Robust suboptimal fuzzy equalizer in nonlinear DS-CDMA systems

Direct-sequence Code-division multiple-access (DS-CDMA) has merged as proper format for wireless communication systems. As a result of multiple-access interference (MAI), inter-symbol interference (ISI), narrowband interference (NBI) and nonlinearities in channels, DS-CDMA systems can suffer deterioration in performance. In practical application, it is difficult to design optimal equalizer for nonlinear DS-CDMA systems. Here, we use fuzzy models as the nonlinear interpolation of several linear channels. Based on fuzzy linear interpolation channel, a robust suboptimal fuzzy equalizer is proposed to efficiently compensate the nonlinear channel, MAI, ISI and channel noise to reconstruct the transmitted signals for each user. The robust suboptimal equalization design problem is transformed to a linear matrix inequality problem, which can be efficiently solved convex optimization technique.