CA1334444C - Off-premises cable television channel interdiction method and apparatus - Google Patents

Abstract

Off premises cable television interdiction apparatus comprises a microprocessor actuation and control means for actuating and con-trolling a plurality of frequency agile voltage controlled oscillators.
The voltage controlled oscillators selectively jam only unauthorized premium programming transmitted in the clear from a headend to a particular subscriber. Each voltage controlled oscillator is allocated a continuous band of frequencies consistent with the elimination of jamming signal frequency harmonics which may disturb authorized programming at a higher channel frequency. The microprocessor actuation and control means provides a calibration mode and a normal mode of operation. During the normal mode of operation, a frequency hopping rate on the order of four thousand hertz is achievable. The method of interdiction comprises the steps of generating and storing voltage control words for operating the oscillators consistent with a head end selected jamming factor for a particular channel to be jammed and addressably transmitted and stored premium program-ming authorization data.

Description

OFF-PREMISES CABLE TELEVISION CHANNEL
INTERDICTION METHOD AND APPARATUS

BACKGROUND OF THE INVENTION
1. Te~hn;~l Field This invention relates to cable television systems and, more particularly, to a method and apparatus for applying remotely con-trolled and remotely applied interdiction or j~mmina signaLc to pre-vent reception of unauthorized television rh~nn~lc.

2. D~.;yLion of the Prior Art At a headend of a cable television system, a scrambler is nor-mally provided to enco~le premium television ch~nnelC. ~he applied scr~mh~ing precl~ldPs reception by an unauthorized converter/decoder at a co~nPcted premicps. Data represellting ~h~nnelc or tiers of pro-gr~mminC are ad~l~ably transmitted to a particular converter/
decoder and stored in an authorization memory. As a result of the add~esæd tr~ncmicsion, a sllhseqlJently transmitted program is autho-rized in that the decoder portion of the converler/decoder will be selecllvely en~'ei to decode the scr~mhled premium ch~nnel or program.
Several varieties of scr~mhline techniques are applied today.
Each manufacturer has its own scheme which may be incomp~tible with others. Nevert~lele-cc~ most popular scr~mt~1ine systems today are based on sync su~ære~ion, in which the sync information is hidden from the television receiver's sync separator, usually by moving it to a level occnpied by picture information (moving the sync tip to an equivalent picture level of 40 IRE units is common). Some systems mo~ ate the picture carrier with a sine wave phased to suppress the horizontal hl~n~inc interval. Most systems today switch to the suppressed level at the beginning of the hl~nking interval and switch out at the end. Most though not all suppress the vertical hl~nking interval. Some systems dynamically invert the video, either on a line-by-line or a field-by-field basis. This must be done carefully to avoid artifacts caused by inverting and reinverting around different levels, and by differential gain and phase of the system. Synchronization is restored either by the provision of synchronous amplitude mod~ ted pulses on the sound carrier, by digital information placed in the verti-cal interval or by phase modulation on the picture carrier.
The provision of one scrambler per premium ch~nnpl at the he~rlçnd and the inclusion of a descrambler in each converter/decoder at the premises of the television receiver is particularly e~el~ive.
Furlhe~ ore, by providing the converterklecoder on premises has turned out to be a great temptation to service pirates who imagina-tively seek ways to receive premium ch~AnnPIc. As a result, cable tel-evision eq~ipmPnt manufacturers have entered into a veritable war with such pirates resulting in complicated service authorization pro-tocols in some instances involving multiple layers of encryption by both in-band and out-of-band data tr~ncmi-csion further increasing the costs of the cor.~,e, ler/decoder.
Fuflherl.lore, all scrAmhling systems leave artifacts in the hor-izontal hlAnL~inC interval in the form of steps on the front and back porches. Normally these are not a problem, but if a television rece.ver does not have adequate overscan, then the steps can show up as light bars on one or both sides of the picture. Further, if a televi-sion receiver uses back porch sampling for automatic gain control an~/or black level r~3toration, and the sAmpling period e~lends into the time of the descrAmhling step, the television will show the wrong black level and may show flicker in the picture. In systems in which pulse trains are applied to the sound carrier, a buzz carried by har-mor~ics of a 59.94 Hz signal can be noticed in some television ~eceive.s.
Con~equently, the cable industry has r~;orted to look for new terhnology and to take a second look at technology developed in the early stages of development of cable television such as the application of negative and positive traps and more recent techniques such as interdiction.
Negative trap tech~-~logy is viewed by many manufacturers as a viable alternative to sync suppression scr~mblin~ methods. A nega-tive trap is b~Cic~lly a narrow band reject filter. Traps are located at the drop to a subscriber~s dwelling and attenuate a significant portion of a premium television ch~nnel rendering that ch~nn~ nllc~ble by the subscriber.
In the conventional emhoAiment~ negative traps are made using L-C filter techniques. The result is a notch with finite quality Q and finite shape factor. ~n the case of a single ch~nnel negative trap, the center of the notch is usually located at the picture carrier frequency of the ch~nnel to be removed. This technique, sometimes called a static negative trap, requires attenuation at the picture carrier of at least 60 dB to be effective.
Negative trap systems have several advantages that make them attractive for cable television applications. One primary advantage is the ability to deliver a bro~lh~nd cable television spectrum to the subscriber's converter/dæcodPr. Conventional sync supp-~ion sys-tems utilize descr~mhling set-top conve-ler/decodels which deliver inherently narlo~.L.and signals. Negative traps are usually mounted outside the subscriber~s home (typically at the tap) and thereby mini-mize the elrposure associated with placing hardware inside the subscriber's dwelling. Finally, some cable television operators view the negative trap as a more secure means of subscriber control than is sync s~pr~ion, as picture reconstruction is viewed as substantially more difficult.
However, the negative trap system requires hardware in loca-tions where no revenue is generated for the cable television system.
Moreover, negative traps have several severe practical limitations.
L-C band reject filters have Q and shape factor limitations. Quality factors Q for L-C f~ters are typi~ally limited to less than 30. This means that for a negative trap located at rh~nn~l 8 (picture carrier at 181.25 MHz) the 3 dB bandwidth of a negative trap is typically 6 MHz (or the bandwidth of a b~eb~nd television ch~nn~l). This trap would result in significant deterioration of the lower adjacent ~h~nnel.
Then the television receiYer tuned to the lower adjacent rh~nnel~
rather than having to contend with a 15 dB picture-to-sound ratio, may have to contend with a sound carrier reduced an additional 6 dB
or so. Freqllency stability as a function of time and temperature is also a significant concern. Many cable television system operators have instituted a regular negative trap change-out program based on the ~ccllmption that after a certain period of time and temperature cycling, frequency drift will render negative traps ~c~l~c5~
C~cca~l~hility is another significant concern. Finite return loss and non zero insertion loss limit the mlmher of single ch~nnPI nega-tive traps which can be c~ccaded~ AS the nllmber of services to be secured incr-~asP~s, the negative trap decrFases in appeal. Moreover a change in ch~nnPI line-up requires a significant invesllllent in hard-ware and manpower in this scenario.
Recently, a new type of negative trap has been introduced.
The dynamic negative trap cor~ls of a notch filter that is designed to be mo~hllated with respect to frequency. The notch is centered about the picture carrier but is deviated slightly from side to side.
The televLsion ch~nnP~ is rendered unll-s~hle by the introduction of unwanted amplitude and pha~se rno~ tion on the picture carrier.
This terhniqup~ requires a notch depth signiflcantly less than that of static negative traps (typically 40 dB). Additionally, the intentionally introduced fre~uency mo~ tion reduces somewhat the requirement for frequPn~y stability.
The dynamic negative trap, ho~ever, has several disadvan-tagP~ A power source is required in order to aCcomplich the fre-yuenc~ mod~ tion. More significant is the parasitic mo~lJl~tion that thLC terhni~ue produces on the adjacent television ch~nnPlC.
Positive trap systems also utilize a narrow band-rejector notch filter. Ho~eve~, unlike negative trap systems which are used to attenuate or trap a premium ch~nnPl tr~ncmicsion, the notch filter is used to ~ilore the premium television ch~nnel. In this scenario, an interfering signal is placed inside the premium television ch~nnPI at the cable television he~n-l This interfering signal is then removed at the subscriber~s dwelling by use of the notch filter. Ideally this notch filter removes only the interference without removing a significant amount of tele-vision information.
The positive trap technique is seen as having several advan-tages by the cable television system operator. It is concidered advan-tageous to have the interference present in the secured ch~nnPl~ on the cable television distribution plant (unlike the negative trap system in which the ch~nnpl~ to be secured are "in the clear~l on the distribu-tion plant). It is very attractive from a financial standpoint to require subscriber hardware only at those locations where a subscriber wishes to recei~e a secure service. Thus, any capital investment is ~-ccociated with a point of revenue generation.
The conventional embodiment of the positive trap system uti-lizes L-C notch filters to remove the interfering signal. These L-C
notch filters suffer from the same limitations as do L-C negative traps ~ c~eed above. Consequently, L-C based positive traps are limited to the lower end of the cable television spectrum. Quality Q
and shape factors have also restricted the numh~er of locations for the interfering signal within the television ch~nnph The location for the interfering signal in the con~,entional em~iment of the positive trap system is midway between the pic-ture carrier and sound carrier. The energy density (and hence infor-mation density) in this area of the spectrum is relatively low. One reason thls location was chosen was that it minimi7ed the impact of any television information removed along with the interfefing signal by the notch filter, and thereby improved the quality of the recovered televl~lon signal. It would be expected that t~le jamminc carrier would normally have minim~l effect on the adjacent ch~nnPI televi-sion picture unless a television has un~ y poor rejection 2.25 MHz above the picture carrier. The j~mmer does add another carrier which the tuner will haYe to contend with, which might cause some de~ladation in a marginally overloaded case.

Despite this location, the quality Q and shape factor limita-tions of conventional L-C positive traps do remove a signif icant amount of useful television information. The result is a noticeable "softening" of the television picture as a result of attenuation of high frequency information. Predistortion at the headend can improve this performance but falls far short of being able to correct it completely.
This location for the interfering signal also facilitates the job of the video pirate. This pirate can easily tolerate a degraded signal and hence can lecoYer a use~hle picture using techniques easily available (such as the classic twin lead quarter wave stub with an ~ min~lm foil slider for fine tuning). Also, positive trap systems require a higher per premium ch~nnel cost than a negative trap system.
A relatively recent te~hnique for premium ch~nnpl control is the interdiction system, so-called because of the introduction of an interfering signal at the subscriber~s location. Most emho~liments con-sist of a pole-mounted ~nclQsure designed to serve four or more sub-scribers. Thi~s enClQsl~re contains at least one microprocessor con-trolled oscillator and switch control electronics to secure several tel-evision ch~nnelc. Control is accomplished by injecting an interferingor j~mminc signal into unauthorized ~h~nnele from this pole-mounted ~n~lo~lre.
For efficiencyls sake, it is known to utilize one oscillator to jam several premium television ch~nn~le. This technique not only reduces the amount of hardware required, but also m~ mi7Pe the system fleY~ ty~ The oscillator output j~mminC signal frequency is sequ~ntially moved from ch~nnel to ch~nn~l Coneequently~ the oscil-latorls fre~luen~ agile and hops from j~mminC one premium cl~nne frequency to the next.
One such system is known from U.S. 4,450,481 in which a single frequency agile oscillator provides a hopping gain-controlled j~mming signal output to four high frequency electronic switches. Each switch is ~cociated with one subscriber drop. Under microprocessor control and depen-linc on which subscribers are authorized to receive trans-mitted premium progr~mmir~a, the microprocessor selectively gates the j~mmina signal output of the single oscillator via the switches into the path of the inComine broadband television signal to each sub-scriber. Conceq~lently, an unauthorized subscriber upon tuning to a premium chAnnPl will receive the premium ch~nnPI on which a jam-ming signal at approximately the same f requency has been superimposed.
In the known system, it is indicated that sixteen ch~nnel.c may be j~mmed by a single voltage controlled frequency agile oscillator.
With respect to one premium chAnnel, this translates to a situation in which the jAmming signal can only be present one sixteenth of the time or an approximately 6% jAmming interval. The rate of hopping is also indicated at 100 bursts per second of jAmming signal at a par-ticular frequency or a 100 hertz hopping rate. Consequently, the effectiveness of the jAmming signal is question~hle.
Cable television chAnn~lC and, of course, premium service may extend over a wide range of frequencies, for exampie, from 100 to 350 megahertz. In the known embodiment, the single oscillator pro-vided must be frequency agile over a wide range. It is further recog-nized that the j~mming signal output of the single oscillator must be within a range of 100-500 KHz above or below the video carrier fre-quency. Conceq~ently, a synthP-ci~Pr having an internal reference is provided to assure the reAcon~hle accuracy of the jAmming signal out-put of the oscillator to the tolerable 100-500 KHz band above or below the video carrier.
It is indicated that the jAmming signal is at a high relative power and is gain controlled to exceed the amplitude of the video carrier by 5 to 20 dB. Because of the high output power relative to the premium ~h~nnel video carrier power and the difficulty of pre-cise~ j?mminE the premium chAnnPl frequency, such an interdiction system leaves considerable opportunity for improvement. Because the oscillator is frequency hopping, its spectrum tends to spread out around the picture carrier, generating a slightly different situation as far as the required adjacent channel rejection characteristics of the television are concerned.
Firstly, it is important that the jAmming frequency be con-trolled so as to place the interferences as close as p~Csihle to the picture carrier. Secondly, it is also important to limit the peak amplitude of the interfering signal so as not to significantly exceed the video peak envelope power in order to ensure that there are not residual artifacts on adjacent ch~nn~lc. However, in the known sys-tem, adjacent ch~nnPl artifacts are also created since the j~mming signal is intentionally placed below the video carrier and consequently proximate to an adjacent ch~nn~l Also, the rate of frequency hop-ping is limited in the known emho~liment as a result of its application of conventional f requency control techniques during the hopping process.
The known interdiction system has proven to be particularly susceptible to adjacent ch~nnel artifacts from the above described amplitude and frequency selections which can dissatisfy subscribers.
Furthermore, the subjective perception of the depth of j~mmina an unauthorized premium ch~nnPI is relatively unsatisfactory resulting from the limited m~ximllm six percent j~mming interval when sixteen premium ~h~nnelC are j~mmed by a single oscillator and the relatively low rate of frequency hopping.
SUMMARY OF THE INVENTION
Many of the above-stated problems and related problems of the prior art have been solved with the principles behind the present invention, an off-premises television channel interdiction method and apparatus c~p~hle of remotely controlled j~mmine depth and fre-quency at reduced power. After considerable investigation into the known art and through experimentation, it has been determined that an optimum placement of a j~mming signal is within the approximate range eAlPn~linc from the video carrier to 250 kilohertz above the video e~rrier, a j~mming signal placement much below the video car-rier creating artifacts in the next lower adjacent ch~nnel- Such a placement is between the video carrier and the audio carrier for the same premium ch~nnPI. Also, from the head end, the j~mming carrier may be precisely est~hliched at a frequency resolution of 50 KHz as a digitally step-wise selectable frequency within the 250 KHz range above the video carrier. A ten bit voltage control word is applied by way of a digital to analog converter to a voltage controlled oscillator to control the frequency of the j~mminE signal within this frequency range or to provide a j~mming signal outside the range, for example, if the audio carrier is to be intentionally jammed. Furthermore, to insure the accuracy of the frequency of the j~mming signal and to limit j~mminE signal frequency harmonic interference, a plurality of oscillators are provided, each operating within a particular narrow band of the cable television spectrum. The sum of all such narrow bands shall be equivalent to the entire spectrum over which j~mming is desired, recognizing that the cable television spectrum to be ~mmed may itself be discontinuous or that some overlap in bands may be desired. In particular, four separate oscillators are provided whose outputs are separately filtered to elimin~te the appearance of har-monics of the j~mmine signal output which can interfere with televi-sion reception on other ch~nn~lc higher in the spectrum. Each oscil-lator may be intentionally limited to j~mming a m~imllm of four rh~nn.slc within its band resulting in approximately a factor of four improvement in j~mming interval over the prior art. Furthermore, each plurality of oscillators is provided on a per subscriber or per drop basis.
Also, in accordance with the principles behind the present invention, the j~mmin~ signal power is limited within the range of -2.5 dB and +6.5 dB or +2 dB nominal of the video carrier power level.
Col~cequently~ there is less chance of adjacent ch~nn~l interference than in the kwn prior art system.
Furthermore, it has been determined that j~mminE depth, the sul~jeclive perception of one viewing a scr~mhled television ch~nnel on a nllmher of different television receivers, is improved by improv-ing the.freql~ency hopping rate to approximately four kilohertz, a factor of twenty increase in rate over the known system, all other parameters ~eing equal such as amplitude and frequency of the jam-ming signal. As will be discussed herein, the present embodiment is ~p~hle of achieving frequency hopping rates of this magnitude because it is not limited by conventional f requency locking techniques.

-lo- 1 334444 The microprdc~r of the present apparatus further controls the provision of power to the plurality of oscillators. If the subscriber is authorized to receive all premium cha~elc within the band secured by a given oscillator, that oscillator may be powered down for the duration. Furthermore, no residual j~mming signal output power will pass through an intentionally open switch during a powered up condi-tion as might occur in the prior art interdiction system.
Common circuitry is shared by a plurality of subscribers, for e~r~mrle, up to four, and is housed in a pole-mounted, strand-mounted or pedeslal ho~ginc. The common circuitry comprises automatic gain control circuitry for regulating the level of video carrier. The com-mon circuitry also comprises a data receiver, a data decoder and a microproc~or which may be individually add~ised. The common circuitry separately ~leco~iPc for each adll~ed and in service sub-scriber mod~lP any comm~n~c and data transmitted from the he~-len-l The microproce~Ccor of the common circuitry comm~nicates with the microproc~-C~or of the subscriber module any decoded data related to the particular subscriber served by that subscriber mod~le. The decoded data, for e~mple, indicates indiYidually addl~d ~h~n~el or program authorization data or globally transmitted channPl frequency and j~mminC depth data rece,ved from the he~dend for storage in mic~o~.~c~ior memory.
During a normal mode of operation, the microprocPCcor of the suhccriber mod~le actuates or powers up each required oscillator and transmit. frequency data toward all required oscillators for jamming any and all unauthorized ch~nnplc at a jam factor selected for a par-tic~ar,premium ch~nnPl~ In particular, a sixty-four position memory may be l~e.~Pd for slo,in~ ten bit voltage control words. An algo-rithm of the subscriber mod~le microprocessor loads the voltage con-trol word memory deyen~ling on the level of service chosen by the subscriber. ~n one extreme where a particular subscriber is autho-rized to receive all premium ch~nnelc but one, three of the oscillatorc may be ~ered down and the rem~ining oscillator is c~p~hle of con-~inl~olJCly j~mmina the one unauthorized ch~nnel reculting in a 100%
j~mmins interval.

lf a particular subscriber at a given point in time has sub-scribed to none of the sixteen ch~nnels offered, all four oscillators are sequentially triggered and sixty-four voltage control words are pro-vided in a pseudo-random sequence toward the four oscillators. The application of such a pseudorandom sequence discourages pirating.
Jam factor as defined herein is a parameter selectable and globally transmitted by the headend to equate to the relative degree of j~mming to be applied to different premium ch~nnele. For exam-ple, it may be appropriate to jam highly restricted progr~mminC at a higher jam factor. In accordance with the present invention, a total of sLl~leen voltage control words may be allocated to one premium ch~nnPI- Conceque~tly, these sixteen control words are analogous to j~mminC time slot intervals which can be allocated by the he~dend to improve j~mminC depth. For example, if three premium programs are provided by the he~dencl over ch~nnelc within the allocated band of one oscillator at a particular point in time, these sixteen time slots or their r~ ;ve jam factors may be allocated at eight, four and four respectively (totalling sixteen) to effectuate, for the least jammed ch~nnel and allowing a five percent overlap, a minimllm 20% j~mmine interval. As already indicated, if the subscriber subscribes to all of these three ch~nn~lc~ the microproc~sor algorithm will power down or deactuate the oscillator entirely or increase the j~mming interval ~r~l llonate to the degree of premium service subscribed to and the a~l~ued ~mmir~ factors.
Perio~ic~lly and at power up, the present apparatus enters a calibration mode of operation, for ex~mple at approximately thirty minute,intervals. From the front end, premium ch~nn~l frequency data is globally transmitted for storage in memory of the micro~ro cessor of the commor circuitry. The common circuitry microproces-sor c~lcUl~tes in turn c~lci)lates a divide by factor for a programma-ble prescaler of the subscriber module and an expected time between frequency counts and forwards these calculations to the microproces-sor of the subscriber modl~le.
The programm~hle prescaler or frequency divider is provided in a feedback path from the plural oscillators to the microprocff~or of -the subscriber mo~ule. During the calibration mode, only one oscilla-tor is pu~.ored at a time. The transmitted and stored frequency data is translated into a best guess voltage control word. As a result, the j~mming signal frequency of the only po~vered up oscillator is fed back through the prescaler which divides down the high frequency output for counting by the microprocessor. The microprocessor cal-culates a count in accordance with the known time interval between recei\,ed outputs of the prescaler. The count is then compared with the expected count and the voltage control word adjusted accordingly.
After a m~YimlJm of ten such calculations, starting with the most significant bit of the voltage control word, a particular control word is precisely est~hli~hed in voltage control word memory. In sequence, all sixteen control words for each provided oscillator or all sixty-four words are piecisely estahlished, the entire ~roc~lure requiring only a fraction of a secon~l- Consequently, no me~nineful intelligence can be obtained during the calibration mode if a subscriber coincidentally attempts to view an unauthorized premium rh~nnel. Thus, the cali-bration mode in combination with the provision of plural narrow band oscillators assures j~mming signal frequency control.
As a co~-ce~ enre of the calibration mode of operation and the structure of the present apparatus, the j~mming carrier can be prac-tically positioned anywhere within the 250 kilohertz band above the video carrier or even elsewhere if desired, for example, for j~mminC
the audio carrier. During the thirty minute interval in times of tem-perature variations, there is an opportunity for frequency drift of a given j~mminc signal frequency. However, the drift if e~istent is ac~ally desirable in the sense that such a drift will thwart any would-be pirates attempting to trap the j~mmin~ signal with a notch filter.
As ~lluded to before, the jamrni-la signal frequencies may also be intentionally varied by varying the voltage control words for j~mming a given premium ch~nn~l~ Furthermore, they may be ~pplied in a ~seudo random sequence. Consequently, a would-be pirate would have to follow the same pseudo-random sequence and sequentially actuate a plurality of notch filters, all at the same frequencies as are replesented by the associated voltage control words as well as 13 l 334444 anticipate the natural frequency drift previously alluded to in order to pirate the premium television signal.
Importantly also, the application of a calibration mode of operation, as distinct from a normal mode of operation, permits the ~ ent apparatus to achieve much higher frequency hopping rates than the known system during the normal mode of operation. Because there is no requirement for the application of slow conventional frequency lorki~g terh~;ques during the normal mode of operation, a desirable four kilohertz hopping rate is achievable.
Other aspects of this invention are as follows:
Cable television premium ~-hAnr~l interdiction apparatus for selectively jamming unauthorized premium programming transmitted to a subscriber comprising:
a plurality of m controlled oscillators for separately interdicting within an allocated continuous portion of a broA~hAn~ cable television ~e~ m, the sum of all such allocated portions comprising the total spectrum to be jammed, the allocated continuous portion of the ~e_~-~m selected such that jamming signal frequency harmonic interference may be alleviated by a filter means, and microproceCcor actuation and control means, ,e~ol.sive to an addressed communication from a headend, for selectively actuating and ~G~ olling a plurality of n jamming frequencies provided by the plurality of m controlled oscillators, m being less than or equal to n.

Cable television premium channel interdiction apparatus for selectively jamming unauthorized premium programming transmitted to a subscriber comprising:
a plurality of m controlled oscillators, each said oscillator separately interdicting within a continuous portion of a broA~hAn~ cable television spectrum, the sum of said continuous portions comprising a total spectrum to be jammed, ~.., 13a 1 334444 a plurality of filters, each said filter associated with each said oscillator, each said continuous portion selected from the cable television spectrum such that jamming signal frequency harmonic interference is alleviated by each said filter, and microprocessor actuation and control means for selectively actuating and controlling a plurality of n jamming frequencies provided by the plurality of m controlled oscillators, m being less than or equal to n.

Cable television premium channel interdiction apparatus for selectively jamming unauthorized premium programming transmitted to a subscriber comprising microprocessor actuation and control means for selectively actuating and controlling a plurality of n jamming frequencies provided by a plurality of m ,LLolled oscillators, m being less than or equal to n, a maximum of m jamming frequencies being applied for jamming unauthorized premium programming transmitted to a particular ~h~riber at one point in time, the mi~ v~oc__-or actuation and cGI.Llol means having a calibration mode of operation and a normal mode of operation, and, during a normal mode of operation, a frequency hopping rate on the order of four thousand hertz is providable.
A cable television premium rhAnnel interdiction method for selectively jamming unauthorized premium ~G~Lamming transmitted to a ~h~criber comprising the steps of receiving globally transmitted frequency and jamming factor data for each premium chAnn?l, receiving addressably transmitted ~hAnnel or premium ~r oylamming authorization data, generating and storing control word data ~-,poncive to the frequency, jamming factor and authorization data and - 13b 1 334444 sequentially applying jamming signals to unauthorized premium programming responsive to the stored control word data.
Apparatus for use in cable television premium channel interdiction apparatus, the apparatus for calibrating a particular jamming frequency of a jamming signal output of a jamming oscillator of the interdiction apparatus and comprising:
a processor unit, responsive to a count of the output frequency of the jamming oscillator, for adjusting a voltage control word in a voltage control word memory, the voltage CG1ILLO1 word being related to the jamming signal output frequency of the jamming oscillator.
A method for use in a cable television premium ~hAnnel interdiction apparatus, the method for calibrating a particular jamming frequency of a jamming signal o~L~L of a jamming oscillator of the interdiction apparatus, the method comprising the steps of loa~ing a voltage CG~L~ ol word memory with a voltage cG..Llol word related to the jamming signal output frequency of the jamming 06cillator, counting the jamming Rignal G~L~uL frequency of the jamming oscillator, and adjusting the voltage ~o~L~ol word responsive to the frequency count.
These and other advantages of the present method and apparatus for providing remotely and addressably controlled interdiction will now be explained with reference to the drawings and the following detailed description of one embodiment.
~Klkr ~ -,lON OF THE DRA~INGS
Figure 1 is an overall system block diagram showing the inherent compatibility of the present interdiction apparatus with existent cable television systems comprising premium ~n~el scramblers, addressable data transmitters, and subscriber converter/decoders.
B

Figure 2 i6 a block schematic diagram of an addressable common control circuit for the plurality of provided subscriber modules in accordance with the present invention comprising a broadband signal tap, a microproces~Qr, a data receiver and decoA~r and an automatic gain control circuit.
Figure 3 is a block schematic diagram of one subscriber module comprising a microprocessor for selectively actuating and controlling the output frequency provided by each of four voltage cG~ olled oscillators such that during a normal mode of operation sixteen premium channels may be jammed at a minimum twenty percent jamming interval and, during a calibration mode, a feedback path is provided to the mi~ G~e~Qr through a ~L Gyl ammable prescaler to precisely establish jamming signal frequencies.

Figure 4 is a frequency plan for allocating the broA~hA~ cable television spectrum among four separate bands, each of which bands comprising a plurality of rh-nnels greater than or equal to four but, ~, -14- l 334444 of which plurality, only four ~h~nnelc may be j~mmeid at a 20% jam-ming inter~ral.
Figure S is a detailed block schematic diagram of one emh~o~
ment of a feedback loop structure for implementing the calibration mode of operation of the present invention.
Figure 6 is a block diagram of the voltage control word memory in connection with the sequential provision of oscillator j~mming fre-quency signal outputs during a normal mode of operation.
Figure 7 is a timing diagram for the emho~iimPnt of Figure 3 during a normal mode of operation in which each interdiction control signal is particularly depicted.
DETAILED DESCRIPTION
Referring more particularly to Fig. 1, there ic shown a general block diagram of a cable television system employing the principles of the present invention. By cable television system is intended all sys-tems involving the tr~ncmicsion of television signals over cabie toward remote locations. For ex~mple~ a cable television system may comprise a community antenna television distribution system, a satel-lite signal distribution system, a broadcast television system, a private cable distribution network, either industrial or educational, or other forms of such systems. Each remote location of a television receiver may comprise the location of a particular subscriber to a subscription television service, plural subscribers, single subscribers having plural television receiYe.s or private locations in a private cable distribution nel....l~. Concequently~ the term subscriber, when used in this appli-cation and the cl~im-c, referc to either a private subscriber or a com-m9rCi~l user of the cable television system. ~eade~ 100 as used in the present application and claims is defined as the connecting point to a serving cable 110 for distributing television ch~nnPlc to sub-scriber locations. For reference purposes, an Electronic IndustriPc Association (E.I.A .) standard cable television f requency allocation schPme is employed and referred to herein; ho~rever, by means of the following ~icclos~re of the present invention, one may apply the prin-ciples to other known standard_ or non-standard frequency alloca-tionc. Furlhe.lllore, a National Television Suhcommittee (N.T.S.C.) standard composite television signal at b~ceb~nd is generally consid-ered in the following description; however, the principles of the pre-sent invention apply equally to other standard and non-standard b~ceb~nd television signal formats.
He~dend 100 comprises a source of television progr~mming 101. Television program source 101 may be a satellite television receiver output, a program produced by a television studio, program material Leceived over a microwave or broadcast television linl~, a cable television link output, or any other source of television pro-gr~mming consistent with the present invention. The program source material need not be limited to conventional television but may com-prise teletext, videotex, program audio, utility data, or other forms of comm~nication to be delivered to a remote location over the serving cable 110.
Program material provided by source 101 may be premium or otherwise restricted or desirably secured from receipt at unauthorized rec~iver locations. To this end, each channPl or program to be sec.,re~ is generally scramhled by scrambler 102 provided at he~dend 100. By the use of the term premium ch~nnPl or premium program-ming in the present ~E~plication and claims is intended a ch~nn~l or program which is desired to be secured from unauthorized receipt either bec~ce of its premium or restricted status.
Normally, all premium progr~mminc in known cable television systems is scr~m~)led However, in accordance with the pre_ent invention, premium progr~mming is transmitted in the clear, and interdiction is ~pplied at off-premises interdiction apparatus 130 to jam reception of unauthorized premium progr~mminc.
Co~ )ently, during a transition period in which heade~cl 100 pr~vides scr~mhl~ television progr~mmin~ a~C well as premium pro-gr~mming in the clear, a scrambler 102 will be provided so long as converler/decoders 150 are provided to subscribers for unscr~mbling scr~mh~ed program tr~ncmiccion. In certain instances, converler/deco~lers 150 may be entirely replaced by interdiction apparatus 130 of the present invention.

Also, at the he~dend, there is normally an addr~ hle data transmitter 103 for transmitting global comm~n~C and data to all sub-scribers or add-~ed communications for reception by a unique sub-scriber. Such data tr~ncmiccion may be conducted over a separate data carrier from the cable television spectrum, for eX~mple~ at 108.2 megahertz. It may also be transmitted over an unused default ch~nnel from the television spectrum. Global comm~nflC generally take the form of operation code and data while addr~ed communications fur-ther comprise the unique address of a particular subscriber.
In another alternative embo~limpnt~ such comm~)nications may take the form of in band signals sent with a television ch~nnPl super-p~sed upon an audio carrier during, for example, the vertical inter-val of the video signal. Such data comml~nications further compli~te data reception at intervention apparatus 130 in accordance with the present invention and are desirably elimin~ted. Ho~.ever, in band signaling is sometimes required for the operation of certain conve~ ter/decode~s 150 known in the art.
Concequently, he~-len~ 100, cable television distribution cable 110, and con-verter/decoders 150 and television receivers 1~0 at a typical subscriber premises 181 comprise a typical known cable tele-vision system. Channel program or authorization data is transmitted via an aw~ hle data transmitter 103 over a cable 110. At a pole 120 or from a pedestal 140 at under~,,ound cable locations, the serving signal is ~llop~ed via drop 115 to a subscriber location. Drop 115 is ~ Fcted to a col~entional conve, ler/~lecoder 150 which serves sev-eral functions. RPspon.~ive to an add~sed comml~nication from h~a~yd transmitter 103, ch~nnel or program authorization data is updated in an authorization memory if the address ~cori~ted with the aW~d commnnication matches a unique address of the subscriber de~oder 150. For exampIe, the subscriber address may comprise a plurality of bits over and above the actual nl~mber of subscribers in a system, additional bits insuring the security of the address. The pre-mium ch~nnpl or program is then stored in the authorization memory of the con~,erter/decoder 150. Television programminC is normally converted to an otherwise unused ch~nnel such as ch~nnel 3 or 4 of the telèvision spectrum by a converter portion of con\,erler/decoder 150. Its premium status is cl~erked against the data stored in authori-zation memory. If the progr~mming is authorized, the deco~ler por-tion of the converler/decoder is en~hled to decode authorized scram-bled premium progr~mming.
The provided television receiver may be a con~entional televi-sion receiver 1~0 or may be a so-called cable ready television receiver 171. ReC~ ce of the advent of cable ready television receivers 171, there is no longer a requirement at a subscriber premises 181 for the cGn~,e~ ler portion of the con~erler/de~oder 150 as a con~,e- ler is built into such television receive.~. -In accordance with a cable television system provided withinterdiction apparatus 130 of the present invention, a hol~eing is mounted on a strand supporting cable 110, to a pole 120, or provided via a pedeslal 140. Inside the hollcinE is common control circuitry for t~r~pinG into the broa~ih~n-i television and data trancmicsion spectrum.
Referring to the first pole 120 from the left of Fig. 1, there is shown a strand-mounted apparatus serving two drops 115 to subscribers.
Altogether, four subscribers and up to four drops 115 may be served by interdiction apparatus 130. R~side~c the common control circuitry, four plug-in subscriber modl~l~c may be provided for one hollcing.
Also, if desired, additional services may be provided via other plug-in units of the hol~cinc such as impulce pay-per-view, subscriber polling involving two way data communication, meter reading, energy man-agement or other services.
Desirably, all eq~lipmPnt 161 may be removed from the sub-s~bo. premises 182. However, for the provision of additional serv-ices, some on premises eq~irment may be unavoi~1~h~e. For pul~oses of this description, premises 182 will be ~cs~med to inl~lude at least one non-cable ready conventional television receiver 1~0. Conse-quently, subscriber equipment 161 must at least comprise a tun~hle convert~r for converling a received cable television ch~nnel to an unused ch~nnel such a_ ch~nnel 3 or 4 for reception on conventional television receiver 1~0.

Power for interdiction apparatus 130 may be provided over the cable from the he~dend 100 or be provided via the subscriber drop 115 or by a combination of such means. Forseeably, power may be even provided by rechargeable means such as solar cells or other external or replaceable internal sources such as batteries. Consequently, sub-scriber eq~ ment 161 may also comprise a source of power for inter-diction apparatus 130.
Interdiction apparatus 130 may be secured in a tamper r~ist-ant housing or othe. ~. ise secured such as in a locked equipment closet of an apartment comple~. If located in a place eXI~ to the ele-ments, the hollcinc should be water-tight. Also, the hollsing should be designed to preclude radio frequency leakage.
At premises 183, the subscriber is prP~cumed to have a cable-ready television leceiver 171. Concequently~ subscriber unit 162 may be entirely Plimin~ted or comprise simply a power feed to interdiction apparatus 130.
Premises 184 pictorially repr~sents a subscriber location served by an un~.~,lo~nd cable 110 via a plurality of L,edes~als 140, in which cable distribution amplification and branchinG equirment and drops 115 are normally provided. In accordance with the present invention, ped~tal 140 may comprise an off-premises hollcinG for interdiction apparatus 130. Subscriber equirment 162 may comprise a converter, an additional service device and a power unit as described in refer-ence to subs~.iber eql~ipm~nt 161 or nothing at all as described in reference to subscriber equipment 162.
Interdiction apparatus 130 is uniquely a~ hle by he~en~
lO~us,t as is conve. ler/deco~e~ 150. If two bits of a plural bit unique subscriber a~la~s are associated with uniquely identifying one plug-in slot for one of four subscriber mod~P.s, commQn control circuitry may be uniquely ad~sed with rem~ininC address data not used to secure the data commllnication. Just as premium progr~mminC is transmit-ted in the clear and since no data communication is n~c~arily required with a subscriber premicps~ a subscriber address need not be transmitted in a secure form in accordance with the princirl~s of the present invention. Neverthel~ss, address security may be desirable so long as converler/decoders 150 or other unique address requisite e~ rment is provided at a premi~Ps.
Interdiction apparatus 130 comprises a~d~essable common con-trol circuitry and up to four plug-in subscriber modules. Upon receipt of subscriber specific premium program or ch~nnel authorization data, the data is stored at interdiction apparatus 130. Interdiction apparatus 130 further comprises automatic gain control circuitry of the com mon control circuitry. Channel interdiction circuitry associ-ated with each subscriber module jams unauthorized premium pro-gr~mminE dropped via a particular drop 115 to a particular subscriber.
Consequently, interdiction apparatus 130 iS reasonably compatible with add~ hle authorization data tran~miccjon known in the art.
No scr~mhling of premium rh~nnP~c (and no resulting artifacts) is necessary or desirable. Furthermore, no additional forms of service security are nPcp-cc~ry such as ch~nn~l encryption, in-band ch~nnel or tier verification or other security measures. The would-be service pirate must attempt to remove a particular pseudo-randomly timed j~mming signal placed at a varying frequency or seek to tamper with the off-premises apparatus 130 or derive a signal from shiPlded and bonded cable 110 which should likewise be maintained secure from radio frequency leakage.
The com mon control circuitry of interdiction apparatus 130 will now be described by means of the block diagram Fig. 2 for serving four subscriber modlllPs in accordance with the block diagram Fig. 3.
R~fe.lin~ particuIarly to Fig. 2, a feeder cable 110 is shown entering interdiction apparatus 130 at FEEDER IN and leaving at FEEDER
OUT. Power PWR may be provided via the feeder cable by means of a subs~riber drop or locally by internal or e,~lel.lal means. Depending on the source of power PWR, input power may be of alternating or direct current.
A directional coupler 210 which may be In the form of a plug-in modllle taps into the broadband serving cable 110. A broadband of radio frequency signals is thus output to highpass filter 220. Highpass filter 220 passes a band of frequencies comprising at least the data carrier frequency or frequencies (in a bi-directional application) and the cable television chAnn~l spectrum. Referring briefly to Fig. 4, the cable television spectrum may comprise a frequency band from at least 120 MHz to 350 MHz.
An automatic gain control circuit comprise_ variable attenuator 230, RF amplifier 233, directional co~rler 232, and AGC
control circuit 231. The automatic gain control circuit appropriately regulates the broa~ And RF signal power to fall within est~h~iched limit..
Also connPcted to directional co!~rler 232 is a data receiver 240 for receiving data from the add~Ahle data transmitter 103 located at h~adend 100. Data receiver 240 receives data transmitted, for eY~mp~. over a data carrier of 108.2 megahertz and provides unpro-cessed data to data decoder 250. In accordance with an est~hliehed protocol, such data may be in the form o~ an operation code, a sub-s~.ib~r unique address and Aceoci~A~ted data. Data decoc~er 250 pro-cesees the data and provides the separately transmitted data to microprocF~ r 260 for further interpretation in accordance with a built-in algorithm. Microproc~;~r 260 is most efficiently chosen to alleviate a. many ~ o~ihilities from any microproc- ~:or provided for an individual subscriber mo~ P and so is most conveniently an eight bit mic~c~r having eight kilobytes of internal code such as a Motorola 68HCO5C8.
Rc~ data may be stored in uninterruptable memory 270 by microproc~ 260. Data may be temporarily stored in memory 2~0 or more permanently stored and su~equently downlo~d~P,d when needed to a ~ sc.iber m~le via a serial peripheral interface bus .ecllng mic.op~cP~r 260 with separate microproc~ors associ-ate~th each provided subscriber mo~
Micrup,oc~--~r 260 cor~ceyuently interprets both global com-mllnir~tionS ad~l~;ed to common control circuitry or commnnir~-tions a~l~d to unique subscriber mod~lPs. If appro~-iate, micro-proce~or 260 ignores global or ad~ied communications to other interdiction apparatus 130 or to converter/~ecoder;, 150 (Fig. 1).
~Y~mrl~s of global communications peculiar to interdiction apparatus 130 are premium rh~nnel frequency data and i~mminC factor data A

-for each premium ch~nnel or rh~nnpl over which premium program-ming at a particular point in time is provided via headend 100. Exam-ples of addlessed communications include communications comprising premium ch~nnel or progr~mming authorization information or com-munications instructing the common control circuitry to deny or pro-vide service to a particular su~scriber.
If two way services over the serving cable are anticipated, a data transmitter (not shown) must be provided in the common control circuitry of Fig. 2 or a separate telephone link from the subscriber location to the headend may be provided. Serial peripheral interface bus 290 may be a two way colnml~nications linlc by way of which link mi~,oprocessors 300 (Fig. 3) associated with subscriber modules may, at least, provide status reports to microproc~or 260 upon inquiry.
Radio frequency splitter 280 provides bro~lb~nd radio fre-quency signals comprising at least the cable television service spec-trum of Fig. 4 separately to each subscriber modllle that is provided.
If a rave.se path is required for speci~l additional services, a signal comhin~r (not shown) of a plug-in special service module may be provided for receiving communications from each of the four su~
scriber mod~ s in an opposite m~nner to splitter 280. Certain data may be transmitted back toward the ll~adened via the speri~l service plug-in module (also, not shown) associated with the additional special service.
Re~erring more particularly to Fig. 3, there is shown an overall bloclc srh~m~tiC diagram of a subscriber mo~ule in accordance with the present invention. A micro~rocessor 300 is associated with a pa~
ticulars,~ .iber module and communicates with microproc~r 260 of Fig. 2 over a serial peripheral interface bus. Microprocessor 300 may comprise an eight bit microproc~or equipped with only two kilobytes of microco~le, this microprocessor being relieved of overall control r~r~ihilities by microprocessor 300. Consequently, micro-proc~or 300 may conveniently comprise a Motorola 68HC05C3 microl~rocessol or similar unit.
A reYelse path may be provided via a lowpass filter 392 to a speci~l service module (not shown in Fig. 2) of common control circuitry as described in Fig. 2 from a corresponding special service mod~le on the subscriber premicp-s. Such a reverse path is completed to the subscriber via terminal OS. AlsO power may be transmitted up the subscriber drop to the module of Fig. 3 and withdrawn at terminal OS.
The broatlh~nA radio frequency television spectrum signal from Fig. 2 is provided to terminal IS. Referring to the path connecting terminal IS to terminal OS, there are connected in series a service denying switch 389, an amplifier 38~, a j~mmi~a signal combiner 384, and a high pass filter 391. Service denying switch 389 is under control of microprocessor 300. In the event of an addr~ed communication from headend 100 indicating, for e~mple, that a subscriber is to be denied service for non-payment of a bill, service denying switch 389 may be opened. In addition, a high frequency amplifier 387 may be po~e.ed down under control of microproce~or 387 whenever service is to be deni~ Otherwise, amplifier 387 may be set at discrete gain levels, under microproc~or control, to provide sl~pplemental gain to the broaAb~nd television signal if a subscriber has a plurality of tele-vision receivers over and above a nominal amount.
J~mmin~ signals are interdicted at directional combiner 385 under microp~oc~r control. ReC?IISe of the directional characteris-tic of ~mplifier 387, j~mminC signals cannot inadv~r~ently reach the common control circuitry of Fig. 2 or the serving cable 110. J~mming signals are interdicted at a level approximately within a range of -2.5 db to +6.5 db or +2dB nomin~l of the video carrier power level of the unauthorized premium ch~nnel frequency to be j~mmecl They are moOEt. co~l~/eniently interdicted for video carrier jammine approxi-mately within a range of frequencies ~xlen~ltn~ from the video carrier to 1 250 k;lohertz above the video carrier toward the audio carrier of the ch~nnPl to be j~mme~ In accordance with the present interdic-tion apparatus, the frequency is selectable by the he~dend 100 and so may be chosen to jam the audio carrier at a frequency closer to that carrier if desired. Also, the power levelof the j~mmincsignal may be varied via global data tr~n-cmiccion-c if, for eY~mple~ audio carrier j~mming is desired. Such interdiction on a per ch~nnPl basis between the video and audio carriers minimizPs adjacent ch~nnPl artifacts.
Highpass filter 391 prevents any return path signals from reaching comhinPr 385 and passes the bro~Ahand spectrum incl~Aing any j~mming signals toward terminal OS. Reverse path signals, for Plrample in this emho~liment, if present, may be radio frequency sig-nals below 100 megahertz. The broa~lb~nd television spectrum is pre-sumed to be in the 100-350 megahertz range consistent with Fig. 4.
Ho~,lever, interdiction of premium ch~nnPI viewing may be allocated anywhere desired within a broader or discontin~loll-c cable television ~ c~ , to be jammed. Cor~cequently, filters 391 and 392 are designed in accordance with this or similarly selected design criteria to block or pass bro~lh~n~l television or rever~e path signals as required.
Microprocessor 300 controls four voltage controlled oscillators 341-344, each of which oscillators jams premium ch~nnel frequencies within an allocated continllollc range of frequencies. Since premium progr~mming may be transmitted anywhere in the cable television spectrum, the sum of all such allocated portions comprises the entire television spectrum to be jamme l In accordance with the present invention, the television spectrum to be j~mmed may comprise dis-cont1~uo~lc portions or intentionally overl~rpinC portions.
Referring briefly to Fig. 4, the spectrum allocation to the plu-rality of four voltage controlled oscillators in one emhor~iment will be ~ d in view of certain principl~c~ Firstly, it is desirable to elim-inate j~mminG signal harmonic interference to authorized ch~nnelC
w~hiQ the allocated band. For e~mple~ a harmonic of a relatively low fraquenc~ signal, for example, 100 MHz can lnterfere with a ch~nnel at a harmonic of this frequency in the upper part of the cable television spectrum. In other words, the allocated band should be limited for an oscillator to fall within one third of an octave, and, conce~.lently all frequency harmonics may be blocked by filters 351, 352, 353 and 354 ~c~oci~ted with each oscillator. Oscillator 341 denoted OSC l, for e~mrle, is active in a band extPn~ing from 126 to 158 megahertz while filter 351 will bloc}~ harmonics above the in-~iuded ~h~nnçle 15-20 of the mi~lh~n~
Cable he~dend service providers tend to select premium chan-nel allocations in the midband range covering ch~nnelc 15-22. Conse-quently, the band of oscillator 342, for example, may be selected to overlap the band allocated to oscillator 341.
In order to achieve a j~mming interval of 20%, each oscillator may be restricted to j~mming only four premium ch~nn~lc. As will be described in connection with a discussion of Figs. 5, 6 and ?, j~mming depth may be automatically increased for a particular subscriber dependent upon the subscriberls level of service. Also, by allocating an overlap of bands as between first and second oscillators 341 and 342, for çx~mple, all eight ch~nn~l~ of the mi-lh~nd may be jammed by means of the present interdiction apparatus leaving two ch~nnelc of the hiEhh~n~l which still may be jammed via oscillator 342. Conse-quently, according to Fig. 4, oscillator OSCl may jam four of the six allocated ch~nnel frequencies of the miflh~nd while oscillator OSC2 may jam an overlapping band comprising ch~nn~lC 19-22 of the mi~h~n~i and ch~nnelc ?-10 of the highband. The range of j~mming signal frequencies for oscillator OSC2 is selected within the range of 150-194 megahertz consistent with the desirable Plimin~tion of har-monic interference.
Consistent with these design principles, no band overlap is shown for oscillator OSC3 or oscillator OSC4. Neverthel~-ce, the respective frequency ranges of 198-254 megahertz and 258-326 mega-hertz of these oscillators Pliminate any danger of harmonic interfer-ence. Low pass filters 353 and 354 cut off harmonic frequencies abo~re the upper limits of these respective rangec. Oscillator OSC3 provides j~mming signals for j~mmine four premium ch~nnPlc selected from rh~nn~le 11-13 of the highband and ch~nn~l.c 23-29 of the superband. Eight premium ch~nnels may be jammed at a reduced jam-ming factor of these ten channels. Oscillator OSC4 is provided for jamming from rh~nnel 30 in the superband to channel 41 extending into the hyperband. Four channels of these twelve may be jammed at a 20% j~mminC interval; however, eight may be jammed at a reduced js~mming factor.
MicroprocPcsor 300 is connected by a bus system to memory and buffer circuits comprising RAM's 311 and 312 and buffer 310.
MicroprocP-ccor 300 operates at a clock frequency of, for example, four megahertz provided by ClOck 336. Counter 335 is shown as a separate elemerlt; however, counter 335 is provided essentially for counting the output frequencies of j~mming oscillators 341-344 during a calibration mode of operation and so may comprise an Plement of microproc~or 300.
Microprocessor 300 is also connected to digital to analog con-verter 320. During a normal mode of operation, digital to analog con-verter 320 conver~ a ten bit voltage control word to analog voltage outputs which are, in turn, provided to analog multirlP~rer 330. The analog voltage outputs of the analog multiple~tp~r 330 are stored and held at s~mple and hold circuits 33~-340 for ~pplic~tion to oscillators 341-344. Via a two bit parallel select bus, analog voltage signal out-puts are seq~entially gated by analog multiplP. YPr 330 over leads FREQ 1-4 toward the oscillators 341-344. ~n accordance with the princirlP~s of the present invention, these signals may be provided in a ~seudorandom sequence to thwart pirating attempts as will be described in reference to Fig. 6.
Microl,roc~,csor 300 is connected to each oscillator 341-344 via r~Etlve oscillator power lines OPWR1-4 for actuating the oscilla-tors. Each oscillator may be powered down during a normal mode of operation if a subscriber is authorized to recei~/e all ch~nnPlc within its allocated band at one point in time. Furthermore, during a cali-bration mode, one oscillator may be po~e.ed up for calibration while all other oscillators are powered down.
Microproce~or 300 is further connected to four high frequency PIN diode switches 361-364. During a normal mode of operation, these switches are selectively opened for a brief interval for, for e~mplP~ teen micr~cecof -lc while an ~ccoci~ted oscillator changes or hops from one j~mmina signal frequency output to another. Never-thPlpsc~ ~ccllminc four ch~nnPl j~mming by a particular oscillator at a jam factor of four, a four thousand hertz frequency hopping rate is easily achievable via these PIN diode switches.
Also connPcted to the outputs of each oscillator are associated low pass filters which serve to cut off all harmonics of jAmming signal frequency output. These low pass filters may be connected either to the inputs or to the outputs of switches 361-364 although connection in series between its associated oscillator and high frequency switch is shown in Fig. 3.
The j~mming signal outputs of all four oscillators are combined at signal combiner 365. From signal combiner 365, the combined out-put is directionally coupled by coupler 3~0 to progr~mm~hle prescaler 3~5 and to signal attenuator 380.
Progr~mm~hle prescaler 375 is only powered via lead PREPWR
when required during a calibration mode. In accordance with a pro-gr~mm~hle divide-by factor, a divided down output frequency is pro-vided to microprocessor 300 for counting. When powered down, no output signal results.
During a normal mode of operation, the comhined j~mming signal outputs of attentuator 380 are comhined at directional coupler 385 with the passed incoming broadband television signal from the common control circuit of Fig. 2. As the subscriber is presumed to have paid their bill, switch 389 and amplifier 387 are assumed to be powered. As a result of the combining of j~mming signals with the bro~ih~nd spectrum (thus far transmitted in the clear), the subscriber will only receive in the clear premium or restricted progr~mming which the subscriber is authorized to receive.
Referring more particularly to Fig. 5, there is shown a block s~h~ tic diagram of one embodiment of a feedback loop useful in describing the calibration mode of operation. The calibration mode, occupying a fraction of a second, assures relatively frequency stable operation during a normal mode of operation. Furthermore, because of the calibration mode, there is no requirement for the application of slow conventional frequency locking techniques and a high operation frequency hopping rate of four thousand hertz may be achieved during the normal mode of operation. The embodiment shows the calibration - 2~ - 1 3 3 4 4 4 4 of one particular o_cillator OSC. The depicted loop indicates an application specific integrated circuit ASIC connected to subscriber moflllle microprocessor 300. This circuit ASIC may be clocked at twice the microprocessor rate and comprise the previously discus ed voltage control word memory RAM as well as progr~mm~hle prescaler 375. A word adjust and select bus 501 is shown which may separately access and adjust all voltage control words in voltage control word memory RAM. When add~ed, the voltage control word memory is connected via bus 511 to digital to analog converter 320. Digital to analog con~/erter 320 is connected via s~mple and hold circuit SH to oscillator OSC to which power is ~pplied under micro~roces_or con-trol via lead OPWR. Via directional coupler 370, the j~mmine signal output of oscillator OSC is fed back toward microprocessor 300. At fixed pre_caler 376, the high fre~uency output is divided down by a fixed divide-by factor. The divided down j~mminC fre~luency output i then output to progr~mm~hle prescaler 375. Progr~mm~hle prescaler 375 is under control of microprocessor 300. R~or~-ci~e to premium ch~nnPI freq~lency data tran_mitted from the headend to micropro cessor 260 of Fig. 2, microprocessor 260 in turn generates divide by factor and time between count data for transmittal to microproc~c~or 300 via the serial peripheral interface bus (Fig.'s 2 and 3). Micro~ro cessor 300 programs the divide by factor of progr~mm~hle prescaler 375 via lead 502 and receives a countable frequency output of pro-gr~mm~hle prescaler 375 via lead 503. Microprocessor 300 then counts the output at inclu~ed counter 335.
The provision of application specific integrated circuit ASIC
as~sist,s in miniaturizing the subscriber modllle of Fig. 3 and relieves the outboard memory requirements of microproc~sor 300. On the other hand, the provision of a limited voltage control word memory in circuit ASIC may restrict the opporl~nity of microproc~-~or 300 to re~llocate addr~ hle slots to other oscillators when one oscillator is ~wered down as will be described in greater detail in reference to Fig. 6. The provision of a second or fixed prescaler in comparison with the single progr~mm~hle prescaler shown in Fig. 3 is desirable if - 28 - l 3 3 4 4 4 4 the frequency range of the television spectrum to be j~mmed extends into the hyt)e~band.
Referring now to Fig. 6, there is shown one emho~liment of a voltage control word memory having sixty-four memory locations with add~esses 1-64. At every fourth memory location 1, 5, 9 and so on is located a voltage control word associated with a first oscillator.
For the convenience of est~hliching a convention for d;cc~lcsion, f 10 .
. . f lE will be assumed to refer to sixteen frequency control words for a first oscillator OSC1 and are n~mhered in hP~r~decim~l notation from O-E. As indicated above in reference to circuit ASIC memory requirements, the sixteen memory slots may be permanently associ-ated with oscillator OSC1; however, such a design choice limits the f~ee~lll of re~lloc~ting voltage control words to other oscillators.
Voltage control words are entered into voltage control word memory for each oscillator in sequence provided the oscillator will be ~pFlied for j~mming. First, it will be ~ccumed that all four oscillators will be ~rpliP~I, each for j~mming four premium ch~nnPlc. As will be seen, this is a simplified ~Cc~mption which ~csumP~s a subscriber is authorized to receive no premium ch~nnelc and, furthermore, it will be ~ccllmed that all premium ch~nnpl~ are to be j~mmed at the same jam factor four.
In this Plr~mrle, sixteen voltage control words will be entered in memory for each oscillator, four of which control words may be the same, each four similar control words being related to one premium el frequen~y to be jammed. Thus, four groups of four similar control words are entered into sixteen memory locations 1, 5, 9, 13 . .
.61~oc oscillator OSC 1. These are indicated as f 10 to f lE. In a simi-lar m~nner, si2-tæn voltage control words are entered into memory locations 2, 6, 10, 14 . . . 62 for oscillator OSC2. These are indicated as f20 . . .f2E. Then, sixteen voltage control words are entered into memory locations 3, ~, 11, 15. . . 63 for oscillator OSC3, indicated as f30. . . f3E. Lastly, sixteen voltage control words are entered into memôry locations 4, 8, 12, 16,. . . 64 for oscillator OSC4, indicated as f40. . . f4E.

The calibration algorithm for lo~ n~r a first ten bit voltage control word flO into a first memory location 1 for a first oscillator OSC 1 will now be described in some detail. From the do~n loaded frequency data from microprocessor 260, a first progr~mm~hlP
divide-by factor is transmitted via lead 502 to set progr~mm~hle prescaler 3~5. All other oscillators OSC2-4 are powe.n~ down via leads OPWR2-4, and oscillator OSC1 is powered up via lead OPWRl (shown in Fig. 5 as oscillator OSC and lead OPWR respectively).
From the premium ch~nnel frequency data, a first ten bit volt-age control word flO is stored in memory location 1 ~.:prese,lting a first best estimate of j~mming frequency by microprocpccor 300 via bus 501. The word is transmitted to digital to analog converter 320 where it is conve, led to an analog voltage. The analog multiplPxPr (not shown in Fig. 5) selects a lead FREQl from the multirle~rer to oscillator OSCl. ~oncequently, the analog voltage output of the dig-ital to analog converter is provided to sample and hold circuit SH or 33? for application to oscillator OSCl. Signal comhinPr 365 (not shown in Fig. 5 for simplicity) only passes the j~mmina signal output from oscillator OSCl to directional coupler 3~0 bec~ ce all other oscillators OSC2-4 are L~owered down at this time. Via directional co~rler 370, the j~mming signal output is provided to fixed prescaler 3?6. Fixed prescaler 3~6 divides down the output frequency of the oscillator OSC1 to a first frequency. According to the divide by fac-tor loaded into progr~mmahle prescaler 375, the first frequency out-put of fixed prescaler 376 is further divided down to a frequency which may be counted by counter 335 of mic.oproc~;or 300. Recog-ni~ that the oscillator output frequency may be hllnl:3.~ of mega-hertz and the clock for microproc~sor 300 runs at only four mega-hertz, the freq~ency provided via lead 503 should be sufficiently divided down to be counted with re~con~hle accuracy. Since the fixed time between counts is known to microprocessor 300 having been downlo~ded from microprocessor 260, counter 335 counts the fre-quency input on lead 503. The resulting count is comp~red with the expected count and the microproce~sor adjlLsts the control word accordingly. As a result, microprocessor 300 repeatedly enters the algorithm until the voltage control word stored in memory as accu-rately as p~cihle reflects the premium ch~nn~l frequency to be e 1 Then, this process is repeated four times for four premium ch~nnPI frequencies to be j~mmed by the oscillator OSC.
During the process of lo~ n~ the four premium ch~nnPl fre.-quPnri~c for a particular oscillator into the voltage control word memory, there are two subordinate s~hPmPe by which the four voltage control words for a single premium rhannPI may be intentionally var-ied. In a first subordinate srhpme~ via hP~d~n~ 100, four different freque~ciec may be intentionally selected with reference to one pre.-mium ch~nnP~. Given a resolution of 50 kilohertz provided by the least significant bit positions of a ten bit voltage control word, the four different frequencies may be selected by he~dend 100 anywhere within the 250 kilohertz range above the premium ch~nn~pl video car-rier for most effective premium ch~nnpl j~mming. In a second subor-dinate srheme microproc~sor 300 may be progr~mmed to intention-ally vary the entered voltage control word to be at or about the expected downloaded frequency, for e~r~mplP., at fifty kilohertz above or below the expected frequency. Co~ce~ ntly, if the he~dend selects only one frequency for a first premium chann~, for example, at 200 kilohertz above the video carrier, then voltage control words will be entered into memory equivalent to video carrier plus 150 kilohertz, 200 ~cilohertz and 250 kilohertz. Both :juborulinate schemes thwart pirates attempting to notch out the j~mmin~ signal frequency which is intentionally varied by these schem~c~
J~mminC factor is a term related to the loa~1inc of the sixteen val~agç control words into voltage contrd word memory for a partic-ular oscillator. A jamming factor is selected for each premium chan-nel and is globally transmitted from the he~Pn-l ~ four premium t~hannelC are to be j~mmed by each of four oscillators OSCl-4 and all are to be ~mmed at the same j~mmin~ interval, each has a jamming factor of four. If a subscriber subscribes to all four premium ch~n~Plc ~-csori~ted with oscillator OSCl, then oscillator OSC1 may be powered down and no voltage control words entered in memory during calibra-tion for this oscillator. If a subscriber subscribes to two of the four ~h~nnPIe, the microproc~or may allocate the sixteen control words for the first oscillator to the two unauthorized premium ch~nnel fre-quencies to be j~mmed Col~eeql)ently, the microprocessor may allo-cate eight control words each to j~mminC the two unauthorized pre-mium ~h~nnPIe thus automatically increasing the j~mming interval or depth of j~mminE based on the j~mminC factor and the given reduced level of premium program authorization. J~mming factor may be intentionally selected, for P~mple~ at a high level, for ex~mple, eight for one especi~lly sensitive program in relation to two other ch~nnPI
to be j~mmed by the same oscillator which may be allocated jam fac-tors of four each, the total of all such jam factors being equal to the m~iml-m nllmher of voltage control words, in this ex~mple, sixteen ~soci~ted with the oscillator.
Voltage control words may be read from memory or written into memory so they may be read out in a particular pseudo random seql)ence so that a pirate would have to know the pse~dorandom sequPnce in order to appropriately time any notch filtering. For Plr~mple, let fll-fl4 be the four premium t~h~nnel frequencies to be j~mmed by oscillator OSC1. Addlesses 1, 5, 9, and 13 may store volt-age control words for fll, fl2, fl3 and fl4, respectively. However, the next four ad~lr~;~ 1~, 21, 25, and 29 may store the voltage con-trol words in a different order, for Plr~mrle, fl4, fl3, fl2, fll r~ec tively. The order may be further varied in the rem~ining eight ad~;~3 so, when the voltage control words are applied to oscillator OSC 1 during a normal mode of operation, the output frequency of the j~mminc signal will vary according to the psel)dorandom se~uence of da~a e,ntry.
The calibration mode is entered at initial turn-on to generate the si~ty-four voltage control words for slordge in voltage control word memory co.--~s~on~i~n¢ to the desired j~mming signal ~requen-cies. Periodically, the subscriber module reenters the calibration mode to update the control words for drift which may result from either the oscillator or the digital to analog conver~er operation.
Such drift if maintained within, for e~mple, 50 kilohertz of the selected freque*cy is actually desirable in that it further complicates the efforts of a would-be pirate. Also, as already indicated the peri-odically performed calibration mode permits a higher rate of fre-quency hopping, for Plr~mrle, four kilohertz during normal operation than would be p~ hle with conventional frequency control methods such as phase locked loops. Calibration requires but a fraction of a second and, conse~llently, no intelligible television information may be obtained at a television receiver tuned to an unauthorized premium ch~nnel, Referring now more particularly to Figs. 6 and 7 with refer-ence to the s~hPm~tic block diagram of Fig. 3, the normal mode of operation will now be P~rp~ ed Referring first to Fig. 3, micropro-cessor 300 upon entering a normal mode of operation causes a first voltage control word stored in memory address 1 of the voltage con-trol word memory of Fig. 6 to be transmitted toward oscillator OSCl.
Digital to analog conve~ ler 320 converts the ten bit word 0010110101 to an analog voltage level. Under control of a two bit select bus, ana-log multirle~r~r 330 selects lead FREQl for transmitting the analog voltage signal for ~lora~,re and hol-ling at s~mplP and hold circuit 337.
All four oscillators are prPs~med to be po-.erad for this example under control of micr~procPssor 300 via leads OPWR 1-4. Conse-quently, powered up oscillator OSCl provides a jamminc signal fr~
quency output FREQ 2 consistent with the analog voltage signal input provided via analogy mul~iplP~Pr 330.
Referring to Fig. 7, the normal mode of operation for the eY~mple under ~iscn~cion is shown in the form of a timing diagram.
At the output of the digital to analog conve. ~er is shown at time tO an analog voltage level representing frequency FREQ 1 for oscillator OSCl. Also, during time interal tO - tl, the analog multirl~P~pr 330 is shown connecllng the digital to anlaog con~rerler 320 to oscillator OSCl. While the analog multiple~er is only connPcted to oscillator OSCl for the duration tO-tl, the applied analog voltage is stored and held for the duration tO-t4. Consequently, the output of oscillator OSCl is shown continuoll~ly applied from time tO-t4.
Under control of microprocessor 300 via lead OSSWl, switch 361 is briefly o~en~ while frequency FREQ 1 is est~b~i~hPd at the output of oscillator OSCl and then immediately closed. Switch 361 stays closed for the duration until the output of oscillator OSCl hops from irequency FREQ 1 to FREQ 2. Just prior to time t4, switch 361 is again opened in accordance with signal OSSWl. Concequently at the output of switch 361, the j~mming signal output of oscillator 341 is briefly interrupted.
At time t4, the digital to analog cor,~,erler 320 is signaled to change the output frequency of oscillator OSCl to fre~uency FREQ2.
As before, the analog multtr1~er 330 gates an analog voltage level, this time re~r2senting frequency FREQ 2 to be held at s~mple and hold circuit 337. As a result, oscillator OSC2 now provides a j~mming signal frequency output consistent with frequency FREQ 2 until time t8.
Meanwhile, switch 361 which was opened shortly before time t4 in accordance with switch control signal OSSWl is again closed at a point in time shortly after time t4. At any point in time during a normal mode of operation when one of the high fre~uency switches 361-364 is opened, there will result a loss of a portion of the overall j~mmil~¢ interval during which a j~mming signal would be ~pp~
Ne~/e.~hel~c, the resulting danger of the presence of no switches 361-364 is that during a hopping from one fre~luen~ to the next, an undesirable transition signal may result at a fre~uency and level which may distort authorized premium programing. If four premium program rh~nn~l frequenci~s are to be j~mme~l by a particular oscilla-tor, each such period of an open state of a normally closed high fre-y~enc1 switch 361-364 amounts to no more than 5% of the overall interya~ t0-t64 (not shown).
In a similar m~nner, a first fre.l.lenc~ FREQ 1 is esPhlished for oscillator OSC2. Referring again to Fig. 6, it will he sccn that at memory address 2 is voltage control word 1010010110 which is pro-vided toward oscillator OSC2. In accordance with Fig. 7, at time tl an analog voltage level is output from digital to analog converter 320 r~resenting this word. At a time just prior to time tl, switch 362 is opened in accordance with signal OSSW2. Once frequency FREQ 1 is e_t~hlich~ at the output of oscillator OSC2 or at a time just after time tl, switch 362 is again closed in accordance with signal OSSW2 provided by microproce-C~or 300.
As the normal mode of operation continues, all sixty-four memory locations shown in Fig. 6 are sequentially add~essed and pro-vided for operating oscillators OSCl-4. In accordance with Fig. ~, only the first seven words are repr~nted as having been provided for selecting the first three frequencies for oscillator OSCl and two fre-quencies each for oscillators OSC2-4; however, the process for con-trolling all sixteen frequen~ s for each oscillator may follow in the sequence shown or intentionally vary.
In order to thwart pirates and referring to Fig. 7 for oscillator OSCl, it may be seen how frequencies may be output in a pseudorandom sequence. Output f requencies FREQ 1, FREQ 2, FREQ 3, FREQ 4 are shown output in intervals t0-t4, t4-t8, t8-tl2, and inferentially, tl2-tl6 respectively. In the next intervals, the fre-quencies may be provided, in stead, in the sequence FREQ 4, FREQ 3, FREQ 2, and FREQ 1. Then, in the next succ~ive intervals the fre-quencies may be provided in yet a third different sequence, for exam-ple, FREQ 2, FREQ 3, FREQ 4, FREQ 1. During the last four succes-sive intervals e,.ter~l;nC from t48 to t64, the order of Aprli~d frequen-cies may be altered again, for PY~m~le, FREQ 3, FREQ 4, FREQ 1, FREQ 2. The ~seudorandom sequence may be defined and downloaded from the heAdend or developed internally by either microyroc~c~or 260 of F~g. 2 or micro~rocessor 300 of Fig. 3.

_ -.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Cable television premium channel interdiction apparatus for selectively jamming unauthorized premium programming transmitted to a subscriber comprising:
a plurality of m controlled oscillators for separately interdicting within an allocated continuous portion of a broadband cable television spectrum, the sum of all such allocated portions comprising the total spectrum to be jammed, the allocated continuous portion of the spectrum selected such that jamming signal frequency harmonic interference may be alleviated by a filter means, and microprocessor actuation and control means, responsive to an addressed communication from a headend, for selectively actuating and controlling a plurality of n jamming frequencies provided by the plurality of m controlled oscillators, m being less than or equal to n.

2. Cable television premium channel interdiction apparatus for selectively jamming unauthorized premium programming transmitted to a subscriber comprising:
a plurality of m controlled oscillators, each said oscillator separately interdicting within a continuous portion of a broadband cable television spectrum, the sum of said continuous portions comprising a total spectrum to be jammed, a plurality of filters, each said filter associated with each said oscillator, each said continuous portion selected from the cable television spectrum such that jamming signal frequency harmonic interference is alleviated by each said filter, and microprocessor actuation and control means for selectively actuating and controlling a plurality of n jamming frequencies provided by the plurality of m controlled oscillators, m being less than or equal to n.

3. The cable television interdiction apparatus of Claim 1 or 2 wherein the number m of controlled oscillators is four.

4. The cable television interdiction apparatus of Claim 1 or 2 wherein the number n of jamming frequencies is sixty-four.

5. The cable television interdiction apparatus of Claim 1 or 2 wherein the number m of controlled oscillators is four and wherein a first allocated portion of the broadband cable television spectrum comprises Electronic Industries Association standard midband channels fifteen through nineteen, a second portion comprises channels nineteen through twenty-two and highband channels seven through ten, a third portion comprises highband channels eleven through thirteen and superband channels twenty-three through twenty-nine and a fourth portion comprises superband channels thirty into the hyperband through channel forty-one.

6. The cable television interdiction apparatus of Claim 1 or 2 wherein the microprocessor actuation and control means particularly comprises memory means for storing in a first portion channel or program authorization data, in a second portion premium channel frequency data, in a third portion, jamming factor data, the memory means further comprising a fourth memory portion for storing control words representative of the n jamming frequencies, the microprocessor means, during a normal mode of operation, sequentially controlling an outputting of the control words from the fourth memory portion and deactuating at least one of the m controlled oscillators depending upon the status of the first channel or program authorization memory portion.

7. The cable television interdiction apparatus of Claim 5 wherein the microprocessor actuation and control means further comprises a programmable prescaler means coupled to a combined output of the plurality of m controlled oscillators, a frequency counter, and a means of adjusting the control words in the fourth memory portion of the memory means, the microprocessor means, during a calibration mode of operation, precisely establishing the control words in accordance with premium channel frequency data in the third memory portion of the memory means.

8. The cable television interdiction apparatus of Claim 5 wherein the control words each comprise ten bits of data.

9. The cable television interdiction apparatus of Claim 1 or 2 wherein the microprocessor actuation and control means particularly comprises a common control circuit comprising a microprocessor, a data receiver and a data decoder, the data receiver, responsive to communication from the headend, providing data to the data decoder, the data decoder, responsive to the data provided by the data receiver, for decoding the data and transmitting the decoded data to the microprocessor and an actuation and control microprocessor for each subscriber, the actuation and control microprocessor being coupled to the microprocessor of the common control circuit, each actuation and control microprocessor being further coupled to the m controlled oscillators, m controlled oscillators being provided for each subscriber.

10. The cable television interdiction apparatus of Claim 9 wherein the number m of controlled oscillators is four.

11. The cable television interdiction apparatus of Claim 9 further comprising a watertight and radio frequency leakage resistant housing including means for connecting electronically to a broadband television cable coupled to the headend, the housing for housing the common control circuit, at least one actuation and control microprocessor and at least m controlled oscillators associated therewith, one actuation and control microprocessor and its associated m controlled oscillators comprising elements of a plug-in subscriber module.

12. The cable television interdiction apparatus of Claim 10 wherein the watertight housing houses a maximum of four plug-in subscriber modules.

13. The cable television interdiction apparatus of Claim 1 or 2 wherein the microprocessor actuation and control means particularly comprises means for selectively actuating and deactuating each of the plurality of m controlled oscillators.

14. The cable television interdiction apparatus of Claim 1 or 2 wherein the microprocessor actuation and control means particularly comprises service control means, responsive to an addressed communication from the headend, for denying reception of cable television channel programming by the subscriber.

15. The cable television interdiction apparatus of Claim 1 wherein filter means is provided for filtering jamming signal outputs of each of the m controlled oscillators, each filter means for passing jamming signal frequencies and blocking harmonics associated with the respective continuous portion of the broadband cable television spectrum allocated to an associated controlled oscillator.

16. The cable television interdiction apparatus of Claim 1 or 2 wherein a jamming signal output of a controlled oscillator for jamming a particular premium channel is within the approximate range extending from the video carrier frequency of the premium channel to be jammed to 250 kilohertz above the video carrier channel frequency.

17. The cable television interdiction apparatus of Claim 1 or 2 wherein a jamming signal output of a voltage controlled oscillator is within the approximate range of -2.5 dB to +6.5 dB or nominally at +2.0 dB
relative to the power level of the video carrier power level of the premium channel to be jammed.

18. The cable television interdiction apparatus of Claim 1 or 2, the plurality of m voltage controlled oscillators and the microprocessor actuation and control means comprising a subscriber unit.

19. The cable television interdiction apparatus of Claim 5 wherein a jamming signal output frequency of a controlled oscillator for jamming a particular premium channel is selectable anywhere between the video and audio carrier frequencies of the premium channel to be jammed with a predetermined resolution provided by the control word associated with the jamming signal frequency.