A fuzzy logic system for interference rejection in code division multiple access

The spread spectrum modulation presents a more robust interference rejection capability than the non code-based modulations. DS-SS communications are unlicensed and quite often used to support missions on mobile platforms. In particular, the unlicensed bands such as the Industrial Scientific and Medical (ISM) can seriously saturate the interference rejection of the spread spectrum systems. To overcome this drawback it is possible to use an interference canceller (IC) before the despreading stage. In order to design an optimum IC to suppress analog and digital interferences, we have to implement the Conditional Mean (CM) and the Maximum-A-Posteriori criteria. However, both filters present a high computational burden which reduces their real feasibility. In addition, the communication scenario could be corrupted by Gaussian or/and Non-Gaussian noise, which makes more complex the structure of the optimum detector. This paper proposes an interference canceller based on Fuzzy Logic that allows to suppress either analog or digital interferences and decreases the computational burden of the CM estimator and MAP detector.