Short-block equalization techniques employing channel estimation for fading time-dispersive channels

The objective of the present study is reliable digital communications over fading channels with severe time-dispersion. The authors present three short-block equalization techniques based on linear, nonlinear decision-directed, and maximum-likelihood estimation principles. Short alternating blocks of data and training symbols are used. In contrast to the recursive symbol-by-symbol equalization approaches usually employed, each data block is detected as a unit. These schemes require an estimate of the channel impulse response. This is considered an advantage from the adaptation point of view, since channel response estimation is one of the simplest adaptation requirements of any equalization process. Performance is evaluated for QPSK (quadrature phase-shift keying) and BPSK (binary phase-shift keying) signaling using a Rayleigh fading-channel model with severe time-dispersion. The degradation from ideal for the three schemes was about 5, 2.5, and 1 dB respectively