Method for receiving multicarrier digital signals

DETAILED DESCRIPTION An important consideration in the context of such systems is to find a system-conformal signal in the situation where a receiver is switched on or is tuned into another channel.
To do this, the receiver has to be able to distinguish between different services, for example to distinguish digital signals from analogue signals or digital DVB signals from digital DAB signals.
Both digital signals and analogue signals (for example PAL television signals) may occur in certain frequency bands, in which case the center frequencies may differ from the specified channel mid-frequencies.
The invention is based on an improved method for tuning when receiving multicarrier digital signals, or for checking the system conformity of such received digital signals.
At the receiver end, coarse time synchronization linked to mode detection and, possibly and additionally, coarse AFC (automatic frequency correction) are carried out initially both for searching for and identifying received signals, as well as for continuously monitoring them.
In coarse time synchronization, the time signal is correlated with the time signal shifted by a wanted symbol length Tu.
This correlation may be carried out more than once, for example five times per data frame.
In this correlation, signal samples of different length Tu are used, depending on the respective mode, and the correlation result maxima obtained from this are then used to deduce the present mode (for example 2K or 8K modes).
If no usable correlation result maximum is obtained, the correlation steps may be repeated.
The guard interval used is determined, and a sampling window is then positioned, based on the interval between the maxima and/or their amplitudes, taking account of the mode.
This can be done by once-off setting of a counter which is synchronized to the symbol sequence (Tu+.
DELTA.
) and outputs a time window of duration Tu.
In the following text, this time window is also called the sampling window or FFT window.
A basic oscillator used in this case, and thus the position of the window as well, are corrected in subsequent steps via fine time synchronization