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-loopbackward 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 user’s 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。