科技英语中英文对照翻译.doc

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 cellularcommunication systems.Private mobile radioTerrestrial 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,typically120dBm 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 others 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 1EV DO revision A (sometimes called IS-856A). Here 1refers 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。 : 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 Telecommunicat