Abstract: In a system where 2-level modulation and 4-level modulation of communication signals exist, an apparatus (107) demodulates either modulation scheme by demodulating (301) a received signal under the presumption that it is a 4-level signal, and if the received signal is detected (309) to be a 2-level signal, the signal is then demodulated (319) as a 2-level signal.

Abstract: A multi-level digital signal data stream termination detector is set forth that utilizes detection of multiple relatively short detection patterns separated by a time less than a predetermined allowable time to detect digital data stream termination even in the presence of simulcast distortion.

Abstract: A multi-edge clock recovery method is provided that may be used with data streams having at least three (3) levels. According to the invention, when each threshold is crossed, it generates data edges for that particular threshold. These data edges latching the polarity of the recoverd clock at the time the corresponding threshold was crossed, thereby indicating the "late" and "early" edge information for that threshold crossing with respect to the falling edge of the recovered clock. Immediately following the decoding of the most recent multi-level symbol, the appropriate threshold for the data transition is determined. The decoded values of the sumbols preceding and following the data edges determine which threshold should be selected for "late" and "early" edge indications. The recorded late/early data edge status for this selected threshold is then used for determining when it is necessary to correct the phase of the recovered clock.