OFDM receivers

摘要

A DRM receiver has a pre-FFT time synchroniser (28), located prior to the FFT circuit (18), which is used to synchronise the receiver to the incoming symbols to a reasonable level of accuracy, before handing over to a post-FFT time synchroniser (30) . The pre-FFT algorithm generates a number of waveforms which are used to detect the presence and location of the guard interval. The data before the FFT can be used to obtain relatively crude time and frequency synchronisation, and then decision logic is used to switch to using the post-FFT algorithms. The pre-FFT synchroniser delays the signal (50) by the duration of the appropriate active symbol period, correlates (52) the delayed and undelayed signals to provide a correlation signal representing the result of the correlation, and detects (46) the centre of mass of the pulses in the correlation signal, to provide a synchronisation signal. The post-FFT synchroniser generates an estimated channel impulse response (72,74), squares the estimated channel impulse response to provide an estimated power channel impulse response, combines (76) the estimated power channel impulse response with a weighting function to generate a signal which is a measure of the damage done to the signal response as a function of window position, the side portions of the weighting function being substantially of quadratic form, and locates (78) a minimum in the resultant waveform, to provide a synchronisation signal.