WO2002015428A2

WO2002015428A2 - Spread spectrum transmission for expanding information capacity in existing communication transmission systems

Info

Publication number: WO2002015428A2
Application number: PCT/US2001/041734
Authority: WO
Inventors: Walter S. Cicora; Ted Hartson
Original assignee: Dotcast, Inc.
Priority date: 2000-08-15
Filing date: 2001-08-15
Publication date: 2002-02-21
Also published as: AU2001287182A1; WO2002015428A3; UY26890A1

Abstract

Systems and processes for including spread spectrum transmissions within television and radio broadcast channels without substantial degradation of the broadcast programming. The spread spectrum transmissions may carry components of the same television or radio programming, they may be the same programming, or they may be content that is unrelated to the programming. Disclosed are systems and processes for accomplishing such spread spectrum transmissions in a manner that compensates for robustness of signal components, by among other things time varying and/or varying frequency of the spread spectrum transmissions. Also disclosed are systems and processes for abating carrier signals to compensate for the effects of the spread spectrum transmissions in the channel. Further disclosed are systems and processes for conducting such transmissions in a cellular communications system.

Description

Communications System Improvement for Expanded Information

Capacity for Existing Communication Transmission Systems

Using Spread Spectrum Techniques.

BACKGROUND AND SUMMARY

The standard method for over-the-air transmission of television signals in the United States in called NTSC. This is an analog system in which the picture is transmitted in a vestigial sideband modulation format on the visual carrier and the sound component transmitted as frequency modulation on a separate sound carrier. Relatively recent developments in the television industries have focused upon the transmission of High Definition Television (HDTV), which requires a substantial increase in transmitted information and hence greatly expands the required baseband video signal bandwidth. Great progress has been made in the area of digital TV bandwidth compression so that one or more HDTV signals can be conveyed in the standard television bandwidth of 6 MHz. These HDTV developments have, by a combination of techniques, substantially reduced the bandwidth required for fully digital transmission of the video information. Subsequently, it was determined that the same compression techniques can be used to put multiple "Standard Definition Television", SDTV, signals in the same bandwidth. Both of these techniques, HDTV and SDTV, are generically called Digital Television, DTV. A further move from the original HDTV goal is the allowance by the Federal Communications Commission, FCC, of data transmission instead of television transmission.

The development of DTV and its acceptance as a future broadcast standard has also led to the requirement for a transition period between broadcasting the present analog TV to that of broadcasting compressed DTV. Since the transmission of standard analog NTSC will remain for many years before the complete transition to DTV, the availability of a technique allowing simultaneous, minimally-interfering transmission of digital signals within the same channel as an analog NTSC signal would result in a two (or more) channel capacity increase in the existing broadcast frequency assignments. Alternatively, data transmission can be accommodated in addition to or instead of DTV along with the analog NTSC signal.

A more detailed discussion of conventional analog and digital television signals is contained Chapters 2 and 3 in one of the inventor's texts "Modern Cable Television Technology, Video, Voice, and Data Communications", Ciciora, Farmer & Large, 1999 Morgan Kaufmann Publishers, ISBN 1-55860-416-2 which is incorporated by reference. U.S. Patent application 09/062225 filed April 17, 1998, and corresponding PCT publication number WO 99/55087 dated October 22, 1999 both entitled "Expanded Information Capacity For Existing Communications Transmission Systems," having as inventors Hartson, Dickinson and Ciciora (the "EIC documents"), are also useful background as they apply to this invention, and are incorporated by reference. While the focus of this work has been on NTSC television signals, it applies equally well to any signal transmission system.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view showing synchronization pulses in analog video signals.

Fig. 2 is a schematic view showing composite monochrome analog television signals.

Fig. 3 is a schematic view showing a cellular approach to spread spectrum transmission of data in analog television programming.

DETAILED DESCRIPTION The standard NTSC format allocates 6 MHz of spectrum to the transmission of the combined video and audio signals. The visual carrier is placed 1.25 MHz above the lower band edge and the aural carrier 5.75 MHz above the lower band edge. The visual information is impressed on the visual carrier using a vestigial sideband amplitude modulation (AM) technique so that the frequency components below the visual carrier occupy no more than the 1.25 MHz of the available spectral assignment, while the frequency range allocated to the visual information extends for approximately 4.2 MHz above the visual carrier.

The color information is carried on the color subcarrier of the main visual carrier at approximately 3.58 MHz above the visual carrier (4.83 MHz above the lower band edge). The modulation of the color information is both in-phase and quadrature and contains more lower sideband components than upper.

The aural information is carried on the separate aural carrier at 4.5 MHz above the visual carrier (5.75 MHz above the lower band edge) and is normally frequency modulated (FM) with a peak deviation of 25 KHz over the range of audio frequencies extending to somewhat above 15 KHz.

Other opportunities exist which make possible the transmission of additional information within the normal TV spectral assignments. A great deal of experience has accumulated with digital transmission of Closed Captioning for the hearing impaired and Teletext in the Vertical Blanking Interval, VBI.

One company called WavePhore, Inc. utilizes a signal which puts single sideband phase shift data in the area of approximately 3.9 to 4.2 MHz above the visual carrier (5.15 MHz to 5.45 MHz above the lower band edge) and is capable of transmitting in the order of 500 Kbits / second while causing only minor interference to the analog television signal.

Digideck, Inc has developed another approach of transmitting data within the NTSC broadcast format. This technique is called the D-Channel and operates at a reduced level in the lower frequency portion of the video vestigial sideband is capable of transmission of something in the order of 750 Kbits per second with only minor interference to the analog television signal and is covered under U.S. patent(s).

The FCC has authorized the use of the prior art systems for transmitting digital data in analog television systems and invited other inventors to come forth with improved systems for this type of data transmission in Report & Order (R & O), "Digital Data Transmission Within the Video Portion of Television Broadcast Station Transmissions", in MM docket No. 95-42. The present invention is consistent with that invitation. The primary requirements for such systems is that a) they do not interfere with other legitimate users of the radio spectrum, and b) they do not materially impact the primary application licensed by the FCC, in this case the transmission of analog television signals. Most of the prior art systems degrade but do not destroy the use of the analog television signal.

In order to transmit a digitally compressed NTSC signal, a data transmission rate in the order of 1.5 to 5 megabits per second will be required when employing present day compression techniques. The above-mentioned prior art systems are incapable of these high data rates without causing significant and unacceptable interference to the analog NTSC signal. Several of these systems can be used simultaneously. The present invention applies the well-known techniques for spread spectrum communications to the simultaneous transmission of data and analog NTSC television signals, other television signals and other types of signals, including AM and FM radio.

There are a variety of well-known spread spectrum techniques. Code Division Multiple Access, CDMA, will be used for purposes of illustration but not limitation. An excellent reference on this subject is "CDMA, Principles of Spread Spectrum

Communication" by Andrew J. Viterbi, Addison Wesley, ISBN 0-201-63374-4 which is incorporated herein by reference.

With the CDMA method of spread spectrum communications two or more pseudo-random code words are selected to represent two or more messages. If just two code words are selected, they can represent logical "1" and "0" values for binary digital communications. In this case, one logical bit is transmitted at a time. Other combinations of code words can be used to provide more choices of data transmission. For example, if four code words were selected, two logical bits would be transmitted at a time.

The receiver for such CDMA signals uses well-known correlation techniques to compare the received code word against expected code words in a mathematical process called cross-correlation. If a match is found, a signal is declared to have been received. In the case of a binary signaling scheme, the correlator looks for either the code word representing a logical "1" or the code word representing a logical "0". In this way, binary digital communications can be established.

A principal advantage of CDMA techniques is that a trade-off can be made between the length of the code word and the signal level required for reliable detection. The longer the code word, the lower the signal level required for reliable detection. Of course, the longer the code word, the slower the data transmission rate.

The correlator in the receiver discriminates against signals that are not the selected code words. These signals can be an NTSC television signal or other code words or other signals of any kind. The greater the difference between the selected code word(s) and the signals which are to be discriminated against, the more successful will be the identification of the selected code words in the presence of these other signals.

The present invention applies these well-known techniques in an inventive manner. The CDMA transmission must be completely contained within the television channel's 6 MHz in order to satisfy the FCC's requirement that no interference be provided to other users of the radio spectrum. The secondary FCC requirement is that the additional data signals do not significantly deteriorate the primary application of the spectrum as licensed. Thus an NTSC television signal must continue to provide satisfactory service to its audience. Marketing and business decisions are required to determine the amount of tolerable deterioration.

Spread Spectrum Data Transmission: Several choices for transmission of the spread spectrum data exist. The spread spectrum data could be limited to the visual bandwidth portion of the televisions spectrum and combined with the video signal. The spread spectrum data could also be limited to aural bandwidth and combined with the modulated aural signal. Since the spread spectrum data signal must be of low power, perhaps the best method is to have a separate signal source spanning the entire 6 MHz bandwidth and combining the data signal with the television signal before the transmitting antenna. Alternatively, a separate antenna may be used.

Depending on the strength of the aural signal transmitted by the NTSC transmitter, the aural portion of the spectrum may be more immune to interference since the Frequency Modulated aural signal is itself a type of spread spectrum signal. Thus different data signal power levels may be possible over the aural portion of the television spectrum relative to the visual portion of the television spectrum. The higher visual frequencies provide the fine detail in the television picture. Noise in these areas is less noticeable since it is very fine grained. Thus it may be possible to allow a higher-powered spread spectrum signal to span both the aural frequencies and the higher visual frequencies in the television spectrum. Signal to Noise: The simultaneous transmission of an NTSC signal and a spread spectrum data signal will result in the appearance of noise on the television receiver's screen and possible interference in the audio signal. Both of these deteriorations are already familiar to consumers. They are unavoidable in the physical world because of the presence of interfering signals and the fundamental presence of electrical noise from the random motion electrons in all matter. The spread spectrum data signal will add more of the same type of interference.

The interference caused by simultaneous data and NTSC transmission has two significant impacts. The first impact concerns those consumers very near the NTSC signal source who are accustomed to pristine signals. Their reception will deteriorate slightly and appear like the signals received by customers a modest distance farther away from the signal source. The second impact concerns those at the limits of tolerable reception. As the NTSC signal propagates outward from the source, it loses its strength and becomes noisy. At some distance from the signal source, consumers will consider the signal too noisy to be worth watching. The simultaneous transmission of data and the NTSC signal will bring that distance closer to the signal source, depriving some consumers of their signal by making it intolerably noisy.

The fact that consumers who are located a modest distance from the signal source find the signal completely acceptable means that those who were accustom to pristine signals will also find the signal acceptable, even if it is slightly deteriorated. Only those with excellent receivers will notice any difference. Those at the limits of reception are likely few in number. They are likely receiving most of their signals from other closer transmitters. Also, the high penetration of cable television and direct broadcast satellite services further limits the number of consumers who might notice any even minor deterioration of service.

Longer CDMA code words may be selected. This reduces the required code signal power for reliable reception and minimizes the impact on consumers with pristine reception and consumers who are at the limits of tolerable noise. Of course, the longer code word means a slower data transmission rate. Data Transmission Matched to the Television Signal: The NTSC television signal has several different components that vary in their susceptibility to interference. The maximum strength of a television signal is during its synchronization pulses. See Figure 1. These signals can tolerate the most interference before they fail to serve their intended purpose. In fact, the synchronization system is so robust that a normal television receiver synchronizes an extremely noisy picture and makes it stationary on the receiver screen well beyond the point where the picture is recognizable. An additional factor is that the noise present during the synchronization pulse is not visible on the television screen since the electron beam is blanked for the retrace. See text: "Modern Cable Television Technology, Video, Voice, and Data Communications", Ciciora, Farmer & Large, 1999 Morgan Kaufmann Publishers, ISBN 1-55860-416-2. Because of these facts, two possibilities arise. The first is to transmit data only during the blanking portion of the data signals. The second possibility is to transmit two different levels of signals, a stronger one during the blanking pulses and a weaker one during the rest of the time. This would maximize the data reach of the strong signal while minimizing the impact on the NTSC signal. An extension of this innovation is to take advantage of other times when the interference to the video signal is not possible. During the lines in the vertical blanking interval, no video appears on the screen. Nearly all television receivers have an "over-scan" region that does not appear on the screen. These transmission periods can be used for either exclusive data or higher strength data.

A further possibility is to take advantage of the fact that noise is less visible during the darker portions of the video. See Figure 2. By analyzing the video and finding the darker parts of the video, higher strength data can be transmitted during those periods.

A Cellular Approach: Rather than transmitting the data from a single point and requiring it to be of sufficient strength to reach the limits of the service area, it is possible to utilize multiple lower power data transmitters. See Figure 3. Data transmitters in adjacent geographical areas might use different code word sets to avoid interference at the areas of overlap. In this way, each transmitter has relatively lower power and reduces the interference seen on the television screen. The data transmitters may be synchronized to the video to take advantage of the innovations already described.

Multipath: A common problem in television transmission systems is the presence of multipath. The Multipath phenomenon is the simultaneous reception of multiple signals having a direct path and also reflections off of other surfaces. These signals arrive with multiple delays and overlap each other causing confusion in the receiver. Some environments such as large cities and hilly country have a great deal of multipath interference while other environments such as cable television systems or areas of flat terrain have little or no multipath.

The transmission rate of the present invention is variable and is set to optimize the environment being used. Thus a relatively fast transmission rate could be used in cable systems or areas of flat terrain. A relatively slow transmission rate would provide long pulses and greater immunity to multipath problems in an environment of multiple reflectors.

Other Television Systems: The main discussion has been on NTSC television. It will be appreciated by those of ordinary skill in these arts that this invention applies to other television and other signals as well. Simultaneous Use: Of course, this invention can be used simultaneously with devices, systems and processes disclosed in the EIC documents, and with VBI transmissions.

Claims

What is claimed is:

1. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating a second signal onto a subcarrier in said communications channel; and c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel.

2. A process according to claim 1 in which the communications channel is a television channel.

3. A process according to claim 1 in which the carrier and subcarrier are modulated using different modulation methods.

4. A process according to claim 3 in which the first signal, second signal and third signals are components of said information being communicated.

5. A process according to claim 1 in which the first signal and the third signal comprise the same television programming.

6. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel according to a first modulation process; b. modulating a second signal onto a subcarrier in said communications channel according to a second modulation process, the second modulation process comprising a process different from the first modulation process; and c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel, wherein the first signal, second signal and third signal are components of said information being communicated.

7. A process according to claim 6 further comprising modulating, using spread spectrum techniques, a fourth signal onto a predetermined bandwidth within the communications channel.

8. A process according to claim 6 in which the third signal is modulated onto the predetermined bandwidth at a power level that corresponds, at predetermined times, to the robustness of said carrier.

9. A process according to claim 6 in which the communications channel is a television channel.

10. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel according to a first modulation process; b. modulating a second signal onto a subcarrier in said communications channel according to a second modulation process; and c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel, d. wherein said modulation according to spread spectrum techniques is conducted at power levels that vary, at predetermined times, according to the robustness of at least one of said carrier and said subcarrier.

11. A process according to claim 10 in which said modulation according to spread spectrum techniques occurs only at times when the robustness of at least one of said carrier and said subcarrier are in maximum ranges.

12. A process according to claim 11 in which said communications channel is an analog television channel and said modulation according to spread spectrum techniques occurs during occurrence of synchronization signals in said carrier.

13. A process according to claim 10 in which said communications channel is an analog television channel and said modulation according to spread spectrum techniques occurs during times when robustness of said carrier to interference varies.

14. A process according to claim 10 in which said modulation according to spread spectrum techniques occurs according to direct sequence spread spectrum techniques.

15. A process according to claim 10 in which said modulation according to spread spectrum techniques occurs according to frequency hopping spread spectrum techniques.

16. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel according to a first modulation process; b. modulating a second signal onto a subcarrier in said communications channel according to a second modulation process; and c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel, d. wherein at least one of said carrier and said subcarrier feature time varying signal strength with differing robustness to interference, and said modulating according to spread spectrum techniques occurs according to said signal strength of at least one of said carrier and said subcarrier.

17. A process according to claim 16 wherein said modulation according to said spread spectrum techniques occurs only when said carrier is within maximum signal strength ranges.

18. A process according to claim 17 wherein said communications channel is a television channel.

19. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel according to a first modulation process; b. modulating a second signal onto a subcarrier in said communications channel according to a second modulation process; and c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel, d. wherein at least one of said carrier and said subcarrier feature time varying signal strength with differing robustness to interference in different parts of their frequency spectra, and said modulating according to spread spectrum techniques occurs in a part of the channel where robustness to interference is greatest.

20. A process according to claim 19 wherein said modulating according to spread spectrum techniques occurs in a part of the channel where robustness of the carrier to interference is greatest.

21. A process according to claim 19 further comprising modulating, according to spread spectrum techniques, a fourth signal onto a predetermined bandwidth within the communications channel, and said modulating of said third signal and said fourth signal occur in parts of the channel where robustness to interference is greatest.

22. A process for enabling communication of information at least partly via spread spectrum techniques in a cellular transmission system, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating a second signal onto a subcarrier in said communications channel; c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel, using different spread spectrum code words for at least two cells of a plurality of cells in the cellular transmission system.

23. A process according to claim 22 wherein a different code word is used for each cell.

24. A process according to claim 22 wherein different information is communicated from each cell.

25. A process according to claim 22 in which said communications channel is a television channel.

26. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating a second signal onto a subcarrier in said communications channel; c. modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel; and. d. modulating an abatement signal onto the carrier to compensate at least in part for effects of the third signal in the channel.

27. A process according to claim 26 in which the communications channel is a television channel.

28. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating, according to spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel; c. wherein the first signal and the second signal comprise information programming.

29. A process according to claim 28 in which the first signal and the second signal comprise part of the same information programming.

30. A process according to claim 28 in which the first signal comprises analog television programming, and the second signal comprises video content.

31. A process according to claim 28 in which the first signal comprises analog television programming, and the second signal comprises data.

32. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating, according to spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel; c. wherein the first signal comprises analog television programming and the second signal is abated to compensate for effects on said television programming of said modulating according to spread spectrum techniques.

33. A process for enabling communication of information, comprising: a. modulating a first information programming signal onto a carrier in a communications channel; b. modulating, according to spread spectrum techniques, a second information programming signal onto a predetermined bandwidth within the communications channel, c. wherein said modulation according to spread spectrum techniques is conducted at power levels that vary, at predetermined times, according to the robustness of said carrier.

34. A process according to claim 33 in which said modulation according to spread spectrum techniques occurs only at times when the robustness of said carrier is in maximum ranges.

35. A process according to claim 34 in which said communications channel is an analog television channel and said modulation according to spread spectrum techniques occurs during occurrence of synchronization signals in said carrier.

36. A process according to claim 33 in which said communications channel is an analog television channel and said modulation according to spread spectrum techniques occurs during times when robustness of said carrier to interference varies.

37. A process according to claim 33 in which said modulation according to spread spectrum techniques occurs according to direct sequence spread spectrum techniques.

38. A process according to claim 33 in which said modulation according to spread spectrum techniques occurs according to frequency hopping spread spectrum techniques.

39. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating, according to spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel; and c. wherein the carrier features time varying signal strength with differing robustness to interference, and said modulating according to spread spectrum techniques occurs according to said signal strength of the carrier.

40. A process according to claim 39 wherein said modulation according to said spread spectrum techniques occurs only when said carrier is within maximum signal strength ranges.

41. A process according to claim 39 wherein said communications channel is a television channel.

42. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating, according to spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel, c. wherein said carrier features time varying signal strength with differing robustness to interference in different parts of its frequency spectrum, and said modulating according to spread spectrum techniques occurs in a part of the channel where robustness to interference is greatest.

43. A process according to claim 42 wherein said modulating according to spread spectrum techniques occurs in a part of the channel where robustness of the carrier to interference is greatest.

44. A process according to claim 42 further comprising modulating, according to spread spectrum techniques, a third signal onto a predetermined bandwidth within the communications channel, and said modulating of said second signal and said third signal occur in parts of the channel where robustness to interference is greatest.

45. A process for enabling communication of information at least partly via spread spectrum techniques in a cellular transmission system, comprising: a. modulating a first signal onto a carrier in a communications channel; and b. modulating, according to spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel, using different spread spectrum code words for at least two cells of a plurality of cells in the cellular transmission system.

46. A process according to claim 45 wherein a different code word is used for each cell.

47. A process according to claim 45 wherein different information is communicated from each cell.

48. A process according to claim 45 in which said communications channel is a television channel.

49. A process for enabling communication of information, comprising: a. modulating a first signal onto a carrier in a communications channel; b. modulating, according to spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel; and. c. modulating an abatement signal onto the carrier to compensate at least in part for effects of the second signal in the channel.

50. A process according to claim 49 in which the communications channel is a television channel.

51. A system for enabling communication of information, comprising: a. a source for providing a first signal; b. a source for providing a second signal; c. a source for providing a carrier; d. a first modulator adapted to modulate the first signal onto the carrier in a communications channel; e. a second modulator adapted to modulate, using spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel; f. wherein the first signal and the second signal comprise information programming.

52. A system according to claim 51 in which the communications channel is a television channel.

53. A system according to claim 51 in which the first and second signals are components of the same information programming.

54. A system according to claim 51 in which the first and second signals comprise different information programming.

55. A system according to claim 51 further comprising a source for generating an abatement signal to compensate for effects of the second signal in the channel, and a modulator for modulating the abatement signal onto the carrier.

56. A system according to claim 51 wherein said second modulator is adapted to modulate the second signal at power levels that vary, at predetermined times, according to robustness of the carrier.

57. A system according to claim 51 wherein said first modulator is adapted to modulate the carrier with time varying signal strength that features differing robustness to interference, and said second modulator is adapted to modulate the second signal according to the signal strength of the carrier.

58. A system according to claim 51 wherein said first modulator is adapted to modulate the carrier with time varying signal strength that features differing robustness to interference, and said second modulator is adapted to modulate said second signal in a part of the channel where robustness to interference is greatest.

59. A system for enabling communication of information in a cellular transmission system, comprising: a. a source for providing a first signal; b. a source for providing a second signal; c. a source for providing a carrier; d. a first modulator adapted to modulate the first signal onto the carrier in a communications channel; e. at least one second modulator adapted to modulate, using spread spectrum techniques, a second signal onto a predetermined bandwidth within the communications channel using different spread spectrum code words for at least two cells of a plurality of cells in the cellular transmission system; f. wherein the first signal and the second signal comprise information programming.