Full Duplex Bidirectional Transmission on Coaxial Cable in CATV Network

Abstract

Systems and methods for achieving full duplex bidirectional transmission across coaxial cable in a hybrid fiber-coaxial cable TV network. Some preferred systems and method will attenuate reflections propagated within the coaxial cable. Other preferred systems may echo-cancel reflections propagated within the coaxial cable.

1 . An Optical Network Unit (ONU) comprising a first input receiving a downstream optical signal from a head end and a plurality of high isolation ports each receiving a respective upstream RF coaxial signal from, and transmitting a respective downstream RF coaxial signal to, a respective one of a plurality of subscribers, each high isolation port capable of attenuating RF reflections. 
     
     
         2 . The ONU of  claim 1  having an RF splitter and an active amplifier interposed between the RF splitter and each high isolation port, the active amplifier amplifying signals in the downstream direction. 
     
     
         3 . The ONU of  claim 2  including a directional coupler between each active amplifier and its associated high isolation port. 
     
     
         4 . The ONU of  claim 1  including a combiner and a switched filter between the combiner and the splitter. 
     
     
         5 . The ONU of  claim 4  where the high isolation port where the switched filters reject reflections at low frequencies. 
     
     
         6 . A system comprising:
 a head end;   an Optical Network Unit (ONU) comprising a first input receiving a downstream optical signal from the head end and a plurality of ports each receiving a respective upstream RF coaxial signal from, and transmitting a respective downstream RF coaxial signal to, a respective one of a plurality of subscribers; and   a plurality of cable modems each connected to a respective one of the plurality of ports, where the ONU attenuates reflections of the downstream signal from at least one of the plurality of cable modems.   
     
     
         7 . The system of  claim 6  where at least one cable modem echo cancels reflections. 
     
     
         8 . The system of  claim 6  where the CMTS echo cancels reflections. 
     
     
         9 . The system of  claim 6  where at least one cable modem discards a range of frequencies in the downstream signal and uses that range to transmit an upstream signal. 
     
     
         10 . The system of  claim 9  where the range of frequencies is between 100-200 MHz. 
     
     
         11 . The system of  claim 6  where at least one cable modem transmits an upstream signal at a frequency range above that of the downstream signal. 
     
     
         12 . The system of  claim 6  where the ONU attenuates reflections using at least one of: (i) an active amplifier; and (2) a switched filter. 
     
     
         13 . A method comprising:
 propagating a downstream signal from a head end to each of a plurality of subscribers through an ONU connected to the head end by an optical cable and each of the plurality of subscribers by an RF coaxial cable;   propagating respective upstream signals from each of the plurality of subscribers through the ONU to the head end; and   isolating RF reflections in the ONU.   
     
     
         14 . The method of  claim 13  including the step of canceling reflections at a selective one or more of the head end and a cable modem of at least one of the plurality of subscribers. 
     
     
         15 . The method of  claim 13  where the reflections are isolated by an active amplifier in the ONU positioned between an RF input to a subscriber and a splitter. 
     
     
         16 . The method of  claim 15  including the step of directing upstream signals to a second amplifier using a directional splitter. 
     
     
         17 . The method of  claim 13  including the step of filtering the respective upstream signals from the plurality of subscribers and subsequently combining the filtered upstream signals. 
     
     
         18 . The method of  claim 13  including the step of discarding a range of frequencies in the downstream signal and uses that range to transmit an upstream signal. 
     
     
         19 . The method of  claim 18  where the range of frequencies is between 100-200 MHz. 
     
     
         20 . The method of  claim 13  including the step of transmitting an upstream signal at a frequency range above that of the downstream signal. 
     
     
         21 . The method of  claim 13  including the step of transmitting an upstream signal in a frequency overlapping with that of the downstream signal.