一种基于直扩码分多址系统的复信号空时扩频算法

基于直扩码分多址系统下行链路，提出了一种针对复信号的空时扩频算法．该算法采用发射分集技术，将空时分组编码与直接序列扩频相结合，依靠空时分组码和扩频码的双重正交特性以及复信号自身的特性，充分利用了空域和时域资源设计出新的收、发和解码算法，解决了复信号空时分组编码非正交所导致的解码复杂度过高的问题，将最大似然检测简化为一个线性过程．在独立瑞利衰落信道和给定收、发天线数的条件下，能够实现系统所能达到的最大的分集增益．理论分析及仿真结果表明，与未加扩频的发射分集系统及现有的空时扩频算法相比，该算法不仅能够显著提高数据传输速率，增大系统容量，还具有误码性能好，解码复杂度低、接收机结构简单等优点．

New Space-Time Spreading Scheme of Complex Signals Based on Direct Sequence Code Division Multiple Access

A new scheme of space-time spreading of complex signals based on the downlink of direct sequence code division multiple access (DS-CDMA) systems is presented. Using transmit diversity techniques, the new scheme combines the space-time block code (STBC) with spreading codes. Depending on the characteristic of complex signals and the dual orthogonality of STBC and spreading codes, the scheme can utilize the resources of space and time efficiently, and it transfers the maximum-likelihood detection into a linear processing with a simplified decoding process to resolve the high complexity problem caused by the unorthogonality of the complex signal STBC. Over independent Rayleigh fading channels, this scheme can achieve the maximum possible diversity gain for a given number of transmit and receive antennas. Theoretical analysis and simulation results show that the proposed scheme outperforms the systems of transmit diversity without spreading and existing space-time spreading algorithms in terms of transmission rate, system capacity, bit error rate performance and implementation complexity.