Subcarrier And Power Allocation In OFDMA-based Cognitive And Relay System

In 21th century, Cognitive radio has been a key research direction in wireless communication. It's an intelligent spectrum sharing technology, which can make the usage of spectrum more efficent by allowing the unlicensed users to opportunistically occupying the licensed spectrum, and relief the crisis of spectrum resource scarcity. Bringing relay into cognitive radio network is a brand-new attempt. The traditional cellular relay network has been a big success in the design of topology structure in wireless network, because the spectrum efficency can be enhanced a lot by relay. In this dissertation, we first introduce the concept and feture of cognitive radio and cognitive relay, then we propose a scenario of cognitive relay and investigate the subcarrier and power allocation problem. In addition, we discuss the subcarrier allocation problem in the uplink of multi-user accessing to relay network. Finally, the design and architecture of OFDMA-based software radio platform have been researched.Firstly, in the context of cognitive OFDM system, we investigate how to use relay to improve the transmission performance of secondary user in current cognitive network. Usually, relay can assist not only primary user but secondary user, too. The network model consists multiple cognitive transceiver pairs and a single primary user. We solve the unbalance spectrum resource availability problem between the secondary transmitters and receivers caused by spectrum diversity and the space distance with the relay node. We focus on the allocation of subcarrier and power. Meanwhile, with the help of relay, the initialization and synchronization will be much easier, the hiding terminal problem can be solved properly, too.Secondly, we propose a novel heuristic algorithm to solve the subcarrier allocation problem in the uplink multiuser OFDM relay system. Our algorithm is excellent in the low computational complexity for the realization of the subcarrier allocation problem. Multiuser access to the relay station on the subcarriers that selected according to the weight factors decided by the queue length and waiting time. Then based on the user capacity obtained in the first hop, we develop an optimization problem for the enhancement of system capacity using user-grouped subcarrier pairing strategy. Furthermore, we propose a heuristic algorithm with simple steps to solve the problem.Orthogonal Frequency Division Multiplexing (OFDM) is a promising multicarrier transmission technique in the future 4G wireless communication system. It's convenient to realize spectrum resource control and management through spectrum combination and split. With these advantages, OFDM has been widely used in cognitive radio system, and become the first choice of spectrum multiplexing and modulation. The researches of this dissertation are all based on OFDMA. Cognitive user can make full use of spectrum resource dynamically through OFDMA. Finally, the system is based on software defined radio (SDR), we give the hardware platform architecture of cognitive radio transceiver.