SYSTEM FOR MINIMIZING UPSTREAM NOISE IN A SUBSCRIBER RESPONSE CABLE TELEVISION SYSTEM

• US 3,750,022 A
• Filed: 04/26/1972
• Issued: 07/31/1973
• Est. Priority Date: 04/26/1972
• Status: Expired due to Term

• Current Assignee: Sam Reisenfeld, Samuel J. Curry
• Original Assignee: Sam Reisenfeld, Samuel J. Curry
• Inventors: Curry, Samuel J., Reisenfeld, Sam
• Primary Examiner(s): Mayer, Albert J.
• Application Number:
  US05/247,622
• Time in Patent Office: 461 Days
• Field of Search: 325/31,51-55,62-65,67,308,309,363 178/5.4TE,DIG.13 328/103,165
• US Class Current: 725/125
• CPC Class Codes: H04B 3/46 Monitoring; Testing
• CPC Class Codes: H04N 7/173 with two-way working, e.g. subscriber sending a programme selection signal

Abstract

A system for substantially reducing the effects of noise and interference in the upstream transmission path of a two-way CATV system. In one embodiment, a local processing center located at the headend of the cable television system locates a noise source and then commands selected phantom subscriber units in the system to close predetermined radio frequency switches to only allow a desired upstream transmission to be passed to the headend and to switch out all other upstream transmission paths not being used.

Claims

1. In a cable television network including a central station, a plurality of remotely located subscriber stations and a cable distribution network for allowing the central station to transmit downstream TV and digital signals to the subscriber stations and to receive frequency bands of upstream digital and TV signals from the subscriber stations, a system comprising:

a plurality of first means coupled to different positions in the cable distribution network, each of said first means only being responsive to command signals specifically addressed thereto from the central station for generating control signals; and

plurality of second means respectively coupled in line at a plurality of different positions in the cable distribution network, each of said second means further coupled to an associated first means and being responsive to first control signals therefrom in a first mode of operation for blocking all upstream signals applied thereto, each of said second means being responsive to the first control signals in a second mode of operation for allowing at least one band of upstream signals to pass therethrough.

2. The system of claim 1 wherein each of said plurality of second means comprises:

a plurality of upstream filters respectively having a plurality of different bandpass frequencies for respectively passing the different bands of upstream digital and TV signals therethrough; and

a plurality of first upstream switches respectively coupled in series with said plurality of upstream filters, each of said first upstream switches being controlled by an associated first control signal to open when the associated first control signal is in a first state and to close when the associated first control signal is in a second state.

3. The system of claim 1 further including:

a plurality of third means, each of said third means being coupled to an associated one of said first means and in series with an associated one of said second means for controlling the amplitude of any upstream signals therethrough in response to second and third control signals from the associated one of said first means.

4. The system of claim 3 wherein each of said third means includes:

fourth means coupled to the associated one of said second means for attenuating any upstream signals therethrough as a function of the second control signals, and fifth means serially coupled between said fourth means and a preselected part of the cable distribution network for amplifying any upstream signals passing through said fourth means as a function of one of the third control signals.

5. The system of claim 4 wherein said central station includes:

sixth means being responsive to excessive upstream noise from any external source injected into the cable distribution network between two adjacent first means for causing the central station to send command signals to said two adjacent first means, one of said two adjacent first means being responsive to the command signals applied thereto for causing its associated fifth means to increase the amplification of any upstream signals passing therethrough by a first predetermined amount, the other one of said two adjacent first means being responsive to the command signals applied thereto for causing its associated fourth means to increase the attenuation of any upstream signals passIng therethrough by a second predetermined amount.

6. The system of claim 4 wherein said fifth means includes an amplifier whose gain is controlled as a function of the amplitude of the third control signal.

7. The system of claim 4 wherein said fourth means includes:

a plurality of attenuators each having a different attenuation, a plurality of second upstream switches respectively coupled in series with said plurality of attenuators, and a third upstream switch, any upstream signals applied to said fourth means being applied to each of said second and third upstream switches, each of said second and third upstream switches being controlled by an associated second control signal to open when the associated second control signals in a first state and to close when the associated second control signal is in a second state, said fourth means operating to allow any upstream signals to pass through only one of said second and third upstream switches at any given time.

8. The system of claim 7 wherein said fifth means includes an upstream amplifier whose gain is controlled as a function of the amplitude of the third control signal.

9. The system of claim 8 wherein each of said plurality of second means comprises:

a plurality of upstream filters respectively having a plurality of different bandpass frequencies for respectively passing the different bands of upstream digital and TV signals therethrough; and

a plurality of first upstream switches respectively coupled in series with said plurality of upstream filters, each of said first upstream switches being controlled by an associated first control signal to open when the associated first control signal is in a first state and to close when the associated first control signal is in a second state.

10. The system of claim 9 wherein said central station includes:

sixth means being responsive to excessive noise from any external source injected into the cable distribution network between two adjacent first means for causing the central station to send command signals to said two adjacent first means, one of said two adjacent first means being responsive to the command signals applied thereto for causing its associated upstream amplifier to increase the amplification of any upstream signals passing therethrough as a function of the amplitude of the associated third control signal, the other one of said two adjacent first means being responsive to the command signals applied thereto for causing its associated fourth means to increase the attenuation of any upstream signals passing therethrough as a function of the first and second states of each of the associated second control signals.

11. The system of claim 9 wherein said central station includes:

sixth means for controlling the operation of said plurality of first means; and

seventh means, coupled to said sixth means, being responsive to excessive upstream noise above a predetermined level in the cable distribution network for enabling said sixth means to selectively command said plurality of first means to block all upstream paths except those necessary to complete upstream signal paths to the central station in order to minimize the reception of upstream noise at the central station.

12. In a cable television network including a television control site and a plurality of remotely located television sites coupled to the television control site by way of a network of cables for allowing the television control site to transmit frequency bands of downstream TV and digital signals to the television sites and to receive frequency bands of upstream digital and TV signals from the television sites, a system for minimizing the reception of upstream noise at the television control site, said system comprising:

a plurality of control units each coupled in line with a cable at a different preselected location of the network of cables for controlling within a range of from complete attenuation to some predetErmined level of amplification the amplitude of any upstream signals applied thereto;

first means located at the television control site for controlling said plurality of control units in a plurality of modes of operation; and

second means, coupled to said first means, being responsive to excessive upstream noise above a predetermined level in the network of cables for causing said first means to initiate a search mode of operation wherein said first means selectively controls each of said plurality of control units to completely attenuate any upstream signals applied thereto in order to try to isolate the excessive upstream noise, said first means going into a first mode of operation whenever the excessive noise is isolated to some location between two adjacent control units in order to cause one of the two said adjacent control units to increase the amplitude of any upstream signals therethrough by a first amount and to cause the other one of the two said adjacent control units to decrease the amplitude of any upstream signals therethrough by a second amount.

13. The system of claim 12 wherein each of said control units includes:

third means coupled to the network of cables for respectively generating first and second control signals during the search and first modes of operation in response to command signals from said first means;

fourth means coupled in line with a preselected cable for increasing the amplitude of any upstream signals therethrough as a function of the first control signals; and

fifth means coupled to said fourth means for decreasing the amplitude of any upstream signals therethrough as a function of the second control signals.

14. The system of claim 13 wherein said first means goes into a second mode of operation whenever the excessive noise cannot be isolated to some location between two adjacent control units and each of said control units further includes:

sixth means in said third means for generating third control signals during the second mode of operation in response to command signals from said first means;

seventh means, coupled in series with said fourth and fifth means, being responsive to the third control signals in a first operational condition for substantially blocking any upstream signals applied thereto, and being responsive to the third control signals in a second operational condition for allowing at least one band of the upstream signals to pass through said control unit, said plurality of control units being selectively controlled by said first means to only open upstream paths in the network of cable that are necessary to allow upstream signals to pass to the television control site in order to minimize upstream noise.

15. The system of claim 14 wherein each of said seventh means includes:

a plurality of upstream filters respectively having a plurality of different bandpass frequencies for respectively passing the different bands of upstream TV and digital signals therethrough; and

a plurality of first upstream switches respectively coupled in series with said plurality of upstream filters, each of said upstream switches being controlled by an associated third control signal to open when the associated third control signal is in a first state and to close when the associated third control signal is in a second state.

16. In a cable television network including a central station, a plurality of remotely located substations and a distribution network for transmitting a plurality of downstream and upstream signals between said central station and said substations, a system comprising:

a plurality of first means coupled to different portions of said distribution network between said central station and said remote substations, each of said first means being capable of generating control signals in response to command signals from said central station; and

a plurality of second means serially disposed in said distribution network, each of said second means furTher coupled to an associated first means and being responsive to control signals therefrom in a first mode of operation for attenuating all upstream signals, each of said second means being further responsive to control signals in a second mode of operation for transmitting at least some of said upstream signals.

17. A cable television system comprising:

a cable distribution network;

a control site coupled to said cable distribution network for transmitting downstream TV and digital signals thereinto;

a plurality of remote sites coupled to said cable distribution network for receiving the downstream TV and digital signal and for selectively transmitting frequency bands of upstream TV and digital signals to said control site;

a plurality of first circuits selectively coupled to said cable distribution network, each of said first circuits responding to command signals specifically addressed thereto by said control site for generating control signals in a plurality of modes of operation, each control signal having first and second operating states; and

a plurality of switching circuits selectively coupled in line with cables in the cable distribution network, each of said switching circuits being responsive to first control signals in a first mode of operation for not allowing any upstream signals to pass therethrough, each of said switching circuits being responsive to first control signals in a second mode of operation for allowing at least one band of upstream signals to pass therethrough, said control site thereby selectively controlling said plurality of switching circuits to close all upstream transmission paths in each frequency band except those paths needed to complete the transmission of upstream signals to said control site.