Subcarrier and Power Allocation in OFDM Based Cognitive Radio Systems

Cognitive Radio (CR) which aims to improve the spectrum utilization by accessing opportunistically the spectrum originally licensed to a primary system is a promising concept. OFDM is regarded as a potential technology for CR systems and dynamic resource allocation is an important task in such systems. This paper focuses on the sub carrier and power allocation algorithms which are to maximize secondary users´ transmitted data rate while adjusting the interference introduced to the PU band below a threshold and maintaining the total power under a limit. The issue of sub carrier allocation in multi-user CR networks is firstly discussed. Secondly, three sub optimal power allocation algorithms based on LWF (linear water-filling algorithm) which have less complexity than the optimal algorithm are proposed. Simulation results show that the power interference algorithm based on linear water-filling scheme (LWF-PI) offers the best performance among the sub optimal power allocation algorithms, which is the closest to the optimal scheme.