Research On Resource Optimization Algorithmin In Underlay Spectrum Access Strategy With Cooperatation

With the growth of wireless users and traffic demand, the spectrum scarcity issue is becoming more and more prominent, which restricts the development of wireless communication systems. Numerous studies reported by the Federal Communications Commission indicate that the licensed spectrum is largely under-utilized ranging from as low as 15% to 85%. To solve the spectrum scarcity issue, Cognitive Radio is proposed as a way to improve the spectrum utilization. While guaranteeing the interference below the tolerable levels, CR can get the opportunity to access the primary spectrum. However, there is mutual interference between the primary users and the secondary users in the traditional underlay spectrum access strategy. Meanwhile, the secondary users can access the licensed spectrum only when the direct transmission link is good enough to bear the extra interference caused by the secondary users. Cooperative diversity technology belongs to the space diversity technique. And in order to improve the link reliability, it introduces relay channel between the source and destination to reduce the wireless link path fading impact. This thesis studies the underlay spectrum access strategy which is combined with the cooperative diversity technology and proposes anti-interference strategies of secondary user selection from different perspectives in multi-user system. The spectrum resource optimization has also been studied to improve the licensed spectrum utilization. The detail of this thesis can be summarized as follows(1)For the issue of selecting among the secondary users in the multi-user system and the interference in the underlay spectrum access strategy, two anti-interference selection strategies are proposed in this thesis which are based on the optimal performance of the secondary users in the multi-user system In these two strategies, the system selects one secondary user or two to access the primary spectrum by maximizing the secondary system’s transmission rate while guaranteeing the primary system to achieve its target rate. The primary and secondary systems will not experience the interference between them as in both strategies the secondary users use disjoint bandwidth to transmit primary and secondary signal. The joint optimization of time and bandwidth allocation is studied to improve the performance of the system. Simulation results show that the proposed strategies can improve system performance and benefit both of the primary and secondary users.(2)Considering the unfairness among the secondary users of the selection strategy, this thesis proposes two anti-interference selection strategies based on the fairness of the secondary users. In these two strategies, the system chooses one secondary user or two to access the licensed spectrum based on the channel conditions, the secondary information’s throughput and the primary information’s throughput. Simulation results show that the proposed strategies improve the system fairness significantly.