| Summary: | 博士 === 長庚大學 === 電機工程學系 === 99 === The broadband wireless access network (BWAN) is one of the techniques to provide roaming or nomadic users with connection to Internet access service. This technique is composed of base stations (BSs) and mobile stations (MSs). The BS is used as a role of router/gateway to process packets from/to Internet to/from MSs. It is a bridge between wireless and Internet network to transfer packets. Recent increase in sensitive delay applications, e.g., video conferencing media streams, and high speed equipments are equipped on roaming user, have created some problems in the BS that would be the bottleneck for data transmissions: First, All packets in the BS are required to be first looked up to find their destinations in the network layer for packet relaying/forwarding. This IP lookup mechanism will cost considerable overheads even if the traffic is local, i.e., mobile stations (MSs) communicating with each other within the coverage area of a BS. Hence, the local traffic will greatly degrade the system performance when the transmitted data is heavy. For this drawback, a fast cross-layer cut-through switching mechanism (CCSM) is proposed for supporting media access control (MAC) layer packet switching in IEEE 802.16 networks.
As a solution to maintain efficiency during the heavy data transmissions, the BS needs to be connected to a high speed backbone, i.g., MPLS. The integration of the wireless IEEE 802.16 network and the wired MPLS system (802.16-MPLS) need to be enhance the ability of packet transformation, and thus an end-to-end label switching protocol (ELSP) is proposed for the Integration of 802.16-MPLS networks. The traffic can then be switched via the MAC layer without involving the network layer.
To sustain users roaming in the global mobile wireless networks, a good handover mechanism is also essential for fast handover and quality-of-service (QoS). Against this drawback, a pre-coordination handover mechanism (PHM) is proposed with label of ELSP for quality of service. By using signal-to-noise ratio (SNR) measurement and the probability of attenuating SNR, PHM manages MSs on the boundary area. The PHM calculates the measured SNR error to revise various parameters and precisely predict the remaining time of MS in the system. By comparing this time with the standard handover processing time, the SBS is found to have precisely predicted the handover time point. Hence, PHM can pre-coordinate with the TBS at the exactly necessary time before the handover.
Simulation and analysis results reveal that the CCSM and ELSP overhead of the IP lookup processing in the BS significantly degrade the performance of the IEEE 802.16e network. However, the proposed mechanisms can effectively resolve these drawbacks in terms of the network access delay as well as the throughput. The advantages provided by the PHM reduce both occupation time and the chance of handover failure; it improves HT to as low as 12 milliseconds while still being fully compatible with the IEEE 802.16e standard.
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