High-security cable television access system

A poach-resistant system enabling cable television subscribers to receive upon request certain programs otherwise unavailable (i.e., "secure") while precluding such reception by non-requesting subscribers as well as non-subscribers. Before transmission of such a secure program the roster of subscribers is scanned at a central control station having compiled subscribers' requests for that program, and a resulting string of pulses corresponding in sequence to the respective subscribers is punctuated with program command pulses timed to designate those subscribers who have requested the program. Transmission of the resultant program command signal string over the cable to junctions with leads to the respective subscribers' television sets results in unblocking of such junction for each of the requesting subscribers only.

This invention relates to control of access to wired or similarly channeled 
program transmission, a prominent example being subscriber cable 
television, wherein reception is blocked in non-requesting subscribers and 
is unblocked to requesting subscribers, usually on a program-by-program 
basis and with corresponding accrual of charges to be paid by the 
requesting subscribers. Such programs may be termed "secure" to 
distinguish them from programs otherwise readily available to subscribers. 
Inasmuch as this application is concerned specifically therewith it will 
be understood that in the absence of contrary designation herein any 
program mentioned is intended to be a secure program even if not so 
identified. 
Numerous attempts to control access to subscription cable television 
program transmission have been made but have proved largely unsuccessful 
for a variety of reasons, such as being on the one hand so simple as to be 
readily defeated at a subscriber's television receiver, or on the other 
hand so complex as not to be suited for use with existing cable setup. 
Easy poaching by non-paying subscribers or outsiders renders presentation 
of expensive programs uneconomical, whereas costly reworking of the lines 
to accommodate a complex control system is not even economically feasible. 
Inability to resolve that dilemma has precluded subscription cable 
television from presenting the anticipated quality and range of programs 
and has resulted in considerable subscriber dissatisfaction and consequent 
constraint upon expansion of cable television. 
A primary object of the present invention is provision of a highly secure 
system for controlling access to cable television or similarly channeled 
communication programs. 
Another object of this invention is a poach-resistant access control system 
readily installable in existing cable television facilities with minimal 
modification. 
A further object of the invention is embodiment of components of such 
access control system in an outside junction between the cable and the 
lead to each subscriber's television receiver. 
Other objects of the present invention, together with means and methods of 
attaining the various objects will be apparent from the following 
description and the accompanying diagrams of a specific embodiment 
thereof, which is presented by way of example rather than limitation.

In general, the objects of the present invention are accomplished, by a 
system of withholding and alternatively providing to cable television 
subscribers access to programs transmitted over the cable, wherein such 
access is normally precluded by blocking the junction between the cable 
and the further pathway to any given subscriber's television receiver. It 
comprises recording program requests from identified subscribers, storing 
in a memory for each such program the identity of each subscriber 
requesting access thereto, retrieving from the memory preparatory to 
transmitting such program the identity of each subscriber having requested 
access to such program transmission, coding such requests in signal form 
and transmitting the resultant signal string via the cable to the 
junctions thereof with the further pathways to the respective subscribers' 
television receivers, detecting at each subscriber's junction whether the 
signal string contains a coded request by such subscriber for access to 
such program and, if so, unblocking the junction to enable such program to 
be transmitted therethrough and along the further pathway to such 
subscriber's television receiver. This method effectively defines secure 
programs. 
More particularly, the invention provides a method of providing, to 
requesting cable television subscribers, access to such secure program 
signals transmitted over the cable and via interconnections including tap 
offs and down leads to the subscriber's television receivers. It does so 
by generating a string of clocking pulses corresponding to serial 
numbering of all the subscribers, combining program command pulses with 
the clocking pulses corresponding to the respective requesting subscribers 
in the clocking string and thereby producing a program command signal 
string, transmitting the program command signal string via the cable to 
each of the subscribers' tap offs, and at each subscriber's tap off 
separating the command pulses from the clocking pulse string, generating a 
pulse characteristic of such subscriber's number clocked synchronously 
with the clocking pulse string, and utilizing each requesting subscriber's 
command pulse, in coincidence with that subscriber's characteristic pulse, 
to gate the requested program signals to that subscriber's television 
receiver. 
This invention, in apparatus embodiment of the foregoing system and method, 
features an interconnecting poach-resistant tap off, between the cable and 
the down lead to a subscriber's television receiver, comprising means for 
blocking program transmission from the cable to the down lead, means for 
inactivating the blocking means, and control means including 
signal-responsive structure identifiable with the given subscriber rather 
than any other subscriber and adapted to decode a correspondingly 
identified command pulse from a command pulse signal string transmitted 
from the station over the cable, the control means also including means 
responsive to such decoded command pulse and effective to inactivate the 
blocking means and thereby receive program transmission. 
FIG. 1 shows schematically apparatus components useful according to this 
invention, with those at or in the vicinity of a transmitter or central 
control station grouped at the left, with those at a subscriber's location 
grouped at the right, and with the cable extending therebetween, and to an 
intervening tap off junction. 
At the STATION LOCATION a RECORDER receives the subscriber's requests (from 
a TELEPHONE at the subscriber's location) each other subscriber also 
having telephone or other access to the recorder. A SEQUENTIAL PLAYBACK 
unit is located between the RECORDER and a MEMORY and is adapted, upon 
MANUAL COMMAND or a signal from the CONTROL UNIT to which the MEMORY is 
connected, to update the memory with identification of subscribers 
requesting program access and is adapted also to actuate automatic 
ACCOUNTING equipment so as to ensure that those subscribers are billed for 
the requested program. The CONTROL UNIT output is connected to the CABLE, 
as are the PAID CHANNEL(S) and any OTHER CHANNELS of program transmission. 
At the intervening SUBSCRIBER LOCATION a TAP OFF at the junction with the 
CABLE connects with a DOWN LEAD to the subscriber's TELEVISION RECEIVER. 
An AC POWER OUTLET supplies the TELEVISION RECEIVER and also a DC POWER 
SUPPLY (low voltage) connected to the DOWN LEAD to power the control 
circuitry in the TAP OFF, which has a RECEPTION INDICATOR associated 
therewith. A CHANNEL SELECTOR enables selection of one from among a 
plurality of secure PAID CHANNELS when present. Also here is the 
subscriber's TELEPHONE already mentioned as useful in transmitting program 
requests which alternatively might be delivered in person, by mail, etc., 
and recorded in like manner--or be sent via the TV cable in a compatible 
bilateral system. 
FIG. 2 shows much of the apparatus and interconnection indicated in the 
preceding view, some of it more pictorially and some of it in greater 
detail. A subscriber's telephone 10 is connected to switch 12, shown in 
operator position, further connected through a plurality of keysets 24-1 
to 24-N, with respective touch-tone keyboards 14-1 to 14-N for from 1 to N 
operators to use in recording any given subscriber's program request in 
one of corresponding set of recorders 20. Any suitable number may be used 
commensurate with the request load: designated here as RECORDER 20-1, 
RECORDER 20-2, RECORDER 20-3, ...RECORDER 20-N. In the alternative 
AUTOmatic position of switch 12 a subscriber's call so received is exposed 
to RECORDED SUBSCRIBER INSTRUCTIONS 22 prescribing the form and content of 
a request, which so given is routed through AUTOMATIC INTERFACE unit 21 to 
one of the recorders. The recorders' output is made available via 
Sequential Playback means 19, as at the instance of Manual Playback 
Command means 18, to the central control unit in FIG. 3. 
Cable 26 receives transmitted TV program via secure PAID CHANNEL(S) and 
OTHER CHANNELS through VHF AMP 25 and proceeds to the indicated 
subscriber's TAP OFF 28 at the junction with that subscriber's down lead 
27 to television receiver 5 (FIG. 2). Also connected to the down lead is 
low-voltage dc power lead 7 supplied by dc power supply 8 connected to an 
ac outlet, thereby energizing the TAP OFF via the down lead. Visual 
indicator 29 on the TAP OFF is provided to indicate secure program 
reception. The TAP OFF is provided with seal S as an indication of 
construction that cannot be opened without breaking the seal. The TAP OFF 
is shown on part of the cable suspended in the air as a further deterrent 
to tampering. Of course, if a cable is underground rather than above 
ground the tap off can be located in a locked pedestal, where it would be 
accessible only to authorized personnel. 
Channel selector 6 is useful in selecting from among a plurality of 
simultaneous secure paid programs whose transmission via a corresponding 
plurality of channels is unblocked to the television receiver. Such 
selection may be made by filter selection, by frequency conversion through 
action of a local oscillator, or through other appropriate action of the 
channel selector which is shown with five selection positions: A, B, C, D, 
and E. If only a single secure paid channel is unblocked, no selection 
action would be in order. 
FIG. 3 shows the CONTROL UNIT of FIG. 1, comprising circuitry such as is 
conveniently located at or in the vicinity of a cable television station 
or similar central location. Here there are a plurality of memory units 
30: designated as MEMORY 30-1, MEMORY 30-2, MEMORY 30-3, . . . MEMORY 
30-N. Each such memory can store the identification of subscribers 
requesting access to a given program, together with suitable indication of 
such request. Each such memory may be connected into the rest of the 
circuit by MEMORY SELECT COMMAND unit 47, and MEMORY 30-1 is shown so 
connected to receive DATA IN via INTERFACE AND DECODE unit 41 from the 
recorders via SEQUENTIAL PLAYBACK unit 19 shown in FIG. 2, and directed to 
the proper address(es) by the SELECT part of COUNT OR SELECT unit 42. 
These various components are subject to actuation by MANUAL KEY-IN unit 31 
connected as shown in FIGS. 2 and 3, which is also adapted to actuate the 
COUNT part of unit 42 so as to provide DATA OUT to switch 13 and 
therethrough to the rest of the CONTROL UNIT, shown here. Three-way switch 
13 is manually actuable by MANUAL ALL OPEN ALL CLOSE unit 32 and is shown 
set at its intermediate DATA OUT position between its leftmost (grounded) 
position and its rightmost (Vcc+) position, the consequences of which are 
described further hereinafter. 
It should be understood that each such memory is preferably of conventional 
random-access, single-bit per location type and that there are as many 
memories as there are secure programs that can be requested. Thus, if 
there are five such programs per day requestable up to thirty days in 
advance, a total of 150 memories would be required. Each memory has a 
separate and unique location therein corresponding to each subscriber in 
the set or roster of all subscribers, addressable in suitable manner by 
numerical designation, as by each subscriber's account number, for 
example. After a preliminary clearing routine (0's in each location), the 
memories are updated from time to time with the randomly received and 
recorded program requests, through the SELECT part of MEMORY SELECT 
COMMAND unit 47, and for any given memory (corresponding to a particular 
requested secure program) each requesting subscriber's location therein is 
addressed and a logical "1" stored as DATA IN. Thus, when the appropriate 
memory is scanned just before the scheduled time for transmission of a 
given secure program, via the COUNT part of COUNT OR SELECT unit 42 in 
serially addressing each subscriber's location therein in synchronism with 
the clocking pulses, each clocking pulse corresponding to a requesting 
subscriber is punctuated by a mark or command pulse, thereby converting 
the string of clocking pulses to a command pulse signal string. 
Consequences of such evidence that certain subscribers wish to receive the 
program are described more fully below. 
FIG. 4 shows graphically a half dozen signal waveforms or pulse strings, 
designated as a to f, present during operation of the CONTROL UNIT, shown 
in the last preceding view, at locations therein so indicated. Operation 
of that unit to provide an unblocking command for each subscriber who has 
requested (and has paid or is being billed for) a secure program is now 
described by reference to both FIGS. 3 and 4. 
Shortly before transmission of a given secure paid channel program begins, 
the corresponding memory (here MEMORY 30-1) is selected, as by keying in a 
memory code via MANUAL KEY-IN unit 31 through MEMORY SELECT COMMAND 47. 
The MANUAL KEY-IN unit also is useful for keying last minute request data 
via INTERFACE AND DECODE unit 41 directly into the memory, bypassing the 
recorders. SQUAREWAVE GENERATOR 35 provides waveform a, preferably at some 
medium audio frequency (e.g., 500 Hz.), which is inverted by inverter 36, 
and then clocks DIVIDE by 3 counter 37 so as to provide waveform b of 
period T at its Q output, which is fed to COUNTER 43. As indicated, 
counter 37 is negative edge triggered by the inverted signal and is 
clocked thereby in sychronism with the output of the square wave 
generator. BISTABLE unit 38, which is similarly triggered by the inverted 
signal has its Q output connected to reset R of counter 37 to synchronize 
it with the positive transition from that signal so that the counter will 
stabilize before its first useful negative transition input. Such input 
occurs when a logical zero is placed on the D terminal of the BISTABLE 
through START TRANSMISSION unit 33, which may be operated manually or 
automatically, as on a time basis. Signal waveform b now clocks COUNTER 
43, which in turn through the COUNT section of unit 42 addresses each 
location in the memory sequentially and determines whether at each 
subscriber location a program request has been stored, such as in the form 
of a logical "1". Those locations containing such a coded request produce 
an output pulse, two such pulses being shown on signal waveform c, 
corresponding to subscribers 71 and 74 where the first pulse shown in 
waveform b corresponds to subscriber 70 and the last pulse shown complete 
corresponds to subscriber 75. Signal waveform c is anded in AND gate 44 
with basic square waveform a, producing signal waveform d, which shows 
three pulses at each occurrence of the long pulse in c. Signal waveform d 
is ored with clocking waveform b in OR gate 45, giving split-phase mark 
composite waveform e in which the second or negative half of the clocking 
waveform corresponding to each of the requesting subscribers is punctuated 
by a shorter command pulse, whereupon e is properly designated in its 
entirety as a program command signal string. AND gate 46 receives both e 
and the Q output from BISTABLE 38, and functions as a switch, being opened 
when a logical "1" appears at such output to pass the program command 
signal string to MODULATOR unit 40 fed with a radio frequency carrier from 
RF OSCILLATOR unit 39. The RF waveform modulated with the program command 
signal string is amplified by RF AMPLIFIER unit 34 and then passes along 
cable 26 (to the junctions with the lead-ins to the respective 
subscriber's television receivers). As already indicated each subscriber 
has a tap off between the cable and the subscriber's down lead to the 
receiver, and the circuitry of such a tap off is shown in more detail in 
the next view. 
FIG. 5 shows TAP OFF 28 circuitry useful in accordance with this invention, 
and FIG. 6 shows graphically signal waveforms or pulse strings present 
during operation thereof. Operation of this unit to unblock program 
transmission (and to reblock it) to the television set of such subscriber, 
having requested it, is now described with reference to these last two 
views. 
The first component encountered in down lead 27 from the TAP OFF junction 
(after a dc blocking capacitor, unnumbered) is the SIGNAL TRF AMPLIFIER 
unit 58. The amplified output signal is fed to DEMODULATOR unit 59 which 
extracts command pulse signal string e' (shown after being squared up in 
SHAPER 62 and so designated to distinguish it from its original 
counterpart shown in FIG. 4), only a portion thereof being illustrated. 
The final component interconnecting with down lead 27 to the subscriber's 
television receiver (except for another unnumbered dc blocking capacitor) 
is NOTCH FILTER AND CONVERTER unit 60. When active a notch filter acts 
like the inverse of a bandpass filter, screening out a band of frequencies 
as by shunting them to ground; when the notch filter is deactivated or 
switched off, such band of frequencies will be transmitted by it. Between 
the DEMODULATOR and latter unit is the circuitry so depicted in FIG. 5, 
which functions as follows. 
Demodulated and shaped command pulse signal string e' is fed directly to 
inverter 63 and to AND gates 67 and 69. AND gate 67 also receives a 
stretched and inverted version produced by MONOSTABLE 68 (with a time 
constant of less than T/2, say 5T/12) from the negative excursions of e' 
after passage through capacitor 81. After inversion by inverter 65, the 
stretched waveform is combined with e' in AND gate 67 to recover a 
clocking counterpart b' (FIG. 6) of the original clocking string lacking 
program command pulses. This string is fed to the count terminal of ripple 
counter 82 and clocks it accordingly provided that a logical "0" appears 
at reset input R. This occurs on the first positive transition of signal 
e' applied through inverter 63 to MONOSTABLE unit 64, which is negative 
edge triggered and has a time constant greater than T (say, 3T/2) thus 
maintaining its logical "1" output so long as the signal is present. This 
output is inverted to inverter 66 and is applied to reset R input of the 
ripple counter, thus rendering the clocking input effective. 
Ripple counter 72 as shown has a capacity of ten bits and is specifically 
prewired to produce a logical "1" output from AND gate 84 when the count 
reaches "74" as the exemplified subscriber's serial identification. The 
wired Q outputs are anded in gate 84, and the wired Q outputs are anded in 
gate 83, whose output in turn is also applied to AND gate 84. The output 
of gate 84 is shown in FIG. 6 as signal waveform or single pulse h, which 
is anded with clocking pulse b' (from gate 67) in AND gate 85 to give a 
shorter pulse, i, delayed to the rise of the next clocking pulse and whose 
rising edge triggers BISTABLE unit 86, which transfers the logical state 
on D input of the BISTABLE to the Q output. 
AND gate 69 ands command pulse signal string e' with the signal from 
MONOSTABLE unit 68, whose time constant is short (e.g., 5T/12), resulting 
in signal waveform g containing only the requesting subscribers' command 
pulses, the clocking pulses having been eliminated. Applied to and 
stretched by MONOSTABLE unit 80, also with a short (e.g., 5T/12) time 
constant, this gives signal waveform j. Positive edge 34' of pulse 34 
shown at i and introduced at C will transfer a logical "1" (when present) 
from input D to output Q of BISTABLE unit 86, thus rendering the TAP OFF 
responsive only to this particular subscriber's command pulse rather than 
to any of the others in the command pulse signal string. 
The logical "1" now stable at output Q of the BISTABLE actuates NOTCH 
FILTER SWITCH 61, which in turn lights reception indicator 29 as well as 
(more importantly) deactivating the NOTCH FILTER, whereupon transmission 
of secure PAID CHANNEL(S) programs continues via down lead 27 to the 
subscriber's television receiver shown in previous views. 
Upon conclusion of program transmission the notch filters of all 
subscribers are readily reactivated to reblock secure program transmission 
from any of the down leads to the television receivers. The arm of switch 
13 (FIG. 3) is moved to the left, disconnecting it from DATA OUT of any 
memory and connecting it to ground, thereby grounding one of the inputs to 
AND gate 44. The output from that gate is then a logical "0" (regardless 
of the other input, which is original square wave a) and when ored with 
the DIVIDE BY 3 output in OR gate 45 provides the latter (i.e., the 
clocking pulse string free of command pulses) as output. This output is 
modulated transmitted over the cable, and demodulated at each subscriber's 
tap off, the result being that the signal j and input D of BISTABLE unit 
86 remain at logical "0" throughout the entire count and, as the count 
reaches each subscriber's number in turn, the rising edge (54') of pulse 
34 in signal waveform i transfers that logical "0" from D to output Q of 
BISTABLE 86, thus blocking further reception of secure programs by 
reactivating the NOTCH FILTER part of unit 60. Only about a minute or less 
is required to unblock the tap offs of subscribers having requested the 
next program transmission, as already described in detail. 
If it should become desirable to open all tap offs so as to transmit any 
given program (or group of programs ) to the television receivers of all 
subscribers, the arm of switch 13 is thrown to the right so as to provide 
a logical "1" as the upper input to AND gate 44, which has the original 
square wave as the lower input. The output from gate 44 ored with the 
DIVIDE BY 3 output then provides command pulse signal string e having a 
command pulse punctuating every clocking pulse. Accordingly, when each 
subscriber's prewired count is reached, the subscriber's notch filter will 
be deactivated. Upon conclusion of such free transmission further 
transmission may be blocked with switch 13 moved to the opposite position 
as already described. 
Designation of unit 60 as NOTCH FILTER AND CONVERTER indicates that the 
unit includes means, such as a frequency converter, whereby a paid channel 
can be shifted to appear on a channel to which the subscriber's receiver 
can be tuned in conventional manner. If a band of several different 
channels is controlled by the notch filter, such as up to five channels 
between 115 and 165 MHz, the subscriber may choose from among them by 
switching channel selector 6 to control selection means in the tap off, 
such as a voltage controlled oscillator (not separately shown). 
Alternatively, sequential stepping means (also not shown) similarly 
remotely activated by the subscriber could be employed with like result. 
Notwithstanding subscriber's control over selection from among unblocked 
channels it will be understood that the subscriber has no control whatever 
over unblocking of the transmission except by way of requesting it as 
first described. 
Such security of the access system of this invention is preserved in the 
face of possible electrical power intermittency or attempts by a 
subscriber to influence the tap off circuitry through manipulating the 
electrical power connection via plug 8 (FIG. 2). By ensuring application 
of a momentary logical "1" (after passage through inverter 87) at reset R 
of BISTABLE 86 (FIG. 5) the network of resistors 88 and 89 and capacitor 
90 in the power lead preclude the presence of an unblocking logical "1" at 
the Q output of the BISTABLE except as intended by way of a command pulse 
for the subscriber in the command pulse signal string sent over the cable 
from the control station at the head end of the cable. 
No unusual chemical composition or structural material is required in the 
practice of this invention, which can be carried out, as disclosed, with 
only conventional devices to realize high-security cable television access 
as desired. The beneficial results include dependability of operation with 
out undue complexity, and with ready applicability to existing cable 
television systems, assuring both broadcaster and subscriber of program 
security. 
It should be understood that the foregoing circuitry disclosure of modular 
components to carry out the objects of this invention is merely exemplary 
and that an appropriately programmed minicomputer could be substituted at 
the head end to provide all the required control functions, including 
generating the program command signal string, as will be apparent to 
persons skilled in the art. 
Other modifications may be made, as by adding, combining, or subdividing 
parts or steps or by substituting equivalents, while retaining advantages 
and benefits of the present invention, which itself is defined in the 
following claims.