The Reaserch And Implementation Of Channel Estimation In OFDM System Based On IEEE802.11a Standard

Wireless local-area network (WLAN) is a type of local area network that uses high-frequency radio waves rather than wires to communicate between nodes. With high spectrum usage and immunity to multi-path fading, orthogonal frequency division multiplexing (OFDM) technology has been widely used in many advanced digital communication systems. The research and application of the OFDM wireless LAN technology is being paid more and more regard to. This thesis is to make research on the key technologies of WLAN, and it includes the study and implementation schemes of OFDM channel estimation, channel equalization, automatic gain control as well as package detection according to IEEE 802.11a standard.During the study of OFDM channel estimation algorithms, it is discovered that the least square (LS) channel estimation algorithm has low complexity while its performance decays when signal noise ratio (SNR) is low; the time-domain algorithm, Minimum Mean-Square Error algorithm, estimation algorithm based on FFT and singular value decomposation (SVD) have good performance, but the high computational complexity limits the application. This thesis proposes a smoothing scheme with low complexity based on least square channel estimation algorithm and its amendment. Not like conventional LS algorithm the new schemes make good use of the correlation between nearby sub-channel response in WLAN indoor environment, and weighted smoothes the sub-channel response. The performance of the proposed channel estimation is demonstrated by computer simulation. The MSE performance is better than LS algorithm in low SNR as well as the Bit-Error-Ratio performance. We get same MSE with about 3dB lower SNR and same BER performance with approxamate 1dB lower SNR. The result of channel estimation is used to compensate the sub-channel response, in other words, to equalize the received data. This thesis proposes the low complexity implementation scheme of channel estimator and equalizer.The accuracy of package detection relates to the network throughput performance. The thesis introduces the algorithm and implementation of the delay-autocorrelation package detector. After analyzing the specificity of the Wireless LAN data package, the thesis proposes a scheme of automatic gain control loop suited for IEEE802.11a physical layer. Also we discuss some computation complexity issues in algorithm implementations.