Data rate compression device for cable television return path using bandpass puncturing

• US 20030154495A1
• Filed: 03/19/2002
• Published: 08/14/2003
• Est. Priority Date: 02/12/2002
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finisar Corporation (II-VI Incorporated)
• Inventors: Sage, Gerald F.
• Granted Patent: US 8,156,535 B2
• Time in Patent Office: Days
• US Class Current: 725/121
• CPC Class Codes: H04N 21/437 Interfacing the upstream path of the transmission network, e.g. for transmitting client requests to a VOD server flow control in data networks H04L47/10; streaming protocols, e.g. RTP or RTCP, H04L65/65; scheduling or organising the servicing of application requests in data packet switching networks H04L67/60
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

An apparatus for and a method of transmitting analog return signals in a digital return path of a cable television system (CATV) is disclosed. In one embodiment, at a node of the CATV system, an analog CATV return signal is converted to a stream of digital samples at approximately 100 MHz. Signals outside of a desired frequency band are removed with a digital filter having predetermined filter coefficients. The resulting stream of digital samples is up-sampled to generate another stream of digital samples at a rate that is four times the center frequency of a predetermined frequency band. The resulting stream is then punctured to generate yet another stream with a data rate that is lower than 100 MHz. Zero samples are removed, and the remaining digital samples are serialized and converted to optical signals for transmission via an optical medium of the CATV return path. A reverse process at a hub or head end of the CATV return system restores the signals of the desired frequency band.

Claims

1. A signal encoder for use in a cable television return path and configured to receive a first stream of digital samples from an analog-to-digital converter, the first stream of digital samples being representative of an analog return path signal that is sampled at a first data rate, the signal encoder comprising:

a bandpass interpolation filter configured to receive the first stream of digital samples and to substantially remove signals outside of a predetermined frequency band;

up-sampling logic configured to up-sample outputs of the bandpass interpolation filter and to generate a second stream of digital samples at a second data rate, the second data rate being a predetermined integer multiple of a center frequency of the predetermined frequency band;

puncturing logic configured to puncture the second stream of digital samples at a predetermined odd integer rate and to generate a third stream of digital samples at a third data rate that is lower than the first data rate.

2. The signal encoder of claim 1, wherein the second data rate is four times the center frequency of the predetermined frequency band.

3. The signal encoder of claim 1, wherein the up-sampling logic comprises a numerically controlled oscillator coupled to multiple phase taps of the bandpass interpolation filter.

4. The signal encoder of claim 1, wherein the center frequency is less than one half of the first data rate.

5. The signal encoder of claim 1, wherein the puncturing logic selectively replaces digital samples of the second stream with zeros according to the predetermined odd integer rate.

6. A device for use in a cable television return path, comprising:

an analog-to-digital converter configured to convert an analog return signal to a first stream of digital samples at a first data rate;

a bandpass interpolation filter configured to receive the first stream of digital samples and to substantially remove signals outside of a predetermined frequency band;

up-sampling logic configured to up-sample outputs of the bandpass interpolation filter and to generate a second stream of digital samples at a second data rate, the second data rate being a predetermined integer multiple of a center frequency of the predetermined frequency band;

puncturing logic configured to puncture the second stream of digital samples at a predetermined odd integer rate and to generate a third stream of digital samples at a third data rate that is lower than the first data rate;

a serializer configured to convert the third stream of digital samples to a serial bit stream; and

an optical transmitter driven by the serial bit stream to generate an optical signal for transmission in optical medium of the return path of the cable television system.

7. The signal encoder of claim 6, wherein the second data rate is four times the center frequency of the predetermined frequency band.

8. The signal encoder of claim 6, wherein the up-sampling logic comprises a numerically controlled oscillator coupled to multiple phase taps of the bandpass interpolation filter.

9. The signal encoder of claim 6, wherein the center frequency is less than one half of the first data rate.

10. A signal decoder for use in a cable television return path and configured to receive a first stream of digital samples that is generated by a transmitter bandpass interpolation filter having predetermined filter coefficients and that is punctured at a predetermined rate, the signal decoder comprising:

zero-insertion logic configured to insert zeros in the first stream of digital samples according to the predetermined rate to produce a second stream of digital samples; and

a bandpass interpolation filter having the predetermined filter coefficients configured to filter the second stream to generate a third stream of digital samples; and

up-sampling logic configured to up-sample the third stream of digital samples to form an output stream of digital samples at an output data rate higher than that of the first stream of digital samples.

11. The signal decoder of claim 10, wherein the output data rate is approximately 100 MHz.

12. The signal encoder of claim 10, wherein the up-sampling logic comprises a numerically controlled oscillator coupled to multiple phase taps of the bandpass interpolation filter.

13. 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;

zero-insertion logic configured to insert zeros in the first stream of digital samples according to a predetermined rate to produce a second stream of digital samples; and

a bandpass interpolation filter having predetermined filter coefficients configured to filter the second stream to generate a third stream of digital samples;

up-sampling logic configured to up-sample the third stream of digital samples to form 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.

14. The signal decoder of claim 13, wherein the output data rate is approximately 100 MHz.

15. The signal encoder of claim 13, wherein the up-sampling logic comprises a numerically controlled oscillator coupled to multiple phase taps of the bandpass interpolation filter.

16. A method of transmitting analog return signals in a digital return path of a cable television system, the method comprising:

converting an analog return signal to a first stream of digital samples at a first data rate;

filtering the first stream of digital samples to substantially remove signals outside of a predetermined frequency band with a first digital filter having predetermined filter coefficients;

up-sampling the filtered stream of digital samples to generate a second stream of digital samples at a second data rate, the second data rate being a predetermined multiple of a center frequency of a predetermined frequency band;

puncturing the second stream of digital samples at a predetermined odd integer rate to generate a third stream of digital samples;

converting the third stream of digital samples to an optical signal for transmission in the return path of the cable television system.

17. The method of claim 16, further comprising:

converting the optical signal to a fourth stream of digital samples;

inserting zeros in the fourth stream of digital samples according to the predetermined odd integer rate to generate a fifth stream of digital samples;

filtering the fifth stream of digital samples with a second digital filter having the predetermined filter coefficients;

up-sampling the filtered stream of digital samples to an output data rate; and

converting the up-sampled stream of digital samples to an analog signal.