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BACKGROUND OF THE INVENTION
1. Technical Field
2. Description of the Relevant Art
Cable, satellite and over-the-air broadcast and subscription television
systems, generally referred to herein as television systems, have been
known since the 1970's which involve the transmission of addressed data to
terminals on a carrier signal or subcarrier of a broadcast signal. In
cable television systems in particular, a data carrier is chosen to be
outside of the bandwidth of the transmission of a multiplexed frequency
spectrum of television channels (an out-of-band carrier). The out-of-band
carrier, for example, is chosen, for example, to be near the FM radio
channel band, such as at 108.2 MHz, and the addressable data is, for
example, frequency shift key modulated on the out-of-band carrier. The
data typically comprises an address field and a data or message field. If
the address matches the address of the apparatus to which it is directed,
then, the data field is accepted by the apparatus. The data of the data
field may command the apparatus in some way and, in particular, may
contain command data or an operand, sometimes referred to as a transaction
code, and other data to be operated on by the command. Some data fields
are global in nature and maybe accepted by all receiver apparatus. Other
data fields are uniquely addressed to either a selected group of
terminals, one terminal location which may have a plurality of terminals
or to one terminal.
With the passage of time, cable television systems have become more
complex. The signal distribution apparatus may comprise amplifiers which
may be controlled by the addressed data transmitted from the headend of a
cable television system. The gain and equalization provided by such
apparatus may be automatically controlled from the headend. Likewise, tap
apparatus which may, for example, comprise interdiction, trap or other
signal denial apparatus may be controlled by addressable command from the
headend. The terminal apparatus, also, which may, for example, comprise
signal descrambling apparatus, may be controlled by addressable command.
The need for greater communications capacity to control the several
apparatus forms and variety of services that can be controlled from a
headend has precipitated a requirement to transmit addressed and even
non-addressed data from a headend by other means. One alternative system
that has been developed is to utilize the sound carrier, which accompanies
a video carrier, together comprising a single video channel. For example,
the sound carrier may be amplitude modulated with data that accompanies a
channel. The data may not be addressed data. The data sent on the sound
carrier may be utilized, for example, as a channel or program identifier
to identify the accompanying video or program content. On the other hand,
the data may comprise addressed data to supplement or replace the
out-of-band data transmission of addressed data. This in-band audio data
transmission is controlled by a known in-band data controller, sometimes
referred to as a headend controller, in a manner so that a system control
computer utilizes both in-band and out of band data transmission to
advantage. For example, immediate commands of importance to signal
distribution or terminal apparatus are transmitted immediately and less
immediately required data is transmitted on a less frequent basis. Such a
headend controller and system is particularly described by U.S. Pat. No.
5,058,160, incorporated herein by reference. The in-band audio data rate,
however, may be slow and may be at a rate only approximating the line rate
or 15,734 bits per second.
One other problem with in-band audio data communication over the sound
carrier of a video channel is that the data is typically inserted into
only premium channels by a television signal scrambler, also referred to
herein as an encoder. In other words, the data receiver of terminal
apparatus must be tuned to a scrambled channel in order for the data
receiver to receive the in-band audio data transmission. An in-band audio
data receiver of a cable television terminal capable of displaying channel
identification information is described in pending U.S. application Ser.
No. 07/800,002, filed Nov. 29, 1991 and incorporated herein by reference.
With the advent of so-called on screen display of data accompanying a
particular channel, for example, a channel program guide for the viewed
channel, there has been a related need to increase the data carrying
capacity of the channel. For example, it is desirable to turn to a
particular cable television channel and, by remote control, cause a
display of the program guide for the evening's entertainment on that
channel, in stead of the program content for a period of time, with
accompanying program audio or other audio content. A television terminal
with programmable background audio and video is described in U.S. Pat. No.
4,991,011, incorporated herein by reference.
Also, there is a great need to provide new and additional services over the
cable television network. These services include telecommunications, both
voice and data, captioning, teletext, facsimile, digital audio, video game
and computer software downloading. All of these services will require
greatly increased utilization of the available cable television spectrum.
It is now proposed that over-the-air broadcast programs carry captioning
data on one of the lines of the vertical blanking interval. It has also
been long required that lines of the vertical blanking interval be
reserved for certain test purposes. Also, in Europe, it has been known for
some time to provide teletext services on certain lines of the vertical
blanking interval. Consequently, it has been generally known for some time
to transmit in band video data in the vertical blanking interval of a
baseband video signal of a television system.
With the increased data carrying capacity requirement, there is a
requirement to remain compatible with existing in-band and out-of-band
data carrying schemes so that a cable television system operator need not
replace their existing cable distribution and terminal apparatus which is
a great capital investment. Consequently, there remains a problem in the
cable television industry to greatly increase the data throughput from a
headend through the signal distribution plant.
II. SUMMARY OF THE INVENTION
The problems and related problems of known cable television data
transmission arrangements are solved by the principles of the present
invention which has the following objects:
It is an object of the present invention to identify and to utilize an
additional means of data transmission from a headend. This additional
means may include, and not be limited to, the utilization of portions of
the vertical blanking interval of the video picture signal.
It is a further object of the present invention to remain compatible with
existing signal distribution and terminal apparatus. Consequently,
existing services and features of known cable television systems will be
provided in known manner or, at least, in a manner which is not a
significant variant from known techniques which would require considerable
terminal modification or even replacement.
It is a further object of the present invention to utilize the additional
means of data transmission for new and additional services. These new
services may include the delivery of telecommunications, both audio and
video, program channel guide and other services, some of which have
already been enumerated above.
It is a further object of the present invention, to the extent possible, to
make out-of-band and in-band transmission schemes similarly simple to
decode so that software storage capacity at terminal or signal
distribution apparatus is minimized and the storage of received data
facilitated. To meet this object, the data may be transmitted in similar
length packets comprising a number of bytes M, an even number between 8
and 24 or N, an even number of bytes between 12 and 36. Then, simple
transactions or messages may comprise M or N bytes and more complex
transactions or messages may comprise from 2M to 8N bytes in length. The
transactions may be, then, of several types depending on their length
which may be most simply designated A, B, C, D, E . . . and so on as
necessary but maintain a commonality determined by the packet parameters M
and/or N and/or 2. Once formatted into transactions, the data may be
transmitted over any one of provided in-band audio, in-band video or
out-of-band data channels.
In keeping with the objects of the present invention, in-band and
out-of-band data transmission is utilized to greatly increase the data
throughput from a headend to signal distribution apparatus or to a
terminal. The vertical blanking interval, to the extent it is not utilized
for required services such as captioning, is utilized for the transmission
of high data throughput services such as program channel guides which
require frequent and periodic update. The transmission via the vertical
blanking interval is suggested to be at a data rate on the order of a
known teletext data rate at 5.7 megabits per second. Out-of-band
transactions are utilized to update terminal memory and to control signal
distribution apparatus in known manner. However, as described above, a
commonality is suggested according to the principles of the present
invention for data transmission schemes for any of the three forms of data
transmission: in-band audio, in-band video and out-of-band.
According to the principles of the present invention and for in-band video
data, a pedestal is provided, for example, at a selectable 70, 80 or 100
IRE level, and, then, an in-band video data receiver data slices in the
vertical blanking interval signal at half the chosen pedestal level.
Through analog and digital circuitry of the in-band video or vertical
blanking interval data receiver, the circuitry determines the location of
the vertical blanking interval and the form of the data expected to appear
on a given line. An addressed out-of-band or in-band audio data
transaction may be utilized to establish the capabilities of given
terminal apparatus to decode particular lines. For example, lines 10-12
may be coded in one form, lines 13-16 in another form, and so on until
line 21, which is reserved for passed through captioning (while another
line may provide captioning in a second language according to the
principles of the present invention). In an alternative embodiment, the
pattern of the in-band video data may be utilized for its recovery and
recognition. The requirement for predisposition of the terminal to receive
data from predetermined lines is thus avoided. In either embodiment, the
captioning signals and other signals that are required to be forwarded
toward the television receiver will not be decoded by the signal
distribution or terminal apparatus according to the present invention or
otherwise disturbed from being received by the television receiver.
In one preferred embodiment, lines 7, 8 and 9 of the vertical blanking
interval of the picture signal may be utilized to transmit in-band video
data for, for example, descrambler control or for new services. These
lines are normally utilized for transmitting equalizing pulses after
serrated synch pulses signifying the vertical synchronizing pulse.
According to the present invention, the in-band video data, transmitted
with certain of the equalizing pulses removed, will be stripped off the
incoming video signal at an in-band video data receiver to meet a
requirement that no signals above 0 IRE be transmitted on these lines to
the television receiver. Furthermore, the receiver automatically replaces
any removed equalizing pulses.
The form of in-band video data for descrambling control may comprise, for
example, selection data for selecting one of a plurality of modes of
descrambling, such as video inversion, synch inversion, gated synch
suppression at varying levels, video line shuffling, sine wave suppression
or any of the other well known means of scrambling. Another form of
descrambling control data comprises timing data, that is, when is a
particular form of descrambling to begin and end. A flag, for example, may
be utilized in the vertical blanking interval to say "start" and to define
a descrambling mode window, for example, a number of fields, or, in
another embodiment, the start of a particular form of descrambling may be
defined by one flag and the end of the particular form of descrambling by
another. Other features of the present invention described herein include
the utilization of a field flag to denote odd/even field and time of day.
Other utilization of the in-band video data transmission may include, but
not be limited to include any of the enumerated services described above
such as program channel guide, teletext, facsimile, telecommunications and
so on.
If all six equalizing pulses present at lines 7, 8 and 9 are removed, then,
a terminal according to the present invention may regenerate the removed
equalizing pulses, which are required to be passed to the television
receiver. By removal of all the equalizing pulses, practically a 200
microsecond data window is provided, (three lines.times.63.5
microseconds/line in an NTSC standard video waveform) beginning after the
last serrated synch pulse and concluding with the first full width
horizontal pulse at line 10. In another embodiment, the three equalizing
pulses of lines 7, 8 and 9 appearing in synch with horizontal pulses will
not be removed; only the three equalizing pulses appearing between these
are removed. Even in this embodiment, the available data window is only
reduced by approximately 10 microseconds.
Preferably, each line of vertical blanking interval utilized for in-band
video data transmission comprises at least a fifty microsecond data window
for transmitting 25 four bit bytes. The data may include, for example, a
one byte pedestal of one microsecond duration to provide a data slicing
level for bipolar data detection and evaluation.
Consequently, an in-band video data inserter according to the present
invention modifies the normal television synchronization signal and may
conveniently comprise a portion of a television scrambler or a cable
television modulator or comprise a separate integral element. An in-band
data inserter was first described in the afore-mentioned U.S. application
Ser. No. 07/800,002 filed Nov. 29, 1991 for providing in-band audio data
transmission on non-scrambled channels. According to the principles of the
present invention, an in-band data inserter for non-premium channels may
provide either in-band audio or in-band video data insertion; then, an
in-band receiver need not be tuned to only scrambled television channels
to receive in-band video data.
One connected to the cable television distribution plant via a pirate
terminal, which is not equipped to regenerate equalizing pulses, will
receive a signal on any channel carrying in-band video data, regardless of
whether it is scrambled, that is not in accordance with NTSC broadcast
signal standards. The intentionally degraded picture signal may result in
some vertical distortion on some television receivers. This is an
advantage in discouraging signal piracy.
Also, according to the principles of the present invention, new services
are transmitted over the vertical blanking interval of the video signal
while known services are provided over the sound carrier (in-band audio)
or via an out-of-band data carrier. A cable television operator may
utilize and program delivery of data services in accordance with the
present invention any way they choose, by automatically predetermining
through system control computer and headend controller processes how both
sound carrier and baseband video blanking interval forms of in-band and
out-of-band data transmission be carried out.
These and other principles of the present invention will be best understood
through the following description of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block schematic diagram of a cable television system
incorporating the principles of the present invention comprising a
headend, signal distribution apparatus and subscriber terminal apparatus.
FIG. 2 is a block schematic diagram of a television signal scrambler shown
in FIG. 1.
FIG. 3 is a block schematic diagram of an in-band video data inserter which
may comprise a portion of a scrambler or a television channel data
inserter of the headend of FIG. 1.
FIG. 4 is a block schematic diagram of in-band/out-of-band data terminal
apparatus of FIG. 1 incorporating the principles of the present invention
showing a demodulating and descrambling circuit 404, for receiving in-band
audio and video data, and a data and control circuit 402 coupled for
receiving out-of-band data and the decoded in-band audio and video data.
FIG. 4a and 4b are block schematic diagrams showing one process of
demodulating and descrambling circuit 404 and data and control circuit 402
of FIG. 4 in greater detail for recovering in-band video data.
FIG. 4c is a block schematic diagram showing one process of demodulating
and descrambling circuit 404 of FIG. 4 in greater detail for recovering
in-band audio data.
FIG. 5 shows television signal waveforms for transmission of in-band video
data during the vertical blanking interval of the television picture
signal; FIG. 5a showing a standard television signal; FIG. 5b showing, by
way of example, equalizing pulses removed at lines 7, 8 and 9; and FIG. 5c
showing data inserted at lines 7, 8, and 9; and
FIGS. 6(a), 6(b), and 6(c) show television signal waveforms utilized in
conjunction with FIGS. 4a and 4b in recovering in-band video data.
FIG. 7 is a table showing a proposed data transaction packet scheme for
transmitting data via each of three signals, in-band video data, in-band
audio data, and out-of-band data, the data packet schemes being as
compatible as possible to promote decoding and data storage efficiency.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to FIG. 1, there is shown a headend 100 coupled to signal
distribution apparatus 165, the signal distribution apparatus for
distributing signals from headend 100 to terminal apparatus 150 of a cable
television system. While a cable television system is shown and described,
several of the principles of the present invention may be equally applied
in a satellite, over-the-air broadcast, subscription television system or
other television system known in the art. Headend 100 is shown as
comprising all elements above the dashed line separating signal combiner
106 from distribution apparatus 165 and terminal apparatus 150. Headend
100 equipment need not all be located at one site, but may be located at
several sites controlled by the site where at least the system control
computer 120 is located. The headend 100 of a cable television system
receives a plurality of television channel signals and other sources of
program content, which may include video games or digital audio, or even
telecommunications signals which become inputs to modulators, signal
processors and such of a headend 100. The input video channels to
modulators 105a-105g are denoted "Audio+Video In." There are also shown a
number of connections between each modulator 105a -105g and scramblers
104a-104f and data inserters 107a and so on. These are denoted in FIG. 1
by the "audio", "video" and baseband "BB" labels associated with the
connecting lines. The receivers for receiving the various services are not
shown but may include satellite signal reception, video broadcast
reception or telecommunications receivers. The headend then formats and
transmits the various services over the available cable television
spectrum for delivery to subscriber locations 150. The services are
delivered via cable 170 which may be coaxial or optical fiber which
comprises a portion of signal distribution apparatus 165 and connects, for
example, signal combiner 106 to apparatus 175 and apparatus 175 to
terminal apparatus 155a,b,c or tap 180. Amplifiers, equalizers, couplers,
taps and other signal distribution apparatus to deliver the signal to the
proximity of the subscriber's premises 150 are generally shown as
apparatus 175. Also shown in signal distribution block 165 is tap 180
which generally refers to known types of signal distribution apparatus
proximate to the subscriber's premises 150 which may comprise, for
example, signal denial apparatus such as addressable taps, traps, or
interdiction apparatus. Either form of signal distribution apparatus 175,
180 may be remotely addressed from headend 100 via an out-of-band
transaction from addressable transmitter 140. Signal distribution
apparatus 165 is generally not equipped to receive in-band data
transmissions. Consequently, all communications, regardless of whether
they are addressed communications or not, are transmitted to signal
distribution apparatus 165 via addressable out-of-band transmitter 140.
At headend 100, there is generally a billing computer 110 and a system
manager computer 120. Billing computer 110 includes a subscriber database
and generates a monthly bill for the subscribers in the system based on
level of service and any pay-per-view and impulse pay-per-view purchases.
Billing computer 110 may comprise a personal or other data processing
computer known in the art. Known billing computer systems include the
products of CableData.
The system control computer 120 is interfaced to billing computer 110. The
system control computer 120 may be an Intel 486 microprocessor based
machine such as an IBM Model 90 equipped with a 200 megabyte hard drive
running under the UNIX (R) operating system with 32 megabytes of RAM or
another data processing computer known in the art. These computers are
generally utilized to generate transactions for delivery to signal
distribution apparatus 165 or subscriber locations 150. The billing
computer 110 is especially concerned with the authorization for delivery
of pay-per-view and premium services. Such authorization is translated by
system control computer 120 into an out-of-band or in-band addressed data
transmission to authorize the premium service delivery according to known
processes. System control computer 120 receives transactions such as
authorization transactions from billing computer 110 and formats and
forwards transactions to headend controller 130 and addressable
transmitter (ATX) 140.
The system manager computer 120, in turn, may communicate through headend
controller 130 to ATX 140 over a telecommunications path. Headend
controller 130 determines the control of data transmission via in-band
means, either in-band audio or in-band video. Out-of-band data is properly
formatted and directly delivered to addressable data transmitter 140 or
via headend controller 130 which serves as a data pass through from the
above-described telecommunications link, if used. Addressable data
transmitter 140 modulates the data, for example, by frequency shift keying
or other data modulation technique, on an out-of-band carrier, for
example, at 108.2 MHz for transmission.
The headend controller 130 forwards in-band data to one of a plurality of
scramblers 104a-f or, via a selected scrambler, or directly to, one or a
group selected from a plurality of data inserters 107a and so on. The
scramblers 104a-f operate to modulate in-band data on baseband video or on
the audio carrier data channel. The scramblers interface with modulators
105a-105f or non-scrambled channel modulators 105g and so on. There may be
as many scramblers 104 as there are premium scrambled channels of a
system. Furthermore, a scrambler may be utilized on a non-premium channel
for data insertion. By premium channel is intended a television channel
utilized for the delivery of some premium charge services such as channels
dedicated to certain programming such as Home Box Office or Disney or
channels on which, at least some of the time, premium program events are
shown, for example, pay-per-view events.
Any of a number of different scrambling schemes for scrambling a television
signal are known. Details of particular scrambling operations are not
described, but it is important to appr | | |
