CA2407321A1 - Two way cable system with noise-free return path - Google Patents
Two way cable system with noise-free return path Download PDFInfo
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- CA2407321A1 CA2407321A1 CA002407321A CA2407321A CA2407321A1 CA 2407321 A1 CA2407321 A1 CA 2407321A1 CA 002407321 A CA002407321 A CA 002407321A CA 2407321 A CA2407321 A CA 2407321A CA 2407321 A1 CA2407321 A1 CA 2407321A1
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- frequency band
- signals
- feeder line
- cable system
- high frequency
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/22—Adaptations for optical transmission
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/10—Adaptations for transmission by electrical cable
- H04N7/102—Circuits therefor, e.g. noise reducers, equalisers, amplifiers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N7/17309—Transmission or handling of upstream communications
Abstract
The return path for a signal in a cable system uses a portion of the 50-750 MHz frequency band to send signals from each set-top box therein to a receiver at the feeder line end. A band stop filter is placed in each auxiliary feeder line to prevent the return signal from set-top boxes being received by more than one feeder line end. The feeder line end has a receiver for the signal from set-top boxes and a means to transmit the signal back to the headend via various mediums. The size of the return path is operator selectable. Further more this system eliminates virtually all ingress noise picked up by the collection of set-top boxes, home wiring and drop wiring entering the cable system.
Description
WO 01/82618 PCT/CA01/OO~s6 TWO WAY CABLE SYSTEM WITH NOISE-FREE RETURN PATH
REFERENCE TO RELATED APPLICATIONS
This application is a Continuation in Part of Application Serial No. 09/541, filed April 3, 2000 to the applicant of the present application.
FIELD OF THE INVENTION
This invention relates to cable systems and more particularly to such systems with a sufficiently noise free return path to support high bandwidth two-way broadband, multimedia content delivery to and from the home.
BACKGROUND OF THE INVENTION
It is well known that the return path in a cable system is noisy and is frequently referred to as a "noise funnel". There are three primary sources of such noise: Thermal, fiber optic link and ingress. Thermal noise is generated in each of the active components (amplifiers and receivers). The fiber optic link noise is generated in the return laser, fiber and headend receiver. Ingress noise arises through home wiring and connections and constitutes the major source of noise. A complete discussion of the return path and the noise characteristics is provided in "Return Systems for Hybrid Fiber/Coax Cable TV
Networks" by Donald Raskin and Dean Stoneback, 1998 Prentice Hall, Inc.
Traditional cable systems have a major trunk along which signals are transmitted from a headend in a forward direction to set-top boxes located in homes or business facilities connected to the feeder lines. Connection of set-top boxes to a feeder line is provided by connecting each set-top box to the feeder line via a tap. In the usual organization of a cable system there are many set-top boxes connected to each feeder line.
Moreover, each feeder and/or trunk line includes bi-directional amplifiers which pass signals in a high frequency band in the forward (downstream) direction, and in a low frequency band in the return (upstream) direction, which is well understood in the art.
Signals in the low frequency band originate at set-top boxes and are used to communicate in the upstream direction to the headend.
The problems with present return paths in cable systems arise from the fact that the path from the set-top to the tap in the feeder line (the inside wiring and the drop) is characterized by an unacceptable level of noise (ingress) which is picked up in the home wiring and in drop cable in the low frequency band where the set-top box transmits.
Further, no other band (relatively free of such ingress noise) in a low-split cable system is available for transmission from the home to the headend. Present low-split cable systems are wedded to transmission from the cable headend in a high frequency band and transmissions from set-top boxes in a low frequency band.
Yet the financial expectations of two way, broadband channels via a cable system are so compelling that significant resources are being dedicated towards solving the ingress noise problems in the return paths. The present remedial solutions are expensive, cause system shut down, cause system instability, require repeated service calls to subscribers facilities, and frequent home and drop rewiring or installation of special traps.
Moreover, with corrosion and deterioration of lines and connectors, there is a high likelihood that continued attention by cable operators will be necessary.
In the last ten years the cable industry has been retrofitting its cable infrastructure to allow for two-way communications on the cable plants. This is referred to in the industry as activating the return path; the return path being in the 5-40 MEiz frequency band. The design of the return path started with rebuilds in the late 70's. In the late 80's the larger cable companies began to segment their service area into smaller groups called "nodes", and changed their trunk system in many cases from using just co-axial cable and trunk amplifiers to a hybrid fiber/co-axial cable system (HFC). At the same time active and passive devices were replaced to increase the frequency spectrum in the downstream direction from 50-350 MHz plants to 50-750 MHz, in some cases up to 850 MHz.
The increased downstream frequency band allows cable companies to offer more channels of video services. The increased bandwidth also can be used for digital services in the forward direction. Also, by now activating the return path, two-way services such as impulse pay-per view, interactive TV, cable modems, telephone service, and additional services can be offered.
In the activation of the return path, it has been found by most of the cable companies, that the 5-40 MHz frequency band, especially the 5-15 MHz spectrum is extremely noisy. Because of the presence of the noise, most of the services presently available in the lower frequency band are digital services that can often work with low carrier to noise signal levels. But since the noise is not consistent, services are seriously impaired at times. Thus, a large number of cable companies are currently looking for ways to reduce the noise in the 5-40 MHz frequency band. Most of the approaches have been to reduce the number of homes connected to each node thereby reducing the total accumulated noise collected in each segment of the node. There have also been approaches involving the installation of 5-50 MFIz blocking filters to reduce the noise from inactive subscriber's homes in the 5-50 MHz frequency band from entering the main cable distribution network. The current best approach is to divide the cable system into many nodes which service as few as fifteen homes which is in effect providing a system of small clusters of homes, each connected directly to the node.
BRIEF DESCRIPTION OF THE INVENTION
The present invention is based on the realization that a portion of the downstream frequency band (i.e. 50-750 MHz) can be used, in part, to carry the return path signal from a set-top box. That portion of the frequency band is presently used to provide TV signals and digital signals from the headend to the home. But that portion of the band cannot presently be used to carry return path signals.
In accordance with the principles of this invention, the noise picked up in home appliances, drops, connectors, etc and transported to the corresponding node in the feeder line is avoided by reconfiguring the set-top box to transmit in the high frequency band rather than in the low frequency band where most of the noise occurs. The signals from the set-top box proceed in the downstream direction to the feeder line end, which in addition is equipped with a receiver (optical transmitter) and a fiber back to the node or directly to the headend. The result is that set-top box transmissions travel in the forward direction to the feeder line end where they are received and transmitted (optical transmitter) via a fiber to the node or the headend. The noise (home to feeder line tap) is avoided since the lower frequency band in which the majority of the ingress noise is located is not utilized. In this context, each feeder line end has terminators) and the receiver (i.e. optical transmitter) plus fiber link may be placed just after the last amplifier (terminal) in the feeder line and before the feeder line separates to different line terminator(s). The portion of the feeder line between the last amplifier (terminal) and the position where the feeder line separates line terminators) is referred to herein as the feeder line end.
Specifically, applicant herein adds to the cable system relatively inexpensive equipment which permits the set-top box to feeder line end portion of the return path to function as a forward path. This is accomplished, in one embodiment, by providing at each feeder line end a optical transmitter and fiber link. The optical transmitter receives the signals in the high portion of the band and transmits the signal via a fiber link back to the node or headend. The nature of this system is that it virtually eliminates ingress noise from house wiring and the drop, which is shown schematically on page 57 of the above-noted publication. It provides a further advantage of allowing the system operator to choose the size and location of the return band within the 50-750 MHz frequency spectrum.
In another embodiment, each feeder line end includes a receiver and a demodulator to decode the received data. The decoded data is then used to modulate a new signal. The regenerated signal does not contain the noise that was contained in the received signal. It is in effect a noise free signal. A optical transmitter than send the signal via the fiber to the node or headend.
Thus, in accordance with the principles of this invention, a technique is provided for eliminating the ingress noise in the low frequency band from house wiring, devices) in the home, and the drop from entering the cable system by not using the lower frequency band where most of the ingress noise resides. Each of the forward amplifiers already has a high pass filter blocking the low frequency band being amplified in the forward direction.
The higher frequency band is used to carry the return signal from the feeder line end to the node or the headend. Due to the substantial noise reduction, much higher modulation schemes such as QAM-16, QAM-32, QAM-64, QAM-256 etc may be employed. Current modulation schemes also become much more reliable and have much lower bit error rates.
The return signals are not restricted to modulated signals. All kinds of signals (i.e. video signals, radio signals) can originate from the subscriber locations. Overall it makes the return path in a cable system much more usable. With the resulting higher reliability there is likely to be fewer customer calls for service and higher customer satisfaction. The size of the return path is totally flexible and the system operator can choose any size and location in the frequency band for the return signal. Furthermore, since the return path for each feeder line end can be brought back separately to the headend, the effective size of the return path for the overall system is substantially larger than the existing system could allow.
This invention, illustratively, utilizes a portion of the 50-750 MHz frequency band to carry the return signal from the subscriber locations, rather than the 5-40 MHz frequency spectrum. But the return signal is transmitted first forward to the feeder line end where it is picked up and brought back to the cable headend. At the end of each of the feeder lines is a receiver that operates, illustratively in the 50-750 MHz band to receive the "return" signal. For example, the 300-350 lVYf3z band could be used to carry the return signal "forward" to the feeder line end. The signals in this band are received by the receiver (i.e. optical transmitter) at the end of the feeder line. The signals are then send via a fiber link to the node or to the cable headend The ingress noise in the lower frequency band is total avoided since the lower frequency band is not utilized. The system also does not require reverse amplifiers and thereby also avoiding the need to align reverse amplifier signal levels that is time consuming and painstaking work.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic representation of a prior art cable system including cable headend, trunk, nodes and illustrative set-top box locations;
Fig. 2 is a graphic representation of portions of the frequency band presently used for cable headend, set-top box, and bi-directional amplifier operation in prior art cable systems;
Fig. 3 is a graphic representation of typical ingress noise levels for transmissions in the low frequency band of Fig. 2;
Fig. 4 is a schematic representation of a cable system in accordance with the principles of this invention;
Fig's SA - SD are graphical representations of portions of the frequency band used for the headend, the set-top box, the bi-directional amplifier, and the optical transmitter of the arrangement of fig 4.
Fig's 6A- 6F and 7A- 7F are representations of signal processing schemes and related graphical representations of portions of the frequency band used for feeder line ends in cable systems in accordance with the principles of this invention;
Fig 8 shows a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier and an optical transmitter for a cable system in accordance with the principles of this invention;
Fig 9 shows a graph of ingress noise and portion of the frequency spectrum in which set-top boxes transmit in accordance with the principles of this invention;
Fig 10 is a schematic representation of an alternate embodiment of this invention;
Fig 11 is a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier and optical transmitter respectively for a cable system in accordance with the principles of this invention;
Fig 12 is a graphical representation of a band pass filter for use in embodiments of this invention; and Fig's 13, 14, and 15 are schematic representations of a prior art set-top box and alternative set-top boxes useful in embodiments of this invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THIS
INVENTION
Fig. 1 shows a schematic block diagram of a prior art cable system to establish a point of reference and terminology for the description of illustrative embodiments of this invention: Specifically, Fig. 1 shows a cable system 10 with a cable headend 11 and a major trunk 12. Trunk 12 typically comprises a coaxial cable and is connected to node or hubl3. Node 13 is connected to the cable headend via optical fiber (or a coaxial cable) 14 and (for the former) includes a optical transmitter for providing return signals from a subscriber set-top box to the cable headend.
The major trunk includes a plurality of bi-directional amplifiers represented, illustratively, at 17 and 18. The trunk also includes bi-directional bridger amplifiers 20 and 21 to which feeder lines 22, 23 and 24 are connected as indicated. Also shown is a auxiliary feeder line 26 which also includes bi-directional amplifiers (represented at 27) and tap 28 to which a drop cable 29 to a set-top box is connected.
A trunk cable end terminator is present at the end of trunk 12 as indicated at 30.
The end of a feeder line 24 has line terminators at 31 and 32.
Fig. 2 shows a set of related graphs of signal level versus frequency for the headend, the set-top box, and the bi-directional amplifiers respectively, for a prior art cable system. In the prior art system, the cable headend illustratively, receives signals in the 5-40 MHz band and transmits over the entire, illustratively, 50-750 MHz band. The set-top box operates in just the opposite manner. Specifically, the set-top box transmits in the 5-40 MHz band and receives signals in the 50-750 MHz band.
The bi-directional amplifiers pass signals forward, (away from the headend) in the 50-750 MHz band and pass return (toward the headend) signals in the 5-40 MHz band.
Thus, signals from a set-top box in the 5-40 MIiz band occur exactly where most of the ingress noise occurs. Fig. 3 shows a curve 33 representing the accumulated ingress noise with maximum ingress in the 5-40 IVfriz band. It is clear that the usefulness of the present return path can be severely limited by ingress noise.
Fig. 4 is a block diagram of a cable system in accordance with the principles of this invention. The system 40 comprises a headend 41 connected to a node (or hub) 42 by fiber optic (or coaxial) cable 43. The node contains one or more return optical transmitters (for fiber optic systems). The system also includes a major trunk 45 with amplifiers 47 and 48 (there usually are more amplifiers and they are located usually 500-1500 feet apart) with bridger amplifiers 50, and 52. In one embodiment a feeder line 56 is shown connected to bridger amplifier 50 and line end terminator 58. A high pass filter 59 and an optical transmitter 60 is located between the last amplifier (terminal) 57 and feeder line terminator 58 . The optical transmitter feeds into fiber 91 that goes to node 42. It could be routed directly to cable headend 41 and the principals of this invention would still apply. The frequency spectrum modulating the optical transmitter 60 is shown in Fig.
5A.
In another embodiment, a feeder line 61 has feeder line ends at terminators 62 and 65. A band pass filter 63 and an optical transmitter 64 are located after the last amplifier 53 and before terminators 62 and 65. The band pass falter only passes signals in the 300-350 MHz frequency band, the frequency band in which the set-top boxes transmit. The optical transmitter 64 feeds the signal into fiber 92 that goes to node 42.
The frequency spectrum modulating optical transmitter 64 is shown in Fig. 5B.
Illustrative of a further embodiment, a feeder line 66 has a feeder line end terminator 69 which includes a band pass filter 67, a demodulator 70, modulator 71, and an optical transmitter 68. The band pass filter only passes signals in the 300-350 MHz frequency band; the frequency band in which the set-top boxes transmit. Only one demodulator is shown in Fig. 4 for illustrative purposes. There can be multiple demodulator and modulator pairs, all separated in the frequency spectrum over the 300-350 MHz frequency band. The combined output of the modulators can be over any frequency spectrum. In the illustrative embodiment of fig. 4, the modulator 71 output is over the 140-190 MHz frequency spectrum. The frequency spectrum modulating optical transmitter 68 is shown in Fig. SC. In a further embodiment a feeder line 110 has a feeder end at 80 which includes a band pass filter 81, a frequency band block converter 83 which converts the block of frequency band 300 to 350 MHz to 50 to 100 MI3z, and an optical transmitter 82. Again, the band pass filter only passes signals in the 300-350 MHz frequency band; the frequency band in which the set-top boxes transmit. The frequency spectrum modulating optical transmitter 82 is shown in Fig. SD. Use of a block converter allows different frequency bands to be used for communication back to the node, where I S the various signal for the feeder line ends are combined together into a single signal but separated in the frequency band, and sent back to the cable headend.
In Fig. 4, fiber 92 is shown connected to node 42. The fiber could be routed directly to the headend with no additional processing of the signal at node 42. The complete frequency spectrum 50-750 MHz could then be received at the headend.
This would provide the system operator the capability of checking the quality of the signals sent on the network plus the receive the signals sent back by the set-top boxes.
Fig. 6A shows one possible embodiment of signal processing at node 42 of Fig.
4.
In this particular case all the signals received from feeder line ends at node 42 are combined into a signal and the combined signal is carried to the headend via a single fiber cable. Fig. 6A shows a fiber input into optical receiver 1 S 1. The input to optical receiver 1 S 1 could be the signal transmitted on fiber 92 of Fig. 4. Fig. 6B shows the frequency spectrum output of optical receiver 1 S 1. The optical receiver 1 S 1 output signal is fed into a combiner 1SS. Similar outputs of optical receiver 152, 153, and 154 are also fed into S combiner 1SS. Fig. 6C shows the frequency spectrum of optical receiver 152.
Fig. 6D
shows the frequency spectrum output optical receiver 153. Fig. 6E shows the frequency spectrum output of receiver 154. The frequency spectrum output of combiner 1SS
is shown in Fig.6A. The frequency spectrum of optical receivers 1 S 1, 1 S2, 1 S3, and 1 S4 are combined and overlap in the frequency output spectrum of combiner 1 SS. In this particular case only one of the set-top boxes transmits at a particular frequency at the same time. The output of each of the set-top boxes is in-effect time division multiplexed. Fig.
6A shows only four fiber returns but the principal would be the same where the number of return fibers is substantial greater. The output of combiner 1SS is fed into optical transmitter 156. The output of optical transmitter 1 S6 is a fiber cable back to the headend.
1 S The signal processing at the headend is similar to that of the prior art system. Table 1 shows various other kinds of devices and mediums that can replace an optical transmitter and fiber at the feeder line end and still achieve the same objective of getting the received signals from the set-top box at the feeder line end back to the headend. A
person skilled in the art would recognize, that if the device and medium are changed at the feeder line end, a receiver that is compatible with the medium and transmitter device would be required at the cable headend to receive the signal. Any required signal conversion could also be made at the feeder line.
Fig. 7A shows another embodiment of signal processing at node 42 of Fig. 4. In this embodiment the signals received from each of the feeder lines is frequency division multiplexed into a single signal. The frequency division multiplexed signal is sent back via fiber to the headend. Fig. 7A shows a fiber input into optical receiver 141. The input to optical receiver 141 could be the signal transmitted on fiber 92 of Fig. 4.
Fig. 7B shows the frequency spectrum output of optical receiver 141.
High Pass Filter 59 of Fig. 4 is operative to receive signals illustratively in the 50 to 750 MHz band. The set-top boxes in the system of Fig. 4 are also operative to transmit in the 50 to 750 MHz band. Thus, transmissions from a set-top box (the return transmissions) are received first by receivers at the feeder line ends before they are transmitted via the fiber link to the cable headend. The principals of this invention would still apply where the optical transmitter and fiber link are changed to a cable amplifier and co-axial cable.
Table 1.
Device at feeder Return Medium line end Optical Transmitter Fiber Optic Cable Amplifier Co-axial cable Wireless transmitterAir Microwave transmitterAir Satellite TransmitterAir and Space Telephone Modem Telephone Line It is to be understood that in accordance with the principles of this invention, signals from a set-top box are in a frequency band which travels to a receiver at the feeder line end rather than in a return path to the cable headend.
But each feeder line end, also in accordance with the principles of the invention, includes means for receiving those signals and transmitting those signals back to the node or the cable headend. In the Fig. 4, the means for receiving signals in the 50-750 MHz band are optical transmitters 60, 64, 68 and 82. The optical transmitters feed the signal into the fiber and those signals are received at the node or cable headend.
Fig. 8 shows a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier, and an optical transmitter respectively for a cable system in accordance with the principles of this invention. As shown in Fig.
8, the headend can receive in the 50-750 MHz band, but does not transmit over the entire 50-750 MHz band. The 300-350 MHz portion is notched out. The set-top box transmits in the 300-350 MHz portion and receives in the 50-300 MHz and in the 350-750 MHz bands.
The amplifiers operate only in the forward direction and carry signal away from the headend. Not having reverse amplifiers removes the necessity of having to align the reverse amplifiers which is time consuming and painstaking work.
I S It is clear from Fig. 8 that signals transmitted by set-top boxes in the system of Fig.
4 are passed in a "forward" direction to the corresponding feeder line end where they are received, and transmitted back to the node or cable headend.
Fig. 9 shows a graph of ingress noise 100, corresponding to that of Fig. 3, along with the portion of the frequency spectrum 300-350 MHz in which set-top boxes transmit in accordance with the principles of this invention. It is clear that ingress noise is insignificant over the portion of the spectrum now used by set-top boxes in the system of Fig. 4, Thereby providing return signals virtually free of ingress noise in the return path to the cable headend.
A system, in accordance with one of the embodiments of the principles of this invention, also includes band stop (notch) filters (i.e. 112) at the start of auxiliary feeder lines (i.e. 110) in the system (of fig. 4) to ensure that transmissions from a set-top box in the 50-750 MHz band are only received by one feeder end in the system. Such a band stop filter 112 is located at the start of auxiliary feeder line 110 to ensure that the signal for each set-top box is received only at one feeder end (i.e. the signal from set-top box 55 is received by band pass filter 67 only, since band stop filter 112 blocks the signals from being received by band pass filter 81.
Fig. 10 shows a system similar to that of Fig. 4 where the bi-directional amplifiers of the prior art system of Fig. 1 are maintained to provide a system where the prior art set-top boxes can continue to function as before in this new combined system that allows for new set-top boxes to transmit in the 50-750 MHz band and prior art set-top boxes to transmit in the 5-40 MHz band.
Fig. 11 shows a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier, and optical transmitter respectively for a cable system in accordance with the principles of this invention. As shown in Fig. 1 l, the headend can receives in the 50-750 MHz band and also in the 5-40 MHz as in the prior art, but does not transmit over the entire 50-750 MHz band. The 300-350 MHz portion is notched out. The new set-top box transmits in the 300-350 MHz portion and receives in the 50-300 MHz and in the 350-750 MHz bands. The bi-directions amplifiers operate as before to carry 5-40 MHz signals towards the headend and 50-750 MHz signal in the forward direction away from the headend. This embodiment shows a combined system where the prior art set-top boxes and the novel set-top boxes of this invention operate in a combined system. This combined system offers a solution to cable operators to continue to serve existing customers with their existing (prior art) set-top boxes and new customer using the set-top boxes in line with the principles of this invention. Thereby retaining the existing system and upgrading the system in line with the principles of this invention.
Fig. 12 shows a graphical representation of a band stop filter which passes signals in the 5-750 MHz band except for signals in the 300-350 MHz (notch) portion of the band. The presence of such filters prevents signals from a set-top box (in the MHz band) from being received by more than one feeder end.
Fig's. 13 and 14 show schematic representations of a prior art set-top box and a set-top box in accordance with the principles of this invention, respectively.
In the prior art set-top box of Fig. 13, a high pass filter 104 excludes signals in the 5-40 MHz band and passes signals in the 50-750 MHz band. The set-top box also includes a low pass filter 101 which excludes signals in the 50-750 MHz band and passes signals in the 5-40 MHz band.
The set-top~box of Fig. 14 is considerably different. Specifically, the set-top box of Fig. 14 includes a band stop filter 102 which passes SO-750 MHz but notches out signals in the 300-350 MHz band. The set-top box also includes a band pass filter 103 which passes signals in the 300-350 MHz band. Thus, the set-top box ofFig. 14 receives and transmits in the same (high) band (i.e. 50-750 MHz) whereas the set-top boxes of the prior art receive and transmit in high and low (considerably different) bands respectively.
Fig 14, further shows an optional feature in the set-top box that would allow the set-top box to also transmit a return signal in the low frequency band (5-40 MHz) as done by the prior art set-top box. This optional feature would work with the system of Fig. 10 that allows the headend to receive in the 5-40 MHz band and in the 50-750 MHz band.
This new set-top box would now have two separate frequency bands in which the headend can receive signals from the set-top box.
Fig. 4 also shows an auxiliary feeder line 110 extending from feeder line 66.
It is important that a transmission from a set-top box of the system of Fig. 4 be received only by the receiver at the end of one feeder line to which the transmitting set-top box is connected. In order to prevent signals from, for example, a set-top box connected to feeder line 66 being received by a receiver 82 (optical transmitter) connected to an auxiliary feeder line (110), the auxiliary feeder line includes a band stop filter 112 to exclude such transmissions as discussed herein before.
Alternatively, the cable headend may be configured to poll (i.e. enable) a set-top box and the corresponding feeder line end optical transmitter simultaneously so that only signals from that receiver are received at the headend. The cable headend will of course, require additional software in this case. This would allow the cable operator to choose the size and location of the return frequency band. Frequency agile band stop filters and frequency agile band pass filters can also be used in the system to utilize any portion of frequency band desired by the system operator. The frequency bands selected herein are only illustrative and other bands and/or notches may be suitable as is clear to one skilled in the art. For example, the operator could use the 700 MHz and up band for the return path. In this case the configuration of the set-top box would change to that shown in Fig.
15. The optional feature shown in Fig. 15 allows this new set-top box to also send signals to the headend via the 5-40 MHz band. This set-top box can communicate with the headend in the 5-40 MHz frequency band and in the 700 MHz and up frequency band.
There are various ways for the signals received at node 42 of Fig. 4 to be brought back to the cable headend 40 of Fig. 4. The embodiment of Fig. 7A shows receipt of fiber 92 of Fig. 4 being received by optical receiver 141. Fig 7B shows the frequency spectrum received by optical receiver 141. The 300-350 MHz frequency band ofFig. 7B is directly mapped to 300-350 MHz frequency band of Fig. 7A. Fig. 7C shows the frequency band received by optical receiver 142. Block frequency converter 146 of Fig. 7A
converts the 300 MHz (f~) to 350 MHz (fd) frequency band to 240 MHz (fd) to 290 MHz (f~) frequency band. The frequency spectrum of optical receiver 141, block frequency converters 146, 147, and 148 are combined by combiner 149. The frequency spectrum output of combiner 149 is shown in Fig. 7A. Fig. 7A shows that each of the feeder line outputs is separate in the frequency spectrum of combiner 149. This allows one set-top box in each of the feeder lines to transmit at the same frequency and at the same time as another set-top box in another feeder line. Thereby provide a substantially higher effective return bandwidth for the cable system.
It is anticipated that the novel set-top boxes shown herein may have wireless capability added to them to allow them to communicated wireless to other devices in the home and business facilities such as personal computers, videophones, telephone etc.
The optical transmitters, optical receivers, high pass filters, band pass filters, band stop filters, converter receivers, transmitters and other components herein are all commercially available or easily configured from available components. Any such components operative as required herein may be used in accordance with the principles of this invention.
It is to be understood that although the invention has been described illustratively in terms of a set-top box, any two-way communication device, such as a cable modem, can be used.
REFERENCE TO RELATED APPLICATIONS
This application is a Continuation in Part of Application Serial No. 09/541, filed April 3, 2000 to the applicant of the present application.
FIELD OF THE INVENTION
This invention relates to cable systems and more particularly to such systems with a sufficiently noise free return path to support high bandwidth two-way broadband, multimedia content delivery to and from the home.
BACKGROUND OF THE INVENTION
It is well known that the return path in a cable system is noisy and is frequently referred to as a "noise funnel". There are three primary sources of such noise: Thermal, fiber optic link and ingress. Thermal noise is generated in each of the active components (amplifiers and receivers). The fiber optic link noise is generated in the return laser, fiber and headend receiver. Ingress noise arises through home wiring and connections and constitutes the major source of noise. A complete discussion of the return path and the noise characteristics is provided in "Return Systems for Hybrid Fiber/Coax Cable TV
Networks" by Donald Raskin and Dean Stoneback, 1998 Prentice Hall, Inc.
Traditional cable systems have a major trunk along which signals are transmitted from a headend in a forward direction to set-top boxes located in homes or business facilities connected to the feeder lines. Connection of set-top boxes to a feeder line is provided by connecting each set-top box to the feeder line via a tap. In the usual organization of a cable system there are many set-top boxes connected to each feeder line.
Moreover, each feeder and/or trunk line includes bi-directional amplifiers which pass signals in a high frequency band in the forward (downstream) direction, and in a low frequency band in the return (upstream) direction, which is well understood in the art.
Signals in the low frequency band originate at set-top boxes and are used to communicate in the upstream direction to the headend.
The problems with present return paths in cable systems arise from the fact that the path from the set-top to the tap in the feeder line (the inside wiring and the drop) is characterized by an unacceptable level of noise (ingress) which is picked up in the home wiring and in drop cable in the low frequency band where the set-top box transmits.
Further, no other band (relatively free of such ingress noise) in a low-split cable system is available for transmission from the home to the headend. Present low-split cable systems are wedded to transmission from the cable headend in a high frequency band and transmissions from set-top boxes in a low frequency band.
Yet the financial expectations of two way, broadband channels via a cable system are so compelling that significant resources are being dedicated towards solving the ingress noise problems in the return paths. The present remedial solutions are expensive, cause system shut down, cause system instability, require repeated service calls to subscribers facilities, and frequent home and drop rewiring or installation of special traps.
Moreover, with corrosion and deterioration of lines and connectors, there is a high likelihood that continued attention by cable operators will be necessary.
In the last ten years the cable industry has been retrofitting its cable infrastructure to allow for two-way communications on the cable plants. This is referred to in the industry as activating the return path; the return path being in the 5-40 MEiz frequency band. The design of the return path started with rebuilds in the late 70's. In the late 80's the larger cable companies began to segment their service area into smaller groups called "nodes", and changed their trunk system in many cases from using just co-axial cable and trunk amplifiers to a hybrid fiber/co-axial cable system (HFC). At the same time active and passive devices were replaced to increase the frequency spectrum in the downstream direction from 50-350 MHz plants to 50-750 MHz, in some cases up to 850 MHz.
The increased downstream frequency band allows cable companies to offer more channels of video services. The increased bandwidth also can be used for digital services in the forward direction. Also, by now activating the return path, two-way services such as impulse pay-per view, interactive TV, cable modems, telephone service, and additional services can be offered.
In the activation of the return path, it has been found by most of the cable companies, that the 5-40 MHz frequency band, especially the 5-15 MHz spectrum is extremely noisy. Because of the presence of the noise, most of the services presently available in the lower frequency band are digital services that can often work with low carrier to noise signal levels. But since the noise is not consistent, services are seriously impaired at times. Thus, a large number of cable companies are currently looking for ways to reduce the noise in the 5-40 MHz frequency band. Most of the approaches have been to reduce the number of homes connected to each node thereby reducing the total accumulated noise collected in each segment of the node. There have also been approaches involving the installation of 5-50 MFIz blocking filters to reduce the noise from inactive subscriber's homes in the 5-50 MHz frequency band from entering the main cable distribution network. The current best approach is to divide the cable system into many nodes which service as few as fifteen homes which is in effect providing a system of small clusters of homes, each connected directly to the node.
BRIEF DESCRIPTION OF THE INVENTION
The present invention is based on the realization that a portion of the downstream frequency band (i.e. 50-750 MHz) can be used, in part, to carry the return path signal from a set-top box. That portion of the frequency band is presently used to provide TV signals and digital signals from the headend to the home. But that portion of the band cannot presently be used to carry return path signals.
In accordance with the principles of this invention, the noise picked up in home appliances, drops, connectors, etc and transported to the corresponding node in the feeder line is avoided by reconfiguring the set-top box to transmit in the high frequency band rather than in the low frequency band where most of the noise occurs. The signals from the set-top box proceed in the downstream direction to the feeder line end, which in addition is equipped with a receiver (optical transmitter) and a fiber back to the node or directly to the headend. The result is that set-top box transmissions travel in the forward direction to the feeder line end where they are received and transmitted (optical transmitter) via a fiber to the node or the headend. The noise (home to feeder line tap) is avoided since the lower frequency band in which the majority of the ingress noise is located is not utilized. In this context, each feeder line end has terminators) and the receiver (i.e. optical transmitter) plus fiber link may be placed just after the last amplifier (terminal) in the feeder line and before the feeder line separates to different line terminator(s). The portion of the feeder line between the last amplifier (terminal) and the position where the feeder line separates line terminators) is referred to herein as the feeder line end.
Specifically, applicant herein adds to the cable system relatively inexpensive equipment which permits the set-top box to feeder line end portion of the return path to function as a forward path. This is accomplished, in one embodiment, by providing at each feeder line end a optical transmitter and fiber link. The optical transmitter receives the signals in the high portion of the band and transmits the signal via a fiber link back to the node or headend. The nature of this system is that it virtually eliminates ingress noise from house wiring and the drop, which is shown schematically on page 57 of the above-noted publication. It provides a further advantage of allowing the system operator to choose the size and location of the return band within the 50-750 MHz frequency spectrum.
In another embodiment, each feeder line end includes a receiver and a demodulator to decode the received data. The decoded data is then used to modulate a new signal. The regenerated signal does not contain the noise that was contained in the received signal. It is in effect a noise free signal. A optical transmitter than send the signal via the fiber to the node or headend.
Thus, in accordance with the principles of this invention, a technique is provided for eliminating the ingress noise in the low frequency band from house wiring, devices) in the home, and the drop from entering the cable system by not using the lower frequency band where most of the ingress noise resides. Each of the forward amplifiers already has a high pass filter blocking the low frequency band being amplified in the forward direction.
The higher frequency band is used to carry the return signal from the feeder line end to the node or the headend. Due to the substantial noise reduction, much higher modulation schemes such as QAM-16, QAM-32, QAM-64, QAM-256 etc may be employed. Current modulation schemes also become much more reliable and have much lower bit error rates.
The return signals are not restricted to modulated signals. All kinds of signals (i.e. video signals, radio signals) can originate from the subscriber locations. Overall it makes the return path in a cable system much more usable. With the resulting higher reliability there is likely to be fewer customer calls for service and higher customer satisfaction. The size of the return path is totally flexible and the system operator can choose any size and location in the frequency band for the return signal. Furthermore, since the return path for each feeder line end can be brought back separately to the headend, the effective size of the return path for the overall system is substantially larger than the existing system could allow.
This invention, illustratively, utilizes a portion of the 50-750 MHz frequency band to carry the return signal from the subscriber locations, rather than the 5-40 MHz frequency spectrum. But the return signal is transmitted first forward to the feeder line end where it is picked up and brought back to the cable headend. At the end of each of the feeder lines is a receiver that operates, illustratively in the 50-750 MHz band to receive the "return" signal. For example, the 300-350 lVYf3z band could be used to carry the return signal "forward" to the feeder line end. The signals in this band are received by the receiver (i.e. optical transmitter) at the end of the feeder line. The signals are then send via a fiber link to the node or to the cable headend The ingress noise in the lower frequency band is total avoided since the lower frequency band is not utilized. The system also does not require reverse amplifiers and thereby also avoiding the need to align reverse amplifier signal levels that is time consuming and painstaking work.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic representation of a prior art cable system including cable headend, trunk, nodes and illustrative set-top box locations;
Fig. 2 is a graphic representation of portions of the frequency band presently used for cable headend, set-top box, and bi-directional amplifier operation in prior art cable systems;
Fig. 3 is a graphic representation of typical ingress noise levels for transmissions in the low frequency band of Fig. 2;
Fig. 4 is a schematic representation of a cable system in accordance with the principles of this invention;
Fig's SA - SD are graphical representations of portions of the frequency band used for the headend, the set-top box, the bi-directional amplifier, and the optical transmitter of the arrangement of fig 4.
Fig's 6A- 6F and 7A- 7F are representations of signal processing schemes and related graphical representations of portions of the frequency band used for feeder line ends in cable systems in accordance with the principles of this invention;
Fig 8 shows a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier and an optical transmitter for a cable system in accordance with the principles of this invention;
Fig 9 shows a graph of ingress noise and portion of the frequency spectrum in which set-top boxes transmit in accordance with the principles of this invention;
Fig 10 is a schematic representation of an alternate embodiment of this invention;
Fig 11 is a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier and optical transmitter respectively for a cable system in accordance with the principles of this invention;
Fig 12 is a graphical representation of a band pass filter for use in embodiments of this invention; and Fig's 13, 14, and 15 are schematic representations of a prior art set-top box and alternative set-top boxes useful in embodiments of this invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THIS
INVENTION
Fig. 1 shows a schematic block diagram of a prior art cable system to establish a point of reference and terminology for the description of illustrative embodiments of this invention: Specifically, Fig. 1 shows a cable system 10 with a cable headend 11 and a major trunk 12. Trunk 12 typically comprises a coaxial cable and is connected to node or hubl3. Node 13 is connected to the cable headend via optical fiber (or a coaxial cable) 14 and (for the former) includes a optical transmitter for providing return signals from a subscriber set-top box to the cable headend.
The major trunk includes a plurality of bi-directional amplifiers represented, illustratively, at 17 and 18. The trunk also includes bi-directional bridger amplifiers 20 and 21 to which feeder lines 22, 23 and 24 are connected as indicated. Also shown is a auxiliary feeder line 26 which also includes bi-directional amplifiers (represented at 27) and tap 28 to which a drop cable 29 to a set-top box is connected.
A trunk cable end terminator is present at the end of trunk 12 as indicated at 30.
The end of a feeder line 24 has line terminators at 31 and 32.
Fig. 2 shows a set of related graphs of signal level versus frequency for the headend, the set-top box, and the bi-directional amplifiers respectively, for a prior art cable system. In the prior art system, the cable headend illustratively, receives signals in the 5-40 MHz band and transmits over the entire, illustratively, 50-750 MHz band. The set-top box operates in just the opposite manner. Specifically, the set-top box transmits in the 5-40 MHz band and receives signals in the 50-750 MHz band.
The bi-directional amplifiers pass signals forward, (away from the headend) in the 50-750 MHz band and pass return (toward the headend) signals in the 5-40 MHz band.
Thus, signals from a set-top box in the 5-40 MIiz band occur exactly where most of the ingress noise occurs. Fig. 3 shows a curve 33 representing the accumulated ingress noise with maximum ingress in the 5-40 IVfriz band. It is clear that the usefulness of the present return path can be severely limited by ingress noise.
Fig. 4 is a block diagram of a cable system in accordance with the principles of this invention. The system 40 comprises a headend 41 connected to a node (or hub) 42 by fiber optic (or coaxial) cable 43. The node contains one or more return optical transmitters (for fiber optic systems). The system also includes a major trunk 45 with amplifiers 47 and 48 (there usually are more amplifiers and they are located usually 500-1500 feet apart) with bridger amplifiers 50, and 52. In one embodiment a feeder line 56 is shown connected to bridger amplifier 50 and line end terminator 58. A high pass filter 59 and an optical transmitter 60 is located between the last amplifier (terminal) 57 and feeder line terminator 58 . The optical transmitter feeds into fiber 91 that goes to node 42. It could be routed directly to cable headend 41 and the principals of this invention would still apply. The frequency spectrum modulating the optical transmitter 60 is shown in Fig.
5A.
In another embodiment, a feeder line 61 has feeder line ends at terminators 62 and 65. A band pass filter 63 and an optical transmitter 64 are located after the last amplifier 53 and before terminators 62 and 65. The band pass falter only passes signals in the 300-350 MHz frequency band, the frequency band in which the set-top boxes transmit. The optical transmitter 64 feeds the signal into fiber 92 that goes to node 42.
The frequency spectrum modulating optical transmitter 64 is shown in Fig. 5B.
Illustrative of a further embodiment, a feeder line 66 has a feeder line end terminator 69 which includes a band pass filter 67, a demodulator 70, modulator 71, and an optical transmitter 68. The band pass filter only passes signals in the 300-350 MHz frequency band; the frequency band in which the set-top boxes transmit. Only one demodulator is shown in Fig. 4 for illustrative purposes. There can be multiple demodulator and modulator pairs, all separated in the frequency spectrum over the 300-350 MHz frequency band. The combined output of the modulators can be over any frequency spectrum. In the illustrative embodiment of fig. 4, the modulator 71 output is over the 140-190 MHz frequency spectrum. The frequency spectrum modulating optical transmitter 68 is shown in Fig. SC. In a further embodiment a feeder line 110 has a feeder end at 80 which includes a band pass filter 81, a frequency band block converter 83 which converts the block of frequency band 300 to 350 MHz to 50 to 100 MI3z, and an optical transmitter 82. Again, the band pass filter only passes signals in the 300-350 MHz frequency band; the frequency band in which the set-top boxes transmit. The frequency spectrum modulating optical transmitter 82 is shown in Fig. SD. Use of a block converter allows different frequency bands to be used for communication back to the node, where I S the various signal for the feeder line ends are combined together into a single signal but separated in the frequency band, and sent back to the cable headend.
In Fig. 4, fiber 92 is shown connected to node 42. The fiber could be routed directly to the headend with no additional processing of the signal at node 42. The complete frequency spectrum 50-750 MHz could then be received at the headend.
This would provide the system operator the capability of checking the quality of the signals sent on the network plus the receive the signals sent back by the set-top boxes.
Fig. 6A shows one possible embodiment of signal processing at node 42 of Fig.
4.
In this particular case all the signals received from feeder line ends at node 42 are combined into a signal and the combined signal is carried to the headend via a single fiber cable. Fig. 6A shows a fiber input into optical receiver 1 S 1. The input to optical receiver 1 S 1 could be the signal transmitted on fiber 92 of Fig. 4. Fig. 6B shows the frequency spectrum output of optical receiver 1 S 1. The optical receiver 1 S 1 output signal is fed into a combiner 1SS. Similar outputs of optical receiver 152, 153, and 154 are also fed into S combiner 1SS. Fig. 6C shows the frequency spectrum of optical receiver 152.
Fig. 6D
shows the frequency spectrum output optical receiver 153. Fig. 6E shows the frequency spectrum output of receiver 154. The frequency spectrum output of combiner 1SS
is shown in Fig.6A. The frequency spectrum of optical receivers 1 S 1, 1 S2, 1 S3, and 1 S4 are combined and overlap in the frequency output spectrum of combiner 1 SS. In this particular case only one of the set-top boxes transmits at a particular frequency at the same time. The output of each of the set-top boxes is in-effect time division multiplexed. Fig.
6A shows only four fiber returns but the principal would be the same where the number of return fibers is substantial greater. The output of combiner 1SS is fed into optical transmitter 156. The output of optical transmitter 1 S6 is a fiber cable back to the headend.
1 S The signal processing at the headend is similar to that of the prior art system. Table 1 shows various other kinds of devices and mediums that can replace an optical transmitter and fiber at the feeder line end and still achieve the same objective of getting the received signals from the set-top box at the feeder line end back to the headend. A
person skilled in the art would recognize, that if the device and medium are changed at the feeder line end, a receiver that is compatible with the medium and transmitter device would be required at the cable headend to receive the signal. Any required signal conversion could also be made at the feeder line.
Fig. 7A shows another embodiment of signal processing at node 42 of Fig. 4. In this embodiment the signals received from each of the feeder lines is frequency division multiplexed into a single signal. The frequency division multiplexed signal is sent back via fiber to the headend. Fig. 7A shows a fiber input into optical receiver 141. The input to optical receiver 141 could be the signal transmitted on fiber 92 of Fig. 4.
Fig. 7B shows the frequency spectrum output of optical receiver 141.
High Pass Filter 59 of Fig. 4 is operative to receive signals illustratively in the 50 to 750 MHz band. The set-top boxes in the system of Fig. 4 are also operative to transmit in the 50 to 750 MHz band. Thus, transmissions from a set-top box (the return transmissions) are received first by receivers at the feeder line ends before they are transmitted via the fiber link to the cable headend. The principals of this invention would still apply where the optical transmitter and fiber link are changed to a cable amplifier and co-axial cable.
Table 1.
Device at feeder Return Medium line end Optical Transmitter Fiber Optic Cable Amplifier Co-axial cable Wireless transmitterAir Microwave transmitterAir Satellite TransmitterAir and Space Telephone Modem Telephone Line It is to be understood that in accordance with the principles of this invention, signals from a set-top box are in a frequency band which travels to a receiver at the feeder line end rather than in a return path to the cable headend.
But each feeder line end, also in accordance with the principles of the invention, includes means for receiving those signals and transmitting those signals back to the node or the cable headend. In the Fig. 4, the means for receiving signals in the 50-750 MHz band are optical transmitters 60, 64, 68 and 82. The optical transmitters feed the signal into the fiber and those signals are received at the node or cable headend.
Fig. 8 shows a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier, and an optical transmitter respectively for a cable system in accordance with the principles of this invention. As shown in Fig.
8, the headend can receive in the 50-750 MHz band, but does not transmit over the entire 50-750 MHz band. The 300-350 MHz portion is notched out. The set-top box transmits in the 300-350 MHz portion and receives in the 50-300 MHz and in the 350-750 MHz bands.
The amplifiers operate only in the forward direction and carry signal away from the headend. Not having reverse amplifiers removes the necessity of having to align the reverse amplifiers which is time consuming and painstaking work.
I S It is clear from Fig. 8 that signals transmitted by set-top boxes in the system of Fig.
4 are passed in a "forward" direction to the corresponding feeder line end where they are received, and transmitted back to the node or cable headend.
Fig. 9 shows a graph of ingress noise 100, corresponding to that of Fig. 3, along with the portion of the frequency spectrum 300-350 MHz in which set-top boxes transmit in accordance with the principles of this invention. It is clear that ingress noise is insignificant over the portion of the spectrum now used by set-top boxes in the system of Fig. 4, Thereby providing return signals virtually free of ingress noise in the return path to the cable headend.
A system, in accordance with one of the embodiments of the principles of this invention, also includes band stop (notch) filters (i.e. 112) at the start of auxiliary feeder lines (i.e. 110) in the system (of fig. 4) to ensure that transmissions from a set-top box in the 50-750 MHz band are only received by one feeder end in the system. Such a band stop filter 112 is located at the start of auxiliary feeder line 110 to ensure that the signal for each set-top box is received only at one feeder end (i.e. the signal from set-top box 55 is received by band pass filter 67 only, since band stop filter 112 blocks the signals from being received by band pass filter 81.
Fig. 10 shows a system similar to that of Fig. 4 where the bi-directional amplifiers of the prior art system of Fig. 1 are maintained to provide a system where the prior art set-top boxes can continue to function as before in this new combined system that allows for new set-top boxes to transmit in the 50-750 MHz band and prior art set-top boxes to transmit in the 5-40 MHz band.
Fig. 11 shows a set of related graphs of signal level versus frequency for a cable headend, a set-top box, an amplifier, and optical transmitter respectively for a cable system in accordance with the principles of this invention. As shown in Fig. 1 l, the headend can receives in the 50-750 MHz band and also in the 5-40 MHz as in the prior art, but does not transmit over the entire 50-750 MHz band. The 300-350 MHz portion is notched out. The new set-top box transmits in the 300-350 MHz portion and receives in the 50-300 MHz and in the 350-750 MHz bands. The bi-directions amplifiers operate as before to carry 5-40 MHz signals towards the headend and 50-750 MHz signal in the forward direction away from the headend. This embodiment shows a combined system where the prior art set-top boxes and the novel set-top boxes of this invention operate in a combined system. This combined system offers a solution to cable operators to continue to serve existing customers with their existing (prior art) set-top boxes and new customer using the set-top boxes in line with the principles of this invention. Thereby retaining the existing system and upgrading the system in line with the principles of this invention.
Fig. 12 shows a graphical representation of a band stop filter which passes signals in the 5-750 MHz band except for signals in the 300-350 MHz (notch) portion of the band. The presence of such filters prevents signals from a set-top box (in the MHz band) from being received by more than one feeder end.
Fig's. 13 and 14 show schematic representations of a prior art set-top box and a set-top box in accordance with the principles of this invention, respectively.
In the prior art set-top box of Fig. 13, a high pass filter 104 excludes signals in the 5-40 MHz band and passes signals in the 50-750 MHz band. The set-top box also includes a low pass filter 101 which excludes signals in the 50-750 MHz band and passes signals in the 5-40 MHz band.
The set-top~box of Fig. 14 is considerably different. Specifically, the set-top box of Fig. 14 includes a band stop filter 102 which passes SO-750 MHz but notches out signals in the 300-350 MHz band. The set-top box also includes a band pass filter 103 which passes signals in the 300-350 MHz band. Thus, the set-top box ofFig. 14 receives and transmits in the same (high) band (i.e. 50-750 MHz) whereas the set-top boxes of the prior art receive and transmit in high and low (considerably different) bands respectively.
Fig 14, further shows an optional feature in the set-top box that would allow the set-top box to also transmit a return signal in the low frequency band (5-40 MHz) as done by the prior art set-top box. This optional feature would work with the system of Fig. 10 that allows the headend to receive in the 5-40 MHz band and in the 50-750 MHz band.
This new set-top box would now have two separate frequency bands in which the headend can receive signals from the set-top box.
Fig. 4 also shows an auxiliary feeder line 110 extending from feeder line 66.
It is important that a transmission from a set-top box of the system of Fig. 4 be received only by the receiver at the end of one feeder line to which the transmitting set-top box is connected. In order to prevent signals from, for example, a set-top box connected to feeder line 66 being received by a receiver 82 (optical transmitter) connected to an auxiliary feeder line (110), the auxiliary feeder line includes a band stop filter 112 to exclude such transmissions as discussed herein before.
Alternatively, the cable headend may be configured to poll (i.e. enable) a set-top box and the corresponding feeder line end optical transmitter simultaneously so that only signals from that receiver are received at the headend. The cable headend will of course, require additional software in this case. This would allow the cable operator to choose the size and location of the return frequency band. Frequency agile band stop filters and frequency agile band pass filters can also be used in the system to utilize any portion of frequency band desired by the system operator. The frequency bands selected herein are only illustrative and other bands and/or notches may be suitable as is clear to one skilled in the art. For example, the operator could use the 700 MHz and up band for the return path. In this case the configuration of the set-top box would change to that shown in Fig.
15. The optional feature shown in Fig. 15 allows this new set-top box to also send signals to the headend via the 5-40 MHz band. This set-top box can communicate with the headend in the 5-40 MHz frequency band and in the 700 MHz and up frequency band.
There are various ways for the signals received at node 42 of Fig. 4 to be brought back to the cable headend 40 of Fig. 4. The embodiment of Fig. 7A shows receipt of fiber 92 of Fig. 4 being received by optical receiver 141. Fig 7B shows the frequency spectrum received by optical receiver 141. The 300-350 MHz frequency band ofFig. 7B is directly mapped to 300-350 MHz frequency band of Fig. 7A. Fig. 7C shows the frequency band received by optical receiver 142. Block frequency converter 146 of Fig. 7A
converts the 300 MHz (f~) to 350 MHz (fd) frequency band to 240 MHz (fd) to 290 MHz (f~) frequency band. The frequency spectrum of optical receiver 141, block frequency converters 146, 147, and 148 are combined by combiner 149. The frequency spectrum output of combiner 149 is shown in Fig. 7A. Fig. 7A shows that each of the feeder line outputs is separate in the frequency spectrum of combiner 149. This allows one set-top box in each of the feeder lines to transmit at the same frequency and at the same time as another set-top box in another feeder line. Thereby provide a substantially higher effective return bandwidth for the cable system.
It is anticipated that the novel set-top boxes shown herein may have wireless capability added to them to allow them to communicated wireless to other devices in the home and business facilities such as personal computers, videophones, telephone etc.
The optical transmitters, optical receivers, high pass filters, band pass filters, band stop filters, converter receivers, transmitters and other components herein are all commercially available or easily configured from available components. Any such components operative as required herein may be used in accordance with the principles of this invention.
It is to be understood that although the invention has been described illustratively in terms of a set-top box, any two-way communication device, such as a cable modem, can be used.
Claims (64)
1. A cable system including a headend for providing forward signals in a high frequency band and a cable node, said node being connected to said headend via a two-way communication path, said system including a major trunk having a plurality of forward amplifiers there along, said system including a plurality of feeder lines each extending between ones of said amplifiers and feeder line ends, each of said feeder lines including a terminal amplifier at a first position before anyone of said plurality of feeder line ends, said system including first means for receiving said forward signals and second means responsive to said forward signals for retransmitting said signals in a high frequency band, said first and second means being located in each feeder line at said first position, said system including a return communication path connected between each of said second means and said node.
2. A cable system as in claim 1 wherein said return communication path comprises a fiber optic cable and said second means comprises an optical transmitter.
3. A cable system as in claim 1 wherein said major trunk also includes reverse amplifiers.
4. A cable system as in claim 1 also including at least one auxiliary feeder line connected between an amplifier in said major trunk and at least one feeder line end, said auxiliary feeder line including a band stop filter.
5. A cable system as in claim 2 wherein each of said feeder lines also includes a high pass filter at said first position.
6. A cable system as in claim 2 wherein each of said feeder lines also includes a band pass filter at said first position.
7. A cable system as in claim 6 wherein each of said feeder lines also includes a demodulator and a modulator at said first position.
8. A cable system as in claim 7 wherein the demodulator-modulator pair for each feeder line is operative at a different frequency.
9. A cable system as in claim 1 wherein each of said feeder lines includes a block frequency converter.
10. A cable system as in claim 1 wherein said node includes a combiner for signals transmitted thereto for transmission to said headend via a single fiber cable.
11. A cable system as in claim 9 also including set-top boxes connected to said feeder lines, each of said set-top boxes being configured to transmit at a different frequency.
12. A cable system as in claim 1 also including set-top boxes connected to said feeder lines, each of said set-top boxes being configured to transmit at the same frequency, said node including means for frequency division multiplexing of the signals from said feeder lines.
13. A cable system as in claim 1 also including set-top boxes connected to said feeder lines, one set-top box in each of said feeder lines being configured to transmit at the same frequency in the high frequency band and at the same time as another set-top box in another said feeder line, said node including means for frequency division multiplexing of signals from each of said feeder lines.
14. A cable system as in claim 12 wherein said set-top boxes are configured to transmit in the 50 to 750 MHz band.
15. A cable system as in claim 1 also including at least one auxiliary feeder line, said auxiliary feeder line including a band stop filter located at a position where said auxiliary feeder line connects to one of said feeder lines.
16. A cable system as in claim 11 wherein said set-top boxes transmit in the 350 MHz portion of the frequency spectrum and receives in the 50 - 300 MHz and in the 350 - 750 MHz portion of the frequency band.
17. A cable system as in claim 12 wherein said set-top boxes transmit in the 350 MHz portion of the frequency spectrum and receives in the 50 - 300 MHz and in the 350 - 750MHz portion of the frequency spectrum.
18. A cable system as in claim 11 wherein each of said feeder lines includes a band stop filter for preventing signals from one of said set_top boxes from being received by more than one feeder line end.
19. A cable system as in claim 12 wherein each of said feeder lines includes a band stop filter for preventing signals from one of said set_top boxes from being received by more than one feeder line end.
20. A set-top box including a band pass filter operative to pass signals in the 300 -350 MHz band, said set-top box being configured to both receive and transmit in the same portion of the frequency spectrum, said set-top box also configured to transmit a return signal in the 5-40 MHz band.
21. A set-top box including a high pass filter to pass return signals in the 700 MHz and up band, said set-top box being configured to receive in the 50 - 700 MHz band, said set-top box also configured to transmit in the 5-40 MHz band.
22. A cable system as in claim 2 wherein said headend includes means for polling a set-top box and the corresponding feeder line end optical transmitter simultaneously so that only signals from the receiver at that feeder line end are received at the headend.
23. A cable system including a cable headend for transmitting forward signals in a high frequency band and for receiving return signals in a high frequency band, said system including at least one node connected to said headend via a two way communication path, said system also including a major trunk connected between said node and a major trunk end, said major trunk including forward amplifiers there along and being devoid of return amplifiers for signals in the low frequency band.
24. A cable system including a cable headend configured for transmitting forward signals in a high frequency band and for receiving return signals in a high frequency band, said system including a node connected to said headend via a two way communication path, said system including a major trunk connected between said node and a trunk end and including forward amplifiers there along, said system being devoid of reverse amplifiers, said system including a plurality of feeder lines each extending from said major trunk to a plurality of feeder line terminators and including a terminal amplifier located at a first position before anyone of said plurality of feeder line terminators, said system including a return path for signals in said high frequency band, said return path being connected between said feeder line at said first position and said cable headend.
25. A cable system including a cable headend for transmitting forward signals in a high frequency band and for receiving return signals in a high frequency band, said system including a node connected to said headend via a two way communication path, said system including a major trunk connected between said node and a trunk end and including forward amplifiers there along, said system including a plurality of feeder lines each connected between said major trunk and a plurality of feeder line ends, each of said feeder line ends including first means for receiving forward signals in said high frequency band and second means responsive to forward signals in said high frequency band for retransmitting said signals in said high frequency band, said system including means connected between each of said feeder line ends and said headend for carrying said signals in said high frequency band.
26. A set-top box including a band stop filter and a receiver, said band stop filter being operative to exclude a first portions of a frequency band in which signals can be applied to said receiver, said set-top box also including a band pass filter and a transmitter, said band pass filter being operative to pass from said transmitter only signals in the excluded first portion of the frequency band, said set-top box also includes a low pass filter that is operative in low frequency band and a second transmitter also operative in the low frequency band.
27. A set-top box as in claim 26 where the low pass filter frequency band is below 50 MHz.
28. A set-top box including a low pass filter and an associated receiver, said low pass filter being operative to pass to said receiver only signals in a low portion of a high frequency band, said set-top box also including a relatively high pass filter and a transmitter, said relatively high pass filter being operative to pass from said transmitter only signals in a high portion of said high frequency band, said set-top box also including a low-low pass filter that operates in the frequency band that is lower the said low pass filter and an associated second transmitter operating in the low-low frequency band.
29. A set-top box as in claim 28 where the low-low pass filter frequency band is below 50 MHz.
30. A cable system comprising a major trunk and a plurality of feeder lines, each of said feeder lines being connected between a node in said trunk and a feeder line end, each of said feeder lines including a plurality of taps and a two-way communication device connected to each of said taps, each of said feeder lines including forward amplifiers for passing signals in a high frequency band forward from said headend to said two-way communication devices and for passing "return" signals in said high frequency band to said feeder line ends, said two way communication devices being configured to both receive and transmit in said high frequency band, each of said feeder line ends including a receiver for receiving transmissions in said high frequency band and a means for retransmitting received transmissions in said high frequency band to said node.
31. A cable system as in claim 30 wherein said receiver is an optical transmitter.
32. A cable system as in claim 30 wherein both of said two-way communication devices and said headend transmit in said high frequency band.
33. A cable system as in claim 30 wherein said feeder line end also includes a fiber link to the node.
34. A cable system as in claim 30 wherein at least one of said feeder lines includes an auxiliary feeder line, said auxiliary feeder line including a band stop filter.
35. A cable system as in claim 33 wherein at least one of said feeder lines includes an auxiliary feeder line, said auxiliary feeder line including a band stop filter.
36. A cable system as in claim 30 wherein said two-way communication devices include set-top boxes.
37. A cable system as in claim 34 wherein said two-way communication devices include set-top boxes.
38. A system comprising a major trunk and a plurality of feeder lines connected between said trunk and respective feeder line ends, each of said ends including a receiver for signals in a high frequency band, said system including a headend connected to said trunk and two-way communication devices connected to said feeder lines, both said headend and said two-way communication devices being configured to transmit signals in said high frequency band, said feeder lines including forward amplifiers which pass signals forward to said two-way communication devices only in said high frequency band and pass return signals forward to said feeder line ends only in said high frequency band, said feeder ends including first means for receiving signals in said high frequency band and a second means for transmitting said signals in said high frequency band.
39. A system as in claim 38 wherein said devices comprise set-top boxes.
40. A system as in claim 38 wherein said first means comprises a receiver of signals in said high frequency band and second means for generating signals for transmitting in said high frequency band.
41. A system as in claim 38 wherein said second means comprises a frequency converter and a transmitter for transmitting signals in said high frequency band.
42 A cable system including a cable headend and a major trunk, said trunk having taps there along, said system having at least one feeder line connected between one of said taps and a feeder line end, said feeder line including at least one set-top box, said set-top-box and said cable headend being configured to transmit signals indifferent portions of a high frequency band, said set-top and said cable headend also being configured to receive signals in said high frequency band.
43. A cable system as in claim 42 wherein said feeder line end having a means to receive signals in said high frequency band and transmit received signals in said high frequency band.
44. A cable system as in claim 43 wherein said system includes means for including a notch in said high frequency band in which said headend does not transmit, said set-top box being configured for transmitting in said notch.
45. A cable system as in claim 43 wherein said feeder line end also having a block frequency converter.
46. A cable system comprising a cable headend, a return node and a plurality of feeder lines, each of said feeder lines being connected between said return node and a feeder line end, each of said feeder lines including a plurality of taps, a plurality of two-way communication devices connected to said taps, said cable headend and said two-way communication devices being configured to transmit in a high frequency band, each of said feeder line ends including first means for receiving transmissions in said high frequency band and second means for re-transmitting the received transmissions in a high frequency band via a fiber link.
47. A cable system as in claim 46 wherein said second means includes a frequency converter.
48. A cable system as in claim 46 wherein said second means includes a demodulator and a modulator.
49. A cable system as in claim 46 wherein said fiber link goes back to said return node.
50. A cable system as in claim 46 wherein said fiber link goes back to said cable headend.
51. A cable system as in claim 46 including an auxiliary feeder line extending from a tap in one of said feeder lines to a (auxiliary) feeder line end, said auxiliary feeder line including a band stop filter and said tap, said auxiliary feeder line also including a receiver and means to retransmit receives signals in the said high frequency band back to said node.
52. A cable system as in claim 46 wherein said two-way communication devices comprise set-top boxes.
53. A cable system as in claim 46 wherein said headend is configured to transmit in said high frequency band except for a notch portion therein, and said two way communication device is configured to transmit in said notch portion.
54. A cable system as in claim 52 wherein said headend is configured to transmit in said high frequency band except for a notch portion therein, and said set-top box is configured to transmit in said notch portion.
55. A cable system as in claim 53 wherein said two way communication device includes a band stop filter with an associated receiver of signals from said headend, said device also including a band pass filter and an associated transmitter.
56. A cable system as in claim 54 wherein said set-top box includes a band stop filter with an associated receiver of signals from said headend, said set-top box also including a band pass filter and an associated transmitter.
57. A cable system as in claim 46 also including reverse amplifiers that pass signals in the low frequency band.
58. A cable system including a block frequency converter at least first and second feeder line ends, said feeder line ends also including an optical transmitter.
59. A cable system as in claim 58 including forward amplifiers that carry signals in the high frequency band.
60. A cable system as in claim 59 including reverse amplifiers that carry signals in the low frequency band.
61. A cable system as in claim 58 including set-top boxes that have means to receive and transmit in said high frequency band.
62. A cable system including a feeder line and an auxiliary feeder line extending therefrom via a bridger amplifier, said auxiliary feeder line including a band stop filter at said bridger amplifier, said auxiliary feeder line also including a receiver to receive signals in the high frequency band and an optical transmitter at the end thereof.
63. A cable system as in claim 62 which also includes forward only amplifiers in the auxiliary feeder line.
64. A cable system as in claim 62 which also includes bi-directional amplifiers in the auxiliary feeder line.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US55762900A | 2000-04-25 | 2000-04-25 | |
| US09/557,629 | 2000-04-25 | ||
| PCT/CA2001/000556 WO2001082618A2 (en) | 2000-04-25 | 2001-04-25 | Two way cable system with noise-free return path |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2407321A1 true CA2407321A1 (en) | 2001-11-01 |
Family
ID=24226238
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002407321A Abandoned CA2407321A1 (en) | 2000-04-25 | 2001-04-25 | Two way cable system with noise-free return path |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP1287693A2 (en) |
| CN (1) | CN1439226A (en) |
| AU (1) | AU2001252082A1 (en) |
| CA (1) | CA2407321A1 (en) |
| NZ (1) | NZ522452A (en) |
| WO (1) | WO2001082618A2 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5881362A (en) * | 1994-11-30 | 1999-03-09 | General Instrument Corporation Of Delaware | Method of ingress noise reduction in calbe return paths |
| GB2313274A (en) * | 1995-01-30 | 1997-11-19 | Motorola Inc | Method and system for clearing a frequency band |
| DE19531118A1 (en) * | 1995-08-24 | 1997-02-27 | Sel Alcatel Ag | Electrical transmission system, with a broadband distribution network for TV and audio signals, and with a possibility for interactive services |
| EP0762766A3 (en) * | 1995-09-12 | 1997-11-05 | AT&T Corp. | Network apparatus and method for providing two-way broadband communications |
-
2001
- 2001-04-25 CA CA002407321A patent/CA2407321A1/en not_active Abandoned
- 2001-04-25 EP EP01925260A patent/EP1287693A2/en not_active Withdrawn
- 2001-04-25 AU AU2001252082A patent/AU2001252082A1/en not_active Abandoned
- 2001-04-25 WO PCT/CA2001/000556 patent/WO2001082618A2/en not_active Application Discontinuation
- 2001-04-25 CN CN 01811662 patent/CN1439226A/en active Pending
- 2001-04-25 NZ NZ522452A patent/NZ522452A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| EP1287693A2 (en) | 2003-03-05 |
| CN1439226A (en) | 2003-08-27 |
| WO2001082618A9 (en) | 2001-12-06 |
| AU2001252082A1 (en) | 2001-11-07 |
| NZ522452A (en) | 2004-07-30 |
| WO2001082618A2 (en) | 2001-11-01 |
| WO2001082618A3 (en) | 2002-04-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20050127 |