Adaptive Interference Suppression for CDMA Systems using Interpolated FIR Filters with Adaptive Interpolators in Multipath Channels

TL;DR

This paper introduces an adaptive receiver structure using interpolated FIR filters with adaptive interpolators for DS-CDMA systems in multipath channels, improving interference suppression and performance.

Contribution

It proposes a novel adaptive receiver scheme with time-varying interpolators and efficient algorithms, enhancing interference mitigation in multipath CDMA systems.

Findings

Achieves superior BER convergence and steady-state performance.

Reduces complexity compared to previous reduced-rank receivers.

Effective in mitigating MAI and multipath effects.

Abstract

In this work we propose an adaptive linear receiver structure based on interpolated finite impulse response (FIR) filters with adaptive interpolators for direct sequence code division multiple access (DS-CDMA) systems in multipath channels. The interpolated minimum mean-squared error (MMSE) and the interpolated constrained minimum variance (CMV) solutions are described for a novel scheme where the interpolator is rendered time-varying in order to mitigate multiple access interference (MAI) and multiple-path propagation effects. Based upon the interpolated MMSE and CMV solutions we present computationally efficient stochastic gradient (SG) and exponentially weighted recursive least squares type (RLS) algorithms for both receiver and interpolator filters in the supervised and blind modes of operation. A convergence analysis of the algorithms and a discussion of the convergence properties of the method are carried out for both modes of operation. Simulation experiments for a downlink scenario show that the proposed structures achieve a superior BER convergence and steady-state performance to previously reported reduced-rank receivers at lower complexity.