Spatial shaping in cognitive MIMO MAC with coded legacy transmission

This work considers the coexistence of a cognitive multiple-input multiple-output (MIMO)multiple access channel (MAC) system with a single-antenna legacy link which has a rate requirement. The legacy rate constraint is transformed into an interference constraint profile with individual interference temperature constraints (ITC) for the cognitive users. By spatial shaping (transmit covariance matrix optimization, linear precoding), an iterative algorithm is proposed to optimize the sum capacity of the cognitive MIMO MAC system, in which each user updates its transmit strategy with the transmit strategies of the other users fixed. The optimal single-user transmit strategy is obtained by comparing the achievable rate of two iterative algorithms, where transmit covariance matrix with either rank-one or rank-larger-than-one is optimized.