Abstract
An adaptive minimum mean-square error (MMSE) array receiver based on the fuzzy-logic recursive least-squares (RLS) algorithm is developed for asynchronous DS-CDMA interference suppression in the presence of frequency-selective multipath fading. This receiver employs a fuzzy-logic control mechanism to perform the nonlinear mapping of the squared error and squared error variation, denoted by (,), into a forgetting factor. 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. This receiver is capable of providing both fast convergence/tracking capability as well as small steady-state misadjustment as compared with conventional LMS- and RLS-based MMSE DS-CDMA receivers. Simulations show that the fuzzy-logic LMS and RLS algorithms outperform, respectively, other variable step-size LMS (VSS-LMS) and variable forgetting factor RLS (VFF-RLS) algorithms at least 3 dB and 1.5 dB in bit-error-rate (BER) for multipath fading channels.
Highlights
Direct-sequence code-division multiple access (DS-CDMA), a specific form of spread-spectrum transmission, has been adopted as the multiaccess technology for nonorthogonal transmission in the third-generation (3G) mobile cellular systems, such as wideband CDMA (W-CDMA) or multicarrier CDMA (MC-CDMA)
An asynchronous BPSK DS-CDMA system with the number of users K = Kintra + Kinter is considered in the presence of frequency-selective multipath fading
The settings of the MBFs parameters required for the Fuzzy inference system (FIS) of the fuzzy-logic controller (FLC)-LMS and FLC-recursive least-squares (RLS) are shown in Figures 2 and 3, respectively
Summary
Direct-sequence code-division multiple access (DS-CDMA), a specific form of spread-spectrum transmission, has been adopted as the multiaccess technology for nonorthogonal transmission in the third-generation (3G) mobile cellular systems, such as wideband CDMA (W-CDMA) or multicarrier CDMA (MC-CDMA). An adaptive robust MMSE arrayreceiver is proposed based on a fuzzy-logic controlled LMS or RLS algorithm for space-time joint asynchronous DS-CDMA signals. In [14], the authors proposed the variable forgetting factor linear least-squares (VFF-LLS) algorithm to improve the tracking capability of channel estimation These works motivate the development of the linear MMSE CDMA receiver with a fuzzy-logic controlled two-parameter system of (e2, Δe2) instead of (e2, NT ), where Δe2[n]=|e2[n]−e2[n− 1]| indicates the squared error variation at time n. An adaptive linear MMSE array receiver is employed and implemented by the fuzzy-logic controlled LMS and RLS algorithms.
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