MIMO Cognitive Radio: A Game-Theoretical Approach

The concept of cognitive radio has recently received great attention from the researchers' community as a promising paradigm to achieve efficient use of the frequency resource by allowing the coexistence of licensed (primary) and unlicensed (secondary) users in the same bandwidth. In this paper we propose and analyze a totally decentralized approach, based on game theory, to design cognitive MIMO transceivers. We consider underlay/interweave networks, where primary users establish proper null and/or soft shaping constraints on the transmit covariance matrix of secondary users, so that the interference generated by secondary users be confined within the interference-temperature limits. We formulate the resource allocation problem among secondary users as a strategic noncooperative game, where each transmit/receive pair competes against the others to maximize the information rate over its own MIMO channel, under transmit power and/or null/soft shaping constraints. We first characterize the Nash equilibria of the proposed game, showing that they can be equivalently rewritten as the solutions of a MIMO waterfilling nonlinear fixed-point equation. Based on this result, we then design low-complex asynchronous distributed algorithms that converge to the Nash equilibria of the games. ©2008 IEEE.