  This paper presents a novel efficient receiver design for wireless
communication systems that incorporate orthogonal frequency division
multiplexing (OFDM) transmission. The proposed receiver does not require
channel estimation or equalization to perform coherent data detection. Instead,
channel estimation, equalization, and data detection are combined into a single
operation, and hence, the detector is denoted as a direct data detector
(D^{3}). The performance of the proposed system is thoroughly analyzed
theoretically in terms of bit error rate (BER), and validated by Monte Carlo
simulations. The obtained theoretical and simulation results demonstrate that
the BER of the proposed D^{3} is only 3 dB away from coherent detectors with
perfect knowledge of the channel state information (CSI) in flat fading
channels, and similarly in frequency-selective channels for a wide range of
signal-to-noise ratios (SNRs). If CSI is not known perfectly, then the D^{3}
outperforms the coherent detector substantially, particularly at high SNRs with
linear interpolation. The computational complexity of the D^{3} depends on the
length of the sequence to be detected, nevertheless, a significant complexity
reduction can be achieved using the Viterbi algorithm.
