| Summary: | 博士 === 國立臺灣科技大學 === 電子工程系 === 97 === Constructing conventional wired networks at urban and suburban areas will result in issues such as high cost and the difficulty of deployment. However, with the massive high bandwidth demand of subscribers, IEEE 802.16/16e wireless metropolitan network (worldwide interoperability for microwave access, WiMAX) wishes to use wireless communication, long distance transmission, and high bandwidth to overcome the last mile access problem. IEEE 802.16j standard mainly rely on multi-hop relay node deployment to enhance the WiMAX system performance; this will eliminate the possibility of shadowing and blocking problems on wireless transmission, while at the same time, increase the transmission range and reduce implementation cost. Multi-hop relaying helps transmission path evolve from single hop to two hops or multiple hops, the connection establishment and Intra-BS handoff scheme for mobile users was the main topic in multi-hop relay WiMAX networks.
In this thesis, we study centralized and decentralized MS-triggered Intra-BS handoff and connection establishment schemes. Both base satation (BS) and corresponding transparent relay nodes will detect the SNR between mobile users and BS/relay nodes as basis for handoff decision. In centralized Intra-BS handoff scheme, BS lead connection setup and handoff decision for mobile users; in decentralized Intra-BS handoff scheme, mobile users connection setup and handoff decision would need support of relay nodes from multi-hop relay. We first define the detailed signaling procedures based on the IEEE 802.16/16e standard. The method of same-frame-delivery is proposed to avoid unnecessary transmission delay that multi-hop relay might cause. The proposed centralized and decentralized Intra-BS handoff and connection establishment schemes can improve packet transmission rate and transmission delay, and enhance the network performance.
WiMAX networks support multimedia traffic transmission. Due to the fact that wireless transmission is prone to interference and channel condition is time varying, scheduled packets may not be transferred because of bad channel condition. Based on average received SNR each user is assigned to proper adaptive modulation/coding. The SNR from physical layer presents to the scheduler of data link layer for packet scheduling to improve system throughput. This scheduling scheme first evaluates the delay tolerance of real-time packets, schedules real-time packet transmission is based on the channel condition, then the residual bandwidth is allocated to non-real-time packets. The proposed cross-layer scheduling scheme can greatly improve network throughput, fulfill QoS requirement of real-time traffic, and provide long-term fairness of non-real-time traffic at the same time.
Multimedia traffic plays an important role in the Internet, however, Best effort (BE) traffics such as World Wide Web access and file transfer still take up a substantial portion of Internet traffic. Improving transmission rate of BE traffic will improve WiMAX’s network throughput as well. In WiMAX networks, users with BE traffic contend for bandwidth from BS in order to get transmission opportunity. Truncated binary exponential backoff scheme is employed for retransmission. Parameters of contention window are controlled by BS and are periodically broadcast to users. If contention window size could be properly managed, collision rate can be reduced and therefore improves BE traffic throughput. In this thesis, we study contention window assignment scheme in the BS. According to bandwidth requests and the number of user collided, the BS dynamically changes contention window size. This scheme can optimize the transmission rate and transmission delay of bandwidth request for BE traffics.
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