GB2038137A

GB2038137A - Coding and decoding of TV signals

Info

Publication number: GB2038137A
Application number: GB7940978A
Authority: GB
Original assignee: Oak Industries Inc
Current assignee: Oak Industries Inc
Priority date: 1978-12-04
Filing date: 1979-11-27
Publication date: 1980-07-16
Also published as: FR2443778A1; DE2947943A1; NL7908569A; GB2038137B; AU5309779A; GR82329B; NL188137C; CH661398A5; MX147755A; NL188137B; FR2443778B1; CA1150818A; DE2947943C2; BR7907803A; JPS63131287U; JPS5588481A; IL58735A0; IL58735A; AU526049B2

Abstract

A method of coding and decoding video signals includes suppressing synchronization pulses during the video horizontal and vertical blanking intervals by gates 16 and 22 and inserting clock and address information in the suppressed intervals by a line modulator (36) and an address gate (44) respectively. Digital sound information may be inserted in the suppressed horizontal blanking intervals by a gate (30). At the receiver the unsynchronized video and the clock information are detected by a video detector and the clock is used to control a sync pulse generator to provide the sync pulses which are then recombined with the unsynchronized video. The digital sound information is used to provide program audio which is then combined with the above-described video signal to provide a television signal useable in a receiver. <IMAGE>

Description

SPECIFICATION Coding and decoding of TV signals The present invention relates to means for coding and decoding the video and/or audio signals and is applicable to pay television systems.

According to one aspect of the present invention, there is provided a method of coding and decoding video signals including the steps of: (a) at the transmitter suppressing synchronizing pulses during the video horizontal and vertical blanking intervals, and inserting clock information in the suppressed intervals, (b) at the receiver detecting the unsynchronized video and the clock information, using said detected clock information to control a sync pulse generator, and combining the detected video and sync pulses to provide a usable video signal.

Preferably, the method includes the step of inserting address signals in the suppressed blanking intervals at the transmitter, and using said address signals in the receiver decoding process.

Digital sound may be inserted in the suppressed horizontal blanking intervals and utilized at the receiver to provide the audio portion of the television signal, the digital sound may provide either the primary audio signal or an alternate sound channel.

According to another aspect of the present invention, there is provided means for coding television signals including: (a) means for suppressing synchronizing pulses during the horizontal and vertical blanking intervals of the video waveform, and, (b) means for inserting authorization and clock signals for use in reconstituting the video synchronizing signals (in the suppressed blanking intervals).

According to a further aspect of the present invention, there is provided means for decoding a coded television signal in which the synchronizing pulses during the video horizontal and vertical blanking intervals are suppressed and in which clock signals are inserted in the suppressed blanking intervals, including: (a) means for detecting the clock signals, (b) sync pulse generating means connected to said detecting means and operable by said clock signals, and, (c) means for combining pulses from said pulse generating means and the video signal having suppressed synchronized pulses to provide a usable television signal.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a block diagram of the transmitting portion of the described subscription television system, and Figure 2 is a block diagram of the receiver utilized with the transmitting arrangement of Fig. 1.

The present invention relates to subscription television systems in which over the air television signals are coded at the transmitter and include, with the video signal, signals for use in enabling and authorizing decoding circuitry at individual receivers. The synchronization pulses in the horizontal and vertical blanking intervals of the video signal are suppressed to approximately 25% of the original amplitude.

Thus the picture will be distorted in both horizontal and vertical directions and will be completely unusable unless the required decoding equipment is operable. Clock signals for operating the sync pulses generator in each receiver are inserted into the vertical blanking intervals. In addition authorization or address signals for enabling the decoding equipment are also inserted in the vertical blanking intervals. The audio portion of the television signal may be clear or not coded. In the alternative, the audio portion can be digitized and the digital sound information inserted in the horizontal blanking intervals. In the later instance, the sound is reconstituted at each receiver and the program audio is then recombined, at the receiver, with the decoded video.As a further alternative, audio information can be included in the described horizontal blanking intervals to provide an alternate sound channel.

In Fig. 1 the program video signal is provided on line 10 and the audio signal on line 1 2. The video signal provides one input for a sync processor 14 and for a gate 16. The sync processor will provide several independent signals for use as described. The first output, along line 1 8 to gate 16, is effective to operate gate 1 6 in a manner to suppress the sync pulses during the vertical interval of the video signal. Thus the signal at the output of gate 1 6 is the normal video signal with the vertical interval suppressed, preferably to a level of approximately 25 percent of its original amplitude.

The second output from sync processor 14, along line 20, is connected to gate 22. The other-input for gate 22 is the video signal from gate 1 6. The signal from sync processor 14 provided at gate 22 is effective to suppress the horizontal blanking interval to approximately 25 percent of its original amplitude. Thus, the output from gate 22 is the original video signal with both the horizontal and vertical blanking intervals suppressed to approximately 25 percent of their original amplitude.

A clock generator is indicated at 24 and may provide a clock signal of 3.58 mhz. One output from clock generator 24 goes to divide circuit 26 which provides an output signal of 31.5 khz which is the sound sampling fre quency. To digitize sound, with a maximum frequency of 1 2 khz, it is necessary to have a sampling frequency of at least 24 khz. For a dynamic range of 48 dB there should be 8 bits so that the minimum bit rate will be 1 92 K bit/second. Because the synchronization frequency is approximately 1 5 khz and the sampling frequency should be at least 24 khz it has been determined to combine two sound samples into each horizontal blanking interval.

Delay circuit 28 is effective to delay every other or alternate sound samples as provided at the sampling frequency of 31.5 khz from divide circuit 26. Thus, each horizontal blanking interval will have two sound samples. In order to properly reconstitute the audio signal it will be necessary that at the decdder onehalf of the total number of bits inserted in each horizontal blanking interval be delayed.

In practice, it has been determined that 24 bits per horizontal blanking interval time slot may be utilized with 2 eight bit sound samples and the remaining 8 bits utilized for synchronization and control. Thus, the signal from delay circuit 28 will be as described and will provide one input for gate 30. At the other input for gate 30 is a timing signal from sync processor 14 along line 32 which will cause insertion of the described digital sound information into the horizontal blanking intervals.

Clock generator 24 is connected to a divide circuit 38 which provides clock signals for utilization at the receiver at 4/7 of the clock frequency of 3.58 mhz. In this connection, the frequencies provided herein are only illustrative and the invention should not be limited thereto. The output from divide circuit 38 is connected to line modulator 36 which has a further input, along line 34, from sync processor 14 which is utilized to control the insertion of the clock signals in the first nine lines of the suppressed vertical blanking interval.

Line modulator 36 receives, from gate 30, the video signal with suppressed horizontal and vertical blanking intervals and with the inserted digital sound. The output from modulator 36 will be the described signal with the addition of clock signals during the first nine lines of the suppressed vertical blanking interval.

A line counter 40 is connected to sync processor 14 and has its output connected to a computer 42. The output from computer 42 is connected to an address gate 44. Computer 42 contains the addresses of all subscribers authorized to receive subscription programs.

Not all addresses with be sent in every vertical blanking interval, but rather they will be sequentially fed by the computer to the address gate for insertion in the vertical blanking interval after the clock signals in the first nine lines. Assuming 48 bits per address, and one address per line, with twelve unused lines, it is possible to insert twelve addresses in each vertical blanking interval. In normal operation, however, prior to the actual transmission of the subscription program, all receivers will be addressed as it will be possible to utilize the entire video transmission. The addressing during each vertical blanking interval can be utilized to continually enable the decoders in each receiver once they have been initially enabled by a transmission prior to the start of the subscription program.Thus, the output from address gate 44 will be the abovedescribed video signal, with the digital sound inserted in the horizontal blanking interval and with address or enabling information in the vertical blanking interval after the above-described clock signals. This signal is sent to transmitter 46 which will then transmit the described signal over the air for reception by those subscribers having the necessary decoding equipment.

Fig. 2-illustrates the decoding apparatus at the receiver. A tuner 50 which may be either a UHF or VHF tuner is connected to an IF filter 52 providing an approximate 45 mhz output signal which is in turn passed to a video detector 54. The output from detector 54 is the above-described video signal and is connected to a decoder 56 and a combining circuit 58. Decoder 56 will provide one output of the above-described clock signal along line 60 to sync generator 62. The output from sync generator 62 which will be the vertical and horizontal sync pulses suppressed at the transmitter is sent to combining circuit 58 whose output is thus the reconstituted video with appropriate sync signals. Sync generator 62 will be continuously providing normal sync pulses, but the clock signals from decoder 56 are necessary to properly coordinate the timing of the sync generator and the video signal.

A second output from decoder 56 is the digital sound information which is connected to a digital to analog converter 64. The output from converter 64 will be the reconstituted audio signal. A 4.5 mhz oscillator 66 is connected to an FM modulator 68 which receives the audio signal from converter 64 with the output from modulator 68 being the audio portion of the original television signal at a 4.5 mhz frequency. This signal is passed to a combining circuit 70 which receives the combined video signal from combining circuit 58. Thus, the output from combining circuit 70 is the video and audio portions, properly decoded, of the original television signal.

The third output from decoder 56, the address or enabling information which had been previously inserted in the vertical blanking interval is passed to an address authorisation decoder 72 which compares the decoded address with the address of the receiver. If there is comparison, switch 74 is enabled to permit modulator 76 to function in the appropriate manner. Modulator 76 changes the frequency of the video and audio signals from combining circuit 70 to an RF signal at the appropriate frequency for use in a television set. Normally this will be channel three or four, unused channels in many areas. The output from modulator 76, a channel three or channel four television signal will be passed through filter 78 and then to the television receiver.

The subscription television system described herein not only provides adequate safeguards to preventing piracy of the signal, but does so in a reliable and relatively uncomplex manner.

The vertical and horizontal synchronization is removed from the video signal and is provided at the receiver by an independent sync generator the timing of which is controlled by clock signals forming a part of the transmitted video. Substantially complete picture distortion is effected by removal of both horizontal and vertical synchronization.

The audio may be coded as described, in the form of digital sound. In the alternative, the audio may be transmitted clear, without coding. In such event the horizontal blanking interval can be used to provide an alternate sound channel, or it can have no coding information superimposed thereon. As another alternative, the clock and address information described as being inserted in the vertical interval can be inserted in the horizontal blanking interval. Thus it is possible to utilize the horizontal blanking interval for an alternate sound channel, for coded audio information, for no signal at all or for additional code data supplementing that superimposed on the vertical blanking interval.

Whereas the preferred form of the invention has been shown and described herein, it should be realized that there may be many modifications, substitutions, and alterations thereto.

Claims

1. A method of coding and decoding video signals including the steps of: (a) at the transmitter suppressing synchronizing pulses during the video horizontal and vertical blanking intervals, and inserting clock information in the suppressed intervals, (b) at the receiver detecting the unsynchronized video and the clock information, using said detected clock information to control a sync pulse generator, and combining the detected video and sync pulses to provide a usable video signal.

2. A method according to claim 1, wherein the clock information is only inserted in the suppressed vertical blanking intervals.

3. A method according to claim 1 or claim 2 including the step of inserting address signals in the suppressed blanking intervals at the transmitter, and using said address sigr.n.s in the receiver decoding process.

4. A method according to any preceding claim by including the step of inserting digital sound information in the suppressed horizontal blanking intervals at the transmitter and detecting said digital sound information at the receiver.

5. A method of coding video signals including the steps of: (a) suppressing synchronizing pulses during the video horizontal and vertical blanking intervals, (b) inserting clock information in the suppressed vertical intervals, and, (c) inserting address signals in the suppressed vertical intervals.

6. A method according to claim 5 including the step of inserting digital sound signals in the suppressed horizontal blanking intervals.

7. A method of detecting and reforming video signals in which the horizontal and vertical blanking intervals have been suppressed and in which clock information and authorization signals have been inserted in the suppressed blanking intervals including the steps of: (a) detecting the unsynchronized video, clock and authorisation signals, (b) using said clock signals to control a sync pulse generator, (c) recombining the unsynchronized video and sync pulses, (d) modulating the combined signal to provide a signal usable in a television receiver, and (e) using said authorization signals to control the operation of one of above-described decoding steps.

8. A method according to claim 7 wherein digital sound signals are inserted in the horizontal blanking intervals of the video signal and including the steps, at the receiver, of detecting the digital sound signals, providing an audio signal therefrom, and combining the audio and video signals.

9. Means for coding television signals including: (a) means for suppressing synchronizing pulses during the horizontal and vertical blanking intervals of the video waveform, and (b) means for inserting authorisation and block signals for use in reconstituting the video synchronizing signals (in the suppressed blanking intervals).

10. Means according to claim 9 including means for providing digital sound information representative of the audio portion of the television signal, and means for inserting said digital sound information in the suppressed horizontal blanking intervals.

11. Means for decoding a coded television signal in which the synchronizing pulses during the video horizontal and vertical blanking intervals are suppressed and in which clock signals are inserted in the suppressed blanking intervals, including: (a) means for detecting the clock signals, (b) sync pulse generating means connected to said detecting means and operable by said clock signals, and, (c) means for combining pulses from said pulse generating means and the video signal having suppressed synchronized pulses to provide a usable television signal.

1 2. Means according to claim 11 wherein said coded television signal includes digital sound information inserted in the horizontal blanking intervals, said decoding means including: (d) means for detecting said digital sound information and for providing therefrom a reconstituted audio signal, and (e) means for combining said reconstituted audio signal with said video signal.

1 2. A method of coding and decoding video signals substantially as hereinbefore described with reference to the accompanying drawings.

13. Means for coding and decoding television signals substantially as hereinbefore described with reference to the accompanying drawings.