Codec supporting PCM modem communications over a universal digital loop carrier
AssigneeRaychem Corporation
InventorsPeter Gade Ruether, Carolyn Gaye Ford
Life of this patent
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Abstract
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. The 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.
Claims28
A codec supporting quantization level sampling (QLS) communications with a PCM modem over a digital loop carrier (DLC) having an analog connection to a central office (CO) line interface, said CO line interface having a digital-to-analog converter (DAC), a clock controlling the DAC, and a reconstruction filter, said codec comprising:
- an analog-to-digital converter (ADC) synchronized to the CO clock for converting analog signals from the CO line interface into corresponding digital signals;
- an equalizer receiving said digital signals from said ADC and providing a transfer function to substantially compensate for distortions introduced by said CO line interface reconstruction filter and the signal path from said CO line interface reconstruction filter to said ADC;
- and
- a slicer sampling the output of said equalizer to output digital data over said DLC that reproduces the digital data entering the CO line interface.
A telecommunications system comprising:
- a PCM modem;
- a central office (CO) switch communicating with said PCM modem over a digital network, said CO switch having a CO clock;
- a CO line interface connected to said CO switch having:
- (a) a digital-to-analog converter (DAC) controlled by said CO clock converting digital data received from said PCM modem into an analog signal;
- and
- (b) a reconstruction filter limiting the bandwidth of said analog signal output by said DAC;
- and
- a digital loop carrier (DLC) having a central office terminal (COT) with an analog connection to said CO line interface, said COT including a codec having:
- (a) an analog-to-digital converter (ADC) synchronized to the CO clock for converting analog signals from the CO line interface into corresponding digital signals;
- (b) an equalizer receiving said digital signals from said ADC and providing a transfer function to substantially compensate for distortions introduced by said CO line interface reconstruction filter and the signal path from said CO line interface reconstruction filter to said ADC;
- and
- (c) a slicer sampling the output of said equalizer to output digital data over said DLC that reproduces the digital data entering the CO line interface.
A method for reconstructing an input PCM signal after a digital-to-analog conversion followed by a filter, said method comprising:
- receiving the analog signal generated from the input PCM signal by the digital-to-analog conversion;
- converting said analog signal to a second digital signal using a sampling rate synchronized to the digital-to-analog conversion;
- converting said second digital signal to a third digital signal using a plurality of adaptive equalizers, each trained to process one PCM symbol in a repeating group of PCM symbols from said analog-to-digital conversion step, said equalizers providing a transfer function to substantially compensate for the distortion introduced by said filter and the signal path from said filter to said analog-to-digital conversion step;
- and
- converting said third digital signal to an output PCM signal, said output PCM signal being equal to said input PCM signal.
A method for supporting communications with a PCM modem over a digital loop carrier (DLC) having an analog connection to a central office (CO) line interface, said CO line interface having a digital-to-analog converter (DAC), a clock controlling the DAC, and a reconstruction filter, said method comprising:
- initially training an adaptive equalizer to provide a transfer function to substantially compensate for distortion introduced by said CO reconstruction filter and the signal path from said CO reconstruction filter over said analog connection;
- and
- in an operational mode:
- (a) converting analog signals from the CO line interface into corresponding digital signals using a sampling rate synchronized to the CO clock;
- (b) equalizing said digital signals using said adaptive equalizer to process said digital data;
- and
- (c) sampling the output of said adaptive equalizer to output digital data over said DLC that reproduces the digital data entering the CO line interface.
Dependencies are inferred from the claim text.