| Cognitive radio can improve spectrum utilization through making the cognitive users share the spectrum resource of the primary users while the interference introduced to the primary users is not serious. OFDM has high spectrum efficiency which can allocate frequency resource adaptive. So OFDM can be used in cognitive radio to allocate the unused spectrum and power for cognitive users in order to improve the flexibility and spectrum efficiency.In this thesis, resource allocation algorithm OFDM-based cognitive radio systems would be researched which considering the main users'interference limitation and the cognitive users' transmission limitation allocate resource in the unused spectrum for cognitive users. How to make full use of the detected frequency holes can be considered as how to allocate the subcarriers and the transmit power of the subcarrier. The thesis firstly introduces the cognitive radio's principle and key technologies, and OFDM-based cognitive radio, then mainly research the single cognitive user and multiuser resource allocation from the rate maximization aspect.An improved simple relative cost greedy bit loading single user resource allocation scheme is given in this thesis, which could make the cognitive user achieve high transmission rate in the interference limited state and power limited state, then this resource allocation scheme is extended to resolve mulituser power allocation problem, which could make the cognitive users achieve high transmission rate and reduce the computation complexity. Finally, a multiuser multi-interference limits suboptimal power allocation strategy is proposed, which allocate the subcarriers and power to cognitive users through changing the primary users'interference limitation to each cognitive user's maximal interference power introduced to the primary users. This power allocation strategy includes optimal scheme, fair scheme and three-step fair scheme. This paper also analyzes the simulation results for all allocation alogrithms. |
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