Arrangements for data timing recovery from distorted signals for use in adaptive modems with multi-level coding.

摘要

The submission makes use of the fact that where an adaptive equaliser (APS) is incorporated in a modem, some sort of training sequence is employed prior to the transmission of the data message. This training sequence usually incorporates a block of pseudo-random data (DIS) transmitted at the basic symbol rate to provide the equaliser (APS) with a relatively less distorted signal to operate on. During the training period both threshold-derived timing (TCTRL) and Nyquist-derived timing (NTRL) are produced. The Nyquist-derived timing (NTRL) is then phase-shifted (APS) to correspond to the threshold derived timing (TCTRL) which is valid during the training period. The phase shift (APS) is then fixed so that, when multi-level coding is introduced valid timing can still be obtained from the Nyquist-derived timing signal (NTRL). In addition in the event of transmission interruptions the invention allows timing recovery without the need for a new training cycle.