Concatenated Precoded OFDM for CFO Effect Mitigation

Orthogonal frequency-division multiplexing (OFDM) is highly sensitive to carrier frequency offset (CFO), which not only causes intercarrier interference (ICI) among subcarriers but introduces complex multiplicative distortion (CMD) to all detected subcarrier symbols as well. Due to unknown CFO, both ICI and CMD are time variant, thus complicating the data demodulation at the receiver. In conjunction with a training-prefixed data frame structure, a concatenated precoder that is constructed by concatenating an outer modified correlative precoder with an inner reduced Hadamard precoder is proposed in this paper to process data symbols prior to OFDM modulation and to enable joint estimation on channel multipath and constant CMD (CCMD), time-variant CMD (TCMD) estimation and compensation, and ICI suppression at the receiver in the presence of CFO. Simulation results show that the proposed system provides much better error performance than conventional signal coding approaches in the presence of CFO and multipath fading.