Research On Optimization Of Resource Allocation Algorithms In Cognitive Radio Networks

With the rapid development of wireless communication technology and the explosive growth of wireless business, the frequency spectrum resource is becoming more and more scarce, which is non-renewable. However, researches show that the scarcity of spectrum is not because of its lack of physics but because of the fixed spectrum assignment policy which makes a large part of assigned spectrum not been fully utilized. This motivates the development of cognitive radio(CR), which is exploited as a communication paradigm to improve spectrum utilization rate.Resource management and allocation is an important technology affecting the system performance in the cognitive radio system, especially the cognitive user distribution and power allocation, which has received widespread attention. In this dissertation, we investigated the resource allocation algorithms in cognitive radio networks(CRN). Moreover, by integrating with cooperative relay technology, CR can achieve higher spectrum efficiency. Therefore, we analyze the performance of cognitive relay network.The main contents of this dissertation include three parts as follows:(1) The optimizations of multi-channel cooperative spectrum sensing in CR networks are investigated. In order to maximize the average throughput of the CRN, we formulate an optimization problem of multi-channel cooperative spectrum sensing in Rayleigh environment. Through the proposed algorithms, the following three key questions can be solved:1)the problem of how to assign SUs to cooperatively sense the channels; 2)the problem of how to obtain the optimal sensing time; 3)the problem of how to obtain the optimal sensing threshold. Because the proposed algorithms are for resource allocation, we apply the algorithm to OFDM system to verify the effectiveness and applicability of the algorithm.(2) The joint optimization of multi-channel spectrum sensing and power allocation in CR networks is investigated. The optimization problem of jointly designing SU allocation, sensing time, and power allocation is order to maximize the average throughput of the CRN under total transmit power constraint of the CRN and total interference power constraint of primary network. Through theproposed algorithms, the following key questions can be solved: 1)the problem of how to assign SUs to cooperatively sense the channels; 2)the problem of how to obtain the optimal sensing time and sensing threshold; 3) the problem of how to choose SUs to transmit data; 4)the problem of how to allocate the power. Through the simulation, we proved that the performance of CRN is improved by joint designed.(3) System performance of an amplify-and-forward(AF) cognitive relay network is analyzed. The outage probability of cognitive relay network is derived for the approximate expression under transmission power and interference power of source node and relay node. Monte Carlo simulations are shown to validate the accuracy of the analytical results, and the error is analyzed and explained.