Research On Resource Optimization And Allocation For Wireless Cooperative Communication Systems

The characteristic of multipath fading in wireless channel is one of the main obstacles in improving the system capacity and enhancing the quality of service for future wireless communication. Through sharing the antennas of multiple distributed transmitters or receivers to create virtual antenna arrays, cooperative communication is helpful to combate the fading induced by multipath propagation and thus enhance the system reliability. In addition, cooperative communication bears a lot of advantages in practical application, such as saving terminal power, improving system spectral efficiency, expanding the coverage of wireless networks, balancing the system payload, etc. Cooperative communication will play an important role in disaster relief, intelligence transportation and wireless access. It will be widely applicable in the next generation of wireless network, such as multi-hop cellular networks, multi-hop wireless local area network, wireless Ad Hoc networks and wireless sensor networks.To further improve the system performance with limit wireless resource, optimal resource allocations play an important role in the application of wireless communication. With the theory of convex optimization, this dissertation mainly discussed the resource allocation in the wireless cooperative communication.Chapter 2 study the optimal resource allocation for OFDM cooperative networks. The uplink scenario of a cellular cooperative OFDM network is considered, in which multi-relays can forward the source's message to base station. With mathematical modeling method, a mathematical optimization problem is transformed from original communication problem. We show that this problem is formulated as a mixed binary integer programming problem, which is hard to find the global optimum in terms of computational complexity. Thus with convex parallel decomposition, a low-complexity joint optimization scheme of opportunistic relaying strategy and power allocation is proposed. First, the opportunistic relaying strategy is given by making use of the equivalent channel power gain for every subcarrier. Second, a low-complexity power allocation algorithm is proposed with KKT optimal condition and equivalent water-filling algorithm. In multi-users cooperative communication, different users often have different quality of services, which may be different data transmission rates. Thus, how to fairly and efficiently allocate resources among multiple nodes is an important problem in wireless resource allocation research area. The main strategy is focused on how the cooperative relaying can both improve throughput and ensure fairness in the multi-user cellular networks. In chapter 3, the uplink scenario of multi-user cooperative network is investigated, in which the resource is allocated to the users with the consideration of both fairness guarantee and throughput enhancement. We show that the optimization problem is formulated as non-convex optimization problem, which is hard to find the global optimum in terms of computational complexity. Thus we decompose the optimization problem into two sub-problems of opportunistic relaying strategy and power allocation. First, the opportunistic relaying strategy is given based on the criterion of maximizing end-to-end capacity for each user. Second, a low-complexity power allocation scheme is proposed with KKT condition.A two-way relaying system based on the physical-layer network coding (PLNC) technique can improve the spectral efficiency than traditional one-way cooperative system. With making the best of the broadcasting characteristic of wirelees signal, the main idea using PLNC is that the relay node converts the mixed signal from two terminals to a PLNC-modulated signal, which can significantly improve the capacity in relay-based systems. In chapter 4, a network scenario of two-way relaying over OFDM is considered, in which two nodes wish to exchange information via a relay using physical-layer network coding (PLNC). Assuming full channel knowledge, an optimization problem with maximizing the achievable sum rate of the PLNC protocol under a sum-power constraint is was investigated. We show that the optimization problem is non-convex, which is difficult to find the global optimum solution in terms of computational complexity. Then a low-complexity optimal power allocation scheme is proposed for practice implementation. First a link capacity diagram is employed for power allocation on each subcarrier. Second, an equivalent convex relaxed optimization problem and KKT conditions is proposed for power allocation among each subcarrier.Since the channel between the first hop (source-relay) and the second hop (relay-destination) varies independently, proper subcarrier mapping at the relay has been shown to improve the average end-to-end capacity evidently. In chapte 5, two-way relaying network over OFDM using analog network coding is considered. To maximum the system capacity, an ordered subcarrier mapping scheme is firstly proposed, which is verifed on the optimality of system capcity gain. Second, the performance anlsysis of the proposed scheme is given, where closed-form expressions were provided for the outage probability,system capacity and bit errer ration of the mapped subcarrier pair link.