MULTIUSER DETECTION TECHNIQUES FOR NARROW-BAND INTERFERENCE SUPPRESSION IN SPREAD-SPECTRUM COMMUNICATIONS

Due to the scarcity of frequency allocations for emerging personal com munications services, it has been proposed that spread spectrum (SS) s ignals be used in such services so that they can be overlaid on existi ng frequency band occupants. Such SS signals would be constrained in p ower so as not to interfere with pre-existing, narrowband users. In vi ew of this application, suppression of strong narrowband signals that interfere with commercial SS communications systems is being investiga ted with renewed interest. Previous research has modeled narrowband us ers as sinusoidal or autoregressive signals, and consequently has advo cated use of predictive filtering to suppress such signals. In this pa per it is shown that when the narrowband interferer is in fact a digit al communications signal these methods are less effective than techniq ues derived from multiuser communications. In particular, by modeling a narrowband user as a digital signal, optimal and asymptotically (low background noise) optimal linear algorithms for the recovery of the S S bit stream are developed. This technique represents not only a promi sing new approach to narrowband interference suppression, but also a n ew application for multiuser detection theory.