Joint Detection and CFO Estimation for QAM Constellations

In this paper we propose the use of QAM constellations, specifically 4, 16, and 64-QAM, in severely time-dispersive channels and with moderate CFOs (Carrier Frequency Offsets). We consider an SC-FDE (Single Carrier Frequency-Domain Equalization) and assume that previously to the equalization procedure a coarse CFO estimation and compensation is performed. Since the coarse CFO estimate can have a significant error leading to a residual CFO we present and evaluate a receiver with joint detection and carrier synchronization in order to guarantee a good BER. We employ frequency-domain iterative DFE (Decision Feedback Equalization) receivers denoted by IB-DFE (Iterative Block-Decision Feedback Equalization), which are combined with a DD (Decision-Directed) CFO estimator. Our aim is to determine the synchronization requirements for 4, 16, and 64-QAM and compare several methods for the DD CFO estimators when using these QAM constellations.