Cable television spread spectrum data transmission apparatus

• US 4,912,721 A
• Filed: 04/29/1988
• Issued: 03/27/1990
• Est. Priority Date: 04/29/1988
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Pidgeon, Rezin E. Jr., Thompson, Leo J., Zendt, Frederick T.
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US07/188,478
• Time in Patent Office: 697 Days
• Field of Search: 375/1, 380/34, 380/12, 455/5
• US Class Current: 375/149
• CPC Class Codes: H04B 1/70712 with demodulation by means of convolvers, e.g. of the SAW type SAW convolvers in general G06G7/195
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

Apparatus for transmitting data spread across at least a portion of the bandwidth of a cable television channel comprises a carrier signal oscillator, a frequency divider, a pseudorandom sequence generator and two exclusive OR gates. A first exclusive OR gate serves to spread a data signal across the pseudorandom noise sequence generator having a much higher chip rate than the bit rate of the data signal. The second exclusive OR gate modulates the spread spectrum data signal to a carrier frequency for transmission over the cable television channel. The apparatus may be applied for return path transmission in the 0-30 megahertz band which is high susceptible to interference noise and provides approximately a 20 dB signal to interference ratio advantage over known data coding and transmission schemes. A microprocessor normally present in a cable television terminal may format data for transmission, control the spread spectrum modulation process and control gain control circuitry for introducing an appropriate power level into the cable plant.

Claims

1. A data transmission apparatus for use in transmitting data spread across at least a portion of a spectrum provided for a cable television channel of a cable television system comprising a cable television signal distribution plant susceptible to interference noise from proximate power lines, telephone lines, defective cable television signal distribution apparatus of the distribution plant, ineffective grounding of cable sheaths, radio frequency interferences and other sources of interference noise, the data transmission apparatus comprising:

a controller, responsive to an incoming data signal, for providing a stepwise digital control signal for controlling the power level of a signal input to the cable television signal distribution plant, for providing the incoming data signal at a data bit rate to a spread spectrum data signal generator and for controlling the operation of a carrier signal oscillator;

the carrier signal oscillator, responsive to the controller, for providing a carrier signal at a frequency consistent with the frequency of the cable television channel;

a frequency divider, responsive to the carrier signal oscillator, for providing a sequencing signal;

a pseudorandom sequence generator, responsive to the sequencing signal, for generating a predetermined pseudorandom chip sequence at a chip rate an order of magnitude greater than the data bit rate for transmission on the cable television channel within at least a portion of the spectrum corresponding to the cable television channel;

the spread spectrum data signal generator, responsive to the pseudorandom sequence generator and the data signal output of the controller, for generating a spread spectrum data signal;

a carrier signal modulator, responsive to the carrier signal oscillator and the spread spectrum data signal generator, for modulating the spread spectrum data signal for transmission over the cable television channel; and

a programmable power amplifier for amplifying the modulated spread spectrum data signal output of the carrier signal modulator in accordance with said stepwise digital control signal from the controller.

2. The data transmission apparatus of claim 1, the cable television channel being a channel selected within a reverse path frequency band.

3. The data transmission apparatus of claim 1, the spread spectrum data signal generator comprising an Exclusive-OR gate.

4. The data transmission apparatus of claim 1, the carrier signal modulator comprising an Exclusive-OR gate coupled to the programmable power amplifier.

5. The data transmission apparatus of claim 2, the cable television channel being channel T7.

6. The data transmission apparatus of claim 1 comprising means for simultaneously transmitting a video signal and the modulated spread spectrum data signal, the power level of the video signal being substantially above the power level of the modulated spread spectrum data signal so as to not interfere with television reception.

7. A data reception apparatus for use in receiving data spread across at least a portion of a spectrum provided by a cable television channel of a cable television system comprising a cable distribution plant susceptible to interference noise, the data reception apparatus comprising:

a quadrature demodulation circuit for removing a spread spectrum data signal from a carrier of the cable television channel;

a Costa loop, responsive to the quadrature demodulation circuit, for synchronization of the quadrature demodulation circuit with a carrier signal modulator of a cable television transmitter;

a pseudorandom sequence generator for generating a pseudorandom chip sequence identical to a pseudorandom sequence generated at said cable television transmitter, the chip rate of said chip sequence being much greater than the data bit rate;

a digital correlation loop, responsive to the quadrature demodulation circuit, for correlating and synchronizing the pseudorandom chip sequence generated at the cable television receiver with the sequence generated at the cable television transmitter; and

a quadrature mixer, responsive to the pseudorandom sequence generator and the quadrature demodulation circuit, for recovering the data signal from the spread spectrum data signal.

8. The data reception apparatus of claim 7, wherein the Costa loop synchronizes the quadrature demodulator by mixing with the spread spectrum data signal a generated frequency and by mixing with the spread spectrum data signal a frequency 90°

out of phase with said generated frequency.

9. The data reception apparatus of claim 8, wherein the Costa loop further comprises a voltage controlled oscillator for generating said generated frequency.

10. A cable television data transmission system for transmitting data spread across at least a portion of a spectrum provided by a cable television channel of a cable television system, comprising a cable television signal distribution plant susceptible to interference noise from proximate power lines, telephone lines, defective cable television signal distribution apparatus of the distribution plant, ineffective grounding of cable sheaths, radio frequency interferences and other sources of interference noise, the data transmission system comprising:

a controller, responsive to an incoming data signal, for providing a stepwise digital control signal for controlling the power level of a signal input to the cable television signal distribution plant, for providing the incoming data signal at a data bit rate to a spread spectrum data signal generator and for controlling the operation of a carrier signal oscillator;

the carrier signal oscillator, responsive to the controller, for providing a carrier signal at a frequency consistent with the frequency of the cable television channel;

a frequency divider, responsive to the carrier signal oscillator, for providing a sequencing signal;

a first pseudorandom sequence generator, responsive to the sequencing signal, for generating a predetermined pseudorandom chip sequence at a chip rate for transmission on the cable television channel within at least a portion of the spectrum corresponding to the cable television channel;

the spread spectrum data signal generator, responsive to the first pseudorandom sequence generator and the data signal output of the controller, for generating a spread spectrum data signal;

a carrier signal modulator, responsive to the carrier signal oscillator and the spread spectrum data signal generator, for modulating the spread spectrum data signal for transmission over the cable television channel;

a programmable power amplifier for amplifying the modulated spread spectrum data signal output of the carrier signal modulator in accordance with said stepwise digital control signal from the controller;

a quadrature demodulation circuit for removing said spread spectrum data signal from a carrier of the cable television channel;

a Costa loop, responsive to the quadrature demodulation circuit, for synchronization of the quadrature demodulation circuit with the carrier signal modulator;

a second pseudorandom sequence generator for generating a pseudorandom sequence identical to the predetermined pseudorandom chip sequence generated by the first pseudorandom sequence generator;

a digital correlation loop, responsive to the quadrature demodulation circuit, for correlating and synchronizing the pseudorandom chip sequence generated by the second pseudorandom sequence generator with the sequence generated by the first pseudorandom sequence generator; and

a quadrature mixer, responsive to the second pseudorandom sequence generator and the quadrature demodulation circuit, for recovering the data signal from the spread spectrum data signal.

11. The cable television data transmission system of claim 10, the cable television channel being a channel selected within a reverse path frequency band.

12. The cable television data transmission system of claim 10, the spread spectrum data signal generator comprising an Exclusive-OR gate.

13. The cable television data transmission system of claim 10, the carrier signal modulator comprising an Exclusive-OR gate coupled to the programmable power amplifier.

14. The cable television data transmission system of claim 10, the chip rate being at least an order of magnitude greater than the data rate.

15. The cable television data transmission system of claim 11, the cable television channel being channel T7.

16. The cable television claim transmission system of claim 10, wherein the Costa loop synchronizes the quadrature demodulator by mixing with the spread spectrum data signal a generated frequency and by mixing with the spread spectrum data signal a frequency 90°

out of phase with said generated frequency.

17. The cable television data transmission system of claim 16, wherein the Costa loop further comprises a voltage controlled oscillator for generating said generated frequency.