Research On Framework Optimization And Power Optimization Problems In Cognitive Radio Systems

As the rapid development of wireless communication technology, there are growing demands for wireless spectrum resources, and then the lack of spectrum resources has become a bottleneck restricting the development of wireless communication. Spectrum is a finite resource, but the traditional fixed spectrum allocation strategy has been confirmed have very low spectrum utilization rate, so maximize the spectrum efficiency is the only way to solve the frequency spectrum resource scarcity. Cognitive radio technology arises under this background, it can improve the spectrum utilization significantly and alleviate the spectrum scarcity problem in wire-less communications.In cognitive radio systems, cognitive users through spectrum sensing to get channel state information, and then access the frequency bands that are allocated to primary users as well as detected to be idle under the condition of ensuring the quality of service of primary users, so accurate spectrum sensing is the premise of guarantee the performance of the system. On this basis, the SU transmit at a certain power, From the primary users’point of view, it has the absolute priority relative to the cognitive user, and the system must ensure that the interference caused by cognitive users the primary uses’ tolerable range; On the other hand, from cognitive users’point of view, its benefit is capture the spectrum hole and access it to realize data transmission so as to maximize the ergodic throughput of SU.At present, most of the studies are based on the assumption that the primary user has a constant occupancy state during the entire frame duration. In other words, they assumed that the primary user is either active or inactive for the whole secondary frame period which means do a simple binary spectrum sensing. But In reality, the primary user can arrives or departs the licensed channel at any time randomly; the dual spectrum will not accurately reflect the change of channel state. At the same time, almost all of the literature about CR system that can refer to are using cycle frame structure which consists of a sensing time slot at the frame header and a data transmission time slot after the header for spectrum sensing. They can not carry out at the same time, therefor there exist an inherent tradeoff between them.Based on the above reasons, in this paper, we propose a quaternary spectrum sensing model that based on a new frame structure. First of all, through the special receiver structure at SU-RX, the spectrum sensing and the data transmission can carry out simultaneously, and both of them can be maximized, thus improve the throughput of the system. On this basis, we consider the traffic of primer user which is more realistic and prove the quaternary spectrum sensing model.On the basis of the new model that proposed above, this paper also studies the optimal power allocation problem under the PU’s Outage loss constraint and average interference power constraint in order to maximize the ergodic throughput of a cognitive radio, finally this two protection strategies are compared and analyzed MATLAB simulation.