On Adaptive Contention Resolution Schemes for IEEE 802.16 BWA Systems
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Research Article On Adaptive Contention Resolution Schemes for IEEE 802.16 BWA Systems Chih-Heng Ke1 and Der-Jiunn Deng2 1 Department 2 Department
of Computer Science and Information Engineering, National Kinmen Institute of Technolgoy, Taiwan of Computer Science and Information Engineering, National Changhua University of Education, Taiwan
Correspondence should be addressed to Der-Jiunn Deng, [email protected] Received 28 January 2009; Accepted 17 May 2009 Recommended by Dmitri Moltchanov According to the latest version of the IEEE 802.16 standard, the mandatory contention resolution method is the truncated binary exponential backoff, with the initial window size and the maximum window size controlled by the base station. However, the problem of choosing the right set of backoff parameters for the current network level remains unsolved and left as an open issue since this strategy might incur a high collision probability and the channel utilization could be degraded in congested scenario. In this paper, we propose two pragmatic adaptive algorithms, namely semi-dynamic and quasi-dynamic contention resolution schemes, that allow the base station to adjust its backoff window size based on current channel status. By controlling the size of backoff window according to varying network conditions, both schemes are able to achieve higher performance in comparison with the legacy IEEE 802.16 standard. Copyright © 2009 C.-H. Ke and D.-J. Deng. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction High-speed transmission, fast deployment, and cost saving have made Broadband Wireless Access (BWA) systems a rapidly emerging field of activity in computer networking, attracting significant interests in the communities of academia and industry. In the mean time, the IEEE standard for BWA systems, IEEE 802.16 [1–3], has gained global acceptance and popularity in wireless computer networking markets and is also anticipated to take place of broadband access solutions like digital subscriber line (DSL) and cable. The IEEE 802.16 standard specifies two modes for sharing the wireless medium: point-to-multipoint (PMP) and mesh (optional) modes. In the PMP mode, the nodes are organized into a cellular-like structure, where a base station (BS) serves a set of subscriber stations (SSs) within the same antenna sector in a broadcast manner, as shown in Figure 1. The communication path between SSs and BS has two directions: uplink channel (from SSs to BS) and downlink channel (from BS to SSs). The downlink channel is a broadcast channel, while the bandwidth of uplink channel is shared by the SSs. The subframe in uplink channel includes three
periods: Initial Maintenance period, Request Connection Opportunities period, and Scheduled Data grants period. The BS announces these periods and associates burst classes in the preceding downlink subframe’s uplink map (ULMAP)
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