Determining symbol synchronisation in an OFDM receiver in response to one of two impulse response estimates

摘要

A receiver determines a symbol synch time for recovering data from a symbol of signal samples generated in accordance with orthogonal frequency division multiplexing, the symbol including a guard period which carries data repeated from a data bearing part of the symbol. The receiver comprises a pilot assisted tracker which is operable to determine an adjustment to the symbol synch time from a pilot assisted channel impulse response estimate, a guard adapted filter processor comprising a filter and a filter controller operable to adapt the impulse response of the filter to the signal samples from the guard period. The controller is operable to excite the filter with the symbol signal samples to generate an output signal which provides a further representation of the channel impulse response. A symbol time adjustment estimator is operable to adjust the symbol synch time in accordance with the adjustment provided by at least one of the pilot assisted tracker and the guard adapted filter processor. The receiver provides an improved estimate of the symbol synch time by combining a pilot assisted tracker with a guard adapted filter processor. The pilot assisted tracker estimates the symbol synch time from a channel impulse response estimate generated from pilot signal samples. By combining this with the adjustment estimated by the guard adapted filter processor, an ambiguity in a relative time of arrival of signal paths of the channel impulse response with respect to the main signal path is obviated.