| Summary: | 碩士 === 雲林科技大學 === 電機工程系碩士班 === 98 === Worldwide interoperability for microwave access (WiMAX) protocol not only provides high speed network access and rapid deployment in remote districts, but also solves the last mile problem in a wired network system. The second version of WiMAX standard, the fixed WiMAX (IEEE 802.16-2004) standard, is based on the orthogonal frequency division multiple (OFDM) technique. OFDM is not a multiple-access technique. Rather, it is a modulation technique which delivers many independent data streams that can be used by different clients. Some preceding OFDM systems are DSL, IEEE 802.11a/g, and the unimplemented previous version of WiMAX (IEEE 802.16). All of them use single-client OFDM, where the sub-carriers are used by a single client at the same time. The new version of WiMAX (802.16e-2005) uses a different technique, known as orthogonal frequency division multiple access (OFDMA) technique. Based on OFDM, OFDMA is developed for supporting mobility in cellular systems. It has the advantages of high computational performance, low power consumption, flexible scheduling, integrated high-speed peripherals, complete software platforms, and comprehensive development tools. In OFDMA, multiple clients can share sub-carriers and time slots. The frame structure of the physical layer in OFDMA is similar to that defined in OFDM, which contains DL-MAP and UL-MAP. The DL-MAP includes customer downlink message, and the UL-MAP includes customer uplink message. One of main missions of OFDMA is to efficiently allocate a set of data messages into DL-MAP or UL-Map. These data messages can also be called protocol data units (PDU) or MAC protocol data units (MPDU). In this thesis, we focus on the algorithms that can allocate a set of PDUs in the DL-MAP. We call them algorithms the PDU allocation algorithms or the MPDU allocation algorithms. Generally speaking, an efficient PDU allocation algorithm should meet the following requirements: (1) the fewer leftover spaces, (2) the concentrated and contiguous available spaces, and (3) the fewer number of frames. In this thesis, we propose an efficient PDU allocation algorithm as a DL-MAP scheduler in OFDMA. Our algorithm firstly factorizes and adjusts the size and shape of each PDU, efficiently selects the best-fitting shape for its allocation, and records available spaces to support the allocation of the next PDU. In addition to meeting the requirements of an efficient PDU allocation algorithm, our PDU allocation algorithm can also be applied to both the on-line and off-line modes. Computer simulation results show that our PDU allocation algorithm reduces leftover spaces by approximately 5.6% to 48.9% when compared to the existing PDU allocation algorithms in the literature.
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