一种性能更好的MIMO-OFDM系统MAP信道估计算法

A MAP Channel Estimation Algorithm for MIMO-OFDM Systems with Better Performance

基于期望最大化(EM)的最大后验信道估计算法(MAP)在高信噪比(SNR)下将很难获得较低的估计误差,并且,对于导频辅助的MIMO-OFDM系统,OFDM符号的数据传输效率随着发送天线的增加而明显下降.为改善这两种缺陷,引入一种等效的信号模型来改善高SNR下的估计性能;在相邻多个OFDM符号内使用相移正交导频序列和联合估计来提高系统的数据传输效率和估计性能;根据角域内信道间的独立性来减小噪声对估计的影响.通过仿真实验可知,所提算法具有更小的估计误差和更高的数据传输效率.

Maximum a posteriori（MAP） channel estimation algorithm usually uses expectation maximum（EM） algorithm to decrease the high computation.However,this kind of operation has a difficulty in obtaining ideal estimation performance at high signal to noise ratio（SNR） because of the convergent feature of EM algorithm.In addition,for pilot-based multiple-input multiple-output with orthogonal frequency division multiplexing（MIMO-OFDM） systems,data transmission efficiency of OFDM symbol will be reduced with the increasing number of transmit antennas.In order to improve these two drawbacks,firstly,an equivalent signal model is introduced to improve the convergent property of EM algorithm at high SNR.Then,to enhance the data transmission efficiency,joint estimation is implemented by making use of phase shifted orthogonal pilot sequences over multiple OFDM symbols.What＇s more,channel matrix is transformed between time domain and angle domain and the concept of angle domain is used to reduce the effect of noise on the estimation by using the spatial independence of MIMO channel in channel matrix of angle domain.Through performance analysis and simulation results,it is indicated that the proposed algorithm has lower estimation error and higher data transmission efficiency than the raw MAP algorithm based on EM process,which only requires increasing the computational complexity a little bit.