System for transparent transmission and reception of a secondary data signal with a video signal in the video band

• US 5,557,333 A
• Filed: 02/24/1994
• Issued: 09/17/1996
• Est. Priority Date: 06/14/1991
• Status: Expired due to Fees

• Current Assignee: WAVO Corporation
• Original Assignee: WavePhore, Inc.
• Inventors: Montgomery, Gerald, Gerdes, Richard C., Jungo, Charles
• Primary Examiner(s): Harvey, David E.
• Application Number:
  US08/201,169
• Time in Patent Office: 936 Days
• Field of Search: 348/392, 348/427, 348/429, 348/436, 348/469, 348/473, 348/474, 348/460, 348/486, 348/488, 348/492, 370/69.1
• US Class Current: 348/473
• CPC Class Codes: H04N 1/00098 via a television channel, e.g. for a series of still pictures with or without sound
• CPC Class Codes: H04N 5/445 for displaying additional information H04N5/50 takes precedence
• CPC Class Codes: H04N 7/0803 using frequency interleaving, e.g. with precision offset
• CPC Class Codes: H04N 7/081 the additional information signals being transmitted by means of a subcarrier
• CPC Class Codes: H04N 7/10 Adaptations for transmission by electrical cable H04N7/12 takes precedence

Abstract

Signal processors for permitting the transparent, simultaneous transmission and reception of a secondary data signal with a video signal in the video band is disclosed. The signal processor in the transmitter rasterizes the data at the horizontal scanning rate and modulates the data with a data carrier at a non-integral multiple of the horizontal scanning rate to obtain frequency interleaving. The data is transmitted during the active video portion of each video line.

Claims

1. A signal processor for combining data in the same communications channel as a video signal for an image, the video signal having a video bandwidth and having horizontal and vertical blanking interval defined by sync pulses and an active video intervals between blanking intervals, the video signal having luminance and chrominance information frequency interleaved with each other, the data being uncorrelated to the image, the signal processor comprising:

means for receiving a video signal and the data signal;

means for detecting the frequency of at least one of the blanking and active video intervals and the sync pulses; and

means responsive to the detecting means for modulating the data within the video bandwidth with carrier; and

combining the modulated data with the video signal without phase inversion of the data such that the modulated data signal is present during at least some parts of each active video interval but not during the blanking intervals such that the modulated data information is frequency interleaved with both the chrominance and the luminance information such that the phase of the data remains substantially unaltered between successive fields.

2. The signal processor described in claim 1, wherein the spectral envelope of the video signal has gaps, and wherein the modulating means comprises:

means for generating the carrier at a frequency about a quarter non-integral multiple of at least some of the sync pulses for modulating the data.

3. The signal processor described in claim 1, wherein the spectral envelope of the video signal has gaps, and wherein the modulating means comprises:

means for generating a data carrier based upon the frequency of at least some of the sync pulses for modulating the data without phase inversion of the carrier in every other field; and

means responsive to the data carrier for frequency interleaving the data with the video information.

4. The signal processor described in claim 2, wherein the means for modulating further includes means for rasterizing the data signal with the blanking interval of the video signal.

5. The signal processor of claim 3, wherein the modulating means further includes means for limiting the bandwidth of the rasterized data.

6. The processor of claim 5, wherein the means for limiting the bandwidth of the rasterized data comprising an encoder for encoding rasterized data in one of the formats of the group comprised of NRZ, RLL, FM, Manchester and MFM coding data formats.

7. The signal processor of claim 1, wherein the video and the modulated data signals have signal levels and wherein the ratio of the video signal level and the modulated data level is controlled to reduce interference from modulated data on the video signal.

8. A method for transmitting data other than a video signal in the same communications channel as a color video signal comprised of chrominance and luminance information frequency interleaved with each other being transmitted in a given frequency band, the color video signal having a video bandwidth and active and blanking intervals with a sync frequency, and the video signal, and the data being uncorrelated with respect to each other, the method comprising:

detecting the active video intervals; and

transmitting the data at frequencies within the band substantially centered around quarter non-integral multiples of the sync frequency without phase inversion of the data during at least some of the active video intervals and the transmitting the data further includes blanking the data signal other than during the active video .period whereby the data signal is rasterized.

9. The method of claim 8, wherein the method for detecting the active video intervals comprises detecting the blanking intervals of the video signal.

10. The method of claim 9, wherein the intervals are defined by sync pulses, and wherein the video spectrum envelope has gaps and transmitting the data comprises:

generating a data carrier at a frequency that is a quarter non-integral multiple of the sync frequency for modulating the data based upon one of at least some of the intervals between sync pulses; and

modulating the data carrier with a data signal corresponding to the secondary data such that the phase of the data is not altered by more than π

/2 radians prior to modulation whereby the modulated data carrier falls within the gaps of the video signal when modulated by the data carrier, whereby frequency interleaving is obtained.

11. A system for combining a secondary data signal with a color frequency interleaved video signal having audio information in a frequency band above frequency bands of luminance and chrominance information interleaved with each other, horizontal sync pulses at a predetermined rate and gaps in the video frequency spectra, the system comprising:

a timing circuit responsive to the sync pulses, the timing circuit producing a data carrier at a frequency that is an odd quarter non-integral multiple of the rate;

a combiner having at least two inputs;

a video portion providing the primary video signal to one input of the combiner;

a secondary data portion providing a second input to the combiner;

a blanking interval detector producing a blanking signal indicating the time periods of the blanking interval;

the secondary data portion including;

a data buffer receiving the secondary data and providing rasterized data at an output based upon the blanking signal and the secondary data without altering the phase of the secondary data substantially;

a modulator for providing a modulated data signal responsive to the data carrier and the output of the data buffer, the modulated data signal being coupled to the second input of the combiner such that the spectra of the modulated data signal lies substantially within the gaps of the video spectra such that the modulated data is only present during the blanking intervals.

12. The system of claim 11, the secondary data portion further including a scrambler coupling the rastorized data to the modulator, wherein the rastorized data received by the modulator is scrambled.

13. The system of claim 11, wherein the secondary data signal includes a clock that controls the rate at which data is stored in the buffer.

14. The signal processor of claim 11, wherein the signal processor section further includes an encoder for limiting the bandwidth of the rasterized data.

15. The signal processor of claim 11, wherein the primary video signal is an NTSC signal.

16. The signal processor of claim 11, wherein the secondary data signal is a compressed video signal.

17. The signal processor of claim 11, wherein the buffer is an elastic buffer.

18. The signal processor of claim 11, wherein the signal processor further includes a filter receiving the video signal and producing as an output a signal that is a reduced portion of the spectra of the video signal containing the video information and the output of the filter being supplied to an inverting input of the combiner.

19. The signal processor of claim 11, wherein the signal processor further includes means for detecting at least one of luminance and chrominance transitions in the video signal above a predetermined limit and for inhibiting data transmission such that no modulated data is provided to the combiner while the portion of the primary video signal containing those transitions reaches the combiner.

20. The signal processor of claim 11, wherein the signal processor further includes means for detecting at least one of luminance and chrominance transitions in the video signal above a predetermined limit and for inserting a unique code in the modulated data to inform a receiver that transmission of secondary data will be halted temporarily.

21. A signal processor for separating a data signal from a rasterized video signal having horizontal and vertical blanking intervals at predetermined intervals and having chrominance and luminance information frequency interleaved in a bandwidth and the data information being contained substantially in an unused portion of the same bandwidth, the processor comprising:

a timing circuit generating a timing signal at a predetermined frequency based upon the rate of the horizontal intervals;

a band pass filter passing as an output the frequencies for the data signal; and

a data separator responsive to the timing signal and the output of the filter for outputting the data signal at a data rate above about 100 kilobits per second without altering the phase of the data signal substantially.

22. The signal processor of claim 21, wherein transmission of the data signal has been inhibited during intervals when the video signal represents relatively sharp transitions between pixels and the processor comprises a video processor for detecting information in the signal representing sharp transitions, and the separator further includes a data synchronizer responsive to the video processor.

23. The processor of claim 21, wherein the timing circuit outputs a pulse representing the blanking intervals and the separator uses the pulse to recognize the blanking intervals in the transmitted data signal.

24. The processor of claim 21, further including a phase compensator for compensating the data signal for any phase distortion of the filter, and the data separator further includes a synchronous data detector for detecting data in the phase compensated data signal.

26. The system of claim 21, wherein the data signal synchronously modulates a data carrier.

25. A system for adding a secondary data signal to a primary video signal blanking intervals defined by sync pulses and a frequency baseband, the data signal being uncorrelated to the video signal, the system comprising:

means for detecting at least some of the sync pulses in the video signal;

means for modulating a data carrier within the baseband based upon the detected sync pulses with the data without altering substantially the phase relationship of the data to provide a modulated data signal having the frequency band of the modulated data carrier at least partially overlapping the video band of the video signal; and

means for combining the modulated data signal with the video signal such that the data signal is transparent to a receiver designed to receive the video signal.

27. An apparatus for injection of a data signal into a rasterized, frequency interleaved, color baseband video signal having blanking intervals a color carrier located in an upper half of the video bandwidth and a bandwidth with an upper limit, the apparatus comprising:

a rasterizer providing blanking intervals in the data signal to form a rasterized data signal;

a carrier generator generating a data carrier to modulate the rasterized data signal to produce a modulated, rasterized data signal without phase inversion of the carrier or the data, the frequency of the carrier lying within the color baseband video signal;

a filter to attenuate at least some of the frequencies between the video carrier and the data carrier to produce a filtered video signal; and

a combiner to inject the modulated, rasterized data signal into the filtered video signal at a sufficiently low level of injection such that the data creates no visible artifacts on the screen of a television receiver.

28. The apparatus of claim 27, wherein the frequency of the data carrier is near the upper limit of the video bandwidth.

29. The apparatus of claim 27, wherein the data carrier is at a frequency that is at about a one quarter non-integral of the blanking interval frequency.

30. The apparatus of claim 29, wherein the injection level is such that the video signal is not perceptible to a viewer at a television receiver receiving the combined signals.

31. The apparatus of claim 28, wherein the portion of the bandwidth of the video signal where the data signal is injected is filtered.

32. A method for injecting data other than a video signal in the same communications channel as a color video signal having a given frequency baseband with color and luminance portions, the video signal having a video bandwidth and active and blanking intervals, the color portion and luminance portion of the video signal being frequency interleaved at evenly spaced frequency gaps with the luminance portion and the video signal and the data being uncorrelated with respect to each other, the method comprising:

detecting the active video intervals; and

injecting data having a data rate of greater than one hundred kilobits per second at frequencies within the baseband during at least some of the active video intervals but not during the blanking intervals and without causing visibly discernable interference effects at the receiver.

33. The method of claim 32, wherein the method for detecting the active video intervals comprises detecting the blanking intervals of the video signal.

34. The method of claim 33, wherein the intervals are defined by sync pulses, and wherein the video spectrum envelope has gaps and the step of transmitting the data comprises:

generating a data carrier for modulating the data based upon one of at least some of the intervals between sync pulses; and

modulating the data carrier with a data signal corresponding to the secondary data to fall within the gaps of the video signal when modulated by the data carrier, whereby frequency interleaving is obtained.

35. A system for interleaving a secondary data signal with a color video signal having color and luminance portions of the video signal spaced equidistant from each other to provide a frequency interleaved signal and having horizontal sync pulses at a predetermined rate, the system comprising:

a timing circuit responsive to the sync pulses, the timing circuit producing a data carrier at a frequency that is a non-integral multiple of the predetermined rate and a timing signal at an integral multiple or submultiple of the rate;

a combiner having at least two inputs;

a video portion providing the primary video signal to one input of the combiner;

a secondary data portion providing a second input to the combiner;

a blanking interval detector producing a blanking signal indicating the time periods of the blanking interval;

the secondary data portion including;

a data buffer receiving the secondary data and providing rasterized data at an output based upon the blanking signal and the secondary data;

a modulator for providing a modulated data signal responsive to the data carrier, the modulated data signal being coupled to the second input of the combiner.

36. The system of claim 35, the secondary data portion further including a scrambler coupling the rastorized data to the modulator, wherein the rastorized data received by the modulator is scrambled.

37. The system of claim 35, wherein the secondary data signal includes a clock that controls the rate at which data is stored in the buffer.

38. The signal processor of claim 35, wherein the signal processor section further includes an encoder for limiting the bandwidth of the rasterized data.

39. The signal processor of claim 35, wherein the primary video signal is an NTSC signal and the secondary data signal is a digital signal.

40. The signal processor of claim 35, wherein the secondary data signal is a compressed video signal.

41. The signal processor of claim 35, wherein the buffer is an elastic buffer.

42. The signal processor of claim 35, wherein the signal processor further includes a filter receiving the video signal and producing as an output a signal that is a reduced portion of the spectra of the video signal containing the video information and the output of the filter being supplied to an inverting input of the combiner, whereby noise in the data signal is reduced.

43. The signal processor of claim 35, wherein the signal processor further includes means for detecting at least one of luminance and chrominance transitions in the video signal above a predetermined limit and for inhibiting data transmission such that no modulated data is provided to the combiner while the portion of the primary video signal containing those transitions reaches the combiner.

44. The signal processor of claim 35, wherein the signal processor further includes means for detecting at least one of luminance and chrominance transitions in the video signal above a predetermined limit and for inserting a unique code in the modulated data to inform a receiver that transmission of secondary data will be halted temporarily.

45. A signal processor for separating a data signal frequency interleaved with a rasterized video signal having horizontal and vertical blanking intervals at predetermined intervals, the processor comprising

a timing circuit generating a timing signal at a predetermined frequency based upon the rate of the horizontal and vertical intervals;

a band pass/comb filter passing as an output the frequencies for the data signal;

a data separator responsive to the timing signal and the output of the filter for outputting the data signal.