Generalized linear precoder and decoder design for MIMO channels using the weighted MMSE criterion

We address the problem of designing jointly optimum linear precoder and decoder for a MIMO channel possibly with delay-spread, using a weighted minimum mean-squared error (MMSE) criterion subject to a transmit power constraint. We show that the optimum linear precoder and decoder diagonalize the MIMO channel into eigen subchannels, for any set of error weights. Furthermore, we derive the optimum linear precoder and decoder as functions of the error weights and consider specialized designs based on specific choices of error weights. We show how to obtain: 1) the maximum information rate design; 2) QoS-based design (we show how to achieve any set of relative SNRs across the subchannels); and 3) the (unweighted) MMSE and equal-error design for fixed rate systems.