A New Equalizer in Doubly-Selective Channels for TDS-OFDM

Various factors contribute to the intercarrier interference (ICI) in orthogonal frequency-division multiplexing (OFDM), which violates the orthogonality among subcarriers and greatly degrades the performance. Traditional ICI compensation methods incorporate iterative estimation and cancelation for pilot subcarriers, bearing too much complexity and reducing the spectral efficiency. In this paper, a novel channel equalization method is proposed for time domain synchronous-orthogonal frequency-division multiplexing (TDS-OFDM), where fast and accurate channel estimation is achieved by utilizing the padded pseudo-noise sequence in consecutive blocks. The new equalizer refers to fast suboptimal-minimum mean square error structure, other than traditional overlap-add structure, inspired by the fact that linear convolution structure is better preserved than circular convolution structure in TDS-OFDM under time-varying channels. With the approximation of linear time-varying channel, the proposed equalizer achieves considerable performance with low complexity (linear) and no additional spectral overhead.