Research On Cooperative Communication And Spectrum Management For Cognitive Radio Network

Current wireless networks are characterized by a static spectrum allocation policy. Recently, with the growing in spectrum demand due to the developing of multi-service, the traditional static spectrum policy faces spectrum scarcity in particular spectrum bands. In contrast, a large portion of the assigned spectrum is used sporadically, leading to underutilization of a significant amount of spectrum. Hence, dynamic spectrum access techniques were recently proposed to solve these spectrum inefficiency problems. The key enabling technology of dynamic spectrum access techniques is cognitive radio (CR) technology, which provides the capability to share the wireless channel with licensed users in an opportunistic manner. Moreover, Cooperative communication is a new communication paradigm that promises significant capacity and multiplexing gain increase in wireless networks. And spectrum management is a significant issue that coordinates CR users to select the best available channel to transmission. In this dissertation, we analyze the application of cooperative communication technologies and spectrum management problem for cognitive radio. Specifically, our research work consists of the following parts:1. Performance of two-way relay system was investigated. Cooperative relaying is a significant issue among cooperative communications. By reason of the spectral efficiency loss of half-duplex mode, two-way relaying method which involved in network coding idea was proposed, in two-way relay system, two sources exchange their information through one relay node. Firsly, we made the performance analysis of two-way multi-relay system with channel estimation error. With the derivation of effective signal-to-noise ratio at the transceiver and its probability density function, we can get lower bound expression for average bit error rate. Simulation results were performed to verify the analytical results. Moreover, we derived the close-form formulation of outage probability for the two-way relay system with the help of modified Bessel Function of the first kind. This work was a fundamental theoretical research and was meaningful for guiding the cooperative communication in cognitive radio network.2. In a CR network architecture, the components include both a primary network and a secondary network. Traditional cooperative technologies of wireless communication can be applied for primary users. For secondary users, cooperative technologies are mainly about cooperative spectrum sensing. Research details are as follows:1) Distributed antenna based coordinated multiple point transmission. In order to overcome large inter-cell interference of users at the cell boundary, coordinated multiple point transmission and reception was proposed; On the other hand, distributed antennas system has been widely focused both in academic and industrial field due to advantages over conventional centralized communication systems. Distributed antenna based coordinated multiple point transmission was proposed and we evaluated effect of number and position of antennas on system spectrum efficiency. This work was meaningful for both primary network and framework based secondary network.2) Performance analysis of reporting cooperative sensing data. The processing of cooperative sensing consists of sensing channel and reporting channel. There is challenging problem to cooperative spectrum sensing because reporting channels are normally subject to fading or heavy shadowing.The accuracy of reporting data is critical for the performance of cooperative sensing. We considered a scenario involving both relaying link and broadcasting link, and investigated the BER performance in common receiver with channel estimation error.3. Investigation was made upon spectrum management problem for cognitive radio network. Using the OFDM-based modulation scheme, the spectrum management can be reduced to the transmit power control. Power allocation problem is often modeled as optimization problems. With the selfish action of secondary users, we modeled the power allocation problem as a non-cooperative game which focused on the multiuser competitive feature. We studied the problem of power allocation in CR networks involving pricing utility. With the help of variational inequality and optimization theory, the existence of nash equilibrium was proved. In traditional research, many users co-exist over a long period of time. In other words, user set is unchanged in their analysis. But in fact, the cognitive radio environment is dynamic which leads to uncertainty characteristic. Robust optimization approach was being used to model the dynamic power control problem. Iterative algorithm was also proposed to solve this problem.