Suppression of FM adjacent channel interference

Within current RF allocations, increases in communication traffic have resulted in a trend toward spectral crowding. Effects of adjacent channel interference have traditionally been minimized by geographically isolating channel assignments, or by over-spacing channel centers, inefficiencies which will be unacceptable for future needs. As a result of increased density of communication signals, future receiver hardware will require digital signal processing techniques for suppressing adjacent channel interference. Over the last few years, there have been research efforts aimed at solutions for this type of interference, especially in FM communications Of specific interest here is a mathematical structure developed in [7] addressing suppression of such interfering components after discrimination, where bandwidth reduction results in savings in computation requirements. Initial attempts to apply adaptive filtering techniques to this structure indicated that fundamental problems existed with the formulation. In this paper, this technique is closely scrutinized, and we demonstrate that significant baseband improvements are unlikely for general modulating signals, contrary to published claims.