Note: Descriptions are shown in the official language in which they were submitted.
~ . .
TELEVISION INFORMATION SYSTEM
BACKGROUND OF THE INVENTION
Cable Television
A significant proportion of television entertainment is presently
delivered by way of cable television systems. In general, these systems
can receive broadcast television signals on e common antenna or set of
antennas, amplify the signals, and distribute them along transmission
lines either at their original frequencies or after conversion to different
frequencies. The transmissiGn lines are connected $o the television sets
of the system's subscribers, usually through a decoding or filtering device
which is intended to prevent non-subscribers from receiving the signals.
Frequency conversion is often necessary in systems which handle programs
broadcast from outside the local area, sin~e there is ~ good chance
that signals will be received from two different stations which operate
on the same chQnnel. ~A standsrd broadcast television ch~nnel in the
United States is a band of frequencies 6 MHz in width.)
Cable television systems are slso well suited to transmit non-
broadcast programming to ~eir ~ubscribers. Such programs originate
within the cable television system itself, for example by displaying a
motion picture to ~ television camera and using the resulting electrical
signal to modulate a carrier freqency.
ln either case, cable television systems consist of our main parts:
a head end, the main trunk c~ble distribution system, feeder cables and
~ops from feeder cables to the subscriber's TV sst. A cable television
head end includes the television receiving antennas ~or off-~ir pick up
and microwave and/or satellite receivers for other direct television
~L6~3~
programmin~ QS well as equipment that originates local programming.
From the head end, trunk lines transport the signal to feeder lines which
carry signals past each hom e.
The integrity of trunk cables is not meant to be breached by
t~pping off signaLs for direct distribution to subscriber homes. Rather
this is accomplished with a feeder cable. The signals on feeder cables
come from amplifiers (bridger amplifiers) bridged across the trunk cable
at distribution points. Thereîore, in many cases, feeder cables must
parallel or backtrack side-by-side with the trunk cable in order to have
a cable that can be tapped to feed a signal to subscribers. Signal
losses in feeder cQbles may require line extender amplifiers approximately
every 1500 feet. These multi-ch~nnel amplifiers c&use problems
themselves. Repeated amplification of bro~dband television signa]s causes
noise, inter-modulation distortion and echoes, increasing with each
amplification, thereby limiting the distance that signals can be
transmitted while mQintaining a given standard of picture quality.
Cable losses increase wi~h frequency P~ well as w;th distance.
Thus, the superband VHF portion of the c~ble spectrum, 216 to 300
MHz, is subject to greater loss than the highband and lowband VHF, 54
MHz to ~16 MHz.
While the TV channel allocation spans the spectrum from 54 to
890 MHz, a c~ble television system utilizes only a small part of this
spectrum. The first cable television systems were built in the early
1950's to provide broadcsst channels to subscribers in areas that could
not receive off-air signa]s. These early 5-channel systems used the
standard television frequencies from 54 to 88 MHz for distribution of
these broadcast channe]s. When the state of the art ~dvanced to include
12 channels, cable used the high VHF spectrum of 174 to 216 MHz as
well. Th~ie 12 channels could be received without a converter. To
increase to 21 channels, cable systems used the midband spectrum from
108 to 174 MHz to add nine additional channels; these ~hannels required
using a frequency converter since the television set tuners could not
accom modate these midband ch~nnels . C~rent 35-channel systems add
14 additional channels by using 216 to 300 MHz. To accomplish this,
frequency converters were upgr~ded. Plans exist now to add another
33;1
25 channels, extend the cable television spectrum to 450 MHz. Thus,
~s cable television systems add channels, they use increasingly higher
frequencies. This can only be done at the cost of ~reater signal
attenuation.
The upper frequency limit on trunks is established by the
performance of linear broadband smplifiers and by trunk cable
attenuation, which increases with increasing frequen~y. Feeder cable
length is limited to about 1500 feet by the attenuation at the highest
frequencies carried on the feeder. Therefore, the gap between the
highest VHF television frequency at 216 M~Iz and the lowest UHF
tele~ision frequency at 470 MHz establishes a natural barrier to attempted
carriage of both VHF and UHF signals on a cable system.
Bidirectional Unicable Switchin~ System
An improvement in cable television system technology was
introduced by U.S. Patent 4,077,0069 issued to Nicholson on February
28, 1978. Briefly, the Nicholson patent describes a bidirectional cable
television system in which each subscriber has a dedicated television
carrier frequency and channel for receipt of any signals which the system
is capable of sending to that subscriber, except for FM radio broadcasts
which are sent to everyone at the original frequencies (in the band from
88 to 108 MHz). The heart of Nicholson's system is the control station
at the head of each feeder line (at its intersection with the trunk line).
The control stations receive all incoming television programs transmitted
along the trunk line, as well ~ requests from subscribers who wish to
view a particular channel. The incoming channels are first converted
to a single intermediate frequency channel, ~hen the particular program
that a subs~riber wishes to view is routed by switches to ~ frequency
converter which converts it to the subscriber's dedicated ehannel. The
selected program is finally output to the feeder line together with
programs requested by other subscribers and converted to their dedicated
channels. At the subscriber terminhl, one bandphss Iilter separates FM
radio broadcasts from the feeder line, and another separates the
programming which w~s converted to that subscriber's dedicated channel.
~or further details regarding this system, ~e reader is referred to the
Nicholson patent itself.
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Videotext_Systems
In the past few years, the revolution in information technology
has led to the research, development and field testing of "videotext"
systems --a technology which uses electronic devices for the widespread
dissemination and retrieval of information~ These systems have in
common the ability to AllOW subscribers access to large d~ta bases of
information using a modified or adapted television terminal.
While there is little doubt that these "electronic newspapers" have
widespread applicability, use on a mass basis has been delayed by the
high costs of developing these new technologies and by the perceived
obstacles to acceptance by consumers and information providers (cost of
terminal equipmentl cost of system usage, primitive display systems).
While existing system delineations are bl~red, the following summary
categorizes them as either ~'viewdata" or "teletext."
Teletext systems are one-way videotext systems in which
information in digitQl form is plaeed on unused portions of the television
signal by means of special terminal equipment built-in or attached to
fl television set. Unlike viewdata, where the subscriber interacts
individually with the data base, in teletext the complete data base is
cycled continuously and it is evailable simultaneously to all subscribers.
Using a keypad, the desired information is selected by ~e subscriber
~s it is cycled, stored in a local memory, decoded find format ted for
use by a character generator, and displ&yed on a television receiver.
In the United States the makeup of a tele/ision picture limits,
for all practical purposes, information transrnission of teletext to only
two lines (1~ and 18) of the Vertical Bl~nking Interval (VBI). Therefore,
the potential size of the teletext data b~se is limited by the amount
of information that can be cycled in a time period acceptable to the
subscriber. Using these two lines, 90 pages of text can be cycled in
60 seconds; field trials have indicated that this is an ~macceptable limit.
Experiments using VBI lines below 17 and 18 to increase the information
capacity have not been very successful.
Teletext has many obstacls~ to widespread use and consumer
~cceptance. Some of the most obvious are the retrieval time and size
of the data bank, the cost of equipment in the home, the rudimentary
3~L
graphics, and the absence of privacy. Because the subscriber selects
information ~s it is cycled, the size of the data bank is limited by an
acceptable waiting time. In the U.S. where only 2 lines of the YBI
are available for data transmission, teletext is, for all practical purposes,
still a narrowband and consequently slow system. To use the teletext
system, the subscriber must rent or purchase a modified television
receiver with ~ keypad, a decoder with memory, a character generator
for visual display, and ~ p~ge grabber. A less-sophisticated version has
a keypad, set top modulator and decoder. Even the most prim itive
terminals presently cost several hundred dollars more than conventional
television. Even with mass production, the terminal costs will be too
great for the occasional user. The primitive alphanumeric and graphic
displ~ys have limited marketability. Because all subscribers have access
to the same information at the same time, teletext has limited
acceptability for information providers who want to restrict their
information to special users. Teletext a~so has limited appeal to
information providers becauæ the one-way system makes it impossible
to record and charge for the specific page reguested.
Viewdata is a narrowband, interactive switched system employing
telephone lines to transport inform~tion from data banks to subscribers.
IJI R viewdata system, typically tl:e subscriber requests information via
a keypad or a keyboard attached to a telephone line. This information,
stored either in central or localized data banks, is forwarded to the
subscriber in p~ge packets, stored in the interactive "terminal" and
formatted for display on a color television receiverO The display consists
of alphanumeric chara~ters and stylized graphics.
Access to viewdatA systems involves individualized, interactive
tree searches. An information request leads the subscriber to general
information; the subscriber refines his request, which le~ds to more
specific pages. Thus, the process of~en involve3 several interactions
before the subscriber obtains the desi~ ed information.
Information providers therefore face ~ mapr ch~llenge: to design
the "search" system to ensure that the subscriber does not get lost or
frustrated in his d~ta search. The information provider, in structuring
his information, must think like his subscriber and must strive to create
a "friendly system" which will allow the subscriber to retrieve the desired
information with as little trouble as possible.
To accomplish this interaction, typical viewdata terminal equipment
consists of a keyboard, microprocessor, memory, display controller, a
coior television and a 1200 bit/s modem to allow transmission of digital
cata over standard telephone lines. A separate dedicated telephone drop
is needed to avoid tying up regular telephone service. The narrow
telephone bandwidth limitation of the viewdata system frequently results
in lengthy retrieval intervals. For example, in u typical viewdata system,
a simple tree search, involving perhaps five interactions, can often take
60 seconds because of the wait time necessary for each page to be
displayed on the television screen (6 to 11 seconds per page). A more
complex search can take even longer.
In addition, while the system allows the subscriber access to a
very large central c,ata base, or an ~limited number of localized or
specialized data bases, the system can easily be overloaded when
subjected to very many sim ultaneous requests.
Because each information request is individualized -- only the
subscriber receives the information requested over his own private
telephone line -- the system can be adapted for groups requiring a
secure channel.
Typically, the graphic display systems for viewdata are
rudimentary; ~ey are not c~pable of producing true photographic
representations. Instead, alphanumerics and picture-like graphics are
produced by using a mosaic sub~element matrix of two columns and
three rows per character. The process is primitive and slow. A second
gen~ration viewdata system, now under development9 has refined graphic
capability. Its graphic display of 960 lines by 1280 picture elements,
1,2a8,800 pixel loeations, provides nearly 20,000 times as much deWl as
the earlier systems. This refinement is not without its ~radeoffs: the
systemls alpha-geometric deeoder costs nearly ten times that of a first
generation decoder; f~ther, transmitting a graphic image using this "best
case" stylized graphic system may take hours.
While exhibiting much potential, the widespread ~doption of
Yiewdata systems faces several types of obstacles, including length of
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retrieval time and complexity of the search process, cost of equipment
in the home, cost of using the system, and rudimentary graphics.
The use of narrowband telephone equipment means that a simple
request may take as long as 60 seconds; more complex requests may
involve much longer times. E~ecause of the interactive nature of the
system, a subscriber may become frustrated in his seareh if the
information is not sufficiently coded and cross referenced. The subscriber
may not find what he needs.
In order to use a viewdata system, the subscriber, in addition to
a dedicated telephone line, needs an adapted television receiver equipped
with a keypad, memory, microproce~sor, end display controller. Prototype
mode]s cost approxintately $2,000-$3,000. Even if mass production could
substantially reduce the price to a target of 50% more than a standard
color television, only the most serious subscribers (businesses and
prof ssionals) could afford the system.
A typical system involves three charges: a local telephone call,
an overall charge for the use of the system on a per minute basis (with
variations for peak or off-peak usage), and a price for accessing the
data base. This last charge is a per-page price established by the
information provider. Rntes vary according to the type of information
requested, ranging from $.02 to a maximum of $1.00 per page.
Advertisements may be free, an index to information available at nominal
rates, and specialized, technical informatlon commanding the highest
rates. Thus, a typical request may cost $.25 ~ ~ge, far above the
cost of a daily newspaper or even a phone call to elicit the equivalent
information.
While the display can present textual information adequately, the
inability to reproduce photographs makes these systems poor candidates
for mass marketing where ~e ability to see the actual product and
compare it with similar products is essential.
Cable Television Systems With Videotext
Cable television systems, although used only experimentally Ior
information retrieval and dissemination, have many inherent advantages.
The greater spectrum available to cable systems allows them to transmit
many channe~s ~ older systems norm~lly carry 12 channels and newer
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ones 35 channels (although systems capable of as many as 128 channels
are currently being proposed in larger urban markets). Thus, the
allocation of a large amount of spectrum space to date is possible.
Further, because the channels are wideband, data can be transferred
f ester.
Finally, the wide bandwidth available through cable television
systems provides for transmission of standard television photo images in
V30 of a second (in ~ddition to alphanumeric and graphic representations).
However, in order for a subscriber to "hold pictures" each terminal
device would have to be equipped with a "frame gr~bber" which would
select the television photo image frames, store them in ~ local memory
at the terminal location, and refresh them for the television screen.
"Frame grabbers" currently have only been produced in small quantities
and are very expensive.
Since all cable systems provide a one-way distribution to the
home, teletext, which is ~ one-way system, can easily be adapted for
cable systems without limiting use to lines in the vertical blanking
interval. An entire television channel could be devoted to teletext.
However, in order to store photo images, a frame grabber would be
required at the subscriber location, in addition to the terminal equipment
necessary for broadcast telete~t (keypad, decoder, modulator).
Viewdata (interactive) ~pplications ~re also possible with cable
television systems. Two-wsy systems alreRdy allow for return data from
subscriber locations. Older on~way systems will require the addition
of amplifiers ~nd filters, or retrofitting with a second cable.
Cable networks, linked via satellite, can provide a viewdata user
with access to data banks at different locations, or with a central data
bank located at the head end.
Cable television, which has already established the tradition of
monthly subscrio~er charges for services, can market videotext as an add-
on service, offering subscribers teletext, viewdata, or both, or a monthly
service charge, or charging per page on computer interfaced two-way
systems.
While the use of cable television solves some of the problems
inherent in teletext or viewdata by providing greater spectrum and
3~
bandwidth, and is capable of transmitting photo images, there
are still obstacles to mass use, including the cost of terminal
equipment, but problem of privacy, and the design of existing
systems.
Any market resistance to high subscriber terminal
costs which would limit marketing of viewdata or teletext
would also limit cable television. The advantage of cable
television over viewdata (not counting the elimination of
exorbitant telephone line costs) is the ability to display
"photographic" images which could be transmitted at a rate of
30 per second. However, this advantage is immediately weaken-
ed or even dissipated by the prohibitive cost of installing a
"frame grabber" with memory storage at each subscriber loca-
tion. Mass marketing is inhibited or vitiated.
SUMMARY OF THE INVENTION
An object of an aspect oE the present invention is
to adapt the latest cable television technology, as exemplified
by the Nicholson patent, to the dissemination and retrieval
of information. Using the present invention, individual sub-
scribers are able to receive selected information from databanks through the same system which brings them television
programming, and to receive it on their own, unmodified tele-
vision sets. Accordi~gly, an object of an aspect of the
present invention is to provide information to subscribers
withou~ the need for expensive terminal equipment at the sub-
scribers' locations.
An object of an aspect of the present invention is
to give subscribers quick access to information from a large
data bank, a combination which is impossible under existing
teletext systems. An object of an aspect of the present
invention is to maintain privacy in an information retrieval
system by giving each subscriber a dedicated television channel;
a collateral object is to maintain privacy in such a system
without the need for each subscriber to have an information-
dedicated telephone line.
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An object of an aspect of the present invention
is to allow subscribers to an information-delivery system
to receive photographic information and no-t merely stylized
graphics.
A cable televisi.on and information system in
accordance with an aspect of the present invention is
capable of transmitting selected data to subscribers. In
addition to the VHF television channels on which each subscriber
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receives regular programming, a UHY television channel is dedicated or
assigned to each subscriber to deliver information. The use of an entire
6 MHz UHF channel for information guarantees that a great deal of
information can be transmitted in 8 short time, thus satisfying the
requirement for minimal retrieval time. The large bandwidth also allows
photographic information to be delivered to subscribers' television sets.
This cable television system includes a head end, trunk lines, bridger
amplifiers, control stations, feeder lines and a central computer connected
to the he&d end. The control stations include an information retrieval
system for extracting inIormation from the trunk lines and converting
the frequencies carrying the information to the proper dedicated UHF
frequencies. The cable television and information system also includes
a subscriber station which includes ~ keyboard for selection of data to
be displayed.
In the above cable television and information system, specialized
equipment is concentrated at the eontrol station, out of resch of the
subscriber. Thus, the amount of specialiæed equipment required is only
a fraction of what would be needed if each subscriber's home were so
equipped, since one set of equipment in this system can serve many
subscribers.
The subscriber generates data selection instructions identifying the
desired data by typing the appropriate chara~ters on the keyboard. Radio
frequency signals corresponding to the keystrokes and to the station's
identification number are transmitted alGng the feeder line to the control
station, which demodulates and stores the signa~s. They also travel to
the head end. At the head end, these data selection instructions are
routed to the central ~omputer~ where they are decoded.
The central computer locates the selected data, either in its own
internal data sources or in an external d~ta source, if one is available
to the system. The central computer then retrieves the d~ta from the
source, decodes it to a "scene1' if it is teletex$, formats it for display
on a teleYision set, and~ if necessary, attaches an identifying number
to the data. This number will be used by the control station to
determine whether to extract the data from She trunk, which subscriber
requested the information, and, therefore, at which dedicated UHF
6~
frequency to transmit it along the feeder cable. Finally, the central
computer sends the selected data to the head end, where it is transmitted
along the trunk line to the control station.
At the head end, data may be stored either in digital form, or,
especially in the case of still slides, in analog form. The system ha
the option of transmitting the selected material along the trunk line to
the control station in either digital or analog form. Digital transmissions
can be made distortion-free, while ~nalog transmission may be subject
to some distortion. Digital transmission is slower (by ~bout a factor
of 10). A single television frame in digital form would require a
transmission time of about 1/3 seeond whereas frames in analog form
can be transmitted at a rate of 30 per second. In the preferred
embodiment, however, all information is transmitted from the head end
to the control station in analog form; consequently, if it is stored as
digital data, it must be converted to analog by a digital-to-analog (D/A)
converter. The head end uses the analog information to modulate a
band of freguencies designated for downstream communication -- the
downstream channel ~ which is preferably within the VHF range.
At each control station, the identifying numbers corresponding to
the data requests of subscribers connected to that particular control
station are stored. The data selected by individual subscribers then is
extracted from ~e trunk line by a frame grabber. Each subscriber~s
data or information, in the fsrm of a television frarne, is routed, in
accordance with the identify~ng number, to one of several frame stores
at the control StAtion. The d~ta frame is stored so that it can be
continuously transmitted to the subscriber. The information is stored
in digital form, converted to analog by a digital-to-analog (D/A)
converter9 and then used to modulate a ~igue carrier frequency
corresponding to the particular subscriber's television set.
The modulated carrier frequency occupies a standard UHF
television channel dedicated or assigned to a p&rticular subscriber. All
subscribers are sssigned different UHF television channels for transmission
of information. At the output of the control station, the carrier
modulated with the selected data is inserted into ~he feeder line which
~erves the home of the subscriber who requested the data. VHF
programming and information transmission on dedicated UHF channels
occur on the s~me feeder lines. At the subscriber's terminal, a filter
is connected to the subscriber's television set to block all channels
except the channels bringing him programming or information. Only
VHF programming channels and the dedicated or assigned UHF information
channel reach the subscriber's set.
With this invention, the individually assigned subscr5ber channel
can be received on a standard television set. Subscriber terminal costs
are limited to a simple keypad and oscillator, since the bulk of the
equipment necessary for information transmission is located at the
common control st~tion. When using a common feeder c~ble for both
television programming and videotext, entry into the house can be made
by using a single drop with a splitter at the rear of the television set~
An important advantage of this system in information retrieval is
the assurance of privacy. Because each user has his own private
dedicated chennel, only the individual requesting information will be able
to receive it. Unlike conventional cable television where the ¢able
functions as a "party line," here eAch subscriber has his own private
line.
This invention can use either the regular cable television feeder
line or a separate f0eder line. With a separate feeder line, the number
of feeder lines from a single control station can be increased and the
number of dedicated channels on ea¢h line can be increased by using
the spectrum from 890 MHz down to 50 MHz for Q total of 140 channels
per feeder.
Another feature of this invention is the use of the concept of
an inverted spectrum. As previously noted, cable television was forced
to use increasis~ly high frequencies as additional programming services
created a demand for more channels. This use of higher frequencies
caused the associated problem of increased attenuation. The greater
the distance these high frequency signa]s were transported, the greater
the signal loss. To avoid this problem, the present invention assigns a
6 MHz channel to each subscriber on ~n inverted basis. Channel
allocations consist of the UHF channels 14 through 83, using the spectrum
470 to 890 MHz. There are 70 channels available in this range so that
on a single feeder cable, 70 different subscribers can
each be allocated a channel. Using the inverted spectrum
concept, the subscriber closest to the control station
is assigned -the highest channel - 83 (884 to 8gO MHz) -
and the most distant subscriber the lowest - 14 (470 to
476 MHz). This allows the highest frequency (subject to
the greatest attenuation with distance) to be transported
the shortest distance. Therefore, each subscriber
receives a clear picture without the need for amplifiers
along the feeder cable.
If subscriber density exceeds 70 homes per
mile, then non-standard channel assignments are made
in each cable television system on the unused portion
of the spectrum until it overlaps the basic system,
which will be at about 216 to 300 MHz in current cable
systems. Also, as the UHF frequency falls below 470
MHz, a one-channel set-top converter will be required.
Using this distribution pattern, the present invention
can accommodate a virtually limitless number of program
services since only the program selected by the subscriber
need be transported along -the feeder to the subscriber's
private line.
An aspect of this invention is as follows:
In a cable television system containing a
plurality of television receivers connected to a transmis-
sion line for transmitting television signals including
programming to the receivers, wherein selected data is
transmitted on the transmission line along with the
programming, an information system for displaying the
selected data on a selected one of the television receivers,
comprising:
data extraction means connected to the transmis-
sion line for extracting the selected da-ta therefrom;
switching means connected to said data extraction
means for routing the selected data in accordance with
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the identity of the selected one of the television
receivers on which the da-ta is to be displayed;
storage means connected to said switching means
for storing the selected data; and
a plurality of modulators, each of said modu-
lators being connected between said storage means and the
transmission line and operating at a unique carrier
frequency associated with a particular television receiver,
to modulate the carrier frequencies with the data stored
in said storage means.
Other objects and features of the present
invention will be apparent from the following description
taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE ~RAWINGS
Fig. 1 shows the electromagnetic spectrum Erom
O to 300 MHz, giving the allocations of several bands
and nomenclature of several channels.
Fig. 2 is a block diagram of a prior art cable
television system.
Fig. 3 is a block diagram of the subscriber
terminal of a prior art videotext information system
described above as teletext.
Fig. 4 is a block diagram of the subscriber
terminal of a prior art videotext information sys-tem
described above as viewdata.
Fig. 5 is a block diagram of the subscriber
terminal of the present invention.
Fig. 6 is a block diagram of an entire informa-
tion system in accordance with the present invention.
Fig. 7 is a detailed block diagram of the
control station which is a part of the present invention.
3~
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Fig. 8 illustr~tes one embodiment of a feeder cable system in
accordance with the present invention.
Fig. 9 shows detaiLs of subscriber drops in the system of the
present invention.
Figs. 10 and 11 are diagrams of the electromagnetic spectrum from
O to 890 MHz, showing channels available for use with the present
invention.
Fig. 12 is a flow diagram for the computer program of the central
computer used with this invention.
Fig. 13 is ~ flow diagram for the ~omputer program of the mini-
computer used in the control station of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
_ . _
Fig. 1 shows the allocation of VHF broadcast television channels
and other radio channels. A conventional cable television system
delivering standard VHF channe]s and FM radio will transmit the band
of frequencies from 54 to 108 MHz and the band 174 to 216 MHz to
all subscribers. Subscribers can therefore receive VHF televi~ion and
FM radio on ~modified receivers. A cable television system using a
dedicated channel for e~ch subscriber, such as described in the Nicholson
patent~ U.S. Patent No. 4,077,006, ~s well as a system which transmits
a greater number of programs th~n can be shown on the twelve standard
VHF channe]s, will make use not only of these standard channeLs (2
through 13) but also of the midband and superband channels ~A through
W). Consequently, a cable system which does not give each subscriber
a dedicated channel can tele.rise 35 programs to ~n unlimited number
of subscribers. On the other hand, the system described in the Nicholson
patent ~an televise an urllimited number of programs to 35 subscribers
on e~ch ~eeder line.
Fig. 2 illustr~tes & typical c~ble television system. At the head
end 100, equipment is provided to receive incoming television programming
by various me&ns or to create locally-originsted programs. After
amplification and any other necessary signal processLng, ~11 channels are
transmitted at their original frequencies, from 54 to 300 MHz, ~long
the trunk line 102. Although only one trunk line is shown, there may
be several, depending upon the particular system's design. Trunk lines
~Z~ 3~
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102 connect the head end 100 with all bridger amplifiers 104.
The bridger amplifier 104 is a conventional unit (for example,
Station SP-2T-2W using two TF-30 high-low split filters, manufactured
by Jerrold Electronics Corp. of Philadelphia, Pa.). It amplifies both
upstream and downstream signals. The upstream signals, if any, will
most often be requests by subscribers to view particular programming,
although some systems may enable subscribers to send other signals to
the head end.
The subscriber's television set 110 is attached to feeder line 106
through any necessary filters snd converters 107. The set 110 is a
standard television receiver able to receive VHF channels 2 through 13
and UHF channels 14 through 83. If programming is to be trarlsmitted
along feeder line 106 on other than these standard channels, a converter
will be necessary.
A subscriber terminal for a videotext information system called
teletext is illustrated in Figure 3. Data, as weU as normal television
programming, is received at lthe subscriber's ~ntenna 112. ~lthough an
individual antenna can be provided or e~ch subscriber, community
antennas are equally useful with teletext. Television programming is
delivered directly to the sntenna terminals of the unmodified television
set 110. Incoming signals are also sent to the decoder and character
generator 114.
Because all available d~ltA iS cycled continuously in a teletext
system, in order to view a particular page of data on a television set,
the subscriber rleed only key his request into his keypad 116. This
request is processed by the decoder and character generator 114, which
selects the requested pQge from ~e continuously-transmitted ~ta,
decGdes it into characters for television display, and sends the characters
to the on-channel modulator llB. There, the data is used to modulate
the carrier frequency îor ~e television channel on which the subscriber
receives dat~. The data-modulated carrier is then input to the unmodified
television set 110, where it is demodulated and the data viewed by the
subscriber.
Figure 4 shows ~e subscriber termir~l of ~nother type of videotext
system called viewdata. ~ubscribers to viewdata receive information
16
through a dedicated telephone 120, which provides two-way
communications with the data source. Requests for information are
typed into a keyboard 122, encoded by the decoder and ch~racter
generator 124, ~nd modulated for telephone transmission by modem 126.
Requests are then transmitted along telephone lines to the data source,
where the requested information is retrieved and transmitted back to
the subscriber. Modem 126 demodulates the incoming data, and decoder
~nd character generator 124 decodes it into characters which are then
displayed on the subscriber's television set 128. The viewdata television
set 128 is a modified set, including the decoder snd character generator
124 and the modem 126.
The subseriber terminal of the present invention is shown in block
diagr~m form in Fig. 5 and is generally identified by reference number
129. Coaxial cable 130 is a feeder line in ~ cable television system
which carries television programming to the subscriber's unmodified
television set 110. A b~ndpass filter 132 is interposed between cable
130 and television set 110 to block all frequencies except the subscriber's
dedicated UHF information channel. For television program reception,
a parallel VEIF bandpass filter lOû would be included.
The subscriber wishing to view information first types an "all
clear" signal into the keypad unit 134. Keypad unit 134 contains a small
snemory and an oscillator in addition to the keypad. If the keypad is,
for example, the standard twelve-button numerical type, the all clear
signal may be a single keystroke on one of the two non-numerical
buttons. This signal clears the keypad's memory ~nd prepares it to
receive a new data request. Next, the subscriber keys in the catalogue
number indicating which data is to be displayed on his television. (He
may obtain this number, for example, from a printed catalogue distributed
by the cable system operator; or the catslogue itself may be available
electronically, by way of the information system of the present invention.)
As the eatalogue number is entered, it is stored in the memory. When
the entire number h~s been stored9 the subscriber types in a "transmit"
signal (which, once again, may be one of the two non-numerical buttons
on a twelve-button keypnd), causing the data reguest, which is made up
of the catalogue number, plus a station identification number which has
3~
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been preset within the keypad, to be transmitted as a radio-frequency
pulse train to the control station. Transmission of the pulse train is
accomplished at the radio frequency of the keypad's oscillator, which
operates on a return channel (a band of frequencies designated for
upstream transmission) preferably within the range from 6 to 30 MHz.
Many keypad oscillators may operate on the same return channel. A
low pass filter 136 at the output of keypad unit 134 ensures that only
signals below 30 MHz are passed to the cable 130, thus preventing
interference with television programming and data being transmitted
along th e cable.
Figure 6 shows the cable television system of Fig. 2 modified in
accordance with the present invention to deliver selected data to
subscribers over dedicated UHF television channels. A subscriber selects
data to be Yiewed on his television set by generating data selection
instructions as described above in connection with Fig. 5. The
instructions are transmitted from subscriber terminal 129 along the feeder
line 106 back to the bridger amplifier 104 and control station 140. The
control station, whose operation will be described in greater detail below,
demodulates the data request and stores both ~e station identification
number and the catalogue m~mber of the data. ~t the same time, the
data request ~lso passes through the bridger Qmplifier 104 which amplifies
it and switches it onto trunk line 102 which carries it to the head end
100.
At the head end, central computer 138 demodulates and stores
the data selection instructions. Computer 138 lo~stes the selected data
using its catalogue number by se&rching either the computer's own
internal data sources, or external sources connected to the system. The
catalogue number is used to refer to a directory which the computer
138 calls up from, for example, magnetic disc storage. Such indirect
addressing allows more fle~bility in the operation of the system. Internal
data ssurces may be, for example, magnetic disc and tape 137, or still
pictures in the form of slides 139. The data retrievable by this system
may be stored in either &nalog or digital form. After loc&ting and
copying the selected data, ¢entral computer 138 decodes i~, if it is
stored as teletext (in digital fsrm), to ~ analog (NTSC) "scene," and
3~
~ 18 -
arranges it in the proper format for display on a television screen. If
it is already stored in analog form, the decoding is unnecessary. Data
stored in the computer's local sources will preferably be stored with
the catalogue number alreHdy in the vertical blanking interval (VBI). If
it is not there, the central computer 138 inserts the catalogue number
into the YBI before transmission. Although in the preferred embodiment
the VBI is used to carry the c&talogue number, it will be appreciated
that this number may be placed anywhere in the transmission. The
~elected data and its c~talogue number are then sent to the head end
100 which transmits them the appropriate number of times along the
trunk line 102 to the bridger amplifier 104 and control station 140~
Although in the preferred embodiment the station identification number
is not used by central computer 138 to control data flow, because the
catalogue number is used by the control station 140 to determine which
subscriber should receive the data, it is possible for computer 138 to
make use of the station identification number in other ways. For
example, it may be used by the computer to determine which control
station 140 requested ~e data and thereupon to attaeh to the data an
additional signal which will "alert" that control station to the fact that
data is arriving for one of its subscribers. Also, whereas in the preferred
embodiment all reguested information is tr~nsmitted along all trunk lines,
the station identification number may be used to select the proper trunk
line for data transmission, thereby reducing unnecessary traffic on the
other lines. Furthermore, if it is desired to charge subscribers for data
requests, or if statistics of such requests ~re to be kept, the station
identification number will be needed by central computer 138~ Head
end 100 need transmit A bla~k-~nd-white fr~me only once. If it is
transmitting a ~olor frame, that need be tr~nsmitted only once if a
frame grabber is used which will grab a single color fr~me. However,
with the particul~r frsme grabber used in this system, color frames
must be transmitted three times because the presently available frame
grabber grabs the three colors seri~lly.
Referring now to ~ig. 7, a control station 140 is associated with
each bridger amplifier 104 to direct selected dlata to the proper
subscriber. Esch control station 140 includes an upstream demodulator
~L6~
- 19 -
142, a downstream demodulator 144, a frame gr~bber 146, a mini-computer
148, several frame stores 150 (each of which includes a digital-to-analog
(D/A) converter 152), and a modulator 154 for each subscriber. Also
part of the control station are two switching circuits controlled by the
mini~omputer, one switching circuit 156 determining which frame store
receives the output of the frame grabber, and the other 158 determining
to which modulator the output of the frame stores is sent. The number
of frame stores 150 included in the control station 140 need not be as
large as the number of modulators; only enough frame stores are needed
to handle the peak volume of dats requests.
Upstre~m demodulator 142, which is a conventional unit3 receives
and demodulates data reguests from subscribers on a return ¢hannel
within the range of B to 30 MHz. When the arithmetic and logic unit
(ALU) of mini-computer 148 detects an output from demodulator 142, it
stores it in the mini-computer's RAM. This information, it will be
recalled, consists of a station identification number and a catalogue
number. The catalogue number in the RAM will be compared by the
mini-computer to the catalogue numbers in Rll OI the VBI's of frames
arriving on trunk line 102. If a match is found, the frame will be
grabbed. The station identification number will be used by the mini-
computer to direct the output of the appropriate frame store 150 to
the proper subscriber's modulator 154, by ~ontrolling switching circuit
158.
All analog frames ~rriving at control station 140 from trunk line
102 on the ~HF downstream channel are demodulated by downstream
demodulator 144, a}so a com~entional unit. From there, they are sent
to both the mini~omputer 148 and ~e frame grabber 146. In the
absence of instruction from mini~omputer 143, switching circuit 156 is
open with respect to all frame stores 150, and the frame grabber 146
does not grab ~rames. Mini~omputer 148 examines every VBI, comparing
the catalsgue numbers in the intervals to the catalogue numbers stored
in its RAM. Whenever ~ rnatch is found, the mini~omputer 148 signals
frame grabber 146 to retrieve the demodulated frame and at the same
time operates switching circuit 156 ~ as to direct the frame with that
catalogue number to one of the frame stores 150. Also at the same
3~
- 20 -
time, the mini-computer operates switching circuit 158, in accord~nce
with the station identification number stored along with the catalogue
number, so as to direct the output of the same frame store to the
modulator 154 corresponding to the subscriber who requested the data.
The frame grabber is released to enable it to grab subsequent frames.
Bec~use the frame stores 150 store frames in digital form in
RAMs, whereas only analog information can be received on subscribers'
television sets, a D/A conYerter 152 is a part of each frame store lS0
and causes the digitally-stored frame to be converted to analog form
before being output. In order to make the frames available to the
frame stores 150 in digital form, frame grabber 146 includes an A/D
converter at its input.
Analog data is then used by each modulator 154 to modulate a
unique UHF carrier frequency associated with the television set of the
subscriber who reguested the data. The modulated carrier occupies a
channel of frequencies adjacent the carrier frequency corresponding to
the subscriber's dedicated UHF television channel.
The data, in the form of a modulated UHF carrier, then is sent
to combiner 160 where it is combined with VHF signals which are also
traveling downstream and placed on feeder line 106 for reception by the
requesting subscriber.
The frame grabber 146 is a commercially-available device
m~nufactured by Matrox Electronic Systems, Ltd., Montreal, Que. It is
capable of grabbing a color frame Qnd outputting it in real time, although
it stores the three colors serially ~nd separately. The Matrox frame
g} ~bbPr includes the necessary A/D ~onverter, logic, and memory to
perform its f~ctions. Switching circuits 156 and 158 may be~ for
example, convenffonal cross~ar switching arrangements using pen diodes
as the individual switches. The control station's mini-computer, although
not itself a conventional unit, is built in a conventional manner from
standard logic ~d memory c~rds.
At each subscriber location, as shown in Fig. 5, one or more
bandpass filters are colmected between the feeder line 106 and the
television set 110. If television programming is to be received on a
dedicated VHF channel, a YHF bandpass filter 108 is included. To
~1~2165~3~
-- 21 --
receive selected data on a dedicated UHF channel, the subscriber will
require ~ UHF bandpass filter 13~. These UHF bandpass filters block
all frequencies except the UHF channel assigned or dedicated to the
particular subscriber.
Subscribers to the cable television information system of the
present invention are able to re~eive selected data on a standard,
unmodified television set 110, as long as the set is able to receive UHF
channels 14 through 83 (470 to 890 MHz). In order to receive information
which has ~ke~dy been requested and is bein~ transmitted along the
feeder line, the subscriber must tune his television set to his dedicated
UHF channel. If it is tuned to any other UHF channel, bandpass filter
132 will block any signals which may be arriving on that channel, and
the television set will receive nothing. S:)nly when the subscriber's
television set 110 is tuned to his dedicated UHP information channel will
selected data be received.
If the number of subscribers on a given feeder line exceeds 70,
the number of stand~rd UHF channels, more subscribers can be added
to the same feeder line by using non-standard UHF channels and even
extending the spectrum into the VHF range. In Fig. 8, for example,
an embodiment cf this invention is shown in which 1400 subscribers are
served by a single bridger flmplifier and control station. If Qll of the
frequencies from 50 through 890 MHz are alloc~ted to dedicated
information channels, 140 6-MHz channels are available for ~ssignment
to subscribers. Using ten feeder lines and connecting 140 subscribers
to each, 1400 subscribers can be served. It should be emph~sized,
however, that television programming ~ould not be received on standard
VHF channels in this embodiment without the use of separate feeder
lines for programming. Here, all ~hannels from 50 to 890 MHz are
dedicated to information; the st~ndard VHF television ~hannels fall within
~is range (see Fig. 1) and therefore would be used for data reception
rather than programming. Separate feeder lines 106 must be used for
television programming.
~ ig. 9 shows the choice between using one or two feeder lines
106 -- one of the feeder lines is shown ~s a dashed line and the other
as a solid line. In systerns using a single feeder line 106 for both data
6~
-- 22 --
and television programming ("same feeder" systems), the dashed feeder
line would not be present. Both feeder lines would be present in
systems using separate feeder lines 106 for data ~d programming
("separate feeder" systems).
Fig. 9 also illustrates the inverted spectrum feature of this
invention. Bandpass filter 136, which is connected between the feeder
line 106 and the television set ~IQ belongir~ to subscriber A, is tuned
to UHF channel 83, the highest-frequency UHF channel, because
subscriber A is located clo6er to ~e bridger amplifier and control station
than any other subscriber. Because higher frequency signals attenuate
to a much greater degree with distsnce ~lon~ the feeder line thsn lower
frequency signals, channels of descending frequency are allocated to
subscribers of incre~sing distance from the bridger amplifier and control
station. Since subscriber B is more distant than subscriber A from the
bridger amplifier end control station, it is assigned a lower frequency
UHF channel, channel 82. Subscriber C, farther still, has UHF ~hannel
81. A similar allocation of channels is m~de for the remainder OI the
subscribers connected to feeder line 106.
Set-top converters 162, which are also shown in Fig. 8, are used
whenever the subscriber's dedicated information channel (or television
programming channel~ is not one of the standard VHF or UHF television
channels 2 through 83. In $hat ca~e, an unmodified television set 110
is unable to receive the dedic~ted channel unless it is converted to one
of the stand~rd channe}s. Each subscriber's converter 162 need only
convert one channel--his dedicated channel-- to a standard television
chennel (two converters would be required, of course9 if both the
subscriber's dedicated inIormation channel ~nd his dedicated programming
channel were non-standard).
In Figs. 10 and 11, the number of ~v~ilable channels in the same
feeder system of Figure 9 is comp~red to the number of availeble
channels in the separate feeder system by showing the allocation of the
electromagnetic spectrum. In both figures, shaded are~s are those
channels for which a set-top converter 162 is required. In Fig. 10, the
cross-hatched ~res (labelled "possible overlap") indicates channels which
may or may not elready be dedicated to television programming in the
~2~
- 23 -
particular cable television system under consideration. If dedicated to
programming, they are unavail~ble for data transmission. There are 42
possible channels between 216 and 47 0 MHz. In a 21-channel cable
television system, none of these are used for programming, so all 42
could be dedicated to data. A 35~har,tnel cable television system adds
14 programining channels to the 21-channel system by using the VHF
frequencies from 216 to 300 MHæ. In such a system, only 28 information
channels would be ~vailable below 470 MHz. The &rea labelled "overlap
with entertainment" indicates channels which normally would be used for
programming in any given cable television system. There is no possible
overlap with entertainment in separate feeder systems (as shown in Fig.
11).
Figs. 12 and 13 illustrate the program steps performed by central
computer 138 and mini-computer 148, respectively, during the operation
of the invention.
Although illu~ttrative embodiments of the present invention have
been described in detail with reference to the accompanying drawings,
it is to be understood that the invention is not limited to those precise
embodiments and that various char~es or modifications may be effected
therein by one skilled in the art without departing from the scope or
spirit of the invention. For example7 the highest frequency used for
dedicated subscriber channels should not be considered as limited to
UHF channel 83 (884 to 890 MHz) but may be ~s higlt as the state of
the ~rt will allow.
