Narrowband jammer suppression in coded DS-CDMA channels

Existing narrowband jammer suppressors for DS-CDMA, typically function independently of the multiuser interference cancellation strategy used. Besides, certain high-performance jammer suppression techniques, e.g., linear MMSE suppression, assume that the powers and frequencies of the interfering signals are known, or that they can be adaptively estimated. The former is never true in practice and the latter is not feasible when long spreading codes are used. The present work eliminates these restrictions, by applying the idea of iterative MMSE multiuser interference suppression, introduced earlier by the authors, to this context. The first iteration in this procedure is effectively MMSE multiuser interference cancellation; the parameters of the jammers are unknown at this stage. The outputs of all users' soft decoders (applied to the demodulator outputs of this iteration) are then fed back to subtract their (estimated) cumulative contribution from the received signal vector; the residue comprises the narrowband jammers embedded in wideband noise, so that the former can be piecewise interpolated over chip intervals of appropriate duration, and thence subtracted from the received signal for the succeeding iteration. The soft-decoded feedback estimates of the interfering signals are also used in each iteration to perform soft MMSE multiuser interference suppression, in conjunction with subtractive interference cancellation. The approach is extended to exploit the enhanced separation (in the spatial sense) that is afforded by employing multisensor receivers.