时变CDD-OFDM系统中的改进EM信道估计

针对循环延时分集OFDM系统中的时变信道估计导频开销较大问题,提出了一种递归的改进期望最大化（EM）信道估计方法。该方法首先建立时变信道基扩展模型（BEM）与符号时间平均信道脉冲响应之间的数学关系,然后用其预测EM信道估计的初值,从而一方面利用了BEM参数的慢变特性来提高时变信道的预测精度,另一方面利用了BEM的简约化参数特性来保持算法实时性。仿真结果表明,当信噪比大于15 dB时,改进方法有效降低了判决辅助方法的误差传播效应,其误码性能接近理想信道时的性能。

Improved Channel Estimation for CDD-OFDM Systems in Time-varying Channels

For reducing the pilot overhead used in time-varying channel estimation of orthogonal frequency division multiplexing system with cyclic delay diversity (CDD-OFDM), an improved expectation maximization (EM) based channel estimation scheme with recursive fashion was proposed. In the proposed scheme, the mathematical relationship between the basis expansion model (BEM) of time-varying channels and the symbol time-averaged channel impulse response was firstly established and then was used to predict the initial value of the EM based channel estimator, and as a result, the parsimonious parameterization properties of the BEM and the slow variations of the BEM parameters could be exploited to improve the channel prediction accuracy and make the algorithm real-time, respectively. Simulation results showed that when the signal to noise ratio is above 15dB, the proposed scheme effectively reduce the error propagation of decision directed channel tracking scheme, and has nearly the same bit error rate performance as that with perfect channel state information.