Power Control And Relay Selection In Two-Way Relay Wireless Systems

Relay technology is a key point of next-generation networks, aiming to provide reliable transmission, high throughput and wide area coverage, especially in the case of poor condition of direct link. Due to the inherent spectrum loss of traditional one-way relay systems, this thesis studies two-way relay systems with higher spectral efficiency, and proposes an energy-efficient power allocation strategy in two-phase and three-phase amplify-and-forward (AF) relay systems. Cognitive radio (CR) technology, as an intelligent spectrum sharing technology, can automatically search for "spectrum holes" resources and reuse non-renewable spectrum resources, through cooperative spectrum sensing by secondary users (SUs). This thesis combines relay and CR technology, and investigates cooperative communication strategy and sensing-throughput tradeoff problem in wireless CR systems. Further, an optimized relay selection strategy is proposed in energy-constrained wireless CR two-way relay systems, so as to improve the long-term throughput and extend the lifetime of CR system. In this thesis, work mainly includes the following three aspects:1) This thesis addresses energy-efficient power allocation (PA) issues for amplify-and-forward (AF) two-way relay systems. In the practical wireless systems, all users are powered by the battery energy, so it is inconvenient to replace battery frequently. Therefore, this thesis proposes an energy-efficient PA strategy for two-phase and three-phase two-way systems with single relay or multi-relay, under a certain transmission data rate of source nodes, aiming to minimize the system energy consumption. Numerical results show that this energy-efficient PA strategy can balance the system performance and achieve about3dBw power gains compared to the uniform PA.2) This thesis proposes a novel frame structure to reduce the reporting overhead, and investigates cooperative spectrum sensing communication process and the sensing-throughput tradeoff problem. Besides, three secondary user (SU) selection strategies are proposed in this thesis. In cooperative communication process, if a large number of SUs are involved in the reporting phase, it will bring heavy reporting overhead. Therefore, this thesis designs a novel frame structure, and under perfect/imperfect reporting channel, proposes different SUs selection strategy to optimize system performance. Simulation results show that there exists an optimal number of reporting SUs to maximize the system throughput.3) This thesis proposes an optimized relay selection strategy to improve the long-term throughput and extend the lifetime of system. In wireless CR two-way relay systems, secondary user pretends as a relay node of primary systems, employing decode-and-forward (DF) relay protocol to process received signals. When the secondary user as a relay assists the primary user pair to communicate, it also achieves data transmission of the secondary system. In practical communication system, since the initial battery energy of all users are limited and each data transmission would consume a certain energy, only a limited amount of data information can be delivered before all energies ran out. Therefore, this thesis proposes an optimized relay selection strategy to improve the long-term throughput and extend the lifetime of system, which fully considers three factors, i.e. the transmit power required for each data transmission, the remaining energy of relay nodes as well as the probability of system outage. Through the proposed relay selection strategy, the long-term throughput can be improved and the lifetime of system can be extended effectively.