Ofdm-based Ieee802.11a Wireless Lan And Its Adaptive Bit Allocation Study

Orthogonal Frequency Division Multiplexing is one of key technologies in mobile communication fields.It is suitable for high rate data transmission in wireless channels because it can combat Inter-Symbol interference and muiti-path fading efficiently. Now it has become an attractive technology. At present,OFDM technology has been used in many fields,such as wireless local network. The adaptive OFDM technology can enhance the performance and can conquer the technology vulnerability.In this thesis,we first discuss the basic theory of OFDM,and how to realize the DFT and IDFT based on OFDM system. Based on its packet structure,mathematical methods for OFDM synchronization,PAPR,channel estimation and subcarries allocation are proposed in this paper. And it is given for the new OFDM based on wireless LAN standard IEEE802.11a. In this paper, we study adaptive OFDM with both perfect and imperfect CSI for the variable bit rate case, where a target bit error rate is set. And we give a new adaptive bits allocation based on OFDM. At the last part we simulate OFDM system in MATLAB platform. Results show that the performace is dramatically affected by the number of modulation stages and that of the subcarriers. The results are referential to the research of OFDM technology.