Cable television system with digital reverse path architecture

• US 6,523,177 B1
• Filed: 04/01/1999
• Issued: 02/18/2003
• Est. Priority Date: 04/01/1999
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Brown, Douglas E.
• Primary Examiner(s): Faile, Andrew
• Assistant Examiner(s): HUYNH, AN SON PHI
• Application Number:
  US09/283,498
• Time in Patent Office: 1,419 Days
• Field of Search: 725/105, 725/114, 725/111, 725/117, 725/118, 725/119, 725/121, 725/127, 725/129, 359/125, 359/167
• US Class Current: 725/121
• CPC Class Codes: H04J 14/0226 Fixed carrier allocation, e.g. according to service
• CPC Class Codes: H04J 14/0247 Sharing one wavelength for at least a group of ONUs
• CPC Class Codes: H04J 14/0252 Sharing one wavelength for at least a group of ONUs, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU
• CPC Class Codes: H04J 14/0282 WDM tree architectures
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

A cable television system (100) includes forward and reverse paths. Reverse path circuitry within an optical node (400) of the system (100) receives reverse analog electrical signals from subscriber equipment (140) and generates therefrom a multiplexed reverse digital optical signal. The reverse digital optical signal is transmitted over a fiber optic cable 420 to a cable television hub (430), the reverse path portion of which includes no active circuitry. The hub (430) multiplexes the reverse digital optical signal with other reverse digital optical signals from other nodes to generate one or more forwarded digital optical signals at a hub output, wherein generation of the one or more forwarded digital optical signals requires only passive devices in the reverse path of the hub (430). The hub (430) is coupled to headend equipment (460) by one or more fiber optic cables (445, 450), and the headend equipment (460) receives the one or more forwarded digital optical signals and recovers therefrom the reverse analog electrical signals provided to the optical node (400).

Claims

1. In a cable television (CATV) system including a headend that provides video and data to a plurality of subscriber equipment via a hybrid fiber/coax (HFC) network that includes a fiber portion, a coax portion, and a node for connecting the fiber portion to the coax portion, a reverse path of the HFC network including a digital optical node, a hub, and a headend, the reverse path comprising:

in the digital optical node,

a plurality of inputs for receiving from the coax portion of the HFC network a combined reverse analog RF signal comprising RF reverse path signals from the plurality of subscriber equipment;

a plurality of analog-to-digital (AID) converters each coupled to an input for converting the combined reverse analog RF signal into a reverse digital signal;

a multiplexer for multiplexing the reverse digital signals from the plurality of A/D converters into a single multiplexed digital stream; and

a digital optical transmitter for generating a reverse digital optical signal in accordance with the single multiplexed digital stream; and

in the headend,

a receiver for recovering a digital electrical signal from the reverse digital optical signal;

a demultiplexer for demultiplexing the digital electrical signal to generate demultiplexed signals; and

a plurality of digital-to-analog (D/A) converters for converting the demultiplexed signal to the combined reverse analog RF signal.

2. The CATV system of claim 1, wherein the combined reverse analog RF signal includes video, audio, and data signals.

3. The CATV system of claim 1, further comprising:

in the hub,

a dense wave division multiplexer (DWDM) for multiplexing the single multiplexed digital stream with other single multiplexed digital streams from other digital optical nodes to generate one or more forwarded digital optical signals at a hub output, wherein generation of the one or more digital optical signals in the reverse path.

4. The CATV system of claim 3, wherein the headend further comprises:

a dense wave division demultiplexer for demultiplexing the one or more digital optical signals and for providing the demultiplexed signals to the receiver.

5. The CATV system of claim 1, wherein the digital optical transmitter transmits the reverse digital optical signal at a single wavelength.

6. The CATV system of claim 1, wherein the reverse path further comprises:

in the hub,

an optical splitter for splitting the reverse digital optical signal into two reverse digital optical signals; and

in the headend,

an optical switch for receiving the two reverse digital optical signals and generating therefrom a single reverse digital optical signal.