EURASIP Journal on Wireless Communications and Networking 
Volume 2005 (2005), Issue 2, Pages 117-129
doi:10.1155/WCN.2005.117

A Theoretical Framework for Soft-Information-Based Synchronization in Iterative (Turbo) Receivers

Nele Noels,1 Vincenzo Lottici,2 Antoine Dejonghe,3 Heidi Steendam,1 Marc Moeneclaey,1 Marco Luise,2 and Luc Vandendorpe3

 1Department of Telecommunications and Information Processing, Ghent University, Gent 9000, Belgium
2Department of Information Engineering, University of Pisa, Pisa 56122, Italy
3Communications and Remote Sensing Laboratory, Université Catholique de Louvain, Louvain-la-Neuve 1348, Belgium
Received 13 May 2004; Revised 29 September 2004

Abstract

This contribution considers turbo synchronization, that is to say, the use of soft data information to estimate parameters like carrier phase, frequency, or timing offsets of a modulated signal within an iterative data demodulator. In turbo synchronization, the receiver exploits the soft decisions computed at each turbo decoding iteration to provide a reliable estimate of some signal parameters. The aim of our paper is to show that such “turbo-estimation” approach can be regarded as a special case of the expectation-maximization (EM) algorithm. This leads to a general theoretical framework for turbo synchronization that allows to derive parameter estimation procedures for carrier phase and frequency offset, as well as for timing offset and signal amplitude. The proposed mathematical framework is illustrated by simulation results reported for the particular case of carrier phase and frequency offsets estimation of a turbo-coded 16-QAM signal.