Enhanced precoder for secondary user of MIMO cognitive radio in the presence of CSIT uncertainties in the desired and interference links

Abstract

This paper advances the design of transmit precoder for a secondary user (SU) coexisting with a primary user (PU) in multiple-input multiple-output (MIMO) cognitive radio, where the channel state information at transmitter (CSIT) of SU is inaccurate in both the desired link (DL) to its receiver and the interference link (IL) to the PU. The design seeks to maximize performance in the worst scenario, by optimizing the capacity of SU while maintaining a given quality of service (QoS) of PU at the most unfavorable uncertainty errors of the two links. The proposed technique improves the previous design by solving for the precoder in a more accurate and efficient manner, and by using the variable metric projected subgradient method. The most unfavorable realization in the DL is obtained by the alternate-iterate optimization method and the worst uncertainty realization in the IL is derived from the projected subgradient method. The convergence properties and computational complexity of the proposed algorithm are analyzed. Numerical results confirm the proposed precoder has better performance than the previous solution while having lower practical time complexity, especially when the PU has higher tolerance level of SU interference.