Linear precoding for time-varying MIMO channels with low-complexity receivers

This paper considers linear precoding for time-varying multiple-input multiple-output (MIMO) channels. We show that linear minimum mean-squared error (LMMSE) equalization based on the conjugate gradient (CG) method can result in significantly reduced complexity compared with conventional approaches. This reduction is achieved by incorporating a condition number constraint into the precoder optimization framework, which leads to clustered eigen-values of the measurement covariance matrix. The cost is a small increase in MSE compared to the optimal precoder.