Research On Radio Resource Management Policies In MIMO-OFDM Systems

Next-generation (4G) mobile communication systems are expected to support multimedia traffics with diverse QoS requirements. In the physical layer of 4G air interface, MIMO and OFDM are adopted as key technologies to provide robustness and significant increases in spectral efficiency. At the same time, the efficient resource allocation policy in MAC layer is also important in maximizing the resource utilization and the multiuser diversity gain while guaranteeing the QoS requirements of different traffics. Therefore, the main task of the thesis is studying on resource allocation problem in MIMO-OFDM systems, including uplink CQI feedback, cross-layer packet scheduling and inter-cell interference coordination. The contents of the thesis are presented as follows:In MIMO-OFDM/FDD systems, frequent CQI feedback of all active users is required to employ the frequency selective packet scheduling and link adaptation, and the CQI feedback reduction scheme must be designed carefully to avoid substantial uplink overhead amount while providing enough information for BS scheduler. Based on the analysis of the best-n and the threshold based CQI feedback mechanisms, a novel hybrid CQI feedback scheme is studied through simulation which combines the advantages of the two classic schemes by taking the traffic and QoS conditions of users into consideration. The hybrid scheme can achieve a good tradeoff between the downlink throughput and the uplink feedback overhead while guaranteeing the users'fairness.In MIMO-OFDM/TDD systems, it is assumed that perfect downlink CSI can be obtained at BS for the reciprocity of the TDD channels. Firstly, the single-traffic packet scheduling problem is formulated by introducing the utility function to evaluate the users'satisfication degree with resources allocated. The optimization objective is set to be maximizing the system utility while guaranteeing the QoS requirements of different traffics. Then, the optimum theorems are obtained to provide theoretical foundation for the exsiting non-real-time and real-time scheduling algorithms respectively. Finally, a hierarchical scheduler for multiple traffics and the corresponding scheduling scheme are studied. The hierarchical scheme can achieve global optimization by dividing resources properly among different traffic-flow groups, on the basis of local optimization achieved by the existing singal-traffic scheduling algorithms.The inter-cell interference is an inherent problem in cellular mobile communication systems. In OFDMA systems, Inter-cell interference coordination is a promising approach to solve the problem. Firstly, the multi-cell resource allocation problem is formulated with the optimization objective of maximizing the system total utility, based on the frequency and power planning rule of SFR, and then the local optimum solution is obtained. After that, a semi-static distributed ICIC scheme is proposed which apply the concept of spectrum pooling into ICIC and can be carried out in the flat network architecture. Simulation results show that, the proposed scheme can improve the cell edge throughput effectively.A summary is given at the end, where the future research directions related to this thesis are also pointed out.