Coded DS-CDMA Systems with Iterative Channel Estimation and no Pilot Symbols

TL;DR

This paper introduces a DS-CDMA system that performs channel estimation, demodulation, and decoding iteratively without pilot symbols, improving spectral efficiency and interference suppression.

Contribution

It proposes an EM-based channel estimation algorithm that operates without pilot symbols, enhancing system simplicity and performance in DS-CDMA systems.

Findings

Elimination of pilot symbols simplifies system design.

Iterative estimation improves interference suppression.

Enhanced spectral efficiency and bit error rate performance.

Abstract

In this paper, we describe direct-sequence code-division multiple-access (DS-CDMA) systems with quadriphase-shift keying in which channel estimation, coherent demodulation, and decoding are iteratively performed without the use of any training or pilot symbols. An expectation-maximization channel-estimation algorithm for the fading amplitude, phase, and the interference power spectral density (PSD) due to the combined interference and thermal noise is proposed for DS-CDMA systems with irregular repeat-accumulate codes. After initial estimates of the fading amplitude, phase, and interference PSD are obtained from the received symbols, subsequent values of these parameters are iteratively updated by using the soft feedback from the channel decoder. The updated estimates are combined with the received symbols and iteratively passed to the decoder. The elimination of pilot symbols simplifies the system design and allows either an enhanced information throughput, an improved bit error rate, or greater spectral efficiency. The interference-PSD estimation enables DS-CDMA systems to significantly suppress interference.