Technique for reverse transport of data in a hybrid fiber coax cable system
In a hybrid fiber coax (HFC) cable system, data is communicated upstream from user terminals to a headend of the system to realize various interactive services. The user terminals generate analog modulated signals representing the user data, which populate different channels in a reverse passband of the system. In accordance with the invention, the analog modulated signals are transformed to the corresponding digital baseband signals containing the data. The resulting digital baseband signals are optically transmitted to the headend, thereby efficiently utilizing the limited capacity of the fiber optical portion of the HFC cable system.
1. A system in a headend of an HFC cable arrangement, the system comprising:
an optical receiver for converting an upstream optical signal to a composite baseband signal representing a plurality of information streams;
a demultiplexing device responsive to the composite baseband signal for generating the plurality of information streams;
a plurality of modulators, coupled to said demultiplexing device, each of the plurality of modulators corresponding to a different one of the plurality of information streams, each modulator for producing a corresponding modulated analog signal from one of said plurality of information streams;
a combiner for combining a plurality of modulated analog signals generated by said modulators to produce a combined modulated analog signal; and
a subsystem for processing the combined modulated analog signal to realize the service.
2. The system of claim 1 ,
wherein the upstream optical signal includes data from a plurality of different user terminals; and
wherein the subsystem for processing recovers data from respective ones of the different user terminals and reformats the recovered data into Internet Protocol (IP) packets as part of an interactive service.
3. The system of claim 1 wherein the at least one information stream includes data bits.
4. The system of claim 1 further comprising an apparatus for providing cable television, which is different from the service.
5. The system of claim 4 wherein a signal representing the cable television travels in a direction different from that of the optical signal in the HFC cable arrangement.
6. The system of claim 1 wherein the subsystem includes a device for modulating a designated carrier with the at least one information stream to form a modulated signal.
7. The system of claim 1 wherein the subsystem includes a cable modem termination system (CMTS).
8. The system of claim 7 wherein the CMTS includes an analog input interface.
9. The system of claim 1 wherein the composite baseband signal is encoded in accordance with an error correction coding technique.
10. The system of claim 1 , wherein said subsystem for processing the combined modulated analog signal has an analog input interface for receiving said combined modulated analog signal.
11. The system of claim 1 ,
wherein said headend is coupled to a distribution node by an optical fiber which supplies said optical receiver with said upstream optical signal and which receives a downstream optical signal from said headend.
12. A method of operating a headend of an HFC cable arrangement, the method comprising:
receiving an upstream optical signal;
converting the received upstream optical signal to a composite baseband signal representing a plurality of information streams;
generating from the composite baseband signal, the plurality of information streams;
modulating at least some of said plurality of information streams to produce modulated analog signals, a separate modulated analog signal being produced from each of said at least some of said plurality of information streams;
combining a plurality of said separate modulated analog signals generated to produce a combined modulated analog signal;
and processing the combined modulated analog signal to realize the service.
13. The method of claim 12 ,
wherein the upstream optical signal includes data from a plurality of different user terminals; and
wherein processing the combined modulated analog signal to realize the service includes:
recovering data from respective ones of the different user terminals from said combined modulated signal and reformatting at least some of the recovered data into Internet Protocol (IP) packets as part of an interactive service.
14. The method of claim 12 wherein the at least one information stream includes data bits.
15. The method of claim 12 wherein in processing the at least one information stream, a designated carrier is modulated with the at least one information stream to form a modulated signal.
16. The method of claim 12 wherein the composite baseband signal is encoded in accordance with an error correction coding technique.
17. The method of claim 12 , wherein
modulating at least some of said plurality of information streams includes modulating each of the at least some of said plurality of information streams using a different carrier frequency corresponding to a separate channel.
18. The method of claim 17 , wherein
processing the combined modulated analog signal to realize the service includes:
recovering data from individual user terminals; and
reformatting the data into Internet Protocol packets.
19. The method of claim 17 , wherein processing the combined modulated analog signal to realize the service includes:
recovering data from individual user terminals; and
reformatting the data into ATM cells.
20. The method of claim 12 ,
wherein receiving said upstream optical signal includes receiving said upstream optical signal from a distribution node which is coupled to the headend by an optical fiber, said distribution node being coupled to a plurality of user terminals.