Research On Resource Allocation In Wireless Systems With Network Coding

With the rapid development of wireless data services, mobile communication system requires higher data rate, broader coverage, and lower delay. The next generation mobile communication system employs many new technologies, such as OFDM (Orthogonal Frequency Division Multiplexing), MIMO (Multiple-Input Multiple-Output), and cooperative relay to improve system performance. Network coding (NC) is a significant research achievement in the field of information technology in recently. Through combining the packets in the process of storing and forwarding messages at network node, NC can enhance network capacity and utilization. The application of NC in wireless networks has received widespread attention for the broadcast nature of wireless link.Efficient resource allocation is crucial to improve the performance of wireless systems. Due to the introduction of NC, resource allocation algorithm in traditional relay networks is no longer applicable. Therefore, the novel resource allocation schemes according to NC technical feature should be studied. This dissertation focuses on the thesis of wireless NC resource allocation, and presents a thorough and comprehensive research on power allocation, relay selection, subcarrier assignment and subcarrier pairing for different NC scenarios. The main work and contributions of this dissertation are listed as follows.1. Research on resource allocation for network coded two-way relay channels in single-carrier systemsAn Nth best relay selection scheme (Nth-RS) with NC is proposed in single-carrier two-way relay systems, and the performance is analyzed. Being different from traditional best relay selection scheme, this dissertation considers a general case, where the Nth best but available relay is selected. Firstly, the exact expression of outage probability for Nth-RS scheme is derived. Then, in order to simplify analysis, the closed-form upper bound and lower bound of outage probability are also presented. The analysis reveals that the diversity order of the proposed Nth-RS scheme equals to (M-N+l), where M is the number of relay nodes. In order to improve system performance, transmit power between sources and relay is optimally allocated to minimize outage probability under total power constraint. The expressions are verified by simulation, and the results show that Nth-RS scheme with optimal power allocation can achieve substantial improvement.2. Research on resource allocation for network coded two-way relay channels in multi-carrier systemsDue to applying OFDM technology in next generation mobile communication wireless systems, this dissertation further studies the optimization problem considering power allocation, relay selection and subcarrier pairing for multiple network coded based two-way relays in multi-carrier systems under individual power constraints or total network power constraint. A unified optimization framework is presented to solve this problem. Firstly, by applying Lagrange dual decomposition method, the multi-carrier problem is decomposed into multiple subproblems. Then, power allocation, relay selection and subcarrier pairing are solved, respectively. Finally, the Lagrange variables are iterated by subgradient method to obtain optimal solution. The analysis indicates that the complexity of proposed optimal resource allocation algorithm (ORA) is only a polynomial function of subcarriers and relay nodes number. Based on this framework, we further propose three low-complexity suboptimal algorithms. Simulation results show that ORA scheme can achieve substantial performance improvement. And it indicates that the impact of optimizing partial resource.3. Research on resource allocation for network coded uplink multiple-access relay channels in single-carrier systemsConsidering single-carrier uplink multiple access relay scenario where two users communicate to destination node via multiple selective relay nodes, this dissertation investigates optimal power allocation and relay selection. The difference between two-way relay channels and multiple access relay channels is firstly presented, and the optimization problem is formulated. Then, we solved the problem to propose a resource allocation algorithm of jointly optimizing power allocation and relay selection by two steps. Simulation results present the performance gains of proposed algorithm, and indicate the impact of relay number on the system performance.4. Research on resource allocation for network coded uplink multiple-access relay channels in multi-carrier systemsIn uplink OFDM systems, joint resource allocation and user scheduling is a complicated problem, and it even gets intractable with large user and subcarrier number. This dissertation further investigates the resource allocation for multi-user multiple-access relay channels with NC in OFDM systems. We study a joint optimization problem considering source node pairing, subcarrier assignment, power allocation, and subcarrier pairing to maximize the sum capacity under per-node power constraints. The problem is solved by optimizing three separate sub-problems: subcarrier assignment and user pairing sub-problem, subcarrier paring sub-problem, and power allocation sub-problem by applying convex optimization, respectively. Simulation results show that the proposed scheme can achieve substantial gains with polynomial time. And the impact of relay location and user number is also evaluated.