直扩分层空时结构在下行衰落相关MIMO中的应用

为了提高分层空时结构在下行衰落相关多输入多输出系统中的传输性能，提出了一种结合了特征波束形成的直扩分层空时结构．发射机利用信道空域协方差矩阵的特征矢量，对每一层发射码元进行扩频和特征波束形成加权，形成正交的空域特征波束来承载扩频后的信号码元；接收机则通过解扩处理分离来自不同波束上的信号，有效地抑制了共信道干扰．新结构的优点是无需设计扩频序列并且可以应用干下行传输，其代价是要占用一定的扩频频谱资源．实验结果表明，新结构明显优干基于迫零算法的分层空时结构．

Application of DSSS based layered space-time architecture to downlink correlated fading MIMO systems

To improve the performance of LSTA(Layered Space-Time Architecture) in downlink correlated fading MIMO (Multiple-Input Mulitple-Output) systems, a novel DSSS(Direct Sequence Spread Spectrum) based LSTA combining eigenbeamforming is proposed. The transmitter takes advantage of the eigenvectors of the SCM(Spatial Covariance Matrix) of the correlated channels to spread and weigh the signals of each layer. The spatial eigenbeams are formed to carry the signals being spread. The receiver distinguishes the signals from different beams via dispreading operations; therefore co-channel interferences are eliminated effectively. The proposed scheme has the some advantage of dispensing with designing OSS and can be applied to downlink transmission at the cost of loss in the spreading spectrum. Simulation results show that the new scheme greatly outperforms ZF-LSTA(LSTA using ZF algorithm).