Adaptive interference suppression using fuzzy-logic-based space-time filtering techniques in multipath DS-CDMA

An adaptive robust linear minimum mean-squared error (MMSE) array-receiver based on the fuzzy-inference-based recursive least-squares (RLS) algorithm is developed for asynchronous DS-CDMA interference suppression in the presence of frequency selective multipath fading. This array-receiver employs a fuzzy-logic control mechanism to perform the substantially nonlinear mapping of a two-parameter input vector of the squared error and squared error variation, denoted by (e², Δe²), into a scalar forgetting factor λ. For the real-time applicability, a computationally efficient version of the proposed receiver is derived based on the least-mean-square (LMS) algorithm using the fuzzy-inference controlled step-size μ. The proposed receiver achieves an arithmetic complexity similar to the conventional LMS and exponentially windowed (EW) RLS versions of the MMSE DS-CDMA receiver plus the slightly fuzzy-incurred computational cost. Moreover, this receiver is capable of providing both fast convergence/tracking capability as well as small steady-state misadjustment as compared with the conventional LMS and EW-RLS MMSE DS-CDMA receivers. Simulations are conducted to evaluate the convergence and tracking behavior of the proposed receiver with the amount of the L-sample iteration, the array of the M-element receiving antenna, and the size of the P-variable fuzzy set. The performance advantage of the receiver over other DS-CDMA receivers is investigated.