Resource Scheduling Algorithms In Relay Based OFDMA Systems

Orthogonal Frequency Division Multiple Access (OFDMA) is an important multiple access technique in wireless broadband systems and it has been extensively applied in various broadband communication systems. Relay technology can expand the cell coverage and improve the system throughput effectively. Therefore, it has become a key technology of the next generation communication systems. Combing OFDMA with relay can take full advantages of the two technologies to continually optimize the system performance and has become a research hotspot in recent years.The paper derived from the cooperation project between the laboratory and some company. The author mainly concentrates on the research and simulation of the resource scheduling algorithms in relay based OFDMA systems. The resource scheduling problem in both OFDMA system and the relay based OFDMA system are studied in this dissertation. The specific content of the study includes the following two aspects.Firstly, the resource scheduling algorithms in OFDMA cell systems have been studied in this dissertation. Consider two conventional scheduling algorithms, i.e., the maximum throughput algorithm and the proportional fair algorithm, in single cell OFDMA systems. Neither of them considers the packet delay, which is an important quality of service (QoS) index in the scheduling process. In order to enhance the QoS of cell-edge users and make full use of the multiuser diversity, a modified proportional fair scheduling algorithm is proposed in this dissertation. In the proposed scheme, the scheduler considers channel condition, user throughput and packet delay in the scheduling process, and the priority metrics are reasonably designed according to the idea of the proportional fair scheme to make the final scheduling decisions. Simulation results verify that the proposed algorithm can achieve better system performance compared with its counterparts.Secondly, this dissertation studies the scheduling algorithms in relay based OFDMA systems. The introduction of the relay into the system makes the scheduling problem more complicated. The scheduler needs to make a rational resource allocation between the relay link user and the direct link user. This dissertation extends the idea of the traditional proportional fair scheme into the relay based OFDMA systems and proposes a new scheduling algorithm. The proposed scheme not only considers the channel condition but also considers the user throughput and packet delay in the scheduling process. Compared with the two-hop proportional scheduling algorithm, the propose scheme can achieve higher system throughput and lower average packet delay with approximately the same user fairness. Therefore, the proposed scheme can make a better tradeoff between system performance and user fairness.