Research On The Key Techniques Of IEEE 802.11a Physical Layer And The Improvement Of Throughput

WLAN (Wireless Local Area Network) is an important part of future mobile communications systems. In order to meet the need of accessing flexibly the Internet with high rate at great ease, WLAN is being researched and established around the world. WLAN features mobility, low cost and wire line failure free.This thesis does a lot of research work about the key techniques of IEEE 802.11a, which is the main protocol of WLAN. In the protocol, OFDM is employed. OFDM is a special multi-carrier transmission method, which can resist frequency selective fading. The characteristic of OFDM is that subcarriers are orthogonal, so interference is minished between subcarriers and the spectral efficiency is enhanced. The protocol gives a description of frame structure and uses preamble training symbol for synchronization and channel estimation. In the physical layer, channel coding is convolution coding. This thesis expounds principle of convolution coding and decoding, especially on viterbi decoding. At the same time, analyses the transmission principle and structure of physical layer. Diversity technique is also described detailed, spatial diversity is the emphasis. Alamouti encoding is recommended in transmit diversity. The principle of MRC is analyzed in receive diversity.The thesis makes use of matlab emulator to simulate IEEE802.11a physical layer system. The main research is the influence of spatial diversity on throughput of WLAN.Improvements of throughput are compared for different kinds of diversity .Under the same channel environment, throughput curves are depicted with different modulation. Of course, data rates vary with modulation. The result shows that diversity plays an important part in improving the throughput of physical layer. And receive diversity is more effective than transmit diversity. If the channel condition is better, modulation with high data rate is advisable. On the contrary, modulation with low data rate is advisable under bad channel condition.