EP0806116A1 - Selective interdiction of television channels - Google Patents
Selective interdiction of television channelsInfo
- Publication number
- EP0806116A1 EP0806116A1 EP95944387A EP95944387A EP0806116A1 EP 0806116 A1 EP0806116 A1 EP 0806116A1 EP 95944387 A EP95944387 A EP 95944387A EP 95944387 A EP95944387 A EP 95944387A EP 0806116 A1 EP0806116 A1 EP 0806116A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- signal
- channel
- εaid
- headend
- signals
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/167—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
-
- 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
-
- 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
Definitions
- the present invention relates generally to multichannel television systems and more particularly to interdiction devices for selectively scrambling television channels at subscriber sites.
- Subscription television distribution systems
- providers typically provide a basic block of television channels to subscribers at a subscriber site for a basic monthly fee and one or more premium television channels for additional fees.
- the physical connection itself controls access to the basic channel ⁇ while premium channels are often "scrambled" (encrypted) at their source, i.e., the headend, by the provider to restrict their viewing to only subscribers who pay the additional fee.
- providers may provide unscrambled (in-the-clear) channels to each subscriber site where the provider physically places an interdiction device which blocks, e.g., attenuates or scrambles, selected channels to stop unauthorized subscribers from receiving the selected channels.
- a system in accordance with the present invention is characterized by a selective interdiction device located at a subscriber site that operates on a block of television channels, decrypted at the subscriber site, such that the interdiction device jams one or more selected channels, e.g., premium, by combining a jamming signal within the frequency range of the channels to be interdicted.
- a selective interdiction device located at a subscriber site that operates on a block of television channels, decrypted at the subscriber site, such that the interdiction device jams one or more selected channels, e.g., premium, by combining a jamming signal within the frequency range of the channels to be interdicted.
- a preferred subscriber site apparatus useful in a system for distributing from a system headend 1 ) multiple channel signals defining an RF band, each channel signal having respective video synchronization components in time coincidence and 2) a common timing reference signal within said band and synchronous with said synchronization components, and wherein each of said channel signals is encrypted in accordance with a common encoding rule comprises a) a timing recovery circuit responsive to said common timing reference signal for generating at least one sync signal, b) a single decoder responsive to said sync signal for simultaneously decrypting all of said channel signals in accordance with the inverse of said encoding rule to generate multiple decrypted channel signals, each capable of directly causing a conventional television 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 signals to render it incapable of directly causing said television receiver to produce an intelligible image.
- a preferred subscriber site apparatus useful in a system for distributing from a system headend 1) multiple channel signals defining an RF band, each channel signal having respective video synchronization components in time coincidence and 2) a common timing reference signal within said band and synchronous with said synchronization components, and wherein each of said channel signals is encrypted in accordance with a common encoding rule comprises a) an interdiction apparatu ⁇ for periodically inserting a jamming signal into said RF band to generate an interdicted RF signal, b) a timing recovery circuit responsive to said common timing reference signal for generating at least one sync signal and c) a single decoder responsive to said sync signal and said interdicted RF signal to simultaneously decrypt multiple channel signals in accordance with the inverse of said encoding rule to generate a recovered multichannel signal comprising multiple decrypted channel signals capable of directly causing a conventional television receiver to produce an intelligible image and at least one scrambled channel signal incapable of directly causing said television receiver to produce an intelligible
- Figure IA illustrates that decryption is typically restricted to a single selected channel signal in prior art subscription television distribution systems
- Figure IB illustrates that decryption provides simultaneous access to all encrypted channel signals in a subscription television distribution system in accordance with the present invention
- Figure 5 illustrates a typical composite video signal
- Figure 6A is an enlarged view of the picture and horizontal synchronization components of a plurality of composite video signals,-
- Figure 6B illustrates the composite video signals of Figure 6A with like components in time coincidence
- Figure 6C illustrates an exemplary encoding rule for encoding the components of the composite video signals of Figure 6B;
- Figure 6E illustrates a plurality of video IF carriers, each amplitude modulated with a different one of the encoded composite video signal ⁇ of Figure 6D;
- Figure 6F illustrates a decoding rule which is the inverse of the encoding rule of Figure 6C;
- Figure 6G illustrates the video IF carriers of Figure 6E after modification in accordance with the decoding rule of Figure 6F
- Figure 7 illustrates the command transmi ⁇ ion ⁇ tructure comprised of multiple data bytes and a reference pulse that are added to a selected channel signal
- Figure 8 illu ⁇ trate ⁇ the relation ⁇ hip of the command transmission structure of Figure 7 to a typical 525 line, 60 HZ television signal;
- Figure 9 illu ⁇ trate ⁇ the relation ⁇ hip of the reference pul ⁇ e to the tenth horizontal ⁇ ync pulse in the televi ⁇ ion signal of Figure 8;
- Figure 10 illustrates the relationship of the command tran ⁇ mission structure of Figure 7 to a typical 625 line, 50 Hz television signal;
- Figure 11 illustrates the relationship of the reference pulse to the eighth horizontal ⁇ ync pulse in the televi ⁇ ion ⁇ ignal of Figure 10;
- Figure 13 is a top level block diagram of an up/down converter embodiment of the data modulator of Figures 3B and 12 ;
- Figure 14 is a detailed block diagram of a preferred up/down converter as shown in Figure 13 ,-
- Figure 15 i ⁇ a block diagram of a preferred embodiment of the decoder portion of the downconverter/decoder a ⁇ shown in Figure 4;
- Figure 17 is a simplified block diagram showing the use of a selective multichannel interdiction device of the pre ⁇ ent invention that ⁇ electively jams predetermined premium channels,-
- Figure 18 i ⁇ a block diagram of a preferred selective multichannel interdiction device that jams predetermined premium channels by adding a jamming ⁇ ignal to each of the ⁇ elected premium channel ⁇ ignal ⁇ ;
- Figure 19 Show ⁇ an exemplary flow chart for a controller that control ⁇ the combining of a jamming signal with the multichannel television signal; and Figure 20 i ⁇ a block diagram of a preferred embodiment of the present invention combining a selective interdiction device with a decoder.
- typical prior art televi ⁇ ion di ⁇ tribution systems provide sub ⁇ cribers with a plurality of encrypted television channel signals 20 but restrict decryption 22 to the production of one decrypted channel signal 24 at a time.
- a ⁇ ub ⁇ criber can cau ⁇ e any one of the encrypted channel signals 20 to be decrypted for viewing on a television set but cannot at the same time record another decrypted channel signal on a video cassette recorder or use another channel signal for a
- one prior art sy ⁇ tem use ⁇ a plurality of decoder ⁇ , e.g., 22A-22N, one for each encrypted channel signal, that respectively decode the channel signal ⁇ which are then upconverted by a plurality of upconverter ⁇ 25A-25N to a new channel frequency 26A-26N.
- Figure IB illustrates that encryption/decryption sy ⁇ tem ⁇ taught by the pre ⁇ ent invention facilitate decryption 28 of all encrypted channel signals 30 simultaneou ⁇ ly ⁇ o that a complete set of decrypted channel signal ⁇ 32 i ⁇ ⁇ imultaneously available in their original frequency slots. Therefore, a subscriber can have each of a plurality of subscriber receivers (e.g., television set ⁇ , video cassette recorders) receiving a different channel signal ⁇ imultaneou ⁇ ly while al ⁇ o u ⁇ ing modern televi ⁇ ion processing features, e.g., picture-in-picture, which require simultaneous availability of multiple channel signal ⁇ .
- subscriber receivers e.g., television set ⁇ , video cassette recorders
- An encryption/decryption proces ⁇ 40 in accordance with the invention, i ⁇ shown in Figure 2.
- Television distribution systems typically include a "headend" where a plurality of television channel signal ⁇ from different sources, e.g., satellite TV signals, standard broadcast VHF and UHF signal ⁇ , are captured, combined and fed into the ⁇ y ⁇ tem.
- headend generation 42 of multichannel televi ⁇ ion ⁇ ignal ⁇ begin ⁇ with a plurality of video sources 44 which each provide a composite video signal 45 including picture and synchronization components (as ⁇ hown in Figure 5 and further described below) .
- the composite video signal ⁇ 45 are encrypted 50 and used to modulate 52 separate channels to place them into separate frequency channels for distribution.
- a process of time synchronization 54 is imposed to place like components of the compo ⁇ ite video ⁇ ignal ⁇ 45 in a predetermined time relation ⁇ hip.
- Di ⁇ tribution 60 to ⁇ ubscriber sites 66 of the channel signal ⁇ generated at the headend may then be accomplished by a variety of well known proces ⁇ e ⁇ , e.g., cable tran ⁇ mission or wireles ⁇ over-the-air transmission, as a common RF signal 68 that contains each composite video signal in a distinct frequency slot.
- the common RF signal 68 comprised of a plurality of television channel signals separated in frequency, arrive at the subscriber site ⁇ 66 in time synchronization so that decryption 70 can be performed on all channel signals simultaneou ⁇ ly.
- Figure 3A show ⁇ a block diagram of a headend 100 in which baseband composite video source ⁇ 102A-102N are each connected to ⁇ eparate electronic delay device ⁇ ⁇ uch a ⁇ frame ⁇ ynchronizers 104.
- the frame ⁇ ynchronizers 104 selectively delay the composite video signals from the sources 102A-102N to place like components, e.g., picture and synchronization components, in time synchronization with reference to a crystal controlled video reference 105, thus generating time synchronized composite video signal ⁇ 106.
- the encoded IF carriers 113 are preferably upconverted from a standard IF frequency and frequency multiplexed in standard television transmitter ⁇ 114 for di ⁇ tribution to ⁇ ub ⁇ criber ⁇ ite ⁇ a ⁇ the common RF ⁇ ignal 68.
- the RF frequency ⁇ lot ⁇ are typically ⁇ pecified in accordance with industry standard ⁇ .
- MMDS Multichannel Multipoint Di ⁇ tribution Service
- MMDS include ⁇ 33 channel ⁇ lot ⁇ within a transmission frequency range of 2500-2686 MHz and 2150- 2162 MHz.
- the timing reference generator 108 generates the common timing reference signal 109 which is transmitted with the synchronized video signal ⁇ to provide master timing information for decoding synchronization.
- This signal is preferably combined with a selected encoded IF carrier 113 to form a data modulated IF carrier 115, by a data modulator 116.
- the data modulator 116 is placed in a selected channel at the headend but it may alternatively be inserted (indicated by broken line) into a transmitter 117 to be carried by an otherwise unused RF channel 118.
- the data modulator 116 may alternatively be present on more than one of the video channels prior to the transmitters 114 and selectively enabled at the headend.
- Authorization data statu ⁇ (de ⁇ cribed further below) i ⁇ al ⁇ o preferably combined with the common timing reference ⁇ ignal 109 and transmitted to selectively enable or disable decoding at each sub ⁇ criber ⁇ ite.
- FIG 4 illustrates a block diagram of a downconverter/decoder 120 suitable for simultaneous decryption at subscriber sites of the common RF signal 68 received from the headend 100 of Figures 3A and 3B.
- downconver ⁇ ion electronic ⁇ 121 are shown essentially comprised of an input RF amplifier 122, a mixer 123 and a local oscillator 124.
- the input RF amplifier 122 amplifies and buffers the common RF signal 68 that was alternatively broadcast or distributed via cable from the transmitters 114 of Figures 3A and 3B.
- the common timing reference ⁇ ignal (109 in Figure ⁇ 3A and 3B) i ⁇ recovered in a data/timing receiver 127.
- Specific structure in the receiver 127 for recovery of the common timing reference signal 109 is primarily dependent upon the type of timing signal selected. Exemplary recovery structure ⁇ are di ⁇ clo ⁇ ed in U.S. Patent ⁇ 4,706,283; 4,802,214; 4,926,477; and 4,928,309, previou ⁇ ly referred to above and incorporated herein.
- the data/timing receiver 127 can apply gain control ⁇ ignal ⁇ 128 to a variable gain amplifier/attenuator 130 which ⁇ imultaneously modifies the IF carrier envelopes with signal 126 in accordance with the decoding rule to generate decoded channel signals 132.
- the variable gain amplifier/attenuator 130 is a single element that operates on a single multichannel television signal derived from the common RF signal 68. It is this ability to operate upon all television channel signals by a single element that is referred to in this application as "simultaneous".
- FIG. 6A is an enlarged view of the picture components 222 and horizontal synchronization components 224 of a plurality of compo ⁇ ite video ⁇ ignal ⁇ 220A-220N.
- Each horizontal ⁇ ynchronization component 224 is seen to include a horizontal synchronization pulse 242 and, as in the case of color television, a color bur ⁇ t ⁇ ine wave 244 (indicated by the sine wave envelope) .
- like components of the video signal ⁇ 220 are first aligned in time coincidence as shown in Figure 6B and their amplitude then modified in accordance with a ⁇ elected encoding rule.
- an exemplary encoding rule having an encoding pattern 250 of Figure 6C, will be used.
- the pattern 250 is visually indicated by two lines 251 equally vertically spaced about a centerline 252 in which the vertical spacing between line ⁇ 251 indicate ⁇ gain. Thu ⁇ , the pattern 250 ha ⁇ ⁇ egment ⁇ 253 with a gain 254 interleaved with ⁇ egment ⁇ 255 having a decreased gain 256.
- the encoding pattern 250 is synchronized with the composite video ⁇ ignal ⁇ 220A-220N of Figure 6B to have gain ⁇ egment ⁇ 253 and gain ⁇ egment ⁇ 255 time coincident re ⁇ pectively with picture component ⁇ 222 and horizontal ⁇ ynchronization component ⁇ 224.
- the pattern 250 and the particular time ⁇ ynchronization de ⁇ cribed above are for illu ⁇ trative purpo ⁇ es only; any encoding rule and time synchronization may be used that will prevent unauthorized television receivers from properly displaying the video signal.
- a plurality of encoded video ⁇ ignals 260A-260N is produced having picture components 222' and horizontal synchronization components 224' as shown in Figure 6D. Synchronism between one of the gain segment ⁇ 255 and a corre ⁇ ponding horizontal ⁇ ynchronization component 224" i ⁇ indicated by the broken line ⁇ 266. Thu ⁇ , in the encoded compo ⁇ ite video ⁇ ignal ⁇ 260A-260N, the horizontal ⁇ ynchronization component ⁇ 224 are reduced relative to the other video component ⁇ .
- a plurality of video IF (intermediate frequency) carrier ⁇ 270A-270N have each been amplitude modulated with a different one of the encoded video ⁇ ignals 260A-260N to have amplitude envelopes 271A-271N as shown in broken line ⁇ .
- the modulated video IF carrier ⁇ thu ⁇ have portion ⁇ corresponding to the components of the encoded composite video signals 260 of Figure 6D, e.g., picture portions 272 and horizontal synchronization portions 274 correspond respectively to picture components 222' and horizontal synchronization components 224' .
- the decoding pattern 278 is synchronized with the modulated video IF carriers 270 of Figure 6E in the same manner as was done with the encoding pattern 250 of Figure 6C and the composite video signal ⁇ 220 of Figure 6B, i.e., gain ⁇ egment ⁇ 253 and gain ⁇ egments 255 are made time coincident respectively with picture portion ⁇ 272 and horizontal ⁇ ynchronization component ⁇ 274.
- the common timing reference signal may preferably be inserted in synchronization components, i.e., horizontal or vertical, to 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 signals.
- the illustrated preferred method embodiment aligned corresponding video components in time coincidence for simultaneou ⁇ decryption at ⁇ ub ⁇ criber sites but other embodiments of the invention may synchronize (i.e., place in a predetermined time sequence) corresponding video components for synchronou ⁇ decryption at ⁇ ubscriber ⁇ ite ⁇ .
- one byte i ⁇ preferably included a ⁇ a validity check byte 310 for the authorization data. Additionally, the validity check byte 310 may be used to determine valid receive timing synchronization.
- a video frame is comprised of 525 interlaced horizontal lines of video information divided into two fields at a 30 Hz frame rate. The beginning of each field is signified by vertical sync components 312 and 314, defining a vertical synchronization interval, that cause a vertical retrace during which the screen is blanked. Video information need not be present during the vertical synchronization interval since the screen is blanked.
- a preferred embodiment use ⁇ the vertical ⁇ ynchronization interval, defined by vertical sync components 312 and 314 and comprised of multiple horizontal lines, to transmit the authorization data without interfering with the displayable video information.
- Transmis ⁇ ion of the fir ⁇ t data block 300 comprised of the first start sequence 306, a first set of data bytes 318, six data bytes in a preferred embodiment, and the reference pulse 304, begins with the time period defined by the first horizontal line 316.
- the reference pul ⁇ e 304 i ⁇ preci ⁇ ely ⁇ ynchronized with a horizontal ⁇ ync pul ⁇ e 320 that follow ⁇ the tenth horizontal line 322.
- the transmission period for the first data block 300 is contained within the time period for horizontal line ⁇ 1-10, a ⁇ ⁇ hown in Figure 8.
- thi ⁇ data is defined as a combination of bits comprised of marks, i.e., "l”s or “high”s, and space ⁇ , i.e., "0" ⁇ or “low” ⁇ .
- marks i.e., "l”s or "high”s
- space ⁇ i.e., "0" ⁇ or "low” ⁇ .
- start sequences 306 and 308 are used in combination with the validity check byte 310 to define detection periods corresponding to horizontal lines 1-10 and 263-272.
- the start sequence ⁇ 306, 308 are each defined by a memori ⁇ of unique data bits, all "l"s in a preferred embodiment.
- a transmission rate is chosen that permits the transmis ⁇ ion of an 11-bit start sequence 306, six 11-bit characters 318 and ⁇ till provide ⁇ ufficient time to preci ⁇ ely place the reference pul ⁇ e 304 in ⁇ ynchronization with the horizontal sync pulse 320 following the tenth horizontal line 322.
- a bit rate of 140,625 bps is used.
- the reference pulse 304 is de ⁇ cribed here in reference to a particular video signal, e.g., 220B, it should be recognized that since all of the video signal ⁇ 220A-220N are synchronized by frame synchronizers 104, the reference pulse 304 will be precisely synchronized to the horizontal sync pulse following the tenth line for all of the video signals.
- a particular video signal e.g., 220B
- the reference pulse 304 will be precisely synchronized to the horizontal sync pulse following the tenth line for all of the video signals.
- a first data block 327 is placed within horizontal lines 624 and 9 and a second data block 328 is placed within horizontal lines 311 and 320.
- the reference pulse 330 is precisely placed in synchronization with the horizontal sync pulse following the eighth line 332.
- the television channel ⁇ elected for transmitting the authorization data is fixed, e.g., always set to a predetermined channel N.
- the downconverter/decoder 120 is preferably configured to scan channels within its frequency range to identify the channel containing the authorization data. Alternate embodiments may alter the data channel selection according to a predetermined algorithm, e.g., a different channel for each time period, a first data channel identifies a next data channel, etc.
- the common timing reference signal 109 can alternatively be coupled to any one or all of a plurality of data modulators 116.
- a ⁇ elect ⁇ ignal (not ⁇ hown) can optionally enable a particular data modulator 116 to add the common timing reference ⁇ ignal 109 to a selected channel.
- Figure 12 there is shown an expanded block diagram of a portion of the encryption proces ⁇ ing of video channel N, as shown in Figure 3B, showing the interface of the encoder 112N and the IF modulator 110N to the data modulator 116.
- the encoded IF carrier 113N from the IF modulator 110N is modulated by the data modulator 116 during the time period corresponding to the vertical synchronizing component 226, i.e., the vertical synchronization interval, in respon ⁇ e to the common timing reference signal 109 and sent via the data modulated IF carrier 115 to the transmitter 100N.
- the data modulator 116 is only present on a selected channel 1-N in a preferred embodiment. In another embodiment, the data modulator 116 may be present for all N channels but may be enabled only for the selected channel or alternatively for a plurality of channels. Alternatively, a single data modulator 116 may be switched to the selected channel.
- the timing reference generator 108 under control of a microcontroller 340, generates the common timing reference signal 109 in synchronism with a clock 342 received from the crystal controlled video reference 105.
- the common timing reference ⁇ ignal 109 additionally preferably compri ⁇ e ⁇ the authorization data for specifying authorized subscriber .
- Authorization information i ⁇ maintained in a system controller (not shown) and communicated via signal path 344 to the microcontroller 340 where it is formatted a ⁇ the authorization data onto the common timing reference ⁇ ignal 109.
- the common timing reference ⁇ ignal 109 contain ⁇ three data ⁇ tate ⁇ corre ⁇ ponding to no data, a mark and a space, thus causing the data modulator 116 to alter the encrypted IF signal 113 on receipt of a mark or space but leave the encrypted IF signal 113 unaltered when receiving a third, no data, state signal.
- the cry ⁇ tal controlled video reference 105 deliver ⁇ a sync signal 346 to the data modulator 116 to enable data modulation only during the vertical synchronization interval.
- the data modulator 116 u ⁇ e ⁇ FSK (frequency ⁇ hift keying) to modulate the encoded IF carrier 113 of a ⁇ elected MMDS channel with the authorization data and the reference pul ⁇ e 304 during the vertical ⁇ ynchronization interval.
- the data modulator 116 receive ⁇ the common timing reference ⁇ ignal 109, compri ⁇ ed of the reference pul ⁇ e 304 and the authorization data comprised of set ⁇ of data byte ⁇ 318 and 324 u ⁇ ed to authorize or deauthorize each ⁇ ubscriber.
- the outputs of the data modulator 116 are the audio and video carriers, FM modulated with the set ⁇ of data byte ⁇ 318 and 324 and the reference pul ⁇ e 304 during the vertical ⁇ ynchronization interval.
- the preferred data modulator 116 is characterized by: 1) the difference between the output frequencies of the modulated carriers are the same as their respective input carrier frequencies, 2) the sy ⁇ tem should not add noise or distortion to the modulated carriers, and 3) the audio and video carriers should match in deviation and phase. Since the audio carrier is typically produced as a beat frequency between the audio and video IF carriers, if the audio and video IF carriers do not match in phase and maintain the frequency difference of the original carriers, an unwanted hum could be produced.
- the encoded IF carrier 113 is comprised of a separate video IF carrier 350 and audio IF carrier 352.
- the video IF carrier 350 and the audio IF carrier 352 are typically at 45.75 MHz and 41.25 MHz, respectively, and are nominally separated in frequency by 4.5 MHz.
- the reference IF carrier 353, generated by the up/down converter 348, is comprised of a separate video carrier+data signal 354 and audio carrier+data signal 356, both of which are uniformly FSK modulated in respon ⁇ e to the common timing reference signal 109.
- the data respon ⁇ ive frequency deviation for the carrier ⁇ 350 and 352 is ⁇ 25 KHz.
- Signals from each oscillator 372, 374 are split and respectively sent to two mixers 358, 362 and 360, 364.
- the audio carrier 352 is upconverted u ⁇ ing the first local oscillator 372 and then downconverted to the original IF frequency using the FM modulated second local oscillator 374. Since the same frequency modulated local oscillator 374 is used in the downconversion of the audio and video carriers, the frequency deviation of both carriers will be es ⁇ entially identical.
- the decoder portion 400 receive ⁇ the downconverted common RF ⁇ ignal 126, recover ⁇ the common timing reference ⁇ ignal 109 contained within u ⁇ ing the data/timing receiver 127, and in response generates gain control signals 128 to instruct the gain amplifier/attenuator 130 to operate upon the downconverted common RF signal 126 according to the inverse of the selected encoding rule, e.g., reinserting horizontal and vertical components, to generate the decoded channel ⁇ signal 132.
- the decoded channels signal 132 can be distributed to one or more standard television receivers which can independently receive one or more decoded television channels.
- the data receiver's 402 principal purpose is to retrieve the common timing reference signal 109 from a selected channel within the common attenuated signal 410 and to deliver the common timing reference signal 109 as the decoded data output signal 406, representative of the authorization data and the precisely timed reference pulse 304.
- the data receiver 402 is comprised of a first IF 420, a second IF 422 and a data detector 424.
- the first IF 420 receives the common attenuated signal 410, typically having a frequency range of 222 to 408 MHz corresponding to CATV channels 24 to 54, and downconverts the ⁇ elected channel to a fixed frequency first IF output signal 426.
- the blanking level is not attenuated by the encryption.
- the decoder 400 perform ⁇ the inverse of the selected encoding rule to restore the sync and blank signals to proper levels using a pair of two level RF attenuator ⁇ , a blanking ⁇ witch 434 and a sync switch 436.
- An amplifier 438 isolate ⁇ the blanking and ⁇ ync switches 434, 436 to prevent signal interactions.
- the amplifier 438 is preferably a linear amplifier capable of handling multiple high level carriers with low distortion.
- a pad 440 helps to isolate the ⁇ ync ⁇ witch 436 from poor external impedance matching.
- the input attenuator 408 is activated when the downconverted common RF signal 126 reaches a certain level. This prevents distortion of both the gain amplifier/attenuator 130 and the data/timing receiver 127.
- the receive signal strength indicator 412 generated by the data detector 424, provides information for the controller 404 to determine at what level to ⁇ witch in the input attenuator 408 via the attenuator control ⁇ ignal 414.
- the data receiver front end include ⁇ a high i ⁇ olation amplifier 444 to i ⁇ olate a fir ⁇ t local o ⁇ cillator 446.
- a pad 448 at the input of the amplifier 444 prevent ⁇ di ⁇ tortion of the amplifier 444 from the multiple carrier ⁇ within the downconverted common RF signal 126.
- a pad 450 at the output of the amplifier 444 provides an ea ⁇ y broadband match to the input of a fir ⁇ t mixer 452 and also prevent ⁇ distortion. Both attenuators 448 and 450 also help i ⁇ olate the first local oscillator 446.
- the second IF 422 is chosen to produce and demodulate an IF frequency, e.g., 10.7 MHz, for which ceramic bandpas ⁇ filter ⁇ are readily available.
- a ⁇ econd frequency ⁇ ynthe ⁇ izer 460 identical to the fir ⁇ t frequency synthesizer 454, is used to phase lock a second local oscillator 462.
- a first ceramic filter 464 follows the second mixer 456 and set ⁇ the demodulation bandwidth.
- An IF amp 466 follow ⁇ the first ceramic filter 464 and helps to limit the signal.
- a ⁇ econd ceramic filter 468 follow ⁇ the IF amp 466 for additional band ⁇ haping.
- a gain limiter amplifier 470 follow ⁇ the second ceramic filter 468 for hard limiting.
- a quadrature detector 472 follows the limiter amplifier 470 and demodulates the FSK data.
- the input signal preferably deviates ⁇ 25 KHz and has a data rate of 140,625 bits per second.
- Demodulated data from the quadrature detector 472 enters a data slicer 474 where uncertain data edges are cleaned up, made absolute and fed to the controller 404 as the data output signal 406.
- the controller 404 In order to perform the inverse of the selected encoding rule, e.g., to insert the sync and blanking signal ⁇ , at precisely the correct position in time, the controller 404 is phase locked to the time reference provided from the synchronized signals at the headend. This time reference, originally generated from the common timing reference signal 109 at the headend, become ⁇ available to the controller 404 as part of the demodulated data signal 406.
- the controller 404 performs the inverse of the selected encoding rule with a sync and blank generator that locks itself to the edge of a received reference pulse to avoid sync drift. In a preferred embodiment, this locking is accomplished by altering the clock frequency of the controller 404.
- the controller 404 i ⁇ comprised of a proces ⁇ or 476, preferably a microcontroller, executing software at a rate controlled by a voltage controlled crystal oscillator 478.
- the processor 476 sends a feedback signal 480 to a digital to analog converter 482 which drives the voltage controlled crystal oscillator 478 and effectively changes the clock frequency and thus the execution speed of the processor 476.
- the channel select 430 and the second IF frequency select signals 432 are thus responsively altered, phase locking the data receiver 402 to the decoded data signal 406.
- the controller 404 As discussed in reference to the data modulator 116, data is only sent during prescribed periods, the vertical synchronization intervals.
- the controller 404 under ⁇ oftware control, recognize ⁇ the reference pulse 304, and a combination of the first start sequence 306, the second start sequence 308 and the validity check byte 310, to ensure that the controller 404 is ⁇ ynchronized with the common timing reference ⁇ ignal 109.
- the controller 404 alter ⁇ its clock frequency and/or the time window during which it looks for the data block ⁇ 300 and 302.
- encryption/decryption method and apparatu ⁇ embodiment ⁇ have been di ⁇ clo ⁇ ed herein which make a plurality of distributed television channels ⁇ imultaneou ⁇ ly and automatically available to authorized ⁇ ub ⁇ criber ⁇ . Additionally, a single channel system using the di ⁇ closed modulation and demodulation methods is also considered within the scope of the present invention.
- the previously disclosed invention can advantageously ⁇ imultaneou ⁇ ly decode a block of televi ⁇ ion channel ⁇ ignal ⁇ .
- the pre ⁇ ent invention u ⁇ es an interdiction device to selectively scramble television channel signals from within the block of locally decrypted channel signal ⁇ .
- Figure 17 ⁇ how ⁇ the u ⁇ e of a preferred interdiction device 510 which selectively jams a multichannel television (TV) channel signal 512, an unencrypted signal, from a typical prior art television distribution sy ⁇ tem (not ⁇ hown) to generate a ⁇ ignal 514 to provided ⁇ ub ⁇ criber ⁇ with a plurality of unencrypted televi ⁇ ion channel ⁇ ignal ⁇ a ⁇ well as a plurality of ⁇ electively encrypted/jammed channel ⁇ ignals. While ⁇ uch a ⁇ y ⁇ tem can be u ⁇ ed in various environments, e.g., over-the-air and conventional cable subscriber systems, it is particularly useful in combination with the previously disclosed decoder 400.
- TV television
- sy ⁇ tem not ⁇ hown
- the interdiction device 510 is programmable and capable of selectively scrambling a plurality of television channel ⁇ throughout the range of otherwi ⁇ e unencrypted televi ⁇ ion channel ⁇ from ⁇ ignal 512.
- the preferred interdiction device 510 primarily comprise ⁇ : 1) a frequency synthesizer/VCO 516 (a jamming ⁇ ignal generator) for generating a jamming signal, e.g., an FM-modulated sine wave, 2) a controller 518 for directing the frequency synthesizer/VCO 516 to generate a jamming, signal 520 for a selected television channel, 3) a mute switch 522 under control of the controller 518 for only enabling the output of the jamming signal 520 when the frequency synthe ⁇ izer/VCO 516 ha ⁇ locked to a predetermined jamming frequency for each selected channel, and 4) a summer 524 for combining the multichannel television channel signal 512 and the generated jamming signal 520 passed by the mute switch 522.
- a frequency synthesizer/VCO 516 a jamming ⁇ ignal generator
- a controller 518 for directing the frequency synthesizer/VCO 516 to generate a jamming, signal 520 for
- the controller 518 contains a channel interdiction table 526, which corresponds to the preselected channels that are to be jammed. Each of these channels correspond to specific frequencies for each geographical area, e.g., USA, Europe, etc., and to particular transmis ⁇ ion standards, e.g., NTSC or PAL. (See, e.g., Table I below depicting frequency assignment ⁇ for a VHF Sy ⁇ tem M (6 MHz) USA.)
- a ⁇ econd table (not shown) within the controller 518 is preferably used to convert each channel designation to its corresponding frequency.
- table 526 may directly contain frequency designation ⁇ corre ⁇ ponding to the ⁇ elected channel ⁇ .
- the table 526 may alternatively be preloaded, e.g., ⁇ tored in nonvolatile memory, or may be loaded via communication between the controller 518 and ⁇ ome external device, e.g., via a communication interface 527.
- the multichannel televi ⁇ ion ⁇ ignal 512 can contain authorization data via the communication interface which can be decoded to instruct identified controllers 518 to add or delete entries from its channel interdiction table ⁇ 526.
- the controller 518 command ⁇ the frequency synthesizer/VCO 516 via a control interface 528 comprised of a frequency select bus 530 (used to select the desired jamming frequency corresponding to a selected channel) and a lock signal 532 (used to provide a feedback statu ⁇ signal) .
- the frequency synthesizer/VCO 516 takes a di ⁇ crete, i.e., a nonzero, amount of time (a function of the de ⁇ ign of the frequency synthe ⁇ izer/VCO 516) to lock to the de ⁇ ired jamming frequency. Once the de ⁇ ired jamming frequency i ⁇ achieved, the jamming frequency is preferably maintained for a period of time before a next jamming frequency is selected.
- the lock signal 532 is then generated by the frequency synthe ⁇ izer/VCO 516 which can be u ⁇ ed to notify the controller 518 that the de ⁇ ired jamming frequency ha ⁇ been achieved.
- the lock ⁇ ignal 528 i ⁇ generated by a frequency comparator within the frequency ⁇ ynthe ⁇ izer/VCO 516 which compares the jamming signal 520 to the frequency commanded by the controller 518.
- the controller 518 in block 542 in ⁇ tructs the mute switch 522 via the mute control signal 534 to commence jamming the selected television channel.
- the controller alternatively waits a predetermined time period or waits for the lock signal 532 to be returned from the frequency synthe ⁇ izer/VCO 516.
- the output of the mute ⁇ witch 522 must be maintained during block 544 for a sufficient time period, e.g., at least one frame period, to adequately jam the selected television channel.
- the controller in block 546 enables the mute ⁇ witch 522 via the mute control signal 534 (if the next channel to be interdicted is not adjacent to the current channel) .
- the process then cyclically repeats, starting at block 538, with the next entry in the channel interdiction table 526.
- a first time period related to the lock time in block 540 and a second time period defined by the predefined time period in block 544 there are two time periods involved in this cyclical process, a first time period related to the lock time in block 540 and a second time period defined by the predefined time period in block 544. Accordingly, there is a maximum cycle rate (for a particular implementation) , that this process can be repeated. This cycle rate determines the maximum number of channels (five in an exemplary embodiment) that can continuously (as viewed by a subscriber) be interdicted. Accordingly, in an alternative embodiment, a plurality of frequency synthesizer/VCOs 516 are multiplexed such that one can be approaching its jamming frequency (in block 540) while another is dwelling at its jamming frequency (in block 544) .
- Figure 18 additionally ⁇ how ⁇ the ba ⁇ ic ⁇ tructure of the preferred frequency synthesizer/VCO 516 which is primarily comprised of 1) a video frequency synthesizer 548, 2) an audio frequency synthe ⁇ izer 550, 3) a summer 552, and 4) a VCO 554 (voltage-controlled oscillator) .
- the video frequency synthe ⁇ izer 548 e.g., a National LMX1511A or Fujit ⁇ u MB15A02, is commanded to select a particular frequency, e.g., the base video carrier frequency of the television channel offset by a jam frequency, e.g., a frequency approximately half way through the television channel or approximately 3 MHz, via the three wire bus 530 comprised of clock, data, and enable signals (an interface particularly well- suited for sharing with additional frequency synthe ⁇ izer ⁇ ) .
- the frequency synthesizer 548 generates an analog video VCO control signal 556 that commands the VCO 554 to generate the desired frequency.
- a feedback signal 558 is returned to the frequency synthe ⁇ izer 548 where it is compared in frequency with the frequency commanded by the controller 518. When a match is achieved the lock signal 532 results and this status signal is communicated to the controller 518.
- Channel 44 has a video carrier of 343.25 MHz with the preferred jamming frequency at 346.25 MHz (343.25 MHz plus a preferred offset of 3 MHz).
- the preferred jamming frequency of channel 50 is at 382.25 MHz (379.25 MHz plus a preferred offset of 3 MHz).
- a preferred embodiment additionally comprises the audio frequency synthesizer 550, which in an exemplary embodiment divides a frequency output 560 of the frequency synthesizer 548 to generate a digital audio VCO control signal 562.
- the analog video VCO control signal 556 and the digital audio VCO control signal 562 are summed by summer 552 to generate a VCO control signal 564 which controls the VCO 554 to generate a frequency-modulated jamming signal that will jam both the video and audio portions of the selected television channel.
- Figure 20 shows a preferred embodiment of the present invention comprised of the multichannel interdiction device 510 combined with the previously disclosed decoder 400. While the prior decoder 400 disclosed significant improvements over the prior art by permitting a single apparatus to simultaneously decrypt all or none of the transmitted channels according to transmitted authorization data, it did not permit the provider to restrict access to selected channels. 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 tier ⁇ .
- the data in the interdiction table 516 i ⁇ then u ⁇ ed to control the operation of the frequency ⁇ ynthe ⁇ izer/VCO 516 and the mute ⁇ witch 522 u ⁇ ing the control interface 528 and mute control ⁇ ignal 534 according to the previously described algorithm.
- This improved combination now permits the simultaneou ⁇ reception of multiple unencrypted ⁇ ignals (suitable for picture-in-picture use) while still permitting the provider to withhold access to selected channels.
- a standardized jamming amplitude ratio be achieved between the jamming signal at the mute switch output 536 and the multichannel television channel signal 512. Without this standardization, undesirable results could occur. For example in a first mode, one might attempt to pirate a jammed television signal by amplifying the common scrambled input source 572 to overcome the jamming signal. However, if a standardized jamming amplitude ratio is maintained, the input source 572 would automatically be attenuated and this pirating attempt would fail. Conversely in a ⁇ econd mode, if an abnormally small input source 572 should be present, a proportionally large jamming signal could tend to spill over and effect adjacent channels.
- a receive signal strength indicator (RSSI) 574 from the data receiver 568, indicative of the amplitude of the commonly scrambled input source 572 is used to control an AGC amplifier 576 to standardize the amplitude of a common attenuated signal 578 operated on within the decoder 400.
- RSSI receive signal strength indicator
- an AGC amplifier could be used to control the amplitude of the jamming frequency.
- authorization data is generally sent on a predetermined authorization data channel .
- the predetermined channel can be varied to further limit pirating.
- a preferred channel interdiction table can be structured to take advantage of these embodiments .
- a first entry for each channel correspond ⁇ to a delta frequency from the authorization data channel frequency and a ⁇ econd entry ⁇ pecifie ⁇ whether this channel is to be interdicted.
- a pirate would need to know at least the present authorization data channel, any scheme for varying the authorization data channel, and the data within the interdiction table.
- pirating is further complicated.
- the present decoder / interdiction device 566 can simultaneou ⁇ ly decode all of the tran ⁇ mitted channel ⁇ by rever ⁇ ing the encoding proce ⁇ done to a plurality of ⁇ ynchronized channels.
- this encoding is done by first synchronizing a plurality of video inputs at the headend and then suppressing the horizontal and vertical sync signal of the synchronized video inputs. Consequently, once the microcontroller determines the proper timing, a blanking control line 584 and sync control line 586 can simultaneously decode all of the received channels to generate the multichannel television channel signal 512, the input signal to the interdiction device 510.
- the pre ⁇ ent invention can take advantage of this relationship to optimize its temporal placement of the jamming signal 520 within each channel frequency range. Therefore, in this embodiment the predefined period of block 544 i ⁇ preferably defined by thi ⁇ known timing relationship; permitting the single frequency synthesizer/VCO 516 to jam a larger number of television channels.
- interdiction/jamming step can precede the simultaneou ⁇ decrypting step with similar result ⁇ .
Abstract
Description
Claims
Applications Claiming Priority (3)
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 |
WOPCT/US95/08721 | 1995-07-11 | ||
PCT/US1995/016827 WO1997003523A1 (en) | 1995-07-11 | 1995-12-21 | Selective interdiction of television channels |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0806116A1 true EP0806116A1 (en) | 1997-11-12 |
EP0806116A4 EP0806116A4 (en) | 2000-06-28 |
Family
ID=22249456
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95944387A Withdrawn EP0806116A4 (en) | 1995-07-11 | 1995-12-21 | 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 |
AU693766B2 (en) * | 1992-01-08 | 1998-07-09 | Multichannel Communication Sciences, Inc. | Multichannel television signal scrambling and descrambling 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 WO PCT/US1995/016827 patent/WO1997003523A1/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 AU AU46450/96A patent/AU4645096A/en not_active Abandoned
- 1995-12-21 BR BR9510615A patent/BR9510615A/en not_active Application Discontinuation
-
1998
- 1998-01-09 OA OA9800003A patent/OA10754A/en unknown
Non-Patent Citations (2)
Title |
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No further relevant documents disclosed * |
See also references of WO9703523A1 * |
Also Published As
Publication number | Publication date |
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OA10754A (en) | 2002-12-11 |
AU4645096A (en) | 1997-02-10 |
BR9510615A (en) | 1999-04-27 |
AP896A (en) | 2000-11-17 |
WO1997003523A1 (en) | 1997-01-30 |
EP0806116A4 (en) | 2000-06-28 |
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