Distributed robust beamforming for MIMO cognitive networks

Beamforming for multi-input multi-output (MIMO) cognitive networks is considered in the presence of channel uncertainty induced by errors in estimating cognitive-to-primary channels. A robust beamforming problem is formulated to optimize an appropriate cognitive radio network-wide performance metric, while enforcing protection of the primary system. In spite of the non-convexity of the resultant optimization problem, a block coordinate ascent algorithm is developed with provable convergence to a stationary point. Enticingly, the novel scheme also lends itself naturally to a distributed implementation. Numerical results are reported to corroborate the analytical findings.