Improved and weighted sum rate maximization for successive zero-forcing in multiuser MIMO systems

We propose an improved algorithm for optimizing the transmit covariance matrices for successive zero-forcing (SZF) precoding in multiple-input multiple-output systems. We use a conjugate gradient projection method to solve the optimization problem. Our algorithm improves upon the existing method twofold. First, the existing covariance optimization method, with higher SNRs or more simultaneously supported users, can yield a lower sum rate than when using block diagonalization (BD), when theoretically SZF should never be inferior to BD. In comparison, our method consistently provides a higher throughput than BD. Several simulations demonstrate our algorithm's enhanced performance, which exceeds the existing method's sum rate by up to 12% in the examined cases. Second, our proposed algorithm also supports the maximization of a weighted sum rate with SZF, to incorporate quality of service (QoS). To our knowledge, no other work in the literature considers a weighted sum rate and/or QoS with SZF.