WO1994024825A1 - Codage et decodage coordonnes dans le temps d'un signal de message - Google Patents

Codage et decodage coordonnes dans le temps d'un signal de message Download PDF

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Publication number
WO1994024825A1
WO1994024825A1 PCT/SE1994/000338 SE9400338W WO9424825A1 WO 1994024825 A1 WO1994024825 A1 WO 1994024825A1 SE 9400338 W SE9400338 W SE 9400338W WO 9424825 A1 WO9424825 A1 WO 9424825A1
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WO
WIPO (PCT)
Prior art keywords
receiving unit
transmitting unit
unit
signal
reference time
Prior art date
Application number
PCT/SE1994/000338
Other languages
English (en)
Inventor
Erik Rickard SÖDERQVIST
Original Assignee
Soederqvist Erik Rickard
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 Soederqvist Erik Rickard filed Critical Soederqvist Erik Rickard
Priority to AU65475/94A priority Critical patent/AU6547594A/en
Publication of WO1994024825A1 publication Critical patent/WO1994024825A1/fr
Priority to SE9503590A priority patent/SE514480C2/sv

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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
    • H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
    • H04N7/1675—Providing digital key or authorisation information for generation or regeneration of the scrambling sequence

Definitions

  • the invention relates to a method for coordinately coding and decoding a TV signal or other message signal which is transmitted from a transmitting unit to at least one receiving unit in a state, coded by means of an encoder incorporated in the transmitting unit, during simultaneous transmission of a separate control signal, generated by the transmitting unit and utilized in the receiving unit to cause a decoder, incorporated in the latter unit, to accomplish a decoding operation on the received message signal, timely coordinated with the coding operation.
  • Such coordinated coding and decoding of a message signal is used especially in subscription TV systems in order to prevent an unauthorized utilization of the coded signal transmitted from the transmitting unit.
  • control signal is of a rather simple kind, which means that the information contained therein may rather easily be read by means of a comparatively simple pirate decoder by which the coded message signal may be decoded also at an unauthorized receiving location.
  • the invention has for its purpose to provide an improved method of the kind initially set forth which offers a highly increased safety against an unauthorized utilization of the transmitted coded message signal by using a new type of control signal.
  • the method according to the invention is primarily characterized in that the transmitting unit is caused to generate a control signal, consisting of a continuous data stream, composed of subsequent frames of mutually equal length, each of which contains a predetermined frame synchronization word which defines a cyclically recurring reference time for the transmitting unit and which is utilized in the receiving unit to determine a corresponding cyclically recurring reference time for the receiving unit, at least some of said frames also containing data which define the time for an alteration of the operating mode of the encoder, related to said reference time for the transmitting unit, and which are utilized in the re ⁇ DCving unit to determine a time for a corresponding alteration of the operating mode of the decoder, related to said reference time for the receiving unit.
  • control signal of the above kind which may be made completely asynchronous or approximately synchronous in relation to the message signal, one will obtain a strongly increased safety against an unauthorized utilization of the transmitted coded message signal. Moreover, the need for effecting a separation of sync pulses from the message signal at the receiving end, in order to make it possible to decode the received coded message signal, is eliminated.
  • the method according to the invention may also be applied on a transmission system wherein two or more message signals are transmitted simultaneously from the transmitting unit to the receiving unit, individually coded by means of respective encoders incorporated in the transmitting unit, and said signals are decoded in the receiving unit by means of respective decoders in ⁇ corporated in this unit.
  • the transmitting unit may be caused to generate a single control signal serving to control the decoding of all message signals.
  • the message signals may be coded and decoded in synchronism with each other.
  • at least some of the message signals are preferably coded and decoded in non-sychro- nism with each other.
  • the trans ⁇ mitting unit may be caused to generate a control signal, consisting of frames, at least some of which contain data which define individual times for altering the operating mode of different encoders and which are utilized in the receiving unit to determine corresponding individual times for altering the operating mode of different decoders.
  • the invention also relates to an arrangement for coordinately coding and decoding a TV signal or other message signal which is transmitted from a transmitting unit to at least one receiving unit in a state, coded by means of an encoder incorporated in the transmitting unit, during simultaneous transmission of a control signal, generated by the transmitting unit and utilized in the receiving unit to cause a decoder, incorporated in the latter unit, to accomplish a decoding operation on the message signal received by the receiving unit, timely coordinated with the coding operation.
  • Figure 2 shows a block diagram of a receiving unit
  • FIG 3 is a diagrammatical illustration of a control signal transmitted from the transmitting unit of Figure 1 to the receiving unit of Figure 2, and Figure 4 shows two time diagrams, illustrating the mutual relationship between the times for certain events taking place in one or the other of said units.
  • the transmitting unit shown in Figure 1 and generally designated 10 has been assumed to comprise only two TV signal channels designated A and B. However, the number of such channels may be substantially larger.
  • Each channel contains a satellite receiver 11, a modula ⁇ tor 12 and an encoder 13.
  • the re- ceived radio frequency signal which is modulated with a TV program, is demodulated to the base band, i.e. to audio and video level.
  • the demodulated video signal V or V , respectively, and the demodulated audio signal A or A n , respectively, are then- fed to modulator 12 which generates an uncoded radio frequency signal RF or RF , respectively, modulated with the TV program in question.
  • This signal is suppled to encoder 13 which converts it into a coded signal RF ' or RF ' , respective- ly, which is fed to an output terminal 14 which is common to both channels A and B and which may be connected to a cable network forming part of the subscription TV system in question.
  • the coding operation in each channel effected on the uncoded TV signal RF or RF , respectively, in encoder 13, may be of different kinds but may preferably consist in frequency shifts, for instance of the kind described in PCT/SE92/00737.
  • the coding operation involves that the encoder 13 is caused to switch from one operating mode to another at short inter- vals, in order hereby to generate a coded signal RF * or RF JD' , respectively, having a successively shifting character.
  • the equipment serving to cause said alteration of the operating mode of the encoder 13 in each channel A and B, respectively, comprises , on the one hand, some components common to both channels and, on the other hand, some components occurring as separate com ⁇ ponents within each channel.
  • the common components primarily consist of a clock 15, a first counter 16, a second counter 17 and a third counter 18, while the individual separate components within each channel con ⁇ sist of a sync separator 19, a register 20 and a compa ⁇ rator 21.
  • Clock 15 generates a continuous series of clock pulses, the frequency of which may for instance be assumed to be 1 MHz. These clock pulses are supplied to counter 16 which is a cyclic counter which for instance may be assumed to count cyclically from 0 to 19999. Counter 16 will then have a cycle length of 20 ms and a counting resolution of 1 ⁇ s .
  • the two other counters 17 and 18 are identically equal to counter 16 and thus, they will also count cyclically from 0 to 19999 at a cycle length of 20 ms and a reso ⁇ lution of 1 ⁇ s.
  • counters 17 and 18, which are both connected to the output of counter 16, are indi ⁇ vidually programmable in order to be able to count with a certain individual displacement in time in relation to counter 16.
  • counter 17 and 18 may be programmed from a microprocessor 22.
  • the output signal from the second counter 17 is continuously supplied to the input of each one of the two register 20 which belong each to one channel A or B, respectively.
  • Each register 20 has a control input con ⁇ nected to the output of the appurtenant sync separator 19.
  • Sync separator 19 which receives video signal V or V D , respectively, from satellite receiver 11, may hereby supply a load pulse to register 20 each time a vertical sync pulse appears in video signal V or V_,, respectively.
  • This output signal from comparator 21 is supplied to encoder 13 where it serves as a load pulse which may cause the encoder to load an instruction regarding a new operating mode for the encoder, previously received from micropro ⁇ cessor 22, into a control circuit incorporated in the encoder.
  • said instruction may con ⁇ sist in an altered value of the frequency of a local oscillator, controlled by means of a phase locking cir ⁇ cuit and connected to a mixer which also receives the uncoded signal RF A or RF , respectively.
  • the alteration in the operating mode of encoder 13 will then consist in an alteration in the frequency shift operation effected by the encoder on the TV signal passing therethrough.
  • the transmitting unit shown in Figure 1 also comprises a data generator 23 and a data modulator 24.
  • Data gene ⁇ rator 23 has for its purpose to generate a control data signal S n for controlling the decoding in an authorized receiving unit of the coded TV signals RF ' and RF ' transmitted over output terminal 14.
  • Control signal S is supplied to data modulator 24 which generates a radio frequency signal RF which is modulated with the control signal and fed to the output terminal 14 in order to be transmitted to the receiving unit together with signals RF ' and RF ' .
  • control signal S n consists of a continuous data stream, composed of subsequent frames F of mutually equal length.
  • data generator 23 is caused to generate frames F having a length corresponding to the cycle length of said counter, i.e. 20 ms, and each of which contains a frame synchronization word FW, con ⁇ sisting of an easily identifiable bit pattern having a specific character deviating from the character of the information contained within the remaining sections of the frame and which for instance may be Manchester- coded.
  • the frame synchronization word FW defines a cyclically recurring reference time T f ( Figure 4) for the transmitting unit to which the time t, In or t,ID, respectively, for the occurrance of the vertical sync pulse as well as the time t culinary A or t» , respectively, for an alteration of the operating mode of decoder 21, which is displaceable in relation to the firstmentioend time, may be related for each one of the two channels A and B.
  • control signal S is also caused, within predeter ⁇ mined sections of the total space within each frame F or within at least some frames F, to contain informa ⁇ tion I or I , respectively, about the count at the moment stored in register 20 of each channel A and B.
  • This count consists of the count of counter 17 which was written into register 20 in connection with the occurrance of the next preceding vertical sync pulse in video signal V A or V ⁇ , respectively, and defines the time t,IA.- or t,I n B for the occurrance of the vertical sync pulse, related to reference time T f .
  • the reason why information I and I does not necessarily have to be transmitted to the receiving units within each frame of control signals S is that times t, and t, will vary in relation to reference time T f at a very slow rate if, as assumed above, the time interval between the vertical sync pulses of video signals V and V is at least approximately equal to the cycle length of counters 16, 17 and 18.
  • control signal S also serves to transmit the required enabling signals from microprocessor 22 to the authorized receiving units and to provide these units with information, obtained from the microprocessor, about the algorithms according to which the operating mode of the decoders contained in the receiving units has to be altered in order to correspond to the alteration in the operating mode of encoders 13.
  • the receiving unit shown in Figure 2 and generally designated 25 has an input terminal 26 which may be connected to the output terminal 14 of transmitting unit 10 for instance through a cable network and over which the receiving unit may be supplied with the radio frequency signals RF A. ' , RFts' and delivered by the transmitting unit.
  • a data demodulator 27 serving to demodulate signal RF n and to re-create the control signal S generated by data generator 23 in transmitting unit 10
  • two decoders 28 which serve to decode respecitve ones of the two coded signals RF ' and RF ' and to generate a corresponding uncoded radio frequency signal RF " and RF " which is modulated with a TV program and which may be fed to a TV and/or video set 38, connected to the two decoders.
  • data demodulator 27 and decoders 28 are provided with built- in band pass filters for filtering out those of the three signals received over input terminal 26 which are not intended to be utilized in the respective unit.
  • receiving unit 25 is provided with two decoders 28 in order hereby to be in a position to decode the two coded signals RF ' and RF ' simultaneously.
  • the receiving unit may be provided with only one decoder, in which case it may decode only one incoming coded signal at a time.
  • it may also be provided with more than two decoders in order hereby to be able to decode more than two incoming coded signals simul ⁇ taneously.
  • the receiving unit 25 is provided with a special control equipment for the decoders.
  • This control equipment comprises a parity check logic 29, a frame synchronization logic 30, a frequency recovery logic 31, two registers 32, namely one for each decoder 28, and a microprocessor 33. These components of the control equipment are all connected to the output of data demodulator 27 in order hereby to receive the control data signal S re-created by the data demodulator.
  • the control equip ⁇ ment also comprises a comparator 34 for each decoder 28 and a counter 35, a clock pulse generator 36 and a phase locking logic 37 for controlling the latter.
  • counter 35 is designed as a cyclically operating counter which counts from 0 to 19999. It receives clock pulses having a frequency of 1 MHz from clock pulse generator 36 which is controlled from phase locking logic 37 which, in its turn, is supplied with, on the one hand a signal derived from control data signal S by means of frequency recovery logic 31 and having a frequency of for instance 62,5 kHz, corresponding to the bit rate of signal S , and on the other hand, a reference signal of the same frequency, obtainable from counter 35.
  • the cycle length of counter 35 will be the same as the cycle length of counter 16, 17 and 18, i.e. 20 ms.
  • frame synchronization logic 30 By means of frame synchronization logic 30, a check is made to ascertain that control data signal S from data demodulator 27 contains faultless frame synchronization words FW and that these words occur every 20 ms.
  • frame synchronization logic 30 detects a first correct frame synchronization word FW, it de ⁇ livers a signal to counter 35 to reset said counter to zero.
  • a cyclical ⁇ ly recurring reference time T f ' ( Figure 4) for the receiving unit is determined which corresponds to the reference time T ,- for the transmitting unit and to which the time t_ ' or t- ' , respectively, for an altera ⁇ tion of the operating mode may be related for each decoder 28.
  • the frame synchronization logic 30 When detecting the frame synchronization word following next upon the first frame synchronization word, the frame synchronization logic 30 will deliver an enabling signal to the two registers 32, provided that the frame synchronization logic simultaneously receives a cyclically generated flag, delivered from counter 35. This enabling signal will then remain as long as faultless frame synchronization words and flags from counter 35 are detected every 20 ms by the frame synchronization logic.
  • the information I and I D -----, respectively, contained in control data signal S ⁇ D and relating to the count, at a given instant stored in register 20 of each channel A and B of the transmit ⁇ ting unit, is utilized to write the same count into the corresponding register 32.
  • the information I and I D ----- respectively, contained in control data signal S ⁇ D and relating to the count, at a given instant stored in register 20 of each channel A and B of the transmit ⁇ ting unit, is utilized to write the same count into the corresponding register 32.
  • these registers have to be supplied with the above- mentioned enabling signal from frame synchronization logic 30 as well as with an enabling signal from parity check logic 29.
  • each register 32 is continously fed to one input of the corresponding comparator 34, which receives the output signal from counter 35 at its other input.
  • comparator .34 will deliver an output signal each time the count at the output of counter 35 is equal to the count stored in the corres- ponding register 32.
  • comparator 34 of channel A this occurs at the time t» '
  • compa ⁇ rator 34 of channel B it occurs at the time t ' .
  • the output signal from the comparator is fed to the corres ⁇ ponding decoder 28 where it serves as a load pulse which may cause the decoder to load into a control circuit thereof an instruction relating to a new operating mode of the decoder, previously received from microprocessor 33.
  • This instruction should be such as to adapt the alteration in the operating mode of decoder 28 to a simultaneously caused alteration in the operating mode of the corresponding encoder 13 in transmitting unit 10.
  • informa ⁇ tion relating to those further channels and corresponding to I A. and I_B may suitably occur at fixed locations for said information following immediately after the illustra- ted locations for I and I .
  • Signal S may also be utilized to transmit all other required information from transmitting unit 10 to receiving unit 25.
  • it may be utilized for the transmission from microprocessor 22 of the transmitting unit to micro ⁇ processor 33 of the receiving unit of information about various algorithms for the alteration of the operating mode of each decoder 28 contained in receiving unit 25.
  • signal S n also contains information about the location within said signal where the information I and I , respectively, occurs.
  • registers 32 which also receive a continuous time information from counter 30.
  • registers 32 may be caused to receive I, or Ister.
  • T f designates a cyclically recurring reference time. This reference time occurs each time counter 16 assumes a zero value and it may for instance be brought to coincide with the end of the frame synchronization word FW.
  • the time for the occurrance of the vertical sync pulse in each of video signals V. and V R is designated t 1 1 ⁇ and t 1 1 D -----, respectively. This time is defined in an unambiguous manner in relation to reference time T __.
  • ⁇ ref by the count from counter 17 written in register 20 of channel A or B, respectively, and the programmed displacement in time between the operating cycles of counter 17 and counter 16.
  • the time for an alteration of the operating mode of encoder 13 in channel A or B, respectively, is designa- ted t ⁇ ⁇ and t--, respectively. This time occurs when the count of counter 18 is equal to the count from counter
  • FIG. 4 In the lower portion of Figure 4, there is shown a time diagram illustrating times for events occurring in receiving unit 25. This time diagram starts from the same starting time as the diagram shown in the upper portion of Figure 4 which means that it also illustrates the mutual relationship between times having reference to the transmitting unit and times having reference to the receiving unit.
  • T f ' designates a cyclically recurring reference time for the receiving unit. This time is displaced in relation to reference time T £ ⁇ ref for the transmitting unit by a time interval corresponding to the delay of control data signal S n occurring, on the one hand, in connection with the output of said signal from data generator 23 in the transmitting unit and, on the other hand, in connection with the input of said signal into receiving unit 25.
  • a slig ⁇ htly J increased disp ⁇ lacement between Tre c f ' and Tref may occur as a consequence of the delay of signal RF caused by the transmission of said signal from the trans ⁇ mitting unit to the receiving unit.
  • this delay does not have any significance, as signals RF Pi' and
  • the individual time for an alteration of the ope- rating mode of each decoder 28, serving to decode a respective one of the two signals RF.' and RF ' , is designated t ⁇ " and t ⁇ ' , respectively.
  • this time occurs when the count at the output of counter 35 is equal to the count stored in the corresponding register 32.
  • counter 35 will operate in full synchronizm with counter 18 and start a new counting cycle simultaneously with the latter.
  • transmitting unit 10 and receiving unit 25 ensures that the receiving unit may accomplish a decoding operation on the trans ⁇ mitted coded TV signals which is timely coordinated with, or synchronous with, the coding operation effected in the transmitting unit without making it necessary at the receiving end to effect any separation of the vertical sync pulses from said signals in order to facili ⁇ tate such a coordination.

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  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Abstract

Un signal de message (RFA, RFB) est transmis d'une unité de transmission (10) à au moins une unité de réception (25) dans un état codé à l'aide d'un codeur (13). Simultanément, un signal de commande séparé (SD), généré par l'unité de transmission (10), est transmis et un décodeur (28) dans l'unité de réception (25) effectue une operation de codage sur le signal de message codé reçu (RFA', RFB'), coordonné dans le temps avec l'opération de codage. Le signal de commande (SD) consiste en un flot de données continues composé de blocs (F) d'égale longueur. Chaque bloc (F) contient un mot prédéterminé de synchronisation de bloc (FW) qui définit un temps de référence de récurence cyclique (Tref) pour l'unité de transmission (10) et qui est utilisé dans l'unité de réception (25) afin de déterminer un temps de référence de récurence cyclique correspondant (Tref') pour cette unité. Au moins certains blocs (F) contiennent également des données qui définissent le temps (t2A, t2B) pour une altération dans le mode de fonctionnement du codeur (13), en relation audit temps de référence (Tref) pour l'unité de transmission (10), et qui sont utilisés dans l'unité de réception (25) afin de déterminer un temps (t2A', t2B') pour une altération correspondante du mode de fonctionnement du décodeur (28), en relation audit temps de référence (Tref') pour l'unité de réception (25).
PCT/SE1994/000338 1993-04-15 1994-04-15 Codage et decodage coordonnes dans le temps d'un signal de message WO1994024825A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU65475/94A AU6547594A (en) 1993-04-15 1994-04-15 Coordinately coding and decoding a message signal
SE9503590A SE514480C2 (sv) 1993-04-15 1995-10-13 Koordinerad kodning och avkodning av en meddelandesignal

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9301236A SE9301236L (sv) 1993-04-15 1993-04-15 Sätt och anordning för koordinerad kodning och avkodning av en TV-signal eller annan meddelande signal
SE9301236-7 1993-04-15

Publications (1)

Publication Number Publication Date
WO1994024825A1 true WO1994024825A1 (fr) 1994-10-27

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SE (1) SE9301236L (fr)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1061744A2 (fr) * 1999-04-26 2000-12-20 Sarnoff Corporation Contrôle d'accès à un flux de données

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3789131A (en) * 1972-08-03 1974-01-29 Oak Industries Inc Selective coding system for subscription television
US3885089A (en) * 1973-02-16 1975-05-20 Hughes Aircraft Co Television scrambling system
US4590519A (en) * 1983-05-04 1986-05-20 Regency Electronics, Inc. Television signal scrambling/descrambling system
DE3501178C2 (fr) * 1985-01-16 1987-11-05 Blaupunkt-Werke Gmbh, 3200 Hildesheim, De
US4731839A (en) * 1985-01-09 1988-03-15 Radio-Television Beige de la Communaute Francaise Method for coding and de-coding audio and video information
US4817144A (en) * 1987-03-12 1989-03-28 Zenith Electronics Corporation Secure TV scrambling system using framing code switching

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3789131A (en) * 1972-08-03 1974-01-29 Oak Industries Inc Selective coding system for subscription television
US3789131B1 (fr) * 1972-08-03 1988-04-26
US3885089A (en) * 1973-02-16 1975-05-20 Hughes Aircraft Co Television scrambling system
US4590519A (en) * 1983-05-04 1986-05-20 Regency Electronics, Inc. Television signal scrambling/descrambling system
US4731839A (en) * 1985-01-09 1988-03-15 Radio-Television Beige de la Communaute Francaise Method for coding and de-coding audio and video information
DE3501178C2 (fr) * 1985-01-16 1987-11-05 Blaupunkt-Werke Gmbh, 3200 Hildesheim, De
US4817144A (en) * 1987-03-12 1989-03-28 Zenith Electronics Corporation Secure TV scrambling system using framing code switching

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1061744A2 (fr) * 1999-04-26 2000-12-20 Sarnoff Corporation Contrôle d'accès à un flux de données
EP1061744A3 (fr) * 1999-04-26 2003-05-14 Sarnoff Corporation Contrôle d'accès à un flux de données

Also Published As

Publication number Publication date
SE9301236D0 (sv) 1993-04-15
SE9301236L (sv) 1994-10-16
AU6547594A (en) 1994-11-08

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