CA1216931A - Television information system - Google Patents

Television information system


Publication number
CA1216931A CA000501597A CA501597A CA1216931A CA 1216931 A CA1216931 A CA 1216931A CA 000501597 A CA000501597 A CA 000501597A CA 501597 A CA501597 A CA 501597A CA 1216931 A CA1216931 A CA 1216931A
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French (fr)
Bruce E. Lovett
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Bruce E. Lovett
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Priority to US06/363,959 priority Critical patent/US4450477A/en
Priority to US363,959 priority
Priority to CA000424720A priority patent/CA1203890A/en
Application filed by Bruce E. Lovett filed Critical Bruce E. Lovett
Priority to CA000501597A priority patent/CA1216931A/en
Application granted granted Critical
Publication of CA1216931A publication Critical patent/CA1216931A/en
Application status is Expired legal-status Critical




This television information system transmits selected video picture information to one of a number of subscribers who have television sets connected to the system. First, the subscriber makes a selection by transmitting a request to the head end. A central computer interprets the request, searches the available data banks for the information, and records it. Next, the information along with en identifying number is returned to the system and sent to a control station.
At the control station, the identifying number is used to route the information to a particular modulator associated with the subscriber who made the request. The information is stored and used to modulate a unique carrier frequency which has been dedicated to that subscriber.
The control station sends the modulated carrier frequency (containing the selected information) to a feeder line to which may be connected a number of subscribers, including the one who made the request. If the requesting subscriber's television set is tuned to his carrier frequency, he can receive the requested information. Privacy is assured by dedicating to each subscriber a different carrier frequency and associated television channel, and by filtering out all other channels which might be transmitted on the feeder line.
Standard, unmodified television sets may be used with this system;
and rapid retrieval of information from large data banks is possible.


~ . .


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.

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 33~

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 33~

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.
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.

- 9a -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 3~

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


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 L6~3~
- 13a -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.
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.


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.
_ . _ 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~

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 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~

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~

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~

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~

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~

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~

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.
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.


The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. 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 data therefrom;
switching means connected to said data extraction means for routing the selected data in accordance with the identity of the selected one of the television receivers on which the data 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.
CA000501597A 1982-03-31 1986-02-11 Television information system Expired CA1216931A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US06/363,959 US4450477A (en) 1982-03-31 1982-03-31 Television information system
US363,959 1982-03-31
CA000424720A CA1203890A (en) 1982-03-31 1983-03-29 Television information system
CA000501597A CA1216931A (en) 1982-03-31 1986-02-11 Television information system

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