Threshold-based opportunistic zero-forcing beamforming for two-user downlink systems with outage constraints

In this paper, we present the exact outage analysis of the two-user downlink systems using the threshold-based opportunistic zero-forcing beamforming (TBO-ZFB) with a second mobile station's outage constraint. TBO-ZFB dynamically switches between a beamforming weight vector and a zero-forcing beamforming (ZFB) weight vector (using linear precoding for first mobile station (MS)) by comparing the values between a second MS's signal-to-noise ratio (SNR) and a predetermined threshold. We provide that the threshold is satisfied with the second MS's outage constraint. Numerical results show that the outage performance of first MS using TBO-ZFB is better than the ZFB and the threshold is satisfied with the second MS's outage constraints.