In this paper we propose the use of QAM constellations,
specifically 4, 16, and 64-QAM, in severely timedispersive
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 IBDFE
(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.