Ingress Noise Inhibiting Network Interface Device and Method for Cable Television Networks

• US 20100095344A1
• Filed: 10/13/2008
• Published: 04/15/2010
• Est. Priority Date: 10/13/2008
• Status: Active Grant

• Current Assignee: PPC Broadband Incorporated (Belden Inc.)
• Original Assignee: PPC Broadband Incorporated (Belden Inc.)
• Inventors: Halik, Gregory F., Newby, Charles F., Kellogg, Matthew
• Granted Patent: US 9,647,851 B2
• Time in Patent Office: Days
• US Class Current: 725/125
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 12/2898 Subscriber equipments DSL modems H04M11/062; cable modems H04L12/2801
• CPC Class Codes: H04N 21/2402 Monitoring of the downstream path of the transmission network, e.g. bandwidth available traffic monitoring in data switching networks H04L43/00; monitoring data switching networks utilization H04L43/0876
• CPC Class Codes: H04N 21/2408 Monitoring of the upstream path of the transmission network, e.g. client requests monitoring data switching networks utilization H04L43/0876; scheduling or organising the servicing of application requests H04L67/60
• CPC Class Codes: H04N 21/6118 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 7/104 Switchers or splitters

Abstract

Ingress noise from subscriber equipment is mitigated or prevented from reaching a cable television (CATV) network. All upstream signals including ingress noise are initially transmitted to the CATV network whenever their instantaneous power exceeds a threshold which typically distinguishes ingress noise from a valid upstream signal. Whenever the instantaneous power is below the threshold, ingress noise is blocked from reaching the CATV network. A gas tube surge protection device is included to resist component destruction and malfunction arising from lightning strikes and other high voltage, high current surges.

Claims

1. A network interface device for connecting subscriber equipment to a cable television (CATV) network over which downstream signals in a first frequency band from a headend of the CATV network are transmitted to the subscriber equipment and valid upstream signals in a second different frequency band are transmitted from the subscriber equipment to the headend, the network interface device having an upstream noise mitigation circuit which mitigates ingress noise into the CATV network in the second frequency band, comprising:

an upstream filter which filters upstream signals before delivery to the CATV network;

a detector connected to the upstream filter which determines an instantaneous level of power of the upstream signals filtered by the upstream filter, and which supplies a power signal related to the instantaneous power of the upstream signals;

a threshold circuit which establishes a threshold level of power which characterizes valid upstream signals, and which supplies a threshold signal related to the established threshold level of power;

a comparator connected to the detector and the threshold circuit which compares the power signal to the threshold signal, and which asserts a trigger signal when the power signal exceeds the threshold signal;

a switch connected to the upstream filter and having a normal position and an activated position, the normal position isolating and terminating signals from the upstream filter and the activated position conducting the upstream signals from the upstream filter to the CATV network, the switch assuming the activated position in response to the assertion of a control signal and assuming the normal position in response to the de-assertion of the control signal; and

a control circuit connected to the comparator and to the switch, the control circuit asserts a control signal to the switch immediately upon assertion of the trigger signal and de-asserts the control signal to the switch at or after de-assertion of the trigger signal.

2. A network interface device as defined in claim 1, wherein the control circuit further comprises:

a timer receptive of the trigger signal and operative to assert a timing signal for a predetermined time period commencing upon the assertion of the trigger signal; and

wherein;

the control circuit responds to the timing signal to de-assert the control signal when the trigger signal is de-asserted or upon expiration of the predetermined time period.

3. A network interface device as defined in claim 2, wherein:

the predetermined time period established by the timer is approximately as long as an amount of time required to transmit a valid maximum-length upstream signal.

4. A network interface device as defined in claim 3, wherein:

the control circuit de-asserts the control signal after the trigger signal is de-asserted and upon expiration of the predetermined time period.

5. A network interface device as defined in claim 4, wherein the control circuit further comprises:

an integrator circuit which integrates the trigger signal over a predetermined integration time to achieve an integration value; and

wherein;

the control circuit responds to the integration value to de-assert the control signal when the integration value is less than a preestablished value.

6. A network interface device as defined in claim 5, wherein:

the predetermined integration time is less than the predetermined time period.

7. A network interface device as defined in claim 6, wherein:

the control circuit de-asserts the control signal in response to a first one of the following conditions to occur;

(a) the integration value is less than the preestablished value at the end of the predetermined integration time,

(b) at the expiration of the predetermined time period if the trigger signal has been de-asserted at or before the expiration of the predetermined time period, and

(c) at the de-assertion of the trigger signal.

8. A network interface device as defined in claim 7, wherein the control circuit further comprises:

a first timer which establishes the predetermined integration time;

a second timer which establishes the predetermined time period; and

a latch which sets to assert the control signal in response to the assertion of the trigger signal and which resets in response to a reset signal;

a gate which logically combines signals representative of the conditions (a) and (b) and (c) and asserts the reset signal to the latch in response to the first one of the conditions to occur.

9. A network interface device as defined in claim 1, wherein:

the upstream filter constitutes a first upstream filter;

the switch constitutes a first switch;

the first upstream filter is connected to the first switch; and

the noise mitigation circuit further comprises;

a second upstream filter which filters upstream signals before delivery to the CATV network;

a second switch connected to the first switch and to the second upstream filter, the second switch having a normal position and an activated position, the normal position of the second switch terminating the second upstream filter, and the activated position of the second switch conducting the upstream signals from the first switch and the first upstream filter through the second upstream filter to the CATV network; and

wherein;

the first and second switches assume activated positions in response to the assertion of the control signal and assume normal positions in response to the de-assertion of the control signal.

10. A network interface device as defined in claim 9, further comprising:

a signal splitter/combiner connected to the first and second upstream filters which divides downstream signals from the CATV network into active and passive downstream signals within the network interface device and which combines passive upstream signals from passive subscriber equipment and active upstream signals from active subscriber equipment into upstream signals transmitted to the CATV network; and

wherein;

the passive downstream signals are transmitted through the network interface device without substantial conditioning to the passive subscriber equipment and the passive upstream signals are transmitted through the network interface device without substantial conditioning to the CATV network;

the active downstream signals are conditioned when transmitted through the network interface device to the active subscriber equipment and the active upstream signals are conditioned when transmitted through the network interface device to the CATV network;

the active upstream signals are conducted through the first and second upstream filters to the signal splitter/combiner for transmission to the CATV network when the first and second switches are in their activated positions; and

ingress noise in the second frequency band originating from active subscriber equipment is conducted through the first upstream filter and is isolated and terminated when the first switch is in the normal position.

11. A network interface device as defined in claim 9, wherein a drop cable connects the network interface device to the CATV network and the drop cable has a characteristic impedance value, and the upstream noise mitigation circuit further comprises:

a first termination resistor connected to terminate the first upstream filter when the first switch is in the normal position;

a second termination resistor connected terminate to the second upstream filter when the second switch is in the normal position; and

wherein;

the first and second termination resistors have impedance values substantially equal to a characteristic impedance of the drop cable.

12. A network interface device as defined in claim 1, further comprising:

a gas tube surge protection device connected within the network interface device where the upstream and downstream signals are conducted to and from the CATV network, the gas tube surge protection device operative to shunt high voltage and high current surges from the components and subscriber equipment.

13. A network interface device comprising components which conduct upstream and downstream signals to and from a cable television (CATV) network and subscriber equipment, the network interface device further comprising:

a gas tube surge protection device connected within the network interface device where the upstream and downstream signals are conducted to and from the CATV network, the gas tube surge protection device operative to shunt high voltage and high current surges from the components and subscriber equipment.

14. A method of mitigating upstream ingress noise to a cable television (CATV) network, comprising:

transmitting downstream signals in a first frequency band from a headend of the CATV network to subscriber equipment;

transmitting valid upstream signals in a second different frequency band from the subscriber equipment to the headend;

filtering the upstream signals including ingress noise to confine the frequency of the upstream signals to the second frequency band;

determining an instantaneous power content of the upstream signals;

establishing a threshold power level which characterizes valid upstream signals from the subscriber equipment;

comparing the instantaneous power content to a threshold power level;

conducting the filtered upstream signals to the CATV network whenever the instantaneous power content is equal to or greater than the threshold power level; and

preventing the filtered upstream signals from reaching the CATV network when the instantaneous power content is less than the threshold power level.

15. A method as defined in claim 14, further comprising:

conducting the filtered upstream signals to the CATV network for a predetermined time period after the instantaneous power content equals or exceeds the threshold power level.

16. A method as defined in claim 15, further comprising:

establishing the predetermined time period as approximately equal to an amount of time required to transmit a valid maximum-length upstream signal.

17. A method as defined in claim 16, further comprising:

integrating a value representative of the instantaneous power content over a predetermined integration time to arrive at a integration value; and

preventing the filtered upstream signals from reaching the CATV network after expiration of the predetermined integration time if the integration value is less than a predetermined threshold power level.

18. A method as defined in claim 17, further comprising:

establishing the predetermined integration time as less than the length of time required to transmit a single valid minimum-length upstream signal.

19. A method as defined in claim 18, further comprising:

blocking the filtered upstream signals from reaching the CATV network after expiration of a predetermined amount of time after initiation of the predetermined amount of integration time if the integration value is less than a predetermined threshold power level; and

the predetermined amount of time is substantially equal to the amount of time required to transmit a single valid maximum-length upstream signal.

20. A method as defined in claim 14, further comprising:

dividing downstream signals from the CATV network into active downstream signals and passive downstream signals at premises of a subscriber;

transmitting the passive downstream signals to passive subscriber equipment;

transmitting the active downstream signals to active subscriber equipment;

conditioning the active upstream signals from the active subscriber equipment;

not conditioning the passive upstream signals from the passive subscriber equipment;

combining non-conditioned passive upstream signals and the conditioned active upstream signals into upstream signals transmitted to the CATV network;

determining an instantaneous power content of the active upstream signals; and

preventing noise in the second frequency band originating from active subscriber equipment from reaching the CATV network when the instantaneous power content of the active upstream signals is less than the threshold power level.