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WO1998039920A1 - Communication ascendante sans fil mettant en oeuvre une conversion de frequence - Google Patents

Communication ascendante sans fil mettant en oeuvre une conversion de frequence Download PDF

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Publication number
WO1998039920A1
WO1998039920A1 PCT/US1998/003718 US9803718W WO9839920A1 WO 1998039920 A1 WO1998039920 A1 WO 1998039920A1 US 9803718 W US9803718 W US 9803718W WO 9839920 A1 WO9839920 A1 WO 9839920A1
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WO
WIPO (PCT)
Prior art keywords
frequency
cable
signal
upstream
way
Prior art date
Application number
PCT/US1998/003718
Other languages
English (en)
Inventor
Paul Baran
Mark Laubach
Ali Raissinia
Original Assignee
Com21, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Com21, Inc. filed Critical Com21, Inc.
Priority to AU64398/98A priority Critical patent/AU6439898A/en
Publication of WO1998039920A1 publication Critical patent/WO1998039920A1/fr

Links

Classifications

    • 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

Definitions

  • the present invention relates to an over-the-air upstream path for data transmission on a cable TV system.
  • the present invention relates to converting standard one-way cable systems into a two-way system by converting the same signal into different frequencies for wireless upstream communications.
  • the use of a separate telephone line return for the upstream cable subscriber signals is well known and is used in a number of different cable modems.
  • the idea of heterodyned frequency translation per se is also old art.
  • the use of frequency translation in cable systems is probably best developed in the RAD concept used to transmit PCS signals over a cable system.
  • the RAD concept includes the use of inexpensive antennas and frequency shifters as a two way delivery mechanism to remote PCS devices. Over-the-air, two-way signals from cordless Personal Communications Service telephones, say at 1800 MHz from a number of remote antenna sites are frequency shifted and carried to and from one or more central sites. Today, only 10-15% of the cable plants have been converted to two-way operation.
  • the present invention provides a solution whereby a transparent radio return path is temporarily or permanently used for providing upstream communications, which allows cable operators to be able to selectively upgrade their systems on an as-needed basis. Costs are minimized by leveraging off the same frequency, scheduling, and modulation schemes to keep the conversion from the radio path signal to the signal on the cable as simple and straightforward as possible. And optionally at a later date, removing the radio path sections to use the conventional cable upstream path.
  • the present invention pertains to a method and apparatus for converting a traditional one-way cable system into a two-way system by utilizing an over-the air radio frequency (RF) return path to provide upstream communications.
  • RF radio frequency
  • a transmitter applique is attached to a subscriber's conventional two-way cable modem that normally operates in a given modem frequency range generally at 5 to 42 MHz.
  • This transmitter applique heterodynes the normal upstream cable modem signal to a frequency suitable for transmission over-the-air.
  • a matched reverse heterodyning of the received signal is performed via a receiver applique.
  • This applique transposes the received signal back to the transmitting modem's original frequency and modulation format where it is received by the normal cable head end modem without any modifications.
  • the exact same receiving equipment and frequency channelization are preserved by making the use of the radio path essentially transparent to the overall cable system.
  • the cable customers using this invention are those typically having a two-way cable modem that use a remote controlled noise blocking filter at the junction of the drop cable, to the cable tap at the feeder.
  • This same signal, as used to open the noise blocking filter, can be used in the present invention to turn on and off the RF transmitter in the transmitter applique.
  • the transmitter applique is a small unit containing the circuitry required to perform the superheterodyning of the original modem frequency to a radio frequency suitable for over-the-air transmission.
  • the output of the transmitter in the applique is fed to a coax cable to convey the radio signal to a transmitter antenna.
  • the transmitter applique is mounted in close proximity to the two-way cable modem and thus is able to receive power and control signals from the two-way cable modem to minimize cost.
  • the transmitter applique is interposed remotely between the cable modem and feeder tap, with the output of the applique's over-the-air signal connected to an antenna and thence received by one or more receiving antennas which are connected to the cable plant head end.
  • neither the frequencies nor the precise modulation used nor the formatting is modified to keep the conversion from the radio path signal to the signal on the cable as simple and straightforward as possible. While the purpose of using the radio path is to defer the expense of insertion of diplexing filters and reverse amplifiers throughout the entire cable system path until enough two way users are present to justify the common expenditure of the plant upgrade, there will be instances where the radio path alone will suffice forever and the full upstream cable conversion be indefinitely deferred.
  • Figure 1 shows a block diagram of a standard one-way cable TV network that has been upgraded into a two-way system by adding a radio return link.
  • Figure 2 is a circuit diagram of a transmitter applique unit and its connection to the two-way cable modem.
  • Figure 3 is a circuit diagram of the receiving site frequency downconverter.
  • Figure 4 is a circuit diagram of a receiver applique.
  • Figure 5 shows a block diagram of a standard one-way cable TV network that has been upgraded according to the present invention with a radio return link for enabling two-way communications .
  • Figure 6A shows a one-way line extender amplifier in a shielded case in a cable system.
  • Figure 6B shows a plug-in diplexing filter module for two- way operation in a shielded case of a cable system.
  • Figure 6C shows an upstream amplifier module for two-way operation in a shielded case of a cable system.
  • FIG. 7 shows that an upstream radio link can be added in lieu of the upstream amplifier module.
  • Figure 8 shows an exemplary transmitting antenna 801 as may be connected to a transmitter applique.
  • a transmitter applique is attached that converts an upstream modem signal on a coaxial line (e.g., in the 5-42 MHz band) into a frequency range suitable for over-the- air radio transmission to the cable head end or to one or more intermediate points.
  • a coaxial line e.g., in the 5-42 MHz band
  • two-way cable modem is not to be limited to simple conventional two way TV cable modems, but also includes all types and variations of subscriber terminal units ( ⁇ TUs) , interactive TV set-top boxes, etc.
  • ⁇ TUs subscriber terminal units
  • the selected radio channel can be one that is suitable for transmission without the necessity of separate FCC licensing, such as the frequency ranges 902-928 MHz. or 2400-2483.5 MHz or 5725-5850 MHz.
  • an inverse transformation is performed, shifting the received band back to the 5-42 MHz range where the received signal can be processed by a conventional head end controller.
  • the up conversion and reciprocal down conversion process is performed by a conventional superheterodyning process, whereby a signal having one frequency is converted into a higher or lower frequency by mixing it with a locally generated signal and filtering out the undesired modulation products.
  • FIG. 1 shows a block diagram of the present invention in its simplest form.
  • a head end unit 101 of a cable TV (CATV) plant transmits data/TV signals downstream over standard coaxial cable 102 to a two-way cable modem 103 installed at a subscriber's location.
  • CATV cable TV
  • the subscriber transmits data back upstream by using transmitter applique 104 to upconvert the signal generated by the cable modem 103 into a radio frequency suitable for over-the-air transmission via transmitting antenna 105. This radio signal is then received by antenna 106. A receiver applique 107 downconverts the received signal which is then sent to the head end unit 101 for further processing.
  • transmitter applique 104 is comprised of circuitry required to perform the conversion from 5-42 MHz to a frequency suitable for radio transmissions. It can be a standalone unit or integrated as part of the cable modem 103. It should be noted that the present invention can be used with a variety of cable modems. One example is the P3 two- way cable modem designed and manufactured by Com21, Inc. of Milpitas, CA. Transmitter applique 201 accepts downstream as well as upstream communications. On the downstream side, a downstream signal in the 5-42 MHz range being transmitted over a standard cable system is accessed by tap 202 via feeder cable 203.
  • This signal is then fed through drop cable 204 to applique 201, which passes it on as an input to the STU 205.
  • a directional coupler 206 is used to direct the 5-42 MHz upstream data signal from STU 205 to a mixer 207.
  • the mixer 207 takes the 5-42 MHz data signal and mixes it with a higher frequency signal (e.g., 886 MHz) to attain a suitable RF frequency for transmission over the airwaves.
  • the higher frequency signal can be provided by an oscillator block 240. Additional circuitry may be added to provide for greater frequency and phase accuracy.
  • a combination of filters 221-222, amplifiers 223-224, local oscillator 225, and divider 226 are used to provide the appropriate signal processing, which is well known in the art.
  • the output of the applique 201 is a coax cable conveying the RF signal suitable for connection to an antenna 208.
  • the transmitted power and transmitting antenna gain are chosen to provide a signal sufficient to reach one or more receiving antennas having an electrical path to the cable plant head end. It is desirable that the upstream radio transmitter is turned on if and only if there is information to be transmitted upstream. Hence, a switch 209 is used to enable transmission only if there is data to be transmitted.
  • the cable modem also produces a control signal that is used to open up a blocking filter at the junction of the drop cable 204 to the subscriber and the cable tap 202 at the feeder 203. This control signal can be used to control switch 209 for turning on and off the RF transmitter in the applique 201.
  • the head end unit adaptively controls the power level of the transmitted radio signal by sending a power level command over the downstream path to the cable modem 205.
  • cable modem 205 transmits a corresponding power level control signal to a digital-to-analog converter (DAC) 220, which converts the digital signal into an analog signal for controlling the output power of amplifier 221.
  • DAC digital-to-analog converter
  • the upstream RF signal is propagated over the airwaves and eventually picked up by a receiving antenna 106, as shown in
  • a receiver applique 107 associated with a head end unit 101 accepts the RF signal and down converts the signal back to the original 5-42 MHz frequency range. The down converted signal is then sent to a receiver in the head end unit 101 for further processing.
  • FIG. 4 shows a more detailed circuit diagram of a receiver applique 107.
  • RF signals originating from one or more transmitter appliques, propagating over the airwaves, are picked up by a receiving antenna 106.
  • Antenna 106 can be one of any omni-directional antenna configurations, tuned to the frequency of interest.
  • the received RF signals are first amplified by pre-amp 401 and then filtered by SAW filter 402. Additional gain is provided by amplifier 403.
  • the RF signal is then mixed with a lower frequency reference signal by mixer 404.
  • the reference signal is generated by a combination of voltage controlled oscillator 410, divider 411, mixer 412, and low pass filter 413 which is well known in the art. Alternatively, a simple oscillator block 420 may be used instead.
  • the down converted 5-42 MHz signal is then filtered by SAW filter 306.
  • FIG. 5 shows a block diagram of a standard one-way cable TV network that has been upgraded according to the present invention with a radio return link for enabling two-way communications.
  • part of the CATV network can be comprised of standard one-way set-top boxes with no upstream capability; part can be upgraded with two-way cable modems utilizing an all-coax upstream path; and part can be upgraded with two-way cable modems utilizing applique/antennas for an over-the-air upstream path.
  • the delineation between the various stages of a traditional headend all coax internal distribution, one-way coaxial cable distribution network, existing or new all coax distribution, and subscriber homes/offices is shown in this figure.
  • a traditional head end cable TV network is shown as 101.
  • a headend digital communications controller 502 for controlling all digital data traffic to the downstream coaxial cable distribution network 506 via coaxial link 503.
  • a standard analog TV programming source 504 also places an NTSC video signal onto the coaxial cable distribution network 506 via coax 505.
  • a number of distribution or main amplifiers 523 are used to provide the requisite gain.
  • the downstream signals are fed into one or more one-way line extender/bridging amplifiers or junctions 508-509, which routes the signals to the appropriate destinations.
  • a standard one-way set- top box/TV arrangement is shown as 513. Downstream are routed through interconnecting coupler 508, coax 510, coupler 509, coax 511, and splitter 512.
  • a two-way cable modem is shown as 513. Its upstream path is through bi-directional coupler/amplifiers 509 and 508 onto a coaxial return cable 540. It should be noted that a hybrid fiber coax system can be used by adding a fiber terminal and a corresponding fiber node.
  • the cable modem 514 is also two-ways enabled. For its upstream side, a directional coupler 516 routes upstream signals from a two-way cable modem 514 to the transmitter applique 104.
  • the transmitter applique 104 can be placed adjacent to the cable modem 514. Alternatively, transmitter applique 104 may be situated in a remote location a distance away from the cable modem 514. Furthermore, there may be instances whereby multiple two-way cable modems share one or more transmitter appliques.
  • the upstream signal is up converted by transmitter applique 104 and transmitted by the antenna 105 as a radio signal propagated over the airwaves to a receiving antenna 106 connected to a receiver applique 107.
  • Transmitting antenna 105 can be one of any directional antenna configurations used for transmitting RF signals. Note that directional antennas, particularly those having a high front to back ratio are especially useful for practice in the present invention. Transmitter antenna 105 may be mounted on a subscriber's window or remotely situated, such as on a telephone pole, depending on convenience and line-of- sight considerations.
  • the receiver applique 107 down converts the radio signal back down to the 5-42 MHz frequency range and drops it onto cable 519. Cable 519 is connected into coupler 520 which routes the signal to the head end controller 502 on line 521. It should be noted that the cable modem 514 adjusts its upstream power level to insure that the signal arrives at an optimum level at the head end modem.
  • a wide variety of protocols may be used in conjunction with the present invention. (See, for example, "The UPSTREAMS Protocol for HFC Networks" by Mark Laubach, submitted to the P801.14 Cable TV MAC and PHY Working Group, October 23, 1995) .
  • the same protocol and data format is used with the radio return as is used by the upstream coaxial cable system.
  • the cable network can be selectively upgraded.
  • a further embodiment of this invention places the upstream transmitter applique within or adjacent to a line extender, feeder, or trunk amplifier, to allow spanning over the presently one way parts of a mixed one way and two way cable system. This allows several subscribers may share a single upstream applique unit.
  • the amplifier cases generally contain room for diplexing filters and an optional upstream amplifier module.
  • Figure 6A shows a one-way line extender amplifier in a shielded case in a cable system.
  • plug-in diplexing filter modules can be later added for two-way operation, as shown in Figure 6B.
  • an upstream amplifier module can be further added, as shown in Figure 6C.
  • FIG. 7 shows that an upstream radio link can be added in lieu of the upstream amplifier module.
  • cable TV amplifiers are generally mounted on a support unit and are in locations that can serve as antenna sites.
  • a directive antenna can be pointed to a receiving antenna site offering significantly longer ranges than in-house antennas.
  • the receiving antenna would generally be mounted at a receiver connected to a point along a two-way activated portion of the cable system placing both the transmitting and receiving antennas mounted in favorable sites for longer distance transmission.
  • the connection of the receiver would terminate at an activated two-way location, allowing transmission to the cable head end in the 5-42 MHz range.
  • FIG 8 shows an exemplary transmitting antenna 801 as may be connected to a transmitter applique.
  • Transmitting antenna 801 can be one of any directional antenna configuration used for transmitting RF signals.
  • the coax cable 802 extending from a transmitter applique is terminated to a reflector 803.
  • Reflector 803 gives an electrical null. It can be fashioned as part of a rigid support rod which is pivotable 360 degrees about a mount 804. Thereby, the transmitting antenna can be situated so as to point in the direction of a receiving antenna.
  • the mount can be fixed by means of vacuum cups 805 onto a non-conducting environment (e.g., a window) .
  • a balun 806 is used as an interface between the reflector 803 and corporate feed 807.
  • Corporate feed 807 is eventually split twice and terminated into four dipole 300 ohm elements 808.
  • the doubling of power from each of dipoles 808 and elements 809, produces 6 dB of gain.
  • Director elements 810, that are shorter than the dipoles 808, are used to direct the electrical characteristics of the antenna. In this particular application, director elements 810 are designed to have a center frequency of 915 MHz.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

Abstract

Réseau de télévision par câble bidirectionnel possédant une voie descendante normalisée à câble coaxial et en partie une voie de retour ascendante radioélectrique. On utilise une unité tête de câble classique pour émettre un signal descendant par l'intermédiaire d'un réseau de distribution par câble coaxial normalisé, à destination d'un certain nombre d'abonnés. Pour les communications bidirectionnelles, on utilise un modem à câble bidirectionnel installé chez l'abonné pour recevoir des signaux descendants en provenance de l'unité tête de câble via le câble coaxial normalisé. Du côté émetteur, on utilise une interface d'émetteur couplée au modem à câble bidirectionnel de l'abonné pour convertir la fréquence des signaux générés par le modem à câble bidirectionnel, au moyen de techniques superhétérodynes, en fréquence radio adaptée à une émission radioélectrique. Une antenne d'émission, couplée à l'interface de l'émetteur, permet d'émettre des signaux radioélectriques ascendants.
PCT/US1998/003718 1997-03-04 1998-02-25 Communication ascendante sans fil mettant en oeuvre une conversion de frequence WO1998039920A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU64398/98A AU6439898A (en) 1997-03-04 1998-02-25 Wireless upstream communications using frequency conversion

Applications Claiming Priority (2)

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US81118697A 1997-03-04 1997-03-04
US08/811,186 1997-03-04

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001056289A1 (fr) * 2000-01-27 2001-08-02 Spike Broadband Systems, Inc. Systemes et procedes de communication bidirectionnelle hybrides cables/sans fil

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0695092A1 (fr) * 1994-07-29 1996-01-31 AT&T Corp. Procédé et appareil pour effectuer des communications bidirectionelles à large bande pour réseaux

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0695092A1 (fr) * 1994-07-29 1996-01-31 AT&T Corp. Procédé et appareil pour effectuer des communications bidirectionelles à large bande pour réseaux

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
ELDERING C A ET AL: "CATV RETURN PATH CHARACTERIZATION FOR RELIABLE COMMUNICATIONS", IEEE COMMUNICATIONS MAGAZINE, vol. 33, no. 8, 1 August 1995 (1995-08-01), NEW YORK, NY, US, pages 62 - 69, XP000525541 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001056289A1 (fr) * 2000-01-27 2001-08-02 Spike Broadband Systems, Inc. Systemes et procedes de communication bidirectionnelle hybrides cables/sans fil

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Publication number Publication date
AU6439898A (en) 1998-09-22

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