TIMING RECOVERY IN A NETWORK-SYNCHRONIZED MODEM

摘要

A timing technique for a Quantization-Level-Sampling (QLS) modem puts timing information in a downstream pulsed signal transmitted from the public switch ed telephone network (PSTN) to the QLS modem. In response to this timing inform ation, the QLS modem synchronizes to the network sampling clock in the PSTN. In par ticular, the pulsed signal includes data-bearing samples, which were provided by a fa r-end QLS modem, and at least one non-user-data-bearing (NUDB) sample in which the lev el of this NUDB sample periodically alternates. The QLS modem extracts timing informati on from this periodic alternating signal level to synchronize the QLS modem to the network sampling clock.