Research On Optimal Power Allocation In Cognitive Relay Network

With the rapid development of wireless communication technology, the growing diversity of wireless data services and broadband, existing spectrum resources become more and more crowded. However, spectrum efficiency is not high because of conventional static spectrum allocation, a lot of spectrum resources are idle.Cognitive radio technology has the ability to find and use idle spectrum resources, it can solve the contradiction between scarcity of spectrum resources and low utilization of spectrum. In cognitive radio networks, cognitive users perceive idle band that has authorized and borrow band when it do not cause destructive interference to authorized user, greatly improve the spectrum efficiency. On the other hand, relay make long-distance path into a plurality of short-range. It can reduce the transmission power when the quality of the communication is perfect, so it can reduce signal interference between users. Accordingly, the relay work with cognitive radio technology can improve the spectrum efficiency and reduce the power consumption of the communication system. So it can achieve the purpose of improving the capacity and green broadband communications.In this paper, we discuss the optimal power allocation problems under the research background of cognitive relay network, mainly as follows:(1)To minimize the outage probability in a cognitive network of single-user single relay, we proposed a power allocation optimization algorithm. The algorithm minimize the outage probability of cognitive relay system that ensure the communication quality of authorized users, and to meet the cognitive user and cognitive relay itself transmit power limited conditions. First, using KKT condition solved its initial power allocation when relay node meet the conditions of maximum transmission power constraint. Then according to the results, we continue to consider the primary user interference threshold constraints by using two-way iterative search algorithm to adjust, then we can achieve the total power constraints.(2)To minimize system-sum-power consumption in multi-user single relay network, we proposed a power allocation optimization algorithm. Based on the principle that minimizing system-sum-power consumption is equivalent to maximize system energy efficiency. We can get a minimum system power by obtaining the maximum energy efficiency of the system. First, in comparison with channel gain between cognitive source-destination link and cognitive relay-destination link, then cognitive systems can be divided into two parts. Then we separately solve these two parts, The optimal power allocation of one part is determined directly, and minimizing the system-sum-power consumption of the other part is converted into minimizing source-sum-power consumption, which can be solved easily through Karush-Kuhn-Tucker(KKT) condition.(3)Through numerical simulations and performance evaluation for the above algorithm, we further justified the effectiveness of our scheme.