Robust Relay Precoding in MIMO Cognitive Networks with Bounded Channel Uncertainties

This paper investigates robust precoding with bounded channel uncertainties for multi-input multi-output (MIMO) cognitive networks which are equipped with two-way relay (TWR). In the networks, the secondary users (SUs) are allowed to share the spectrum with the primary users (PUs) when the interference temperature (IT) is below a specific threshold. The channel uncertainties are characterized in terms of the spherical uncertainty region, and the transmitting strategy of relay is amplify-and-forward (AF). We consider a min-max problem for the sum of mean square error (SMSE) when IT of the PU and the transmitting power of the relay are below their corresponding thresholds. For solving the problem, we can convert it into a semi-definite programming (SDP). Simulation results manifest the merits of the proposed method.