频率选择性信道下特征波束和空时编码联合分集

Joint eigenbeam and space-time coding over the frequency-selective fading channel for diversity

为了改善宽带下行衰落相关信道下空时码性能,提出了基于空时编码和特征波束结合的方案.该方案结合了特征波束形成和OFDM技术,将空域协方差矩阵的特征矢量作为空时码矩阵的加权矢量,使空时码在空间能量最集中的方向发射.利用特征波束形成和降维处理将衰落相关信道转化成2个发射天线N个接收天线的FIR信道.利用OFDM技术将FIR信道转化为一组相互独立的平行子信道来承载空时码.仿真结果表明与经典Alamouti码相比较,在不同多径数目及不同发射阵元条件下,该方案在信噪比提高的同时,误比特率性能曲线斜率下降更快.在发射阵元为6,多经数目为16的条件下,系统性能提升5 dB.获得了更好的分集增益,并增加了等效信道总功率.

A Space-Time Eigenbeam Coded scheme is discussed to improve the performance of Space- Time Coding for downlink wideband correlated fading channels. This novel transmission scheme combining Eigenbeam forming with OFDM is proposed. A group of eigenvectors of the Spatial- Correlated-Matrix （SCM） is introduced as the weights of the Space-Time code-matrix. The scheme can channel the transmit power in the directions with the biggest gains and convert correlated fading channels into an independent FIR channel with 2 transmitting antennas and N receiving antennas by Eigenbeam forming and reducing the dimensions. Then OFDM is utilized to convert this FIR channel into a group of independently parallel subchannels to carry Space-Time Codes. The BER（Bit Error Rate） performance comparisons with the traditional Alamouti code under different multi-path and transmit antenna conditions, through extensive Monte-Carlo simulation. The simulation results show that the proposed scheme has a lower BER than the traditional Alamouti code and the Signal-to-Noise Rate （SNR） is higher meanwhile. The performance is 5 dB higher than that of the traditional Alamouti code under 6 transmitting antennas and 16 paths. The proposed scheme leads to a better diversity gain and increases equivalent channel total power.