文件名称：分集技术-华为CDMA2000
文件大小：3.95MB
文件格式：PPT
更新时间：2024-05-13 05:52:02
cdma
分集技术 时间分集 采用符号交织，检错纠错编码等方法。 频率分集 通过将信号能量在宽频带中扩展实现的。CDMA将信号扩展到整个1.23MHz上。 空间分集 在BTS采用双接收天线。 在手机和BTS采用RAKE接收，合并不同传输延时的信号。 软切换的时候，MS和多个BTS同时联系，从中选出最好的帧。 CDMA 核心技术 Diversity technology means that after receiving two or more input signals with mutually uncorrelated fading at the same time, the system demodulates these signals and adds them up. Thus, the system can receive more useful signals and overcome fading. A mobile communication channel is a multi-path fading channel and any transmitted signal reaches a receive end by means of multiple transmission paths, such as direct transmission, reflection, scatter, etc. Furthermore, with the moving of a mobile station, the signal amplitude, delay and phase on various transmission paths vary with time and place. Therefore, the levels of received signals are fluctuating and unstable and these multi-path signals, if overlaid, will lead to fading. The mid-value field strength of Rayleigh fading has relatively gentle change and is called “Slow fading”. And it conforms to lognormal distribution. Diversity technology is an effective way to overcome overlaid fading. Because it can be selected in terms of frequency, time and space, diversity technology includes frequency diversity, time diversity and space diversity.