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1、精选优质文档-倾情为你奉上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 distingu
2、ish 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 success
3、ful 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
4、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 serious
5、ly 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 cor
6、e 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
7、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, whi
8、le 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
9、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 reduc
10、e 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,
11、 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 i
12、mprove 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
13、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
14、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 o
15、wns 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-
16、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
17、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 ,
18、 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 wit
19、hin 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
20、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
21、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 d
22、ivided 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，
23、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 spee
24、d, 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 channe
25、l 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
26、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 abun
27、dant 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 wit
28、h 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 eaves
29、dropping 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
30、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
31、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 sprea
32、d 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
33、 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 c
34、onversation 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(
35、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
36、 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,
37、 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 wi
38、th 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 p
39、seudo-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。专心-专注-专业