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An adaptive equalizer scheme is presented in OFDM system for IEEE 802.11a, g wireless LAN. Conventional OFDM system employs a guard interval and a 1-tap frequency-domain equalizer (FEQ) to prevent delay spread distortions. This scheme is simple to implement, but provides low spectral efficiency due to the use of the guard interval. Moreover its performance is poor because of the lack of multipath diversity and the energy loss contained within the guard Interval. In the case where the channel impulse response (CIR) is larger than the guard interval, the system performance is limited by the intersymbol and intercarrier interference. The proposed equalizer scheme consists of an adaptive time-domain equalizer (TEQ) and a 1-tap FEQ using long training OFDM symbols in the preambles. Its performance is better than that of the conventional OFDM system under severe delay spread and noise power conditions, especially in the case where the CIR is larger than the guard interval. This enables a reduction in the size of the guard interval and thus the spectral efficiency of the OFDM system can be improved.
Date of Publication: May 2004