EP1119968A1

EP1119968A1 - Cable television system for transmitting unmodulated data

Info

Publication number: EP1119968A1
Application number: EP99951954A
Authority: EP
Inventors: James E. Cannella, Jr.; Joseph Graham Mobley; Gerald H. Robinson; Peter K. Van Der Gracht; Donald L. Sipes
Original assignee: Scientific Atlanta LLC
Current assignee: Scientific Atlanta LLC
Priority date: 1998-10-14
Filing date: 1999-10-13
Publication date: 2001-08-01
Also published as: BR9913973A; WO2000022822A1

Abstract

A cable television system (100) includes a transmitter (105) for transmitting a forward signal including a first signal having information within a first frequency range and a second signal having baseband data transmitted in a second frequency range. A node (120) receives the forward signal and splits the first signal from the second signal, and a data processing hub (255), such as an Ethernet hub, processes the second signal to arrange the baseband data into data packets. Subsequently, the first and second signals are recombined as a forward signal that is further transmitted within the cable television system (100). At least one tap (125) is included in the system (100) for splitting off a portion of the forward signal to provide the information and the baseband data at subscriber ports (336) of the tap (125).

Description

CABLE TELEVISION SYSTEM FOR TRANSMITTING UNMODULATED DATA

FIELD OF THE INVENTION

This invention relates generally to cable television systems, and more specifically to the supply of data over a cable television system.

BACKGROUND OF THE INVENTION

Conventional cable television systems include a distribution system for transmitting information to subscribers over optical equipment, electrical equipment, or some combination of the two. In many systems, headend equipment transmits optical information signals over optical fibers to a node, where the optical information signals are converted to electrical signals that are then transmitted over an electrical communication medium, such as coaxial cables. The electrical signals are amplified, as necessary, for further distribution throughout the communication system, and taps situated along the communication medium are used to split off portions of the electrical signals to subscribers of the system. The electrical signals are then processed by subscriber equipment, such as televisions, set top terminals, and computers.

In some more recent cable television systems, modulated data can be also be provided via the cable television distribution system to cable modems that are located in subscriber homes and businesses. A cable modem typically filters the television information from the incoming signal so that the data can be demodulated and then processed by a subscriber's computer.

Although the provision of data over the cable television distribution system occurs at relatively fast speeds as compared to data transmitted over conventional telephone lines, many subscribers are unwilling to purchase and use cable modems. In large part, this is due to the higher cost of cable modems and service over the cable television system. Also, since cable modems are not customarily provided as internal components of personal computer systems, use of a cable modem requires the subscriber to wire an additional stand-alone unit to his or her computer. Given the amount of desk space, wires, and cables that are already required to assemble conventional computers, printers, monitors, scanners, and other data processing equipment, this option is not usually desirable from the subscriber's point of view. A still further problem is that cable modems are often limited in bandwidth. Thus, there exists an opportunity to reduce the costs and inconveniences associated with data distribution over cable television systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a cable television system for transmitting unmodulated data to subscribers according to the present invention.

FIG. 2 is an electrical block diagram of an optical node that is included in the cable television system of FIG. 1 and that has an digital transport hub in accordance with the present invention.

FIG. 3 is an electrical block diagram of a tap that is included in the cable television system of FIG. 1 in accordance with the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a block diagram of a communication system 100, such as a cable television system, for providing information to subscribers of the system 100. The system 100 includes a transmitter, such as headend equipment 105, for transmitting information signals comprising data, video, and audio. The information may be transmitted optically from an optical transmitter 116 over fiber optic cable 1 18 to an optical node 120, where the optical signal is converted into an electrical signal. The electrical signal is further transmitted over an electrical communication medium, such as coaxial cable 122, for distribution throughout the communication system 100 in a downstream, or forward, direction.

In accordance with the present invention, electrical signals from a data source 112, such as an information services provider, can also enter the communication system 100. This can be done, for instance, by using a directional coupler 114, diplex filter, or other signal combiner to combine the forward electrical signal that originates from the cable television headend equipment 105 with the unmodulated data signal that originates from the data source 112. Alternatively, the data source 112 can be included as a part of the headend equipment 105, such as through use of a cable modem termination shelf (CMTS). The unmodulated forward data signal is preferably baseband data transmitted according to some standard or proprietary digital link protocol, which could, for instance, comprise an Ethernet protocol. Portions of the forward electrical signal are then split off by taps 125 to subscriber equipment 130, such as computers, televisions, and set top terminals. As mentioned, the data provided by the data source 1 12 is preferably baseband and is also preferably unmodulated. According to the present invention, the term "unmodulated" as used herein means that the data is not frequency translated. Another other forms of modulation may be present for transmission of the baseband data signal.

The forward electrical signal that is optically transmitted over the fiber optic cable 118 has two components, i.e., the broadband cable television signal from the headend equipment 105 and the baseband data signal from the data source 112. The cable television signal can be transmitted over channels within a conventional cable television frequency range, such as 50 to 750 MHz or higher. The data signal is preferably transmitted as Manchester encoded baseband data centered at a 10 Mbps data rate, or at approximately 10 MHz. When the cable television system provides reverse, or upstream, transmission of data from subscriber equipment 130 to the headend equipment 105, care should be taken that the frequency channel selected for downstream unmodulated data transmission is not used for reverse transmissions or for transmission of the downstream cable television information. Since many two-way cable television systems provide data transmissions in the frequency range of 20 to 50 MHz, the unmodulated data signal can, for instance, be transmitted in the forward direction on a 6 MHz channel centered at 10 MHz.

According to the present invention, the optical node 120 includes an Ethernet repeater hub or an Ethernet packet switching hub for processing the downstream baseband data signal for further distribution throughout the system 100. Ethernet repeaters, bridges, and/or switches may be present in other system locations, such as within one or more of the taps 125, for correcting signal deficiencies introduced by lengthy communication links or for many other reasons, such as those related to security or separation.

FIG. 2 shows an optical node 120 for processing the unmodulated data signal transmitted to the node 120 in the forward direction. The forward optical signal, including unmodulated data and modulated cable television information components, is provided to the node 120 via input port 205. The forward optical signal is converted to a forward electrical signal by optical receiver 220 then processed by highpass and lowpass filters 224, 226. The highpass filter 224 preferably passes only the cable television portion of the signal to a forward amplifier 235 and then to another highpass filter 240. The baseband data signal is provided to a data processing hub 255 via the lowpass filter 226. The data processing hub can be, for example, an Ethernet hub that receives baseband data in the forward direction. Such baseband data can already be configured according to an Ethernet protocol, although other baseband data protocols could alternatively be used. If received data is not already configured in an Ethernet protocol, the Ethernet hub 255 arranges the data into Ethernet data packets that are transmitted at approximately 10 Mbps to a lowpass filter 244. The higher frequency amplified cable television signal is then recombined with the lower frequency data signal, which has been processed by hub 255, on the downstream side of the highpass and lowpass filters 240, 244. The combined information is transmitted from the node 120 as a forward signal via port 215, which is coupled back into the cable television distribution system.

The optical node 120 can, if desired, also process reverse information that is transmitted in the upstream direction. Reverse information, as mentioned above, can comprise return cable television information in the 20-50 MHz range as well as return data at approximately 10 MHz. The reverse signal is provided at port 215. The lower frequency unmodulated data provided by subscriber equipment 130 (FIG. 1) is passed by the lowpass filter 244 to the Ethernet hub 255, which processes the data and forwards it to lowpass filter 252.

The return cable television signals, which are modulated and provided at the middle frequency range of about 20-50 MHz, are transmitted as a part of the reverse signal and are passed by the bandpass filter 242 to reverse amplifier 245. The amplified reverse signal is then filtered by another filter 250. Outputs of the filter 250 and the lowpass filter 252 are coupled to an optical transmitter 222, which converts the reverse electrical signal to an optical signal that is transmitted upstream via output port 210 of the node 120. Within the node 120, highpass filter 224 and lowpass filter 226 can be included in a diplex filter 230. Highpass filter 224 should be configured to pass frequencies at which the forward cable television signal is transmitted, e.g., frequencies of about 50 MHz and greater. Lowpass filter 226 should be configured to pass frequencies at which the unmodulated data signal is transmitted in the forward direction, e.g., frequencies below 50 MHz. Filter 250, which could be either a bandpass filter for passing signals of approximately 20-50 MHz or a highpass filter for passing signals of about 20 MHz and greater, and lowpass filter 252, which should pass return unmodulated data signals centered at about 10 MHz, can be similarly included in a diplex filter 250. Highpass filter 240, bandpass filter 242, and lowpass filter 244 can also be included in a single filter package, i.e., a "triplex" filter. Highpass filter 240 should pass forward cable television frequencies, e.g., frequencies of 50 MHz and greater. Bandpass filter 242 should pass return cable television frequencies, e.g., frequencies from 20 up to about 50 MHz, and lowpass filter 244 should pass forward and return unmodulated data signal frequencies, e.g., frequencies of less than 20 MHz. One of ordinary skill in the art will recognize that traditional "highpass", "lowpass", and "bandpass" filters may not be necessary. Instead, any frequency selective devices that accomplish the separation of a desired signal(s) from other signals may be alternatively used. Other low loss coupling devices could be used under some circumstances to split and recombine signals when frequency selection is unnecessary. Furthermore, it will be appreciated that the frequency ranges for the different signals in the system 100 are examples only. The forward and reverse baseband data signals, the forward broadband cable television signal, and the reverse cable television signal can be sent using any data rates and any frequency or frequencies that can be separated from one another by the various processing devices described herein in the node 120, the tap 125, and the headend 105.

Although the system 100 has been described as sending signals that are separated in frequency, other signal separation schemes are envisioned. For example, the forward and reverse baseband data signals, the forward broadband cable television signal, and the reverse cable television signal could be time division multiplexed, in which case many, if not all, of the frequency selective devices could be replaced with devices for recovering signals on a time basis, rather than a frequency basis.

The Ethernet hub 255 preferably functions as a data converter, in addition to any other data processing functions resident therein. More specifically, baseband data to and from the headend equipment 105, i.e., on the upstream side of the hub 255, is transmitted using an optical Ethernet protocol, such as l OBaseFP, lOBaseFB, or lOBase FL, or using another baseband digital link protocol, such as the conventional point-to-point protocol (PPP) or the proprietary 10 Mbps Swif Link protocol owned by Scientific- Atlanta, Inc. Alternatively, baseband data may be provided to or from the hub 255 as a first protocol and then converted to or from a protocol-free baseband signaling protocol such as 10Mbps Manchester.

Baseband data to and from subscriber equipment 130, i.e., on the downstream side of the hub 255, is preferably transmitted using an electrical Ethernet protocol, such as 10Base2 or lOBaseT modified for 75 ohms. The 10Base2 protocol is particularly suitable since coaxial cables are customarily used to transmit electrical signals within cable television systems. The Ethernet hub 255 translates between data protocols utilized on the upstream side of the hub 255 and those used on the downstream side of the hub 255. It will be appreciated that other types of data switches could be alternatively used if Ethernet data transmission is not employed within the node 120. It will further be appreciated that the Ethernet hub 255 may provide multiple outputs in both upstream and downstream directions if additional routing capabilities are desired.

When cable lengths within the cable television system 100 are not too long, taps 125 within the system 100 may be conventional in configuration and manufacture. However, if cable lengths are relatively long, Ethernet repeaters, bridges, or switches may need to be provided within the distribution system. A location that may be suitable for such devices is within one or more taps 125.

Referring next to FIG. 3, a tap 125 that includes an Ethernet device is depicted. The tap 125 includes an input port 302 at which forward signals are received and from which reverse signals are transmitted. The forward signal is provided to a diplex filter 304, which includes a highpass filter 308 for passing the forward cable television signal and a lowpass filter 306 for passing the unmodulated data signal. The cable television signal is passed through the tap to a main output port 303 via a highpass filter 318 portion of another diplex filter 314. A portion of the cable television signal is split off by directional couplers 312, 320 for subsequent transmission to subscriber ports, or "drops," 336 via highpass filters 324, 330, which may be formed as a part of diplex filters 326, 332.

The lowpass filter 306 provides the lower frequency unmodulated data signal to an Ethernet device 310, such as a repeater, bridge, or switch, that corrects for electrical defects in the signal or that could perform packet filtering. The forward unmodulated data signal is then provided to lowpass filters 322, 328 of diplex filters 326, 332. The diplex filters 326, 332 combine the forward cable television signal and the forward unmodulated data signal into a single forward signal that is provided to subscriber drops 336, which are conveniently coupled to subscriber equipment included in the subscriber home or business by a single coaxial cable 338. Within the subscriber premises, the forward signal is split by diplex filter 340, which includes a highpass portion 342 for providing the cable television signal to conventional cable television equipment 346. A lowpass portion 344 provides the unmodulated data signal to a standard Ethernet interface 350 coupled to or included within a host device, such as a computer 352. When the data is transmitted using a 10Base2 Ethernet protocol, an Ethernet converter 348 may be used, if necessary, to convert the data to lOBaseT prior to transmission to the computer 352.

As mentioned above, the host device 352 can provide reverse data, preferably at a data rate of about 10 Mbps, and the cable television equipment 346 can also provide reverse information, preferably in the frequency range of 20-50 MHz. These return signals are combined by diplex filter 340 and provided at subscriber port 336 via the coaxial cable 338. Diplex filter 326 splits the reverse signal into lower frequency signals, i.e., the baseband data signals at about 10 Mbps, and higher frequency signals, i.e., the modulated cable television signals at about 20 MHz to a frequency less than 50 MHz. The return cable television signals are routed through couplers 320, 312 to highpass filter 308, and the return data signals are routed to the Ethernet device 310 and then to lowpass filter 306. Diplex filter 304 combines the reverse components into a single reverse electrical signal that is provided, via port 302, to the node 120 (FIG. 2) for further processing.

As described in reference to the tap 125 and FIG. 3, highpass filters 308, 318, 324, 330, 342 are preferably configured to pass both forward and reverse cable television signal frequencies, e.g., frequencies of greater than approximately 20 MHz. Lowpass filters 306, 316, 322, 328, 344 should pass forward and reverse unmodulated data signals of approximately 10 Mbps.

It will be appreciated that a primary purpose of the Ethernet device 310 and its related diplex filters 304, 314, 326, 332, 340 is to extend transmission distance and perhaps also provide address filtering and that, in smaller systems, none of this additional tap circuitry may be required. Even in larger systems, the Ethernet device 310 and diplex filters may be needed in only one out of every few taps within the system.

According to the present invention, the cable television system 100 includes circuitry that permits the transmission of unmodulated data directly from a data source, such as an ISP, to the subscriber so that no modems are required at the transmitting end or at the receiving end. As a result, the subscriber need not purchase a cable modem at all. which translates into less expensive cable services for consumers. Additionally, a subscriber who wishes to receive data over a cable television distribution system need not purchase a separate stand-alone unit that has to be wired into his or her computer. Instead, all circuitry for data processing is physically located external to the subscriber's premises in the node, and perhaps in the tap, so that no additional space within the premises is required. Preferably, the only equipment that is located in the subscriber's work area is the conventional Ethernet interface 350. which can be incorporated within the computer 352.

What is claimed is:

Claims

1. A cable television system, comprising: a transmitter for transmitting a first signal including information within a first frequency range; a combiner coupled to the transmitter and a data source for combining the first signal with a second signal which includes baseband data transmitted in a second frequency range to generate a forward signal for transmission over a communication medium; a node for splitting the first signal from the second signal, the node comprising a data processing hub for processing the second signal to arrange the baseband data into data packets, subsequent to which the first and second signals are recombined into the forward signal for further transmission wi÷hin the cable television system; and at least one tap for splitting off a portion of the forward signal to provide the information and the baseband data at subscriber ports of the at least one tap.

2. A node for use in a cable television system, the node comprising: an input port for receiving a forward optical signal comprising an information signal in a first frequency range and an unmodulated data signal in a second frequency range; an optical receiver for converting the forward optical signal into a forward electrical signal; a data processing hub for processing the unmodulated data signal to arrange data included therein into data packets; a combiner coupled to an output of the data processing hub for combining the unmodulated data signal, after processing by the data processing hub, with the information signal; and an output port coupled to the combiner for providing the forward electrical signal for further transmission from the node.

3. The node of claim 2, wherein the data processing hub comprises an Ethernet hub.

4. The node of claim 3, wherein the unmodulated data signal received in the forward optical signal is configured according to a first signal protocol, and wherein the Ethernet hub converts from the first signal protocol to a second signal protocol according to which the unmodulated data signal provided in the forward electrical signal is arranged.

5. The node of claim 3, further comprising: a first filter coupled to the optical receiver for splitting the information signal from the unmodulated data signal and for providing the unmodulated data signal to the Ethernet hub.

6. The node of claim 3, further comprising: a second filter for combining the information signal with the unmodulated data signal, after processing by the Ethernet hub, to provide the forward electrical signal at the output port.