mobile and cellular radio移动和细胞广播
in comparison to the relative stability and modest technical developments which are occurring in long haul wideband microwave communication systems there is rapid development and expanding deployment of new mobile personal communication system. These rang from wide coverage area pagers,for simple data message transmission,which employ common standards and hence achieve contiguous coverage over large geographical areas,such as all the major urban centres and transport routes in Europe,Asia or the continental USA.This chapter discusses the special channel characteristics of mobile systems and examines the typical cellular clusters adopted to achieve continuous communication with the mobile user.It then highlights the important properties of current,and emerging,TDMA and code division multiple access(CDMA), mobile digital cellular communication systems.
Private mobile radio
Terrestrial mobile radio works best at around 250 MHz as lower frequencies than this suffer from noise and interference while higher frequencies experience multipath propagation from buildings,etc,section 15.2.In practice modest frequency bands are allocated between 60MHz and 2GHz. Private mobile radio(PMR) is the system which is used by taxi companies,county councils,health authorities,ambulance services,fire services,the utility industries,etc,for mobile communications.
PMR has three spectral at VHF,one just below the 88 to 108 MHz FM broadcast band and one just above this band with another allocation at approximately 170MHz.There are also two allocations at UHF around 450MHz. all these spectral allocations provide a total of just over 1000 radio channels with the channels placed at 12KHz channel spacings or centre frequency offsets. Within the 12khz wide channal the analogue modulation in PMR typically allows 7khz of bandwidth for the signal transmission.when further allowance is made for the frequency drift in the oscillators of these systems a peak deviation of only 2 to 3 khz is available for the speech traffic. Traffic is normally impressed on these systems by amplitude modulation or frequency modulation and again the receiver is of the ubiquitous superheterodyne design,Figure 1.4. A double conversion receiver with two separate local oscillator stages is usually required to achieve the required gain and rejection of adjacent channel signals.
One of the problems with PMR receiver is that they are requiredto detect very small signals,typically—120dBm at the antenna output,corresponding to 0.2 uV,and,after demodulating this signal,produce ann output with perhaps 1W of audio equipment, the first IF is normally at10.7MHz and the second IF is very orten at 455KHz . unfortunately,with just over 1000 available channels for the whole of the UK and between 20000and30000issued licences for these systems,it is inevitable that the average busuness user will have to share the allocated channel with other companies in their same geographical area.
There are various modes of operation for mobile radio communications networks, the simplest of which is singal frequency simplex. In simplex communication, traffic is broadcast, or one way. PMR uses half duplex(see later Table 15.3) where, at the end of each transmission period, there is a handover of the single channel to the user previously receiving, in order to permit them to reply over the same channel. This is efficient in that it requires only one frequency allocation for the communication link but it has the disadvantage that all units can
hear all transmissions provided they are within rage of the mobile and frequencies are allocated for the transmissions. One frequency is used for the forward or downlink, namely base-to-mobile communications. This permits simultaneous two-way communication and greatly reduces the level of interference, but it halves other’s transmissions, which can lead to contention with two mobiles attempting to initiate a call, at the same time, on the uplink in a busy syetem.
Although PMR employs relatively simple techniques with analogue speech transmission there have been many enhancements to these systems over the years . Data transmission is now in widespread use in PMR systems using FSK modulation. Data transmission also allows the possibility of hard copy graphics output and it gives direct access to computer services such as databases, etc. Data prembles can also be used, in a selective calling mode, when initiating a transmission to address a special receiver and thus obtain more privacy within the system.
15.4.5 Trunked radio for paramilitary use集群无线电的军事使用
Another related TDMA mobile radio standard is the European trunked radio(TETRA)network which has been developed as part of the public safety radio communications service(PSRCS) for use by police, utilities, customs office, etc. TETRA in fact is part of wider international collaborations for paramilitary radio use.
In these portable radios there is a need for frequency hopping (FH) to give an antieavesdropping capability and encryption for security of transmission to extend military mobile radio capabilities to paramilitary use, i.e. for police, customs and excise offices, etc. these capabilities are included in the multiband interteam radio for the associated public safety communications office in the USA while Europe has adopted the TETRA standard.
TETRA is essentially the digital TDMA replacement of the analogue PMR systems. The TETRA standard has spectrum allocations of 380 to 400 and 410 to 430MHz, with the lower band used for mobile transmissions and the upper band for base station use. TETRA mobile have 1 W output power and the base stations 25 W using error with the data throughput rate varying, to meet the required quality of service. TETRA can accommodate up to four users each with a basic speech or data rate of 7.2kbit/s. with coding and signaling overheads, the final transmission rate for the four-user slot is 36 kbit/s. this equipment is large and more sophisticated than a commercial cell phone, and it sells for a very much higher price becase the production runs are much small. However, its advanced capabilities are essential for achieving paramilitary communications which are secure from eavesdropping.
15.5 Code division multiple access
Analogue communication systems predominantly adopt frequency division multiple access (FDMA), where each subscriber is allocated a narrow frequency slot within the available channel. The alternative TDMA(GSM) technique allocates the entire channel bandwidth to a subscriber but constrains the subscriber but constrains the subscriber to transmit only regular short bursts of wideband signal. Both these accessing techniques are well established for long haul
terrestrial, satellite and mobile communications as they offer very good utilization of the available bandwidth.
15.5.1
The inflexibility of these coordinated accessing techniques has resulted in the development of new systems based on the uncoordinated spread spectrum concept. In these systems the bits of slow speed data traffic from each subscriber are deliberately multiplied by a high chip rate spreading code, forcing the low rate (narrowband data signal) to fill a wide channel bandwidth.
15.7.2 3G systems
The evolution of the third generation (3G)system began when the ITU produce the initial recommendations for a new universal mobile telecommunications system(UMTS)[www.] The 3G mobile radio service provides higher data rate services ,with a maximum data rate in excess of 2Mbit/s, but the achievable bit rate is linked to mobility. Multimedia applications encompass services such as voice, audio/video, graphics, data, Internet access and e-mail. These packet and circuit switched services have to be supported by the radio interface and the network subsystem.
Several radio transmission technologies(RTT) were evaluated by the ITU and adopted into the new standard, IMT-2000. the European standardization body for 3G, the ETSI Special Mobile Group, agreed on a radio access scheme for 3G UMTS universal terrestrial radio access(UTRA) as an evolution of GSM. UTRA consists of two modes : frequency division duplex(FDD) where the uplink and downlink are transmitted on different frequencies; and time division duplex(TDD) where the uplink and downlink are time multiplexed onto the same carrier frequency. The agreement assigned the unpaired bands (i.e. for UTRA TDD ). TD-CDMA is a pure CDMA based system. Both modes of UTRA have been harmonised with respect to basic system parameters such as carrier spacing, chip rate and frame length to ensure the interworking of UTRA with GSM.
The 3G proposal were predominantly based wideband CDMA(WCDMA) and a mix of FDD and TDD access techniques. WCDMA is favoured for 3G in poor propagation environments with a mix of high modest speed data traffic. It is generally accepted that CDMA is the preferred access
technique and, with the increase in the data rate, then the spreading modulation needs to increase to wideband transmission.
WCDMA is based on 3.84Mchip/s spreading codes with spreading ratio, i.e. , K values, of 4-256 giving corresponging data ratas of 960-15 kbit/s. the upper FDD uplink band I from 1920-1980 MHz is paired with a 2110-2170 MHz downlink. In addition uplink bands II & III at 1850-1910 MHz and 1710-1785 MHz are also paired, respectively, with 1930-1990 MHz and 1805-1880 MHz allocations. the system is configured on a 10 ms frame with 15 individual slots to facilitate TDD as well as FDD transmissions. TDD is more flexible as time-slots can be dynamically reassigned to uplink and downlink functions, as required for asymmetric transfer of large files or video on demand traffic. 3G WCDMA systems use an adaptive multirate speech coder with encoded rates of 4.75-12.2 kbit/s. receivers commonly use the easily integrated direct conversion design, in place of the superheterodyne design . receiver sensitivities are typically -155dBm.
The 3GPP2 standard aims to achieve a wide area mobile wireless packet switched capability with CDMA2000 1×EV DO revision A (sometimes called IS-856A). Here 1×refers to the single carrier 1.25 Mchip/s system. It achieves a 3.1 Mbit/s downlink and a delay sensitive services. The 3GPP standard has gone through many release with R4 in 2001 which introduced packet data services and R6 in 2005 to further increase the available data transmission rate . R6 pioneers the use of high-speed downlink packet access and multimedia broadcast multicast services which offer reduced delays and increased uplink data rates approaching 6 Mbit/s.
In parallel with the European activities extensive work on 3G mobile radio was also performed in Japan. The Japanese standardisation body also chose WCDMA, so that the Japanese and European proposals for the FDD mode were already aligned closely. Very similar concepts have also been adopted by the North American standardization body.
In order to work towards a global 3G mobile radio standard, the third generation partnership project(3GPP), consisting of members of the standardization bodies in Europe, the USA, Japan, Korea and China, was formed. It has merged the already well harmonized proposals of the regional standardization bodies to work on a common 3G international mobile radio standard, still called UTRA. The 3GPP Project 2(3GPP2), on the other hand, works towards a 3G mobile radio standard based on cdmaOne/IS-95 evolution, originally called CDMA2000.
比起相对稳定、适度的技术发展是发生在宽带微波通信系统,有长期快速发展和扩大部署的新的移动个人通讯系统。这些范围包括覆盖范围广，寻呼机，简单的数据信息的传输，采用共同的标准，从而实现连续覆盖广大的地理区域，如所有主要城市中心和运输路线，在欧洲，亚洲和美国大陆。本章讨论的专用信道特性的移动系统和审查的典型蜂窝集群实现了连续的沟通与移动用户。然后，它强调当前重要的属性，和新兴，时分多址和码分多址移动数字蜂窝通信系统。
专用移动无线电
陆地移动无线电工程大约在250兆赫，频率较低的比这更受到噪音和干扰的影响，而更高的频率从建筑物等受多径传播的影响。在实践中，适度的频段为60兆赫兹和2吉赫
之间的分配。专用移动无线电，这是由出租车公司，县议会，卫生主管部门，救护服务，消防服务，公用事业行业等，用于移动通信系统。它有三个谱在高频，一个略低于88至108兆赫调频广播波段和一个刚刚超过这一分配大约170兆赫兹的波段。也有大约450兆赫兹的两个超高频分配，所有这些频谱分配提供放置在12千赫的信道间隔或中心频率偏移的渠道刚刚超过1000个广播频道。也有配置在超高频电台周围,大约450兆赫的两个超高频。所有这些频谱分配共提供超过1000无线电频道与频道放在12千赫通道间距或中心频率偏移。12千赫的带宽通道模拟调制技术，通常允许7 千赫带宽的信号传输。当进一步考虑了频率漂移、峰值偏差，这些振荡器系统，只有2至3千赫提供话音业务。传输前通常对这些系统的幅值调制和频率调制，接收器是无处不在的超外差式设计。双变频接收机两路独立的本地振荡器阶段，通常需要实现所需的增益和抑制相邻信道信号。
一个问题，由接收器，他们需要检测非常小的信号，通常120dBm在天线输出，对应0.2微伏紫外线，而解调后，这个信号，也许会产生输出1瓦的音响设备，第一个是通常在7兆赫，二是经常在455千赫。不幸的是，全英国的这些系统只有1000多渠道,20000和30000之间的执照，这是不可避免的，一般企业用户将和其他在同一地理区域的公司共享信道分配。
有多种操作模式的移动无线电通信网络，最简单的是信号频率。在单工通信，交通广播，或一个方法。它采用半双工，在每个传输周期，有一个切换的单通道的用户先前接收，以便允许他们的答复在同一频道。这是有效的，它只需要一个频率分配的通信链路，但它的缺点是，各单位可以听到提供他们移动的所有的传输动和频率分配的传输。
使用一个频率是为向前或下行，即基础的移动通讯。这允许双向同时通信，大大降低干扰的水平，但它一半的传输其他信号，从而导致两手机试图争夺信号发起呼叫，同时，在上行在繁忙的系统。
虽然调压辐射计采用了相对简单的技术，这些年来，这些系统的模拟语音传输有很多改进。数据传输是目前在调压辐射计系统中广泛使用的垂直记录系统使用的频移键控调制。数据传输也允许的可能性的硬拷贝输出图形，它提供的直接接入电脑服务等数据
库，等等。数据问题，也可以使用，在选择性呼叫模式时，当启动传输地址专用接收机，从而可以获得更多的隐私的系统。
集群无线电的军事使用
另一个相关的时分多址移动广播标准是欧洲集群无线电(专业)网络,已发展为部分公共安全无线电通讯服务(用于警察、公用事业、海关等。欧洲无线集群实际上是更广泛的国际合作为准军事无线电使用。
在这些便携式收音机需要有跳频给出一个能力和安全加密传输扩大军事移动通信能力，准军事部队使用，即警察，海关关长办公室，等。这些功能包括在多团队间的无
线电相关的公共安全通讯公司在美国，欧洲已经通过了欧洲集群无线电(专业)网络标准。
欧洲集群无线电是基本数字替代模拟通信系统时分多址。欧洲集群无线电标准频谱分配380至400和410至430兆赫，与较低频段的使用手机和基站使用上带. 欧洲集群无线电移动1瓦特输出功率和基站25瓦的使用错误的数据吞吐量速率不同，以满足要求的服务质量。欧洲集群无线电可容纳四用户，每个有一个基本的语音或数据率7.2kbit/s。
编码和信令开销，最后传输速率的四用户槽每秒36千赫。该设备是大型和更先进的比商业手机，它比售价要高得多的价格因为生产运行是非常小。然而,重要的是它的高级功能实现准军事交流,是安全的防止偷听。
15.5 码分多址
模拟通信系统主要采用频分多址，其中每个用户分配一个狭窄的插槽内的可用信道。
选择时分多址（通信）技术分配整个信道带宽用户而限制用户可限制用户只能发送定期的短脉冲宽带信号。这两种接入技术是众所周知的长距离地面，卫星和移动通信为他们提供了很好的利用可用带宽。
15.5.1 时分多址的概念
这些协调的访问技术的僵硬，导致在新系统上的不协调,，为扩频概念的发展打下了基础。在这些系统比特速度慢的数据流量从每个用户故意乘以一个高速率扩频码，迫使低速率（窄带信号）填补了宽通道带宽。
演化的第三代系统开始于国际电信联盟为一个新的通用移动通信系统生产的初始建议。第三代移动通信无线业务提供更高的数据传输速率服务,最大数据率超过每秒2兆比特,但可达到比特率与机动性。多媒体应用程序包括服务,如声音、音频/视频、图像、数据、互联网接入和电子邮件。这些包和线路交换服务不得不被支持无线电接口，网络子系统。
国际电信联盟对几个无线电发射技术(码头)进行了评估，纳入到新标准，智能- 2000。欧洲人标准化组织、欧洲电信标准协会特别的运动物体组对于第三代移动通信,,同意一个无线电存取方案让第三代移动通信作为城市轨道交通全球陆上无线接入的演化。超高频由两个模式:频分双工在上行链路上传输和下行是不同的频率,时间分割双工在上行和下行时间在同一载波频率上。该协议分配其他方式(如时分双工
)。手机是一个纯粹的码分多址系统。两个模式已经使超高频就基本系统参数如载体间距、芯片和帧长度率,确保超高频与全球移动通信系统的互联互通。
第三代移动通信的建议被主要基于宽带码分多址和混合访问频分双工,时分双工技术。宽带码分多址是赞成组合的高速度数据流量不大时，在差的传播环境下传播的。一般认为码分多址是首选的访问技术，随着数据速率增加，然后扩频调制需要增加宽带传输。宽带码分多址是基于每秒3.84兆传播扩散率编码后,凯西价值观、4 - 256给相应的数据率的每秒960 –15千比特。上的上行频段从
1920-1980兆赫搭配一个2110-2170兆赫下行。此外，上行频带二及三在1850-1910兆赫和1710-1785兆赫也配对，分别，与1930-1990兆赫和1805-1880兆赫分配。10毫秒与15个插槽的框架，以促进TDD以及软驱传输系统配置。时分双工有更灵活的时隙可以动态分配上行链路和下行链路功能，为所需的不对称传输大文件或视频点播业务提供时隙。第三代无线系统使用一种自适应多速率语音编码器的编码率每秒4.75-12.2千比特。接收器通常使用容易集成直接转换设计，所设计的超外差式接收机。接收器灵敏度通常是-155毫瓦分贝。
标准的第三代合作伙伴计划2的目的是实现广域移动无线分组交换能力与码分多址2000，1伏做修改。在这里，1×指单载波1每秒.25兆的系统。它实现了一个3.1兆位/
秒的下行和时延敏感的服务。第三代合作伙伴项目标准,经过了许多的发布,将会有2001年介绍了表型分组数据服务和2005年R6进一步增加可用的数据传输速率。发展的先驱使用高速下行分组接入和多媒体广播组播服务，减少延误和增加上行数据率接近6兆位/秒。
在与欧洲活动的广泛工作的移动电台还表现在日本。日本标准化机构也选择宽带码分多址移动通信系统，使日本和欧洲的建议的阵线模式已经排列紧密。非常相似的概念也已通过了北美标准机构。
为实现全球第三代移动无线标准，第三代合作伙伴项目，成员组成的标准化组织在欧洲，美国，日本，韩国和中国，形成了。合并以及统一的区域性标准化机构建议一个共同的第三代移动通信系统国际移动无线电标准，仍然被称为无线接入。第三代合作伙伴项目的项目2，另一方面，致力于一个基于码分多址的One/IS-95演变，最初叫码分多址2000的第三代移动无线标准。
ＣＤＭＡ: Code Division Multiple Access 码分多址
WCDMA：宽带码分多址
TDMA：Time Division Multiple Access 时分多址
FDMA：Frequence Division Multiple Access频分多址
PMR：Private mobile radio私人移动广播
VHF：Very High Frequency 甚高频
FM：Frequency Modulation频率调制
UHF：Ultra High Frequency超高频
IF ：intermediate frequency 中频
FH：frequency hopping 跳频
FDD：frequency division duplex 频分双工
FSK：移频键控（Frequency Shift Keying）
UTRA：universal terrestrial radio access 通用陆地无线接入
GSM：global system for mobile communications全球通, 全球移动通信系统
TETRA：European trunked radio泛欧集群
TDD：time division duplex 时分双工
PSRCS ：public safety radio communications service公共安全无线电通信服务
ITU：International Telecommunication Union 国际电讯联盟
UMTS：universal mobile telecommunications system 通用移动通信系统
RTT：radio transmission technologies 无线电传输技术
EV：electron volt 电子伏(特)
3G：The 3rd Generation Telecommunication 第3代移动通信技术
3GPP：第三代合作伙伴项目the 3rd Generation Partnership Project
TD-CDMA：移动
IMT：International Mobile Telecommunications 国际移动通信
ETSI：European Telecommunication Standards Institute欧洲电信标准协会
Bit：比特（二进位制信息单位）
W: watt瓦特
V：volt 伏特
Hz：hertz 赫兹
dBm：decibels above one milliwatt in 600 ohms毫瓦分贝
mobile communications：移动通信
broadcast band：广播波段
mobile digital cellular communication systems：数字蜂窝移动通信系统frequency:频率
amplitude：振幅
channel：频道
duplex：双工
demodulate：解调；检波modulation：调制
transmission：传输interteam:无线电波段time-slots：时隙
drift:漂移
conversion:转换
slot:槽
band:频带
switch：开关
mobile:移动
narrowband：窄带
wideband：宽带
parameter：参数
eavesdropping：窃听
receiver:接收机
transmit:传送
chip：芯片
mode:模式
uplink：上行线路
downlink：下行线路
inflexibility：宇航服division：分工
output：输出
input:输入
synchronous:同步
delay:延迟
integrate：整合
standardization:标准化
capability：容量
database:数据库
accommodate：调解
multiplexed：多路复用encryption:加密superheterodyne：超外差式接收机
bandwidth:带宽
analogue:模拟
Spectrum：频谱
base station:基站
analogue communication system模拟通信系统
trunked radio：集群无线电
individual slots:个人槽
multirate speech coder：多速率语音编码器
mobile radio communications networks:移动无线电通讯网络
data transmission:数据传输
data rate：数据率
data traffic:数据流量
paramilitary communications：军事通信
communication link：通信链路
broadcast multicast services:广播多播服务
transmission rate：传输速率
portable radio：便携式收音机
spreading modulation:传播调制
narrow frequency slot：窄频槽
satellite and mobile communications:卫星和移动通信
narrowband data signal:窄带数据信号
wideband signal：宽带信号
wide channel bandwidth：宽信道带宽
spreading codes：传播代码
spreading ratio：传播比
chip rate：芯片率
basic system：基本系统
adjacent channel signals.：相邻信道信号
selective calling mode:选择呼叫模式
cell phone:手机
mobile radio standard：移动广播标准
receiver sensitivities：接收机灵敏度
singal frequency:标志频率speech traffic：语音业务
base-to-mobile communications：基础的移动通信analogue speech transmission：模拟语音传输
1.To find the area of a square or oblong,you merely multiply its length by its width. 将长乘以宽就可以得到这个长方形的面积。 2.This suggests that matter can be converted into energy. 这就是说物质可以转化为能量，能量也可以转化为物质。 3.Quantum chemistry is still in its infancy. 量子化学仍处于发展初期。 4.Even the protective environment is no insurance against death from lack of oxygen. 即使有防护措施，也不能保证不发生因缺氧而死亡的情况。 5.In any amchine, input work equals output work plus work done against friction. 任何机器的输入功都等于输出功加上客服摩擦所做的功。 6.Earthquakes are generally more destructive of life than volcanic eruptions. 地震通常比火山爆发更具有杀伤力。 7.Heat should be applied slowly to avoid localized overheating. 应慢慢加热以避免出现局部过热现象。 8.How rapidly a fuel burns depends on how thoroughly it is mixed with oxygen or air. 燃料燃烧的速度取决于它与氧气或空气的混合程度。 9.Gene mutation is of great importance in breeding new varieties. 在新品种培育方面，基因突变是非常重要的。 10.Peptides can act directly on the brain to change aspects of mental activity. 肽能够直接作用于大脑，改变各种脑力活动。 11.The language allows a concise expression of arithmetic and logic processes. 这种语言能简要地表达算术和逻辑过程。 12.E-Chemmerce, now offers two main levels of online business intelligence on chemical,platic and energy e-commerce. 《电子化工商务》目前主要提供两个层次的有关化学、塑料和能源电子商务的在线商务信息服务。 13.These images tend to exaggerate the robet’s similarity to human anatomy and behavior. 这些概念常常夸大了机器人与人类在形体和行为方面的相似之处。 14.Since some materials are not demaged easily as others,the possibility exists of developing radiation-resistant parts. 由于有些材料不像另一些那样容易被损坏，所以有可能研制出防辐射的零件。 15.A lot of counties have set up paver stations,chemical fertilizer plants and a hundred and one other factories. 许多县已建立了发电站，化肥厂以及许多别的工厂。 16.The periodic table contains more than one hundred chemical elements belonging to eight families. 元素周期表由属于8个族的100多个化学元素组成。 17.An increase in the oxygen content of coal by 1% reduces the calorific value by some 1.7% . 煤的含氧量每增加1%，其热值则下降约1.7%。 18.Putting two and two together, he came to the conclusion that mechanical energy is different from electrical energy. 他根据事实推断出一个结论：机械能不同于电能。
六、more and more：for rewards worse punishment isdetected unpublished note byaccident inspections victims ofhavingtostay revealed dishonest unlike commit charged demands result hesitate confidential 七、almost as soon：intermediate physically printed isolated anybut pursuing in duplicated remote on experimental christened goals whose impaired removal through transferred resources afford 八、the design of ma：synthesis comparable essential applications substance thermal electrical industrially polishing concrete defined scratch scale proposed objective value obtained known under on 九、Audiences shud：narrowly normal shrinking entertained size barrier thin tools smaller merge compounds machines issues codes portable samples simple means cloned transplantation 十、The t/Space CXV：reduces winged exterior tile developed consists range thick seams through outer sufficiently reentries periodically replaced landed shield employed inaddition via 1.To tru improve the energy efficiency of non-stop computing systems such as switches ,routers,and computers running algorithmic-intensive operations,systems and chip manufacturers need a way to reduce clock speed by a favor of two,and decrease power by a factor of four or more.要真的提高不间断计算系统的能量，像交换机，路由器，和进行强计算的计算机，系统和芯片制造商需要将时钟速度降低二分之一，将能量减少到四分之一或者更多。 2.Since the time of the emission of this radiation,the universe has increased in size by a factor of 1000,so the temperature of the photons has decreased by the same factor.从这个放射物的辐射的时代开始，宇宙的组织增加1000倍，因此光子的温度以相同的倍数减少。 3.When the hot plasma of early universe emitted the radiation we now see,it was receding from our location at about 50times the speed of light.当我梦看到早期宇宙的热等离子体散发辐射的时候，它正以50光年的速度离我们而去。 4.The Uranus is 14 times as large as the mass of the Earth.天王星的质量是地球的14倍。 5.This reaction gives three times as much hydrogen as the reaction of steam with coal.这种反应产生的氢比蒸汽与 木炭反应多2倍。 6.Diamond tools are generally operated at speeds twice those of carbon-steel.金刚石工具通常以2倍于碳钢尺度 而做。 7.In case of electronic scanning the beam-width is broader by factor of two.电子扫描时多数宽度增加了一倍。 8.The output of steel in 1980 was 19times over that in 1970.1980年的钢产量是1970年的20倍。 9.Business may not put much stock in recycling, but when it comes to computing power, researcher’s work in creating the first high-quality reversible computing power supply may be the key to unlocking the power of tomorrow’s computing platforms. 业界可能对回收能量方面没有太大信心，但是谈到计算能力，研究人员从事的创造第一高质量的可逆计算能力的提供可能是开发未来计算平台能力的关键。 10.Reversible computers, or adiabatic systems, recycle their energy to give off extremely little heat, enabling computing power to continue power where existing technology would falter. 可逆计算机即绝热系统，它能够将能量回收，因此只产生很少的热量，使计算能力在现有计算技术无能为力的情况下继续提升. 11.To stave off these problems, researchers have been investigating alternative computing techniques.Quantum computing,has garnered significant publicty. 为了避免这些问题，研究人员一直在研究可替代的计算方法。量子计算已经引起了广泛的关注。 12.Much of the energy needed to make that change is given off in the form of a spark in the case of static energy,or heat in the case of circuitry. 发生这一转变所需的能量在静电情况下表现为瞬间放电，在电路情况下表现为释放热量. 13.The universal chip, dubbed Flattop, is estimated to be several thousand times more energy-efficient than comparable irreversible circuits.However,the chips were proof-of-concept designs and haven’t yet been optimized.It wouldn’t be more efficient for practical applications.称作Flattop（芯片界的航空母舰）的通用芯片的能量效率预计比类似的不可逆电路要高几千倍。然而，芯片的设计停留在概念阶段，仍没有优化。实际应用中不会更高效。
一、长句 The Company’s sole liability in the event of such defects is to repair or replace the Product, at Company’s option, and Company may replace the Product with a remanufactured Product. 如果发生质量缺陷，本公司仅负责修理或更换本产品，具体方法由本公司选择。本公司可以采用再制产品来更换本产品。 二、名词化结构 The heat loss can be considerably reduced by the use of firebricks round the walls of the boiler. 炉壁采用耐火砖可大大降低热耗。 Television is the transmission and reception of images of moving objects by radio waves. 电视通过无线电波发射和接收各种活动物体的图像。 三、被动 Natural rubber is obtained from rubber trees as a white, milky liquid known as latex. This is treated with acid and dried, before being dispatched to countries all over the world. 天然橡胶取自橡胶树，是一种叫“乳胶”的白色乳状液体。在运往世界各国之前，橡胶要经过酸处理和烘干。 四、非谓语 Today the electronic computer is widely used in solving mathematical problems having to do with weather forecasting and putting satellite into orbit. 今天，电子计算机被广泛运用于解决一些数学问题，这些问题与天气预报和把卫星送入轨道有关。 五、时态 When steam is condensed again to water, the same amount of heat is given out as it was taken in when the steam was formed. 当蒸汽重新冷却为水时，所释放的能量与其原来形成蒸汽时所吸收的热量相等。It was understood that atoms were the smallest elements. It is known now that atoms are further divided into nuclei and electrons, neutrons and protons, etc. 以前人们认为原子是最小的结构单元，现在才知道原子还可以分为原子核与电子、中子与质子等。 六、后置定语 The forces due to friction are called frictional forces. 由于摩擦而产生的力称之为摩擦力。
mobile and cellular radio移动和细胞广播 in comparison to the relative stability and modest technical developments which are occurring in long haul wideband microwave communication systems there is rapid development and expanding deployment of new mobile personal communication system. These rang from wide coverage area pagers,for simple data message transmission,which employ common standards and hence achieve contiguous coverage over large geographical areas,such as all the major urban centres and transport routes in Europe,Asia or the continental USA.This chapter discusses the special channel characteristics of mobile systems and examines the typical cellular clusters adopted to achieve continuous communication with the mobile user.It then highlights the important properties of current,and emerging,TDMA and code division multiple access(CDMA), mobile digital cellular communication systems. Private mobile radio Terrestrial mobile radio works best at around 250 MHz as lower frequencies than this suffer from noise and interference while higher frequencies experience multipath propagation from buildings,etc,section 15.2.In practice modest frequency bands are allocated between 60MHz and 2GHz. Private mobile radio(PMR) is the system which is used by taxi companies,county councils,health authorities,ambulance services,fire services,the utility industries,etc,for mobile communications. PMR has three spectral at VHF,one just below the 88 to 108 MHz FM broadcast band and one just above this band with another allocation at approximately 170MHz.There are also two allocations at UHF around 450MHz. all these spectral allocations provide a total of just over 1000 radio channels with the channels placed at 12KHz channel spacings or centre frequency offsets. Within the 12khz wide channal the analogue modulation in PMR typically allows 7khz of bandwidth for the signal transmission.when further allowance is made for the frequency drift in the oscillators of these systems a peak deviation of only 2 to 3 khz is available for the speech traffic. Traffic is normally impressed on these systems by amplitude modulation or frequency modulation and again the receiver is of the ubiquitous superheterodyne design,Figure 1.4. A double conversion receiver with two separate local oscillator stages is usually required to achieve the required gain and rejection of adjacent channel signals. One of the problems with PMR receiver is that they are requiredto detect very small signals,typically—120dBm at the antenna output,corresponding to 0.2 uV,and,after demodulating this signal,produce ann output with perhaps 1W of audio equipment, the first IF is normally at10.7MHz and the second IF is very orten at 455KHz . unfortunately,with just over 1000 available channels for the whole of the UK and between 20000and30000issued licences for these systems,it is inevitable that the average busuness user will have to share the allocated channel with other companies in their same geographical area. There are various modes of operation for mobile radio communications networks, the simplest of which is singal frequency simplex. In simplex communication, traffic is broadcast, or one way. PMR uses half duplex(see later Table 15.3) where, at the end of each transmission period, there is a handover of the single channel to the user previously receiving, in order to permit them to reply over the same channel. This is efficient in that it requires only one frequency allocation for the communication link but it has the disadvantage that all units can
科技的英文说法1： examination 词组习语： translation technology 1.翻译技术 information technology 1.信息技术 network technology 1.网络技术 technology review 1.技术评论 科技的英文例句： 1. Research and technology are said to be chronically underfunded. 据说为研究和技术方面提供的经费严重不足。 2. Our superior technology is our ace in the hole.
我们超众的技术是我们的法宝。 3. Britain needs to bridge the technology gap between academia and industry. 英国需要弥合学术界和企业界之间的技术差距。 4. Worldwide, an enormous amount of research effort goes into militarytechnology. 在世界范围内，大量的研究精力都投入到军事技术上。 5. New technology should provide a secure firewall against hackers. 新技术应该能提供安全可靠的防火墙抵御黑客袭击。 6. The required technology is probably still two years off. 所需技术可能还要两年才能开发出来。 7. This permitted Western manufacturers to play their strong cards: capital andtechnology. 这让西方制造商得以亮出他们的王牌：资金和技术。 8. Many technical experts at the time had doubts about the technology. 当时，许多技术专家对那种工艺抱有疑问。
Unlocking the Climate Puzzle 解开气候之谜 (1)Life has prospered on this planet for nearly four billion years. In that time, climate had fluctuated drastically, from ice ages lasting tens of thousands of years to epochs of steamy heat. With each change, sundry species have benefited and flourished.Others adapted, faltered, or died. Now, many experts believe, humans are imperiling their own ecological niche with the threat of global warming. The vaporous by-products of civilization, in the form of greenhouse gases such as carbon dioxide (C0?), have trapped enough heat in the atmosphere to raise Earth's average surface air temperature a half degree Celsius (one degree Fahrenheit) during this century. If the trend continues, it could alter climate patterns worldwide-thawing glaciers, boosting sea level, scorching plains into deserts, and shifting vegetation zones. （1）生命在这个星球上已经发展了近四十亿年。在这段时间里，气候有大幅波动，从冰河时代到蒸汽时代延续了几千年。每一次改变，各种物种受益和繁荣。其他适应，步履蹒跚，或死亡。现在，许多专家认为，人类正在通过全球变暖危及自己的生态位。在本世纪，文明的气态副产物，以二氧化碳（C0?）等温室气体的形式，把足够的热量困在大气中，来提高地球表面平均气温半摄氏度（1华氏度）。如果这种趋势继续下去，它可能会改变世界范围内的气候模式—融化冰川，提高海平面，把平原烤成沙漠，以及改变植被区。 (2) Or it might not. Global climate depends on combinations of factors interacting in subtle and complex ways that we do not yet fully understand. It is possible that the warming observed during this century may have resulted from natural variations, even though the increase has been much more rapid than what the planet has witnessed over the past hundred centuries. Moreover, the supercomputer simulations used to project future conditions may not be accurate. （2）或者不可能。全球气候取决于各种因素的组合，这些因素以微妙和复杂的方式相互作用，我们还没有完全了解。这是可能的，在本世纪中观察到的变暖可能是由于自然的变化，即使增加已远远超过这个星球在过去的几百个世纪已经见证过的。此外，用于展现未来条件的超级计算机模拟可能是不准确的。 (3) Nonetheless, in 1995, after years of intense study, the Intergovernmental Panel on Climate Change (IPCC), sponsored by the United Nations, concluded tentatively that "the balance of evidence suggests that there is a discernible human influence on global climate". The amount of that influence, the group noted, is unknown because of "uncertainties in key factors", including the degree to which clouds and the oceans affect
计算机冀导那一部分 词汇 pig 金属锭块 dog挡块，止动爪 cat吊锚，履带拖拉机 cock旋塞，吊车 horse支架，铁杆 fish 接合板，夹板 monkey 打桩锤；煤矿通风巷道 fox绳索 belly 炉腰 mild steel structure 低碳钢结构 Bendable switches consist of a continuous 无缝的steel beam. ？可弯曲的开关由连续钢条组成。 曲性道岔由无缝钢条组成。 Bricks are also produced in many different colors and with various finishes, particularly those used for decorative purpose. 砖也可以烧制成许多不同的颜色，具有不同的光洁度，尤其是那些用于装饰的砖。 catalyst 催化剂 Resolving power 分辨率 Combining power 化合价 Base 碱 Base metals 非贵金属 Brass 黄铜 Difficult labor 难产 Foreign Material 杂质 Cast iron 铸铁 In general, the design procedure is not straightforward and will require trial and error. 一般说来，设计过程不是一帆风顺的，而需要反复试验。（简单的） Furnace 炉子 （1）Rubber is not hard, it gives way to pressure. 橡胶性软，受压变形。 （2）Porcelain is commonly used to resist electric current. 陶瓷常用来隔绝电流。 （3）When we speak, sound waves begin to travel and go in all directions. 我们说话时，声波就开始向四面八方传播。 （4）Zinc is easy to obtain from its ore. 锌容易从锌矿中提炼。
U2PPT “Site” refers to the land and other places on, under or through which the Permanent Works or Temporary Works designed by the Engineer are to be executed. “现场”指工程师设计的永久工程或临时工程所需的土地和其他场所，包括地面、地下、工程范围之内或途经的部分。 If we close our eyes, we cannot see anything because our eyelids prevent the rays from entering our eyes. 因为眼睑能阻止光线进入眼内，所以我们闭上眼睛就什么也看不见了。 Traditionally, rural highway location practice has been field oriented, but the modern method is “office” oriented. 传统上，乡村公路定线采用现场定线法，而现在的方法则是采用纸上定线或计算机定线。 In the earlier days of railways, the rules laid down that no train should be allowed to start, even if all signals were clear, until the station master had authorized the guard to give the driver the “right way”. 铁路发展的早期阶段曾规定，即使所有的信号都已开通，列车也不能发车，一直要等到站长已授权站务员给司机发出离站信号。 Curved rails offer resistance to the movement of the train. 弯曲的钢管有碍火车运行。 A detailed calculation of utilizing solar ponds for generation of electricity and seawater desalination are presented. 本文对利用太阳能蓄热发电及海水淡化提出详细计算。 Such observations as these lead to the discovery that there can be rapid erosion when a metal is nonhomogeneous and when it is in connect with water in which some gaseous, liquid and solid substance is dissolved. 像这样的一些观察使人们发现，当金属是非均质金属时，而且当金属与气体、液体或固体物质的水接触时，金属可能很快生锈。 Such a small experiment was designed merely to establish whether the approach was safe. 设计这种小型实验只是为了证实这一方向是否安全。
U1 1.He reported years later；this new-found faculty increased the duo’s odds of winning by 44 percent. 很多年后他透露说/承认，这个新发现的技术增加了两个人44%的胜算。 2.Engineers widely regard this invention as the first wearable computer-an early glimpse at today’s fitness trackers smart watches, and augmented-reality eyewear, and their possible descendants. 工程技术人员大都把这个发明视作第一代可穿戴的电脑设备——今天的健康记录仪，智能手表，AR眼镜以及他们的诸多衍生品皆出自于此。 3.Yet the impact on its wearers was profound-foretelling, perhaps, a future when we depend on our electronic devices to experience life as much as we rely on our eyes,ears, and skin. 然而，它对佩戴者的影响是深远的——它或许预示了这样一个未来：我们不仅依赖眼睛、耳朵和皮肤去感知世界，还会倚重电子设备去感知生活。 4.There are all these other, really rich dimensions of touch that touch screens ignore-such as pressure, contact area, the shape of your hand, and whether you use a pad, knuckle, or nail. 触摸屏忽略了很多其他形式的触感——比如压力、接触面积、手的形状，以及你是使用指肚、指节或指甲来触屏。 5.The seeds of such a future are already here. 由此已经可以窥见到未来的发展。 6.Known as brain-computer interfaces, or BCIs, these systems are found mostly in research laboratories. BCI指人机交互，像这样的系统目前主要还在实验阶段。 7.For many researchers who work in wearable computing, the ultimate goal is to design machines that use data from the brain and body to understand the world in human terms. 对于许多从事可穿戴设备的研究人员来说，他们的最终目标是设计出这样一种机器，它可以收集利用大脑和身体数据并以人类的方式去感知世界。 8.The human and the computer possess “enormously powerful information-processing capabilities”, wrote Edward Tufte, a data-visualization pioneer now at Yale University, in 1989. 早在1989年，耶鲁大学的数据可视化先驱爱德华?塔夫特就曾经说过/提出：“人类和计算机拥有“极其强大的信息处理能力。”
1. This type of spring is extensively used in electrical instruments, and deserves special consideration. 这种弹簧广泛应用于电工仪表中，因此值得专门考虑一下。 (时态) 2. If we had known the properties of the material, we should have made full use of it. 要是当时了解这种材料的特性的话，我们就会充分利用它了。 (虚拟语气) 3. Let P represent the energy which a machine transforms into useful work, and T the total input work, the efficiency of the engine can be expressed as P/T. 假设 P 表示机器已经变成有用功的能量， T 表示总输入功，那么，发电机的效率可以表示为 P/T。 4. Attention must be paid to the working temperature of the machine. 应当注意机器的工作温度。 (被动语态) 5. The solar wind grossly distorts the earth's magnetic field, dragging it out to a long tail. 太阳风使地球磁场的形状发生很大的变化，将它向外拉牵，扯出一条长尾。 6. Television is the transmission and reception of images of moving objects by radio waves. 电视通过无线电波发射和接受各种活动物体的图像。 (名词化结构) 7. An understanding of the essential character of scientific investigation is best acquired from the study of a representative particular science. 要了解科学研究最本质的特点，最好是对特定的典型学科进行研究。 8. Apart from the international agencies controlled by the U.N., many scientific and technological organizations, both governmental and privately owned, are pooling their resources and incorporating themselves into supra-national bodies; a good example is the Organization for Economic Cooperation and Development, with over 20 member-countries throughout the world. 除去联合国直属的国际机构之外，许多科技组织不论是政府的还是私营的，都在将它们的资源汇集起来并将自己合并成超国家的组织。由世界上 20 多个国家参加的经济合作与发展组织就是一个范例。 9. The moon is a world that is completely and utterly dead, a sterile mountainous waste on which during the heat of the day the sun blazed down with relentless fury, but where during the long night the cold is so intense that it far surpasses anything ever experienced on the earth. 月球完全是一个毫无生气的世界，是一片多山的不毛之地。在酷热的白昼，太阳向它倾泻着无情的烈焰，而漫长的严寒却远远不是我们在地球上所能体验到的。 (多长句和逻辑关联词) 10. Computing machines are essentially machines for recording numbers , operating with numbers, and giving the result in numerical form. 计算机本质上是一种记录数字、运算数字并给出数字结果的机器。 (介词的广泛使用) 11. The ON condition makes the data equipment ready to the communication equipment to b e connected to the communication channel. 数据(存储)设备在接通状态时通过通道与通信设备连接。 12. Then the surgeon cut him open and took out the appendix and stitched him up again. 医生切开他的腹部，割除了阑尾，又把他腹部缝好。