Matlab平台下仿真实现2*2, 4*4， 6*6天线Alamouti空时编码的MIMO系统，画出不同信噪比下的性能曲线对比。-2* 2, 4* 4, 6* 6 antenna Alamouti space-time coding MIMO system Matlab simulation platform, draw the comparison of different signal-to-noise ratio performance curve.