自适应子信道分配的多载波CDMA系统

多载波CDMA技术能够提供大的系统容量、对抗瑞利衰落和消除符号间干扰等优点,成为具有发展前景的调制技术之一.本文提出了一种自适应子信道分配的多载波CDMA系统.即对任一用户,根据各子载波上受到的窄带干扰和衰落大小,选择出最佳的传输子载波,则该用户的信息就通过此最佳传输子载波进行传输.通过衰落信道下（同时存在窄带干扰时）的仿真,结果表明：（1）在强的窄带干扰情形下,采用提出的自适应子信道分配算法的改进MC-CDMA系统的性能比采用并行传送方式的传统MC-CDMA系统以及直扩CDMA系统的性能有了很大程度的改善;（2）在弱的窄带干扰情形下,当子载波数目较大时,采用自适应子信道分配算法的误码率性能仍然比采用并行传送方式的传统MC-CDMA系统以及直扩CDMA系统的性能有所改善.

Adaptive Subchannel Allocation for MC-CDMA System

Multicarrier code-division multiple-access is one of the modulation techniques with developing prospects.It has advantages such as the huge system capacity and the capability to fight against rayleigh fading and suppress inter-symbol interference.A MC-CDMA transmission system with adaptive sub-channel allocation is presented.For any of the users,the optimal transmission sub-channels are selected according to the extent of narrowband interferences and magnitudes of fading imposed upon the sub-channels.Each user's data are transmitted over the selected sub-channels.Transmission is simulated through the fading channel with concomitant narrowband interferences.The results show that:(1) In the case of strong narrowband interference,the proposed system gains significant improvement in performance over the conventional MC-CDMA system with parallel transmission and also the direct-extension CDMA system;(2) In the case of weak narrowband interference,when the number of subcarriers is comparatively large,the bit error rate becomes better than those of the conventional MC-CDMA system with parallel transmission and also the direct-extension CDMA system.