Codec supporting pcm modem communications over a universal digital loop carrier

摘要

A codec supports PCM modem communications (e.g., V.90, X2, or K56flex protocols) over a universal digital loop carrier (UDLC) having an analog interface to the central office (CO). The codec includes an analog-to-digital converter (ADC) that is synchronized to the CO clock, and an equalizer that has been trained to provide a transfer function to compensate for the distortion introduced by the CO line interface reconstruction filter and connecting circuits, to minimize resampling error. These features allow the codec to output a PCM stream that accurately reproduces the PCM data at the central office, at data rates sufficient to support PCM modem communications, as well as voice and conventional modem communications. The equalizer can be trained using a remote training unit that transmits a predetermined sequence of training signals to the equalizer. The connection to the training unit can be over a local central office telephone call or over a wide area network that can be accessed through a switched connection. In one embodiment, the equalizer comprises a feed-forward linear equalizer followed by a decision feedback equalizer.