩频并没有节约有限的频率资源。过度的使用虽然得到了补偿，但是可能有很多用户共享这一扩大频率波段（如图4）。
图4.在相同的频带多个用户共享扩频技术。
扩频是宽带技术
相对于常规窄带技术，扩频过程是一种宽带技术。例如，W - CDMA 和UMTS 都是宽带技术，与窄带广播相比，它需要一个比较大的频率带宽。
扩频的优点
抗干扰性能和抗干扰的影响
扩频技术有很多优点。.抗干扰性是最重要的一个优点。有意或无意的干扰和干扰信号都是不希望存在的因为它们不包含扩频密钥。只有期望信号才有密钥，在解扩过程中才会被接收器接收，如图5。
图5.扩频通信系统。注意，解扩链路中数据信号被传输的同时干扰能源也被传输。
输电链 扩频代码 接收链
扩频代码
数据输入
射频输出
射频输入 射频连接 数据输出
数据 干扰 数据扩展和
干扰扩展
数据扩展 数据扩展和干扰 用户1+用户2+用户3+…+用户N
数据输入获得的扩频增益
无论在窄带或宽带中，如果它不涉及解扩过程，你几乎可以忽略干扰。这种抑制反应也适用于其他没有正确密钥的扩频信号。因此不同的扩频通信系统可以工作在同一频段，例如CDMA 。值得注意的是，扩频是宽带技术，但反之则不然：宽带技术不涉及扩频技术。
抗截获
抗截获是扩频通信技术的第二个优势。由于非法的听众没有密钥用于原始信号传播，这些听众无法解码。没有合适的钥匙，扩频信号会出现噪音或干扰。（扫描方法可以打破的这些密钥，但是密钥是短暂的。）甚至更好，信号电平可以低于噪声水平，因为扩频传输降低了频谱密度，如图6。（总能量是相同的，但它是广泛存在于频率的。）因此信息是无形的，这一影响在直接序列扩频（DSSS ）技术上有充分的体现。（在下文的DSSS 作更详细说明。）其他接收机无法“看到”这种传输，它们只能出现在整体噪音水平略有增加的情况下！
图6.在被噪音水平之下的扩频频谱信号。 在没有正确的扩频传输密钥的情况下，接收器不能“看到”传输过程。
抗衰落（多径效应）
无线信道通常具有多径传播，即有一个以上的信号从发射机传到接收器（如图7）。这种多路径可以通过空气的反射或折射以及从地面反射或物体如这些路径建筑物引起。
图7.信号是如何通过多个路径到达接收器的。 这种反射路径（R ）可干扰直接路径（D ）的现象称为解扩过程的同步衰落。因为解扩过程使信号D 与信号R 的同步被拒绝，即使它们包含了相同的密钥。将反射路径的信号应用于解扩是个有用的方法。
扩频技术在CDMA 的应用
请注意，扩展频谱不是一个扩频调制方案，不应与其他调制方式相混淆。例如我们可以使用扩频技术发射一个由PSK 或BPSK 的已调信号。.感谢调制的信号的编码基础，使Rx
R
D
Tx 噪声基准 扩展后的数据
噪声基准
数据传播之前
扩频频谱也可用于其他类型的多址实现（即可以同时进行多个通讯联系和实际或表面上相同的物理介质共存）。到目前为止，有三个主要的方法可用。
FDMA-频分多址
FDMA 分配一个特定的载波频率给通信信道。不同用户使用频谱的切片数是受到限制的（如图8）。在已有的三种多路存取方法中，FDMA 在频带利用方面是效率最低的。FDMA 的方法包括Methods 包括无线电广播，电视，高级移动电话系统AMPS 等。
图8. FDMA 系统中不同的用户的载波频率分配。
TDMA-时分多址
TDMA 的不同用户彼此间发言和听取信息时，是根据定义的时隙分配来处理的（如图
9）。不同的通信信道可以建立一个唯一的载波频率。TDMA 的例子有全球移动通信系统GSM ，DECT ，TETRA 和IS - 136。
图9.在TDMA 系统中不同用户的时隙分配。
CDMA-码分多址
CDMA 的传播是由密钥或代码决定的（如图10）。在这个意义上说，扩频就是一种CDMA 。在发射器和接收器密钥必须提前被定义和确定。它的例子有IS - 95(DS)，IS- 98，蓝牙和无线局域网。
用户1 用户2 用户3 用户N 用户1 用户2 用户3 用户N
时间段 时间段 时间
(ms,us) 用户1 用户2 用户3 用户N
频率
(kHz,MHz,GHz)
Fc1 Fc2 Fc3 FcN
图10.CDMA 系统中相同频带有独特的钥匙或代码。
当然，人们可以结合上述存取方法，例如，全球移动通信系统GSM 结合了TDMA 和FDMA 。GSM 定义了不同的载波频率（细胞）的拓扑领域，并设定时段内每一个细胞。
扩频和（的）编码密钥
在这一点上，值得重申的是扩频的主要特点是一个代码或密钥必须在发射器和接收器之前就是已知的。现代通讯的代码是数字序列必须长期存在和随机出现的，尽可能地显示为“噪音像”。在任何情况下，代码必须确保是可再生的。或者接收器不能提取已发出去的消息。因此，该序列是几乎是随机的 。这样的代码被称为伪随机数（PRN ）或序列。最常用的方法来产生伪随机是基于反馈移位寄存器的。
许多书籍都在介绍伪随机码的发展与特征，但是，实际的发展已超出了这些教材所叙述的。注意的是，建立或选择适当的序列或序列集并不是微不足道的。为了保证有效的扩频通信，伪随机序列必须尊重一定的规律如长度、自相关、互相关、正交。比较受欢迎伪随机序列有Barker 码，M 序列码，Gold 码，Walsh 码等。考虑到存在更复杂的序列集，给它提供了一个更强大的扩展频谱链路。但是这产生了成本问题：扩频和解扩都需要在速度和性能都更复杂的电子产品，数字扩频解扩芯片包含几百万个等效的2输入与非门在几十兆赫间切换。
用户1 用户5
用户4
用户3 用户2
An Introduction to Spread-Spectrum Communications
Abstract:This application note is a tutorial overview of spread-spectrum principles.The discussion covers both direct-sequence and fast-hopping methods.Theoretical equations are given to allow performance estimates.Relation direct-sequence spread-spectrum(DSSS) and frequency-hopping spread-spectrum(FHSS) methods.
Introduction
As spread-spectrum techmiques become increasingly popular,electrical engineers outside the field are eager for understandable explanations of the technology.There are books and websites on the subject,but many are hard to understand or describe some aspects while ignoring others(e.g.,the DSSS technique with extensive focus on PRN-code generation).
The following discussion covers the full spectrum(pun intended).
A Short History
Spread-spectrum communications technology was first described on paper by an actress and a musician!In 1941 Hollywood actress Hedy Lamarr and pianist George Antheil described a secure radio link to control torpedos.They received U.S.Patent #2.292.387.The technology was not taken seriously at that time by the U.S.Army and was forgotten until the 1980s,when it became active.Since then the technology has become increasingly popular for application that involve radio links in hostile environments.
Typical applications for the resulting short-range data transceivers include satellite-positioning systemsGPS，3G mobile telecommunications,W-LAN(IEEE?802.11a,IEEE 802.11b,IEEE 802.11g),and Bluetooth?.Spread-spectrum techniques also aid in the endless race between communication needs and radio-frequency availability-situations where the radio
spectrum is limited and is,therefore,an expensive resource.
Theoretical Justification for Spread Spectrum
Spread-spectrum is apparent in the Shannon and Hartley channel-capacity theorem: C=B×log2(1+S/N) (Eq.1)
I n this equation,C is the channel capacity in bits per second(bps),which is the maximum data rate for a theoretical bit-error rate(BER).B is the required channel bandwidth in Hz,and S/N is the signal-to-nosie power ratio.To be more explicit,one assumes that C,which represents the amount of information allowed by the communication channel,also represents the desired performance.Bandwidth (B) is the price to be paid,bacause frequency is a limited resource.The S/N ratio expresses the environmental conditions or the physical characteristics (i.e., obstacles ,presence of jammers ,interferences,etc.).
There is an elegant interpretation of this equation,applicable for difficult environments,for example,when a low S/N ratio is caused by noise and interference.This approach says that one can maintain or even increase communication performance (high C) by allowing or injecting more bandwidth (high B),even when signal power is below the noise floor. (The equation does not forbid that condition!)
Modify Equation 1 by changing the log base from 2 to e (the Napierian number) and by noting that In=loge.
Therefore:
C/B=(1/ln2)×ln(1+S/N)=1.443×ln(1+S/N) (Eq.2)
Applying the MacLaurin series development for
ln(1+x)=x-x2/2+x3/3-x4/4+…+(-1)k+1xk/k+…:
C/B=1.443×(S/N-1/2×(S/N)2+1/3×(S/N)3-…) (Eq.3)
S/N is usually low for spread-spectrum applications. (As just mentioned, the signal power density can even be below the noise level.) Assuming a noise level such that S/N <<1,Shannon's expression becomes simply:
C/B≈1.443×S/N (Eq.4)
Very roughly:
C/N≈S/N (Eq.5)
Or:
N/S≈B/C (Eq.6)
To send error-free information for a given noise-to-signal ratio in the channel,therefore,one need only perform the fundamental spread-spectrum signal-spreading operation:increase the transmitted bandwidth.That principle seems simple and evident.Nonetheless,implementation is
complex,mainly because spreading the baseband (by a factor that can be several orders of magnitude) forces the electronics to act and react accordingly,which,in turn,makes the spreading and despreading operations necessary.
Definitions
Different spread-spectrum techniques are available,but all have one idea in common:the key (also called the code or sequence) attached to the communication channel.The manner of inserting this code defines precisely the spread-spectrum technique.The term "spread spectrum" refers to the expansion of signal bandwidth,by several orders of magnitude in some cases,which occurs when a key is attached to the communication channel.
The formal definition of spread spectrum is more precise:an RF communications system in which the baseband signal bandwidth is intentionally spread over a larger bandwidth by injecting a higher frequency signal (Figure 1).As a direct consequence,energy used in transmitting the signal is spread over a wider bandwidth,and appears as noise.The ratio (in dB) between the spread baseband and the original signal is called processing gain.Typical spread-spectrum processing gains run from 10dB to 60dB.
To apply a spread-spectrum technique,simply inject the corresponding spread-spectrum code somewhere in the transmitting chain before the antenna (receiver).Conversely,you can remove the spread-spectrum code (called a despreading operation) at a point in the receive chain before data retrieval.A despreading operation reconstitutes the information into its original bandwidth.Obviously,the same code must be known in advance at both ends of the transmission channel. (In some circumstances,the code should be known only by those two parties.)
Figure 1.Spread-spectrum communication system
Bandwidth Effects of the Spreading Operation
Figure 2 illustrates the evaluation of signal bandwidths in a communication link.
Figure 2.Spreading operation spreads the signal energy over a wider frequency bandwidth.
Spread-spectrum modulation is applies on top of a conventional modulation such as BPSK or direct conversion.One can demonstrate that all other signals not receiving the spread-spectrum code will remain ad they are,that is,unspread.
Bandwidth Effects of the Despreading Operation
Similarly,despreading can be seen in Figure 3.
Figure 3. The despreading operation recovers the original signal.
Here a spread-spectrum demodulation has been made on top of the normal demodulation operations.One can also demonstrate that signals such as an interferer or jammer added during the transmission will be spread during the despreading operation!
Waste of Bandwidth Due to Spreading Is Offset by Multiple Users
Spreading results directly in the use of a wider frequency band by a factor that corresponds exactly to the "processing gain" mentioned earlier.Therefore spreading does not spare the limited frequency resource.That overuse is well compensated,however,by the possibility that many users will share the enlarged frequency band (Figure 4).
Figure 4. The same frequency band can be shared by multiple
users with spread-spectrum techniques.
Spread Spectrum Is a Wideband Technology
In contrast to regular narrowband technology,the spread-spectrum process is a wideband technology.W-CDMA and UMTS, for example,are wideband technologies that require a relatively large frequency bandwidth, compared to narrowband radio.
Benefits of Spread Spectrum
Resistance to Interference and Antijamming Effects
There are many benefits to spread-spectrum technology.Resistance to interference is the most important advantage.Intentional or unintentional interference and jamming signals are rejected because they do not contain the spread-spectrum key.Only the desired signal,which has the key, will be seen at the receiver when the despreading operation is exercised.See Figure 5.
Figure 5. A spread-spectrum communication system.Note that the interferer’s energy is spread while the data signal is despread in the receive chain.
You can practically ignore the interference,narrowband or wideband,if it does not include the key used in the dispreading operation.That rejection also applies to other spread-spectrum signals that do not have the right key.Thus different spread-spectrum communications can be active simultaneously in the same band,such as CDMA.Note that spread-spectrum is a wideband technology,but the reverse is not true:wideband techniques need not involve spread-spectrum technology.
Resistance to Interception
Resistance to interception is the second advantage provided by spread-spectrum techniques.Because nonauthorized listeners do not have the key used to spread the original
signal,those listeners cannot decode it.Without the right key,the spread-spectrum signal appears as noise or as an interferer.(Scanning methods can break the code,however,if the key is short.) Even better,signal levels can be below the noise floor,because the spreading operation reduces the spectral density.See Figure 6.(Total energy is the same,but it is widely spread in frequency.) The message is thus made invisible,an effect that is particularly strong with the direct-sequence spread-spectrum (DSSS) technique.(DSSS is discussed in greater detail below.) Other receivers cannot “see” the transmission;they only register a slight increase in the overall noise level!
Figure 6.Spread-spectrum signal is buried under noise level.The receiver cannot “see”
the transmission without the right spread-spectrum keys.
Resistance to Fading (Multipath Effects)
Wireless channels often include multiple-path propagation in which the signal has more that one path from the transmitter to the receiver (Figure 7).Such multipaths can be caused by atmospheric reflection or refraction, and by reflection from the ground or from objects such as buildings.
Figure 7.Illustration of how the signal can reach the receiver over multiple paths.
The reflected path (R) can interfere with the direct path (D) in a phenomenon called fading.Because the dispreading process synchronizes to signal D,signal R is rejected even though it contains the same key. Methods are available to use the reflected-path signals by dispreading them and adding the extracted results to the main one.
Spread Spectrum Allows CDMA
Note that spread spectrum is not a modulation scheme,and should not be confused with other types of modulation.One can,for example,use spread-spectrum techniques to transmit a signal modulated by PSK or BPSK.Thanks to the coding basis,spread spectrum can also be used as another method for implementing multiple access (i.e.,the real or apparent coexistence of multiple and simultaneous communication links on the same physical media).So far,three main
methods are available.
FDMA-Frequency Division Multiple Access
FDMA allocates a specific carrier frequency to a communication channel.The number of different users is limited to the number of “slices” in the frequency spectrum (Figure 8).Of the three methods for enabling multiple access,FDMA is the least efficient in term of frequency-band usage.Methods of FDMA access include radio broadcasting,TV,AMPS,and TETRAPOLE.
Figure 8.Carrier-frequency allocations among different users in a FDMA system.
TDMA-Time Division Multiple Access
With TDMA the different users speak and listen to each other according to a defined allocation of time slots (Figure 9).Different communication channels can then be established for a unique carrier frequency.Examples of TDMA are GSM,DECT,TETRA,and IS-136.
Figure 9. Time-slot allocations among different users in a TDMA system.
CDMA-Code Division Multiple Access
CDMA access to the air is determined by a key or code (Figure 10).In that sence,spread spectrum is a CDMA access.The key must be defined and known in advance at the transmitter and receiver ends.Growing examples are IS-95 (DS),IS-98,Bluetooth,and WLAN.
Figure 10.CDMA systems access the same frequency band with unique keys or codes.
One can,of course,combine the above access methods.GSM,for instance,combines TDMA and FDMA.GSM defines the topological areas (cells) with different carrier frequencies,and sets time slots within each cell.
Spread Spectrum and (De) coding “Keys”
At this point,it is worth restating that the main characteristic of spread spectrum is the presence of a code or key,which must be known in advance by the transmitter and receiver (s).In modern communications the codes are digital sequences that must be as long and as random as possible to appear as “noise-like”as possible.But in any case,the codes must remain reproducible.or the receiver cannot extract the message that has been sent.Thus,the sequence is “nearly random”.Such a code is called a pseudo-random number (PRN) or sequence.The method most frequently used to generate pseudo-random codes is based on a feedback shift register.
Many books are available on the generation of PRNs and their characteristics,but that development is outside the scope of this basic tutorial.Simply note that the construction or selection of proper sequences,or sets of sequences,is not trivial.To guarantee efficient spread-spectrum communications,the PRN sequences must respect certain rules,such as length, autocorrelation,cross-correlation,orthogonality,and bits balancing.The more popular PRN sequences have names:Barker,M-Sequence,Gold,Hadamard-Walsh,etc.Keep in mind that a more complex sequence set provides a more robust spread-spectrum link.But there is a cost to this: more complex electronics both in speed and behavior,mainly for the spread-spectrum despreading operations.Purely digital spread-spectrum despreading chips can contain more than several million equivalent 2-input NAND gates,switching at several tens of megahertz.
中等分辨率制备分离的 快速色谱技术 W. Clark Still,* Michael K a h n , and Abhijit Mitra Departm(7nt o/ Chemistry, Columbia Uniuersity,1Veu York, Neu; York 10027 ReceiLied January 26, 1978 我们希望找到一种简单的吸附色谱技术用于有机化合物的常规净化。这种技术是适于传统的有机物大规模制备分离，该技术需使用长柱色谱法。尽管这种技术得到的效果非常好，但是其需要消耗大量的时间，并且由于频带拖尾经常出现低复原率。当分离的样本剂量大于1或者2g时，这些问题显得更加突出。近年来，几种制备系统已经进行了改进，能将分离时间减少到1-3h，并允许各成分的分辨率ΔR f≥（使用薄层色谱分析进行分析）。在这些方法中，在我们的实验室中，媒介压力色谱法1和短柱色谱法2是最成功的。最近，我们发现一种可以将分离速度大幅度提升的技术，可用于反应产物的常规提纯，我们将这种技术称为急骤色谱法。虽然这种技术的分辨率只是中等（ΔR f≥），而且构建这个系统花费非常低，并且能在10-15min内分离重量在的样本。4 急骤色谱法是以空气压力驱动的混合介质压力以及短柱色谱法为基础，专门针对快速分离，介质压力以及短柱色谱已经进行了优化。优化实验是在一组标准条件5下进行的，优化实验使用苯甲醇作为样本，放在一个20mm*5in.的硅胶柱60内，使用Tracor 970紫外检测器监测圆柱的输出。分辨率通过持续时间（r）和峰宽（w,w/2）的比率进行测定的（Figure 1），结果如图2-4所示，图2-4分别放映分辨率随着硅胶颗粒大小、洗脱液流速和样本大小的变化。
The smart grid Smart grid is the grid intelligent (electric power), also known as the "grid" 2.0, it is based on the integration, high-speed bidirectional communication network, on the basis of through the use of advanced sensor and measuring technology, advanced equipme nt technology, the advanced control method, and the application of advanced technology of decision support system, realize the power grid reliability, security, economic, efficient, environmental friendly and use the security target, its main features include self-healing, incentives and include user, against attacks, provide meet user requirements of power quality in the 21st century, allow all sorts of different power generation in the form of access, start the electric power market and asset optimizatio n run efficiently. The U.S. department of energy (doe) "the Grid of 2030" : a fully automated power transmission network, able to monitor and control each user and power Grid nodes, guarantee from power plants to end users among all the nodes in the whole process of transmission and distribution of information and energy bi-directional flow. China iot alliance between colleges: smart grid is made up of many parts, can be divided into:intelligent substation, intelligent power distribution network, intelli gent watt-hourmeter,intelligent interactive terminals, intelligent scheduling, smart appliances, intelligent building electricity, smart city power grid, smart power generation system, the new type of energy storage system.Now a part of it to do a simple i ntroduction. European technology BBS: an integration of all users connected to the power grid all the behavior of the power transmission network, to provide sustained and effective economic and security of power. Chinese academy of sciences, institute of electrical: smart grid is including all kinds of power generation equipment, power transmission and distribution network, power equipment and storage equipment, on the basis of the physical power grid will be modern advanced sensor measurement technology, network technology, communication
英文原文出自《Advanced Technology Libraries》2008年第5期 Robot Robot is a type of mechantronics equipment which synthesizes the last research achievement of engine and precision engine, micro-electronics and computer, automation control and drive, sensor and message dispose and artificial intelligence and so on. With the development of economic and the demand for automation control, robot technology is developed quickly and all types of the robots products are come into being. The practicality use of robot products not only solves the problems which are difficult to operate for human being, but also advances the industrial automation program. At present, the research and development of robot involves several kinds of technology and the robot system configuration is so complex that the cost at large is high which to a certain extent limit the robot abroad use. To development economic practicality and high reliability robot system will be value to robot social application and economy development. With the rapid progress with the control economy and expanding of the modern cities, the let of sewage is increasing quickly: With the development of modern technology and the enhancement of consciousness about environment reserve, more and more people realized the importance and urgent of sewage disposal. Active bacteria method is an effective technique for sewage disposal，The lacunaris plastic is an effective basement for active bacteria adhesion for sewage disposal. The abundance requirement for lacunaris plastic makes it is a consequent for the plastic producing with automation and high productivity. Therefore, it is very necessary to design a manipulator that can automatically fulfill the plastic holding. With the analysis of the problems in the design of the plastic holding manipulator and synthesizing the robot research and development condition in recent years, a economic scheme is concluded on the basis of the analysis of mechanical configuration, transform system, drive device and control system and guided by the idea of the characteristic and complex of mechanical configuration,
New technique of the computer network Abstract The 21 century is an ages of the information economy, being the computer network technique of representative techniques this ages, will be at very fast speed develop soon in continuously creatively, and will go deep into the people's work, life and study. Therefore, control this technique and then seem to be more to deliver the importance. Now I mainly introduce the new technique of a few networks in actuality live of application. keywords Internet Network System Digital Certificates Grid Storage 1. Foreword Internet turns 36, still a work in progress Thirty-six years after computer scientists at UCLA linked two bulky computers using a 15-foot gray cable, testing a new way for exchanging data over networks, what would ultimately become the Internet remains a work in progress. University researchers are experimenting with ways to increase its capacity and speed. Programmers are trying to imbue Web pages with intelligence. And work is underway to re-engineer the network to reduce Spam (junk mail) and security troubles. All the while threats loom: Critics warn that commercial, legal and political pressures could hinder the types of innovations that made the Internet what it is today. Stephen Crocker and Vinton Cerf were among the graduate students who joined UCLA professor Len Klein rock in an engineering lab on Sept. 2, 1969, as bits of meaningless test data flowed silently between the two computers. By January, three other "nodes" joined the fledgling network.
Computer Program 1 Introduction Computer Program, set of instructions that directs a computer to perform someprocessing function or combination of functions. For the instructions to be carried out, a computer must execute a program, that is, the computer reads the program, and then follow the steps encoded in the program in a precise order until completion. A program can be executed many different times, with each execution yielding a potentially different result depending upon the options and data that the user gives the computer. Programs fall into two major classes: application programs and operating systems. An application program is one that carries out somefunction directly for a user, such as word processing or game-playing. An operating system is a program that manages the computer and the various resources and devices connected to it, such as RAM,hard drives, monitors, keyboards, printers, and modems,so that they maybe used by other programs. Examples of operating systems are DOS, Windows 95, OS\2, and UNIX. 2 Program Development Software designers create new programs by using special applications programs, often called utility programs or development programs. A programmer uses another type of program called a text editor to write the new program in a special notation called a programming language. With the text editor, the programmer creates a text file, which is an ordered list of instructions, also called the program source file. The individual instructions that make up the program source file are called source code. At this point, a special applications program translates the source code into machine language, or object code— a format that the operating system
Hand Column Type Power Machine Follow with our country the rapid development of industrial production, rapidly enhance level of automation, implementation artifacts of handling, steering, transmission or toil for welding gun, spraing gun, spanner and other tools for processing, assembly operations for example automation, should cause the attention of people more and more. Industrial robot is an important branch of industrial robots. It features can be programmed to perform tasks in a variety of expectations, in both structure and performance advantages of their own people and machines, in particular, reflects the people's intelligence and adaptability. The accuracy of robot operations and a variety of environments the ability to complete the work in the field of national economy and there are broad prospects for development. With the development of industrial automation, there has been CNCmachining center, it is in reducing labor intensity, while greatly improved labor productivity. However, the upper and lower commonin CNCmachining processes material, usually still use manual or traditional relay-controlled semi-automatic device. The former time-consuming and labor intensive, inefficient; the latter due to design complexity, require more relays, wiring complexity, vulnerability to body vibration interference, while the existence of poor reliability, fault more maintenance problems and other issues. Programmable Logic Controller PLC-controlled robot control system for materials up and down movement is simple, circuit design is reasonable, with a strong anti-jamming capability, ensuring the system's reliability, reduced maintenance rate, and improve work efficiency. Robot technology related to mechanics, mechanics, electrical hydraulic technology, automatic control technology, sensor technology and computer technology and other fields of science, is a cross-disciplinary integrated technology. Current industrial approaches to robot arm control treat each joint of the robot arm as a simple joint servomechanism. The servomechanism approach models the varying dynamics of a manipulator inadequately because it neglects the motion and configuration of the whole arm mechanism. These changes in the parameters of the controlled system sometimes are significant enough to render conventional feedback control strategies ineffective. The result is reduced servo response speed and damping, limiting the precision and speed of the end-effecter and making it appropriate only for limited-precision tasks. Manipulators controlled in this manner move at slow speeds with unnecessary vibrations. Any significant performance gain in this and other areas of robot arm control require the consideration of more efficient dynamic models, sophisticated control approaches, and the use of dedicated computer architectures and parallel processing techniques. Manipulator institutional form is simple, strong professionalism, only as a loading device for a machine tools, special-purpose manipulator is attached to this machine.
机械设计理论 机械设计是一门通过设计新产品或者改进老产品来满足人类需求的应用技术科学。它涉及工程技术的各个领域，主要研究产品的尺寸、形状和详细结构的基本构思，还要研究产品在制造、销售和使用等方面的问题。 进行各种机械设计工作的人员通常被称为设计人员或者机械设计工程师。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创造性，还必须在机械制图、运动学、工程材料、材料力学和机械制造工艺学等方面具有深厚的基础知识。如前所诉，机械设计的目的是生产能够满足人类需求的产品。发明、发现和科技知识本身并不一定能给人类带来好处，只有当它们被应用在产品上才能产生效益。因而，应该认识到在一个特定的产品进行设计之前，必须先确定人们是否需要这种产品。 应当把机械设计看成是机械设计人员运用创造性的才能进行产品设计、系统分析和制定产品的制造工艺学的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定的。另一方面，应该认真精确的进行所有运算。例如，即使将一个小数点的位置放错，也会使正确的设计变成错误的。 一个好的设计人员应该勇于提出新的想法，而且愿意承担一定的风险，当新的方法不适用时，就使用原来的方法。因此，设计人员必须要有耐心，因为所花费的时间和努力并不能保证带来成功。一个全新的设计，要求屏弃许多陈旧的，为人们所熟知的方法。由于许多人墨守成规，这样做并不是一件容易的事。一位机械设计师应该不断地探索改进现有的产品的方法，在此过程中应该认真选择原有的、经过验证的设计原理，将其与未经过验证的新观念结合起来。 新设计本身会有许多缺陷和未能预料的问题发生，只有当这些缺陷和问题被解决之后，才能体现出新产品的优越性。因此，一个性能优越的产品诞生的同时，也伴随着较高的风险。应该强调的是，如果设计本身不要求采用全新的方法，就没有必要仅仅为了变革的目的而采用新方法。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不受各种约束。即使产生了许多不切实际的想法，也会在设计的早期，即绘制图纸之前被改正掉。只有这样，才不致于堵塞创新的思路。通常，要提出几套设计方案，然后加以比较。很有可能在最后选定的方案中，采用了某些未被接受的方案中的一些想法。
英文翻译 A comprehensive overview of substations Along with the economic development and the modern industry developments of quick rising, the design of the power supply system become more and more completely and system. Because the quickly increase electricity of factories, it also increases seriously to the dependable index of the economic condition, power supply in quantity. Therefore they need the higher and more perfect request to the power supply. Whether Design reasonable, not only affect directly the base investment and circulate the expenses with have the metal depletion in colour metal, but also will reflect the dependable in power supply and the safe in many facts. In a word, it is close with the economic performance and the safety of the people. The substation is an importance part of the electric power system, it is consisted of the electric appliances equipments and the Transmission and the Distribution. It obtains the electric power from the electric power system, through its function of transformation and assign, transport and safety. Then transport the power to every place with safe, dependable, and economical. As an important part of power’s transport and control, the transformer substation must change the mode of the traditional design and control, then can adapt to the modern electric power system, the development of modern industry and the of trend of the society life. Electric power industry is one of the foundations of national industry and national economic development to industry, it is a coal, oil, natural gas, hydropower, nuclear power, wind power and other energy conversion into electrical energy of the secondary energy industry, it for the other departments of the national economy fast and stable development of the provision of adequate power, and its level of development is a reflection of the country's economic development an important indicator of the level. As the power in the industry and the importance of the national economy, electricity transmission and distribution of electric energy used in these areas is an indispensable component.。Therefore, power transmission and distribution is critical. Substation is to enable superior power plant power plants or power after adjustments to the lower load of books is an important part of power transmission. Operation of its functions, the capacity of a direct impact on the size of the lower load power, thereby affecting the industrial production and power consumption.Substation system if a link failure, the system will protect the part of action. May result in power outages and so on, to the production and living a great disadvantage. Therefore, the substation in the electric power system for the protection of electricity reliability,
密级 分类号 编号 成绩 本科生毕业设计 (论文) 外文翻译 原文标题Simple Manipulator And The Control Of It 译文标题简易机械手及控制 作者所在系别机械工程系 作者所在专业xxxxx 作者所在班级xxxxxxxx 作者姓名xxxx 作者学号xxxxxx 指导教师姓名xxxxxx 指导教师职称副教授 完成时间2012 年02 月 北华航天工业学院教务处制
译文标题简易机械手及控制 原文标题 Simple Manipulator And The Control Of It 作者机电之家译名JDZJ国籍中国 原文出处机电之家 中文译文： 简易机械手及控制 随着社会生产不断进步和人们生活节奏不断加快,人们对生产效率也不断提出新要求。由于微电子技术和计算软、硬件技术的迅猛发展和现代控制理论的不断完善,使机械手技术快速发展,其中气动机械手系统由于其介质来源简便以及不污染环境、组件价格低廉、维修方便和系统安全可靠等特点,已渗透到工业领域的各个部门,在工业发展中占有重要地位。本文讲述的气动机械手有气控机械手、XY轴丝杠组、转盘机构、旋转基座等机械部分组成。主要作用是完成机械部件的搬运工作,能放置在各种不同的生产线或物流流水线中,使零件搬运、货物运输更快捷、便利。 一.四轴联动简易机械手的结构及动作过程 机械手结构如下图1所示,有气控机械手(1)、XY轴丝杠组(2)、转盘机构(3)、旋转基座(4)等组成。 图1.机械手结构 其运动控制方式为：(1)由伺服电机驱动可旋转角度为360°的气控机械手(有光电传感器确定起始0点);(2)由步进电机驱动丝杠组件使机械手沿X、Y轴移动(有x、y轴限位开关);(3)可回旋360°的转盘机构能带动机械手及丝杠组自由旋转(其电气拖动部分由直流电动机、光电编码器、接近开关等组成);(4)旋转基座主要支撑以上3部分;(5)气控机械手的张合由气压控制(充气时机械手抓紧,放气时机械手松开)。 其工作过程为：当货物到达时,机械手系统开始动作;步进电机控制开始向下
外文翻译 英文原文 Belt Conveying Systems Development of driving system Among the methods of material conveying employed，belt conveyors play a very important part in the reliable carrying of material over long distances at competitive cost．Conveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will continue to do so．Nowadays，bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine)．The ability to control drive acceleration torque is critical to belt conveyors’performance．An efficient drive system should be able to provide smooth，soft starts while maintaining belt tensions within the specified safe limits．For load sharing on multiple drives．torque and speed control are also important considerations in the drive system’s design. Due to the advances in conveyor drive control technology，at present many more reliable．Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers’ choices[1]. 1 Analysis on conveyor drive technologies 1．1 Direct drives Full-voltage starters．With a full-voltage starter design，the conveyor head shaft is direct-coupled to the motor through the gear drive．Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors．With direct fu11-voltage starters．no control is provided for various conveyor loads and．depending on the ratio between fu11-and no-1oad power requirements，empty starting times can be three or four times faster than full load．The maintenance-free starting system is simple，low-cost and very reliable．However, they cannot control starting torque and maximum stall torque；therefore．they are
第一篇： 航空博物馆与航空展示公园 巴特罗米耶杰·基谢列夫斯基 飞翔的概念、场所的精神、老机场的建筑---克拉科夫新航空博物馆理性地吸取了这些元素，并将它们整合到一座建筑当中。Rakowice-Czyzyny机场之前的旧飞机修理库为新建筑的平面和高度设定了模数比例。在此基本形态上进一步发展，如同裁切和折叠一架纸飞机，生成了一座巨大的建筑。其三角形机翼是由混凝土制成，却如同风动螺旋桨一样轻盈。这个机翼宽大通透，向各个方向开敞。它们的形态与组织都是依据内部功能来设计的。机翼部分为3个不平衡的平面，使内外景观在不断变化中形成空间的延续性，并且联系了建筑内的视觉焦点和室外的展览区。 新航空展示公园的设计连接了博物馆的8栋建筑和户外展览区，并与历史体验建立联系。从前的视觉轴线与通道得到尊重，旧的道路得到了完善，朝向飞机场和跑道的空间被限定出来。每栋建筑展示了一个主题或是一段飞行史。建筑周围伸展出巨大的平台，为特殊主题的室外展览提供了空间。博物馆容纳了超过150架飞机、引擎、飞行复制品、成套的技术档案和历史图片。这里的特色收藏是飞机起源开始的各种飞行器，如Jatho1903、Grade1909、莱特兄弟1909年的飞机模型和1911年的鸽式单翼机。 The first passage: Museum for aviation and aviation exhibition park Bartiomiej Kislelewski The idea of flying, the spirit of place, the structure of the historic airfield – the new Museum of Aviation in Krakow takes up these references intellectually and synthesizes them into a building. The old hangars of the former airport Rakowice Czyzyny set the modular scale for the footprint and the height of the new building. Developed from this basic shape, as if cut out and folded like a paper airplane, a large structure has been generated, with triangular wings made of concrete and yet as light as a wind-vane propeller. The wings are generously glazed and open in all directions. Their form and arrangement depend on the interior uses. In the floor plans of the wings, the three offset