Cable television system with digital reverse path architecture

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 ).

What is claimed is:  
     
         1 . A cable television system for providing signals, the cable television system comprising: 
 forward and reverse paths;    an optical node for receiving a reverse analog electrical signal from subscriber equipment and for generating therefrom a reverse digital optical signal;    a hub for multiplexing 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 in the reverse path of the hub does not require active receivers and transmitters within the hub; and    headend equipment coupled to the hub for receiving the one or more forwarded digital optical signals and for recovering therefrom the reverse analog electrical signal provided to the optical node.    
     
     
         2 . The cable television system of  claim 1 , wherein the reverse path of the hub includes only passive devices.  
     
     
         3 . The cable television system of  claim 2 , further comprising: 
 a fiber optic cable coupled between the optical node and the hub.    
     
     
         4 . The cable television system of  claim 2 , further comprising: 
 one or more fiber optic cables coupled between the hub and the headend equipment.    
     
     
         5 . The cable television system of  claim 2 , wherein the reverse path of the optical node includes: 
 an input port for receiving the reverse analog electrical signal;    analog-to-digital (A/D) converters coupled to the input port for converting the reverse analog electrical signal into digital electrical signals;    a time division multiplexer coupled to the A/D converters for interleaving the digital electrical signals to generate a digital bit stream; and    a digital optical transmitter for generating the reverse digital optical signal in accordance with the digital bit stream.    
     
     
         6 . The cable television system of  claim 5 , wherein the digital optical transmitter of the optical node transmits the reverse digital optical signal at a wavelength of 1550 nanometers.  
     
     
         7 . The cable television system of  claim 5 , wherein the reverse path of the optical node includes two or more A/D converters.  
     
     
         8 . The cable television system of  claim 2 , wherein the reverse path of the hub includes: 
 a dense wave division multiplexer (DWDM) for receiving the reverse digital optical signal and the other reverse digital optical signals to generate a single digital optical signal; and    an optical splitter coupled to the DWDM for splitting the single digital optical signal into the one or more forwarded digital optical signals.    
     
     
         9 . The cable television system of  claim 2 , wherein the headend equipment includes: 
 an optical switch for receiving the one or more forwarded digital optical signals and generating therefrom a single digital optical signal;    a DWDM for demultiplexing the single digital optical signal to generate a plurality of digital optical signals;    a receiver coupled to the DWDM for recovering a digital electrical signal from one of the plurality of digital optical signals;    a time division demultiplexer coupled to the receiver for demultiplexing the digital electrical signal to generate demultiplexed signals; and    digital-to-analog (D/A) converters coupled to the time division demultiplexer for converting the demultiplexed signals to the reverse analog electrical signal.