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Description  |
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FIELD OF THE INVENTION
This application relates to improvements in subscription television
systems. More particularly, the invention relates to apparatus and methods
for communicating individually addressable text messages from a central
location to individual subscribers of a subscription television system.
BACKGROUND OF THE INVENTION
The sophistication of communications systems involving subscription
television is continually increasing. The systems being installed at this
time have greatly improved communications flexibility as compared to those
previously in use, while the quality of the transmitted signal is
continually being improved, as is flexibility in the business arrangements
possible between the subscriber and the broadcaster.
For example, in U.S. Pat. No. 4,484,217 to Block et al., there is disclosed
a subscription television system in which all billing calculations are
carried out at the decoder, that is, at the individual subscriber's
location. When a subscriber makes a payment, e.g., by simply mailing a
check to the broadcaster, the broadcaster then sends a message which is
detected by that particular decoder and used by it to update the user's
credit and/or account balance information. The decoder then controls
whether the user is to have access to a particular program or not in
accordance with this billing information, possibly also in accordance with
other sorts of access controls transmitted by the broadcaster. For
example, each program transmitted may include an indication that it
belongs to a particular "tier" or class of programs. The decoder then
permits access to the program if programs of that tier had previously been
authorized.
The Block et al. patent also discloses that teletext data, that is, textual
information relating to stock market reports and the like, could also be
transmitted using this system. However, the teletext data discussed in the
Block et al. patent appears to be system-wide data, that is, data relevant
to all subscribers of the system more or less equally. The Block et al.
patent does not teach any way in which, for example, an individual
broadcaster may send a chosen subscriber a personal message other than
billing update data, as above.
"Specification of Standards for Broadcast Teletext Signals," a document
published by the British Broadcasting Corporation et al. in September,
1976, describes the teletext broadcasting system in effect in the United
Kingdom. According to this system, teletext information such as
closed-captioned programming is available for the hearing-impaired.
According to this system, as understood by the applicants, the subscriber
simply depresses a button on a key pad comprised by the decoder, and the
decoder then selects alphanumeric data which is transmitted during the
vertical blanking interval of the standard television signal. The decoder
can then add this closed-captioned textual material directly to the video
screen, so that it can be seen by the hearing impaired. Again, however,
this material is transmitted system-wide, and there is no provision made
for transmission of individual messages to individual subscribers.
Those skilled in the art will recognize that there are a number of
constraints on the operation of any successful subscription television
system. For example, there must be an extremely reliable and trustworthy
method of computing charges to be billed to the subscriber and for
communication of credit status updates. It is also desirable that the
subscriber be permitted to prepay for certain classes of service, for
example, to have access to a particular broadcaster's offerings. On the
other hand, it is also desirable that an "impulse" purchase system be
provided such that the viewer could purchase a particular program on a
"pay-per-view" basis when desired. Similarly, it is desired that a running
list of programs purchased by the subscriber be available, such that he
can confirm that he is indeed being billed correctly. It is furthermore
desired that means be provided for securing the system against improper
use, which includes both prevention of viewing of inappropriate subject
matter and purchase of fee-bearing material by persons not authorized to
do so.
The requirement that the credit status be updateable further requires that
communication be possible in both directions between the decoder and the
transmitter. However, it would be inefficient to provide individual uplink
transmission facilities at each decoder, for example, in a satellite TV
system. Therefore, it is desirable that a two-way communications facility
be provided connecting each decoder with the transmitter, but in which the
two data links are not made using the same medium. Therefore, the
communication facility which carries subscription television signals from
the transmitter to the decoder is not the same as that used to carry
payment status information, queries or the like from the decoder to the
transmitter.
As indicated above, the prior art suggests that individual decoders can be
addressed for transmission of billing information. It would also be
desirable if individual user messages could be transmitted to individual
users such as to provide an additional communications facility not
previously made available. If this is to be done, there are several
criteria which must be met. Paramount among these is security;
preservation of the secrecy of the message and its availability only to
the particular addressee is of utmost importance. At the same time, it is
desired to be able to address messages to classes of subscribers, for
example, to transmit civic data or the like.
Another complexity in providing a secure subscription television system is
the fact that the decoder cannot be considered to be in "friendly hands."
That is, unlike an encrypted data channel as used by financial
institutions or in military applications, in which both transmitter and
receiver are in friendly hands, an additional security exposure which must
be faced in connection with a television system is analysis of the
transmitted signal. In a subscription television system, the transmitted
signal must, of course, be protected, as a very important threat is posed
by viewers who have purchased a decoder and attempted to modify it to
bypass the security mechanisms the billing arrangements or the like. A
further problem is posed by those who would make copies of, for example,
television movies using videotape recorders or the like for subsequent
viewing or resale.
It is, therefore, desirable that a system be provided which provides a very
high level of security, both as to the transmitted signal and as to the
operation of the decoder, and one in which some sort of "fingerprint"
identifying the source of an unauthorized copy can be provided.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a subscriber
television system in which individual text messages may be directed to
individual subscribers.
It is a further object of the invention to provide a subscription
television system in which individual text messages can be transmitted to
individual subscribers, in which the message can only be received by the
proper receiver and in which the text is very heavily protected against
improper receipt, that is encrypted, such that it can only be received and
decrypted at the correct decoder, thus providing an additional level of
security to the message handling system.
It is a further object of the invention to provide a subscription
television system in which an individual message can be sent to an
individual user, but in which the individual decoder is enabled to receive
and decrypt the specified message only upon activation by the proper
individual.
It is a further object of the present invention to provide a subscription
television system in which all billing information is generated at the
decoder. The transmitter can transmit indication of receipt of payment and
of additional charges not originating at the decoder to the decoder, such
as sign-up fees. The decoder is thus enabled to generate the bill.
Ultimately, the handling of billing operations is greatly simplified and
paperless billing is made possible.
It is a further object of the present invention to provide a television
subscription system in which a wide variety of teletext messages having
specified formats are available for use by the decoder, in which the
formats can be varied at the transmitter's option, yet in which the memory
required at the decoder location is minimized, to realize economy of
construction of the decoder unit.
A further object of the invention is to provide a subscription television
system in which the identity of a particular decoder used to decrypt a
program can be determined from recordings made using such a decoder.
A further object of the invention is to provide a subscription television
system in which individual text messages can be received by individual
subscribers in response to queries by the subscriber, in response to the
desire of the broadcaster, or upon initiation by the decoder itself.
The above needs of the art and objects of the invention are met by the
present invention, which comprises a system and method for communication
of individual text messages to individual subscribers of a subscription
television system. According to the invention, a number of distinct
"lines" of information are transmitted during each vertical blanking
interval of the video signal. A number of these lines are referred to as
"addressed packets," while another group of lines includes teletext
information. The addressed packets include identification of individual
subscribers which are transmitted in clear text (that is, are not
encrypted) such that the individual decoders recognize their own numbers.
The addressed packets include certain cipher information, used in
decrypting other portions of the information contained in the vertical
blanking interval and the video signal. The addressed packet also
indicates that a particular "page" of teletext information is being
transmitted which is directed to a particular subscriber. The decoder,
having detected existence of a message addressed to it responsive to the
information contained in the addressed packet, then selects subsequently
transmitted teletext "lines" included in subsequent vertical blanking
intervals, and uses these to assemble a teletext "message" which can then
be displayed on the user's television screen.
In a preferred embodiment, the broadcaster continually sends teletext
information which is useful in subsequently assembling messages. The
teletext information repetitively transmitted includes "templates." For
example, should the subscriber seek to ascertain his billing status, he
will so indicate by pressing a button or buttons on a user key pad
comprised by his decoder. A microprocessor comprised in the decoder will
note this request and determine the number of a template suitable for
displaying this information. When that page of text is subsequently
transmitted, as part of the regular sequence of teletext messages, the
microprocessor selects it, and then completes the template by filling in
various dollar amounts and the like unique to the particular subscriber.
This completes assembly of the billing report requested. The
microprocessor then can display the complete billing report. In this way,
the teletext information comprised in the template, that is, the
information needed for the text message which is not user specific, such
as column headings, current dates, the broadcaster's name and address,
which is common to all subscribers, need not be stored at the user
location. This greatly reduces the amount of memory which must be provided
for each decoder. In the same way, the templates can be varied by the
broadcaster, e.g., to update the listing of services made available or the
like.
The microprocessor itself can also generate various reports, for example,
to indicate to the subscriber that his credit is running low. The
microprocessor can select a template page from the sequence of template
pages continually being sent by the broadcaster and can complete it with
user-specific billing information, all as generally discussed above.
In this way, it will be observed that there are three different ways of
providing a teletext message, that is, user-initiated,
broadcaster-initiated, and decoder-initiated.
Finally, the system of the invention includes means for "fingerprinting"
copies of program material made by a subscriber in derogation of the
rights of the copyright proprietor. The address packet includes a flag
which may be set to cause the decoder to add the decoder identification
number to one particular video frame of the film being shown. The addition
of the user identification is generally imperceptible to the user, but
will show up on any copies of the film that are being made. Should the
broadcaster thereafter locate such an unauthorized copy, he can read the
user's identification and thereafter cut off service to that individual or
take other appropriate action.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood if reference is made to the
accompanying drawings, in which:
FIG. 1 shows an overall view of a communication system according to the
invention;
FIG. 2 shows an overall view of the video format according to the
invention, and explains certain nomenclature used for understanding the
system of the invention;
FIG. 3 shows in broad outline the format of the horizontal blanking
interval;
FIG. 4 shows additional details of the format of the horizontal blanking
interval;
FIG. 5 shows an overview of the material carried in the 16 lines of the
vertical blanking interval in a 525 line embodiment of the invention;
FIG. 6 shows in some additional detail the clock recovery data carried in
line 1 of the vertical blanking interval;
FIG. 7 shows in additional detail the framing recovery data carried in line
2 of the vertical blanking interval;
FIG. 8 shows the arrangement of the system data carried in line 3 of the
vertical blanking interval;
FIG. 9 shows the general arrangement and contents of four different types
of addressed packets which can be transmitted in lines 4-8 of the vertical
blanking interval;
FIG. 10 shows the outline of a teletext header line which can be
transmitted in any one of lines 9-13 of the vertical blanking interval;
FIG. 11 shows a text line, that is a line of teletext which may be
transmitted during any one of lines 9-13 of the vertical blanking
interval;
FIG. 12 shows schematically the text processing steps performed according
to the system of the invention, when it is desired that a particular
message be transmitted to an individual subscriber;
FIG. 13 shows in schematic form the hardware of the decoder significant to
understanding the present invention;
FIG. 14 shows in schematic form the handling of the keys and message
processing steps performed, and further details how and where these steps
are performed in the decoder according to the invention; and
FIG. 15 shows in schematic view the data decryption arrangement employed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As mentioned above, it is an important object of the present invention to
provide a communications system in which individual text messages can be
transmitted to individual subscribers in a subscription television system.
This is to be accomplished without adding unduly to the complexity of the
system or its cost, and without requiring any sort of uplink communication
between the decoder and the transmitter. Moreover, the system is to be
provided with unprecedented flexibility in choice of program by both the
broadcaster and the dealer, and the subscriber billing is to be
substantially automated and performed at the decoder. Finally, the whole
system is to be menudriven, that is, the subscriber is to be directed in
operation of the system by messages displayed on his television screen.
These objects of the invention are achieved by the present system, which is
described in the following text, of which the following is a Table of
Contents, and in which reference is made to the accompanying drawings.
A. System Overview
FIG. 1 shows in highly schematic form a communication system suitable for
achieving the objects of the invention listed above. At a first
transmitter location, indicated generally by the numeral 10, the teletext
message sequence is first assembled as indicated at 12. This may include
standard items such as templates, that is, data which provides a format
within which user-specific information can be added by a decoder to
personalize a message; personal messages directed to individual users;
billing status updates, that is, billing information generated in response
to a telephone call or letter from the subscriber to the broadcaster; and
broadcast messages, that is, messages which are out of the ordinary course
of business, but which are transmitted to substantially all or a
predetermined subcategory of subscribers (e.g., that there is some general
danger of which all should be aware).
At 14, the teletext information from item 12 is assembled together with
video information, and in a preferred embodiment of the system of the
invention, with multichannel audio. As will be detailed below in
connection with FIGS. 3 and 4, six channels of digital audio are provided
in the system of the invention. These are transmitted during the
horizontal blanking interval and may be provided on a pay-per-listen
basis, whereby the broadcaster can generate additional revenue from audio
transmission.
At 16, the assembled teletext, video and audio signal is encrypted and/or
scrambled. The encryption is done according to a relatively sophisticated
procedure which is discussed below in connection with FIG. 15. Suffice it
to say at this point that the signal transmitted includes what are
referred to as addressed packets, which among other functions alert an
individual subscriber's decoder that a message has been sent to it, and
teletext information. The subscriber identification portion of the
addressed packet is transmitted in clear text, that is, is not encrypted,
so that it can be detected without decryption. The addressed packet
further contains certain cipher key information used in decrypting system
control data. The system control data in turn includes cipher information
required for decryption of encrypted user messages. Thus, a double level
of security is provided, as only the individual decoder can even receive
the encrypted message, and only that decoder can use the system data which
it must also receive to decode the individual message, which is
subsequently sent. The composite, encrypted signal is transmitted as
indicated at 18. It may travel via a satellite 20, by a landline or a
combination of both to receiving antenna 22. It is there passed to a
decoder which comprises means for detecting the signal, decrypting the
encrypted portions of it, completing any messages requiring any
subscriber-specific data, such as billing status information and the like,
and display of the received messages. Of course, the decoder also permits
user selection of the decrypted audio and video information, and includes
means for maintaining the billing history information related to a
specific user, for restricting access of individuals to the video signal,
prevention of impulse purchase of programs by those not authorized to do
so, and so on, all as detailed below.
The system of the invention is completed by means permitting the user to
communicate with the broadcaster. Ordinarily, the user will only need to
communicate with the broadcaster sporadically, for example, to request
addition of a service, or to pay a bill or the like. Conventional
communications facilities such as the telephone system or the mails are
suited for this function, as indicated schematically at 8. In this way, no
uplink facility at the user's station need be provided.
1. The Communications Format Employed
FIG. 2 shows the overall transmission format of the system according to the
invention. As is conventional in television, 30 "frames" each comprising a
still image are transmitted per second as indicated. Each frame includes
two "fields," as also shown. In a preferred embodiment of the invention,
the video encoding scheme employed is that referred to generally as
"B-MAC." This is an acronym for type B format, Multiplexed Analog
Component system. "Type B" refers to the fact that data is carried
integral to the video signal. See generally Lowry, "B-MAC: An Optimum
Format for Satellite Television Transmission," SMPTE Journal, November
1984, pp. 1034-1043, which discusses in detail the B-MAC format and
explains why it was chosen over various competing systems.
According to the present invention, the vertical blanking interval (VBI) of
each field contains certain "system data" necessary for operation of a
subscription television system according to the invention, as well as
addressed packets and teletext lines used to carry data needed for the
operation of individual decoders and for transmission of messages to
individual subscribers. In the preferred embodiment of the present
invention, the vertical blanking intervals of 16 total fields are used for
complete transmission of all system data required, which includes an
encryption key which is changed every 16 fields, that is, on the order of
three times per second. As also shown in FIG. 2, each line also includes a
horizontal blanking interval (HBI). During the HBI are transmitted six
channels of high quality digitally-encoded audio information, with error
correction, such that the decoder can also be used to supply a high
quality audio signal. This can be used to provide the audio component of
the corresponding video signal (or several versions thereof, in different
languages) or an additional audio signal, such that subscription audio is
also made available according to the system of the invention.
2. The Horizontal Blankinq Interval
FIG. 3 shows the format of the horizontal blanking interval (HBI). In the
preferred embodiment, the HBI consists of 78 total bits of four-level
frequency-shift-keyed (FSK) data. The HBI is interposed between vertical
blanking interval or video information from a previous line and that of
the present line. A typical horizontal blanking interval as shown begins
with a two-bit guard band 30, followed by 45 bits of audio and utility
data 32, a second two-bit guard band 34, twenty bits of color burst
information 36, a further guard band 38, six more bits of data 40 and a
final guard band 42, after which the VBI or the video signal of the
particular frame commences. The position of the color burst 30 within the
HBI varies, to provide signal scrambling; descrambling involves the use of
a repetitively-transmitted key, described below in connection with FIG. 8.
(The actual number of bits of data in each HBI can also be varied
pseudo-randomly, for further security; the average number is fifty-one.)
FIG. 4 shows some additional details of the horizontal blanking interval
data 32 and 40 shown in FIG. 3. In the example shown, fifty-one total bits
of data are provided in each line of the HBI, and each bit is four-level
FSK encoded, such that each bit period includes transmission of two bits.
One bit can be referred to as sign and the other as magnitude as indicated
on FIG. 4. As shown, the first seventy-eight bits are digital audio; thus
each frame provides a thirteen-bit digital representation of a sample of
each of six audio channels. High quality transmission of audio frequencies
up to approximately 15 kHz is thus provided. Following the audio
information are six bits of stepsize and bandwidth information. The
stepsize bits indicate the size of the steps numbered by the thirteen bits
of information preceding, and the bandwidth information relates to the
amount of the amount of emphasis or de-emphasis of the signal employed.
Alternate fields carry the stepsize and bandwidth data. Both these terms
are used as conventional in the Dolby delta modulation scheme, which is
employed in the preferred embodiment of this invention for transmission of
the audio. Following are twelve bits of error correction code (ECC) for
correction of the audio, indicated at 48. Four utility bits follow at 50,
and the last bit 52 of the data are a parity check bits for checking the
parity of the error correction bits 48.
Additional details concerning the horizontal blanking interval format can
be found in co-pending Ser. No. 883,310, filed July 8, 1986, incorporated
herein by reference.
3. Vertical Blanking Interval
FIG. 5 shows the a | | |
