3,919,462
`[in
`United States Patent
`[451 Nov. 11, 1975
`_ A.
`Hartung et al.
`__?_::_
`
`[191
`
`[75]
`
`l5-ll METHOD AND APPARATUS FOR
`SCRAMBLING AND UNSCRAMBLING
`C()MMUN[CAT]0N 51(;NALS
`lnventow Amen F‘ Hartlmg‘ Woodland Hills;
`Frank W. Lehan. Santa Barbara;
`Charles T. Barooshian, Pacific
`P'.lllS'i1(l€S‘. Edward J. Zacliarski.
`Malibu. all of C;i|‘if_
`W1 Assisnee: S-Wm W-‘°vme'.“ C°rv°r=“i°n~
`Sum” Momca‘ Callf
`Aug, 15, 1973
`Filed:
`[22]
`lzll Appl No‘: 388‘439
`
`[52] U.S. Cl. .......... .. 178/5.1; 178/DlG. 13; l78/22;
`325/34
`Int. Cl.”__________________________________________ ,_ H04N 1/44
`Field of Search. .
`..
`..
`178/5.l. DIG. 13, 22;
`325/34
`
`[5l ]
`[58]
`
`[56]
`
`References Cited
`UNITED STATES PATENTS
`l78/5.l
`l()i‘l9(i3
`Shunahan.
`..
`.
`...
`3.106.604
`178/5?‘
`5/1965
`“M537
`CCU” C! M‘
`‘ H p
`‘
`p
`9/[gm W,_d‘kcr_
`3_537.x-,7
`__
`_7
`_
`>>>>>> H 1785]
`3533343 H;ig7()
`Shumhun E‘ at
`p
`‘‘‘‘‘‘‘‘‘‘ H 173,5,
`3.733.355
`5.i‘|973 Harm t-1 at
`_
`173/5.1
`3.757.225
`W197}
`Ulicki
`..
`....... .,
`I78./5.1
`3.777.053
`IEII973 Wiiiig ei al.
`I78/5 I
`3.789.l 3l
`l/i974
`Harrie} ..
`l78/5.l
`3.79(l.7U(l
`2/1974
`Czilliiis et al.
`178/5.l
`3.><m.732
`4/1974
`Reeves.
`..
`178/5.1
`
`p
`
`.
`.
`
`.
`
`.
`
`.
`
`. .
`
`.
`
`.
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`. . .
`
`.
`
`.
`
`.
`
`.
`
`.
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`. . ..
`
`..
`
`..
`
`Prilnurj‘ Emu1iuer—Mai§’nzird R. Wilbur
`‘
`.~l.v.ri.mi:ir E.\uminer—._S. C. Buczinski
`Sgt;/I£i"b.t:fl;r1(. or fu'm——Fulwider. Patton. Rieber
`
`ABSTRACT
`[57]
`Method and apparatus for scrambling and unscram-
`lil1’3.giéTl‘3,i§?$?.“s§;‘3§.‘Z. ‘lII‘1T"i.‘§i~ji'.°pSS.’*T‘g‘§’.l?.."le‘iei‘$.S.§§'.‘ir
`subscribers are known at a central
`transmitting site.
`and control signals encoded into vertical blanking in«
`tervals of the video si nals are addressed to receivers
`authorized to receivegunscrambled transmissions.
`to
`selectively control unscrambling at those receivers. In
`an unscrambler at each subscribers receiver. the con-
`trol signals are decoded. and. if addressed to the par-
`ticular subscribers receiver, operate to enable or dis-
`able the unscrarnbler. or to frequently vary its mode of
`operation.
`thereby greatly increasing the security of
`the system and deterring viewing of scrumbled trans-
`missions. Video scrambling and unscrambling are ef—
`fected by inversion of selected horizontal
`lines of a
`transmitted television picture. and possible modes of
`.
`_
`'
`.
`.
`.
`V
`.
`I
`scrambling and unscrambling include inxersionof al-
`termite groups of equal numbers of lines. inversion or
`non—inversion selected on a llnC-b)-lll1L‘ basis. with an
`appropriate control signal being transmitted with each
`line. and inversion or non—inversion in il preselected
`sequence. as determined by synchronized logic at the
`rgceivefs and [hg transmitting s'|[¢_
`
`52 Claims, 16 Drawing Figures
`
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`PMC Exhibit 214
`
`Apple v. PM
`|PR2016-0075
`
`Page 1
`
`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
`Page 1
`
`

`
`
`
`U.S. Patent
`
`Nov. 11, 1975
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`Sheet 1 of 4
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`3,919,462
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`PMC Exhibit 214
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`Apple v. PM
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`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
`Page 2
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`

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`U.S. Patent
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`Nov. 11, 1975
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`Apple v. PM
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`Page
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`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
`Page 3
`
`

`
`U.S. Patent
`
`Nov. 11, 1975
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`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
`Page 4
`
`

`
`U.S. Patent Nov.11, 1975
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`PMC Exhibit 214
`
`Apple v. PM
`|PR2016-0075
`
`Page
`
`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
`Page 5
`
`

`
`1
`
`3,919,462
`
`METHOD AND APPARATUS FOR SCRAMBLING
`AND UNSCRAMBLING COMMUNICATION
`SIGNALS
`
`2
`signals relating to changes in the scrambling mode. It
`will be apparent that the transmitted signals have to be
`scrambled according to the same mode as that used in
`unscrambling, and that scrambling and unscrambling
`5 have to be completely synchronized.
`There is an unscrambling means. or unscrambler, at
`BACKGROUND OF THE INVENTION
`each subscriber’s receiver, and it basically includes de-
`This invention relates generally to techniques for
`coding means, to decode the control signals and en-
`scrambling and unscrambling television signals, and,
`coded identifiers, identifier comparison means. to ac-
`more particularly,
`to improved scrambling and un-
`scrambling techniques applied to a subscription televi— 10 cept only control signals intended for the particular re-
`sion system controllable by a central computer.
`ceivcr, and scramble decoder means. to unseramble the
`ln subscription television, or “pay-T.V.” systems,
`television signals in accordance with an unscrambling
`subscribers select programs that they wish to view, and
`mode contained in the control signals, The audio por-
`pay to have those programs transmitted to their televi-
`tion of a television signal may also be scrambled, and
`sion receivers, usually along a coaxial cable. One re-
`15 the unscrambler may include means for unscrambling
`quirement for such systems is that the transmitted sig-
`these audio signals at the receiver site.
`nals should be unintelligible to non-subscribers or to
`More specifically, in a presently preferred embodi-
`subscribers who have not paid for a particular program.
`ment of this invention, video signals are scrambled by
`Various methods have been suggested for scrambling
`the inversion of some of the horizontal lines making up
`video signals, such as by inserting time delays, or by in- 30 a television picture. This has the disconcerting effect of
`vetting portions of the video signals so that white and
`reversing the black and white portions of the inverted
`black images are reversed on portions of the television
`lines,
`in a black and white picture. or inverting the
`screen.
`color spectrum in a color picture. The scrambling
`The success of a particular scrambling technique de-
`mode at any instant may be such that. for example, the
`pends, first of all, on whether a program is sufficiently 35 inverted lines form patterns of regularly or irregularly
`scrambled to deter unauthorized viewers from watch-
`spaced bars across the picture, and the bars may be
`ing it in a scrambled condition, and secondly, on how
`made to roll up or down. Furthermore, the scrambling
`difficult it is for a resourceful viewer to circumvent the
`mode may be changed at a rapid rate, producing an al-
`protection provided by the scrambling techniques.
`most infinite variety of moving patterns of inverted
`Some prior systems provide for limited variation of 30 lines on the screen if the signals are not unscrambled
`the mode of scrambling and unscrambling, these gener-
`prior to video display.
`ally requiring the insertion of a coded card, or the like.
`The scrambled video signals produced by inversion
`to correctly unseramble the signals. However, there has
`of some of the horizontal picture lines are unscrambled
`long existed a need for a scrambling technique in which
`at each authorized receiver by one of the unscramblers,
`security can be maximized by rapidly and automatically 35 which are functionally complementary to scrambling
`varying the scrambling mode, without
`the need for
`means at the transmitter. In the preferred embodiment,
`manual intervention by the subscribers, and which will
`receiver identifiers and control signals are encoded into
`effectively deter viewers of the scrambled television
`aconventionallyformed,composite video and synchro-
`picture. The present invention fulfills this need.
`nization signal, specifically in those portions of the
`40 video and synchronization signal relating to vertical
`blanking intervals, during which a conventional televi-
`SUMMARY OF THE INVENTION
`sion picture tube has its electron beam returned to the
`The present invention resides in a method and appa-
`top of the tube after scanning a complete field of the
`ratus for scrambling and unscrambling television sig-
`picture.
`nals, wherein the mode of scrambling and unscram-
`these
`In the unscrambler at a particular receiver,
`bling may be varied automatically and continually in 45
`identifiers and control signals are decoded, and the
`order to increase the security of the system and to deter
`identifiers are compared with the unique identifier as-
`unauthorized viewers. Briefly, and in general tenns, the
`sociated with the receiver. If a match is found, the con-
`method of the invention, as it relates to unscrambling at
`trol signals are further decoded and applied in the un-
`a receiver, includes the steps of receiving encoded con-
`trol signals and encoded identifiers of authorized re- 50 scrambler to enable or disable unscrambling. to change
`ceivers along with scrambled television signals, decod-
`the mode of unscrambling, or to select a particular pro-
`ing the encoded control signals and identifiers, compar-
`gram on a separate frequency channel. If no match is
`ing the received identifiers with a unique identifier as-
`found, the control signals have no special meaning for
`sociated with the receiver, and, if the comparison re-
`the receiver in question. However, a special “all-call"
`sults in a match, automatically unscrambling the televi- 55 identifier is available to allow all receivers in the system
`sion signals in accordance with an unscrambling mode
`to be controlled, regardless of whether or not they have
`contained in the control signals.
`been individually addressed to enable unscrambling.
`The invention is particularly well suited for use in a
`Also, certain control signals have meaning for all re-
`subscription television system in which the subscribers
`ceivers which have been previously specifically ad-
`select programs in advance by direct
`telephone or 50 dressed to enable unscrambling operations. In particu-
`other communication with a central computer. The
`lar, an unscrambler synchronization signal, used to syn-
`computer controls a transmitter which can address
`chronize scrambling and unscrambling, is in this latter
`control signals to unscrambling equipment at each sub-
`category, and, in one embodiment, the unscrambling
`scriber’s receiver by means of a unique identifier asso-
`mode for all enabled unscramblers may be changed by
`65 control signals not associated with a particular identi-
`ciated with that equipment. Thus, the unscrambling
`fier.
`equipment of those subscribers who have selected a
`In one of three alternative embodiments of the inven-
`particular program can be conditioned to unseramble
`tion, the scrambling of unscrambling mode depends on
`the program signals, and to receive subsequent control
`
`PMC Exhibit 214
`
`Apple v. PM
`|PR2016-0075
`
`Page
`
`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
`Page 6
`
`

`
`3
`the selection of a digit from a plurality of digits in a
`counter used to count horizontal picture lines transmit-
`ted or received. The video signal is then inverted. for
`scrambling or unscrambling, only when the selected
`digit is in a particular state.
`In another of the three alternative embodiments.
`each horizontal line of video information is transmitted
`with an encoded signal indicating whether the line is
`inverted or not. The unserambler decodes this signal
`and accordingly unscrambles the video signals.
`In a third alternative embodiment.
`the decision
`whether or not to invert a particular line being scram-
`bled or unscrambled is derived from the contents of a
`register, which is itself scrambled in a predetermined
`manner while the previous line is being transmitted or
`received. Different scrambling modes may be estab-
`lished by storing different starting patterns in the regis-
`ter.
`
`3,919,462
`
`4
`FIG. Sbis a time-amplitude graph of a “stretched"
`vertical synchronization pulse derived from the signal
`of FIG. 5a;
`FIGS. 6u—e are time-amplitude graphs of various tim-
`ing and data signals, and together comprise a timing di-
`agram relating to the operation of the unserambler
`logic of FIG. 3;
`FIGS. 7-9 are block diagrams illustrating three alter-
`native embodiments of a scramble decoder which may
`be included in the unserambler logic of FIG. 3; and
`FIG. 10 illustrates. by way of example, one possible
`form of the accumulator scrambler logic included in
`the alternative embodiment of FIG. 9.
`
`l()
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`As shown in the drawings for purposes of illustration,
`the invention is particularly well suited for use in a
`computer controlled subscription television system, the
`principal components of which are shown in FIG. 1. In
`such a system. signals from a television program source
`12, such as a television camera or a television network,
`are transmitted to paying subscribers, typically. but not
`necessarily, by means of a coaxial cable 13. In order to
`prevent non-subscribers and subscribers who have not
`paid for a particular program from receiving the trans-
`mission. the signals from the television program source
`12 are processed by a scrambler-encoder 14, which
`modifies the signals in some fashion to make them un-
`intelligible to an unauthorized receiver. A modulator
`15 uses the signals from the scrambler-encoder 14 to
`modulate a high frequency carrier for transmission
`along the cable 13. The modulator 15 is conventional
`It will be appreciated from the foregoing that the
`except that its audio portion is realigned to scramble
`present invention significantly advances the state of the _
`.
`.
`.
`.
`.
`.
`15 audio signals by shifting the audio carrier and thereby
`an of 5_°“,‘mbl'"g ‘lrld unscmmbhng telellslon Signals m
`increasing the frequency difference between the video
`subscription television systems. In particular, since the
`and audio Carriers‘
`invention is Operable to Vary the scmmbmlg mode ml}
`Each subscriber to the svstem has a conventional tel-
`idly. and automaticallyl, it provides greatly increased se-
`Cvision receiver I6, and {S Supplied with an ImsCram_
`curity from unauthorized unscramblirig of signals iii- 40 bIeI. I7 Connected between the cable 13 and the I.e_
`“?“d°d only fof °°"'f““ 5‘ftf5°"'_ber5- Vmhout ‘he ncces‘
`ceiver. The unserambler 17 may have associated with it
`5“? Of 5”bS°”b"-I
`'deTmf'°““°" by mamlal means‘
`a converter 20 for converting specially assigned carrier
`M°I€°VeT-
`‘he 5‘3”""bl"‘8 mode "WY be Selected ‘md
`frequencies, used for transmission over the cable, to a
`varied to deter most unauthorized viewers from \vatch-
`frequenq, C0I,I.esPOIIdIIIg I0 an unused numbered CIIaII_
`ing the scrambled video patterns. especially since the 45 “BI to whICh the receiver 16 can be IIIned_ Akhough
`audio signal may also be unavailable to the unautho-
`only one receiver 16ISSh0wII In FIG 1IIIwI"be appI.e_
`Tiled V'l€VV3T5- Othel 35139915 and adwmlages Of ‘he In’
`ciated that, in general, a number of separate receivers
`vention will become apparent from the following more
`WI“ be Connected to the cable 13_
`detailed description taken in conjunction with the ac-
`In the System mus“-aIed_ a Central Computer 13 is
`C0mP3“Yl"g dT3W'lng5-
`50 used to maintain records of available programs and of
`BRIEF DESCRIPTION OF THE DRAWINGS
`programs selected by the subscribers. Each subscriber
`selects the programs he wishes to view (indicated by
`the block 19). and conveys his selections to the central
`computer 13 by means of a telephone 21_ The se[eC_
`55 tions may be communicated to the computer 18 di-
`rectly by means of some digital attachment
`(not
`shown) acoustically coupled to the telephone 21, or
`may be input to the computer by an operator in voice
`communication with the subscribers. Alternatively,
`there may be a reverse communication path along the
`cable 13 to the computer 18, so that a subscriber may
`select programs by operating switches or buttons (not
`shown) at his television receiver 16. However the pro-
`grams are selected is of little consequence so far as the
`present invention is concerned, so long as there is some
`means to determine which subscribers are authorized
`to receive various programs. The scrambler-encoder
`14, which is also connected to the computer 18, typi-
`
`Scrambling of the television signal may also include
`scrambling the audio portion of the signal, by some
`means.
`to further deter unauthorized persons from
`watching a scrambled transmission. Conventionally,
`the audio signal
`is
`transmitted on a
`frequency-
`modulated carrier spaced from the video carrier by a
`preselected frequency difference. In the presently pre-
`ferred embodiment of the invention. the audio carrier
`is shifted away from the video carrier so that the magni-
`tude of the difference between the video and audio car-
`riers is increased,
`thus preventing detection of the
`audio signal in a normally aligned receiver. Unscram-
`bling is effected by a corresponding frequency shift in a
`downward direction.
`
`20
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`I») ‘J!
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`3U
`
`IS 51 block diagram 5h0Wi"g ‘he 5Ub5Y5"3m
`FIG 1
`components of a subscription television system in
`which the invention might 136 Used;
`FIG. 2 is a block diagram showing an unserambler
`which may be employed in the system of FIG. I, and
`showing how the apparatus of the invention might be
`connected with the system;
`FIG. 3 is a more detailed block diagram of unscram-
`bler logic employed in the unserambler of FIG. 2;
`FIG. 4a is a time-amplitude graph of a conventional.
`composite video and synchronization signal;
`FIG. 4b is a graph similar to that in FIG. 4a, in which
`the video signal portions have been inverted;
`FIG. 5a is a time-amplitude graph of a composite
`video and synchronization signal. showing control sig-
`nals encoded into the vertical blanking interval;
`
`60
`
`65
`
`PMC Exhibit 214
`
`Apple v. PM
`|PR2016-0075
`
`Page
`
`PMC Exhibit 2145
`Apple v. PMC
`IPR2016-00753
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`

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`3,919,462
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`5
`cally by a telephone line 22, may then be directed to
`encode appropriate unscrambler control signals for
`transmission with the conventional television signals.
`The present invention is principally concerned with
`improved techniques employed in the scrambler-
`encoder I4 and the unscrambler 17, and FIG. 2 illus-
`trates in block diagram form the unscrambler 17 used
`in a presently preferred embodiment of the invention.
`It will be appreciated, however, that, in systems involv-
`ing signal scrambling and unscrambling, the techniques
`used in unscrambling are functionally complementary
`to those used in scrambling. Consequently, although
`only the unscrambler I7 is described in detail herein, it
`will be understood that complementary techniques are
`used in the scrambler—encoder 14, and that these tech-
`niques will be readily apparent to those of ordinary skill
`in the art.
`
`As will be apparent from FIG, 2, many elements of
`the unscrambler 17 are conventional in the television
`electronics art, and these are described herein only for
`the purpose of illustrating the environment in which the
`improvements constituting the invention will operate.
`The scrambled television signals from the cable 13
`(FIG. 1) are input to the unscrambler 17 through an
`input
`terminal 25 and processed by a conventional
`mixer 26 connected with a conventional oscillator 27
`and channel selector 28. The output from the mixer 26
`is an intermediate frequency (IF) signal, which, as
`shown by the line 29, is connected to conventional cir-
`cuitry performing the functions shown in block 31, in-
`cluding IF amplification, video detection, automatic
`gain control, and audio IF amplification. As shown in
`FIG. 2.
`the output from these conventional circuits
`grouped in block 31 includes a composite video and
`synchronization signal, which is still in scrambled form,
`along line 32, and an audio IF signal, along line 33.
`The scrambled video and synchronization signal on
`Iinee 32 is gated through one of two parallel paths 34
`and 35 including an inverting amplifier 36 and a non-
`inverting amplifier 37, respectively. and controlled by
`conventional gating circuits 38 and 39,, respectively.
`When the gate 39 is open and the gate 38 is closed, the
`composite video and synchronization signal is not in-
`verted and appears. for example, like the signal shown
`in FIG. 4a. However, when the gate 39 is closed and the
`gate 38 opened for the video portions of the composite
`signal, the video portions are inverted, as shown in FIG.
`4b. The composite video and synchronization signal on
`line 32 is also input over line 41 to a synchronization
`Separator 42, which uses techniques well known in the
`art to separate the conventional television synchroniza-
`tion signals from the composite signal, and to transmit
`these along lines 43 and 44 to unscrambler logic 45, the
`detail of which is central to this invention, and will be
`discussed herebelow in connection with FIG. 3.
`The unscrambler logic 45 receives control signals en-
`coded in the composite video and synchronization sig-
`nal along line 46, and operates to generate two basic
`output control signals: and “invert" or “non-invert”
`signal on lines 47 and 48, respectively, connected to
`the gating circuits 38 and 39 to control inversion or
`non-inversion of the video signal, and an “unscramble
`on” or “off ” signal on lines 49 and 51, respectively,
`connected to additional gating circuits 52 and 53, re-
`spectively. to control audio unscrambling. The audio IF
`signal on line 33 takes one of two parallel paths 54 and
`55 as determined by the gating circuits 52 and 53, the
`path 54 passing through an audio unscrambler 56 be-
`
`10
`
`IS
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`25
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`30
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`35
`
`40
`
`45
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`50
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`55
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`60
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`65
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`6
`fore merging with the alternate path 55 and being input
`over line 57 to conventional oscillator and modulator
`circuits 58. The composite video and synchronization
`signal, as unscrambled under the control of the un-
`scrambler logic 45, is also input to the oscillator and
`modulator 58, over line 59, and is there used. together
`with the audio signal input over line 57 to modulate a
`high frequency carrier signal in a conventional manner.
`The carrier signal is output from the unscrambler 17 to
`the receiver 16 through an output terminal 61.
`It has been proposed that subscription television sys-
`tems be assigned so-called “mid-band“ frequencies be-
`tween the frequencies assigned to numbered channels
`in the very high frequency (VHF) range. If this were
`the case, and if the receiver 16 (FIG. 1) were not
`equipped to receive these mid-band channels, the un-
`scrambler illustrated in FIG. 2 would also operate as a
`frequency converter, i.e., it would be tuned to receive
`one of the mid-band frequencies, while the oscillator
`and modulator 58 would be tuned to output a signal at
`a frequency corresponding to an unused numbered
`channel, to which the receiver 16 could be tuned to re-
`ceive the mid-band channels.
`
`The techniques of scrambling and unscrambling tele-
`vision signals as thus far generally described with refer-
`ence to FIGS.
`1 and 2, while not particularly well
`known, are not believed to be novel, but are believed to
`require some emphasis in this specification in order to
`define the environment in which the present invention
`operates, and to convey an appreciation of its novel as-
`pects and advantages. The present invention is princi-
`pally concerned with improvements in the techniques
`of scrambling and unscrambling as specifically embod-
`ied in more detailed aspects of the unscrambler logic
`45 (FIG. 2).
`In accordance with the present invention, the mode
`by which the scrambling and unscrambling operations
`are performed may be varied automatically and rapidly
`in order to increase the security of the system and to
`deter unauthorized viewing. In brief, the scrambler-
`encoder 14 (FIG. 1) encodes into the television signal
`control signals addressed to a particular unscrambler
`17 and directing it to initiate or terminate unscrambling
`operations, to change the mode of unscrambling, or to
`tune to a different incoming program. The unscrambler
`17 (FIG. 1), and more specifically, the unscrambler
`logic 45 (FIG. 2), operate to decode the control signals
`and to perfonn the appropriate control function if it is
`addressed to the unscrambler 17 in question. If a sub-
`scriber has not paid or been charged for a particular
`program, the unscrambler 17 will not be directed to un-
`scramble the program, which can be viewed, therefore,
`only in scrambled form. Since the scrambler-encoder
`14 can be controlled to select a scrambling mode which
`results in extremely disconcerting patterns on the re-
`ceiver 16, most unauthorized viewers are deterred from
`viewing a scrambled program. Furthermore, the system
`has a high degree of security, because the mode of
`scrambling may be rapidly varied in a practically ran-
`dom fashion.
`More specifically, the scrambler—encoder 14 encodes
`control signals in that portion of the normal composite
`video and synchronization signal known as the vertical
`blanking interval. As is well known, a television picture
`is conventionally made up of a number of horizontal
`lines traced by an electron beam of varying intensity.
`usually from the top to the bottom of the picture. A full
`frame of the picture typically consists of two interlaced
`
`PMC Exhibit 214
`
`Apmev.PM
`|PR2016-0075
`
`Page
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`Apple v. PMC
`IPR2016-00753
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`3,919,462
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`7
`fields. each tracing alternate lines in the picture. The
`composite signal producing the trace of a field of the
`picture comprises, as can be seen in FIG. 5a. a video
`signal 71 and a succession of horizontal synchroniza-
`tion pulses 72 used to control transition of the beam
`from one line to the next. Between successive fields of
`
`the picture, there is a vertical blanking interval during
`which the beam is blanked out and positioned for the
`start of the next field. The vertical blanking interval
`conventionally includes a group of equalizing pulses
`73, some wider vertical synchronization pulses 74, a
`further group of equalizing pulses 75, followed finally
`by a number of horizontal synchronization pulses 76
`before the first line of video information in a new field.
`Using a widely known technique, the control signals
`to be transmitted to the unscrambler 17 (FIG. 1) are
`encoded between the horizontal synchronization pulses
`76 which occur towards the end of the vertical blanking
`interval, as shown at 77. The technique is similar, for
`example, to one used by television networks for encod-
`ing time-of-day signals into the vertical blanking inter-
`val. In the presently preferred embodiment, there are
`three “lines” of control signals, each coded in binary
`digital form as a series of pulses, and each line of signals
`being addressed to a particular unscrambler 17 (FIG.
`1). They may conveniently be thought of as “lines" of
`signals or data, since they appear between horizontal
`synchronization pulses in much the same way as lines of
`video information. However, it will be understood that
`the control signals occur between fields of the picture
`and are not normally displayed as video signals. In any
`one vertical blanking interval, control signals may be
`transmitted to up to three separate unscramblers 17,
`using all three “lines”, and, since there are 60 vertical
`blanking intervals per second in television systems in
`the United States, up to
`180 separate unscramblcrs
`may be addressed per second. It will be appreciated
`that a greater number of receivers can be addressed by
`using more “lines" of the vertical blanking interval or
`encoding control signals for more than one unscram-
`bler in a single “line”. In the unused line immediately
`following the control signals, an unscrambler synchro-
`nization signal 78 is encoded from time to time. This
`signal, as will be subsequently discussed in detail, is re-
`quired to synchronize operations of the scrambler-
`encoder 14 (FIG. 1) and the unscrambler 17.
`The unscrambler logic 45 (FIG. 2) receives the com-
`posite video and synchronization signal over the line
`46, this signal including the control signals encoded as
`illustrated and discussed with respect to FIG. 5a. In de-
`coding these control signals, the unscrambler logic 45
`utilizes horizontal and vertical synchronization pulses
`separated from the video signal by the synchronization
`separator 42 and transferred to the unscrambler logic
`45 along the lines 43 and 44 respectively. It will be ap-
`preciated from FIG. 5a, that there is no single vertical
`synchronization pulse as such, but rather a series of
`pulses during the vertical blanking interval. The verti-
`cal synchronization pulse transmitted along the line 44
`is termed a “stretched” vertical synchronization pulse
`and is developed in the synchronization separator 42,
`and illustrated in FIG. 5b.
`It will be seen that the
`stretched vertical synchronization pulse begins after
`the first group of equalizing pulses 73 in the vertical
`blanking interval, and ends after the final group of
`equalizing pulses 75 and immediately before resump-
`tion of the normally spaced horizontal synchronization
`pulses 76.
`
`8
`As will be seen, the stretched vertical synchroniza-
`tion pulse 79 is utilized in the unscrambler logic 45 in
`the decoding ofthe control signals 77 (FIG. Sal and the
`unscrambler synchronization signals 78. It should fur-
`ther bc noted that the horizontal synchronization signal
`developed in the synclironization separator 42 (FIG.
`2), and transmitted to the unscrambler logic 45 along
`the line 43, is also a “strctchcd“ horizontal synchroni-
`zation pulse, including the so-called “front porch“ and
`“back porch" portions of the conventional horizontal
`synchronization pulse, as well as a color burst signal in-
`cluded in color television transmissions.
`The unscrambler logic 45 (FIG. 2) will now be de-
`scribed in greater detail with reference to FIG. 3. Basi-
`cally, the logic illustrated in FIG. 3 operates to receive
`control signals encoded in the composite video and
`synchronization signal, at the terminal 85, to decode
`those control signals, utilizing the stretched vertical
`synchronization pulse input at 86 and the stretched
`horizontal synchronization pulse input at 87, and, if the
`control signals are addressed to the unscrambler in
`question, to place the decoded control signals in a con-
`trol register 88. A scramble decoder 89, altemative em-
`bodiments of which will be discussed with reference to
`FIGS. 7-9, then uses the contents of the control regis-
`ter 88, along with other available signals, to generate
`the “invert" or “non-invert” signal, as shown at 91.
`This signal and its inverse, produced by an inverter 90,
`are the signals transmitted over the lines 47 and 48, re-
`spectively, in FIG. 2, and as will be recalled from the
`description of FIG. 2, these signals are used to control
`the gating circuits 38 and 39 (FIG. 2) and thereby to
`unscramble the scrambed video signals.
`More specifically, the streched horizontal synchroni-
`zation pulses input at 87 are fed to a horizontal syn-
`chronization pulse counter 92, which is a conventional,
`multi-stage,