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Description  |
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DESCRIPTION
1. Field of the Invention
This invention relates to an apparatus which can be used with any type of
audio-video device (TV, monitor, radio etc.) having a tuner which is used
to select a frequency or frequency range, and more particularly to an
apparatus which will provide automatic customized tuning to an arbitrary
frequency(s) in accordance with the selection of a subject matter (topic)
by a user, thereby relieving the user of the necessity of extensive
interaction with the audio-video device in order to locate a channel or
station which carries the desired information.
2. Background Art
In presently used radios and TVs, many stations or channels broadcast
information which covers a wide range of topics including topics such as
news, sports, music, comedies, etc. Within each of these categories many
different breakdowns occur. For example, sports can encompass baseball,
basketball, track and field, horse racing, etc. Within each of these
sub-categories, further breakdowns can be made. For example, baseball
could include baseball games being played by any of the major league or
minor league teams. The selection of a particular station or channel
covering the particular event, for example a particular baseball game, is
not straight-forward, and for that reason many different types of guides
are published to help the user locate the station or channel carrying the
specific program in which he or she is interested.
In the radios in common use today there exist two ways to indirectly select
a broadcasting station. One way is by the use of programmed buttons in
which the user can program a select button to cause the tuner to adjust to
a particular radio station. However, this has several limitations. One is
that the number of favorite stations that can be preselected cannot exceed
the number of buttons or some multiple thereof in the case of those radios
which allow multiple layers of button definition. Further, the select
buttons are only valid for a limited geographic area. In a car radio, this
can be particularly bothersome as hills or range will disrupt reception of
the preferred stations. In order to solve this limitation, radios often
employ a second means of indirectly tuning the radio. This second way is
the socalled "seek" button which allows the user to seek either up or down
the radio spectrum for a strong carrier signal. However, the seek button
also has its limitations as it is best suited for listeners with either a
broad range of subject matter interests or an untiring index finger. For
example, for a listener looking for a classical music station there is no
alternative but to listen to each station in turn, waiting at times if a
commercial is occurring, while repeatedly seeking in order to find that
station which broadcasts classical music.
In the world of television, a similar problem exists which is even more
extensive. Due to the large number of channels available to most viewers,
including the many cable channels now available, a viewer is often
overwhelmed by the number of stations available for viewing. Even when the
viewer knows the exact program and broadcast channel (for example NBC on
2) the viewer will still have trouble locating the program on cable where
the cable channel numbers are often unrelated to the broadcast channel
numbers. This problem is further compounded when the viewer is traveling
and in an area where he or she is unaware of where NBC is to be found or
when the local broadcast station will air the viewer's favorite programs.
A known solution to this problem is the guides which are published and
which describe local programming. However, these guides are now quite
large, often hard to read, not always up to date, and often very
incomplete. Another attempted solution is the listing which can be
broadcast on a fixed cable station where the listing will give a guide to
the local programming. However, the user must first locate this
programming guide station, if it exists, and then must often wait until
the listing scrolls back to the current viewing time.
A very recent development in the use of digital signal coding is the
broadcasting of unique values with program listings. These values are used
to enable automatic VCR recording. A fixed guide listing the various
channels and programs in a selected area will contain a unique code number
for each program. A user punches in the code numbers of the programs which
he or she wishes to automatically record on the VCR. The VCR then
automatically tunes to those programs when they are broadcast and stores
them on tape for later viewing by the user. This type of automatic VCR
recording places the burden of program selection upon the user who must
wade through large program guides (these units do not help the user locate
the code). Further, the selection may be dependent on geographic area,
since there may be a necessity to refer to different guides in different
geographical areas. This type of automatic tuning is similar in some ways
to the tuning of older VCRs with a timer which will allow the user to set
the TV channel and time that the VCR is to be turned on and off. The
difference is that, with this new development, the user need only enter
the program code and the device will then automatically turn itself on and
off based on that code selection.
At the other extreme of automatic tuning are the aforementioned programmed
select buttons for radio or automatic program selection by some new
"smart" radio/TVs based on a knowledge of prior user habits. These devices
provide only a limited "choice" among a fixed list of known entries.
Preprogrammed selections or selections based on prior habit require that
the user have established a stable, geographically fixed environment for
viewing. These "smart" devices will not aid the eclectic user or the new
user.
In all of these types of tuning arrangements, the user must know the
programs that are offered and must make preset selections of specific
programs and times in order to automatically record these programs or to
directly view/listen to them. Prior art techniques do not allow a user to
merely select a subject matter topic (e.g. sports, classical music) where
the unit will then provide dynamic, customized filtering in accordance
with the topic chosen by the user. Further, these prior art devices are
limited to the particular geographic area in which the user is located and
they're fixed in terms of the specific programs that are available and the
specific times during which these programs are broadcast.
It is apparent that there is at best only limited help to a listener or
viewer in locating a station or channel of his or her interest, and in
particular there is no way to allow the listener or viewer to make a
selection based on subject matter (without knowing beforehand the specific
programs that are available) without the necessity of the viewer or
listener struggling through many different channels or stations until the
channel or station sending the desired subject matter is found.
It is therefore an object of the present invention to provide an apparatus
and technique for providing dynamic filtering wherein broadcast signals
are filtered for presentation to a user, in accordance with a choice of a
topic or subject matter made by the user.
It is another object of the present invention to provide an apparatus and
technique wherein a group of broadcast signals is automatically presented
to a user based on a choice of general topic or subject matter of interest
to the user.
It is another object of the present invention to provide an apparatus and
technique for providing dynamic customized filtering of broadcast signals
received by a radio or TV device to allow automatic tuning to a plurality
of broadcast signals carrying topical information relating to a subject
matter choice made by a user.
It is another object of this invention to provide an apparatus and
technique for dynamic filtering of broadcast signals received by a radio
or TV device in accordance with a subject matter choice made by the user,
where the filtering technique is not limited by geographical area.
It is another object of the present invention to provide a low cost, simple
device which can be used with existing TVs or monitors, or radios, and
which will allow a listener or viewer to locate a channel or station
carrying a topic of interest to the user without requiring extensive user
involvement in the location of the channel or station.
It is another object of the present invention to provide a device for
automatic tuning of a TV or radio in accordance with a general topic
selected by the user, where the range of topics from which the selection
is made can be continuously updated, and where the user need not have
knowledge of the available programming.
It is another object of this invention to provide an apparatus for
automatic tuning of any type of audio-video device having a tuner therein
which is used to select an arbitrary frequency or frequency range related
to a chosen subject matter topic, where automatic tuning occurs without
limitation due to geographic area or range from a selected channel or
station and without limitation due to the number of available channels or
stations.
It is another object of the present invention to provide an apparatus for
automatic tuning of an audio-video device in accordance with a topic
selection made by the user, where the advantages of the invention increase
as the number of channels or stations received by the audio-video device
increases.
It is another object of this invention to provide an apparatus and
technique for automatic tuning of any type of audio-video device having a
tuner therein, where the automatic tuning is accomplished in a manner in
which the source of the desired information is substantially invisible to
the user.
It is another object of the present invention to provide an apparatus and
technique which is particularly suited to automatic tuning in a TV set or
monitor to switch between channels or between vertical blanking lines
(VBI) lines in accordance with a topic selection made by a user.
It is another object of the present invention to provide an apparatus which
can be used with a TV set or monitor to allow a user direct access to
information which is not restricted to one broadcast channel or line
cluster within that channel, where the user need only indicate the subject
matter of interest from a menu or list of topics.
BRIEF SUMMARY OF THE INVENTION
This invention allows a user to gain ready access to information broadcast
to a mass audience, and provides automatic user-customized tuning in
accordance with the selection of a general topic of interest by the user.
The user need not know what specific programs are available or the times
of broadcast of particular programs. Tuning is to an arbitrary frequency
or frequency range corresponding to a channel or station broadcasting the
subject matter topic of interest. This topic interest can be selected from
a list which is broadcast with the incoming TV or radio signal, or which
can be located in memory in the apparatus. The menu, or list, can be fixed
or updated in time, and there can be one or many menus or lists. For
example, each TV channel can provide a menu or list characterizing the
type of information it transmits, or there can be a master menu or listing
organizing by subject matter the information carried by many different
channels or stations.
By taking advantage of VBI on television and FM subcarriers on radio the
user is offered more control in locating a broadcast of choice. The
broadcaster can include digital information along with the traditional
signals to allow the apparatus to classify all signal carriers by topic
(not by specific program or time of broadcast). Of course, the signal
carrier can broadcast different programs matching different subject matter
topics at different times of the day. A user makes a topic selection by a
key word or via a hierarchy of menus or lists, in each instance using an
input device such as voice, keyboard, remote control, etc. Internal logic
within the apparatus then instructs the tuner in the TV or radio to
advance to the signal carrier or carriers that match the topic selected by
the user.
The apparatus can broadly comprise a means for receiving any transmitted
digital information that arrives with the broadcast signal, a tuner means
for selecting a frequency or frequency range, a data acquisition means
(decoder) which extracts or translates digital information in the selected
frequency range, a processing means including memory and logic for
controlling the tuner in accordance with a topic selection made by the
user from a menu or list, a user input device which interacts with the
processing means to allow the selection of a topic of interest by the user
and the presentation of a list of topics available to the user, and
optionally a display means for displaying the menu or list of available
topics to the user so that a selection can be made. The digital
information which can be broadcast along with the traditional incoming
signal can be, for example, transmitted in the vertical blanking interval
(VBI) of a TV signal or in an FM subcarrier on an audio signal. Other
formats are possible, and the invention is not limited to any particular
way in which the digital information relating to classification by subject
matter is incorporated in the broadcast signal. Further, the invention is
not limited by the means for receiving the broadcast signal, which signal
can be received via antenna, cable, fiber optics, etc. It is also possible
to have the broadcast signal come directly from a VCR, laser disk, CD, RAM
etc. as in a conference situation where a presentation is to be made via a
tape onto a monitor to be viewed by a large audience. In this latter
situation, a tuner may not be required and the apparatus would then be
used to control the decoder (data acquisition unit) in order to present
information relating to a desired topic chosen by the user.
This apparatus can be used to automatically tune to an arbitrary frequency
in accordance with the subject matter desired to be received by the user,
where that subject matter can be the traditional broadcast signal or
digital information sent along with the traditional signal. For example,
the broadcast signal can contain digital information in addition to the
usual radio or video signal. The present invention can be used for
automatic tuning to a frequency or frequency range in which the
transmitted digital information of interest is automatically selected. In
this situation, the digital information in the broadcast signal could
include coded information identifying the type of information content of
the digital information, as well as the information itself. If the
broadcast signal does not include coded digital information classifying
the transmitted information by subject matter, the menu or list can
contain the classification. For example, the apparatus can store in memory
data which classifies by subject matter the present content of any
broadcast station or channel.
A particularly interesting application is for Teletext information which is
sent with a video signal where many channels transmit information and
where endless loop formats are presently used. In this application, the
inventive apparatus automatically selects the frequency (channel) and VBI
line in which the desired information is located in accordance with a user
selection from a menu or list. The data acquisition means or decoder then
automatically translates the data in that particular line in which the
desired information is located. As the number of channels transmitting
information increases and as the amount of information per channel
increases, the advantage of the present invention becomes even more
apparent since it reduces user involvement and more quickly locates the
desired information.
This device utilizes a multi-step selection process (although the term
"multi-step" is also used in some cases where only one step selection is
required by the user because some preselection process has been
incorporated before the user is asked to select). First, a user is allowed
to select a subject or topic of interest. The device will then present a
targeted display or targeted selection options containing all the programs
meeting the user's current interest. This relieves the user of the burden
of reading an entire program guide. The second step is the user selection
of a program from the targeted list. This allows options and flexibility
for new programming not possible with preprogrammed tuning. This selection
may be explicit, as from a list, or indirect, using a stop/next function
with a seek key.
The terms "menu" and "list", as used herein, are meant to include all
textural and visual presentations which provide a user a way to indicate a
choice of a topic or subject matter. The menu or list can therefore be
formed by icons, real images, graphic lists of topics, etc.
These and other objects, features, and advantages will be apparent from the
following more particular description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of an apparatus allowing automatic
tuning in accordance with a user topic selection as applied to an audio
device, such as an AM/FM radio.
FIG. 2 is a schematic illustration of an apparatus used to provide
automatic tuning in accordance with a user topic selection for use with a
TV set or monitor.
FIG. 3 is another block diagram of an automatic tuning apparatus in
accordance with the present invention used with a TV set or monitor, where
two separate tuners are applied, one of which is used with the digital
information transmitted with the traditional broadcast signal, while the
other is the tuner which is normally a part of a TV set.
FIG. 4 is a block diagram of an apparatus which is particularly suitable
for use with a TV set or monitor, and in particular for a VBI multi-signal
subject tuning device, using fixed or VBI-defined menus from which the
user selects a topic.
BEST MODE FOR PRACTICING THE INVENTION
In a general sense, the invention is an apparatus and technique for
automatic tuning in an audio-video device where the automatic tuning is
customized in accordance with a topic or subject matter selected by the
user. This topic is selected from a menu or list which can be fixed or
alterable to allow continuous updating. Further, this menu or list can be
located in memory in the apparatus, or can be broadcast as part of the
broadcast signal received by the apparatus. A user input device enables
the user to make a topic selection and filter logic, or menu logic, is
used to receive the input from the user and to provide signals which cause
the tuner to advance to the broadcast carrier containing information which
matches the selection made by the user. As an option, the menu or list
available to the user can be shown on a display means such as a TV screen
or a monitor screen, a computer screen, printer, audio output (voice) etc.
The audio or video signal is processed in the usual manner while any
digital information transmitted with the broadcast signal, which is used
to characterize the information content of the signal in accordance with
subject matter, is processed for entry into the menu logic or filter
logic. The tuner will either be advanced continuously until a match is
made, or the tuner will be directly set to a carrier known to provide the
desired subject matter. These principals will be more apparent in the
following discussion, which will describe the invention as applied to both
radio and TV.
FIG. 1 illustrates automatic tuning with an audio device, such as an AM/FM
radio. All radio broadcasting is divided into various subject matter
categories, for example contemporary music, classical music, rock music,
top 40 selections, sports, news, etc. Numbers are assigned to this list so
that the subject matter carried by a particular station is characterized
by a reference number. Each radio station is encouraged to broadcast the
number or numbers of the subject matter category that best suits the
station's broadcast information. This number or numbers is broadcast
within a subcarrier tied to the fundamental carrier frequency. Subcarriers
are already in use for functions such as paging, stock listings, and other
commercial interests. Thus, providing a digital subcarrier indicating a
number corresponding to a subject matter category is easily within present
day capability.
Upon detecting a user-selected topic via an input made by the user, the
apparatus causes the tuner to scan the airwaves via an existing seek
function in the radio. After the tuner detects a clear signal frequency, a
subcarrier decoder checks for a topic category broadcast in the
subcarrier. If a topic category number is present and if the detected
topic number matches the topic requested, the apparatus would stop the
tuner. If there is no match or if the broadcast signal does not include
digital information coding the topic category, the apparatus would advance
the tuner to the next clear signal. At this time the process would repeat,
and the decoder would look for transmitted digital information classifying
the subject matter in the transmitted signal. If the code number
transmitted with the signal matches the code number of the topic selected
by the user the apparatus stops the tuner at that station.
FIG. 1 illustrates a block diagram for carrying out the tuning method
described in the previous paragraph. A user input device 10, such as a
remote control, keyboard, voice activated unit, etc. provides an input to
the filter logic circuit 12. Filter logic circuit 12 is used to compare
the user's topic selection choice with the digital information code
contained in the transmitted AM/FM signal to determine if a match is made.
The broadcast signal is indicated by arrow 14 which is an input to the
tuner 16 contained in the audio device. Tuner 16 provides an input to the
digital decoder 18 which is used to decode a subcarrier transmitted with
the broadcast signal and which would contain a digital code categorizing
the subject matter of the incoming signal. For example, the digital code
could indicate that this station is broadcasting classical music. The
tuner also provides an output along line 20 to the conventional audio
circuits which process the audio signal for output via the speakers. These
conventional circuits are indicated by the signal processing unit 22 which
provides an output via line 24 to the speakers 26.
The digital decoder 18 provides an output via line 28 to the filter logic
circuit 12. The output from decoder 18 is the characterization code
contained in the subcarrier of the AM/FM signal received by the tuner.
Filter logic 12 then compares that code number with the topic selection
made by the user using input device 10. If a match is made, an output is
sent from filter logic circuit 12 to the tuner 16 halting the tuner at
that station. If no match is made, the filter logic will provide an output
telling the tuner to continue to advance, or seek, to the next clear
station. This will continue until a match is made, at which time the
signal from the filter logic circuit 12 will tell the tuner to stop at
that station.
The filter logic circuit 12 can be of conventional design providing the
usual compare functions which cause the tuner to continue to seek new
stations or to stop at the station which provides a match.
FIG. 2 illustrates the application of this invention to a TV set. The use
of FM subcarriers to the audio signal can be used for automatic tuning in
a manner similar to that described with respect to the radio apparatus of
FIG. 1, or the VBI lines can be used to carry the digital information
characterizing the information content of the received signal. In addition
the TV screen display provides advantages which allow a more advanced
system to be constructed, where the system is one that does not rely on
voluntary broadcaster participation. For example, one or more VBI lines
could be purchased on a local station. The tuning logic can be set upon
installation to locate these lines or the logic can instruct the tuner to
scan all VBI lines looking for a unique signal identifying code. This VBI
broadcast would contain many pages to support a hierarchy of menus or
lists for topic selection. For example, SPORTS can be a topic on the main
menu followed by BASEBALL on a second level menu. Such VBI menu systems
are well known in the art and currently in use around the world. Upon
reaching the full topic description (BASEBALL) the VBI decoder would then
display the page(s) of baseball games currently in progress and those
about to begin in the immediate future. This feature is also common in
conventional VBI systems, for example with respect to stock reports which
are currently broadcast with continual updating. The user would then
select the preferred game from the menu display on the TV and the tuner
would automatically advance to that game in accordance with a signal
received from the menu logic circuit. The actual channel location of the
game could be completely invisible to the user but included in the digital
VBI data that creates the menus. In this system, the menus can be
broadcast or can be stored in internal memory. A master menu can be used
to encompass the information content of several TV or cable channels, or
the channels can choose to transmit their own menu or menus.
Referring to FIG. 2, the TV tuner 30 receives an input RF signal as
indicated by arrow 32. This signal can be received by antenna, cable,
fiber optic, etc. It can contain digital information which codes the
information in the RF signal in accordance with subject matter. A menu
logic interface 34 is provided which functions in a manner similar to the
filter logic circuit 12 of FIG. 1. That is, menu logic unit 34 is an
interface between the user and the tuner which reads the menus or lists
and provides a signal indicative of where the tuner should go to locate
channels delivering information which matches the topic selection made by
the user.
A user input device 36 (remote control etc.) is used by the user to make a
topic selection from any menu or listing which could be presented on the
TV display 38. Display 38 is connected to the usual display driver 40,
which is a well known circuit. In FIG. 2, two different signal processing
paths are provided. One is the usual video signal processing path wherein
the video output of the tuner is sent to the standard TV signal processing
circuits 42 and then to a switch 44. The other signal processing circuit
is for the coded digital information which is used to characterize the
information content of the video signal being transmitted by that channel.
This digital information is decoded and used by the menu logic unit 34 to
automatically adjust the tuner. This second signal processing path also
provides an input to switch 44 to enable display of the menu or listing of
interest or the broadcast video signal. Menu logic unit 34 provides a
signal to switch 44 allowing either a menu or the broadcast video
information to be shown on the display.
In more detail, the tuner 30 provides an output via line 46 to the VBI
decoder 48. Decoder 48 decodes the coded digital information broadcast
along with the video signal, and provides an output back to the menu logic
unit 34 via line 50. Decoder 48 also provides an output to a display
generator 52, which is used to provide information suitable for display
onto the display unit 38. This can be either a display adequate for a
computer or a display adequate for a TV.
Menu logic unit 34 provides an output to tuner 30 via line 54. This is the
control signal which instructs the tuner to automatically move to a
channel transmitting information which matches the viewer's selection made
by an input from the user input device 36. Menu logic unit 34 also
provides an input to VBI decoder 48 to control the VBI line being decoded
by decoder 48. As noted, a switch control signal is provided via line 56
from the menu logic unit 34 to switch 44. This switch control signal
determines whether the video signal is passed to the display driver 40 or
whether a menu is passed to the display driver 40.
The components shown in the block diagram of FIG. 2 are well known in the
art. Examples of these will be described in more detail with respect to
FIG. 4, which is a more complete diagram of a system designed to utilize
digital coding information transmitted in the vertical blanking interval.
FIG. 3 is a block diagram of an apparatus for use with an audio-video
device and is similar to the block diagram of FIG. 2, except that a
separate tuner is used for the coded digital information that is broadcast
along with the video signal. The broadcast signal is sent to a tuner 58
whose output is sent to a decoder 60 which decodes the digital coding data
transmitted with the broadcast signal. Decoder 60 provides an output to
the menu logic unit 62 which receives inputs from the user via user input
device 64. A menu display unit 66 is optional, it being possible to
display the menu on the TV set as indicated with respect to the apparatus
of FIG. 2. Menu logic unit 62 provides an input to both the tuner 58 and
decoder 60.
In this embodiment, a separate tuner is provided for the digital
information used to code the incoming broadcast signal in accordance with
subject matter categories. The audio-video device 68 includes the
conventional tuner 70, decoding and image building circuit 72, and outputs
74 to the user. These outputs include display onto the screen of the TV
set or monitor, or speakers in the case of an audio device.
In this apparatus, tuner 58 selects the frequency of the carrier signal and
decoder 60 extracts the digital information which catalogs the transmitted
signal in accordance with subject matter. Menu logic unit 62 receives both
this digital information and a signal from the user indicating the topic
matter of interest. Depending upon a reading of the digital information
transmitted with the broadcast signal, the menu logic unit provides an
output to the tuner and decoder to look for another broadcast signal or
portion within that signal in order to find a match. When a match is
found, a signal is transmitted to the tuner of the audio-video unit 68 in
order to automatically change that tuner.
FIG. 4
FIG. 4 is an apparatus particularly designed for transmitting digital
coding information such as teletext now found in the vertical blanking
interval (VBI) of a broadcast signal. The system of FIG. 4 provides
automatic tuning in accordance with this digital information. As
background, it is well known that digital data is often transmitted along
with an incoming signal, where the digital data can be provided to
selected subscribers, or to the public at large. For example, subscribers
to private systems can receive services related to business and stock
market quotations, where the stock market prices are transmitted over
telephone lines and are received by a modem at the subscriber's terminal.
Having a computer and keyboard entry device enables the subscriber to
selectively access digital data which is sent over the telephone lines, in
order to display this data on a computer screen. Many services of this
type are available, but the expense of the service is not trivial.
Additionally, the subscriber must have a computer and a modem in order to
be able to fully participate in the range of services offered to the
subscriber. Information retrieval and subscriber service systems of this
type which use modems are not within the scope of this invention.
In addition to these subscriber services, many TV channels transmit
programs including digital data, where the digital data is transmitted
with video signals and is stored in the vertical blanking interval (VBI).
This data can be extracted using a decoder which then re-integrates the
translated digital data to a regular video signal that can be displayed on
the TV screen. Close-captioning is done this way where the captions are
displayed on the screen simultaneously with the video picture.
Three major applications of VBI lines exist in common use today. The first
is for TV control data to support color levels, signal synchronization,
and VCR programming control. A second application is line leasing wherein
a company can buy a time slice for a single transmission of data via VBI
to authorized reception sites. A third application is in the delivery of
public information, although access by the public can be restricted by the
use of data encryption, authorization by box ID, or through the use of
custom data formats.
An existing system is the Teletext system authorized by the FCC in lines
10-18 of the transmission band. Teletext is a one-way data transmission
system that is sent out as part of a TV signal, whether the signal is sent
out via satellite, cable, or regular broadcast TV. The Teletext
information is available free of charge to viewers, and there are many
types of Teletext services being offered at this time. These services
cover topics such as cultural affairs, home and catalog shopping, sports,
news, financial information, weather, and other types of statistics. Such
Teletext information is regularly offered by the major networks.
Teletext and graphics are transmitted as digital data squeezed into a
broadcast television signal in the vertical blanking interval. This
interval is the time at the end of each television field when the
cathode-ray beam is cut off while it returns to start the next field.
Teletext is sent as an endless loop of pages where the data for the pages
are transmitted serially at the rate of 13,500 bits per second, per VBI
line used. The total rate of transmission is dependent upon the number of
lines (up to 8) used to transmit the data.
At the user end, a decoder is used to convert the Teletext data to a
regular video signal that can be displayed on a TV screen. Any of the
pages in the loop can be accessed at random. However, because an endless
loop format is used, it takes time for each page to come around in the
loop. This means that there is a delay between the time the page number is
entered and the time that the page actually appears on the TV screen. In
turn, this imposes a practical limit to the number of pages that a
Teletext service can offer. One way to alleviate this delay is to transmit
the more important pages of information more than once within the endless
loop, so that these pages will come up faster. For example, indices are
transmitted several times in the loop since these pages are more important
to the users.
When using Teletext, it is not possible to access any page of information
without the attendant delay in being able to extract and display the
digital information. The endless loop of information is continuously
updated and is often changed so that a desired page is no longer part of
the loop of information that is transmitted. Since the presently available
Teletext decoders are rather expensive, and further since the ease of
extracting information is limited, such systems have not found great
popularity. The apparatus and technique described in U.S. Pat. No.
4,894,789 (K.Y. Yee) addresses these problems and describes a system in
which consumers can economically utilize the digital data that is sent
with video signals. The device of that patent allows a user to extract
selected information and to store and retrieve this information without
the described restrictions normally attendant to the endless-loop format.
As noted, public information is traditionally rebroadcast in very brief (30
seconds) repeat loops which allow the user to jump between information
pages. The disadvantage of the repeating data loops is that a long loop
will bore the user while the user waits for the requested page to arrive,
while a short loop severely limits the amount of information that can be
delivered. To increase the amount of information without increasing the
waiting time, modern decoding boxes can support VBI services that transmit
continuously on several adjacent VBI lines. However, current FCC
limitations allow at most 10 VBI lines per channel. This means that, at
best, a single channel VBI service could offer ten times the information
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