Apply autocorrelation matching method to outdoor wireless LAN on co-channel interference suppression and channel equalization

This paper presents an application of a new signal processing technique, called the autocorrelation matching (AM) method, to outdoor IEEE 802.11b wireless LAN operation. Since wireless LAN uses unlicensed spectrum, outdoor wireless LAN may suffer strong co-channel interference from each other. In addition, delay spread in the outdoor environment is comparable to symbol duration, and thus channel equalization is needed. The AM method can solve these two problems simultaneously by inserting three steps in the wireless LAN signal processing procedure: (1) filtering the transmitted sequence with a specially designed filter (called a pre-filter) before the spreading process at the transmitter; (2) matching the autocorrelation function of a composite signal constructed from multiple received signals with that of the desired signal after the de-spreading process at the receiver; and (3) filtering the composite signal with a filter that is the inverse of the pre-filter. It is proven that, regardless of the existence of co-channel interference and intersymbol interference, a match of autocorrelation functions between the composite signal and the desired signal assures the composite signal equaling the desired signal up to a phase difference, which can then be identified from the synchronization prefix to every wireless LAN data frame. Some preliminary simulation results demonstrate that the AM method is effective and adaptive to non-stationary co-channel interference.