Precoder adaptation and power control for cognitive radios in dynamic spectrum access environments

Cognitive radio (CR) technology is an emerging technique for dynamic spectrum access, which attempts to share licensed spectrum with licensed users opportunistically and dynamically to provide high bandwidth and efficient spectrum utilisation. In this study, the authors address the problem of finding combined precoder and power of CRs for dynamic spectrum sharing in interference networks. First, the authors present the precoder and power optimisation problem in spectrum underlay by considering both power and interference constraints where CR users coexist and transmit simultaneously with primary users. Then the authors particularise the problem of precoder and power adaptation to spectrum overlay where CRs operate only in idle frequency bands obtained from spectrum sensing. In the proposed approach, bandwidth use is expressed in terms of a finite set of discrete resources whose use is optimised by the CR transmitters in terms of achievable rate corresponding to individual link under operating constraints that restrict the operation of unlicensed secondary CR transmitters to protect licensed primary user transmissions. The authors formulate the optimal resource allocation for CR links as a constrained optimisation problem and solve using the Lagrange method. The authors illustrate the proposed algorithm with the help of numerical results obtained from simulations.