Research On Resource Allocation In OFDM Based Cognitive Radio Systems

With the rapid development of wireless technologies, wireless spectrum resource has become increasingly scared. 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. Cognitive radio is an intelligent wireless communication technology which can learn from the environment and can dynamically adjust its internal working condition in accordance with changes in the environment. OFDM is regarded as a potential technology for CR systems, for the reason that OFDM technology has the flexibility to choose frequency to facilitate the realization of the spectrum resource management.This paper focuses on the resource allocation algorithms which are to maximize the 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. In this paper, subcarrier and power allocation are accomplished independently. The issue of subcarrier allocation in OFDM-based CR networks is firstly discussed. Further, for the given subcarrier allocation, three improved power allocation algorithms based on LWF (linear water-filling algorithm) which have less complexity than the optimal algorithm are proposed and compared to the optimal power allocation algorithm. Simulation results show that the PI algorithm offers the best performance among the improved power allocation algorithms, which is the closest to the optimal scheme.