WO1998037596A1

WO1998037596A1 - Two-way communication system utilizing small c-band antenna for downlink and l-band for uplink

Info

Publication number: WO1998037596A1
Application number: PCT/US1998/003441
Authority: WO
Inventors: Bruce B. Lusignan; George Hronopoulos; John Walter Johnson
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-02-21
Filing date: 1998-02-23
Publication date: 1998-08-27
Anticipated expiration: 1999-08-21
Also published as: AU6437798A; TW407405B

Abstract

A low data rate L-band transmitter and antenna is combined with a high data rate C-band receiver and antenna link to a C-band transmitter and an L-band receiver on a geosynchronous orbiting satellite. The receive antenna comprises a three parabolic dish design receiving vertical and horizontal polarizations from the satellite. The L-band transmit antenna is a wire Yagi antenna mounted between dishes.

Description

TWO-WAY COMMUNICATION SYSTEM UTILIZING SMALL C-BAND ANTENNA FOR DOWNLINK AND L-BAND FOR UPLINK

BACKGROUND OF THE INVENTION The present invention is related to U.S. Application Serial No. 08/259,980 entitled "Satellite Communications System, Receiving Antenna & Components for Use Therein" and U.S. Application Serial No. 08/542,493 "Very Small Aperture Terminal and Antenna for Use Therein," which are hereby incorporated by reference as if recited herein in their entirety, including the drawings of each. U.S. Application No. 08/259,980 discloses a unique C-Band TV receive only antenna that is able to receive signals from a satellite in geosynchronous orbit that is transmitting television signals at power levels within FCC limitations, in which the antenna surface area is equivalent to that of a three foot diameter parabolic dish, although the surface area is distributed in a different manner than a parabolic surface. The shape of the antenna aperture creates nulls in the antenna pattern that correspond places where signals from potentially interfering satellites at ± 2°, ± 4°, ± 6°, ..., relative to the satellite of interest, in synchronous orbit might impinge upon the antenna surface. The antenna is able to receive digital television broadcast, DVB, with anywhere from 3 to 10 TV channels per standard C-Band satellite transponder. The number of channels depends on the program content (i.e., the compression rate), tolerance to artifacts, and satellite power. The DVB data stream is also used to deliver other data to consumers, such as data on the world wide web sites, business documents, archives, video games, computer programs, etc.

U.S. Patent Application No. 08/542,493 discloses a low data rate return link (user to control hub station) for the above-mentioned antenna by developing a 6 Ghz feed using the same antenna areas but different combinations of amplitude and phase in the three main areas of the antenna. This VSAT system serves as a small C-Band VSAT terminal that is competitive with current VSAT's because it is smaller and can fit on a user's premises more easily and is not subject to rain fade like Ku-band small VSAT terminals. This technology provides a medium to high data rate link between a user and a central hub. However, some applications do not require a high data rate return link, and in such cases it is a waste to allocate such bandwidth for low data rate applications.

Some manufacturers of communications satellites are launching hybrid satellites combining C-band and Ku-band and now L-band in the same satellite. The new addition of L-band is included to serve the maritime band and newly allocated mobile satellite band. In these applications, the lower frequency allows use of omnidirectional antennas that do not need to be pointed precisely at the satellite for effective communications. Both voice and data are offered through these services. However, the capacity to deliver data is extremely limited through the L-band system.

The present invention is therefore directed to the problem of developing a low cost rapid implementation of a two-way data return link for C-band video service applications, without increasing the size of the overall antenna.

SUMMARY OF THE INVENTION

The present invention solves this problem by combining an L-band uplink with a C-band downlink in a communication system that employs the three dish design for the receive antenna and a small antenna disposed in the gaps of the three dish antenna for transmitting the L-band signals.

According to the present invention, an apparatus for providing two-way communication includes a receive antenna having an aperture that creates nulls in a main beam of the antenna corresponding to a configuration of satellites in synchronous orbit that are transmitting potentially interfering signals, which receive antenna receives a high data rate signal at a first frequency band, and a transmit antenna disposed between gaps in the aperture of the receive antenna, wherein the transmit antenna transmits a low-data rate signal at a second frequency band and does not substantially interfere with reception of the high data rate signal.

In this case, it is particularly advantageous if the transmit antenna uses the positioning of the receive antenna for its positioning due to the fact that the second frequency is lower than the first frequency.

According to an aspect of the present invention, it is also particularly advantageous if the transmit antenna has an antenna pattern with a main beam that is broader than a main beam of an antenna pattern of the receive antenna.

According to another aspect of the present invention, it is further particularly advantageous if the first frequency is a C-band frequency, and the second frequency is an L-band frequency. Other possibilities for the first frequency include Ku-band, or Ka-band.

According to the present invention, a method for providing a high data rate communication link to a user and a low data rate communication link from the user, includes the steps of transmitting a high data rate C-band signal from a geosynchronous orbiting satellite to a user, receiving the high data rate C-band signals at a user site using a small C-band antenna having nulls in its antenna pattern corresponding to potentially interfering signals from a configuration of satellites, and transmitting a low data rate L-band signal to the geosynchronous orbiting satellite using a small L-band antenna being pointed at the geosynchronous satellite as a consequence of pointing the small C-band antenna at the geosynchronous orbiting satellite. In this case, the low data rate L-band signal is relayed from the geosynchronous orbiting satellite to a central hub station on earth.

According to another aspect of the present invention, a device for transmitting video broadcast data to a user and receiving on-demand data from the user includes a central hub station for controlling operation of the device, a means for transmitting a single channel per carrier time division multiple access data signal to the central hub station using a first frequency, a means for receiving at a user site a direct video broadcast from the central hub station using a second frequency, wherein the first frequency includes an L-band frequency and the second frequency includes a C-band frequency, and a means for controlling a mix of data and video within the direct video broadcast at the central hub station based on an amount of incoming data relative to an amount of incoming video.

According to yet another aspect of the present invention, the means for transmitting includes a combined L-band C-band antenna having three equally sized parabolic dishes, a total surface of which is equivalent to that of a three foot diameter dish, and two Yagi antennas disposed between the parabolic dishes so that they do not block reception of signals by the parabolic dishes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 depicts a sketch of the Yagi L-band antennas mated with the C-band micro antenna for combined C-band reception and L-band transmission according to the present invention.

FIG 2 depicts a sketch of the Yagi L-band antennas located between antenna dish components of the C-band micro antenna according to the present invention. FIG 3 depicts a sketch of the hybrid C-band/L-band VSAT receiver/transmitter layout according to the present invention.

FIG 4 depicts a hub station layout used in the present invention.

DETAILED DESCRIPTION The present invention combines the L-band receiver on the satellite with the high bandwidth data delivery system of the C-band system disclosed in the above- mentioned patent applications. The end result is a two-way communication system that is small, versatile and inexpensive. Since the L-band transmitters are already licensed for use by the FCC in mobile applications, no further licensing efforts need be undertaken. Often, these efforts can take longer than the equipment development. The most expensive portion of a conventional L-band communications system is the transmission from the satellite to a small L-band receiver. This satellite-to- VSAT down link requires high satellite power is due to the size of the user's L-band receiver and its corresponding small omnidirectional antenna. On the uplink user-to- satellite the L-band signal reaches the satellite, which relays the L-band signal back to a central hub station on earth, which is significantly larger and requires much less satellite power, and hence is less expensive.

In contrast, the most expensive portion of a C-band communications system is the uplink from the user to the satellite and back to the earth station. This is due to the small size of the transmitting antennas and the resulting power to transmit up to the satellite on the user-to-satellite-to-hub link. Furthermore, the cost of the down link is paid for by the broadcaster, whereas the cost of the uplink is paid for by the individual user.

The present invention essentially removes the most inefficient portions of each of these two systems and combines the remaining portions to create a hybrid communication system that is extremely efficient to operate. The L-band uplink is cheaper to operate than the 4/6 Ghz C-band uplink, even though the parabolic dish is used in both transmit and receive operations.

Modulation Techniques In addition, the present invention provides a hybrid combination of modulation techniques to take advantage of the efficiencies provided in each. For the high data rate signal to the user through the C-band, the present invention uses a multichannel per carrier modulation technique, such as MPEG television standards that use QPSK modulation in the Direct Video Broadcast (DVB) standard. In the normal MPEG format, one or more data channels can be multiplexed with compressed television for sending data to a user. The present invention uses these data channel to transmit voice and/or on-demand data to the user. This voice and/or data is in TDM format within the MPEG data stream.

The L-band uplink uses a QPSK or equivalent energy efficient single channel modulation. It is adjusted to the data rate maximum desired by the service, for examples 10 kilobits per second (kb/s) if compressed voice was the most intense incoming data application. Stations are commanded in turn to use the incoming channel by a demand access protocol.

Applications

The L-band communication portion of this system is a relatively low data rate link. More specifically, this link transmits signals such as voice, or low data applications, but not video applications or higher.

The C-band communications portion of this system is a relatively high data rate link. This link transmits video signals, compressed television, or other broadband signals. Preferably, these signals are in MPEG format, which can be MPEG-2, MPEG-3 or MPEG-4. In the preferred embodiment these television signals are part of the one-way direct-to-home (DTH) television distribution to the service area. The two-way low data rate applications will normally occupy only a small portion of the DTH television service capacity. A low data rate channel at L-band up to the satellite and down to the L-band hub station receiver carries either voice or data from the users to the hub center. The normal digital data channel on one of the MPEG-II data streams in the DVB channel carries voice or data to the user from the hub center. Thus, a two-way voice or low data rate channel exists from the user to the Hub center. Obviously, once the data is in the Hub center, it can be routed to the appropriate location using known other communication links, such as the public telephone switched network, or the Internet.

A hybrid system exists due to the presence of the L-band uplink, which permits broader applications. For example, any application that requires a large downlink but only a relatively small uplink can be satisfied by the present invention, as well as applications for low data rate transmissions in each direction. One such example is direct broadcast interactive television, where the user receives a television broadcast and responds back with some data (e.g., order information or billing information).

The operational simplicity is optimal if the L-band and C-band equipment is located within the same hub station. The central hub station equipment receives incoming signals from L-band receivers and transmits data to the C-band input data ports to be transmitted to the satellite. The "land" side of the equipment will be connected to data banks in the hub, to fiber or microwave links to the city networks, or to other satellite links to foreign destinations. For data: The data stream coming down to the user with the DVB signals carries packets used to manage responses solicited from remote users. (A number of techniques are available). This data stream received from the C-band DVB data stream enables each user periodically to originate a data request. The data request is transmitted at the indicated time by the user's L-band transmitter on a frequency assignment designated by the data packet desired. The incoming packet is received back at the hub station and interpreted by the processor. For small data packets the message is returned through the DVB data stream with a packet addressed to the user. This is suitable for a pay per view order. The message can be used to acknowledge an order, trigger a security decoder for a scrambled channel, or direct the user equipment to a DVB channel carrying a near on demand movie as well. In another application the response may deliver a large data file to the user; the Encyclopedia Britannica, for example, a library of video games, all photos of Marilyn Monroe ever made, all new web pages of the last week, etc. (The data system can be designed to be 100% efficient and deliver files at the rate of $100/ hour for a 5 MB/sec rate, i.e., 30/ 5 Megabits.) A third application is voice. A compressed voice service requires a channel with a data rate of about 10 kb/s in each direction. The voice to the user on C-band is time division multiplexed on the DVB data channel. The voice from the user is single channel per carrier on the L-band. Each 5 MHZ DVB channel will carry about 500 channels of 10 kbit/sec cellular digital voice. The downlink cost is about 50 per hour or 0.001 /min. The incoming L-band link will cost more depending on the design used.

Antenna

For all three applications the hardware is the same at the user end. The direct receive antenna is the design disclosed in U.S. Patent Application No. 08/259,980 (which has been previously incorporated by reference) receiving vertical and horizontal polarizations from the satellite. The L-band transmit antenna is a wire Yagi antenna, a preferred realization of which is either one or two antennas mounted between the circles. Referring to FIG 1, the combined antenna 1 of the present invention is shown.

The combined antenna 1 includes the three parabolic dish antenna 2, 3, 4 disclosed in the previous patent is shown, along with two L-band antennas 5, 6. The C-Band antenna 2, 3, 4 is exactly as described in the prior patent, however, other variations are possible as described therein.

The L-band transmit antennas are located in the gaps between the central reflector 3 and the two side reflectors 2, 4. By placing these transmit antennas 5, 6 in these gaps, the transmit antennas 5, 6 do not interfere with the receive signal.

The L-band transmit antenna 5, 6 consists of two Yagi antennas. These antennas 5, 6 have gain in their main lobes, which when pointed at the satellite of interest provides over ten times the gain of an omnidirectional antenna. By placing the Yagi antennas 5, 6 in the locations shown and pointing them in the same direction as the C-band dish 2, 3, 4 is pointed, the uplink power can be significantly reduced relative to an omnidirectional antenna, which is normally used in L-band mobile applications.

FIG 1A shows an example of a single polarization version of the Yagi antenna 5 used in the present invention in both side view and front view. FIG 1 B shows an example of a multiple polarization version of the L:-band antenna used in the present invention in both front view and side view. Note that in the multiple polarization example, two wires 21, 22 perpendicular to the directional axis 23 are placed at 90° from each other to obtain both vertical and horizontal polarizations, whereas in the single polarization example only one wire 21 perpendicular to the directional axis 23 is used. The horizontal and vertical polarizations can also be connected by phase networks (not shown) to create right-hand and left-hand circular polarizations.

It is also possible that one of the existing C-band dishes 2, 3, 4 or two of them could be used to feed both L-band and C-band. However, the feed structure might be more complicated than the separate Yagi antennas 5, 6. The Yagi antenna 5, 6 is the same as the home television rooftop antenna, only smaller because the frequency is twice as high as the UHF band used in broadcast television.

Two antennas reduce the required power transmitted by half, hence given the symmetry of the design of FIG 1, two antennas are preferable. The crossed antenna option (shown in FIG IB) allows transmissions on vertical and horizontal or circular polarization, if the satellite uses circular polarization ro receive. The Yagi antennas 5, 6 are just thin wire on a metal tube. They can be made springy and as thin as necessary, still meeting survival requirements. If painted black they will be hardly noticed next to the C-band reflectors 2, 3, 4. The Yagis 5, 6 are located between the circles of the C-band antenna 2, 3, 4 so they will not interfere with the C-band antenna receive pattern. See FIG 2.

There are other possible ways to combine L-band and C-band components but this is by far the most efficient. The present invention provides a vast array of two-way services with virtually no change to the DTH TV unit. The present invention would even be able to be added as a retrofit to a receive only antenna since they share common electronics. The L-band only uses the antenna structure of the C- band to point it at the same satellite. It even bypasses the indoor electronics (IRD) used in the present invention.

User System Turning to FIG 3, the incoming C-band signal is received by the three parabolic dishes, and coupled to the backplate 9 and combiner components 11, which are located in an electronics package 9 mounted on the back of the antenna 1. The C-band signals are then sent to the receiver (not shown) in the Star Video IRD 12 located within the house. The IRD 12 is connected to the television (not shown) and/or the computer (not shown).

On the transmit side, data from the computer or television is input to the IRD box 12 by the user and is sent to the L-band transmitter 11, converted to an L-band transmission signal and passed up to the electronics package 9 behind the antenna. The L-band signals are then sent to the L-band transmitter amplifier 10, which amplifies the signals and couples them to the Yagi antennas 5, 6 for broadcast. The broadcast L-band signals are then transmitted to the satellite, since the C-band dishes are already pointed at the satellite within the tolerance of the L-band signals. The satellite receives the L-band signals and transmits them back down to the hub station 13 as shown in FIG 4. Earth Station

The L-band downlink is received by the combined C-band and L-band dish 14, passed to the demand multiplexer 18, and on to the two-way service module 20, which then passes the signals to the appropriate place via land links. On the transmit side, the video servers 19 output DVB television signals to the multiplexer 17, which creates a signal C-Band signal that is transmitted to the satellite by the combined C-band and L-band dish 13. Alternatively, separate C-band 15 and L-band 16 dishes can be used depending upon the space and cost requirements. The satellite then broadcasts the C-Band signals back to earth, which are received by the three parabolic dish antenna 2, 3, 4 of the present invention.

Data requests are sent through the video servers 19 or via land links. DVB data in passes directly to the multiplexer. Depending upon the amount of incoming data and the number of incoming video channels, the exact mix of channels dedicated to data and video is altered in the multiplexer to accommodate the data channels and vice versa. Data requests can be Internet packets, or other computer data, or simply billing and order information from the user about the direct broadcast video service. In sum, the present invention is a unique combination of L-band on demand single carrier per channel time division multiple access modulation on the incoming side or to the hub station with outgoing direct video broadcast data channels with time division multiplexing voice and on demand data delivery. This combination of two previously independent techniques results in a significant cost reduction for the services.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for providing two-way communication comprising: a) a receive antenna having an aperture that creates nulls in a main beam of the antenna corresponding to a configuration of satellites in synchronous orbit that are transmitting potentially interfering signals, said receive antenna for receiving a high data rate signal at a first frequency band; and b) a transmit antenna disposed between gaps in the aperture of the receive antenna, wherein the transmit antenna transmits a low-data rate signal at a second frequency band and does not substantially interfere with reception of the high data rate signal.

2. The apparatus according to claim 1, wherein the transmit antenna uses a positioning of the receive antenna for its positioning due to the fact that the second frequency is lower than the first frequency.

3. The apparatus according to claim 1, wherein the transmit antenna has an antenna pattern with a main beam that is broader than a main beam of an antenna pattern of the receive antenna.

4. The apparatus according to claim 1, wherein the first frequency comprises C-band.

5. The apparatus according to claim 1, wherein the first frequency comprises C-band and the second frequency comprises L-band.

6. The apparatus according to claim 1, wherein the first frequency comprises Ku-band.

7. The apparatus according to claim 1, wherein the first frequency comprises Ka-band.

-11-

SUBST1TUTE SHEET (RULE 26)

8. An apparatus for transmitting and receiving data to and from a geosynchronous satellite spaced from other satellites at a predetermined close spacing, comprising: a) a C-band receive antenna having an aperture creating nulls in a main beam of the antenna that match the predetermined close spacing of the other satellites; and b) a L-band transmit antenna located in a portion of the aperture of the C- band antenna used to create the nulls.

9. The apparatus according to claim 8, wherein the aperture comprises three parabolic dishes placed next to each other and the L-band transmit antenna is disposed in a space between the dishes.

10. The apparatus according to claim 9, further comprising a second L-band transmit antenna located in a space between the dishes.

11. The apparatus according to claim 8, further comprising a second L-band transmit antenna, wherein the aperture comprises three parabolic dishes placed next to each other and the first L-band transmit antenna is located in a space between two of the three parabolic dishes and the second L-band antenna is located between a second two of the three parabolic dishes.

12. The apparatus according to claim 8, further comprising an electronics package mounted behind the antenna, said electronics package including: a) a C-band receiving combiner outputting C-band signals; and b) an L-band transmit amplifier outputting an L-band transmission signal.

13. The apparatus according to claim 12, further comprising a decoder unit for coupling to a television or computer, said decoder unit receiving the C-band signals and outputting television signals or data to the television or computer, and receiving data from the television or computer and outputting data.

14. The apparatus according to claim 12, further comprising an L-band transmitter receiving the data and outputting L-band signals to the L-band transmit amplifier.

15. A method for providing a high data rate communication link to a user and a low data rate communication link from the user, comprising the steps of: a) transmitting high data rate C-band signal from a geosynchronous orbiting satellite to a user; b) receiving the high data rate C-band signals at a user site using a small C- band antenna having nulls in its antenna pattern corresponding to potentially interfering signals from a configuration of satellites; and c) transmitting a low data rate L-band signal to the geosynchronous orbiting satellite using a small L-band antenna being pointed at the geosynchronous satellite as a consequence of pointing the small C-band antenna at the geosynchronous orbiting satellite.

16. The method according to claim 15, further comprising the step of: d) relaying low data rate L-band signal from the geosynchronous orbiting satellite to a central hub station on earth.

17. The method according to claim 15, further comprising the step of: d) transmitting the L-Band signal from an antenna in a gap in the aperture of the C-band antenna.

18. The method according to claim 15, further comprising the steps of: d) transmitting the low data rate L-band signal back to earth to a large dish antenna; and e) transmitting the high data rate C-band signals to the geosynchronous orbiting satellite from earth using the same large dish antenna.

19. The method according to claim 15, further comprising the step of: d) transmitting a return channel to the user via a data channel within the C- band signal, wherein the C-band signal is in MPEG format.

20. A method for providing a high data rate communication link to a user and a low data rate communication link from the user, comprising the steps of: a) transmitting high data rate signal from a geosynchronous orbiting satellite to a user; b) receiving the high data rate signal at a user site using an antenna having nulls in its antenna pattern corresponding to potentially interfering signals from a configuration of satellites; c) transmitting a low data rate signal to the geosynchronous orbiting satellite using a small antenna being pointed at the geosynchronous satellite as a consequence of pointing the receiving antenna at the geosynchronous orbiting satellite; and d) relaying low data rate signal from the geosynchronous orbiting satellite to a central hub station on earth.

21. The method according to claim 20, wherein the high data rate signal is transmitted at C-band.

22. The method according to claim 20, wherein the high data rate signal is transmitted at Ku-band.

23. The method according to claim 20, wherein the high data rate signal is transmitted at Ka-band.

24. The method according to claim 20, further comprising the steps of: e) transmitting the low data rate signal at L-band using a single carrier per channel time division multiple access modulation; f) transmitting the high data rate signal at C-band using a direct video broadcast data channel with time division multiplexing.

25. The method according to claim 24, further comprising the step of: g) transmitting voice in the low data rate signal.

26. The method according to claim 24, further comprising the step of: g) transmitting data in the low data rate signal.

27. A device for transmitting video broadcast data to a user and receiving on- demand data from the user, comprising: a) a central hub station for controlling operation of the device; b) means for transmitting a single channel per carrier time division multiple access data signal to the central hub station using a first frequency; c) means for receiving at a user site a direct video broadcast from the central hub station using a second frequency, wherein the first frequency includes an L-band frequency and the second frequency includes a C-band frequency; and d) means for controlling a mix of data and video within the direct video broadcast at the central hub station based on an amount of incoming data relative to an amount of incoming video.

28. The device according to claim 27, wherein the means for transmitting includes a combined L-band C-band antenna having three equally sized parabolic dishes, a total surface of which is equivalent to that of a three foot diameter dish, and two Yagi antennas disposed between the parabolic dishes so that they do not block reception of signals by the parabolic dishes.

29. The device according to claim 28, wherein the Yagi antennas include two orthogonal sets of wires to receive two different polarizations.