Digital data encoding in video signals using data modulated carrier signals at non-peaks in video spectra

• US 5,663,766 A
• Filed: 01/25/1996
• Issued: 09/02/1997
• Est. Priority Date: 10/31/1994
• Status: Expired due to Term

• Current Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Sizer, Theodore II
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US08/599,500
• Time in Patent Office: 586 Days
• Field of Search: 348/473, 348/475, 348/486, 348/476, 348/598, 348/553, 348/563, 348/564
• US Class Current: 348/473
• CPC Class Codes: H04N 7/08 Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band , e.g. by time division H04N7/007 takes precedence
• CPC Class Codes: H04N 7/081 the additional information signals being transmitted by means of a subcarrier

Abstract

Digital information is encoded in the video portion of a television signal such that "n" (n is an integer) bits of the digital information are carried by each successive frame in a group of frames. The digital information is encoded by modulating a carrier signal, using, for example, either amplitude shift keying (ASK) or frequency shift keying (FSK), and the modulated carrier is then added to the video signal selectively, only in portions of the television program that (a) are not likely to be perceptible by a viewer, and (b) are of sufficient intensity to transmit the data. The video signal including the encoded digital data, may be transmitted, in real time, to a television receiver, or recorded for later playback. In either event, at a receiver, when the video signal containing the encoded information is displayed on a screen, the image is sensed or "viewed" by a photo detector, the output of which is applied to a band pass filter having a center frequency that corresponds to the oscillator frequency(s) in the encoder. The filter output is thresholded or FM detected, so that the receiver can recover the encoded data. By appropriately including checks bits and synchronization patterns, the bit stream output from the decoder can be synchronized, and the original encoded data recovered. Advantageously, the frequency of the oscillator in the ASK or FSK encoder is chosen so that the energy added to the video signal is in a portion of the frequency spectrum that otherwise contains little energy. This makes the added digital data imperceptible to a viewer. If desired, the same data may be repetitively encoded in several groups of frames, so as to increase the redundancy and thus the reliability of the overall system.

Claims

1. A system for communicating digital information in a video signal, said video signal having a spectrum associated therewith, comprising:

an encoder arranged to add a carrier signal modulated by digital information to said video signal, said modulated carrier signal at other than a frequency corresponding to a peak in the video spectrum, and

a receiver arranged to optically sense said video signal and to recover said encoded digital information in said video signal.

2. The invention defined in claim 1 wherein said carrier signal is modulated using amplitude shift keying (ASK), frequency shift keying (FSK), or phase shift keying (PSK).

3. The invention defined in claim 1 wherein said carrier signal containing said digital information is added to said video signal such that said digital information is not likely to be perceptible by a viewer.

4. An encoder arranged to encode n bits of digital information in each successive frame of a video signal, said video signal having a spectrum associated therewith, comprising

a buffer for storing said digital information,

means for obtaining a synchronization signal synchronized with the frame rate of said video signal,

means responsive to said synchronization signal for generating a modulated carrier signal during each frame interval, said modulated carrier signal at other than a frequency corresponding to a peak in the video spectrum, said modulated carrier signal being formed by controlling the output of an oscillator in accordance with the value of the next n bits from said buffer, and

means for combining said modulated carrier signal with said video signal.

5. The invention defined in claim 4 wherein the frequency of said oscillator is chosen so that the energy added to said video signal is in a portion of the frequency spectrum that otherwise contains little energy, so that said digital information is not likely to be perceptible by a viewer.

6. A receiver arranged to recover n bits of encoded digital information included in each successive frame of a video signal, said video signal having a spectrum associated therewith, comprising

a photo detector responsive to the picture generated by said video signal,

means for amplifying the output of said photo detector,

means for filtering the output of said amplifying means to isolate a component at a particular frequency, said frequency being other than a frequency corresponding to a peak in the video spectrum, and

means for applying the output of said filtering means to a decoder to recover said encoded digital information.

7. A receiver, including

a photo detector for viewing a television signal display containing encoded information mixed with a video signal, said video signal having a spectrum associated therewith, said encoded information being represented by at least one frequency component at a frequency which is not likely to be perceptible to a viewer of said video signal, said frequency being other than a frequency corresponding to a peak in the video spectrum,

means including a band pass filter having a center frequency that is the same as said frequency of said frequency component, for isolating said frequency component from the output of said photo detector, and

thresholding means for recovering said encoded information from said isolated frequency component.

8. A method for encoding digital information in the video portion of a television signal such that "n" (n is an integer) bits of the digital information are carried by each successive frame in a group of frames, said television signal having a spectrum associated therewith, comprising the steps of

encoding said digital information using either amplitude shift keying (ASK) or frequency shift keying (FSK), and

selectively adding said encoded digital information to said video signal, only in one or more portions of the spectrum other than those which correspond to a peak in said spectrum,

wherein said encoding steps includes the steps of

storing digital information to be encoded in a buffer,

reading out "n" bits of stored data from the buffer during each frame interval, in synchronization with the video signal frame rate, and

using the output from said buffer to control the state of an ASK or FSK encoder.

9. The method defined in claim 8 wherein said ASK or FSK encoder includes an oscillator arranged to generate an output signal having at least one frequency component chosen so that energy added to said video signal is in a portion of the frequency spectrum that otherwise contains little energy.

10. The method defined in claim 8 wherein after all data in said buffer has been read out and encoded within one group of frames, the encoding process for the same data is repeated using at least one additional groups of frames.

11. The method defined in claim 9 further including the steps of recovering said encoded digital data by

displaying said video signal containing said encoded information on a screen,

capturing the video image on said screen in a photo detector,

applying the output of said photo detector to a band pass filter having a center frequency that corresponds to said oscillator frequency, and

processing the output of said filter to determine, for each portion of each frame, whether or not a component at said oscillator frequency was added to said video signal.