A novel method of channel characterization and equalization in spread spectrum based WLAN

Since a physical channel is causal, intersymbol interference (ISI) arises from past symbols when the channel has a delay spread. Characterization of a multipath channel as a causal channel depends on the detection of the time of arrival of the earliest path. In spread spectrum based modulation, a correlation based approach is used to identify the arrival times of different paths. If the earliest path is weak, the starting instant of the channel impulse response may be taken later than the actual one, corresponding to the time of arrival of the strongest path, thereby resulting in some residual precursor ISI. In the context of direct sequence spread spectrum wireless communication (IEEE 802.11b WLAN standard, for example), a novel method for characterizing the multipath channel is developed which, combined with a decision feedback equalizer, results in a significant cancellation of precursor ISI, thereby improving the bit error rate performance.