Study On Handoff Algorithm And Admission Control Scheme For IEEE802.16e OFDMA Systems

IEEE 802.16e broadband wireless mobile system has attracted great attention recently, which is expected to support high-speed multimedia services applications for mobile stations moving at vehicular speeds. The convergence of multimedia communication and wireless mobile network brings opportunities for broadband wireless network development. However, successful combination of these two technologies presents many challenges such as energy efficiency, seamless end-to-end communications, robustness, etc. The core issue among them is the quality of service (QoS) support in the presence of changing network connectivity due to user mobility, highly variable communication links due to wireless access and traffic diversity due to distinct features of multimedia services. This thesis focuses on the handoff issue and call admission control, which are key technologies for QoS guarantee.The handoff algorithms employed in a wireless mobile network have a significant impact on overall network performance. We develop a soft handoff algorithm based on carrier-to-interference ratio (CIR) for IEEE 802.16e system with both absolute threshold and relative threshold. System performances such as average number of handoffs, handoff outage probability and spectrum utilization are studied by computer simulation.Traditional admission control algorithms are based on bandwidth or channel reservation policy, which may be incompetent in IEEE 802.16e OFDMA systems for two reasons: (1) OFDMA system supports dynamic and flexible resource allocation, and (2) there exists a fundamental tradeoff between bandwidth and power. In this thesis, we propose a novel admission control scheme based on power reservation. Foremost, we introduce a joint subchannel and power allocation algorithm for WiMAX system, which minimizes the overall downlink transmit power by utilizing all available subchannels. Based on this, we propose two power reservation schemes for inter-cell handoff calls and intra-cell handoff calls, respectively. The amount of reserved power is determined in an adaptive manner for optimizing the metric of Grade of Service(GoS).Power reservation scheme may be incompetent in systems where channel resource is relatively scarce. Therefore, two joint power and channel reservation schemes are proposed. Computer simulation is carried out to evaluate the performance of the proposed admission control schemes.