Narrowband Interference Suppress in Spread Spectrum through Snr Improvement

Spread Spectrum (SS) communications offers a promising solution to an overcrowded frequency spectrum aimed growing demand for mobile and personal communication services. The proposed overlay of spread spectrum signal on existing narrowband users implies strong interference for the SS system. This paper discusses how the system performance can be improved by preprocessing to suppress narrowband interference. Linear prediction filters have been proposed since the 1980s for the suppression of narrowband interference. In 1991 Vijayan and Poor proposed nonlinear methods of suppressing the narrowband signal with significant increase in SNR improvement. We derive an enhancement to this nonlinear prediction and achieve further improvement by applying the technique to interpolating filter structures. Of significant interest to the United States military is the ability of an enemy to deny or disrupt the operation of Global Positioning System (GPS). In order to combat this threat the GPS Joint Program Office (JPO) initiated the Tactical GPS Anit-Jam Technology (TGAT) project which yielded a prototype DEF to remove narrowband interference. Finally we extend the results to the case of multiple spread spectrum users and demonstrate how nonlinear filtering can dramatically outperform linear filtering.