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单元二1、对模拟信号的传输的数字方法的使用在电讯系统中变得普遍。有2个原因可以解释这个现象。第一,如果传输的是数字信号而不是模拟信号,那么系统几乎不受影响只要噪声电平不高于它的门限电平。事实是因为,对于长距离传输,数字信号可以再再生器中重新生成,从而产生一个新的、无噪声的信号。并且,只要噪声在一个可比较的模拟系统中,噪声就不会积累。第二、一个数字系统的成分非常适合执行大规模集成电路(LSI)。2、即使在这样一个数字传输系统中,但是,被处理的信号在本质上通常是模拟的。有多种调制手段以实现这种转换,包括脉宽调制PWM、脉幅调制PAM以及脉码调制PCM。在数字电讯系统中,脉码调制是当前最普遍使用的调制系统。脉码调制信号是通过取样、量化和编译模拟信号产生。这个结果是二进制数字的一个系列,即在信号中高低电平的交替。这个系列可以被运用在频率调制中。3.对模拟电压V(t)采样过程包括生成一个脉冲串,在这个脉冲串中,第n个脉冲的幅度等于V(t)在t=nT时的幅值。为了使脉冲串独特地限制V(t)中所包含的信息量,取样速率fc=1/T必须至少是V(t)的光谱中高频成分的2倍大,然后在取样信号中脉冲幅值被量化,并且被转换为一组比特,称之为码组。4. 在实际的PCM长途通信系统中经常利用时分复用方式来传输码字。在TDM系统中,来自几个信道的码字交错着在一条线路上传输。在音频(电话)系统中,通常将24或32路话路复用到一对线路中传输。国际电报电话咨询委员会(CCITT)建议两个主要的架构(“层次”),现在许多全国性的PCM传输网络的使用。在这种体系中,输入复用器将32路信息码交插在一起。其中30路码字代表30路语音信道,其余2路时隙包含随路信令和同步码。第二种体系由图2所示,主要用在美国、加拿大和日本。在这种系统中,24路语音信号在输入端复用在一起。 5. 传输包括把数字编码的语音信号从一个地方发送到另一个地方,而交换包括建立两个话音信道的有效连接,这两个信道是(用来)承载数字信号的。 6. 在数字传输系统中,对信号进行脉码调制和解调的单元被称作编/解码器,或缩写为codec.7. 然后,将单个的模拟语音话路时分复用为24路或30路的组合。接下来,通过一个高速的数字信号编解码器将每一组合转化为数字形式。这种排列导致了器件数量的一些减少,但是,具有足够低的线间串话和噪声,同时又具有所需很高速度的全集成(各路)共用编解码器的设计代表了一个很难的设计问题。此外,编解码器的任何故障都会导致这个单元所服务的所有线路丢失其所需的服务。而且,这种系统需要大量笨重且低速的模拟转换器。最终,所需的模拟多路复用与数字多路复用相比,在实现上更为困难,灵活性亦更差8. 随着近来低成本、高性能集成电路的实用化,可以为每一路语音信道分配一个编解码器,而不是一组信道使用一个编解码器 。每信道一个编解码器的系统,显著减少了串话和噪声的影响 。此外,由于除去了使用体积庞大且贵重的电动机械的部件而显著节省了空间和成本。9.对于通常的3003400 Hz 的语音信道,CCITT推荐的标准取样频率为8000Hz。在每信道一个编解码器的系统,每隔125s对模拟信号取样一次,将样值的幅度转化成一个8比特的码字,然后再连续的传输给复用器。将这个用来转换的125s长的时间间隔称作一帧。10. 数字复用器把对应于24路或30路各路样值的全部比特放在一个帧中,然后传输结果串行比特流。为了在接收机处能够对每一帧的帧头和帧尾进行标识,应该在传输的比特流中加入一些识别信号。例如,在被AT&T称作D2 的24信道8比特PCM系统中,给每一帧中附加了一个比特。从而,在D2系统中,每一帧包含248+1=193 bits 。因此,所传输信号的数据率为193 bits/125s,对应 1.544106bit/s的速率。11. 传统的转换和传输系统的通道组成被列举到图标4中。在发送方向,认购线连接到用户线接口电路(SLIC)。 SLIC的执行两到四线转换,同时还提供振铃访问和过电压保护。信号接着通过发送滤波器,发送滤波器将信号频谱限制在3400Hz附近,因此去掉了超出4kHz的频谱,从而使得以8 kHz 的频率对信号抽样而不出现混频成为可能。此外,频谱的低频部分(300Hz以下)也被发送滤波器抑制掉,以阻止传输线频率噪声。12. 经过滤波的信号,频带被限制在300 to 3400 Hz 范围内,然后以8 kHz 的频率对其进行抽样,转换(编码)为8bit的PCM数据。这种转换是非线性的,即对小信号其生产的数字信号的分辨率要优于大信号。13.非线性模/数转换器输出经过特殊编码的8bit码字,其中第一个bit表示输入x的符号,1表示正极性,0表示负极性,后7位bit表示信号的幅值。14. 编码器的数字输出与其他线路的输出通过时分复用,产生的bit流在信道中传输。在接收端,对输入数据进行解复用,即在各个通路间分配并解码(数/模转换 )。后者则是一个低通平滑滤波器,去除高频率“旁瓣”的信号频谱,从而抚平了楼梯噪声信号。它也经常被用来平衡的罪恶X / x幅度失真的采样和保持阶段推出。15. 在接收端,对输入数据进行解复用,即在各个通路间分配并解码(数/模转换 )。Unit 13Comparison between GSM and CDMA GSM与CDMA之比较Using CDMA/FDD technology, subscribers of CDMA cellular mobile communication system can transmit their information simultaneously through the same channel. On the other hand, the GSM system adopts TDMA/FDD method to transmit and distinguish information from different GSM mobile stations. In addition, in favor of QCELP arithmetic, RAKE receiver, power control and soft switching etc., CDMA shows more advantages in its system performance than the GSM, such as greater anti-interference capability, bigger system capacity, higher successful connection ratio, fewer off-line chances, low probability of intercept(LPI), and so on.使用码分多址/频分双工技术,用户的蜂窝移动通信系统的传输信息的同时,通过同样的渠道。另一方面,该系统采用时分多址/频分双工传输的方法和识别信息从不同的移动台。此外,有利于中国电信集团广州研发中心算术,耙式接收器,功率控制和软开关等,显示出更多的优势在码分多址系统性能比,如更高的抗干扰能力,更大的系统容量,连接成功率较高,离线的机会少,低截获概率(低截获概率),等。1, Power Control and RAKE Receiver功率控制和瑞克接收机When different subscribers send their information to the same BS(base station), different signal power caused by different transmitting distances will consequentially cause interference with each other, especially for those MSs(mobile station) being far away from BS will be seriously disturbed because of their almost submerged signals by signals of the close-to-BS MSs.2 p110In order to solve this problem and keep high system performance, power control technique is introduced in CDMA communication system, which can effectively overcome this cross-disturbance. As one of the core techniques in CDMA cellular mobile communication system, power control can make the signal power from all subscribers to the BS equivalent through adjusting the transmitting power from each subscriber.为解决这一问题,保持较高的系统性能,功率控制技术介绍了码分多址通信系统,它可以有效地克服这cross-disturbance。作为一个核心技术在蜂窝移动通信系统的功率控制,可以使信号功率从所有用户的学士学位相当于通过调整发射功率,从每个用户。Power control can be not only divided to open-loop control and closed-loop control, but also to forward (down) power control and backward (up) power control. For open-loop control method, subscriber adjusts emitting power according to the measured frame error probability, while for the closed-loop power control, base station measures the signal-to-noise ratio of received signals and then adjust the transmitting power of corresponding MS.功率控制不仅可以分为开环控制和闭环控制,而且还提出了(下)功率控制和反向功率控制(上)。开环控制方法,用户调整发射功率根据测量帧错误概率,同时为闭环功率控制,基站测量接收信号的信噪比,然后调整发射功率相应的女士The backward power control in CDMA system can be divided into two kinds of control technique, the open-loop backward power control only used by mobile station, and the closed-loop backward power control that can be adopted by both base station and mobile station. On the other hand, the forward power control is just used to reduce the disturbance from small adjacent districts.反向功率控制系统可分为开环控制技术,反向功率控制用的移动站,以及闭环反向功率控制,可以通过基站和移动站。另一方面,正向功率控制是用来降低干扰小附近的地区。RAKE Reception Technique(瑞克接收技术)Fading and distortion are inevitable for signals transmitted in mobile communication channel because of the unideal characteristics of channel, and then make bad influence on system performance. 变形是不可避免的衰落和信号传输的移动通信信道因为不理想的信道特性,进而会影响系统的性能。The basic theory of RAKE reception technique is: by means of collecting all transmitted signals from multi-path and uniting them, the received signal power can obtain an effective enhancement, which can improve the output SNR and system performance. 3 p110Three, four RAKE receivers are respectively set in each MS, BS in CDMA system in order to receive the arriving branch signal of the same original from different transmitting routes, and then combine them to get an increscent output SNR after their respectively independent demodulation. Thus, in favor of RAKE reception technique, the disadvantageous factor that signal transmitted in multi-path because an advantageous factor in CDMA cellular mobile communication system.三,四的耙式接收器分别设置于每一毫秒,在码分多址系统,以便接收到信号相同的原始分支从不同的传播途径,并结合他们得到一个增大的输出信噪比后分别独立解调。因此,有利于瑞克接收方法,发送信号的不利因素,因为一个有利因素在多径码分多址蜂窝移动通信系统。2 Better Performance of CDMA性能更好的码分多址Greater Anti-interference Capability更大的抗干扰能力Because of spread spectrum modulation, bandwidth of users signal is extremely broadened by the assigned unique pseudo-random sequence, thus the modulated broad band signal owns spectral properties close to Gaussian white noise. Receiving this kind of spread spectrum signal, all the CDMA receivers try to demodulate it using PN sequence created locally , but only one receiver with the same local PN sequence as that in the received signal can convert the broad band noise-like signal into narrow band useful signal , while other receiver is still the insignificant broadband noise except the relative demodulator with the unique local PN sequence .由于扩频调制,带宽用户的信号是非常扩大的分配独特的伪随机序列,从而调制的宽带信号拥有光谱性能接近高斯白噪声。接受这种扩频信号,所有的码分多址接收机尝试使用伪随机序列解调本地创建,但只有一个接收相同的本地伪码序列,在接收信号可以转换成宽带类噪声信号为窄带有用信号,而其他接收器仍然是微不足道的宽带噪声,除了相关解调器与当地独特的伪随机序列。In addition , as far as the narrow band meaningless signal additive to the received signal by the relative receiver with the same unique pseudo-random sequence , it is modulated into broad band signal with extremely lessened power spectral density .Thus , the relative receiver can filter the broad band signal from other users and majority of the meaningless signal out of the filter bandwidth just through a narrowband filter .Therefore , reservation in within the receiver only consists of the narrowband useful signal and little meaningless signal within the filter bandwidth . As a consequent result , the output signal-to-noise ratio is improved largely , that will necessarily leads to greater system anti-interference capability . 此外,至于窄带毫无意义的信号添加剂的接收信号的相对接收相同的独特的伪随机序列,它是调制成宽带信号的功率谱密度非常减少。因此,相对接收器可以过滤宽带信号从其他用户和广大的毫无意义的信号进行滤波器的带宽是通过窄带滤波器。因此,保留在接收由窄带有用信号和小无意义的信号在滤波器的带宽。作为一个必然结果,输出信噪比有较大的提高,这必然会导致更大的系统的抗干扰能力。It can be proved that the more high value of Bn/Bb , the more great system anti-interference capability .由于扩频调制,带宽用户的信号是非常扩大的分配独特的伪随机序列,从而调制可以证明更高价值的Bn/ Bb,更大的系统的抗干扰能力。Bigger System Capacity and Higher Successful Access Ratio更大的系统容量和更高的接入成功率Unlike the TDMA multi-access mode in GSM mobile communication system, signal of each CDMA subscriber is distinguished by the assigned unique PN sequence based on the CDMA technology. Thus, each signal of CDMA subscriber can be transmitted synchronously occupying the entire sub-channel bandwidth divided from the FDD method. So under the equal frequency resource condition, in other word, for the same channel bandwidth, capacity of CDMA system is 45 times larger than that of GSM system.不同的是时分多址接入模式在移动通信系统中,信号的每个用户的特点是独特的伪随机序列的分配基于码分多址技术。因此,每一个信号,用户可同步传输信道带宽占整个分从故障诊断方法。所以在同等频率资源条件,换句话说,在同一信道带宽,码分多址系统容量为45倍以上的系统。In the nature of things, a communication system with big capacity must have high successful access ratio.在事物的性质,通信系统容量大,必须具备较高的接入成功率。In addition, using CELP (Code Excited Linear Predictive) arithmetic for voice code, audio signal in CDMA system can be transmitted with variable speed, with the maximum CELP coded audio signal transmitting velocity is 9.6kbit/s while the subscriber is talking, and the minimum velocity of 1.2kbit/s for the conversation pause. This technique called Voice Activation can reduce the background disturbance among subscribers communicating on one channel at the same time, and enhances the system capacity. For GSM system, this Voice Activation technique cannot be used because of the signal transmitting delay at conversation pause.此外,利用线性预测(码激励线性预测)算法的语音编码,音频信号在码分多址系统可以传播速度可变,以最大线性预测编码的音频信号传输速率为9.6比特每秒而用户说话,和最低速度的1.2比特每秒的谈话暂停。这种技术称为语音激活能降低背景干扰用户间的通信在一个频道在同一时间,并提高了系统容量。全球移动通讯系统,该语音激活技术无法使用,由于信号传输延迟谈话停顿。Better Voice Quality更好的声音质量Using advanced CELP (Code Excited linear Predictive) arithmetic for its digital audio signal code, and 3 RAKE receivers in a handset to receive signals from different directions simultaneously, it is made extremely abundant and dimensional for audio signal spectrum from CDMA handset. Furthermore, vocoder based on the CELP arithmetic in CDMA system can adjust its transmitting velocity and choose corresponding sending power level automatically to reduce the disturbance of noise .Thus, even under the circumstance with loud noise, we can make conversation of good quality without any cacophony. 采用先进的线性预测(码激励线性预测)算法的数字音频信号的代码,在手机和3接收机接收来自不同方向的信号的同时,它是极其丰富和三维音频信号频谱从手机。此外,声码器的线性预测算法在码分多址系统可以调整其传输速度和选择相应的发送功率电平自动减少噪声的干扰。因此,即使在情况下的声音,我们可以把会话质量好无杂音。Lower Probably of Intercept (LPI) 下可能拦截(低截获概率)It is necessary for eavesdropping somebodys conversion that the transmitted conversion information must be captured and then decoded. For CDMA system, signal with users information must be spread spectrum modulated before sent to the common channel with extremely spread spectrum and very low power spectral density. Thus it is too difficult to detect this kind of CDMA signal for the listener-in because its power spectral density is even lower than ambient noise, and its almost impossible for him to distinguish the signal from background noise.这是必要的窃听别人的转换,传输转换信息必须捕获和解码。用于码分多址系统的信号,用户的信息必须发送扩频调制前的共同渠道极扩频和非常低的功率谱密度。因此,这是很难检测到这种信号的收听者因为其功率谱密度甚至低于环境噪声,它几乎不可能为他区分信号从背景噪音。Moreover, even if the signal is captured, what the listener-in can get only broad band noise of insignificance from his demodulator because of his inaccurate local pseudo-random sequence. The probability of right PN sequence pattern necessary for spread spectrum demodulation is one of more than one thousand billion! What a low probability for listener-in to eavesdrop others conversation through CDMA cellular mobile communication system!此外,即使信号捕获的听众,仅能获得宽带噪声微不足道从解调器因为他的不准确的本地伪随机序列。概率的正确的序列模式所必需的扩频解调是超过一千个亿!什么是低概率的听众偷听别人的谈话通过蜂窝移动通信系统!Fewer Off-line chances 离线的机会较少Because of the soft-switching technique, which means “connect-before-break”, its overcome for CDMA that the frequent occurrence of off-time.由于软开关技术,即“connect-before-break”,它克服了码分多址,频繁发生的时间。In mobile communication system, BS is the guarantee for conversation. When subscribers during conversation moving close to edge of the BS demesne, the BS should maintain the communication through its active switching, otherwise the process will be interrupted. During switching period, BSs dominion should shift from “demesne of the local BS (such as A)” to “demesne of A and its neighboring BS(B)” to “demesne of B”, and signal from the moving mobile station will automatically switch to a relatively idle neighboring BS. Thus, only when it is approved that the moving MS has moved to the “demesne of B”, can the connection between the moving MS and its original BS(A) be switched off. So it is not easy for a CDMA conversation to be interrupted by off-line.在移动通信系统,基站是保证谈话。当用户在会话移动接近边缘的学士学位的私有化,如要保持通信通过其主动开关,否则程序中断。在切换期间,英国的主权应该从“私有的地方本科(如)”到“私有和邻近基站(乙)”到“私有”,和信号从移动台移动会自动切换到一个相对空闲周边基站。因此,只有当它是批准移动质谱已移到“私有”,可连接之间的移动和原来的学士学位(一)关闭。所以它是不容易的码分多址的谈话被打断了离线。Unlike the above soft-switching in CDMA, hard-switching method adopted in GMS system executes switching process as break-before-connect ,which happen to be the reversed processing sequence with that of CDMA. That is to say ,when a GSM subscriber during conversation moving close to edge of BSs demesne, the local BS(A) cut off connection with the MS at first , then the MS set new connection with the neighboring BS(B) once again . Thus, communication during this switching will have to be interrupted , that consequently leads to a high off-line ratio.Sample Frequency Layout抽样频率 CDMA subscribers are distinguished by the assigned unique pseudo-random sequence, so neighboring channels can be used for signals transmitting with the same carrier frequency .Thus, its quite flexible to program the system frequency layout, and so for the system expansion.与上面的软开关在CDMA, 硬开关方法采用GMS系统执行开关过程中为“break-before-connect”,恰巧相反的处理序列与CDMA。 也就是说,当一个GSM订户在谈话期间移动接近边缘的废话的私有,当地BS(a)切断了连接和多发性硬化症的在第一,然后设置新连接女士与周边BS(B)又一次。因此,沟通在这个开关将不得不被打断,因此引起很高的离线比率。采样频率的布局CDMA用户区分由指定的独特的伪随机序列,所以邻近频道可以用于信号传输载波频率相同。因此,这是相当灵活的程序系统频率的布局,那么对系统扩张。44页第二段开始,作为第一段,第三单元前半部分没有电子版的,我那里有复印好的Each frame consist of 256 bit and conveys one sample from each speech channel . the overall transmission rate required is therefor 2.048Mbit/s . 每个框架由256位和传达一个采样通道的每个讲话。整体传播率要求是因此2.048 Mbit / s。 this rate of 2.048Mbit/s is ofen referred to as the “primary rate” , since it represents the first level of multiplexing used in the Synchronous Digital Hierarchy (SDH) . 这种水平的2.048 Mbit / s是经常被称为“主率”,因为它代表了第一层的多路复用用于同步数字序列(SDH)。IN North America and Japan the primary level of multiplexing consists of 24 speech signals with a signal bit of synchronizing information for ever 24*8 bit frame , giving a frame size of 193 bit . 在北美和日本主要的水平的多路复用由24个语音信号与一个信号点同步信息永远24 * 8位的框架,让帧的大小的193位。the overall transmission rate required is thus 1.544Mbit/s . 整体传播率要求是因此1.544 Mbit / s。 in this system the signaling information is incorporated into bits “stolen” from the information bearing octets . an early system used in the UK also used 24 channels , with the 8 th bit of each octet being used for signaling and synchronization , leaving 7 bit only to represent each PCM sample of the signal . the quanzation noise was therefor twice as grate than that obtained using 8 bit quanzation . 在该系统中信号信息纳入位“偷走”从信息其字节。一个早期的系统,用于英国也使用24频道,第八届点每八隅体被用于信号和同步,造成7位只代表每个PCM的示例的信号。quanzation多式的噪声的两倍,所得格栅的使用quanzation 8位。 the overall transmission rate for this system was 1.536Mbit/s . however , all UK 24 channel systems have now been replaced with 30 channel systems to CCITT standards , although their impact is still felt , as will be seen later when we discuss the choice of line codes for transmission . 整个这个系统的传输速率为1.536 Mbit / s。然而,英国所有24频道系统现在已经被替换为30通道系统CCITT标准,尽管其影响仍觉得,我们可以看到当我们稍后讨论选择行代码进行传输。6:signaling and synchronization6:信号和同步 We now return to consider in a little more detail the signaling and synchronization signals incorporated into channels 0 and 16 of the 30 channel PCM frame . 我们现在还考虑在一个更为详细的信号和同步信号纳入通道0和16的30个频道PCM框架。 the frame alignment pattern contained in time slot 0 alternates between successive frames as shown in fig.6 . 这个帧同步模式包含在时间的位置0之间交替进行连续帧见图6。 Some of the bits are not part of the specified pattern and these can be used to carry date . one bit in each alternate frame is available for remote alarm signaling purposes to signal loss of frame alignment to the distant station . 一些位不指定模式的一部分,这些可以被用来携带日期。一位在每个替代框架是可用于远程警报信号目的的讯号损失帧同步到远台。Two different methods are in common use for the channel signaling contained in time-slot 16 , the earlist , and currently most widely used , method is that known as “channel associated signaling” . 两种不同的方法一般用于通道信号包含在time-slot 16,最早的,目前人们普遍使用的方法是,被称为“通道相关的信号”。 the frame are numbered sequentially form 0 to 15 . the first four bits of frame 0 , time slot 16 , contain the multi-frame alarming pattern of four consecutive zeros , as shown in fig.7 . 框架顺序编号形式0到15。前四位的第0帧,时间槽16,包含multi-frame惊人的模式的连续四个零,如图7所示。 three of the other four bits are spare and available for use for data . the eighth bit used to signal remote loss of multi frame alignment . 三其他四位是多余的并且可以使用了数据。第八位用于信号远程损失的多帧同步。Inframes 1 to 15 , the time-slot 16 octets are divided into two 4 bit sub-fields as shown in fig.7 . Inframes 1到15、16字节time-slot分为两个4位子图7所示。 the first four bits in frame N ae used for channel n signaling and the second four bits for channel N + 16 signaling . 第4位在帧N ae用于频道N信号和第二个四位频道N + 16信号。这给四位在每个通道的信号,信号信息更新。this gives four bits for signaling in each channel , the signaling information being updated . every 16 in frame , that is , every 2 ms . the four bits per channel give the possiblility of 15 signaling states . the all-
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