| Summary: | 碩士 === 國立雲林科技大學 === 電機工程系碩士班 === 93 === WMANs(Wireless Metropolitan Area Networks) is a portable, wireless network that is favorably employed often used in wide-area transmission applications. Its advantages include wider coverage, higher throughput, and the flexible bandwidth on demand. Despite above advantages, the transmission environment of WMANs is much more complicated than that of WLANs(Wireless Local Area Networks), for example, dynamic multi-path fading and the Doppler effect. Based on the 802.16 specifications, this study proposes a new transmission scheme that combines the adaptive QAM and the characteristic of the binary Gray code to construct multiple sub-channels with different transmission quality respectively. Based on this scheme, we also analyze the capability of sub-channels under different modulation methods and channel coding in various transmission environment. In addition, we also propose an algorithm to improve the low quality of transmission caused by the Doppler Shift. The simulation results show our proposed algorithm can improve the transmission efficiency over various channel conditions and system parameters.
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