High-speed Wireless Lan 802.11n Protocol Key Technology Research

The rapid development of Wireless Local Area Network (WLAN) has not yet broken the bottleneck that the low transmission speed hinders the further development of WLAN. But now , some key technologies for next generation wireless communications can solve the problem by supporting high-speed transmission and ensuring reliable performance. IEEE declared that they had accepted the standard of EWC and passed the 1.0 draft of 802.11n protocol at the first month of 2006 . The draft has made general amendment to 802.11. Based on IEEE802.11n, the transmission speed can be doubled by the application of Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple output (MIMO) technologies on the physical layer; It optionized the data frame and improved network throughput by the adoption of frame convergence, block acknowledge,PSMP ,PCO and so on techniques on the MAC layer.The paper research two aspect on draft 1.0: One is the key technologies in MAC layer, such as convergence frame,BA,PSMP. The orther is the channel estimation in MIMO-OFDM system of 802.11n protocol.In this paper, we investigate two channel estimation methods with training sequences. One is based on LS, the other based on LMMSE. The LS method is low complexity and easy to realize, but it is sensitive to the noise. System's performance degrades quickly when the SNR is low. The LMMSE method provides a better accuracy than the LS method, but the complexity is high relative. To reduce the complexity of LMMSE method, we propose a low rank LMMSE method based on SVD which performance close to the LMMSE method when SNR is lower.For the purpose of tracing the change of channel, we investigate frequency interpolate method which estimate the channel information of pilot sub carriers and then we introduced serveral interpolate algorithm to calculate channel information of the other subcarriers. For 802.11n system, the pilots are use to estimate and correct the phase error which is caused by synchronization error especially. Lastly, the performance of method above are evaluated and compared based on the result of computer simulation of an IEEE802.11n base band system.