Note: Descriptions are shown in the official language in which they were submitted.
~L22~38~;
METHOD AND APPARATUS FOR SUBSCRIPTION BROADCAST
Technical Field
The invention relates to the distribution of
signals, particularly radio or television signals, in such
a way that there is control over their use, such as is the
case for so-called "pay television."
While commercially broadcast television signals
have generally been available to whomever wishes to receive
them, there are other signals which are made available only
to members of a restricted subscriber group. Sometimes the
subscriber has a choice of ordering or not ordering a
particular signal for a given time period. If he does
order and he receives it, he becomes a "user."
although there may be a number of variations in
systems for distributing a signal on a per program basis,
the following description applies to a typical system. The
program signal is generated by a program "producer" entity
and transferred to a distributor, which offers it to
subscribers via cable on an order basis. The program
signal is enciphered. Control of its use is afforded by
controlling the availability of a key for its deciphering.
The subscriber is supplied with a subscriber unit which
incorporates the deciphering equipment and deciphers the
signal of a selected channel for the receiving equipment.
The subscriber unit may also require the delivery of
deciphering key information before it can perform the
deciphering.
The ordering of the program signal by a subscriber
may be on an annual, monthly or shorter term basis. It may
also be on a "per program" basis. A control unit at a
remote location can supply the subscriber unit with a
deciphering key for specific ordered programs. Sustains of
this type are described, for example, in the following
35 U So patents
4~008~369 issued February 15~ 1977 to
D. L. Thrower et at. U. 5. C. 358/8 l lo
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- 4,115,807 issued September 19, 1978 to
H. G. Pines U. S. Of. 358/122
4~325,078 issued April 13, 1982 to
J. C. Sexton et at. U. S. Of. 358/117
4,358,201 issued October 12, 1982 to
C. Socket et at. U. S. Class 358/122
4,369,462 issued January 18, 1983 to
S. A. Tummies et at. U. S. Class 3~8~4
The collection of user statistics, i.e. the number
of orders for a program and the identities or the orderers
for billing purposes, presents some difficulties with
present subscriber systems. If the billing }5 not done
frequently enough, the number of uncollectible subscriber
accounts may become unacceptably high. On the other hand,
if the billing is done too often, the cost of mailing the
bills becomes excessive. For billing and other purposes,
it would be desirable to have an indication of the actual
number of users for a given program.
Signal theft is another difficulty with present
subscriber systems. It is often possible for either
subscribers who have not ordered a program signal or for
nonsubscribers with access to the enciphered signal to find
a way to decipher the signal independently or to
fraudulently cause the control unit to supply the
US deciphering key to the subscriber unit. This cannot
normally be detected and is at the present time thought to
be a relatively wide-spread and persistent problem.
- Another problem with present per program
subscriber systems is their inability to provide the
program producers with an independent means of measuring
the audience sizes for those programs in which they have a
financial interest.
The final, and perhaps most significant problem
with per program ordering systems is that arising from
impulse buying. It appears to be in the human nature of
subscribers to decide shortly before a program offering to
order the program signal. This is likely to completely
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overwhelm the equipment for accepting and recording program
orders where the offered program is of great interest to a
large number of subscribers. The capacity of the order-
taking equipment then becomes a constraint on the sales of
the program signal.
Summary of the Invention
In accordance with the novel method and apparatus
of the present invention, a program signal desired by a
subscriber is automatically ordered by a subscriber unit
lo which has received an order command as a result of the
subscriber operating an order switch on the unit. The
ordering is done over a telephone line. In response to
the order, the subscriber unit receives key deciphering
information over the same telephone line and stores it in
a memory. The ordered enciphered program signal carries
with it auxiliary signals including a control signal which
activates the deciphering means in the unit to use the key
information for deciphering the signal for the duration of
the program. The subscriber unit in accordance with the
invention includes means for automatically placing a
program order over a telephone line and means for storing
deciphering key information received over the telephone
line in response to the order. It also includes means
responsive to control signals accompanying a program
signal for activating the means for deciphering the program
signal. The unit may further be provided with a display
for other information which is supplied with the key
information or by the auxiliary signal.
In accordance with an aspect of the invention
there is provided electronic apparatus of the type
comprising: means for receiving a program signal in an
enciphered form from a signal carrier; means requiring a
deciphering key for selectively deciphering the program
signal and sending it to a receiver instrument r and means
for controlling the activation of the deciphering means;
~L2Z~3~3~
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wherein the improvement comprises: means externally
operable for receiving a program order; means for storing
the program order; means connected to a telephone line for
automatically calling an order to a service number in
response to the program order, and means for automatically
receiving and storing deciphering information delivered
through the telephone line in response to the order calling
for the program to permit the activating means to initiate
deciphering, said activating means being responsive to
control signals delivered with said program signals.
In accordance with another aspect of the
invention there is provided a method of controlling the
deciphering of an enciphered signal, comprising: receiving
an order call from a subscriber unit via a telephone line,
and responding thereto by sending back on that line the
deciphering key information for storage in that unit
without requiring the subscriber unit to identify itself.
Brief Description of the Drawings
FIG. 1 is a partially pictorial flow chart
illustrating the interaction of various elements of a per
program subscription system in accordance with a preferred
embodiment of the present invention.
FIG. 2 is a front, elevation Al, perspective view
of one embodiment of a subscriber unit of the system of
FIG. 1 for deciphering the program signal for use by
receiver equipment with which it is associated.
TV
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FIG. 3 is a rear, elevation Al perspective view of
the subscriber unit of FIG. 2.
FIG. 4 is a schematic graphical representation of
the information content of a deciphering key which is
transmitted to the subscriber unit ox Figs 1-3 in response
to an order.
FIG. 5 is an exaggerated graphical representation
of the frequencies of orders placed as compared to the
orders served for program signals of the system of FIG. 1.
FIG. 6 is a functional block circuit diagram of
the subscriber unit of Figs 2 and 3.
Detailed Description
One example of a system in accordance with the
present invention is the per program television
subscription system 10 shown in FIG. 1 of the drawings. In
the system 10, a program producer 12, a TV network 14, a
broadcast station 16, and a program signal deciphering and
control subscriber unit 18 are all interconnected by means
of a telecommunications network 20. The telecommunications
network 20 features an announcement distribution system 21,
a feature which is now commonly identified as a "900
Service" because at the present time in the United States
any access to the service is most likely to require dialing
"900" as the first three digits of the telephone number
which is identified with the particular announcement
service in question. The announcement distribution system
21 is controlled by a stored program control system 22~
The apparatus required for providing such a service in a
telephone network, as well as the details of its
operation, are well known in the art of telephony and are
described, for example, in the Bell System Technical
Journal, July-August 1981, Vol. 60, no. 6, part 2. on
announcement distribution system of this type has the
capability ox accepting a large number of incoming order
calls for various announcement services and automatically
responding to the individual calls with a predetermined
message.
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In current "900 Service" applications, it is most
frequently the case that the message to be delivered to the
callers is not stored in any equipment of the telephone
company, but rather is provided directly from the premises
of the message creator. The telephone company equipment
rather creates as many copies of the message signal as are
needed to satisfy the instant number of callers who wish to
receive the message. By virtue of this direct 1-to-N
message delivery system, the message creator has complete
control over the message signal and can, for example,
supply repetitions of a brief message or a continuous live
program. This message may be in the form of a voice
announcement or data information.
The same announcement system also includes means
for generating user statistics, such as by recording the
number of orders and the types of orders as they are
received, and also includes a billing system for
automatically correlating the order calls with the identity
of the telephone service lines which were used for making
the order call. This permits the charge for the service to
be billed in the same manner as the billing for the
telephone service, and in some cases means that the charge
or the announcement order may be added as an item to the
telephone service bill. Because such procedures are
presently well known and widely used, they will not be
discussed in further detail herein, except with regard to
advantages that may accrue as a result of their function
within the system 10.
The interconnections of the program producer 12,
the TV network 14, tune broadcast station 16, and the
subscriber unit 18 by the telecommunications network 20 are
accomplished by any of the commonly used signal carrier
media, or combinations thereof, which are suitable for the
type of signal carried. Communications carriers presently
provide a wide range of services appropriate for
connections between producers, television networks, and
broadcast stations. They also provide a telephone service
3L2~:~38S
line, usually in the form of metal wire, to subscribers who
have telephone service. Therefore, the nature of the
interconnection equipment to be used in conjunction with
this invention will also not be discussed in detail herein
except with regard to advantages that may accrue as a
result of their function within the system I
The producer 12 is assumed to be the original
source of the signal which is to be offered as a program
signal for viewing by subscribers on their own receiving
equipment. The program signal from the producer 12 is
forwarded to the network entity 14, which determines
further distribution of it to various broadcast stations
which are geographically distributed to permit wide
dissemination of the program signal. The broadcast
stations 16 send the program signal to the subscriber unit
18 of each subscriber by airwaves, cable (CAT), direct
broadcast satellite (DUBS), or some other suitable program
signal carrier. In the system 10 of FIG. l, the program
signal carrier is represented by electromagnetic radiation
23. It is picked up at the subscriber location by an
antenna 24 and carried to the subscriber unit 18 by leads
26. In some applications, such as in DUBS or CAT, there
may be signal conversion equipment, filters, amplifiers, or
such between the antenna 24 and the subscriber unit 18,
with appropriate leads 26 connecting such devices. The
subscriber unit 18 may be receiving several different
program signals associated with different frequency
channels. One or more of these signals may be in
enciphered form, while others may not be enciphered and may
therefore be available to the general public without
charge.
The subscriber unit 18 is connected to the
communications carrier network 20 by telephone lines 28.
These fines 28 do not need to be dedicated lines. That is,
they need not be used exclusively for the functioning of
the subscriber unit 18, but rather may be the common
telephone service lines of a typical residence with only
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one telephone service. this is a particularly important
aspect ox the invention, since the telephone company's
knowledge of the subscriber's telephone line number permits
proper billing without the necessity of identifying the
subscriber unit 18 itself.
The subscriber unit 18 is connected to the
television receiver 30 of the subscriber by signal leads
32.
It is a feature of the system 10 that the program
signals transmitted by the program signal carrier 23 are
accompanied by auxiliary signals carried within the retrace
interval ox the signal. Techniques or carrying
information within the retrace interval ox a television
signal are well known in the television broadcast art. The
auxiliary signals include control and display signals in
the form of low speed digital information.
Fits. 2 and 3 show the subscriber unit 18 of
FIG. l in greater detail. FIG. 2 shows the front of the
unit 18~ On the extreme left there is located an on-off
power switch 36 which may control the power to the
subscriber unit 18 alone or also control the power to the
receiver 34. To the right of the switch 36 there is an
order call button 38 by which the subscriber can command
the unit 18 to order a desired program. Next to this is a
channel selection switch 40. A rectangular electronic
alphan~mleric display panel 42 is provided for displaying
program and ordering information. On one side ox the unit
18 is a mechanical lock 44 by which the unit 18 may be
disabled to prevent unauthorized use.
FIG. 3 shows the back of the unit 18 with various
electrical connection means including program signal output
terminals 46 by which the program signal passes to the
receiver 34, program signal input terminals 98 by which the
signals picked up by the antenna 24 are received through
the leads 26, an auxiliary power receptacle 50 by which the
receiving equipment power can be controlled by the unit 18,
a power input plug 52 by which line power it supplied to
2~3~
the unit 18, and a pair of telephone jacks 54, 56. The
jack 56 is suited for an extension telephone. The jack 54
is coupled directly to a telephone service.
In the operation of system 10, it is first assumed
that the unit 18 is supplied with power. The auxiliary
signals will supply program information which will appear
on the display 42 to advise the subscriber as to the
availability and time of an offered program. It may also
give the cost to the subscriber. In order for this
information to appear on the display 42, however, it is
necessary that the channel selection switch 40 be in the
position for receiving the signal channel associated with
the offered program. Each of the available channels may
have such display information provided with its program
I signals, so that this display information may be selected
by the subscriber as desired by appropriate positioning of
the channel selection switch 40.
If the subscriber wishes to order a program being
offered, he need only operate the order call button 38
within the time period specified by the displayed
information. This will initiate an order sequence within
the unit 18 by which there will subsequently be an
automatic call to the announcement distribution system 21
of the telecommunications network 20. The call will be
triggered by an appropriate control message provided in the
auxiliary signal. The announcement distribution system 21
will recognize from the telephone number which was called
by the unit 18 that this call requires a particular order
response. It will then make that response by automatically
connecting the call from the unit 18 to an announcement in
tune form of a low speed voice band data signal which
contains a deciphering key.
An example of a deciphering key is shown
schematically in FIG. 4. It consists of a continuously
repeated data message 58 which is 3 seconds long. The
length is chosen for colQpatibility with the prevailing
telecommunications network standards for validating the
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g
call. The key information is in the form of a number of
digitally encoded numerical values which can be used to set
the coefficients of a signal filter. It is noted that
since the amount of information ordinarily needed for
deciphering can be transmitted within only a fraction of
the three second interval, there remains a considerable
amount of time which may be used to transmit owner
information to the unit 180 This may be display
information or operational control information for the unit
18 similar to that contained in the auxiliary signal.
As the unit 18 receives the deciphering key
information, it stores the key within a memory associated
with the selected program channel. Now the unit 18 is
prepared to decipher the program signal on command at the
time it is delivered to the unit 18. At the-start of the -
program, the control signals which are in tune auxiliary
signal delivered with the program will instruct the
deciphering circuitry to become active. The activating
instructions will continue throughout the prewarm later
program will have a different enciphering format and will
therefore require a different key. Thus, although the
later program also carries with it the control signals for
activating the deciphering circuitry, this will be
insufficient for the deciphering process, since the unit 18
will not have in its memory the key information necessary
for the deciphering.
There are a large number of enciphering methods
known in the art which would readily lend themselves to the
system 10. The particular one chosen depends upon the
chosen complexity of the unit 18 and the enciphering
equipment, as well as upon the nature of the particular
signal to be transmitted. The preferred type of
enciphering for use with the system 10 is one in which a
digitally encoded key can be used to correctly set the
coefficients of a deciphering circuit signal filter in the
unit 18 for deciphering. Various enciphering techniques of
this type are known to those in the art of enciphering
` ~22~3~3~
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television signals and can be readily adapted by them for
the system 10. Therefore, the structural details of the
deciphering circuitry necessary for this are not discussed
in detail here.
The order calling apparatus of the unit 18
includes a memory in which an order call instruction prom
the subscriber is held until such time as the unit 18
receives a proper deciphering key when it calls the
announcement distribution system. Any other call result,
such as a busy signal, will cause the unit 18 to retain the
order call instruction in memory. It is further provided
with means responsive to the control signals of the
auxiliary signals carried with the program signal by which
its call initiation is determined to be within a particular
time period as determined by overload sensing equipment of
the announcement distribution system. These features,
described below, are especially advantageous for situations
in which there is a high degree of impulse ordering.
JIG. 5 illustrates graphically the problems which
arise with impulse ordering of program signals. The
baseline 60 represents the passage of time about the
beginning time of the program signal. The ordinate
represents the number of order events. Curvy 62 shows the
number of orders requested over time by subscribers who
have operated the order call switch 38 on their units 18.
Curve 64, on the other hand, shows the number of orders to
which the announcement distribution system has been able to
respond. It is seen that within the short interval between
the end of a normal broadcast and the beginning of the
ordered program signal there is an overload condition of
the announcement distribution system. As discussed above,
the unit 18 will continue to attempt to place the order it
it encounters a busy signal in such an overload condition.
However, the end result may be that in a severe overload
situation the deciphering key information is not delivered
by the time the program is to begin. This would leave the
subscriber as having been billed for the program in its
~Z2~3~35
entirety while not being able to decipher it from its
beginning point. In order to avoid such a state of
affairs, the program signal can be initially transmitted
with a first enciphering. Appropriate control signals
delivered by auxiliary signals transmitted with it will
enable any subscriber unit 18 to decipher the program
signal by the use of deciphering key information which is
already available to the unit 18, either by being hard wired
within it, by being delivered at an earlier time or by
being delivered coincidentally with the control signal to
switch to this first deciphering state. This deciphering
state of the unit 18 will be referred to as the "internal
key if state. The low speed data and control content of the
auxiliary signal can also be used to put the unit 18 into a
state in which the deciphering circuitry is not utilized,
such as when the program signal is not enciphered because
it is intended to be available to the general public This
will be referred to as the "bypass" state.
The probability of overloading of the order
receiving equipment can be reduced by controlling the order
calling of the subscriber units 18 in groups. The groups
would be determined by internal identifiers. For example,
the low speed data and control signals accompanying the
program signal can include order call activation commands
for the units in three different formats which are
sufficiently spaced in time to accommodate the order demand
which is expected for the program. The units would be
provided with corresponding filters by groups, so that a
given call activation command will activate only that group
which has a pass-filter for that signal. The others would
remain in a standby condition until activated by their
respective control signals. In this manner, the order
taking capacity of the system is most effectively used.
Furthermore, the time period allotted for the order calling
of the groups of units 18 can be adjusted as needed as the
orders are taken, due to the availability of the user
statistics kept by the stored program control system 22.
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There are, then, three signal receiving states of
the unit 18. The first is the bypass state, in which the
deciphering circuitry is inactive and the program signal is
transmitted unaltered to the receiver 34. The second is
the internal key state, in which the unit 18 deciphers the
enciphered program signal with the use of internally
available deciphering key information. As described above,
this state can be used if the order call button 38 has been
operated and the key information has not been delivered by
the time the program has started. The third is the ordered
key state, in which the program signal is deciphered using
key information delivered in response to an order call for
that program.
FIG. 6 is a partially pictorial functional block
diagram of the subscriber unit 18. The subunits A-L
illustrated on the left side OX the unit are largely
concerned with the reception and deciphering of the
television signal, while the subunits N-Z on the right side
are largely concerned with the telephone connection and the
reception and processing of the deciphering key and related
messages. The functional details of the subunits can be
readily supplied by those swilled in the art.
Power is delivered throughout by a power supply
subunit A under the control of the switch 36. Subunits B,
I C and D provide standard television receiver functions ox
tuning, IF and Video amplification t and automatic gain
control. Subunit B is an electronic tuner; it receives
channel changes indirectly via controller M, rather than
directly from the channel selector 40, as would be the case
with a mechanical tuner.
The receiver subunit E takes the output of the
amplifier C and extracts auxiliary signals from those
retrace interval lines which have subscription television
header signals. These auxiliary signals are formatted into
control messages and then output to the message buffer J
for use by the controller submit M.
The control message receiver E reports message
L;22~3~
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format and parity errors to the weak station detector F,
which measures both the AGO output level and the message
error rate to determine if a weak station condition must
be reported to the controller M.
It is the principal function of the tuner B and
the amplifier C to prepare the television signal as it
appears at input 48 for deciphering circuitry in the form
ox a descrambler G. The descrambler G has two sets of
input leads controlling its operation: first, those from
the state control switches as set by subunit K; and second,
the deciphering key inputs as delivered by the key delivery
subunit L. The circuits within descrambler G are set to
either bypass or use the descrambling logic upon command
from the state control switch K. The descrambler G resets
to the bypass state whenever it is not receiving power
from subunit A.
The deciphering key is delivered to the
descrambler G to cause it to operate in the proper mode
and with the proper timing for deciphering the television
signal. The deciphered signal is delivered to the RF
modulator subunit H for conversion to a proper signal for
use by the subscriber's television receiver 30. An
adjustment 47 is provided for the subunit H to set the
output channel, typically to VHF channel 3 or 4. A portion
of the deciphered signal is also delivered to an optional
subunit I, which separates and amplifies stereo sound
output signals and delivers those signals to the optional
ports 57 and So for connection into the subscriber's sound
system. In addition, the descrambler G output is in part
delivered to the control message receiver E for purposes-
of receiving enciphered control messages and thereby
testing the performance of the descrambler G.
The controller M receives signals of changes of
condition within unit 18, and then responds by taking the
appropriate action as determined by its associated
programs. For example, the controller M may be alerted to
an arriving message by subunit J; that message may be a
93~3S
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"display text" message. Controller M will then use its
display programs to convert the message data to display
data for output to the display driver subunit N. The
display driver N then creates the appropriate text on the
external display panel 42 and also on the auxiliary data
output port 43.
The controller M notes the position of lock 44
whenever the subscriber activates the order call button 38
or the channel select switch 40. Lock I can thus be used
to prevent the ordering of any program signals, i.e., the
unit 18 must be "unlocked" to allow program signals to be
ordered. Similarly, lock 44 can be used to enable or
disable program viewing on certain program channels. The
subscriber enables the desired channels by placing lock 44
in a "channel enable" position and using the channel
selection switch 40. Controller M will cause the display
42 to indicate the channel numbers and their
enabled/disabled state in response to the subscriber
selections.
The switch hook controller and detector P and the
digit output subunit 0 provide the auto dialer function for
the unit 18. Subunit P determines and controls the
busy/idle state of the subscriber's telephone line to allow
unit 18 to place telephone calls without interrupting
normal telephone usage. Subunit 0 transmits the digits of
the telephone number desired.
The data carrier detector Q, the key and message
buffer R, and the key and message receiver S together
create the receive portion of a low-speed data modem. The
controller M, after placing a call for a deciphering key,
will await a signal from data carrier detector Q indicating
that the call indeed did reach the intended destination.
If that signal is not received within the proper time
interval as set by a control message and timed by the clock
subunit T, then the controller M will abandon the call
attempt. If the call is completed, then the controller M
will await the key and other messages to be delivered via
;293~35
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subunits S and R. Should subunit S not receive an
appropriate key signal, then the controller M will again
consider the call to be incomplete.
The controller M, the memory W, and the clock T
are preferably supplied with back-up (battery power V:
Back-up power is supplied to the controller M via a power
test subunit U which alerts the controller of low battery
condition. Power to restore the battery is delivered from
subunit A when the unit 18 is ON, and from subunit P when
it is OFF.
The memory subunit W provides both RAM and ROM
functions. The program subunit X contains the programs and
permanent data, such as a unit serial number, needed for
operations of unit 18. The shared data subunit Y stores
transient data such as switch hook busy/idle state, which
can be considered as shared by any and all program
channels. This is to be contrasted with the data stored in
the partitioned memory area Z, such as the telephone number
to be called to subscribe to a forthcoming program.
Controller M assigns areas within memory Z based on the
appearance of control messages in message buffer J whenever
a channel selector 40 change is made by the subscriber.
ill data pertaining to orders for programs is kept
segregated by channel within memory Z.
Preferably, each channel that is enabled and
transmitting a control signal is allocated a section of the
memory Z by the unit 18 when it notes the presence of both
the enabling and the control signals. There is no cross
access within memory Z between broadcasting stations.
Moreover, each channel has memory in areas accessible only
to commands received in the auxiliary signal or via the
telephone line, respectively.
General Considerations
The key information which is delivered via the
telephone may itself be enciphered. This might be done by,
for example, disguising the key data within a much longer
~'rZ2~338~
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data signal that is largely chaff, using some numerical
substitution scheme, or using any arithmetic operation that
is reversible. The key would be deciphered or simply
sorted from the chaff by using other data available to the
descrambler G before or during the ordered program. Such
data might be any of:
I data sent in the control signal coincident
with the key data (a "good/bad" control
pattern matching or other deciphering
signal);
I data as in (1), but sent via control signal at
an earlier or later time;
(3) data permanently stored in the box (such as a
protected identifying number, where
"protected" means not known to the
subscriber;
(4) data sent earlier or later via telephone in
the same or different telephone call, such as
for a down payment/final payment scheme, or
for a discount plan for heavy users; or,
(5) some combination of these methods.
A major advantage of this system is the ability of each
television network to create a desired variation of key
delivery scheme using techniques such as described here.
This is possible because each network supplies its own
control signals and telephone signals and can use these
signals to specify the sequences of operations performed by
the descra~bler G in real time.
This system can be of advantage also to networks
which choose not to broadcast their programs on a pay
basis. These networks can still display messages on the
unit 18 if the program signal carries the appropriate
auxiliary signals containing display messages with it.
The order calling procedure of this system can be
used to poll subscribers to obtain their answers to
questions appearing on the display 42 of the unit 18 or
presented in a program being viewed.
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The system 10 above is one specific example of the
present invention. It will be evident from the various
observations below that a person of ordinary skill in the
art may make many modifications in the system 10 without
departing from the spirit of the invention.
The program signal is not limited to one of a
particular frequency or carried by a particular medium. It
may be a television, radio, or other frequency signal. The
enciphering scheme may take any appropriate form which is
suitable for the transmission ox a separate deciphering key
in the form of an electronically transmitted message
capable of being stored in the subscriber unit. The
program signal need be accompanied only by a control signal
for activating the deciphering. The display data signal is
optional. The accompanying control signal may be
transmitted to the subscriber unit in any suitable form so;
long as it bears an appropriate time relationship with the
program signal to permit the activation of the deciphering
contemporaneously with the starting period of the program.
While it is convenient to carry the control signal on the
same channel with the program signal, this is not
essential, and the control signal can be supplied by other
carrier means if that is preferable.
The mass announcement distribution feature of the
system 10 is described because such a feature is presently
in operation in the telephone system of the United States.
Any telecommunications network feature which is capable of
responding to an order call with a deciphering key and of
doing so in a short enough time to meet the demand for
I program orders to an acceptable degree would be suitable.
For example, an electronically programmable private branch
exchange (POX) can be adapted to perform such a function.
The manual lock on the subscriber unit can deny
program orders while neither denying viewing nor canceling
orders already placed. Under certain circumstances it may
be desirable to equip the subscriber unit with a mechanism
for disabling the ordering capability if the unit senses
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that the program signal from the program channel is too
weak to yield an acceptable rendition of the program or
would be likely to result in errors in the control signals.
The unit may also include a memory for recording the
lengths of time that an unsatisfactory signal is received.
This information can be automatically accessed at a future
time and used by the television network to control future
ordering or possibly as the basis for a refund.
The information for display can appear on the
television screen in the Caption area at the top or
bottom of the screen instead of on the subscriber unit.
The display on the unit or otherwise external of the
television picture can take various forms. It may, for
example, be by a printing mechanism connected to the
subscriber unit as slave.
The memory or the subscriber unit i-s preferably of
the type which retains stored information without external
power. This permits a subscriber unit to be provided with
deciphering key information and then transported to another
location for receiving the program. This would make
possible the renting of such units already provided with
the key information for a given time or program.
The connection of the subscriber unit to the
telephone service can be adapted to be cordless. Also, the
unit may be provided with a handset and dial mechanism for
use as a telephone.
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