Throughput Enhancement via Link Adaptation and MIMO Coding in OFDM-Based WLANs

• Main Authors: Tsao Yu-Jui, 曹祐瑞
• Other Authors: Lee Ta-Sung
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/81515288168351351534

碩士 === 國立交通大學 === 電信工程系所 === 92 === The increasing demand for all types of wireless services (e.g. voice, data, and multimedia) promotes fast growing of the high-speed wireless local area networks (WLANs). One of the major efforts in standardizing the medium access control (MAC) and physical (PHY) layers for WLANs is IEEE 802.11. It defines two channel access mechanisms, the basic and RTS/CTS access mechanism, at the MAC layer. Besides, the extended IEEE 802.11a achieves high data rates ranging from 6 Mbps to 54 Mbps by using orthogonal frequency division multiplexing (OFDM) at the PHY layer. With multiple rates, link adaptation (LA), a process to dynamically switch data rates to best match the varying channel condition, becomes increasingly important. In this thesis, we propose an LA algorithm to better exploit the MAC and PHY layer in the IEEE 802.11a WLAN. According to the channel condition, number of contending stations, and data length, the proposed LA algorithm chooses the optimum combination of the access method and data rate to achieve higher throughput in the inherent IEEE 802.11a WLAN. Furthermore, the combining of multiple-input multiple-output (MIMO) coding with OFDM is regarded as a promising technique for enhancing the data rates of next generation wireless communication systems. The MIMO coding can be categorized into two types based on their functionality. Spatial diversity (SD) is used to improve the link reliability while spatial multiplexing (SM) increases the spectral efficiency. For further improvements in the WLAN’s throughput, we modify the proposed LA algorithm so that it can choose the appropriate MIMO coding as well to provide the better link quality or higher data rate according to channel condition. Finally, we evaluate the performance of the proposed algorithms by computer simulations, and confirm that they work well in indoor wireless environments.