OA10754A - Selective interdiction of television channels - Google Patents
Selective interdiction of television channels Download PDFInfo
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- OA10754A OA10754A OA9800003A OA9800003A OA10754A OA 10754 A OA10754 A OA 10754A OA 9800003 A OA9800003 A OA 9800003A OA 9800003 A OA9800003 A OA 9800003A OA 10754 A OA10754 A OA 10754A
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- signais
- channel
- headend
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- 238000000034 method Methods 0.000 claims description 34
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- 238000003780 insertion Methods 0.000 claims 2
- 230000037431 insertion Effects 0.000 claims 2
- 238000013475 authorization Methods 0.000 abstract description 26
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Classifications
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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
- H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
- H04N7/171—Systems operating in the amplitude domain of the television signal
- H04N7/1713—Systems operating in the amplitude domain of the television signal by modifying synchronisation signals
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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
- H04N7/162—Authorising the user terminal, e.g. by paying; Registering the use of a subscription channel, e.g. billing
- H04N7/165—Centralised control of user terminal ; Registering at central
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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
- H04N7/167—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
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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
- H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
- H04N7/171—Systems operating in the amplitude domain of the television signal
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Computer Security & Cryptography (AREA)
- Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
Abstract
With the present decoder/interdiction device combination (566), the microcontroller (518) receives authorization data from a data receiver (568) via its data output (570) that has been inserted at the headend to identify authorized subscribers (preferably identified with a predefined subscriber or box code in the microcontroller (518). The same microcontroller (518) that controls the common decrypting of a commonly encrypted input source (572), loads the channel interdiction table (516) according to the authorization data, e.g., according to tiers. The data in the interdiction table (516) is then used to control the operation of the frequency synthesizer/VCO (516) and the mute switch (522) using the control interface (528) and mute control signal (534) according to the previously described algorithm. This improved combination now permits the simultaneous reception of multiple unencrypted signals (suitable for picture-in-picture use) while still permitting the provider to withhold access to selected channels.
Description
010754
TITLE: SUBSCRIBER SITE METHOD AND APPARATUS FOR DECODING
AND SELECTIVE INTERDICTION OF TELEVISION CHANNELS
INVENTOR: PABLO MILIANI
5 BACKGROUND OF THE INVENTION
The présent invention relates generally to multichannel télévision Systems and more particularly tointerdiction devices for selectively scrambling télévisionchannels at subscriber sites. 10 Subscription télévision distribution Systems (either (1) cable or (2) over-the-air) typically provide a basicblock of télévision channels to subscribers at a subscriber sitefor a basic monthly fee and one or more premium télévisionchannels for additional fees. In a typical cable System, the 15 physical connection itself Controls access to the basic channelswhile premium channels are often "scrambled" (encrypted) attheir source, i.e., the headend, by the provider to restricttheir viewing to only subscribers who pay the additional fee.Alternatively, providers may provide unscrambled (in-the-clear) 20 channels to each subscriber site where the provider physicallyplaces an interdiction device which blocks, e.g., atténuâtes orscrambles, selected channels, to stop unauthorized subscribersfrom receiving the selected channels.
In over-the-air subscriber Systems (often called 25 "wireless cable or TV"), ail channels are generally scrambled atthe headend to prevent unauthorized réception of both basic andpremium channels since the transmitted channels are available toanyone in the geographical service area. Subscribers aretypically provided with a descrambler (décoder) which can 30 descramble (decode/decrypt) only one channel at a time.Therefore, subscriber receivers, e.g., télévision sets,vidéocassette recorders, cân only be tuned to a single selectedchannel and features of modem télévision equipment that processmultiple channels, e.g., "picture-in-picture", are useless. 35 // // //
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SUMMARY OF THE INVENTION
The présent invention is directed to a decryption process which facilitâtes simultaneous decryption of a block of encrypted télévision channels thus making a decrypted block of 5 télévision channels simultaneously available for direct tuningby subscriber receivers. Additionally, the présent invention isdirected to an encryption process which facilitâtes the jammingof selected télévision channels from said decrypted block thusmaking it possible to interdict réception of those selected 10 channels by unauthorized subscribers. The présent invention canbe advantageously used in both over-the-air and hard-wiredsubscription télévision-distribution Systems to providesubscribers with a plurality of simultaneously availabledecrypted télévision channels and selectively encrypted 15 channels, e.g., premium channels. A System in accordance with the présent invention is characterized by a sélective interdiction device located at asubscriber site that opérâtes on a block of télévision channels,decrypted at the subscriber site, such that the interdiction 20 device jams one or more selected channels, e.g., premium, bycombining a jamming signal within the frequency range of thechannels to be interdicted. A preferred subscriber site apparatus useful in aSystem for distributing from a System headend 1) multiple 25 channel signais defining an RF band, each channel signal havingrespective video synchronization components in time coïncidenceand 2) a common timing reference signal within said band andsynchronous with said synchronization components, and whereineach of said channel signais is encrypted in accordance with a 30 common encoding rule comprises a) a timing recovery circuit responsive to said common timing reference signal for generatingat least one sync signal, b) a single décoder responsive to saidsync signal for simultaneously decrypting ail of said channelsignais in accordance with the inverse of said encoding rule to 35 generate multiple decrypted channel signais, each capable of directly causing a conventional télévision receiver to produce an intelligible image, and c) an interdiction apparatus for periodically inserting a jamming signal into at least one of said multiple decrypted channel signais to render it incapable
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010754 of directly causing said télévision receiver to produce anintelligible image.
Alternatively, a preferred subscriber siteapparatus useful in a System for distributing from a Systemheadend 1) multiple channel signais defining an RF band, eachchannel signal having respective video synchronizationcomponents in time coïncidence and 2) a common timing referencesignal within said band and synchronous with said synchronization components, and wherein each of said channelsignais is encrypted in accordance with a common encoding rulecomprises a) an interdiction apparatus for periodicallyinserting a jamming signal' into said RF band to generate aninterdicted RF signal, b) a timing recovery circuit responsiveto said common timing reference signal for generating at leastone sync signal and c) a single décoder responsive to said syncsignal and said interdicted RF signal to simultaneously decryptmultiple channel signais in accordance with the inverse of saidencoding rule to generate a recovered multichannel signalcomprising multiple decrypted channel signais capable ofdirectly causing a conventional télévision receiver to producean intelligible image and at least one scrambled channel signalincapable of directly causing said télévision receiver toproduce an intelligible image.
The novel features of the invention are set forthwith particularity in the appended daims. The invention willbe best understood from the following description when read inconjunction with the accompanying drawings.
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BRIEF DESCRIPTION QF THE DRAWINGS
Figure IA illustrâtes that decryption is typically restricted to a single selected channel signal in prior art subscription télévision distribution Systems;
Figure IB illustrâtes that decryption providessimultaneous access to ail encrypted channel signais in asubscription télévision distribution System in accordance withthe présent invention;
Figure 2 illustrâtes encryption/decryptionprocesses in accordance with the présent invention;
Figures 3A and 3B are block diagrams ofalternative embodiments of an encryption System configured tofacilitate the simultaneous decryption of ail encrypted channelsignais;
Figure 4 is a block diagram of apparatus forsimultaneous decryption of channel signais generated by theSystems of Figures 3A and 3B;
Figure 5 illustrâtes a typical composite video signal ;
Figure 6A is an enlarged view of the picture andhorizontal synchronization components of a plurality ofcomposite video signais;
Figure 6B illustrâtes the composite video signaisof Figure 6A with like components in time coincidence;
Figure 6C illustrâtes an exemplary encoding rulefor encoding the components of the composite video signais ofFigure 6B;
Figure 6D illustrâtes a plurality of encodedcomposite video signais resulting from modification of thecomposite video signais of Figure 6B in accordance with theencoding rule of Figure 6C;
Figure 6E illustrâtes a plurality of video IFcarriers, each amplitude modulated with a different one of theencoded composite video signais of Figure 6D;
Figure 6F illustrâtes a decoding rule which is the inverse of the encoding rule of Figure 6C;
Figure 6G illustrâtes the video IF carriers of
Figure 6E after modification in accordance with the decoding rule of Figure 6F; 4 010754 r
Figure 7 illustrâtes the command transmissionstructure comprised of multiple data bytes and a reference puisethat are added to a selected channel signal;
Figure 8 illustrâtes the relationship of the5 command transmission structure of Figure 7 to a typical 525 line, 60 HZ télévision signal;
Figure 9 illustrâtes the relationship of thereference puise to the tenth horizontal sync puise in thetélévision signal of Figure 8; 10 Figure 10 illustrâtes the relationship of the command transmission structure of Figure 7 to a typical 625line, 50 Hz télévision signal;
Figure 11 illustrâtes the relationship of thereference puise to the eighth horizontal sync puise in the 15 télévision signal of Figure 10;
Figure 12 is an expanded block diagram of a portion of the processing of video channel N as shown in Figure3B;
Figure 13 is a top level block diagram of an 20 up/down converter embodiment of the data modulator of Figures 3Band 12;
Figure 14 is a detailed block diagram of apreferred up/down converter as shown in Figure 13;
Figure 15 is a block diagram of a preferred 25 embodiment of the décoder portion of the downconverter/decoderas shown in Figure 4;
Figure 16 is a detailed block diagram of anexemplary embodiment of the décoder of Figure 15;
Figure 17 is a simplified block diagram showing 30 the use of a sélective multichannel interdiction device of theprésent invention that selectively jams predetermined premiumchannelS;
Figure 18 is a block diagram of a preferredsélective multichannel interdiction device that jams 35 predetermined premium channel s by adding a jamming signal toeach of the selected premium channel signais;
Figure 19 shows an exemplary flow chart for acontroller that Controls the combining of a jamming signal withthe multichannel télévision signal; and 5
Figure 20 is a block diagram of a preferred embodiment of the présent invention combining a sélective interdiction device with a décoder. // // //
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U 010754 6 010754 ο e
DESCRIPTION OF THE PREFERRED EWBODIMENTS
As shown in Figure IA, typical prior arttélévision distribution Systems provide subscribers with aplurality of encrypted télévision channel signais 20 butrestrict decryption 22 to the production of one decryptedchannel signal 24 at a time. Thus, for exatnple, a subscribercan cause any one of the encrypted channel signais 20 to bedecrypted for viewing on a télévision set but cannot at the sametime record another decrypted channel signal on a video cassetterecorder or use another channel signal for a "picture-in-picture" System. In an attempt to address thislimitation, one prior art system uses a plurality of decoders,e.g., 22A-22N, one for each encrypted channel signal, thatrespectively décodé the channel signais which are thenupconverted by a plurality of upconverters 25A-25N to a newchannel frequency 26A-26N.
Figure IB illustrâtes that encryption/decryptionSystems taught by the présent invention facilitate decryption 28of ail encrypted channel signais 30 simultaneously so that acomplété set of decrypted channel signais 32 is simultaneouslyavailable in their original frequency slots. Therefore, asubscriber can hâve each of a plurality of subscriber receivers(e.g., télévision sets, video cassette recorders) receiving adifferent channel signal simultaneously while also using modemtélévision processing features, e.g., picture-in-picture, whichrequire simultaneous availability of multiple channel signais.
An encryption/decryption process 40, in accordancewith the invention, is shown in Figure 2. Télévisiondistribution Systems typically include a "headend" where aplurality of télévision channel signais from different sources,e.g., satellite TV signais, standard broadcast VHF and UHFsignais, are captured, combined and fed into the system. In theprocess 40, headend génération 42 of multichannel télévisionsignais begins with a plurality of video sources 44 which eachprovide a composite video signal 45 including pictùre andsynchronization components (as shown in Figure 5 and furtherdescribed below).
The composite video signais 45 are encrypted 50and used to modulate 52 separate channels to place them into 7 r' t
010754 separate frequency channels for distribution. In addition, aprocess of time synchronization 54 is imposed to place likecomponents of the composite video signais 45 in a predeterminedtime relationship.
Distribution 60 to subscriber sites 66 of thechannel signais generated at the headend may then beaccomplished by a variety of well known processes, e.g., cabletransmission or wireless over-the-air transmission, as a commonRP signal 68 that contains each composite video signal in adistinct frequency slot. Because of the time synchronization 54imposed at the headend, the common RF signal 68, comprised of aplurality of télévision channel signais separated in frequency,arrive at the subscriber sites 66 in time synchronization sothat decryption 70 can be performed on ail channel signaissimultaneously.
Apparatus embodiments for realizing the processesof Figure 2 are illustrated in Figures 3A, 3B and 4. Figure 3Ashows a block diagram of a headend 100 in which basebandcomposite video sources 102A-102N are each connected to separateelectronic delay devices such as frame synchronizers 104. Theframe synchronizers 104 selectively delay the composite videosignais from the sources 102A-102N to place like components,e.g., picture and synchronization components, in time synchronization with reference to a crystal controlled videoreference 105, thus generating time synchronized composite videosignais 106. The crystal controlled video reference 105 iscoupled to a timing reference generator 108 used to synchronously generate a common timing reference signal 109, asdescribed further below.
The time synchronized composite video signais 106are used to amplitude modulate separate video IF carriers in IFmodulators 110 after which encryption is accomplished bymodifying IF envelopes in accordance with a selected encodingrule (code) in encoders 112, thus generating encoded IF carriers113. Typical apparatus for envelope modification includevariable gain amplifiers, variable loss attenuators andselectable signal paths having different gains. Exemplaryenvelope modification apparatus are disclosed in U.S. Patents 8 010754 O < 4,706,283; 4,802,214; 4,926,477; and 4,928,309, the disclosures of which are hereby incorporated by reference.
The modulators 110 and encoders 112 of Figure 3Amay altematively be interchanged, as shown in Figure 3B, to usethe encoder 112 to first encode the time synchronized videosignais 106 by amplitude modification in accordance with aselected encoding rule and then using the résultant signal toamplitude modulate an IF carrier with the IF modulator 110.
Video amplitudes may be modified with apparatus similar to theabove mentioned examples. Spécifie apparatus for video basebandenvelope modification is disclosed in U.S. Patent 4,928,309, thedisclosure of which is hereby incorporated by reference.
The encoded IF carriers 113 are preferablyupconverted from a standard IF frequency and frequencymultiplexed in standard télévision transmitters 114 fordistribution to subscriber sites as the common RF signal 68.
The RF frequency slots are typically specified in accordancewith industry standards. For example, a typical MultichannelMultipoint Distribution Service (MMDS) includes 33 channel slotswithin a transmission frequency range of 2500-2686 MHz and 2150-2162 MHz.
The timing reference generator 108 generates thecommon timing reference signal 109 which is transmitted with thesynchronized video signais to provide master timing informationfor decoding synchronization. This signal is preferablycombined with a selected encoded IF carrier 113 to form a datamodulated IF carrier 115, by a data modulator 116. The datamodulator 116 is placed in a selected channel at the headend but
I it may altematively be inserted (indicated by broken line) intoa transmitter 117 to be carried by an otherwise unused RFchannel 118. The data modulator 116 may altematively beprésent on more than one of the video channel s prior to thetransmitters 114 and selectively enabled at the headend.Authorization data status (described further below) is alsopreferably combined with the common timing reference signal 109and transmitted to selectively enable or disable decoding ateach subscriber site.
Figure 4 illustrâtes a block diagram of adownconverter/decoder 120 suitable for simultaneous decryption 9 <· 010754 at subscriber sites of the common RF signal 68 received from the headend 100 of Figures 3A and 3B. In the block diagram of
Figure 4, downconversion electronics 121 are shown essentially comprised of an input RF amplifier 122, a mixer 123 and a local 5 oscillator 124. The input RF amplifier 122 amplifies and
buffers the common RF signal 68 that was altematively broadcastor distributed via cable from the transmitters 114 of Figures 3Aand 3B. The amplifier 122 feeds a buffered common RF signal 126to the mixer 123 which downconverts the buffered common RF 10 signal 126 using the local oscillator 124, generating a downconverted common RF signal 126. In a preferred embodiment,the common RF signal 68 is received via a microwave antenna (notshown) and subsequently downconverted via the downconversionelectronics 121 as disclosed in U.S. Patent No. 5,440,319 to 15 Joël J. Raymond et al., which is incorporated herein byreference.
From the downconverted common RF signal 126, thecommon timing reference signal (109 in Figures 3A and 3B) isrecovered in a data/timing receiver 127. This receiver 127 also 20 stores a decoding rule which is the inverse of the selectedencoding rule used in the encoders 112 of Figures 3A and 3B.Spécifie structure in the receiver 127 for recovery of thecommon timing reference signal 109 is primarily dépendent uponthe type of timing signal selected. Exemplary recovery 25 structures are disclosed in U.S. Patents 4,706,283; 4,802,214;4,926,477; and 4,928,309, previously referred to above andincorporated herein.
With the common timing reference signal and thedecoding rule available (and preferably after confirmation of 30 the authorization data) , the data/timing receiver 127 can applygain control signais 128 to a variable gain amplifier/attenuator130 which simultaneously modifies the IF carrier envelopes withsignal 126 in accordance with the decoding rule to generatedecoded channel signais 132. In a preferred embodiment, the 35 variable gain amplifier/attenuator 130 is a single element thatopérâtes on a single multichannel télévision signal derived fromthe common RF signal 68. It is this ability to operate upon ailtélévision channel signais by a single element that is referredto in this application as "simultaneous". While a preferred 10 010754 embodiment uses a single variable gain amplifier/attenuator 130, other embodiments may use additional variable gain/amplifiers to synchronously operate upon a multichannel signal derived from the common RF signal 68 in an équivalent manner.
Thus, the decoded channels 132 are nowsimultaneously available and can be distributed throughout thesubscriber site for delivery to multiple subscriber receiverswithout further processing. In addition, once the data/timingreceiver 127 preferably confirms the authorization data, ailchannels will automatically be available for use, i.e., no userinteraction, such as selecting a channel for decoding, will beinvolved. The downconverter/decoder 120 of Figure 4 can beeconomically integrated to reduce subscriber costs.
The invention is further disclosed by a preferredprocess embodiment illustrated in Figures 6A-6G. Description ofthis exemplary embodiment is facilitated by reference to atypical composite télévision video signal 220, shown in Figure5, as specified by télévision industry standards, e.g., NationalTélévision Systems Committee (NTSC).
The signal 220 of Figure 5 has picture components222 altemating with horizontal synchronization components 224and these components are periodically separated by verticalsynchronization components 226 during a vertical synchronizationinterval. The vertical synchronization components 226 generallyinclude equalizing puises 230, vertical synchronization puises232 and horizontal synchronization puises 234. As is wellknown, the horizontal synchronization components 224 andvertical synchronization components 226 enable télévisionreceivers to properly synchronize the picture display.
Figure 6A is an enlarged view of the picturecomponents 222 and horizontal synchronization components 224 ofa plurality of composite video signais 220A-220N. Eachhorizontal synchronization component 224 is seen to include ahorizontal synchronization puise 242 and, as in the case ofcolor télévision, a color burst sine wave 244 (indicated by thesine wave envelope) .
In this preferred method, like components of the video signais 220 are first aligned in time coïncidence as shown in Figure 6B and their amplitude then modified in accordance 11
010754 with a selected encoding rule. To illustrate this amplitudemodification, an exemplary encoding rule, having an encodingpattern 250 of Figure 6C, will be used.
The pattern 250 is visually indicated by two lines' 5 251 equally vertically spaced about a centerline 252 in which the vertical spacing between lines 251 indicates gain. Thus,the pattern 250 has segments 253 with a gain 254 interleavedwith segments 255 having a decreased gain 256. The encodingpattern 250 is synchronized with the composite video signais 10 220A-220N of Figure 6B to hâve gain segments 253 and gain segments 255 time coincident respectively with picturecomponents 222 and horizontal synchronization components 224.
The pattern 250 and the particular timesynchronization described above are for illustrative purposes 15 only; any encoding rule and time synchronization may be usedthat will prevent unauthorized télévision receivers fromproperly displaying the video signal.
When the amplitudes of the video signais 220A-220Nare modified in accordance with the encoding pattern 250, a 20 plurality of encoded video signais 260A-260N is produced havingpicture components 222' and horizontal synchronizationcomponents 224' as shown in Figure 6D. Synchronism between oneof the gain segments 255 and a corresponding horizontalsynchronization component 224" is indicated by the broken lines 25 266. Thus, in the encoded composite video signais 260A-260N, the horizontal synchronization components 224 are reducedrelative to the other video components.
In Figure 6E, a plurality of video IF(intermediate freguency) carriers 270A-270N hâve each been 30 amplitude modulated with a different one of the encoded video signais 260A-260N to hâve amplitude envelopes 271A-271N as shownin broken lines. The modulated video IF carriers thus hâveportions corresponding to the components of the encodedcomposite video signais 260 of Figure 6D, e.g., picture portions 35 272 and horizontal synchronization portions 274 correspond respectively to picture components 222' and horizontalsynchronization components 224' .
In the preferred method, upon receipt at asubscriber site, the video IF carriers 270A-270N are 12 ί \ simultaneously shaped in accordance with the inverse of theencoding pattern 250. Figure 6F illustrâtes this inverse as thedecoding pattern 278 in which the gains 254, 256 hâve beeninverted, i.e., segments 255 now hâve the increased gain 254while segments 253 hâve the decreased gain 256.
The decoding pattern 278 is synchronized with themodulated video IF carriers 270 of Figure 6E in the same manneras was done with the encoding pattern 250 of Figure 6C and thecomposite video signais 220 of Figure 6B, i.e., gain segments253 and gain segments 255 are made time coïncident respectivelywith picture portions 272 and horizontal synchronizationcomponents 274.
As shown in Figure 6B, when the amplitudes271A-271N of Figure 6E are modified in accordance with thedecoding pattern 278, a plurality of video IF carriers280A-280N, with amplitude envelopes 281A-281N, are produced eachhaving picture portions 272 and horizontal synchronizationportions 274 which conform respectively with the picturecomponents 222 and horizontal synchronization components 224 ofFigure 6B. Synchronism between one of the gain segments 255 anda corresponding horizontal synchronization portion 274' isindicated by the broken lines 288. Thus, ail video IF carriersignais hâve been simultaneously decoded at the subscriber sitewithout any change in frequency allocation and aresimultaneously available for use.
In Figures 6C, 6D and Figures 6F, 6G, thesynchronism between the inverse decoding rule 280 and video IFportions 272, 274 was specified to be the same as between theencoding rule 250 and corresponding video components 222, 224.
As previously discussed, this synchronism is realized with acommon timing reference signal synchronous with the encodingwhich is then recovered at the subscriber site for synchronizingthe decoding of the encoded channel signais. Typical modulationmethods for carrying timing reference signais on IF or RFcarriers include amplitude modulation, frequency shift keyingand phase shift keying. A preferred embodiment employingfrequency shift keying is described further below. The commontiming reference signal may preferably be inserted insynchronization components, i.e., horizontal or vertical, to 010754 13 010754 avoid disturbing picture information. The common timing reference signal is preferably combined with authorization data which is coded into one or more video IF carrier signais.
In the preferred method embodiment illustrated inFigures 6A-6G, génération of the video carriers with encodedamplitudes 271A-271N, as shown in Figure 6E, followed thesequence of video signal time alignment, amplitude modificationof video signais in accordance with a selected encoding rule andmodulation of video IF carriers with the encoded video signais.It should be apparent, however, that other method embodiments,in accordance with the invention, may employ other équivalentsequences, e.g., the sequrènce previously described and shown inFigures 3A and 3B.
Also, the illustrated preferred method embodimentsimultaneously décodés modulated IF carriers. It should beapparent to those skilled in the art that équivalent methodembodiments may include transmission techniques such as theupconversion of each IF carrier to one of a plurality of RFfrequency signais followed by frequency multiplexing. Theresulting RF frequency signais may then be modified inaccordance with the inverse of the selected encoding rule tosimultaneously décodé the video signais carried therein. BothIF and RF signais may be generically referred to as channelsignais.
Although the encryption/decryption process shownin the preferred embodiments has been specifically directed toamplitude modification of analog video signais, the teachings ofthe invention may generally be extended to encryption/decryptionof other forms of video signais, e.g., bit streams resultingfrom digitization of analog video signais. Also, althoughhorizontal sync suppression has been shown as an encodingmethod, other encoding methods are also recognized within thescope of the présent invention, including vertical syncsuppression and horizontal and vertical sync suppression.
In addition, the illustrated preferred method embodiment aligned corresponding video components in time coïncidence for simultaneous decryption at subscriber sites but other embodiments of the invention may synchronize (i.e., place 14 V 0 1 0 754 in a predetermined time sequence) corresponding video components for synchronous decryption at subscriber sites.
With reference now to Figure 7, there is shown adiagram of a preferred command transmission structure of thedata that is added to a selected télévision channel forproviding synchronization and the authorization data. The basicstructure of the authorization data is preferably comprised oftwelve data bytes, divided into two data blocks 300 and 302 ofsix bytes each, corresponding to the two interlaced fields whichform a single video frame and a precisely placed reference puise304 used to provide timing information for decrypting the commonRF signal 68. Additionally, start sequences 306 and 308 areprovided to identify the start of each data block. The databytes are preferably used to identify authorized individuals orgroups of authorized subscribers to the otherwise encryptedservice. At least one byte is preferably included as a validitycheck byte 310 for the authorization data. Additionally, thevalidity check byte 310 may be used to détermine valid receivetiming synchronization.
In a typical 525 line, 60 Hz télévision signal, asshown in Figure 8, a video frame is comprised of 525 interlacedhorizontal lines of video information divided into two fields ata 30 Hz frame rate. The beginning of each field is signified byvertical sync components 312 and 314, defining a verticalsynchronization interval, that cause a vertical retrace duringwhich the screen is blanked. Video information need not beprésent during the vertical synchronization interval since thescreen is blanked. Thus, as shown in Figure 8, a preferredembodiment uses the vertical synchronization interval, defined 'by vertical sync components 312 and 314 and comprised ofmultiple horizontal lines, to transmit the authorization datawithout interfering with the displayable video information.Transmission of the first data block 300, comprised of the firststart sequence 306, a first set of data bytes 318, six databytes in a preferred embodiment, and the reference puise 304,begins with the time period defined by the first horizontal line316. While the data transmission protocol is otherwise tolérantto timing variations, the reference puise 304 is preciselysynchronized with a horizontal sync puise 320 that follows the 15 01 0 754 tenth horizontal line 322. The transmission period for thefirst data block 300 is contained within the time period forhorizontal lines 1-10, as shown in Figure 8. Similarlÿ, thetransmission period of the second data block 302, comprised ofthe second start sequence 308 and a second set of data bytes324, six data bytes in a preferred embodiment, is containedwithin horizontal lines 263-272.
Using means discussed below, data is modulatedonto a selected télévision channel during the previouslydescribed vertical synchronization interval. As shown inFigures 7, 8 and 9, this data is defined as a combination ofbits comprised of marks, i.e., "l"s or "high"s, and spaces,i.e., "0"s or "low"s. However, outside of these prescribedperiods, data values are undefined and potentially susceptibleto erroneous détection as marks or spaces. To avoid theseerrors, the start sequences 306 and 308 are used in combinationwith the validity check byte 310 to define détection periodscorresponding to horizontal lines 1-10 and 263-272. The startsequences 306, 308 are each defined by a sériés of unique databits, ail nl"s in a preferred embodiment. Each data byte withinthe first and second sets of data bytes, respectively 318 and324, are preferably transmitted as 8-bit characters according toa conventional 11-bit asynchronous protocol, as shown in Figure9, with one low start bit 325 and two high stop bits 326 percharacter. As is common with asynchronous charactertransmission protocols, the time each character is transmittedis not precisely fixed in time. However, a transmission rate ischosen that permits the transmission of an 11-bit start sequence306, six 11-bit characters 318 and still provide sufficient timeto precisely place the reference puise 304 in synchronizationwith the horizontal sync puise 320 following the tenthhorizontal line 322. In a preferred embodiment, a bit rate of140,625 bps is used. While, the reference puise 304 isdescribed here in reference to a particular video signal, e.g.,220B, it should be recognized that since ail of the videosignais 220A-220N are synchronized by frame synchronizers 104,the reference puise 304 will be precisely synchronized to thehorizontal sync puise following the tenth line for ail of thevideo signais. 16 010754
With reference to Figures 10 and 11, there isshown the interrelationships of the video information and theauthorization data for a télévision signal which uses 625 linesat a 25 Hz frame rate to represent each video frame. In such atélévision signal, as shown in Figure 10, a first data block 327is placed within horizontal lines 624 and 9 and a second datablock 328 is placed within horizontal lines 311 and 320. Thereference puise 330 is precisely placed in synchronization withthe horizontal sync puise following the eighth line 332.
In a preferred embodiment, the télévision channelselected for transmitting the authorization data is fixed, e.g.,always set to a predetermined channel N. However, the downconverter/decoder 120 is preferably configured to scanchannels within its frequency range to identify the channelcontaining the authorization data. Alternate embodiments mayalter the data channel sélection according to a predeterminedalgorithm, e.g., a different channel for each time period, afirst data channel identifies a next data channel, etc. Asdiscussed in reference to Figures 3A and 3B, the common timingreference signal 109 can alternatively be coupled to any one orail of a plurality of data modulators 116. A select signal (notshown) can optionally enable a particular data modulator 116 toadd the common timing reference signal 109 to a selectedchannel.
With reference now to Figure 12, there is shown anexpanded block diagram of a portion of the encryption processingof video channel N, as shown in Figure 3B, showing the interfaceof the encoder 112N and the IF modulator 110N to the datamodulator 116. In a preferred embodiment, the encoder 112Napplies a selected encoding rule, e.g., removing the horizontaland vertical synchronizing components 224, 226 from a timesynchronized video signal 106N, to disable subscribers withoutauthorized decoders from receiving a video channel. Anencrypted video signal 334 is then modulated by the IF modulator110N, generating the encoded IF carrier 113N. In a preferredembodiment, the encoded IF carrier 113N from the IF modulator110N is modulated by the data modulator 116 during the timeperiod corresponding to the vertical synchronizing component226, i.e., the vertical synchronization interval, in response to 17 f'"'" 010754 the common timing reference signal 109 and sent via the datamodulated IF carrier 115 to the transmitter 100N. As describedabove, the data modulator 116 is only présent on a selectedchannel 1-N in a preferred embodiment. In another embodiment,the data modulator 116 may be présent for ail N channels but maybe enabled only for the selected channel or alternatively for aplurality of channels. Alternatively, a single data modulator116 may be switched to the selected channel.
The timing reference generator 108, under controlof a microcontroller 340, generates the common timing referencesignal 109 in synchronism with a clock 342 received from thecrystal controlled video reference 105. As previouslydiscussed, the common timing reference signal 109 additionallypreferably comprises the authorization data for specifyingauthorized subscribers. Authorization information is maintainedin a system controller (not shown) and communicated via signalpath 344 to the microcontroller 340 where it is formatted as theauthorization data onto the common timing reference signal 109.In a preferred embodiment, the common timing reference signal109 contains three data States corresponding to no data, a markand a space, thus causing the data modulator 116 to alter theencrypted IF signal 113 on receipt of a mark or space but leavethe encrypted IF signal 113 unaltered when receiving a third, nodata, State signal. Alternatively, the crystal controlled videoreference 105 delivers a sync signal 346 to the data modulator116 to enable data modulation only during the verticalsynchronization interval.
In a preferred embodiment, the data modulator 116uses FSK (frequency shift keying) to modulate the encoded IFcarrier 113 of a selected MMDS channel with the authorizationdata and the reference puise 304 during the verticalsynchronization interval. The encoded IF carrier 113, as inputto the data modulator 116, is either separate video and separateaudio modulated IF carriers, or the combined video and audiomodulated carriers. In addition, the data modulator 116receives the common timing reference signal 109, comprised ofthe reference puise 304 and the authorization data comprised ofsets of data bytes 318 and 324 used to authorize or deauthorizeeach subscriber. The outputs of the data modulator 116 are the 18 010754 audio and video carriers, FM modulated with the sets of data bytes 318 and 324 and the reference puise 304 during the vertical synchronization interval.
The preferred data modulator 116 is characterizedby: 1) the différence between the output frequencies of themodulated carriers are the same as their respective inputcarrier frequencies, 2) the System should not add noise ordistortion to the modulated carriers, and 3) the audio and videocarriers should match in déviation and phase. Since the audiocarrier is typically produced as a beat frequency between theaudio and video IF carriers, if the audio and video IF carriersdo not match in phase andmaintain the frequency différence ofthe original carriers, an unwanted hum could be produced.
With reference now to Figure 13, there is shown atop level block diagram of an up/down converter embodiment 348of the data modulator 116. In this embodiment, the encoded IFcarrier 113 is comprised of a separate video IF carrier 350 andaudio IF carrier 352. In an exemplary embodiment, the video IFcarrier 350 and the audio IF carrier 352 are typically at 45.75MHz and 41.25 MHz, respectively, and are nominally separated infrequency by 4.5 MHz. The reference IF carrier 353, generatedby the up/down converter 348, is comprised of a separate videocarrier+data signal 354 and audio carrier+data signal 356, bothof which are uniformly FSK modulated in response to the commontiming reference signal 109. In a preferred embodiment, thedata responsive frequency déviation for the carriers 350 and 352is ±25 KHz.
In Figure 14, a detailed block diagram of apreferred up/down converter 348 is shown. The up/down converter348 consiste of a two pairs of mixers 358, 360 and 362, 364, onepair for each carrier, i.e., video 350 and audio 352, undercontrol of a common pair of local oscillators. First and secondoscillators 366 and 368 are VCOs (voltage-controlled oscillators) phase locked to a common crystal oscillator 370.
The first oscillator 366 functions as a local oscillator (LO) 372 to mix each carrier up to an intermediate frequency and thesecond oscillator 368 functions as a second local oscillator 374to mix the signal back down to its original IF frequency. Inthe process of downconversion, the second local oscillator 374 19 Λ''- 010754 is frequency modulated with the data from the common timingreference signal 109. Since the second local oscillator 374changes frequency in response to the common timing referencesignal 109, the downconverted carriers 354 and 356 also changefrequency and additionally contain FSK data providingsynchronization and the authorization data.
The second local oscillator 374 used for thesecond downconversion is frequency modulated as follows. Thephase locked loop of the VCO 368 is used in the seconddownconversion. The common timing reference signal 109 issummed onto a control line 376 of this VCO 368. Since themodulated VCO 368 is used as the local oscillator 374 for thedownconversion, the RF carriers 354 and 356 are also modulatedand thus contain the FSK data.
In Figure 14, the audio and video carriers areseparate and thus, this same process is performed in parallel onboth the video and audio carriers 350 and 352 using the same twolocal oscillators 372 and 374. Signais from each oscillator372, 374 are split and respectively sent to two mixers 358, 362and 360, 364. The audio carrier 352 is upconverted using thefirst local oscillator 372 and then downconverted to theoriginal IF frequency using the FM modulated second localoscillator 374. Since the same frequency modulated localoscillator 374 is used in the downconversion of the audio andvideo carriers, the frequency déviation of both carriers will beessentially identical.
With reference now to Figure 15, there is shown apreferred embodiment of a décoder portion 400 of thedownconverter/decoder 120, as described in reference to Figure4. As previously described, the décoder portion 400 receivesthe downconverted common RF signal 126, recovers the commontiming reference signal 109 contained within using thedata/timing receiver 127, and in response generates gain controlsignais 128 to instruct the gain amplifier/attenuator 130 tooperate upon the downconverted common RF signal 126 according tothe inverse of the selected encoding rule, e.g., reinsertinghorizontal and vertical components, to generate the decodedchannels signal 132. The decoded channels signal 132 can bedistributed to one or more standard télévision receivers which 20
010754 can independently receive one or more decoded télévision channels.
The data/timing receiver 127 is preferablycomprised of a superheterodyne dual conversion FSK data receiver S 402 under control of a controller 404. The controller 404, receives a decoded data output signal 406 from the data receiver402 and generates frequency control signais to phase lock thedata receiver 402 to the decoded data output signal 406.Additionally, the data/timing/receiver 127 preferably comprises 10 an input attenuator 408 that accepts the downconverted common RFsignal 126 and, under control of the controller 404, generates acommon attenuated signal 410 to the data receiver 402 and thegain amplifier/attenuator 130. The controller 404 additionallyreceives a receive signal strength indicator (RSSI) 412 from the 15 data receiver 402 and responsively generates an atténuation control signal 414 to the input attenuator 408. The controlleradditionally generates gain control signais 128 to the gainamplif ier/attenuator 130 comprised of a blanking control line416 and a sync control line 418. These control lines are used 20 for reinserting the vertical and horizontal sync signais, respectively, into the common attenuated signal 410 derived fromthe downconverted common RF signal 126.
The data receiver's 402 principal purpose is toretrieve the common timing reference signal 109 from a selected 25 channel within the common attenuated signal 410 and to deliverthe common timing reference signal 109 as the decoded dataoutput signal 406, représentative of the authorization data andthe precisely timed reference puise 304 ' The data receiver 402is comprised of a first IF 420, a second IF 422 and a data
30 detector 424. The first IF 420, receives the common attenuatedsignal 410, typically having a frequency range of 222 to 408 MHzcorresponding to CATV channels 24 to 54, and downconverts theselected channel to a fixed frequency first IF output signal426. The second IF 422 then further downconverts the first IF 35 output signal 426 to a fixed frequency second IF output signal428. The second IF output signal 428 is input to the datadetector 424 which extracts the decoded data output signal 406and the receive signal strength indicator 412. The channelsélection is determined by the controller 404 by scanning the 21 010754 available channels for data. To scan the available channels,the controller 404 generates a channel select signal 430 to thefirst IF 420 which détermines the amount of frequency downconversion required for the common attenuated signal 410. • 5 The channel select signal 430 is iteratively altered until data is successfully received. Additionally, the controller 404generates a second IF frequency select signal 432 to the secondIF 422. In a preferred embodiment, the operating frequencies ofthe first IF 420 and the second IF 422, as determined by the 10 channel select 430 and second IF frequency select 432 signaisare adjusted by the controller 404 in response to the decodeddata output signal 406, thus phase locking the data receiver 402to the data contained within, i.e., the common timing referencesignal 109. 15 Figure 16 shows a detailed block diagram of an exemplary embodiment of the décoder 400 of Figure 15, comprisedof the first IF 420, the second IF 422 and the data detector424, that sends data to the controller 404 that in turn Controlsthe gain amplifier/attenuator 130, comprised of two switchable 20 RF attenuators, to re-insert sync and blanking signais directlyon cable télévision frequencies. In a preferred embodiment,video channels contained within the downconverted common RFsignal 126 do not contain horizontal or vertical sync puises.
In addition, the horizontal blanking level corresponding to each 25 channel within the common RF signal 68 is preferably attenuatedto prevent détection circuitry of some télévision receivers fromusing the blanking signal as a false sync reference. During thevertical synchronization interval, the blanking level is notattenuated by the encryption. The décoder 400 performs the 30 inverse of the selected encoding rule to restore the sync andblank signais to proper levels using a pair of two level RFattenuators, a blanking switch 434 and a sync switch 436. Anamplifier 438 isolâtes the blanking and sync switches 434, 436to prevent signal interactions. The amplifier 438 is preferably 35 a linear amplifier capable of handling multiple high levelcarriers with low distortion. A pad 440 helps to isolate thesync switch 436 from poor external impédance matching.
The input attenuator 408 is activated when thedownconverted common RF signal 126 reaches a certain level. 22 010754
This prevents distortion of both the gain amplifier/attenuator130 and the data/timing receiver 127. The receive signalstrength indicator 412, generated by the data detector 424,provides information for the controller 404 to détermine at whatlevel to switch in the input attenuator 408 via the attenuatorcontrol signal 414. A résistive splitter 442 provides a signal to boththe gain amplif ier/attenuator 130 and the first IF 420. Therésistive splitter 442 also helps to isolate and preventinteraction with the input attenuator 408.
The data receiver front end includes a highisolation amplifier 444 to isolate a first local oscillator 446.A pad 448 at the input of the amplifier 444 prevents distortionof the amplifier 444 from the multiple carriers within thedownconverted common RF signal 126. A pad 450 at the output ofthe amplifier 444 provides an easy broadband match to the inputof a first mixer 452 and also prevents distortion. Bothattenuators 448 and 450 also help isolate the first localoscillator 446.
The first mixer 452 and the first local oscillator446 combination provide a programmable local oscillatorfrequency range. The data carrier can be any of the videocarriers in this band. The IF frequency is preferably chosen toavoid mixing of carriers within the frequency range. A frequency synthesizer 454 keeps the first localoscillator 446 in phase lock while receiving a referencefrequency from the controller 404. The frequency synthesizer454 is preferably capable of tuning the first local oscillator446 using the channel select signal 430 from the controller 404.'In a preferred embodiment, the controller 4 04 iteratively tunesthe first local oscillator 446 until data is successfullyreceived. Alternatively, the controller 404 is preset to avalue for tuning the first local oscillator 446. A pad 455follows the first mixer 452 to prevent overloading a secondmixer 456 as well as to provide a good input terminât ion for animage filter 458.
The second IF 422 is chosen to produce and demodulate an IF frequency, e.g., 10.7 MHz, for which ceramic bandpass filters are readily available. A second frequency 23 /" 010754 synthesizer 460, identical to the first frequency synthesizer
454, is used to phase lock a second local oscillator 462. A first ceramic filter 464 follows the second mixer 456 and sets the démodulation bandwidth.
An IF amp 466 follows the first ceramic filter 464and helps to limit the signal. A second ceramic filter 468follows the IF amp 466 for additional band shaping. A gainlimiter amplifier 470 follows the second ceramic filter 468 forhard limiting. A quadrature detector 472 follows the limiteramplifier 470 and démodulâtes the FSK data. The input signalpreferably deviates ±25 KHz and has a data rate of 140,625 bitsper second. Demodulated data from the quadrature detector 472enters a data slicer 474 where uncertain data edges are cleanedup, made absolute and fed to the controller 404 as the dataoutput signal 406.
In order to perform the inverse of the selectedencoding rule, e.g., to insert the sync and blanking signais, atprecisely the correct position in time, the controller 404 isphase locked to the time reference provided from the synchronized signais at the headend. This time reference,originally generated from the common timing reference signal 109at the headend, becomes available to the controller 404 as partof the demodulated data signal 406. In this exemplary embodiment, the controller 404 performs the inverse of theselected encoding rule with a sync and blank generator thatlocks itself to the edge of a received reference puise to avoidsync drift. In a preferred embodiment, this locking isaccomplished by altering the clock freqtiency of the controller404. In Figure 15, it is shown that the controller 404 is ' comprised of a processor 476, preferably a microcontroller,executing software at a rate controlled by a voltage controlledcrystal oscillator 478. The processor 476 sends a feedbacksignal 480 to a digital to analog converter 482 which drives thevoltage controlled crystal oscillator 478 and effectivelychanges the clock frequency and thus the execution speed of theprocessor 476. By responsively altering the execution speed ofthe processor 476 in response to the decoded data output signal406, the channel select 430 and the second IF frequency select 24 010754 signais 432 are thus responsively altered, phase locking the data receiver 402 to the decoded data signal 406. . As discussed in reference to the data modulator 116, data is only sent during prescribed periods, the vertical -5 synchronization intervals. The controller 404, under softwarecontrol, recognizes the reference puise 304, and a combinationof the first start sequence 306, the second start sequence 308and the validity check byte 310, to ensure that the controller404 is synchronized with the common timing reference signal 109. 10 When an error is encountered, the controller 404 alters its clock frequency and/or the time window during which it looks forthe data blocks 300 and 302.
From the foregoing it should now be recognizedthat encryption/decryption method and apparatus embodiments hâve 15 been disclosed herein which make a plurality of distributed télévision channels simultaneously and automatically availableto authorized subscribers. Additionally, a single channelSystem using the disclosed modulation and démodulation methodsis also considered within the scope of the présent invention. 20 The previously disclosed invention can advantageously simultaneously décodé a block of télévisionchannel signais. However, providers may still desire to blockthe réception of premium channels, e.g., HBO, thus restrictingsubscribers to service tiers, e.g., 1) basic, 2) basic plus 25 expanded, 3) basic plus expanded plus selected premium channels,etc. To accomplish this task, the présent invention uses aninterdiction device to selectively scramble télévision channelsignais from within the block of locally decrypted channelsignais. 30 Figure 17 shows the use of a preferred interdiction device 510 which selectively jams a multichanneltélévision (TV) channel signal 512, an unencrypted signal, froma typical prior art télévision distribution System (not shown)to generate a signal 514 to provided subscribers with a 35 plurality of unencrypted télévision channel signais as well as aplurality of selectively encrypted/jammed channel signais.
While such a System can be used in various environments, e.g.,over-the-air and conventional cable subscriber Systems, it isparticularly useful in combination with the previously disclosed 25 /-> ! 01 0754 \ / / décoder 400. In embodiments of the présent invention, theinterdiction device 510 is programmable and capable ofselectively scrambling a plurality of télévision channelsthroughout the range of otherwise unencrypted télévision 5 channels from signal 512.
Figure 18 shows a block diagram of the preferred interdiction device 510. Embodiments of the présent inventionare based upon the récognition that télévision channels areallocated separate freguency slots, separated by fixed amounts, 10 e.g., 6 or 8 MHz. If a jamming signal is properly isolated to a fixed channel, only that channel is disrupted/jammed withoutsignificantly effecting eyen adjacent channels. The preferredinterdiction device 510 primarily comprises: 1) a frequencysynthesizer/VCO 516 (a jamming signal generator) for generating 15 a jamming signal, e.g., an FM-modulated sine wave, 2) a controller 518 for directing the frequency synthesizer/VCO 516to generate a jamming signal 520 for a selected télévisionchannel, 3) a mute switch 522 under control of the controller518 for only enabling the output of the jamming signal 520 when 20 the frequency synthesizer/VCO 516 has locked to a predeterminedjamming frequency for each selected channel, and 4) a summer 524for combining the multichannel télévision channel signal 512 andthe generated jamming signal 520 passed by the mute switch 522.
The controller 518 contains a channel interdiction 25 table 526, which corresponds to the preselected channels that are to be jammed. Each of these channels correspond to spécifiefrequencies for each geographical area, e.g., USA, Europe, etc.,and to particular transmission standards, e.g., NTSC or PAL. (See, e.g., Table I below depicting frequency assignments for a > 30 VHF System M (6 MHz) USA.) A second table (not shown) withinthe controller 518 is preferably used to convert each channeldésignation to its corresponding frequency. Altematively,table 526 may directly contain frequency désignationscorresponding to the selected channels. The table 526 may 35 altematively be preloaded, e.g., stored in nonvolatile memory,or may be loaded via communication between the controller 518and some external device, e.g., via a communication interface527. Altematively, as described further below, themultichannel télévision signal 512 can contain authorization 26
r> Q data via the communication interface which can be decoded to instruct identified controllers 518 to add or delete entries from its channel interdiction tables 526. // // // //
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The controller 518 commands the frequencysynthesizer/VCO 516 via a control interface 528 comprised of afrequency select bus 530 (used to select the desired jammingfrequency corresponding to a selected channel) and a lock signal532 (used to provide a feedback status signal). The frequencysynthesizer/VCO 516 takes a discrète, i.e., a nonzero, amount oftime (a function of the design of the frequency synthesizer/VCO516) to lock to the desired jamming frequency. Once the desiredjamming frequency is achieved, the jamming frequency ispreferably maintained for a period of time before a next jammingfrequency is selected. The lock signal 532 is then generated bythe frequency synthesizer/VCO 516 which can be used to notifythe controller 518 that the desired jamming frequency has beenachieved. Preferably, the lock signal 528 is generated by afrequency comparator within the frequency synthesizer/VCO 516which compares the jamming signal 520 to the frequency commandedby the controller 518. Once the controller 518 has beeninformed that a lock has been achieved, the mute switch 522 iscommanded via a mute control signal 534 to permit the jammingsignal 520 to be passed via signal 536 and summed by the summer524 with the multichannel télévision channel signal 512, thusgenerating the selectively scrambled multichannel télévisionsignal 514. This process is repeated for each of the frequencies/channels specified in the table 526.
Figure 19 is a simplified block diagram thatsummarizes the previously described process. In block 538, thecontroller 518 selects the next frequency from the channelinterdiction table 526. After waiting during block 540 for thefrequency synthesizer/VCO to reach the selected frequency, thecontroller 518 in block 542 instructs the mute switch 522 viathe mute control signal 534 to commence jamming the selectedtélévision channel. In block 540, the controller alternativelywaits a predetermined time period or waits for the lock signal532 to be retumed from the frequency synthesizer/VCO 516. In apreferred implémentation, there is no timing relationshiprequired between the timing of the selected télévision channeland the jamming signal. Consequently, the output of the muteswitch 522 must be maintained during block 544 for a sufficienttime period, e.g., at least one frame period, to adequately jam 29 010754 the selected télévision channel. At the end of the time perioddefined in block 544, the controller in block 546 enables themute switch 522 via the mute control signal 534 (if the nextchannel to be interdicted is not adjacent to the current 5 channel). The process then cyclically repeats, starting at block 538, with the next entry in the channel interdiction table526.
As should be apparent to one of ordinary skill inthe art, there are two time periods involved in this cyclical 10 process, a first time period related to the lock time in block540 and a second time period defined by the predefined timeperiod in block 544. Accordingly, there is a maximum cycle rate(for a particular implémentation), that this process can berepeated. This cycle rate détermines the maximum number of 15 channels (five in an exemplary embodiment) that can continuously(as viewed by a subscriber) be interdicted. Accordingly, in analternative embodiment, a plurality of frequency synthesizer/VCOs 516 are multiplexed such that one can beapproaching its jamming frequency (in block 540) while another 20 is dwelling at its jamming frequency (in block 544) .
Consequently, the number of interdicted channels can beincreased.
Figure 18 additionally shows the basic structureof the preferred frequency synthesizer/VCO 516 which is 25 primarily comprised of 1) a video frequency synthesizer 548, 2)an audio frequency synthesizer 550, 3) a summer 552, and 4) aVCO 554 (voltage-controlled oscillator). In an exemplaryembodiment, the video frequency synthesizer 548, e.g., aNational LMX1511A or Fujitsu MB15A02, is commanded to select a 30 particular frequency, e.g., the base video carrier frequency ofthe télévision channel offset by a jam frequency, e.g., afrequency approximately half way through the télévision channelor approximately 3 MHz, via the three wire bus 530 comprised ofclock, data, and enable signais (an interface particularly well- 35 suited for sharing with additional frequency synthesizers) . Thefrequency synthesizer 548 generates an analog video VCO controlsignal 556 that commands the VCO 554 to generate the desiredfrequency. A feedback signal 558 is retumed to the frequencysynthesizer 548 where it is compared in frequency with the 30
010754 frequency commanded by the controller 518. When a match isachieved the lock signal 532 results and this status signal iscommunicated to the controller 518.
With reference to Table I, there is shown a tableof the relevant frequencies for a VHF System M in the USA having6 MHz slots allocated for each télévision channel. Ideally, thefrequency synthesizer/VCO 516 would be tunable to the entirepotential frequency range, e.g., 40-860 MHz, or more.
Practically, this goal may not be easily achievable. Thus, inan exemplary embodiment the frequency synthesizer/VCO 516 istunable between 260-422 MHz, corresponding to télévisionchannels 31-55.
Let's say that an exemplary System was instructedto jam/interdict channels 44 and 50. Channel 44 has a videocarrier of 343.25 MHz with the preferred jamming frequency at 346.25 MHz (343.25 MHz plus a preferred offset of 3 MHz).Similarly, the preferred jamming frequency of channel 50 is at 382.25 MHz (379.25 MHz plus a preferred offset of 3 MHz). Thus,by repetitively switching/dwelling between jamming frequenciesof 346.25 and 382.25 MHz, channels 44 and 50 can be jammed whileleaving the remaining channels unaffected.
As described so far, the jamming signal willadequately disrupt only the video portion of the selectedtélévision channel. Therefore, a preferred embodimentadditionally comprises the audio frequency synthesizer 550,which in an exemplary embodiment divides a frequency output 560of the frequency synthesizer 548 to generate a digital audio VCOcontrol signal 562. The analog video VCO control signal 556 and
J the digital audio VCO control signal 562 are summed by summer552 to generate a VCO control signal 564 which Controls the VCO554 to generate a frequency-modulated jamming signal that willjam both the video and audio portions of the selected télévisionchannel.
Figure 20 shows a preferred embodiment of theprésent invention comprised of the multichannel interdictiondevice 510 combined with the previously disclosed décoder 400.While the prior décoder 400 disclosed significant improvementsover the prior art by permitting a single apparatus tosimultaneously decrypt ail or none of the transmitted channels 31 010754 according to transmitted authorization data, it did not permitthe provider to restrict access to selected channels. With theprésent decoder/interdiction device combination 566, themicrocontroller 518 receives authorization data from a datareceiver 568 via its data output 570 that has been inserted atthe headend to identify authorized subscribers (preferablyidentified with a predefined subscriber or box code in themicrocontroller 518). In this preferred embodiment, the samemicrocontroller 518 that Controls the common decrypting of acommonly encrypted input source 572, loads the channelinterdiction table 516 according to the authorization data,e.g., according to tiers. The data in the interdiction table516 is then used to control the operation of the frequencysynthesizer/VCO 516 and the mute switch 522 using the controlinterface 528 and mute control signal 534 according to thepreviously described algorithm. This improved combination nowpermits the simultaneous réception of multiple unencryptedsignais (suitable for picture-in-picture use) while stillpermitting the provider to withhold access to selected channels.
In order to adequately jam selected channels, itis préférable that a standardized jamming amplitude ratio beachieved between the jamming signal at the mute switch output536 and the multichannel télévision channel signal 512. Withoutthis standardization, undesirable results could occur. Forexample in a first mode, one might attempt to pirate a jammedtélévision signal by amplifying the common scrambled inputsource 572 to overcome the jamming signal. However, if astandardized jamming amplitude ratio is maintained, the inputsource 572 would automatically be attenuated and this piratingattempt would fail. Conversely in a second mode, if anabnormally small input source 572 should be présent, aproportionally large jamming signal could tend to spill over andeffect adjacent channels. However, if the input source 572 isamplified, this undesirable effect would be minimized.
To avoid these undesirable results, a receivesignal strength indicator (RSSI) 574 from the data receiver 568,indicative of the amplitude of the commonly scrambled inputsource 572 is used to control an AGC amplifier 576 to standardize the amplitude of a common attenuated signal 578 32 ( 010754 operated on within the décoder 400. By keeping the amplitude of the jamming signal fixed and continuously varying the common attenuated signal 578, a standardized jamming amplitude ratio can be achieved. Altematively, an AGC amplifier could be used to control the amplitude of the jamming frequency.
As previously described, authorization data isgenerally sent on a predetermined authorization data channel.However, in some embodiments, the predetermined channel can bevaried to further limit pirating. As shown below in Table II, apreferred channel interdiction table can be structured to takeadvantage of these embodiments. In this N-value interdictiontable, a first entry for each channel corresponds to a deltafrequency from the authorization data channel frequency and asecond entry spécifiés whether this channel is to beinterdicted. To attempt to defeat jamming, a pirate would needto know at least the présent authorization data channel, anyscheme for varying the authorization data channel, and the datawithin the interdiction table. Thus, pirating is further
complicated. ENTRY OFFSET FROM DATAFREQUENCY CHANNEL INTERDICT Y/N 1 ΔΡχ Y/N 2 AF2 Y/N 3 af3 Y/N N afm . Y/N
TABLE II
Additional improvements can be provided with thiscombination. As previously disclosed, the présent décoder /interdiction device 566 can simultaneously décodé ail of thetransmitted channels by reversing the encoding process done to aplurality of synchronized channels. Typically, this encoding isdone by first synchronizing a plurality of video inputs at theheadend and then suppressing the horizontal and vertical syncsignal of the synchronized video inputs. Consequently, once themicrocontroller détermines the proper timing, a blanking control 33 010754 line 584 and sync control line 586 can simultaneously décodé ailof the received channels to generate the multichannel télévisionchannel signal 512, the input signal to the interdiction device510. Since, there is a well-known temporal/timing relationshipbetween the horizontal and vertical sync signais, the présentinvention can take advantage of this relationship to optimizeits temporal placement of the jamming signal 520 within eachchannel frequency range. Therefore, in this embodiment thepredefined period of block 544 is preferably defined by thisknown timing relationship; permitting the single frequencysynthesizer/VCO 516 to jam a larger number of télévisionchannels.
The preferred embodiments of the inventiondescribed herein are exemplary and numerous modifications andrearrangements can be readily envisioned to achieve anéquivalent resuit, ail of which are intended to be embracedwithin the scope of the appended daims. For example, theprésent invention can also be used with an unscrambled over-the-air system, e.g., a microwave signal after a downconverter thatprovides an unscrambled multichannel télévision signal.Additionally, the interdiction/jamming step can précédé thesimultaneous decrypting step with similar results. //
II
II
U
H
II
II
H
II
H
H
H
II
H
II
II
II 34
Claims (14)
1. Sufascriber site apparatus useful in a System fordistributing from a System headend 1) multiplechannel signais defining an RF band, each channelsignal having respective video synchronization 5 components in time coincidence and 2) a common timing reference signal within said bandsynchronously related to said synchronizationcomponents, and wherein each of said channel signaisis encoded in accordance with a common encoding 10 rule, said subscriber site apparatus comprising: a data receiver responsive to at least one ofsaid channel signais for recovering said commontiming reference signal; and qcj a single broadband apparatus opérable over said RF band and responsive to said recovered commontiming reference signal for simultaneouslydecoding ail of said channel signais inaccordance with the inverse of said encoding 2Q rule to provide multiple decoded channel signais suitable for direct simultaneousapplication to a conventional télévisionreceiver.
2. Subscriber site apparatus useful in a System for 25 distributing from a System headend 1) multiple channel signais defining an RF band, each channelsignal having respective video synchronizationcomponents in time coincidence and 2) a commontiming reference Signal within said band and 3ü synchronous with said synchronization components, and wherein each of said channel signais isencrypted in accordance with a common encoding rule,said subscriber site apparatus comprising: 35 010754 a timing recovery circuit responsive to saidcommon timing reference signal for generatingat least one sync signal; a single décoder responsive to said common syncsignal for simultaneously decrypting ail ofsaid channel signais in accordance with theinverse of said encoding rule to generatemultiple decrypted channel signais, eachcapable of directly causing a conventionaltélévision receiver to produce an intelligibleimage ; and an interdiction apparatus for periodicallyinserting a jamming signal into at least one ofsaid multiple decrypted channel signais torender it incapable of directly causing saidtélévision receiver to produce an intelligibleimage.
3. A method of selectively scrambling télévision channels from an encrypted multichannel télévisionsignal at a subscriber site, comprising the stepsof : simultaneously decrypting said encryptedmultichannel télévision signal to form adecrypted multichannel télévision signal; determining an interfering frequency for aselected télévision channel signal according toan interdiction table containing data relatedto a plurality of channel signais selected tobe scrambled; 010754 commanding a frequency generator to generate anoutput of said interfering frequency; waiting until said frequency generator haslocked to said interfering frequency: 5 enabling combining of said output of said frequency generator with said decryptedmultichannel télévision signal; dwelling for a predetermined time period toscramble said selected télévision channel <10 signal; disabling combining of said output of saidfrequency generator from said decryptedmultichannel télévision signal; and cyclically repeating said previously recited 15 steps for a next selected télévision channel signal.
4. Subscriber site apparatus useful in a system fordistributing from a System headend 1) multiplechannel signais defining an RF band, each channel 2(j signal having respective video synchronization components in time coïncidence and 2) a commontiming reference signal within said band andsynchronous with said synchronization components,and wherein each of said channel signais is 25 encrypted in accordance with a common encoding rule, said subscriber site apparatus comprising: an interdiction apparatus for periodicallyinserting a jamming signal into said RF band togenerate an interdicted RF signal; 37 010754 a timing recovery circuit responsive to saidcommon timing reference signal for generatingat least one sync signal; and a single décoder responsive to said sync signaland said interdicted RF signal tosimultaneously decrypt multiple channel signaisin accordance with the inverse of said encodingrule to generate a recovered multichannelsignal comprising multiple decrypted channelsignais capable of directly causing aconventional télévision receiver to produce anintelligible image and at least one scrambledchannel signal incapable of directly causingsaid télévision receiver to produce anintelligible image.
A method of distributing multiple video signais,each produced by a different video source at aSystem headend and each containing picture andsynchronization components, to a plurality ofsubscriber sites located remote from said headend,said method comprising the steps of: generating at said headend multiple carriersignais ; modulating at said headend each of said carriersignais vith a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoïncidence; generating a common timing reference signalsynchronous with said time coïncidentsynchronization components; 30 010754 causing each of said channel signais to beencrypted at said headend in accordance with aconunon predetermined encoding rule; modulating a selected encrypted channel signal5 in response to said conunon timing reference signal; distributing said multiple encrypted channelsignais front said headend to said subscribersites as a conunon RF signal; responding at each subscriber site to said10 conunon timing reference signal to simultaneously decrypt ail of the channelsignais distributed thereto by operating uponsaid conunon RF signal with a single décoder inaccordance with the inverse of said encodingrule to generate multiple decrypted channelsignais, each capable of directly causing aconventional télévision receiver to produce anintelligible image; and periodically inserting at each subscriber site2g a jamming signal into at least one of said multiple decrypted channel signais to render itincapable of directly causing said télévisionreceiver to produce an intelligible image.
6. A method of distributing multiple video signais, 25 each produced by a different video source at a System headend and each containing picture and synchronization components, to a plurality of subscriber siteS located remote from said headend, said method comprising the steps of: 39 010754 generating at said headend multiple carriersignais ; modulating at said headend each of said carriersignais with a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoincidence; generating a common timing reference signalsynchronous with said time coïncidentsynchronization components; causing each of said channel signais to beencrypted at said headend in accordance with acommon predetermined encoding rule; modulating a selected encrypted channel signalin response to said common timing referencesignal; distributing said multiple encrypted channelsignais from said headend to said subscribersites as a common RF signal; periodically inserting a jamming signal at eachsubscriber site corresponding to at least oneencrypted channel signal into said common RFsignal to generate an interdicted RF signal;and it-D 010754 responding at each subscriber site to saidconunon timing reference signal and saidinterdicted RF signal to simultaneously decryptmultiple channel signais distributed theretowith a single décoder in accordance with theinverse of said encoding rule to generatemultiple decrypted channel signais capable ofdirectly causing a conventional télévisionreceiver to produce an intelligible image andat least one scrambled channel signal incapableof directly causing said télévision receiver toproduce an intelligible image.
7. Apparatus for distributing multiple video signais,each produced by a different video source at aSystem headend and each containing picture andsynchronization components, to a plurality ofsubscriber sites located remote from said headend,the apparatus comprising: a plurality of modulators at said headend forgenerating multiple carrier signais; a plurality of frame synchronizers at saidheadend for modulating each of said carriersignais with a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoïncidence; a timing reference generator at said headendfor generating a common timing reference signalsynchronously related to said time coïncidentsynchronization components; 41 010754 a plurality of encoders at said headend forcausing each of said channels signais to beencoded in accordance with a conunonpredetermined encoding rule; data insertion circuitry at said headend forcombining said conunon timing reference signalwith a selected encoded channel signal; means for distributing said multiple encodedchannels signais from said headend to_ saidsubscriber sites as a common RF signal; a data receiver at each subscriber site responsive to at least one of said channelsignais for recovering said common timingreference signal; and a single broadband apparatus at each subscribersite to respond to said recovered common timingreference signal to simultaneously décodé ailof the channel signais distributed thereto byoperating upon said common RF signal inaccordance with the inverse of said encodingrule to provide a multichannel signal comprising multiple decoded channel signaissuitable for direct simultaneous application toa conventional télévision receiver.
Apparatus for distributing multiple video signais,each produced by a different video source at aSystem headend and each containing picture andsynchronization components, to a plurality ofsubscriber sites located remote from said headend,the apparatus comprising: U2 010754 a plurality of modulators at said headend forgenerating multiple carrier signais; a plurality of frame synchronizers at saidheadend for modulating each of said carriersignais with a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoincidence; a timing reference generator at said headendfor generating a common timing reference signalsynchronous with said time coïncident synchronization components; a plurality af encoders at said headend forcausing each of said channels signais to beencrypted in accordance with a commonpredetermined encoding rule; a data modulator at said headend to datamodulate a selected encoded channel signal inresponse to said common timing referencesignal; means for distributing said multiple encryptedchannels signais from said headend to saidsubscriber sites as a common RF signal; an interdiction apparatus at each subscribersite for periodically inserting a jammingsignal into said recovered signal to generatean interdicted signal; 43 010754 a timing recovery circuit at each subscribersite responsive to said common timing referencesignal for generating at least one sync signal;and a single décoder responsive to said sync signaland said interdicted RF signal tosimultaneously decrypt said interdicted signalin accordance with the inverse of said encodingrule to generate a recovered mnultichannelsignal comprising multiple decrypted channelsignais capable of directly causing aconventional télévision receiver to produce anintelligible image and at least one scrambledchannel signal incapable of directly causingsaid télévision receiver to produce anintelligible image.
9. Apparatus for distributing multiple video signais,each produced by a different video source at aSystem headend and each containing picture andsynchronization components, to a plurality ofsubscriber sites located remote from said headend,the apparatus comprising: a plurality of modulators at said headend forgenerating multiple carrier signais; a plurality of frame synchronizers at saidheadend for modulating each of said carriersignais with a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoïncidence; 010754 a timing reference generator at said headendfor generating a common timing reference signalsynchchronously related to said time coincidentsynchronization components; 5 a plurality of encoders at said headend for causing each of said channels signais to beencoded in accordance with a commonpredetermined encoding rule; data insertion circuitry at said headend forcombining said common timing reference signalwith a selected encoded channel signal; means for distributing said multiple encodedchannels signais from said headend to saidsubscriber sites as a common RF signal; *15 an interdiction apparatus at each subscriber site for periodically inserting a jammingsignal into said common RF signal to provide aninterdicted RF signal; a data receiver at each subscriber site 20 responsive to at least one of said channel signais for recovering said common timingreference signal; and a single broadband apparatus responsive to said recovered common timing reference signal and 25 said interdicted RF signal to simultaneously décodé said interdicted RF signal in accordance with the inverse of said encoding rule to 010754 provide a multichannel signal comprising multiple decoded channel signais each capable of directly causing a conventional télévision receiver to produce an intelligible image and 5 at least one scrambled channel signal incapable of directly causing said télévision receiver toproduce an intelligible image.
10. Subscriber site apparatus useful in a System fordistributing from a system headend 1) multiple <jq channel signais defining an RF band, each channel signal having respective video synchronizationcomponents in time coincidence and 2) a commontiming reference signal within said bandsynchronously related to said synchronization 15 components, and wherein each of said channel signais is encoded in accordance with a common encodingrule, said subscriber site apparatus comprising: a data receiver responsive to at least one ofsaid channel signais for recovering said common 2Q timing reference signal; a single broadband apparatus opérable oversaid RF band, and responsive to said recoveredcommon timing reference signal for simultaneously decoding ail of said channel 25 signais in accordance with the inverse of said encoding rule to provide multiple decoded channel signais, each capable of directly causing a conventional télévision receiver to produce an intelligible image; and 46 010754 an interdiction apparatus for periodicallyinserting a jamming signal into at least one ofsaid multiple decoded channel signais to renderit incapable of directly causing said télévision receiver to produce an intelligibleimage.
11. In a System for distributing from a System headend 1) multiple channel signais defining an RF band,each channel signal having respective videosynchronization components in time coincidence and 2) a common timing reference signal within said bandsynchronously related to said synchronizationcomponents, and wherein each of said channel signaisis encoded in accordance with a common encodingrule, a method for periodically inserting a jammingsignal into at least one of said channel signais ata subscriber site to render it incapable of directlycausing a télévision receiver to produce anintelligible image, said method comprising the stepsof : simultaneously decoding said multiple encodedchannel signais using said common timingreference signal to form multiple decodedchannel signais; determining an interfering frequency for aselected channel signal; commanding a frequency generator to generate anoutput of said interfering frequency; and combining said output of said frequencygenerator with said multiple decoded channelsignais. U7 010754
12. Subscriber site apparatus useful in a system fordistributing from a system headend 1) multiplechannel signais defining an RF band, each channelsignal having respective video synchronizationcomponents in time coïncidence and 2) a commontiming reference signal within said bandsynchronously related to said synchronizationcomponents, and wherein each of said channel signaisis encoded in accordance with a common encodingrule, said subscriber site apparatus comprising: an interdiction apparatus for periodicallyinserting a jamming signal into said RF band toprovide an interdicted RF signal; a data receiver responsive to at least one ofsaid channel signais for recovering said commontiming reference signal, and a single broadband apparatus opérable over saidRF band and responsive to said recovered commontiming reference signal and said interdicted RFsignal to simultaneously décodé multiplechannel signais in accordance with the inverseof said encoding rule to provide a multichannelsignal comprising multiple decoded channelsignais capable of directly causing a conventional télévision receiver to produce anintelligible image and at least one scrambledchannel signal incapable of directly causingsaid télévision receiver to produce anintelligible image. 010754
13. A method of distributing multiple video signais,each produced by a different video source at aSystem headend and each containing picture andsynchronization components, to a plurality ofsubscriber sites located remote from said headend,said method comprising the steps of: generating at said headend multiple carriersignais ; modulating at said headend each of said carriersignais with a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoincidence; generating a common timing reference signalsynchronously related to said time coïncidentsynchronization components; causing each of said channel signais to beencoded at said headend in accordance with acommon predetermined encoding rule; modulating a selected encoded channel signal inresponse to said common timing referencesignal; distributing said multiple encoded channel signais from said headend to said subscriber sites as a common RF signal; 49 010754 responding at each subscriber site to saidcommon RF signal to recover said common timingreference signal to simultaneously décodé ailof the channel signais distributed thereto byoperating upon said common RF signal with asingle décoder in accordance with the inverseof said encoding rule to provide multipledecoded channel signais, each capable ofdirectly causing a conventional télévisionreceiver to produce an intelligible image; and periodically inserting at each subscriber sitea jamming signal into at least one of saidmultiple decoded channel signais to render itincapable of directly causing said télévisionreceiver to produce an intelligible image.
14. A method of distributing multiple video signais,each produced by a different video source at aSystem headend and each containing picture andsynchronization components, to a plurality ofsubscriber sites located remote from said headend,said method comprising the steps of: generating at said headend multiple carriersignais; modulating at said headend each of said carriersignais with a different one of said videosignais to form multiple channel signais, ailof said channel signais having their respectivevideo signal synchronization components in timecoincicence; generating a common timing reference signalsynchronously related to said time coïncidentsynchronization components; 5D 010754 causing each of said channel signais to beencoded at said headend in accordance with acojnmon predetermined encoding rule; modulating a selected encoded channel signal inresponse to said common timing referencesignal; distributing said multiple encoded channelsignais from said headend to said subscribersites as a common RF signal; -jg periodically inserting a jamming signal at each subscriber site corresponding to at least oneencoded channel signal into said common RFsignal to provide an interdicted RF signal; and responding at each subscriber site to said Ί5 common RF signal to recover said common timing reference signal and said interdicted RF signalto simultaneously décodé multiple channelsignais distributed thereto with a singledécoder in accordance with the inverse of said 2Q encoding rule to provide multiple decoded channel signais each capable of directlycausing a conventional télévision receiver toproduce an intelligible image and at least onescrambled channel signal incapable of directly 25 causing said télévision receiver to produce an intelligible image. 51
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US1995/008721 WO1996002111A1 (en) | 1994-07-11 | 1995-07-11 | Encryption/decryption process and apparatus for a multichannel television system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| OA10754A true OA10754A (en) | 2002-12-11 |
Family
ID=22249456
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| OA9800003A OA10754A (en) | 1995-07-11 | 1998-01-09 | Selective interdiction of television channels |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0806116A4 (en) |
| AP (1) | AP896A (en) |
| AU (1) | AU4645096A (en) |
| BR (1) | BR9510615A (en) |
| OA (1) | OA10754A (en) |
| WO (1) | WO1997003523A1 (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5125100A (en) * | 1990-07-02 | 1992-06-23 | Katznelson Ron D | Optimal signal synthesis for distortion cancelling multicarrier systems |
| US5319709A (en) * | 1991-06-13 | 1994-06-07 | Scientific-Atlanta, Inc. | System for broadband descrambling of sync suppressed television signals |
| ATE207278T1 (en) * | 1992-01-08 | 2001-11-15 | Broadband Innovations Inc | MULTI-CHANNEL TELEVISION SIGNAL ENCRYPTION AND DESCRIPTION SYSTEM AND METHOD |
| WO1993026126A1 (en) * | 1992-06-10 | 1993-12-23 | Scientific-Atlanta, Inc. | Interdiction method and apparatus with frequency change inhibit function |
| US5278908A (en) * | 1992-06-10 | 1994-01-11 | Scientific-Atlanta, Inc. | Interdiction method and apparatus with programmable jamming effectiveness |
-
1995
- 1995-12-21 AU AU46450/96A patent/AU4645096A/en not_active Abandoned
- 1995-12-21 BR BR9510615A patent/BR9510615A/en not_active Application Discontinuation
- 1995-12-21 AP APAP/P/1998/001181A patent/AP896A/en active
- 1995-12-21 EP EP95944387A patent/EP0806116A4/en not_active Withdrawn
- 1995-12-21 WO PCT/US1995/016827 patent/WO1997003523A1/en not_active Ceased
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1998
- 1998-01-09 OA OA9800003A patent/OA10754A/en unknown
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| EP0806116A1 (en) | 1997-11-12 |
| BR9510615A (en) | 1999-04-27 |
| AU4645096A (en) | 1997-02-10 |
| WO1997003523A1 (en) | 1997-01-30 |
| AP896A (en) | 2000-11-17 |
| EP0806116A4 (en) | 2000-06-28 |
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