MC-CDMA信号包络特性的研究

基于CDMA和正交频分复用(OFDM)相组合的多载波码分多址系统(MC—CDMA)作为一种新兴的多载波多址通信方式，在高速数据传输时，其抗符号间干扰的性能明显优于传统的单载波CDMA。但MC—CDMA系统也继承了OFDM信号具有高峰平功率比(PAPR)的问题，这会引起高功率放大器(HPA)出现非线性失真。针对减小MC—CDMA信号PAPR问题，分析了MC—CDMA系统模型以及MC—CDMA信号包络功率与扩频码序列部分自相关函数和部分互相关函数之间的关系，并基于正交Gold码序列和Golay互补序列对16位用户的MC—CDMA信号包络特性进行了仿真。仿真结果表明：当选择Golay互补码作为MC—CDMA系统的扩频码时，系统的信号包络变化较小。因此，对MC—CDMA系统，选择扩频码序列应侧重考虑码字的相关性。

Investigation of the Envelope Character of MC-CDMA Signals

As a new multi-carrier and multiple-access communication method, the multi-carrier CDMA (MC-CDMA) based on the combined scheme of CDMA and OFDM has a distinct advantage over conventional single-carrier CDMA in the performance of anti-ISI, when transmitting high-speed data. However, the MC-CDMA system inherits the problem on the higher peak-average power ratio (PAPR) in the OFDM systems, which will result in the nonlinear distortion in a high power amplifier (HPA). For the reduction of the PAPR of MC-CDMA signal, the MC-CDMA system model and the relation between the signal envelope power of MC-CDMA, the aperiodic autocorrelations and the aperiodic cross-correlations of the spreading code sequences are analyzed. The simulations are made on the signal envelope character in a 16-user MC-CDMA system based on the orthogonal Gold code sequences and the Golay complementary sequences. The simulation results show that when Golay complementary codes are selected as the spreading codes of MC-CDMA system, the fluctuation of signal envelope in the system becomes less. Consequently, the correlations of codes should be emphasized while selecting the spreading code sequences.