Load Balancing Technology For OFDMA Networks

Next-generation cellular networks which are based on Orthogonal Frequency Division Multiple Access (OFDMA) will provide higher spectral efficiency and higher data transmission rate by adopting advanced physical layer techniques and resource management techniques. Even in such networks, users especially those in boundary area would suffer low quality of service due to the severe inter-cell interference (ICI). Therefore, the inter-cell interference is one of the main factors affecting system performance.In cellular networks, admission control (AC) and handover (HO) determine the associations between the base stations and the mobile terminals. In traditional solutions, the two strategies in decision-making merely consider the quality of the physical signal. However, owing to the difference among the cells load, using the traditional strategies can not solve the unbalanced traffic load distribution, which is another major factor affecting network performance.To tackle above two problems, improve the full frequency reuse and the traditional admission control and handover mechanisms are focus of this thesis.Firstly, the implementation principle of Orthogonal Frequency Division Multiplexing (OFDM) is described. And then take WiMAX system for example, the OFDMA frame structure, three general models of radio resource management, interference coordination and control, and load-transfer methods are introduced. Then, considering the ICI mitigation, the Fractional Frequency Reuse (FFR) technology is investigated in details. A system-level simulation platform is build for OFDMA cellular system. Based on this platform, the performance of FFR technology is verified. In order to solve the ICI and unbalanced load distribution, a traffic load balancing (LB) scheme associated with FFR is proposed. By using FFR to carefully plan frequency spectrum, the ICI is mitigated, and the communication quality of cell boundary users is improved. The service level of users in each cell can be presented by the defined Service Level Indication Metric (SLIM). When the cell load is greater than the load threshold, the admission control and handover strategies based on LB are triggered according to the SLIM of users in each cell. Based on the analysis of the simulation results, the communication quality of boundary users is improved compared with the full frequency reuse networks without FFR and load balancing. And the results also show that the proposed schemes can reduce the block probability of hot-spots, balance the load distribution of system to some extent, and compensate for throughput loss caused by FFR.