| Summary: | 碩士 === 國立交通大學 === 電信工程系所 === 93 === IP (Internet Protocol)-based OFDMA (Orthogonal Frequency Division Multiple Access) system is adopted in IEEE 802.16 standard by its great internetworking capability with Internet and its capability to achieve high transmission rate in multipath environment. Instead of providing fixed wireless access services, the standard committee also aims to develop a newer version to support user mobility for mobile communications services. Therefore, development on handoff technology, which is the process to transfer the connectivity of mobile station from one base station to another, is the key to achieve this objective. However, the hard handoff process in current standard will lead to high service disruption time and make user feel uncomfortable on service quality. This paper proposes a proactive base station switching (PBSS) mechanism to reduce service disruption time to satisfy the quality of service (QoS) requirement of real-time services, which is achieved by network pre-registration, data forwarding and fast ranging. This paper also proposes an IEEE 802.16e compatible signaling procedure and a link quality-based PBSS initiation algorithm to realize PBSS mechanism in real system. The simulation results show that the service disruption time can be reduced by PBSS mechanism to satisfy the requirement by real-time services; moreover, the packet loss rate can also be reduced by preventing packets timeout.
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