Joint optimization of rate and outer loop power control for CDMA-based cognitive radio networks

In this paper, we consider a CDMA-based Cognitive Radio (CR) system that involves joint optimization of Outer Loop Power Control (OLPC) and rate control of a cognitive user using Variable Spreading Factors (VSFs) which enhances the average spectral efficiency (ASE) of these users. The cognitive radio system in this paper consists of a number of licensed (primary) users and a cognitive (secondary) user. The bandwidth of the licensed user is allowed to be accessed by the cognitive user under limited interference constraint. Primary and cognitive users employ Code-Division Multiple-Access (CDMA) technology. Considering Nakagami-m flat-fading channels we optimize the system throughput in terms of cognitive user´s ASE under average transmission power constraint and pre-defined interference limit on primary receiver. Numerical results affirm that by using joint-optimization of rate and OLPC in the CR system, the cognitive user´s throughput in high SNRs achieves considerable gain compared to a system that does not employ OLPC.