Blind Estimation of the Phase and Carrier Frequency Offsets for LDPC-Coded Systems

Rodrigue Imad,Mounir Ghogho,Sebastien Houcke

doi:10.1155/2010/293572

Abstract

We consider in this paper the problem of phase offset and Carrier Frequency Offset (CFO) estimation for Low-Density Parity-Check (LDPC) coded systems. We propose new blind estimation techniques based on the calculation and minimization of functions of the Log-Likelihood Ratios (LLR) of the syndrome elements obtained according to the parity check matrix of the error-correcting code. In the first part of this paper, we consider phase offset estimation for a Binary Phase Shift Keying (BPSK) modulation and propose a novel estimation technique. Simulation results show that the proposed method is very effective and outperforms many existing algorithms. Then, we modify the estimation criterion so that it can work for higher-order modulations. One interesting feature of the proposed algorithm when applied to high-order modulations is that the phase offset of the channel can be blindly estimated without any ambiguity. In the second part of the paper, we consider the problem of CFO estimation and propose estimation techniques that are based on the same concept as the ones presented for the phase offset estimation. The Mean Squared Error (MSE) and Bit Error Rate (BER) curves show the efficiency of the proposed estimation techniques.

Highlights

The past few years have seen an increasing demand for efficient and reliable digital communication systems
We present our simulated results to analyze the performance of the proposed blind phase offset and Carrier Frequency Offset (CFO) estimation techniques when applied to Low-Density ParityCheck (LDPC) codes
In order to evaluate the effectiveness of the proposed technique, we compared it to three different techniques of blind phase offset estimation

Summary

Introduction

The past few years have seen an increasing demand for efficient and reliable digital communication systems. In order to protect the transmitted data from noise, errorcorrecting codes are introduced in the transmission scheme. Turbo codes and Low-Density Parity-Check (LDPC) codes have proven their efficiency in detecting and correcting errors, even at low signal-to-noise ratios (SNR) [1, 2]. A degradation in performance of these codes is expected when a phase offset and a Carrier Frequency Offset (CFO) are present in the system. The CFO is usually due to a possible carrier frequency mismatch or a relative motion between the transmitter and the receiver. Two synchronization approaches are often used to blindly estimate the phase offset: the “NonData-Aided” (NDA) and the “Hard Decision Di-rected”

Objectives

Results

Conclusion