A Study Of Outage Performance And Power Allocation Of Cognitive Two-way Relay Networks

In recent years, the booming development of mobile communication makes the degree of electronic information socialization grow increasingly, the requirements such as data rates and quality of service(Qo S) have also been increasing. High rate, large coverage, low cost, low energy consumption and high Qo S have become a new trend of wireless communication system in the future. However, the scarcity and limit of spectrum resources and the time variability and uncertainty of the radio channel have seriously hindered the future development of wireless communication. Fortunately, cognitive radio technology has solved the current spectrum shortage problem and improved the current spectrum utilization effectively. As a new generation of wireless cooperative communications technology, two-way relay system has become a hotspot worthy of research in wireless communication. By means of physical-layer network coding, both the throughput performance and spectral efficiency of two-way relay system have been further improved. In this thesis, cognitive two-way relay networks employing analog network coding(ANC) was studied. Under specific scenarios, we proposed two power allocation strategies and gave the theoretical analysis and simulation. The main contribution of this dissertation is summarized as follows:1. In cognitive network, we introduced ANC into traditional two-way relay system and studied in detail. After fully considering the interference to each other between the licensed user and unlicensed users, the outage performance of the particular scene was analysized in Rayleigh fading channels. We first formulated the individual outage probability by ignoring the channel state information(CSI) uncertainties, and then extended it to take into account imperfect CSI. Numerical and simulation results were presented to vertify our analytical results.2. To ensure the Qo S of primary user and secondary users in cognitive two-way relay system which employs ANC, two different power allocation schemes were proposed as follows:(1).For the case of symmetric traffic requirements, we addressed the problem of power allocation for minimizing the weaker link’s individual outage probability of secondary users with perfect CSI and imperfect CSI. We have given the closed-formed expressions of power allocation scheme under the condition of perfect CSI, while for imperfect CSI one-dimensional search method is employed to achieve optimal powerallocation scheme. Simulation results showed that the proposed power allocation strategy improves the outage performance of secondary users effectively compared with conventional equal power allocation(EPA) scheme.(2).For the case of asymmetric traffic requirements, the power allocation strategy was put forward by maximizing the sum-rate of the success delivery bit from secondary users’ perspective with perfect CSI and the closed form expression of each node power are acquired. In addition, the system performance of the proposed scheme with imperfect CSI was analysized. Simulation results showed that, compared with conventional EPA scheme, the proposed strategy not only improves the sum-rate of the success delivery bit, but also improves the system outage performance effectively.