Abstract: A digital data communication system for transmitting data over a transmission channel. The system is capable of estimating a channel impulse response with high reliability even when the channel is time-varying and suffers from intersymbol interference. Even when the variation on the channel is rapid, the system reduces the influence of demodulation delay particular to a maximum likelihood sequence estimator and thereby realizes highly reliable data transmission.

Abstract: In a space diversity receiver, matched filters and a like number of channel estimators are respectively coupled to diversity antennas to receive sequentially coded symbol sequences. A branch metric calculator receives the outputs of the matched filters and the estimates from the channel estimators to calculate a branch metric of the received sequences for coupling to a maximum likelihood (ML) estimator. The branch metric is obtained by summing branch metric coefficients derived from channel estimates respectively with the output of the matched filters or by summing branch metric coefficients derived from a vector sum of channel estimates with the matched filter outputs. In another embodiment, adaptive channel estimators are provided for deriving channel estimates from received sequences and the output of an ML estimator.

Abstract: An apparatus and a method for reproducing a signal, free of cross-talk and intersymbol interference, from an optical recording medium. The signal reproducing apparatus and method is for use in combination with an optical source for emitting a plurality of light beams directed to a center track, which contains the information to be reproduced, and the tracks adjacent to the center track on a recording medium. The signals received from the reflections of the light beams from the adjacent tracks are processed by a frequency characteristic converter and then added to the signal from the center track to eliminate the cross-talk in the signal from the center track created by the signals from the adjacent tracks.

Abstract: In a receiver responsive to a reception signal subjected to an intersymbol interference and a frequency offset, the reception signal is delivered to a matched filter having a filter characteristic matched with a transmission path and filtered into a filter output signal accompanied by the frequency offset. The filter output signal is sent to a frequency offset estimation circuit to produce an estimation signal representative of an estimation value of the frequency offset. An equalizer is supplied with the estimation signal and a selected one of the reception signal and the filter output signal to equalize the frequency offset and the intersymbol interference.

Abstract: In a space diversity receiver, multiple signal paths are connected respectively to antennas for multipath reception. Each signal path includes a digital demodulator coupled to the antenna and an impulse response detector, or autocorrelator connected to the demodulator for deriving a channel impulse response of each one of the multiple paths. A maximum response detector is connected to each impulse response detector for detecting equalizable delay components which give a maximum response value and a unequalizable delay components. A power ratio of the unequalizable delay components to the equalizable delay components is derived for each signal path and a minimum value of the power ratios is determined and one of the signal paths in which the mininmum value is detected is selected.