WO2000052854A1 - Systeme de television par cable a compensation des retards sur chemin inverse - Google Patents

Systeme de television par cable a compensation des retards sur chemin inverse Download PDF

Info

Publication number
WO2000052854A1
WO2000052854A1 PCT/US2000/005695 US0005695W WO0052854A1 WO 2000052854 A1 WO2000052854 A1 WO 2000052854A1 US 0005695 W US0005695 W US 0005695W WO 0052854 A1 WO0052854 A1 WO 0052854A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical
receiver
television system
cable television
information
Prior art date
Application number
PCT/US2000/005695
Other languages
English (en)
Inventor
Forrest M. Farhan
Original Assignee
Scientific-Atlanta, 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 Scientific-Atlanta, Inc. filed Critical Scientific-Atlanta, Inc.
Publication of WO2000052854A1 publication Critical patent/WO2000052854A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client 
    • H04N21/61—Network physical structure; Signal processing
    • H04N21/6106—Network physical structure; Signal processing specially adapted to the downstream path of the transmission network
    • H04N21/6118—Network physical structure; Signal processing specially adapted to the downstream path of the transmission network involving cable transmission, e.g. using a cable modem
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/03—Arrangements for fault recovery
    • H04B10/032—Arrangements for fault recovery using working and protection systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client 
    • H04N21/61—Network physical structure; Signal processing
    • H04N21/6156—Network physical structure; Signal processing specially adapted to the upstream path of the transmission network
    • H04N21/6168—Network physical structure; Signal processing specially adapted to the upstream path of the transmission network involving cable transmission, e.g. using a cable modem
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/22—Adaptations for optical transmission

Definitions

  • This invention relates generally to fiber optic communications, and more specifically to optical transmitters for use in fiber optic communications.
  • Cable television systems typically include a headend section for receiving satellite signals and demodulating the signals to an intermediate frequency (IF) or baseband.
  • the down converted signals are then modulated with radio frequency (RF) carriers and converted to an optical signal for transmission from the headend section over fiber optic cable.
  • RF radio frequency
  • Optical transmitters are distributed throughout the cable system, such as at headends, for splitting and transmitting optical signals, and optical receivers are provided in remote locations within the distribution system for receiving the optical signals and converting them to radio frequency (RF) signals that are further transmitted along branches of the system over coaxial cable rather than fiber optic cable.
  • Taps are situated along the coaxial cable to tap off downstream (also referred to as "outbound” or "forward") cable signals to subscribers of the system.
  • Conventional cable television systems can also include a reverse path in which upstream (or "reverse” or “inbound”) signals are transmitted from subscriber equipment to the headend equipment.
  • Reverse signals are processed by the taps, the optical nodes and/or hubs, and are finally delivered to the headend equipment, and the reverse signals may be optical or electrical, depending upon the communication media available for upstream transmission.
  • FIG. 1 is a block diagram of a cable television system in accordance with the present invention.
  • FIG. 2 is a block diagram of redundant paths between an optical transmitter and an optical receiver included in the system of FIG. 1 in accordance with the present invention.
  • FIG. 3 is an electrical block diagram of the optical receiver included in the cable television system of FIG. 1 for processing information provided by redundant paths in accordance with the present invention.
  • FIG. 4 is a flowchart depicting an operation of a controller included in the optical receiver of FIG. 3 in accordance with the present invention.
  • FIG. 1 shows a communications system, such as a cable television system 100 having both forward and reverse paths, i.e., having the ability to communicate downstream in the forward direction and upstream in the reverse direction.
  • the cable television system 100 includes a headend 105 for receiving satellite signals that are demodulated to baseband or an intermediate frequency (IF).
  • IF intermediate frequency
  • the baseband signal is then converted to cable television signals that are routed throughout the system 100 to subscriber equipment 130, such as set top decoders, televisions, or computers, located in the residences or offices of system subscribers.
  • subscriber equipment 130 such as set top decoders, televisions, or computers, located in the residences or offices of system subscribers.
  • the headend 105 can, for instance, convert the IF/baseband signal to an optical signal that is transmitted over fiber optic cable 1 l OJn which case a remotely located optical node 1 15 converts the optical signal to an electrical radio frequency (RF) signal for further transmission through the system 100 over coaxial cable 120.
  • RF radio frequency
  • Taps 125 located along the cable 120 at various points in the distribution system split off portions of the RF signal for routing to subscriber equipment 130 coupled to subscriber drops provided at the taps 125.
  • the system 100 also has reverse transmission capability so that signals, such as data, video, or voice signals, generated by the subscriber equipment 130 can be provided back to the headend 105 for processing.
  • the reverse signals travel through the taps 125 and any nodes 1 15 and other cable television equipment, e.g., reverse amplifiers, to the headend 105.
  • RF signals generated by the subscriber equipment 130 travel to the node 1 15, which converts the RF signals to optical signals for transmission over the fiber optic cable 1 10 to the headend 105.
  • the forward signals of cable television systems are typically separated from the reverse signals by frequency division multiplexing. In North America, forward signals are carried in the 50-750 MHz band, and reverse signals are carried in the 5-40 MHz band.
  • a block diagram depicts signal transmission between an optical receiver 210 and an optical transmitter 205, both included in the cable television system 100.
  • the optical transmitter 205 can, for instance, be included in an optical node 115, hub, or headend equipment 105.
  • the optical receiver 210 can likewise be included in another node, hub, or headend equipment 105 that is redundantly coupled to the transmitter 205.
  • the transmitter 205 and the receiver 210 are described hereinbelow as being included in the reverse communication path so that reverse information is redundantly transmitted upstream. It will be appreciated, however, that the diversity provided by redundant digital optical paths could be equally beneficial in the forward distribution system of a cable television system.
  • Information transmitted upstream in the reverse path may originate from subscriber equipment 130, from a hub or node 115, or from a source (not shown) entirely outside the system 100, and, as mentioned briefly in the above Background of the Invention, the upstream information may be relatively important.
  • the information may include subscriber billing information, subscriber inquiries, or status information about system components. Therefore, the system 100 includes redundant paths 215, 220, which are depicted as "Path A" and "Path B.”
  • the optical transmitter 205 includes a separate digital optical transmitter circuit for each redundant path. The details of a digital optical transmitter circuit that can be included in the optical transmitter 205 are set forth in Attorney's Docket No.
  • A-5219 entitled “Digital Optical Transmitter” by Forrest M. Farhan, filed on October 9, 1998 and assigned to the assignee hereof ("Farhan "), the teachings of which are hereby incorporated by reference.
  • a separate digital optical receiver circuit is included in the optical receiver 210, and the details of one such receiver circuit are also taught by Farhan.
  • Information transmitted upstream between the transmitter 205 and the receiver 210 is provided by digital optical signals comprising bits of data transmitted at a predetermined bit rate.
  • Paths A and B are redundant and, typically, diversely routed, failure of one path, such as could occur when a fiber optic cable is inadvertently cut, does not prevent reverse information from being transmitted upstream.
  • the redundant Paths A and B provide a degree of reliability that is not present in systems without redundancy.
  • the diverse paths are unlikely to be exactly the same length. Therefore, time delays are introduced between the two paths. Since many subscriber devices, e.g., DOCSIS cable modems, transmit in predetermined time slots, time delays in a particular path can cause erroneous identification of the transmitting device from which information originates. This can result in missed subscriber inquiries, lack of response to subscribers, and even service disruption.
  • FIG. 3 shows an electrical block diagram of the optical receiver 210, which, according to the present invention, advantageously compensates for time delays between diverse upstream paths, such as Paths A and B.
  • the optical receiver 210 includes an input port 305, 310 for each diverse path that is provided from the transmitter 205 (FIG. 2).
  • the Path A input port 305 is coupled to a first receiver circuit 315 and to a status monitor 325, which can be internal to the receiver circuit 315, as shown, or external to the receiver circuit 315.
  • the Path B input port 310 is coupled to a second receiver circuit 330. Outputs of the first and second receiver circuits 315, 330 are coupled to different poles of a switch 320, which is electrically connected to a receiver output port 350.
  • At least one of the receiver circuits includes a delay circuit 335, which is enabled and disabled by a controller 340.
  • a memory 345 can be programmed with a value indicative of a number of bytes by which an incoming redundant signal should be delayed to compensate for the time delay between Path A and Path B.
  • Path A will be described as the reverse path over which reverse information is normally received, although it will be appreciated that either path could be normally used as long as the delay is introduced into the shorter (and therefore faster) path.
  • the status monitor 325 can be a conventional circuit that monitors the signal on Path A and outputs an alarm signal upon detecting that Path A is not delivering information or is delivering suspect information.
  • the memory 345 is a programmable memory, preferably non-volatile, that stores a predetermined delay value.
  • the value can, for instance, be obtained by measuring information delivery over Path A and Path B to determine the time difference between the two, calculating a number of bytes that can be transmitted in that time period, then storing a value indicative of the number of bytes.
  • a flowchart depicts an example of an operation that can be performed by the controller 340 to provide delay compensation.
  • the controller 340 receives an alarm signal from the status monitor 325, the controller 340 retrieves the delay value from the memory 345, at step 410.
  • the controller 340 then activates, at step 415, the delay circuit 335 of the redundant receiver circuit 330 to delay information received over Path B by the number of bits indicated by the delay value.
  • the controller 340 also provides a control signal to the switch 320, at step 420, directing the switch 320 to couple the receiver output port 350 to the Path B receiver circuit 330, rather than to the Path A receiver circuit 315.
  • the controller 340 continues to monitor the output of the status monitor 325, and when, at step 425, the controller 340 determines that Path A has been restored, the controller 340 causes the switch 320 to again couple the output port 350 to the Path A receiver circuit 315.
  • steps 410 and 415 e.g., retrieval of the number of delay bits/bytes for the delay circuit 335, need not be performed during each cycle shown in the flowchart of FIG. 4. Instead, steps 410 and 415 could be performed a single time (either upon system initiation/provisioning or as needed the first time the paths are switched), after which the delay circuit 335 will store the delay value for subsequent use.
  • conventional status monitoring circuitry could be included in both redundant receiver circuits to monitor both redundant Paths A and B, in which case the controller 340 could control the switch 320 so that it remains coupled to the Path B receiver circuit 330 until a failure has been detected in Path B.
  • the controller 340 could control the switch 320 so that it remains coupled to the Path B receiver circuit 330 until a failure has been detected in Path B.
  • N DTIT S , where T s is the sampling period of the digitized signal.
  • the cable television system described above includes a digital transmission system, perhaps in the reverse path, for transmitting information in the form of digital optical signals.
  • redundant paths can be provided for devices, such as hubs, nodes, and headend equipment, between which digital optical signals are transmitted. Since the diverse paths are unlikely to be equal in length, a time delay compensation circuit can be included in each optical receiver that receives information over redundant paths. As a result, information can be sent between digital optical devices in a simple, more reliable manner. More specifically, the use of redundancy in accordance with the present invention will ensure that burst mode transmission schemes, or any other payload scheme sensitive to path or time delay, will be transported reliably and with minimal service impact during a protection switch. In prior art systems, on the other hand, protection switching can cause significant service impact.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

Abstract

L'invention concerne un système de télévision par câble (100) comprenant un émetteur optique (205) conçu pour transmettre les informations optiques numériques et un récepteur optique (210) pour recevoir les informations optiques numériques. Au moins une première et une seconde voie de communication (215, 220) l'émetteur optique (205) au récepteur optique (210). Le récepteur optique (210) comprend un circuit à retard (335) relié à la première voie de communication (220) pour retarder les informations transmises sur la première voie de communication (220) d'un nombre prédéterminé de bits de manière à compenser les retards associés à la première et à la seconde voie de communication (215, 220).
PCT/US2000/005695 1999-03-05 2000-03-02 Systeme de television par cable a compensation des retards sur chemin inverse WO2000052854A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US26345199A 1999-03-05 1999-03-05
US09/263,451 1999-03-05

Publications (1)

Publication Number Publication Date
WO2000052854A1 true WO2000052854A1 (fr) 2000-09-08

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2000/005695 WO2000052854A1 (fr) 1999-03-05 2000-03-02 Systeme de television par cable a compensation des retards sur chemin inverse

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0637879A1 (fr) * 1993-04-16 1995-02-08 Nec Corporation Dispositif de commutation sans parasite et procédé pour un réseau optique
WO1999005802A1 (fr) * 1997-07-23 1999-02-04 Adc Telecommunications, Inc. Protection multiligne pour reseau de telecommunication

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0637879A1 (fr) * 1993-04-16 1995-02-08 Nec Corporation Dispositif de commutation sans parasite et procédé pour un réseau optique
WO1999005802A1 (fr) * 1997-07-23 1999-02-04 Adc Telecommunications, Inc. Protection multiligne pour reseau de telecommunication

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
BANKAPUR R J ET AL: "SWITCHED DIGITAL VIDEO ACCESS NETWORKS", BELL LABS TECHNICAL JOURNAL,US,BELL LABORATORIES, vol. 1, no. 1, 21 June 1996 (1996-06-21), pages 66 - 77, XP000635762, ISSN: 1089-7089 *
YOSHIAKI SATO ET AL: "ECONOMICAL AND RELIABLE SDH OPTICAL TRANSMISSION SYSTEM", NTT REVIEW,JP,TELECOMMUNICATIONS ASSOCIATION, TOKYO, vol. 7, no. 6, 1 November 1995 (1995-11-01), pages 80 - 84, XP000548928 *

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