Bandpass component decimation and transmission of data in cable television digital return path
View Patent ↗A device for and a method of decreasing the data rate of a digital return path link in a Cable Television Hybrid Fiber-Coax system (CATV system) is disclosed. At the node of the CATV system, the bandwidth of the a digital data stream representative of an analog return signal is limited to a desired frequency band. The bandwidth-limited data stream is then digitally re-sampled at a predetermined multiple of a center frequency of the frequency band. The re-sampled data stream is then separated into two data streams. Then, these separate data streams are digitally decimated to a lower data rate, interleaved and serialized for transmission to a head end of the CATV system. A reverse process reconstructs the original analog return signal's signal components within the desired frequency band at the head end.
1. A signal decoder for use in a cable television return path and configured to receive a first stream of digital samples that include first digital samples interleaved with second digital samples of signals within a predetermined frequency band, the signal decoder comprising:
a deinterleaver configured to deinterleave the first stream of digital samples and generate a stream of first digital samples and a stream of second digital samples;
a first interpolation filter configured to filter the stream of first digital samples;
a second interpolation filter configured to filter the stream of second digital samples;
multiple phase taps of the first interpolation filter configured to up-sample the output of the first interpolation filter to form a first up-sampled stream that has a data rate that is a predetermined multiple of a center frequency of the predetermined frequency band, wherein the multiple phase taps of the first interpolation filter are coupled to a numerically controlled oscillator;
multiple phase taps of the second interpolation filter configured to up-sample the output of the second interpolation filter to form a second up-sampled steam that has a data rate that is a predetermined multiple of a center frequency of the predetermined frequency band, wherein the multiple phase taps of the second interpolation filter are coupled to the numerically controlled oscillator;
combining logic configured to combine the first up-sampled stream and the second up-sampled stream to generate a combined stream of digital samples; and
a bandpass interpolation filter configured to filter the combined stream to generate an output stream of digital samples at an output data rate higher than that of the first stream of digital samples.
2. The signal decoder of claim 1 , wherein the data rate of the first up-sampled stream and the second up-sampled stream is four times the center frequency of the predetermined frequency band.
3. The signal decoder of claim 1 , wherein the combining logic comprises:
a waveform generator configured to generate a first waveform and a second waveform that is 90° out-of-phase of the first waveform, the first waveform and the second waveform both having the center frequency and having a data rate four times of the center frequency;
a first digital multiplier configured to multiply the first up-sampled stream of digital samples with the first waveform;
a second digital multiplier configured to multiply the second up-sampled stream of digital samples with the second waveform; and
an adder configured to add the outputs of the first digital multiplier and the second digital multiplier to produce the combined stream of digital samples.
4. A device for use in a cable television return path, comprising:
an optical data receiver configured to receive an optical signal from an optical medium and to convert the optical signal to a serial bit stream;
a deserializer configured to convert the serial bit stream into a first stream of digital samples each having a plurality of bits;
a deinterleaver configured to deinterleave the first stream of digital samples and generate a stream of first digital samples and a stream of second digital samples;
a first interpolation filter configured to filter the stream of first digital samples;
a second interpolation filter configured to filter the stream of second digital samples;
multiple phase taps of the first interpolation filter configured to up-sample the output of the first interpolation filter to form a first up-sampled stream that has a data rate that is a predetermined multiple of a center frequency of the predetermined frequency band, wherein the multiple phase taps of the first interpolation filter are coupled to a numerically controlled oscillator;
multiple phase taps of the second interpolation filter configured to up-sample the output of the second interpolation filter to form a second up-sampled steam that has a data rate that is a predetermined multiple of a center frequency of the predetermined frequency band, wherein the multiple phase taps of the second interpolation filter are coupled to the numerically controlled oscillator;
combining logic configured to combine the first up-sampled stream and the second up-sampled stream to generate a combined stream of digital samples;
a bandpass interpolation filter configured to filter the combined stream to generate an output stream of digital samples at an output data rate higher than that of the first stream of digital samples; and
a digital-to-analog converter configured to convert the output stream of digital samples to an analog signal.
5. The device of claim 4 , wherein the data rate of the first up-sampled stream and the second up-sampled stream is four times the center frequency of the predetermined frequency band.
6. The device of claim 4 , wherein the combining logic comprises:
a waveform generator configured to generate a first waveform and a second waveform that is 90° out-of-phase of the first waveform, the first waveform and the second waveform both having the center frequency and having a data rate four times of the center frequency;
a first digital multiplier configured to multiply the stream of first digital samples with the first waveform;
a second digital multiplier configured to multiply the stream of second digital samples with the second waveform; and
an adder configured to add the outputs of the first digital multiplier and the second digital multiplier to produce the combined stream of digital samples.
7. A signal decoder for use in a cable television return path and configured to receive a first stream of digital samples that include first digital samples interleaved with second digital samples of signals within a predetermined frequency band, the signal decoder comprising:
a deinterleaver configured to deinterleave the first stream of digital samples and generate a stream of first digital samples and a stream of second digital samples;
a first interpolation filter interpolation filters configured to filter the stream of first digital samples;
a second interpolation filter configured to filter the stream of second digital samples;
multiple phase taps of the first interpolation filter configured to up-sample the output of the first interpolation filter to form a first up-sampled stream, wherein the multiple phase taps of the first interpolation filter are coupled to a numerically controlled oscillator;
multiple phase taps of the second interpolation filter configured to up-sample the output of the second interpolation filter to form a second up-sampled steam, wherein the multiple phase taps of the second interpolation filter are coupled to the numerically controlled oscillator;
combining logic configured to combine the first up-sampled stream and the second up-sampled stream to generate a combined stream of digital samples; and
a bandpass interpolation filter configured to filter the combined stream to generate an output stream of digital samples at an output data rate higher than that of the first stream of digital samples.