Note: Descriptions are shown in the official language in which they were submitted.
1131~62
BACKGROUND OF THE INVENTION
This invention relates generally to security or
subscription television systems and more particularly, it
relates .to a method and system for encoding and decoding.
of standard television signals thereby-enabling reception
. thereof in an intelligible manner only by authorized
.subscribers.
Generally, there are known in the prior art
various types of secure subscription television sytems in
which television signals are transmitted in a coded form
for use only in subscribers' receivers having proper decod-
ing means. In these systems,.the coding is accomplished by
modifying the sound and/or video portions of the television
signals rendering them unintelligible or unpleasant to non-
subscribers or to subscribers who had not paid a fee to
the broadcaster.
In these proposed secure subscription television
systems, upon decodi.ng the modified television signals, it
was generally required that the precise modification signals
must be removed or any missing signals must be generated
and added to the modified television signals to produce a
restored video as similar as possible to its original quality.
Problems existed in these techniques due to the fact that
the quality of the picture was generally subject to degradation
and/or that difficulties were encountered in maintaining criti-
cal phase and other signal relationships in restoration.
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The effectiveness of the secure subscription
television systems is measured by the degree of success
which it has in deterring unauthorized viewers from
watching the modified television signals transmitted and
in preventing the duplication of the decoding means.
Ithas also been experienced that in general the
decoding technique utillzed in the prior art systems could
be easily duplicated by many resourceful viewers and thus
defeat the security thereof. It would, therefore, be
desirable to provide a method and system for encoding and
decoding television signals in which maximum security is
achieved and which will effectively deter unauthorized
viewers in attempting to defeat the security. Moreover,
it is needed to provide a system such that the theft
thereof will be of little use or value.
- In addition, the prior secure subscription
television systems have a disadvantage in that none of
them possess a positive and continuous control means for
controlling automatically the decoder at the various sub-
scriber stations whereby any or all of the decoders become
selectively disabled or "locked out" if it does not receive
the appropriate control signals from the broadcaster period-
ically before a pre-determined interval of time has elapsed.
Thus, it would be desirable to provide a method and system
for encodi'ng and decoding of standard television signals in
1~317~;2
which the decoder at the subscriber's station are dependent
continuously upon contro] signals transmitted by the broad-
caster. In the absence of the periodic control signals, the
decoder will automatically and rapidly become disabled
rendering it essentially useless without the necessity of
- physically traveling to the subscriber's location.
It would also be suitable to provide in connection
with a subscription television system means by which the
subscribers could select the programs desired in a short
time in advance of telecasting in a simple and easy manner.
To this end, telephone communication circuitry can be
provided so that the subscribers can request their programs
to the broadcaster via a telephone interface which will
transmit the subscriber's request to the broadcaster automa-
tically without any great effort on his part other than by
simply depressing a button at the subscriber's site. The
telephone interface would automatically dial the broadcaster's
telephone number, transmit the subscriber's unique account
code to a computer at the broadcaster's site, and thus make
possible the program selection by the subscriber at any time
prior to the broadcast. Further, this would allow the system
to be very reliable and substantially maintenance-free after
the initial installation since all the control signals are
done via over-the-air transmission and requests for service
are done electrically on the telephone interface. There is
eliminated the need to physically travel to the subscriber's
location during normal use so as to supply or retrieve coins,
cards, or tapes and the like for billing purposes as
encountered in some prior art systems.
I3 31762
SU~ARY OF THE INVENTION
Accordingly, it is an over-all objective of the
present invention to provide a new and novel method and
apparatus for encoding and decoding standard television
signals which possess very high security and deter un-
authorized viewers.
Another object of this invention is to provide
an improved method and apparatus for encoding and decoding
standard television signals which restores the scrambled
video and audio signals without degradation in picture
and sound qualities.
~ Another object of this invention is to provide
a method and apparatus for encoding and decoding standard
television signals wherein the scrambling is basically
accomplished by inversion of the video signals of some
horizontal scan lines on a pseudo-random basis to produce
a picture having some video signalsinverted and others not
inverted which is unpleasant to view and virtually unin-
telligible.
Still another object of this invention is to
provide a method and apparatus for encoding and decoding
standard television signals wherein a plurality of unique
pulse-coded control signals consisting of 32-bit binary
pulse trains are transmitted separately to identify individual
authorized subscribers and to provide the information needed
for unscrambling of the video and audio signals in the same
sequence as used for scrambling.
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Still another object of this invention is to
provide a method and apparatus for encoding and decoding
standard television signals wherein the audio scrambling
is accomplished by conversion of analog audio signals to
coded digital audio signals.
Still another object of this invention is to
provide a method and apparatus for encoding and decoding
standard television signals wherein control means continuous-
ly enable decoding means at the various subscriber stations
whereby any or all of the decoder means become selectively
disabled or "locked out" if it does not receive the appro-
priate control signals from the broadcaster periodically
before a pre-determined interval of time has elapsecl.
Yet still another object of this invention is to
provide a method and apparatus for encoding and decoding
standard television signals wherein telephone communication
circuitry allows tile subscribers to request their programs
to the broadcaster via a telephone interface.
Yet still another object of this invention is to
provide a method and apparatus for encoding and decoding
standard televisions signals having means for transmitting
aural barker signals simultaneously with scrambled video
signals and means for receiving the barker signals
regardless of whether the subscriber is authorized to receive
the unscramb]ed video signals so as to promote usage of the
subscription television system.
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In accordance with these aims and objectives,
the present invention is concerned with the provision of
an improved method and apparatus for encoding and decoding
standard television signals for over-the-air or cable
subscription television and the like, but avoids the
difficulties experienced in the prior art systems such a
necessity of critical phase relationship between signals,
degradation in the picture quality, and easy duplication
of the decoder means thereby defeating the security.
Briefly, the present invention provides a method
and system for encoding and decoding of standard television
signals thereby enabling reception thereof inan intelligi-
ble manner only by authorized subscribers. Thevideo scrambl-
ing is effected by inversion of the video signals of some
horizontal scan lines on a pseudo-randam basis to
produce a picture having some video signals inverted and
others not inverted which is unpleasant to view and
virtually unintelligible. The audio scrambling is
accomplished by conversion of analog audio signals to
coded digital audio signals. A plurality of unique pulse-
coded control signals consisting of 32-bit binary pulse
trains are transmitted separately to identify individual
authorized subscribers and to provide the information needed
to unscramble the scrambled audio and video signals. When
there is a comparison between one of the pulse-coded
control signals with a unique address code associated with
a particular subscriber, unscrambling of the video and audio
1~31'7~2
signals occurs in the same sequence as used for scrambling
to provide restored video and audio signals without degrada-
tion in picture and sound qualities. This scrambling technique
is done without affecting or altering the normal specification
for composite video, color and aural transmission or for
the broadcaster's transmitter utilized in the normal
telecasting.
It will. be appreciated from the foregoing that
the present invention provides a new and novel method and
apparatus for encoding and decoding s-tandard television
signals in subscription television systems. In particular,
since the invention utilizes control signals consisting of
32-bit binary pulse trains to identify the various authorized
subscribers each having a different code combination, it
provides a very high security system thereby preventing
unauthorized viewers from unscrambling of the video sig-
nals. Moreover, the audio signals are also scrambled
to increase the security of the systern and to deter most
unauthorized viewers by converting the analog audio signals
to coded digital audio signals. Additionally, the present
invention includes control means for continuously enabling
decoder means at the various subscriber stations whereby any
or all of these decoder means become selectively disabled
or "locked out" if it does not receive appropriate control
signals from the broadcaster periodically before a pre-
determined interval of time has elapsed.
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BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features and advantages
of the invention, as well as the invention itself, will
become more apparent to those skilled in the art from the
following detailed description when read in conjunction
with the accompanied drawings in which like reference
numerals indicate like or corresponding parts throughout
the several views wherein: .
Figure 1 is a simplified, over-all block diagram
of a subscription television system in accordance with the
present invention;
Figure 2 is a block diagram of a television
transmitter at the broadcaster site illustrating the means
for encoding or scrambling the ~tandard television signals,
embodying the present invention;
Figure 3 is a block diagram of a receiver at the
subscriber site for decoding or unscrambling the encoded,
television signals received from the transmitter shown in
Figure 2, according to the present invention;
Figure 4 is a,block diagram of telephone
communication circuitry for interconnection between the
transmitter and receiver, employing the novel methods
of the present invention;
: Figure 5 is a simplified block diagram depicting
circuitry suitable for use as the adder networks 80, 136 of
Figures 2 and 3;
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1~3:1~76~
Figure 6(a) is a time-amplitude graph of a
conventional, normal scanning line in a television signal;
Figure 6(b) is a graph similar to that shown in
Figure 6(a), in which some video signal portions have been
randomly inverted, according to the present invention;
Figure 7 is a spectral distribution of the signals
transmitted in the present invention;
Figure 8(a) is an example of a control signal
consisting of 32 bits, according to the present invention;
Figure 8(b) is an example of a digitized aural
signal consisting of 11 bits, employed in the present
invention;
Figure 9 is a schematic diagram showing circuitry
suitable for use as the shift register 122 of Figure 3;
Figure 10 is a more detailed schematic block
diagram showing circuitry suitable for use in certain of
the blocks of Figure 3;
Figure ll(a) is a schematic diagram il]ustrating
circuitry which may be employed in certain of the other
blocks of Figure 3;
Figure ll(b) is a schematic diagram illustrating
in more detail the circuitry which may be used as the
video switching amplifier 88;
Figure 12 is a schematic diagram showing circuitry
suitable for use as the shift register 152 of Figure 3;
Figure 13 is a block diagram depicting the
circuitry suitable for use as the blocks 146, 150 shown in
Figure 3;
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Figure 14 is a schematic diagram illustrating
circuitry which may be employed in certain of the blocks
of Figure 4;
Figure 15 is a schematic diagram illustrating
suitable circuitry for use as the gating circuit 176 of
Figure 4;
Figure 16 is a schematic diagram showing circuitry
suitable for use as the switches 156 of Figure 4;
Figure 17 is a schematic diagram illustrating
circuitry which may be employed to control the lights 180
and 186 of Figure 4; and
Figure 18 is a schematic block diagram illustrating
- circuitry which may be employed as the master clocks 66
and 130 shown in Figures 2 and 3.
DETAIL~D DESCRIPTION OF THE PREFERRED EMBODI~ENT
Referring now in detail to the drawings, Figure 1
illustrates a simplified, over-all block diagram of a sub-
; scription television system according to the present invention.
It should be understood that this system can be utilized in
various forms of television transmission and reception, in-
cluding over-the-air or cable television. Like reference numerals
have been employed throughout the various drawings to designate
like parts.
In Figure 1, the subscription television system
designated generally by reference numeral 10 consisting of
a transmitter section 12, a receiver section 14, and telephone
communication circuitry 16 located at the receiver section
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14 for communication with the transmitter section 12. A
central computer 18 is used to store information signals
identifying the various authorized subscribers and sends
out these information signals to a transmitter 20 for
transmission over-the-air via an-tenna 22. A synchronizing
(sync) generator 24 is connected to the computer 18 for
synchronizing the information signals sent from the computer
to the horizontal scanning rate used by a television program
source such as television camera 26. In order to prevent
unauthorized viewers from receiving the telecast, the
signals from the television camera 26 are processed by a
code converter 28 along with the same information signals
from the computer utilized to identify the authorized sub-
scribers, which modifies the signals in such a way to be
unintelligible to unauthorized subscribers. These signals
are then sent over-the-air via a transmitter 30 and antenna
32. Analog audio signals from a sound source such as
microphone 34 can also be processed or modified in the
converter 28 by sending the audio signals through an analog-
to-digital converter 31 to produce digitized audio signals.
The scrambled audio signals from the code converter 28 are
also transmitted via the transmitter 20 and antenna 22.
The scrambled television signals, the scrambled
audio signals and the information signals are received by
antenna 36. These signals are then delivered toan RF tuner
38 coupled to an intermediate frequency (IF) amplifier and
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detector 40 which detects the scrambled television signals
and to an RF tuner 42 coupled to an IF amplifier and detector
44 which detects the scrambled audio signals and the infox-
mation signals. The scrambled television signals are sent
to a code converted 52 for re-processing. The information
signals from the detector 44 are sent to a comparison circuit
46 to determine if one of the information signals matches
the unique address associated wi-th a particular subscriber
stored in read-only-memory 48. These same information signals
serve as control signals and are delivered to a code lock-
out circuit 50 as is the output of the comparison circuit
46. When there is a match, the comparison circuit 46
activates the circuit 50 to allow the control signals to
pass through to the code converter 52 which unscrambles the
television signals from the detector 40 and the scrambled
audio signals from the detector 44. The unscrambled television
signals are sent to a modulator 54 for converting the television
signals to a frequency corresponding an unused numbered
channel on a conventional television receiver 56. The
digitized audio signals from the code converter 52 are also
sent to the modulator 54 for transmission on the receiver
56 via a digital-to-analog converter 58 for converting the
digitized.audio signals -to the original analog audio sig-
nals.
Each subscriber can select the programs he wishes
to view by simply depressing switches or bu-ttons (not shown)
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1~3 11 ~762
associated with the telephone communication circuitry 16
located at the receiver section 14. The selections are
transmitted to the computer 18 directly by telephone lines
62. It should be apparent to those skilled in the art that
the present subscription television system can be easily
converted to conventional cable television systems by simply
replacing the antennas 22, 32 and 36 with an appropriate,
interconnected coaxial cable (not shown).
The transmitter section 12 shown in Figure 1 will
now be described in greater detail with reference to Figure.
2. The central computer 18 is utilized to generate randomly
a sequence of codes, each one representing a particular
account number or address of an individual subscriber. Each
of the codes is a pulse train of 32 bits, each OI the bits
being either high ("1" state) or low ("0" state), except
that the first bit is always made to be low and the last bit
is always made to be high so as to facilitate -the detection
; and synchronization by the circuitry in -the receiver section14. Thus, the number of different subscriber codes available
is 23 or 1,073,741,824 since this is the number of possible
combinations of thirty bits each of which can be either high
or low.
These codes are selected by the computer 18 such
that each of the eligible subscriber's code is transmitted
in a pre-determined sequence and is then repeated on a
continuous cycle thereafter. Each of -the 32-bit codes are
113~ ;2
addresses of the individual subscribers located in the
broadcaster's coverage area. When these transmitted codes
are reprocessed at the receiver station 14, it produces the
required information that it utilized to determine the code
used to encode or scramble both the aural and visual portions
of the broadcasted television program.
The broadcast of these 32-bit codes or encoded
signals is synchronized to the horizontal scanning rate
produced by the sync generator 24 as is conventionally
J0 used by the television camera 26 in the standard television
studio. The sync generator 24 provides a pulse pattern
at the rate of 15, 750 times per second (15,734 for color)
which corresponds to 525 horizontal scan lines in the visual
raster of a conventional television picture traced by an
electron beam of varying intensity from the top to the
bottom of the pic-ture in 1/30 of a second. The horizontal
sync pulse or signal output of the generator 24 is connected
via lead line 60 to the inputs of the television camera 26
and a monostable circuit (one-shot) 64. The monostable
circuit allows adjustment in the pulse wldth of the horizontal
sync signal, and its output controls a master clock 66
having pre-set frequency of 16.128 MHz (16.111 MHz for
color) and provides data request signals to the computer 18.
The output pulses from the master clock 66 are phase-locked
to the horizontal scanning rate. The vertical sync pulse or
signal output of the generator 24 is connected via lead line
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68 to an input of the television camera 26 and to monostable
circuit 70 in which the width of the vertical sync pulses
are adjusted and are used to provide interrupt request
signals to the computer 18.
The computer sends out randomly the various 32 -
bit binary subscriber codes on line 72 in a parallel manner
to a parallel-to-serial converter 74. Since a different
32-bit code is sent out by the computer 18 at the rate of
the horizontal scanning frequency of 15,750 times per second
as provided by the sync generator 24, this means that 945,000
individual subscribers can be selectively controlled to
unscramble the transmitted signals every minute. The
converter 74 transforms the codes from parallel into a serial
sequence for modulation of the transmitter 20 via a frequency
shift keying (FSK) FM modulator 76. These same 32-bit codes
of the various subscribers are also made available on line
78 and are processed into corresponding 4-bit codes or
words by an adder network 80. These 4-bit words contain
the information to be utilized in determining the encoding
or scrambling pattern of the video and sound portions of
the broadcasted signals. The details of the adder network
80 will be discussed more fully hereinafter.
The coded signals from the output of the adder
network 80 are coupled to datainput of a D-type gating
flip-flop for synchronization with the horizontal scanning
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rate which is connected to the clock input of the D-type
flip-flop via lead line 84. The output of the flip-flop
82 contains the encoded pattern which scrambles the visual
and aural portion of the televised signal via an active
line gate 86 and a gated video switching amplifier 88 and
an additional adder network 100, respectively. The
switching amplifier 88 consists actually of three separate
amplifiers, one being a non-inverting amplifier 90, a
second being an inverting amplifier 92 and a third ampli-
fier 9~ determining whether the output of the non-inverting
amplifier 90 or the inverting amplifier 92 is fed to its
input. (See Figure ll(b)). Since the active line gate 86
drives the switching amplifier 88, the output of the switch-
ing amplifier will be dependent upon the binary state of the
active line gate 86, which is either in the "1" (high) or
"0" (low) states. The line gate 86 is actuated only during
the portion of the televised signal that contains the actual
visual or picture portion and is de-activated during the
synchronization intervals. When the output of the line gate
86 is in the high state, the video portion of the televised
signal is sen-t through the non-inverting ampliier 90 and
the output of the switching amplifier 88 is not inverted.
However, when the output of the line gate 86 is in the low
state the video portion of the televised signal is inverted.
Since the output of the adder network 80 passed through the
active line gate 86 switches between the two binary states
113~762
on a pseudo-random basisJthis causes some of the video
signal portions at the output of the switching amplifier
88 to be positive and some to be negative, which creates
a mosaic quality in the picture. This scrambled picture
is very unpleasant and completely unintelligible to the
unauthorized viewers. The output of the switching amplifier
88 having the scrambled picture is coupled to an AM
modulator 96 for amplification and modulation. The output
of the modulator 96 is then sent to the transmitter 30
for broadcasting the scrambled picture via the antenna 32.
As is well-known, the original visual information
and the chrominance information originate in the television
camera 26 and a chromatic (color) sub-carrier generator or
phase modulator g8 respectively. As previously mentioned,
the horizontal and vertical syn~hronation signals sent to
the central computer 18 are also used to synchronize the
horizontal and vertical scanniny rate of the television
camera 26. A typical audiosource originating -the micro-
phone 3~ at the broadcaster's site or a similar audio
source such as a tape recorder, film chain, phonograpl~
record and the like is also encoded or scrambled so as to
increase the security of the system by first converting the
original aural signals (analog form) to digital pulse
trains each consisting of 11 bits via the analog-to-digital
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converter 31. Each of the bits are either high ("1" state)
or low ("0" state), but the first bits are always made to
be low and the last bits are always made to be high so as to
facilitate the detection and synchronization by the circuitry
5 in the receiver section 14. Then, these pulse trains of
the digitized aural signals are added binarily with the
4-bit binary outputs of the D-type flip-flop 82 resulting
from the adder network 80 via the additional adder network
100. These resultant ll-bit binaries are converted to
serial pulse trains by a shift register or parallel-to-
serial converter 102. These serial pulse trains are coupled
to a frequency shift keying FM modulator 104 for amplifica-
tion and modulation before being sent to the transmitter 20
and transmitting antenna 22 for broadcast.
In addition, a second audio source 106 can be
processed in an unscrambled form by an FM modulator 108
for transmission via the transmitter 30 and the transmitting
antenna 32. The second audio source 106 is referred to
as a "barker" source and canbe heard by all of the television
receivers. It is utilized for encouraging the viewers to
use the programming of the subscription television system
and is available for announcement and to promote marketing
of the subscription television programs to potential pur-
chasers or other suitable use.
A control terminal 110 is connected to the
computer 18 for con-trolling manually the enabling and
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disabling of various subscribers. A modem 112 is coupled
also to the computer 18 for transferring the program
requests from the various subscribers sent on the tele-
phone line 62 as will be explained in detail in connection
with the telephone communication circuitry 16.
The receiver section 14 shown in Figure 1 of the
drawings will now be discussed more fully with reference to
Figure 3. Each subscriber to the subscription television
system is provided with a housing or box-type enclosure ~not
shown) containing all of the receiver circuitry in the
receiver section 14 including the telephone communication
circuitry 16 for operative connection to his conventional
television receiver 56. The enclosure is typically placed
adjacent or on top of the subscriber's television rece1ver
The enclosure is interconnected between the subscriber's
receiving antenna terminal connections and the television
receiver 56. Power is supplied to the enclosure via a
120 VAC power input terminal located on the enclosure.
This enclosure is further connected to a telephone terminal
outlet (not shown) conventionally supplied by a local
telephone utility company for communication with the broad-
caster to request service of the programs desired via the
telephone communication circuity 16, as will be discussed
more fully later.
All of the transrnitted signals from the transmitting
antennas 22 and 32 and all of the other conventional, unscrambled
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television channel signals are received as incoming signals
on the receiving antenna 36. It should be recalled that the
transmitting antenna 22 is sending out two separate sets of
digitally excited frequency shift keying data signals,
namely, the digital control signals each having a pulse
train of 32-bits and the digital audio signals each having
a pulse train of ll-bits. The other transmit-ting antenna
32 is sendiny out the encoded or scrambled video signals,
the normal chrominance signals, and the "barker" audio
signals.
The incoming signals are now processed by splitting
them into three paths at an RF-splitter 114. One path drives
the RF tuner 38 coupled to the IF amplifier and detector 40
which extracts all of the scrambled video, normal chrominance,
and "barker" audio signals. A second path is processed by
the RF tuner 42 coupled to the IF amplifier and detector 44
for removing all of the digital audio signals and digital
control signals. A third path via lead line 116 is utilized
to receive the other unscrambled channel signals when the
subscription television system is not in use.
It will be apparent that in systems dealing with
scrambling and unscrambling of signals the methods used in
unscrambling are functionally complementary to the ones
used in the scrambling process, and that the unscrambling
and scrambling processes have -to be completely synchronized.
Thus, many of the circuit components that will be discussed
113~
hereinafter in the receiver sec-tion 14 are similar in
operation to those previously mentioned in the transmitt-
ing section 12.
The scrambled video signals from the output of
the detector 40 is connected to a gated video switching
amplifier 118 similar to the switching amplifier 88 for
unscrambling and restoration of the picture back to a normal
image. However, this can occur on]y if proper decoding
signals controlling an active line gate i20 similar to the
line gate 86 will cause inverting or non-inverting of the
video portions of the televised signals on a line for line
basis in exact correspondence to -the scrambling by the
active line gate 86. The reprocessing of the control
signals to generate the decoding signals will now be
~ explained in detail.
An output containing the control signals from the
detector 44 is sent to a serial-to-parallel converter or
shift register 122 and to a pulse de-tector 124. ,Since the
first bits of the incoming pulse train control signals are
always beginning with a low level, the pulse detector 124
is utilized to sense the shift from a high level to a low
level. When the shift is detected, the output of the
detector 124 drives a monostable circuit 126 (one-shot)
to synchronize the receiver circuitry with the transmitter
horizontal scanning rate of 1,570'Hz and also to permit
adjustment of the pulse width from the detector.
,
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Once the shift is detected, the monostable
circuit 126 initiates the counting of a divide-by-eight
counter 128 (. 8). The clock rate of the counter 128
is provided by a master clock 130 similar to the ciock 66
having a pre-set frequency of 16.128 MHz which is actually
16 times greater than the pulse rate of the incoming
control signals and is phase-locked to the horizontal
scanning rate of the transmitter section 12. Thus, after
eight clock pulses are counted, the middle of the first bit
or pulse of a 32-bit incoming control pulse train will be
at the input of the shift register 122. At this point,
a transfer pulse will be generated to shift the first bit
into the shift register 122 for storage.
The output of the counter 128 is coupled to a
divide-by-16 counter I32 (- 16), which is in turn connected
to a divide-by-32 counter 134 ( 32). Subsequent to the
storage of the flrst bit, the counter 128 is stopped and
the counter 132 is activated to count so that 16 pulses
later, the shift register 122 will have at its input the
middle portion of the second bit of the 32-bit pulse train.
Once again, a transfer pulse will be generated to shift now
the second bit into the shift register 122 for storage. The
first bit previously stored will be shifted serially down the
shift register. This process is repeated thirty more times
and as a result will cause all 32-bits to be stored in the
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shift register 122. When the thirty-secondth pulse is
stored, all of the counters 128, 132 and 134 are reset
and made ready for the next control signal. Thus, the serial
control pulse trains each of a full 32-bits will become
stored in the shift register and is made available as
parallel sets of 32 data bits (see Figure 9).
The 32-bits of the shift register 122 are taken
out to an adder network 136 which converts the 32-bits
down to a 4-bit unscrambling code. Thé adder network 136
is identical in operation to the adder network 80 in the
transmitter section 12 and produces the 4-bit unscrambling
code identical to the 4-bit scrambling code used to
scramble the video and aural portion of the originally
transmitted signals. A simplified block diagram of the
adder networks 80 and 136 are illustrated in Figure 5 and
is comprised of seven full binary adder circuits 138 inter-
connected as shown. However, it should be understood that
the 32-bit input lines can be interchanged by their bit
locations on a pre-determined basis to provide increased
security in the system. Thus, this produces the 4-bit
codes at the output of the adder network 136 in a pseudo-
random scrambling pattern.
A D-type clockingflip flop 140 is connected to
the output of the adder network 136 for holding the 4-bit
pattern for the duration of the next horizontal scanning line
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1~3~76;~
in order to decode that scanning line and all of the audio
signals received during that same interval. The flip-flop
140 drives the active line gate 120 for controlling the
switching amplifier 118 to switch its inputs between the
inverted and non-inverted inputs in the same sequence
as the encoding operation by the switching amplifier 88.
In this manner, the horizontal scanning lines at the
transmitter section 12 are reproduced at the receiver
section 14 so that the received video signals will become
restored to the original unscrambled picture.
However, this restoration process is permitted
to occur only if one of the plurality of 32-bit control
signals generated on a pseudo-random basis by the central
computer 18 and transmitted via the antenna 22 is matched
perfectly (bi-t for bit) with a unique 32-bit code assigned
to a particular subscriber's television receiver 56 which
is stored in the read-only-memory (ROM) 48. The transmitted
incoming control signals at the output of the dectector 44
are compared by a comparator 142 with the unique contents
of -the ROM 48. The content of the ROM 48 is synchronized
with the incoming control signals by the counter 134.
If the comparison is unsuccessful, the 4-bit
code in the D-type flip-flop 140 is prevented to be clocked
to the active line gate 120 controlling the switching
amplifier 118 to unscramble the video signals. On the
other hand, if there is a successful match between one of
'.,
~3~6;~
the control signals and the ROM 48 of the particular sub-
scriber, then a flip-flop 144 is set and gates a decode-
enable flip-flop 146 which permits the output signals of the
monostable circult 126 to be sent as clock pulses and set
at the horizontal scanning rate to the D-type flip-flop
140. Unless the clock pulses of the monostable circuit
126 via lead line 148 are passed through the decode-enable
flip-flop 146, the D-type flip-flop 140 will not be activated.
~pon a comparison, the output of the flip-flop
144 also resets a three~minute timeout timer 150 to zero.
When the timer 150 reaches the three-minute mark, it will
cause the decode-enable flip-flop 146 to be reset thereby
stopping the decoding process as the clock pulses to the
D-type flip-flop 140 will be blocked by the flip-flop
146. Thus, continuous decoding is possible and uninterrupted,
restored video and aural signals are available to the
subscriber only if the comparator 142 causes the flip-flop
144 to reset the three-minute timer 150 at least once every
three minutes.
A second output containing the digitized aural
signals from the detector 44 is sent to a serial-to-
parallel converter or shift register 152 to convert the
signals to parallel digital binary form. A subtractor
circuit 154 combines the 4-bit unscrambling codes from the
D-type flip-flop 140 with the encoded digitized aural signals.
76%
The subtractor circuit 154 operates similar to the adder
networks 80 and 136, except that it is actually using
2's complement addition in order to realize unscrambled
digitized aural signals corresponding to the ones at
the output of the analog-to-digital converter 31 in the
transmitter section 12. The output of the subtractor
circuit is connected to the digital-to-analog converter
58 to produce analog signals identical in form to the
original audio signals generated by the source 34 at
the broadcaster's site. Thus, it can be seen that decod-
ing of the aural signals is also dependent upon the D type
flip-flop 140.
The restored video signals at the output of
the switching amplifier 118 and the restored audio signals
at the output of the digital-to-analog converter 58 are
fed into the modulator 54 which converts these signals
to a desired locally unused VHF channel (2-13) as the
secured channel. Typically, channel 3 or 6 can be a
suitable choice. These signals are combined with all of
the other unscrambled television channels received by
the antenna 36 via RF combiner circuit 155. This allows
view of all the channels on the television receiver 56
including the secured channel, and selection of the particular
channel is achieved merely by turning a channel selector
dial (not shown) on the television receiver 56.
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~ '
~3~f 6~
The telephone communication circuitry 16 shown
in Figure 1 of the drawings will now be described in greater
detail with reference to Figure 4. Each subscriber can
select the particu~ar televised program he desires to
recieve by depressing one of a plurality of buttons or
switches 156. It should be understood that any desired
number of buttons or switches can be utilized and connected
to perform various functions. For example, some buttons
can be used to select the particular programs to be viewed
at a desired time while others can be used to cancel or
correct errors in the program request. Once a button
associated with a particular program is depressed, this
selection is transmitted on the telephone lines 62 to a
local telephone company's central office (not shown). In
a large metropolitan area, the central office would then
communicate with another central office which, in turn,
relays the program requests to the computer 18 at the
broadcaster's site via the telephone lines 62 and the
modem 1~12 (modulator-demodulator). This communication
process will now be discussed more fully.
When a subscriber wishes to receive a particular
program, he simply depresses the appropriate button 156
which activates a sequence control network 158 to energize
a hook-switch relay 160 allowing an"off-hook" or "on-line"
condition with the local central office. ~hen a dial tone
is placed on the telephone lines 62 by -the central office,
-29-
dial tone detector or filter 162 causes the sequence control
network 158 to transmit dial address stored in binary form
in a read-only-memory (ROM) 164. This ROM 164 is similar
to the ROM 48 in the recelver section 1~ and in fact, can
be the same one. There are two methods of dial addressing
which are available. First, a multi-frequency tone generator
166 can be used to transmit a designated telephone number
employed by the broadcaster to receive automatic telephone
requests~ The tone generator 166 is known generally by
the trademark "Touch-Tone". Alternatively, a programmable
divide-by-n counter 168 can be provided to in-terrupt current
flow in the relay 160 to dial the designated telephone number.
This latter method is known as the dial pulse method of
dial addressing wherein the number of contact closure interru~-
tions are varied as with a corresponding number on a rotary
dial. A row/column decode 170 converts the dial address from
the ROM 164 either into row and column numbered pairs for the
tone generator 166 or into 2's complements for loading into
the programmable divide-by-n counter 168 for pulse method
dialing via an interface buffer 172 and the hook-switch relay 160.
Once the dialing process is completed, the sequence
control network 158 is arrested and awaits a carrier tone
generated by the modem circuitry 112 at the broadcaster's
site. When filter 174 detects the presence of the carrier
tone, it causes the sequence control network 158 to address
the ROM 164 storing the particular subscriber's code consisting
-30-
~ 317~%
of 32-bits and to send them out in a parallel sequence of four
eight-bit words. A gating circuit 176 is coupled to the
output of the ROM 164 and groups the four words for activat-
ing a voltage-to-frequency converter 178 to generate fre-
quency shift keying modem tones which contain the sub-
scriber's unique address or account code. Subsequent thereto,
the subscriber's request code indicating which of the buttons
156 he has depressed is transmitted via the gating circuit
176 and the converter 178.
After the request code has been transmi-tted, the
sequence control network 158 stops the gating circuit
176 and then awaits for an acknowledgment tone from the
- modem circuitry 112 at the transmitter section 12. When
the acknowledgment tone is detected by acknowledgment tone
filter 175, the sequence control network 158 is disconnected
from the telephone lines 62 by the de-energization of the relay
160 and lights an acknowledgment light 180 for 15 seconds.
While only one acknowledgment light is illustrated, it should
be clear that any number could be provided to indicate which
button corresponding to a particular request was depressed.
However, if no dial tone, carrier tone, or acknowledgment tone
is detected or if any part of the dialing sequence is tied
up beyond a pre-determined time interval, a time-out timer
182 having its input clock pulses set at the horizontal
scanning ra-te via lead line 184 interconnected with lead line
184' (Fig. 3) will reset the sequence control network 158
and activates a faul-t ligh-t 186 for 15 seconds.
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1~3~7~
An lsolatlon transformer 188 is utilized to pro-
tect the telephone communication circuitry 16 and isolates
it from telephone circuits in the local central office.
A holding current coil 190 draws current from the telephone
circuits when the hook-switch relay 160 is closed for causing
the "off-hook" condition to be detected at the local telephone
company's central office which will respond with a dial
tone. It should also be apparent to those skilled in the
art that the account code and request code of the various
subscribers may be placed on storage devices (not shown)
such as disk drives and magnetic tapes for use by the
central computer 18 to generate the account codes of the
various authorized subscribers thereby permitting the
subscribers to view the transmitted scrambled video
and/or audio signals.
Figure 6(a) illustrates the time-amplitude
relationship of a conventional, normal scanning line which
includes the composite video and synchronization signals.
In Figure 6(b), there is shown an example of the transmitted
scrambled video signal of the present inven-tion wherein
certain video portions of the hori`zontal scan line have
been randomly inverted.
Figure 7 shows a spectral distribution in terms
of relative maximum radiated field strength of the signals
transmitted in the present invention verses the frequency
relative to the lowest channel. In particular, the graphical
-32-
~3~6Z
representation of Figure 7 illustrates in the left-hand
half the 6 MHz frequency allocation of a standard television
channel as defined by the F. C. C. As is well known, the
picture or visual carrier signal, the chromatic suhcarrier
frequency, and the center of the barker aural frequency are
located at approximately 1.25 MHz, 4.83 MHz, and 5.75 MHz,
respectively, above the lower frequency end of the television
channel. The right-hand half of Figure 7 depicts the
control signal center frequency and the digital aural fre-
quency which are located respectively at approximately
9 MHz and 11.25 MHz.
Figure 8(a) shows an example of one of the plurality
of unique pulse-coded control signals consisting of a 32-bit
binary pulse train which are transmitted separately by the
broadcaster to identify individual authorized subscribers and
to provide the information needed for unscrambling of the
video and audio signals in the same sequence as used for
scrambling. Figure 8(b) is an example of the scrambled
or coded audio signals, i.e., digitized audio consisting of
a ll-bit pulse train for increasing the security of the
system.
While the various blocks shown in Figures 1 through
4 may take on various forms, suitable circuitry therefor are
illustrated in Figures 9 through 18. Although these schematic
diagrams are believed to be self-explanatory to those skilled
1~3~Z
in the art in view of the foregoing discussion, a brief
description of the operation of each figure is believed to
be in order.
The synchronization of the entire system is
controlled by the master clock 66 of Figure 2, which is
shown in more detail on Figure 18. The master clock 66
consists of a voltage-controlled oscillator 192 having a
capacitor 194 and an input voltage + V. The output of
the voltage-controlled oscillator is fed into an inverter
196 whose output is set at a frequency of 16.128 MHz.
The output of the inverter 196 is fed to all places re-
quiring this frequency output and to a counter 198 (~ by
1024). The frequency at the output of the counter l9B
designated by the lead line 200 is 15,750 Elz which is
delivered to one input of a phase-lock circuit 202. The
other input of the phase-lock circuit 202 designated by
lead line 204 is the horizontal sync pulse from -the
generator 24 (Figure 2). Thus, the voltage output of the
phase-lock circuit 202 on lead line 206 varies via lead line
205 until vvltage-controlled oscillator 192 is phase-locked
to the horizontal scanning rate.
Referring now to Figure 9 of the drawings, there
is shown.in more detail the circuitry of the shift register
122 of Figure 3. The output containing the control signals
from the detector 44 on lead line 208 (Figure 3) is connected
to the lead line 208'. The shift register is composed of a
113~L~6Z
plurality of J-K flip-flops 210 connected serially and a
plurality of inverters 212. The output of the flip-flops
210 labeled 2-231 are connected to the corresponding
inputs of the full adders 138 on Figure 5. In order to
shift the full 32-bits of the control pulse trains into
the flip-flops 210, the transfer pulse is delivered on the
lead line 214 which is connected to the lead line 214' in
Figure 10. The control signals on the line 208' are also
sent via.line 216 which is connected to the lead line
216' on Figure 10 for reception by the pulse de-tector
124. The output of the pulse detector on its lead line 218
is utilized to reset the counters 128, 132 and 134. These
counters are formed by ten J-K flip-flops 220. The clock
input to the counter 128 is on lead line 222 which is connected
to the 16.128 MHz output of Figure 18.
~s will be recalled, the clock frequency is
actually 16 times greater than the pulse rate oE the incoming
control signals. Therefore, after eight clock pulses are counted
the middle of the first bit of the 32-bit incoming pulse
train will be at the input of the flip-flop 210 designated
by lead line 224. However, in practice it has been encountered
that only four clock pulses need to be counted so as to be
in the middle of the first bit. The reason is because of
propagation delays and other inherent delays associated
with electronic circuitry. Thus, a NAND gate 226 is inter-
connected so as to generate a transfer pulse on its lead line
-35-
~317~2
214' after the fourth clock pulse and each sixteen pulses
thereafter. In this manner, the entire 32-bits of the serial
control pulse train is transferred into the flip-flops 210
of Figure 9.
Prior to the transfer of each bit, a comparision
of such bit is being made with one corresponding bit of
the unique 32-bit code stored in the read-only-memory 48
bythe cornparator 142. The output of the comparator is
coupled to the flip-flop 144 whose output is connected to
an input of NAND gate 228. When there is a comparison,
the output of NAND gate 228 on its lead line 230 gates the
decode-and-enable flip-flop 146, which is shown in more de-
tail on Figure 13.
The last J-K flip-flop 232 and the NAND gates 234
in the counter 134 are used to reset all of the counters 128,
132 and 134 after the last pulse or thirty-secondth pulse of
the 32-bit control pulse train. Then, the counters are
ready to sample and compare the next con-trol pulse train.
In Figure ll(a), there is shown in more detail the
circuitry of the blocks 120j 118 and 140 in Figure 3 of
the drawings. The NAND gate 236 has its one input designated
by lead line 238 connected to the output of the decode-and-
enable flip-flop 146 designated by lead line 238' (Figure 13).
The other input to the NAND gate 236 designated by lead line
240 is coupled to the clock rate of 15,750 Hz. The output
of the NAND gate 236 is connected to one input of the active-
-36-
L76Z
line gate 120 and to the clock input of the D-type flip-
flops 242. The other inputs designated by lead lines 244
through 250 are connected to the output of the adder net-
work 136 shown in Figure 5 and designated by 2 through
23. The output of the D-type flip-flop 140 is connected
to the subcontractor circuit 154. The other input to the
subtractor circuit is the digitized aural signals from
the output of the shift register 152 Oll the lead lines 252.
The output of the subtractor circuit 154-is coupled to the
input of the digital-to-analog converter 58 whose output
on lead line 254 is connected to one input of the modulator
54.
The other input to the active-line gate 120 on its
lead line 256 is from the 16.128 MHz output of the master clock
on Figure 18. The active line gate includes ten J-K flip-
flops 258 which are connected in a serial manner. As pre-
viously discussed, the active-line gate 120 will keep the
video switching amplifier 118 in the ron-inverting condition,
except during the active portion of the horizontal scanning
line. The output of the active line gate from NAND gate 260 is
connected to amplifier 117 bf the video switching amplifier
118. The other input to the amplifier 118 on its lead line
262 is from the output of the IF amplifier and detector 40
containing the scrambled video signals. The output of the
amplifier 118 designated by lead line 264 is connected to
the other input of the modulator 54.
1~31762
In Figure 12, there is shown in more detail
the circuitry of the shift register 152 of Figure 3. The
output containing the digitized aural signals from the
detector 44 on lead line 266 (Figure 3) is connected to
the lead line 266'. The shift register is composed of
a plurality of J-K flip-flops 268 connected serially.
The output of the flip-flops 268 labeled 2-21 are
connected to the inputs of the subtractor circuit 154 on
the lead lines 252 (Figure 11). In order.to shift the full
ll-bits of the digitized aural signals in-to the flip-flops
268, the transfer pulse is delivered on the lead line 270
connected to the output of NAND gate 272. The shift register
includes counters 274, 276, and 278. The counter 274 is
a divide-by-eight (. by 8) counter having its clock input
coupled to the aural clock rate output in Figure 13 via
lead line 280. In actual practice, it can be seen that the
NAND gate 272 is interconnected so as to genera-te a transfer
pulse after the fourth clock pulse and each sixteen pulses
thereafter. This is because only four clock pulses are
needed to be counted due to propogation delays in electronic
circuitry hefore the middle of the first bit of the ll-bit
digitized aural signals is at the input of the flip-flop 268
designated by lead line 282. In this manner, the entire ll-bits
of the aural signal is transferred into the flip-flops 268.
All of the counters 274, 276 and 278 are formed
from a plurality of J-K flip-flops 284. The counter 276 is
1~3iL76Z
connected to the counter 274 so as to form a divide-by-
sixteen ( by 16) counter. The counter 278 is inter-
connected with the NAND gate 286 so as to form a divide-
by-ll counter so that all of the counters are reset by the
NAND gate 286 after the last pulse or llth-bit of the
digitized aural signal has been conducted.
Figure 13, there is shown a divide-by-N counter
288 having the various clock rate ou-tputs. The input to
the counter 288 designated by lead line 290 is from the
output of the counter 198 on its lead line 290' in Figure
18. The three-minute output from the counter 288 is used
to reset the decode-and-able flip-flop 146 after three
minutes of time has elapsed to stop further decoding by the
D-type flip-flop 140 unless there is a comparison between
one of the control signals with the unique address of the
read-only-memory 48 prior to that time. The 30-second output
from the counter 288 is connected to the lead line 184
tied to the input of the time-out timer 182 in Figure 4.
The output labeled "clock-rate 217" is connected to the lead
line 294 in Figure 14, and the output labeled "clock-rate 213"
is connected to the lead line 296 in Figure 14.
In Figures 14-17, there is shown in more detail
suitable circuitry which may be used for the telephone
communication circuitry shown in Figure 4 of the drawings.
In Figure 16, there is shown seven buttons or switches 298
for generating the program request code signals at the outputs
-39-
1~3~762
of the NAND gates 300. The output of the NAND gate 302
designated by lead line 304 is connected to the lead
304' on Figure 14 to initiate the telephone dial up
sequence. The lead line 306 is used to control the tele-
phone request code which is connected to lead line 306'
on Figure lg, and the lead line 308 is used to reset
the telephone request code which is connected to lead line
308' also on Figure 14.
In Figure 15, there is shown in details of the
gating circuit 176 composed of a plurality of J-K flip-
flops 310 and NAND gates 312 and 314. The input to the
NAND gates 312 are from the read-only-memory 48 and the
program request code signals from the NAND gate 300.
The transfer of data into the gating circuit is con-
trolled by the lead line 316 which is connected to the
lead line 316' on Figure 14. The output of the gating
circuit is designated by lead line 318 which is connected
to the input of the voltage-to-frequency converter 178.
In Figure 14, there is shown the details of the
sequence control network 158 and the programmable counter
168. The sequence control network includes J-K flip-flops
324. Each of the outputs of the flip-flops is connected
to the read-only-memory 48 and the NAND gate 322 of the
counter 168.
In Figure 17, there is shown a typical light
driver circuit for lightlng the light 180 to indicate a
fault and to light the light 186 to indicate receipt of the
acknowledgement tone. Illumination of either light 180 or
186 is for fifteen seconds as controlled by lead line 181
(15 sec. output) which is connected to lead line 181'
on Figure 13. While there has only been one such circuit
--~o--
~3~iZ
shown, it should be understood that seven are used in this
example to correspond to the number of switches 298.
It will be understood from the foregoing
description that the presen-t invention significantly advances
the state of the art of coding and decoding of standard
television signals which allows the reception thereof in
an intelligible manner only by authorized subscribers.
In particular, the scrambling of the video signals in the
invention is effected by inversion of thé video signals
of some horizontal scan lines on a pseudo-random basis to
produce a plcture having some video signals inverted and
others not lnverted. The scrambling of the audio signals
is effected by conversion of analog audio signals to coded
digital audio signals. Telephone communications circuitry can
also be provided so that the subscribers can request their
programs to the broadcaster via a telephone lnterface.
Whi]e there has been illustrated and described
what is at present to be a preferred embodiment of the
present invention, it will be understood by those skilled
in the art that various changes and modifications may be made
and equivalence may be substituted for elements thereof
, without departing from the true scope of the invention.
In addition, many modifications may be made to adapt a
particular situation or material to the teachings of the
invention without departing from the central scope thereof.
Therefore, it is intended that this invention not be limited
-41-
1~31'76~
to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the
scope of the appended claims.
