WO1997016020A1

WO1997016020A1 - System for dynamic real-time television channel expansion

Info

Publication number: WO1997016020A1
Application number: PCT/US1996/006929
Authority: WO
Inventors: Ganesh Ramaswamy Basawapatna; John James Sie
Original assignee: Encore Media Corporation
Priority date: 1995-10-24
Filing date: 1996-05-17
Publication date: 1997-05-01
Also published as: AU5793796A

Abstract

A system wherein a single active video signal (Vi) along with a plurality of audio (A1--An) and still frame graphics (G1--Gn) signals representing non-active video are transmitted to a receiving site (170) where they are combined as virtual channels to represent a number of different screens of a TV set (175, 175'). The system uses only the bandwidth of a single television channel to provide a viewer with a plurality of screens. At least one of the screens displays the active video signal. Other screens can display non-active video such as text/graphics and/or data. Audio can accompany any screen display. This multiple-screen capability is provided by transmitting a mapping function as a separate signal independent of the video signal to create an effective plurality of virtual channels that can be dynamically switched to time share the active video signal.

Description

SYSTEM FOR DYNAMIC REAL-TIME TELEVISION CHANNEL EXPANSION

FIELD OF THE INVENTION

This invention relates generally to television transmission systems and, in particular, to a system for combining in real time a plurality of audio signals, still frame graphics signals and a selectable video signal and for transmitting all of the signals in a bandwidth substantially equal to that of a single television channel. PROBLEM

Conventional cable and satellite television transmission systems typically devote an entire channel bandwidth to the transmission of a video signal along with an accompanying stereo audio signal and also possibly a data stream representing close captioning or text information. Although there are many television channels available on a typical cable or satellite television system, the channels are limited in number due to limitations imposed by FCC frequency and channel allocations as well as due to the fact that each analog channel requires 6-8MHz of bandwidth. While some spare channels may be available on some cable or satellite systems, the rapid growth of the cable television industry is causing more of the previously unused channels to become unavailable. It is therefore a problem to transmit increased amounts of program information over these diminishing number of channels.

It is also desirable to be able to select and switch, in real time, the correspondence between a given video signal transmitted from an up-link site and a selected television channel number at the receiving end of a cable system on which the video signal is to be displayed. It is further desirable to be able to combine different selected audio signals and text or graphic signals with a given transmitted video signal and to switch between various combinations of such signals in real time at the receiving site. Digital encoding and compression techniques, such as the "MPEG" system for the compression of digitally encoded signals, can be used to increase the amount of data transmitted within a given bandwidth. This increases the number of channels a cable system or a satellite transponder can carry. However, even more spectral utilization is desirable. For example, if a method existed by which a single active video signal and audio plus a number of text and graphics screens could be transmitted in a single compressed video channel so that a multiplicity of screens could share the spectrum space that a single compressed screen now occupies in an MPEG -2 system, it could effectively result in even greater spectrum utilization efficiency than an MPEG -2 system.

SOLUTION The present invention overcomes the foregoing problems and achieves an advance in the art by providing a system that has the real time capability to combine a selectable plurality of audio signals and still frame graphics signals (which can represent text, graphics, or other non-moving video scenes) with a single "active" video signal and to transmit the combination of such signals over the bandwidth substantially equal to that of a single television channel.

The disclosed system transmits a multiplicity of virtual channels within a single compressed video channel. At any given instant, the compressed channel carries a single active video signal along with a number (4 or 5) of still frame graphics signals and audio. The still frame graphics signal is a part of the audio and graphic channels that are transmitted along with the active video signal as a group of"D O.L..Q .E Channels" (Dynamic On Line Channel Expansion Channels) to a TV receiving site. A mapping algorithm allows the active video signal to be applied to any one or more of the "Dolce Channels". All of the channels not receiving the active video signal may receive still frame graphics signals and audio. In accordance with the present invention, an encoder/compressor situated at a transmitting uplink site and having virtual channel mapping circuitry is controlled by external circuitry that generates a mapping function signal which determines the video/audio/graphics signal correspondence for each virtual TV channel at a receiving site. The compressor/encoder receives a plurality of audio signals and still frame graphics signals (which may represent text, graphics, or other still scenes) along with a selected active video signal and transmits all received signals to a remote receiving site in the bandwidth substantially equal to that of a single compressed TV channel after compressing the received signals. The encoder/compressor operates under computer control to insert the received mapping function into the signal it transmits to the remote site. The transmitted mapping function includes information specifying the correspondence between the transmitted signals and the virtual channel numbers on which combinations of these signals are to appear at the receiving end. All of this provides a dynamically selectable plurality of combinations of audio signals, graphic signals, and a single active video signal to be formed as well as the capability of specifying the virtual TV channel number to which each formed combination is to be applied.

Receiving end equipment performs the inverse function of the transmitting end compressor/encoder. It does this by using the mapping function information to determine the correspondence between the various combinations of an active video signal, the audio signals, the still frame graphics signals and the number of the virtual TV channel to which each such combination of signals is to be applied. The received active video signal is routed together with an accompanying audio signal to at least one of the virtual channels on a set top converter of a receiving TV set. The virtual TV channels which do not receive the active video signal can receive a still frame graphics signal and, if desired, an accompanying audio signal. All of this is done under control of the transmitted mapping function.

A TV set at the receiving end, when tuned to the appropriate channel in the set top converter or MPEG receiver, is presented with a single active video signal on a specified channel together with a specified audio signal such as, for example, an audio in a first language. The set top converter does the mapping function. The TV set is typically tuned to a single channel corresponding to the output of the set top converter. The active video signal can also be applied to additional TV channels combined with different audio signals in other languages. This feature, for example, permits the single active video signal representing a musical or theatrical presentation to be presented simultaneously on different channels in different languages. Selected combinations of audio and graphics signals may be applied under control of the mapping function to other channels of the TV set top converter.

The receiving end will typically be the head end of a cable system which receives the transmitted compressed signal and, under control of the received mapping signal, applies the active video signal together with the audio and graphics signals over its cable paths to the TV sets of its subscribers. The signals received by the head end are combined in the manner specified by the mapping function signal so that each specified combination of signals is applied to the TV channel specified by the mapping function. This permits the users served by the cable system to tune to the TV channel carrying the combination of signals that represents the service each subscriber desires. One subscriber may tune to a channel that carries the active video signal in English; another subscriber may tune to a channel that carries the same active video signal but with Spanish audio. Other subscribers may tune to other channels carrying the same active video signal but with audio in other languages. Still other subscribers may tune to channels carrying a first combination of one of the graphic signals and one of the audio signals. Another subscriber may tune to a channel that carries the same graphic signal but with audio in another language. The still frame graphics signals may represent slide show presentations, such as a University lecture that is presented on a plurality of channels but combined with a different audio signal on each such channel so as to present the lecture in different languages.

A plurality of video signals can be received from different program sources by compression/encoding equipment at the transmitting end even though only a single video signal can be transmitted as an active video signal over a single DOLCE channel together with audio and graphics signals. The transmitting end selects the active video signal that is to be transmitted to the remote side containing the head end of the cable system. The system of the present invention provides great flexibility in that the controlling apparatus at the transmitting site generates an active video select command which determines which one of the available video signals is to be transmitted to the remote receiving site. This permits the video signal that is transmitted to be switched from one of the available video signals to another as often as may be desired. This capability is useful in providing the various TV subscribers served with programming that simulates live programming using only the facilities of the a single compressed video channel.

Let it be assumed, for example, that it is desired to provide programming in English, Spanish, Hindi and Mandarin to different TV channels of the remote cable system. Signals that simulate live programming may be transmitted to the remote cable system and applied to four of its channels in the following manner. Doing a first time interval, one of the available video signals representing a moving scene in English may be selected by the transmitting end as the active video signal, transmitted to the remote site, and applied to channel 4 of the cable system together with an audio signal in English. Concurrently, three different graphics signals representing information of interest to Spanish, Mandarin and Hindi speaking people may be transmitted and applied to channels 5, 6 and 7 together with audio in Spanish, Mandarin and Hindi. This condition may persist for the duration of the first time interval, such as for example, one minute. Then, at the beginning of minute two, a different video signal, such as a video of interest to Spanish subscribers may be selected and transmitted as active video signal and applied to channel 5 of the cable TV system. At the same time, accompanying Spanish audio signal is applied to channel 5. The subscribers tuned to channels 6 and 7, namely the Mandarin and Hindi speaking subscribers, continue to receive the same programming they did in the first interval, i.e., still frame graphics and audio signals in Mandrin and Hindi. However, during this second interval, channel 4 receives a graphics signal and English audio. At the beginning of interval 3, a new active video signal may be selected, transmitted and applied to channel 6 of the cable system to present moving video information of interest to Mandarin speaking subscribers together with Mandarin audio. The Spanish speaking subscribers now receive, on channel five, a graphics signal of interest together with Spanish audio. Next, at the beginning of interval 4, another active video signal may be selected, transmitted, and applied to channel 7 of the cable system with the newly selected active video signal being of interest to Hindi speaking subscribers. Accompanying audio in Hindi is applied to channel 7. This process may be repeated sequentially or non-sequentially and as frequently as may be desired so that each subscriber periodically receives an active video signal of interest to each such subscriber together with an appropriate audio signal. Each such subscriber also receives a still frame graphics signal together with an audio signal of interest during time intervals in which an active video signal is not received by the channel to which he is tuned.

As described above, it can be seen that if the sequencing and application of the active video signals to the different receiving site channels occurs frequently together with appropriate audio so that all receiving subscribers receive programming that is of interest to them and that contains moving scenes, sufficiently often so as to be enjoyable.

By this means, subscribers on a plurality of channels may be served with enjoyable programming that is transmitted using only the bandwidth of a single compressed video channel. In other words, the present system uses essentially only the bandwidth of a single compressed video channel to provide a viewer at a remote site with a plurality of TV screens of interest. If desired, more than one of the screens may include the same active video picture with each different screen being accompanied by audio and a different language. Simultaneously, other screens may display only graphics together with audio if desired. Examples of this would be stock market reports and the like. This multi channel capability is provided by a mapping function which creates a plurality of virtual channels that are dynamically and seamlessly switched. Thus, the present invention provides a single active video signal together with a plurality of audio and graphics signals which can be used to provide suitable programming to a plurality of channels of TV sets at a remote site served by a cable TV system or the like. Such capability to send multiple channels within a compressed channel bandwidth is an even more efficient method of spectrum utilization than that envisaged by MPEG -2 and other compression systems.

BRIEF DESCRIPTION OF THE DRAWING The invention may be better understood from a reading of the following description thereof taken in conjunction with the drawing in which: Figure 1 illustrates, a system embodying the invention; Figures 2, 3, and 4, when arranged as shown in Figure 12, illustrate further details of the system of Figure 1 ;

Figures 5, 6 and 7 illustrate further details of the mapping function of the present invention;

Figure 8 illustrates further details of set top converter 150; and Figures 9, 10 and 11 illustrate different possible mapping functions that can be generated by controller 115.

DETAILED DESCRIPTION Definitions

The following definitions are applicable to the present invention: Mapping is the process by which a particular channel of a cable system or of a set top converter of a television set is assigned a unique combination of video, audio and still frame graphics signals. A Video Channel is the bandwidth associated with a transmission path carrying a single channel of conventional television programming. An analog NTSC cable video channel is 6 MHZ wide.

Screen: Signals comprising a video channel can be mapped to a number of different virtual viewable "television channels" at a receiving TV set. A screen is the display provided by an user-selectable TV channel".

An Active Video Channel (AVC) is a virtual channel whose screen consists of a movie, sports action or other type of moving scenes. A screen associated with an AVC is called an "active screen". A screen associated with a non-active video channel displaying still frame graphics such as a non-moving picture or scene is termed a "still screen."

A Still Frame Gra^phics Channel provides a display of data or graphics or other non-moving scenes.

Mapping Function: A mapping function is comprises an n x n x n matrix than maps a composite ViAiGi (video/audio/graphics) vector to a composite VoAoGo vector, where Vi represents the individual video inputs, Ai and Gi are the audio and graphics inputs (at the uplink or transmitting site) respectively, and Vo, Ao, and Go are the corresponding outputs (at the receiving television site). In the present system, the mapping function is supplemented with a lagging function" which is a "screen identifier" which serves to identify the screen with which a given packet of data is associated. System Overview

Figure 1 comprises illustrates a system embodying one possible exemplary embodiment of the present invention as comprising an uplink 105 and headend 170 which communicate via satellite 140. Uplink 105 includes compressor/encoder 110, RF modulator and upconverter 130 together with antenna 135. Compressor/encoder 110 receives a plurality of video signals Vi -Vn over path 101, a plurality of audio signals Al -An over path 102 and a plurality of graphic signals Gl -Gn over path 103. Compressor/encoder 110 also receives an active video select signal 104 from controller 115 over path 106 and receives a mapping function 155 from controller 115 over path 153. The system of Figure 1 can transmit only a single V-video signal at a time from uplink 105 to headend 170 over a single compressed video channel of satellite 140. The active video select signal 104 causes compressor/encoder 110 to select the one video signal Vi -Vn that is to be transmitted at any given time. This selected video signal is termed the active video signal Vi. The mapping function 155 controls the correspondence between the various received A- audio signals, the received G- still frame graphic signals, the active video signal Vi, and the virtual channel number to which each combination of the signals is to be applied to the TV sets at home sites 175' and 175.

The output from compressor/encoder 110 is applied to RF modulator and upconverter 130 which modulate the received signal and upconvert it to the appropriate satellite transponder channel frequency along with other compressed channels. The modulated signal is transmitted from transmitting antenna 135 to satellite 140 which re-transmits it to receiving antenna 145 and 165 at the headend. The transmitted signals are contained in a single compressed video channel and they comprise the selected active video signal Vi from the group of video signals Vi -Vn, ail of the audio signals Al -An and all of the still frame graphic signals Gi -Gn.

Figure 1 illustrates two possible embodiments of equipments at the headend or receive site 170. The first embodiment comprises the transcoder 148 which may be part of the headend equipment of a cable system serving a plurality of home sites 175' via a cable 190. The second altemative for the headend equipment includes receiving antenna 165 together with receiver 176 which directly serves a single home set 175 and its TV 180.

Transcoder 148 at headend 170 transcodes the signal received from antenna 145 over path 146. In so doing, the received signals are demodulated, QPSK modulated and applied to path 190. Transcoder 148 allows a cable operator the capability of changing/deleting channel numbers and also adds ability to add access restrictions, local messages, programming or advertising, etc. The signal sent over path 190 may be in digital form and applied to a set top converter 150 at the home site 175'. The set top converter 150 decompresses the incoming signals received and demodulates them to the appropriate type of analog signal such as NTSC, PAL, or SECAM standards. Mapping circuit 160' receives the transmitted mapping function and establishes the proper correspondence between the active video signal Vi, and the A- audio and G- graphic signals as well as the channel on TV 180' to which the various combinations of these signals are to be applied. In other words, mapping circuit 160' controls the TV channel to which the active video signal Vi is to be applied as well as the A- audio signal that is to accompany the active video signal. Mapping circuit 160' also establishes correspondence between the remaining A- audio signals and the G- still frame graphics signals as well as the TV channels to which each combination of these signals is to be applied.

The signal transmitted from satellite 140 is also received by home receiving antenna 155 at subscriber home site 175. Mapping circuit 160 receives the mapping function transmitted from uplink 105 and operates in conjunction with digital receiver and converter 176 to control the channel number which each of the various combinations of these signals is to be applied to TV 180 in the same manner as already described for mapping circuit 160'.

In connection with the proceeding description of Figure 1, compressor/encoder 110 may, for example, comprise a General Instruments DigiCipher 2 encoder with appropriate input configuration and compression. Controller 115 can be any type of micro processor or firmware circuit which is capable of outputting an active video channel select signal 104 and a mapping function signal 155. Description of Figures 2. 3. and 4

Figures 2, 3, and 4, when arranged as shown in Figure 12, illustrate further details of the system of Figure 1. Figure 2 illustrates the details of the various sources that apply video, still frame graphics and audio signals to the circuitry of Figure 5. Figure 5 illustrates the details of the circuitry that; 1) receives the various audio, still frame graphics and video signals,

2) controls which one of the received video signals is to be transmitted as active video signal Vi,

3) generates the mapping function and

4) transmits the selected active video Vi signal together with the received A- audio and G- still frame graphic signals to the headend circuitry signal shown in detail in Figure 4.

Figure 2 shows a plurality of signal sources of signals P1 -Pn each of which may provide audio, video and still frame graphics signal outputs. These devices could be, for example, Avid "media server model file servers each of which stores still frame graphics signals, video signals and associated audio signals. Each of these devices is controlled by signals applied to path 202 to output any of its stored signals to the circuitry of Figure 3. The audio signals Al -An of sources Pi -Pn are applied over conductors Al -An to the like designated inputs of Figure 3. The graphics signals Gi -Gn are applied from devices Pi -Pn to graphics inputs Gl -Gn of Figure 3. The video signals V1 -Vn of the source devices are applied over path 201 to the video input Vi -Vn of Figure 3. The operation of sources Pi -Pn may be controlled by the circuitry of Figure 3 by the transmission of control signals over path 202 to sources Pi -Pn. Path 202 may comprise a plurality of conductors, each of which is unique to one of signal sources Pi -Pn.

Figure 3 illustrates the details of the uplink portion 105 of the system of

Figure 1. Uplink 105 comprises compressor/encoder 110, RF modulator and upconverter 130 together with antenna 135. Compressor/encoder 110 may be, for example, a General Instrument DigiCipher II encoder.

Compressor/encoder 110 has a plurality of signal inputs including audio inputs A1 -An, graphics inputs Gl -Gn, and video inputs V1 -Vn. These signals are received from the P1 -Pn signal sources on Figure 2. Since a television channel has a bandwidth of only 6 MHZ only one of the video signals, Vl -Vn can be transmitted at a time from uplink 110 via satellite 140 to the headend of Figure 4. This single video signal Vi that is to be transmitted is selected from the group Vi - Vn. Regardless of the video signal Vi selected, all of the A- audio and G- still frame graphics signals are transmitted over the same video channel together with the selected video signal. The reason for this is that the bandwidth requirements to transmit the G- still frame graphics and A- audio signals in a compressed system are negligible when compared to the bandwidth of the single selected active video signal.

The single video signal that is selected for transmission at any one time is termed the active video signal Vi. This signal selection is generated by controller 115 on Figure 3 and transmitted via active video select element 104 and path 106 to switch SW3 which receives all of the signals Vl -Vn on path 201. The active video select signal on path 106 controls switch SW3 so that it only extends the selected one of signals V1 -Vn to its output as the active video signal Vi for transmission to the headend site on Figure 4. Controller 115 may be a personal computer or any type of microprocessor or firmware circuit which is capable of outputting mapping function information and the active video select signal. The format of the command outputted by controller 115 is appropriate to the desired mapping function. Matrix 305 receives the mapping function 155. Switch SW3 may be, for example, a Videotek RS103 PC controllable switch and it executes the active video select command by choosing the appropriate active video signal Vi. The mapping function information received by element 305 includes a channel select signal which is applied to A-D converter and compressor/encoder 301-1. This channel select command specifies the channel numbers on which the selected active video signal Vi will appear on the receiving TV sets of the subscribers served by the cable system shown on Figure 4.

Mapping function 155 and controller 115 generate the mapping information and the channel select command which are extended to channel select and mapping matrix 305 which applies them to tag generator and packetizer 308 to specify the correspondence between the various A-audio signals, the various G- graphics signals and the selected video signal Vi as well as the channel numbers on which the various combinations of these signals are to appear on the set top converter of the television sets of the subscribers served by the headend equipment of Figure 3. The channel select and mapping matrix 305 as well as tag generator 308 comprises a part of the DigiCipher II equipment.

The audio inputs A1 -An are processed by circuits 302-1 through 302-n, each of which comprises an A-D convertor and appropriate digital processing circuitry. The still frame graphics signals, Gl -Gn are processed by circuits 303-1 through 303-n. The selected active video signal Vi is selected by switch SW3 and processed by circuit 301-1 which comprises an A-D converter and compression circuitry. Circuits 302 and 303 also comprise a part of the DigiCipher II equipment.

After being processed by elements 302-, 303- and 301 -, the A- audio, G- still frame graphics, and the active video signal Vi are applied to the packetizing and tagging circuits 310-1 and 310-2 and 310-n of the DigiCipher II. Circuits 310-1 through 310-n segment the received bit streams into appropriate packets and place appropriate linking or tagging information into a header at the beginning of each packet This tagging information provides a correspondence between a given packetized data stream and the receiving end channel number which is used at the home receiving site to route and combine the various audio and still frame graphics signal with each other as well as with the transmitted active video signal Vi. The packetized and tagged A- audio signals are combined into bit streams 116 by multiplexor 315-1. The packetized and tagged G- still frame graphic signals are combined into bit stream 317 by multiplexor 315-2. Packetizing and tagging element 310-n receives the active video signal Vi which is multiplexed with other channels that are transmitted to the same satellite transponder. The packetized and tagged audio, still frame graphics and video signals are applied to multiplexor 315-3 which applies its output bit stream over path 321 to RF modulator and upconverter 130. The bit stream on path 321 is modulated, upconverted, amplified and applied over path 325 to transmitter antenna 135. From there, it is transmitted to satellite 140 by transmitting antenna 135.

Compressor/encoder 110 may be, for example, a DigiCipher II or other MPEG 2 compatible encoder. Upconverter 130 is typically a C/Kuband upconverter, for example, an MITEQ or LNR upconverter for the appropriate frequency band.

The use of digital compression such as MPEG 2 or DigiCipher II results in significantly higher performance and a greater degree of flexibility than is possible with an analog system. The Active Video Channel Vi is selected and each A- and G- signal is treated as a separate channel and compressed as a separate channel for transmission. This provides the advantage that there are no long periods of time (e.g., seconds) wherein the text and graphics do not change. Digital compression allows the bit rate for each channel to be much lower than if a static screen were constantly transmitted. The lower bit rate is due to the fact that adaptive coding schemes recognize that no motion is present and the encoding uses an appropriate low bit rate. The audio signal is compressed with a choice of bit rate dependent on the fidelity desired in the respective compression method.

As a result of using digital compression, the number of additional bits per second required to transmit, for example, five additional still frame video and audio channels is less than 500 Kbps. In a compressed digital system wherein a typical channel uses 10 Mbps, the bandwidth occupied by these additional channels represent less than 5% of the total channel bandwidth. In the present system, it is not perceivable to the viewer that six different screens are effectively occupying the same channel space.

Furthermore, when the active video medium is a motion picture "filrrf , it is possible to achieve higher rates of compression, so that additional data channels do not usurp any needed bandwidth at all. Higher data compression rates are possible in "film mode" are due to the lower framing redundancy present in films as compared to video-taped program material.

Figure 4 discloses further details of headend 170. On Figure 4, headend 170 comprises receiving antenna 145, receiver/demodulator 410/415, which comprises elements of transcoder 148. Signal 141 received from satellite 140 (shown in Figure 1) is applied to RF receiver 410 which downconverts the signal to the appropriate frequency. The downconverted signal is applied over path 403 to demodulator 415. The demodulated signal (which is a data bitstream) is then applied via path 417 to demultiplexer 425. Video bitstream Vi, audio bitstreams Al to An and still frame graphics bitstream Gl to Gn are applied to mapping control element 440. Still frame graphics signal G (n+1), which comprises channel select and channel mapping information (in mapping function 155 of Figure 3) is applied to mapping control element 440. Mapping control element 440 is a part of transcoder 148, which is, for example, a General Instruments DigiCipher II transcoder. Mapping control element 440 converts the received video, audio, and still frame graphics signals into virtual channel mapped bitstreams with appropriate security encoding/scrambling for the particular cable system. These signals are typically QPSK modulated for transmission via fiber or co-axial cables to subscriber homes. The transcoded bitstreams are applied via coaxial cable or fiber optic cable

490 to set-top convertor 150 at home subscriber site 175. Set-top convertor 150 may be, for example, a Hewlett-Packard model CT300 convertor which contains circuitry 360 for mapping the received signals to the appropriate screens as selected by a viewer of TV set 380. The system as illustrated in Figures 2, 3 and 4 utilizes encoder/decoder circuitry which permits a mapping function: Vi~>Vo (o = 1, 2, ... n) to be performed by the compressor/encoder 110 on Figure 1. This enables a 1 x n correspondence between a single active video input channel Vi and a plurality of output channels Vo. Encoder 110 generates a packet containing 1 x n (Vi - Vo) mapping information from tag generator 308 which utilizes information contained in the mapping matrix signal sent over path 307. Mapping Function

Figure 5 illustrates the principle of the mapping function of the present invention. On Figure 5, controller 115 generates mapping function 155 which is applied to elements 310 on Figure 3. Controller 115 also generates the active video select signal which controls switch SW3 to select the active video signal Vi that is applied to digital compression circuit 301-1 in compressor/encoder 110.

Mapping function 155 comprises a matrix of inputs Vi/Ai/Gi, and corresponding outputs Vo/Ao/Go. There is a 1 :n correspondence between an active video input

Vi and active video output Vo. The letter n equals the number of screens which may display the active channel Vi signal. Mapping function 155 also provides an n:1 correspondence between each combination of active video channel Vi and a single audio channel Ai and a single still frame graphics channel Gi.

The elements below line 5-5 on Figure 5 comprises a portion of compressor/encoder 110. Tag commands are generated by mapping function 155 and applied to element 303-(n+ 1) of compressor/encoder 110 as shown in Figure 3. Tag commands are applied to audio bitstream 316 and still frame graphics data bitstream 317. Resultant audio and still frame graphics bitstreams 522 and 524 are then combined by multiplexer 315-3 to form a composite tagged bitstream 321. On Figure 5, blocks 520 and 530 are equivalent to the combination of elements 302-* + 303-*; 310(-1,-2); and 315(-1,-2) on Figure 3. Mapping Function Example

Figures 6 and 7 depict two possible TV channel configurations using the mapping function of the present invention. In Figure 6, compressor/decoder 110 of Figure 1 receives video signals Vi -Vn, audio signals A1-A3, and still frame graphics digital signals Gl -Gn. The mapping function (received in the data stream transmitted over path 153) designates TV channel 20 as the Active Video Channel (AVC). The mapping function further designates the correspondence between the audio inputs A1 to A3 and still frame graphics inputs and Gi -Gn and TV channel 20. The mapping function specifies that channel 20, in addition to receiving the Active Video Channel V1 , also receives audio signal A2 and still frame graphics signal G2. This particular mapping function also indicates that TV channel 17 consists of audio signal A1 and still frame graphics signal G1. Signals Al and Gl are applied to channel 17 modulator 181-1, and signals V1, A2 and G2 are applied to channel 20 modulator 181-2. Either of these channels can be selected for viewing on television set 180 pf transcoder 148.

The channel configuration shown in Figure 6 could represent, for example, the situation in which a viewer can watch a program on either channel 17 or channel 20. Audio signal A1 and still frame graphics signal Gl on channel 17 could comprise a combination of still frame graphics, messages, etc. with voice or music in the background. A typical combination of audio and still frame graphics would provide for applications such as language education, stock market quotes, or home shopping, where the goods to be sold are shown in still pictures which are transmitted. Concurrent with the transmission of channel 17, channel 20 would also be available for viewing. As shown in Figure 6, channel 20 receives with the active video signal V1, in addition to audio signal A2 and graphics signal G2. This combination of signals allows a movie to be viewed with the audio from signal A2. Subtitles could be transmitted as a G2 signal if desired. Figure 7 shows an alternative channel configuration wherein the inputs to encoder 110 are the same as in Figure 6, but where the mapping function has been modified (at the transmitting end of channel 153). As shown in Figure 7, The mapping function designates that Active Video signal V1 is to be applied to TV channels 17 and 20; channel 20 also receives audio signal A2 and still frame graphics signal G2; and channel 17 also receives audio signal A3 and still frame graphics signal G3. Channels 17 and 20 are modulated by modulators 181-1 and 181-2, respectively, and are selectable for viewing on television set 380.

As shown in Figure 7, the mapping function in this causes the Active Video signal V1 to be output to both TV channels 17 and 20. In such a situation, the same movie could be shown on both channels, and different language audio signals (A3 and A1) as well as different still frame graphics streams (G3 and G1) would be output to channels 17 and 20, respectively. Signals A1/A3 and G1/G3 could be dubbing and subtitling in different languages, for example. Channel Mapping at Home Site

Figure 8 illustrates how channel mapping takes place at a cable subscriber's home site 175 or 175'. Set-top convertor 150 (comparable to converter 150 on Figure 1) receives a television signal over cable 190, as shown in Figure 1. Signal 190 could also be supplied by a home satellite receiver on path 142 as also shown in Figure 1. Set-top convertor 800 is typically controlled by user TV channel select remote control device 805. When a user selects a given TV channel, switch controller 810 outputs the selected video channel number to switch 812 which receives an Active Video Signal V on path 813. Switch 812 then outputs the active video signal V on the selected TV channel to decoder/switch/modulator 815. The audio and still frame graphics signals are applied to element 815 as shown by bracket 801 which includes audio channels Ai (I = 1 to n) and still frame graphics signals Gi (I = 1 to n+ 1). Channel G(n+ 1) transmits mapping function 155 to memory 830. Switch controller 820 accesses mapping function memory 830 and provides an input on path 821 to block 815 to control which audio output Ai and data Di is to be applied to each user-selected TV channel. The appropriate outputs are then modulated by element 815 and sent as baseband signals over paths 831 to 833 to television set 180. The functionality described above with respect to Figure 10 is similar to that provided by, for example, a Hewlett-Packard model CX300 or a General Instruments model "Ovation 10" set-top convertor.

Cable subscriber's set-top convertor 800 advantageously contains a resident special character set in ROM 850 to accommodate the use of other language fonts. This allows all text to be sent in the recipient's language using a character set such as ASCII or an appropriate 8 or 16 bit code instead of graphics. The use of a resident character set significantly reduces the required transmission bit rate. DESCRIPTION OF FIGURES 9. 10 & 11

Figure 9 illustrates how a system emboding the present invention may provide enjoyable programming to a plurality of users over different TV channels by using a single 6MHz video channel to transmit a single active video signal together with a plurality of audio and graphics signals to a remote site. Figure 9 also illustrates the single active video signal V1 is time shared with a plurality of TV channels at the remote site to provide enjoyable programming to users tuned to these various plurality of channels. The active video signal V1 is time shared with four different TV channels on Figure 9 so that during each time interval, the active video signal is applied to one TV channel together with accompanying audio while the other channels each receive a unique combination of audio and graphics signals. The active video signal is applied to a different TV channel during each of the different time intervals. Each TV channel receives active video and accompanying audio during one time interval and, during the other time intervals, receives a combination of still frame graphics programming together with accompanying audio. By this means, the subscribers served by the four channels receive active video a sufficiently high percentage of the total time to maintain an interest in the program.

Figure 9 indicates that channels 4, 5, 6 and 7 serve English, Spanish, Hindi and Mandarin programing respectively. The left hand column of Figure 9 specifies time intervals which may comprise a time duration, for example, of one minute. During the first minute (interval 1), channel 4 receives the active video Vi together with accompanying audio A1 which may, for example, be in English. During the same interval 1 , channel 5 and its Spanish speaking audience receives audio A5 in Spanish together with still frame graphics G6, which may for example, represent a still scene of interest to the Spanish speaking subscribers. Channel 6, receives audio signal A9 in Mandarin together with a still frame graphics signal G9 of interest to the Mandarin speaking audience. Similarly, during interval 1 , channel 7 receives audio A13 in Hindi together with a still frame graphics signal G12.

At the beginning of time interval 2 (the second minute), the active video signal V1 is switched from channel 4 to channel 5. At this time, channel 4 receives a graphic signal Gl together with audio A2 in English. Graphic signal Gi may represent a news or other event of interest to English speaking subscribers. Channel 5 now receives active video V1 together with audio A6 in Spanish. The video signal Vi may represent a continuation of the video signal V1 applied to channel 4 during interval one or alternatively, may represent a totally different scene depending on the manner in which program source Pi of Figure 2 is programed. Source Pi may be programmed in advance, in accordance with one altemative, is to provide continuous programing without regard to the nature of the audience of the various channels to which it is applied during each interval. Alternatively, it may be programmed in advance so that there is no topical continuity between the Vl signal that Pi outputs during 1 time interval and the V1 signal Pi outputs during the next time interval. In any event, during interval 2, channel 5 active video signal Vi together with Audio A6 in Spanish. At the same time, channel 6 receives audio A10 in Mandarin and still frame graphics G10 while channel 7 receives audio A14 in Hindi together with graphics signal G13.

During time interval 3, the active video signal Vi is applied to channel 6 together with audio A11 in Mandarin. At this time, channel 4 receives graphics signal G2 together with audio A3 in English; channel 5 receives graphics signal G7 together with audio A7 in Spanish while channel 7 receives graphics signal G14 together with audio A15 in Mandarin.

During interval 4, the active video Vi is applied to channel 7 together with audio A16 in Hindi. At this time, channel 4 receives graphic signal G3 together with audio A4 in English. Channel 5 receives still frame graphics signal A8 together with audio G8 in Spanish while channel 6 receives still frame graphics signals G11 together with audio A12 in Mandarin.

The cycling of the active video signal Vi continues so that at the beginning of time interval 5, active video signal Vi is reapplied to channel 4 together with audio A1 in English. The indicated combinations of still frame graphics and audio are applied to channels 5, 6 and 7 at this time. The cycling of the active video signal V1 continues once during each time interval in the manner above described so that, for example, the active video signal Vi is applied to channel 5 during interval 6, to channel 6 during interval 7, to channel 7 during interval 8 and so on. It is not necessary that video signal Vi always be the video signal that is transmitted to the receiving end site as active video signal. Figure 2 shows a plurality of signal sources Pi through Pn each of which is capable of outputting its own unique video signal such as V1 for source Pi , V2 for source P2, etc. If desired by the programming director, the active video select signal 106 may be changed from time to time to control switch SW3 on Figure 3 so that the active video signal that is transmitted may be any one of the video signals V1 -Vn on Figure 2 and may, if desired, be changed at any time. Thus, with reference to Figure 10, the active video signal need not be signal V1 for all of the indicated time intervals. If desired, signal V1 could be applied as active video signal to channel 4 during interval R + 1, signal V2 could be applied as an active video signal to channel 5 during interval R + 2, signal V3 could be applied during interval R + 3 as active video signal to channel 6 and active video signal V4 could be applied to channel 7 during interval R + 4.

Figure 10 illustrates a programing sequence in which it is desired to apply active video signals from different sources during different time intervals. Thus, on Figure 10 the active video signal Vl is received from source P 1 on Figure 2 and is applied through channel 4 together with English audio during interval R + 1 for the benefit of English speaking subscribers. The indicated combinations of other audio and graphics signals are then applied to channels 5, 6 and 7 for the benefit of their listeners. During time interval R + 2, active video V2 from programed source P2 is applied to channel 5 together with Spanish audio for the benefit of Spanish speaking subscribers. The indicated combinations of graphics and audio are applied to channels 4, 6 and 7 at this time. During interval R + 3, active video signal V3 from source P3 on Figure 2 together with Mandarin audio is applied to channel 7 and during interval R + 4, the active video signal V4 together with audio in Hindi is applied to channel 7. The sequencing of active video from the various P- sources on Figure 2 continues during subsequent intervals so that the active video signal that is applied to any channel during any interval is under the complete control of the program director who during any time interval can select and apply a video signal from any of the P- sources for transmission to the remote site and application to any channel or channels.

Other applied signal combinations are possible. For example, let it be assumed that video signal Vi of source Pi on Figure 2 comprises a theatrical presentation or news event of world wide interest. Let is also be assumed that it is desired by the programming director at the uplink site to provide this video signal to all of channels 4, 5, 6 and 7 at the receiving end and to provide each channel with an associated audio in a language unique to the channel. In this case, as shown on Figure 11, all channels 4, 5, 6 and 7 would receive Vi as the active video signal for the duration of the programming interval. All channels would then receive the Vi as the active video signal but with a unique or different A- audio signal in the language associated with the channels, for example, channel 5 in Spanish audio, channel 6 in Mandarin.

It is seen from the above, that the system of the present invention provides a flexible means of permitting a plurality of TV channels at a receiving site to receive signals transmitted from an uplink site to a headend site over a 6MHz video channel in a manner that provides high quality programming to the subscribers of each TV channel. The system of the present invention also provides flexible programming in the manner indicated in Figure 9 so as to permit a single transmitted active video signal to be time shared with audio and still frame graphic signals to a plurality of TV channels in such a manner so as to provide the viewers of each such channel with enjoyable programing. All of this is done by using the transmission facilities of only a single 6MHz video channel. This extends the capability of a video transmission system, such as a satellite system or cable system by permitting the system to provide programming service to an increased number of TV channels without enlarging the existing signal transmission capabilities of the system.

It is to be expressly understood that the claimed invention is not to be limited to the description of the preferred embodiment but encompasses other modifications. Thus, the term "still frame graphics signal" includes non-moving video scenes as well as data, text, and other types of non-moving video displays. Also, it is to be understood that system of Figures 1-4 can serve a plurality of other television signals that are transmitted from an up-link site 105 receiving sites via satellite 140. Thus, the compressor/encoder 110 can receive and process video signals representing non-DOLCE channels that are to be transmitted in a compressed format to receiving sites.

Claims

WE CLAIM 1) A method of transmitting a plurality of virtual TV channels from a transmitting site (105) to a receiving site (170, 175, 175') using a bandwidth substantially equal to that of a single TV channel by dynamically combining in real time an active video signal (Vi) with a plurality of still frame graphics signals (G^ G and a plurality of audio signals (A^-A.,) into a single TV channel for enabling the viewing of a plurality of TV screens at said receiving site with each screen having a unique combination of said active video signal and said graphics signals and said audio signals, said method comprising the steps of: a) applying said active video signal (Vi) and said audio signals and said still frame graphics signals (G.,-Gn) to combining equipment (110) containing virtual mapping circuitry: b) applying a mapping function (155) from an external source (115) to said combining equipment to establish a correspondence between said virtual TV channels and combinations of said active video signal and said audio signals and said graphics signals; c) operating said combining equipment in response to said application of said mapping function from said external source to transmit said mapping function as a separate signal along with said active video signal and said audio signals and said graphics signals from said combining equipment to said receiving site over a single video channel and; d) forming said virtual channels at said receiving site (170, 175, 175 *) by combining said transmitted signals at said receiving site under control of said transmitted mapping function so that said plurality of virtual channels time share said active video signal, at least one channel at a time, in different time intervals with each channel receiving a still frame graphics signal and/or an audio signal during a time interval in which it is not receiving said active video signal. 2) The method of claim 1 wherein said active video signal (Vi) is applied to at least one of said virtual channels in a first time interval together with one of said audio signals (A^-A while the ones of said virtual channels not receiving said active video signal receive one of said still frame graphics signals (G^-G J and/or one of said audio signals and, in subsequent time intervals, others of said channels, at least one virtual channel at a time, receive said active video signal and one of said audio signals. 3) The method of claim 1, wherein each one of a plurality of said virtual channels receives said active video signal (Vi) and a unique one of said audio signals (A.,~An) during one of said time intervals. 4) The method of claim 1, wherein at least one of said virtual channels receives an audio signal (At-An) and said active video signal (Vi) during a time interval while at least one other of said virtual channels receives a still frame graphics signal (G.,--Gn) representing data and/or an audio signal. 5) The method of claim 1 , wherein, in accordance with said mapping function, at least one of said virtual TV channels receives one of said still frame graphics signals (G^GJ representing a still scene. 6) The method of claim 1, wherein said mapping function is transmitted independently of said active video signal. 7) The method of ciaim 1 wherein said mapping function is inserted into one of said still frame graphics signals; and wherein said step of combining comprises the step of generating selected ones of said screens on said TV set by combining one of said audio channels with one of said still frame graphics signals and said active video signal under control of said transmitted mapping function. 8) The method of claim 1 wherein said active video signal Vi is selected at said transmitting site from one of a plurality of available video signals (V^-V . 9) The method of claim 1 wherein said combining equipment (110) comprises a compressor/encoder (110) and wherein said signals are compressed and transmitted over said single video channel which has the bandwidth of only a single compressed video channel. 10) The method of claim 9 where said method further includes the steps of: (a) converting said active video signal, said audio signals, said still frame graphics signals, and said mapping function to digital data packets (310); (b) tagging (308) each of said packets with a virtual channel number tag corresponding to said mapping function; (c) transmitting said packets in a digital bit stream (136, 141) to said receiving site; and (d) applying, at said receiving site, said active video signal to at least one virtual channel under control of said mapping function. 11) A system for transmitting information representing a plurality of virtual television channels from a transmitting site (105) to a receiving site (170) using a bandwidth substantially equal to that of a single TV channel by dynamically combining in real time an active video signal Vi with a plurality of still frame graphics signals (G1-Gr and a plurality of audio signals (A - A )ninto a single TV channel for enabling the viewing of a plurality of TV screens at said receiving site with each screen having a unique combination of said active video signal and said still frame graphics signals and said audio signals, said system comprising: (a) combining means (110); (b) means f r applying said signals from a program source to said combining means; (c) control means (115) external to said combining means for generating a mapping function (155) to establish correspondence at said receiving site between said virtual TV channels, and:

(1) said active video signal (Vi), and

(2) said audio signals (A^A , and

(3) said still frame graphics signals (G^-G ;

(d) means (101, 102, 103) for extending said signals from said control means to said combining means; (e) means (130, 135) for transmitting said mapping function as a separate signal with said active video signal and said audio signals and said still frame graphics signals from said combining means (110) at said transmitting site (105) to said receiving site (170); and

(f) means (310) controlled by said mapping function at said receiving site for combining onto said virtual TV channels, said audio signals with said still frame graphics signals and said active video signal so that said active video signal is time shared by said virtual channels.

12) The system of claim 11 , wherein each one of a plurality of said virtual channels concurrently receive said active video signal and an audio signal unique to each of said virtual channels.

13) The apparatus of claim 11, wherein at least one of said virtual channels receives an audio signal and said active video signal during a time interval while at least one other of said virtual channels receives a still frame graphics signal representing data and/or an audio signal.

14) The apparatus of claim 11 , wherein, in accordance with said mapping function (155), at least one of said virtual TV channels receives one of said still frame graphics signals representing a still scene.

15) The apparatus of claim 11, wherein said mapping function is inserted into one of said still frame graphics signals; and wherein said means for combining comprises means for generating selected ones of said screens on said TV set by combining one of said audio channels with one of said still frame graphics signals and said active video signal under control of said transmitted mapping function.

16) The apparatus of claim 11, wherein said active video signal (Vi) is selected (202) at said transmitting site from one of a plurality of available video signals (V -V_n). 17) The apparatus of claim 11 , wherein said combining means comprises a compressor/encoder (110) and wherein said signals are compressed and transmitted over said single video channel which has the bandwidth of substantially equal to that of only a single compressed video channel.

18) The system of claim 17 where system further includes:

(a) means (301-1, 310-2) for converting said active video signal and said audio signals and still frame graphics signals, and said mapping function to digital data packets; (b) means (308) for tagging each of said packets with a virtual channel number tag corresponding to said mapping function;

(c) means (130, 135) for transmitting said packets in a digital bit stream to said viewing site; and

(d) means (150, 176) for applying, at said viewing site, said active video signal to at least one virtual TV channel in correspondence with said mapping function.

19) The system of claim 11 wherein said information is transmitted in a digital format using a bandwidth substantially equal to that of a single digitally compressed TV channel, and wherein said combining means comprises a compressor/encoder means (110); and means (101, 102, 103) for applying said signals from a program source (P.,-

-P_n) to said compressor/encoder means;

20) The system of claim 19 where system includes:

(a) means (310-1, 310-2) for converting said active video signal and said audio signals and still frame graphics signals, and said mapping function to digital data packets; (b) means (308) for tagging each of said packets with a virtual channel number tag corresponding to said mapping function; (c) means (130) for transmitting said packets in a digital bit stream to said viewing site; and (d) means (150, 176) for applying, at said viewing site (175, 175*), said active video signal to at least one virtual TV channel in correspondence with said mapping function.