Single wire return device in a fiber to the home system

The present application incorporates by reference in its entirety herein copending U.S. provisional application having Ser. No. 60/441,462, which was filed on Jan. 21, 2003.

This invention relates in general to broadband communications systems, and more particularly, to the field of set-top terminals and a networked multimedia system.

Conventionally, broadband communications systems, such as cable television systems, provide cable television signals and related services including interactive media, telephony signals over a hybrid fiber/coax system. FIG. 1 illustrates a conventional broadband communications system for transmitting forward and reverse audio/video and data signals. In a headend facility 105 , a digital network control system (DNCS) 110 transmits and receives signals from a plurality of digital home communications terminals (DHCTs) 145 installed in the system. In the downstream path, or forward path, signals (e.g., audio/video signals or data signals) are modulated by a quaternary phase shift keying (QPSK) downstream modulator 115 . It will be appreciated that though only one downstream modulator 115 is shown, there are typically many modulators in the headend facility 105 . The signals are typically converted into optical signals and transported over a fiber medium 120 to a node 125 . The node 125 , in a known manner, converts the optical signals into radio frequency (RF) signals for further transmission over coaxial cable 130 . Taps 135 , or splitters, split the signal and transmit the split signal to a plurality of subscriber premises 140 . It will be appreciated that each premises 140 can include a plurality of DHCTs 145 . Each DHCT 145 then receives the forward signals, which is either broadcast to several DHCTs 145 or transmitted to a specific DHCT 145 , and an internal QPSK demodulator 150 demodulates the signal in order to provide an appropriate format for viewing and hearing the signals.

In the upstream path, or reverse path, reverse signals (e.g., data or control signals) originating in the DHCT 145 are modulated with a QPSK modulator 155 and transmitted upstream to a QPSK demodulator 160 ( a - n ) located in the headend facility 105 . Several demodulators (e.g., eight demodulators) are collocated with and each directly coupled to the QPSK downstream modulator 115 via a cable. If a DHCT 145 sends a reverse control signal that requests return signals, the appropriate downstream modulator 115 that is associated with the sending DHCT 145 responds due to a direct coupling between a DHCT 145 , a demodulator 160 , and a modulator 115 .

FIG. 2 illustrates an example of a fiber-to-the-home (FTTH) system 200 . As products and technology evolved, the coaxial cable 130 was replaced with fiber cable 120 that runs directly to the premises 145 . A headend facility 205 , which can be operated by a cable operator or a telephone operator, delivers telephone, audio/video, and data signals over fiber cable 210 to the premises 215 . A fiber splitter 220 may be used to route fiber cable 210 to a plurality of premises 215 . An optical network terminal (ONT) 225 receives the signals and provides the signals to a plurality of output ports depending upon the type signal. For example, one port may be used for plain old telephone service (POTS); another port may deliver audio/video signals over coaxial cable to a DHCT 230 ; and a further port may be used to route Ethernet, or data, signals to computers.

In the headend facility 205 , the QPSK downstream modulator 115 provides audio/video signals, which are typically radio frequency (RF) signals to an optical network 235 . The optical network 235 converts the RF signals into optical signals for transport through the network. An Internet protocol (IP) network 245 receives any Internet signals from connected equipment and routes them to the optical network 235 for transport through the network.

Despite the advantages of running fiber to an ONT 225 in the forward path, there are disadvantages in the reverse path. For example, the DHCT 230 is not able to send reverse RF signals in an FTTH system 200 as in the conventional HFC system 100 of FIG. 1 . One reason is that the ONT 225 currently has a limit of only two wavelengths that are used to receive and transmit signals and cannot, therefore, transmit reverse RF signals. It is possible to work around this weakness by converting the RF signals in the DHCT 230 to Ethernet signals and running an Ethernet cable 235 from each DHCT 230 to the ONT 225 , thereby sending Ethernet signals rather than RF signals. An Ethernet connector (not shown) on the DHCT 230 then transmits the Ethernet signals to the ONT 225 where they are converted into optical signals and then transmitted to the HE 205 . Supplying DHCTs 230 with Ethernet connectors and running Ethernet cable from each DHCT 230 to the ONT 225 , however, is extremely costly and laborious. What is needed, therefore, is a method and apparatus that allows the DHCT 230 to efficiently transmit reverse RF signals in a FTTH system 200 .

The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. In the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 illustrates a conventional broadband communications system for transmitting video and audio signals.

FIG. 2 illustrates an example of a fiber-to-the-home (FTTH) system.

FIG. 3 illustrates the single wire return device in accordance with the present invention in an FTTH system.

FIG. 4 illustrates an example of a downstream modulator address including additional header information and the payload data that is converted into an IP address.

Preferred embodiments of the invention can be understood in the context of a broadband communications system and a local network. Note, however, that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. For example, transmitted broadband signals include at least one of video/audio, telephony, data, or Internet Protocol (IP) signals, to name but a few. Furthermore, the DHCTs can operator independently or as remote devices in a premises network. All examples given herein, therefore, are intended to be non-limiting and are provided in order to help clarify the description of the invention.

The present invention is directed towards a device that efficiently transmits signals in a FTTH system. More specifically, a single wire return device (SWRD) located at a subscriber premises transmits and receives forward and reverse signals, respectively, between an ONT and at least one DHCT. The SWRD is a data conversion device that receives Internet protocol (IP) over DAVIC QPSK from a DHCT, demodulates the QPSK signals, processes the IP packets, and forwards the packets on an Ethernet network to a headend facility. Advantageously, by using the SWRD, the requirement for an Ethernet cable connecting a DHCT to an ONT in order to transmit the reverse signals is no longer necessary. Additionally, hardware changes to the ONT and DHCTs are not necessary in order to implement the present invention.

FIG. 3 illustrates the single wire return device 310 in accordance with the present invention in an FTTH system 300 . In the forward path, the ONT 225 continues to receive optical signals provided by a headend facility 305 . Telephone signals are provided directly to connected telephones in a known manner. Ethernet signals and audio/video signals, however, are provided to the SWRD 310 . An Ethernet switch 350 is coupled to the ONT 225 that receives and provides Ethernet signals to a computer. Audio/video signals (i.e., RF signals) are provided to a diplex filter 315 , where a highpass filter isolates the forward signals, which are typically provided in the range from 45 MHz to 870 MHz. The diplex filter 315 may be coupled to a splitter 320 , for example, that then splits the forward signal for transmission to a plurality of DHCTs 325 . A QPSK demodulator 330 demodulates the forward signals for subsequent processing.

In the reverse path, the DHCTs 325 modulate the reverse signals via a QPSK modulator 335 . The modulated RF signals are transmitted from the common forward-reverse coaxial port instead of transmitting reverse Ethernet signals via the Ethernet port as illustrated in FIG. 2 . If necessary, the splitter 320 combines the signals from the plurality of DHCTs 325 . The reverse signals are provided to the diplex filter 315 and isolated by a low pass filter since reverse signals are typically provided in the range from 5 MHz to 40 MHz. The isolated reverse signals are subsequently provided to a QPSK upstream demodulator 340 for demodulation. A microprocessor 345 then converts the demodulated signals into Ethernet signals. The Ethernet switch 350 then receives the Ethernet signals and combines the reverse signals with other reverse signals, such as signals from the computer located in the premises. The combined signals are subsequently provided to the ONT 225 for conversion to optical signals and transmission over the fiber network.

At the headend facility 305 , an optical network 355 receives the reverse optical signals and, via an Internet Protocol network 360 , provides the signals either to a QPSK downstream modulator 365 or other processing equipment (not shown). In the event the reverse signals are control messages, such as power calibration of the DHCT 325 or DAVIC sign-on messaging, the QPSK downstream modulator 365 receives the control signals. The QPSK downstream modulator 365 modulates the signals and responds accordingly via the optical network 355 .

As mentioned, there are a plurality of downstream modulators 365 a - n that typically serve different areas of the system where each area has different multiple upstream demodulators 340 . Conventionally, the upstream demodulators 340 were collocated, so there was no problem in identifying which downstream modulator 365 a - n needed to respond. In the present invention, however, the downstream modulator 365 is not directly coupled to the upstream demodulator 340 , thereby requiring identification of an associated modulator 365 a - n.

A preferred embodiment of the present invention utilizes fields in header information and inserts the modulator 365 a - n address at the DHCT 325 . It will be appreciated that header information attaches to the data packets for several reasons, such as identifying the packets or identifying a specific DHCT 325 , to name a couple reasons. Accordingly, in addition to the existing header information, the DHCT 325 adds its associated modulator address to the header information in accordance with the present invention. A DHCT 325 receives its associated downstream modulator 365 a - n address, or identification number, at some time and stores that address in memory. The modulator 365 a - n identification is then mapped or converted into an IP address prior to transmission by the SWRD 310 .

FIG. 4 illustrates an example of a downstream modulator address 405 including additional header information and the payload data that is converted into the IP address 410 . When the DHCT 325 sends a reverse signal, the microprocessor 345 in the SWRD 310 converts the downstream modulator address 405 into an IP address 410 . The microprocessor in the SWRD 310 can use the standard ‘gethostbyname’ to map the modulator ID (identification) into an IP address. The underlying network layer may use various methods to convert the modulator ID into an IP address. These methods include a local table loaded into the SWRD 310 or a Domain Name System (DNS) query.

Accordingly, a system and device has been presented that efficiently transmits reverse signals from a plurality of DHCTs 325 to a QPSK downstream modulator 365 . Importantly, the requirement for Ethernet cabling from each DHCT 325 to the ONT 225 has been eliminated. It will be appreciated, however, that related embodiments could be implemented without departing from the scope of the present invention. For example, a different modulation format can be used rather than QPSK. The following claims are intended to capture the invention in light of the detailed information above.