Burst communications method and apparatus

• US 20020094781A1
• Filed: 01/04/2002
• Published: 07/18/2002
• Est. Priority Date: 12/16/1999
• Status: Active Grant

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: Eric Jay Clelland, Kenneth Solomon Wreschner
• Inventors: Wreschner, Kenneth Solomon, Clelland, Eric Jay
• Granted Patent: US 6,665,519 B2
• Time in Patent Office: Days
• US Class Current: 455/67.13
• CPC Class Codes: H04B 7/2125 Synchronisation

Abstract

A transmitter (400) offsets the transmission time and frequency of a burst transmission such that uncertainties in reception time and reception frequency are reduced. The transmitter includes an ephemeris store (454) that includes ephemeris data for one or more possible intended receivers (130). Orbits of possible intended receivers are propagated, and an intended receiver is selected. Transmission time offsets are generated as a function of transmitter location and intended receiver location. Transmission frequency offsets are substantially equal to a Doppler frequency derived from the transmitter velocity and the intended receiver velocity. Guard times and guard bands are reduced in size, resulting in greater available communications bandwidth and simpler receiver designs.

Claims

1. In a transmitter, a method of reducing received signal uncertainties at an intended receiver, the method comprising:

determining a distance from the transmitter to the intended receiver;

determining a signal transit time from the distance;

determining a transmit offset time from the signal transit time; and

offsetting a transmission time by the transmit offset time to produce an offset transmission time.

2. The method of claim 1 further comprising transmitting a burst transmission at the offset transmission time.

3. The method of claim 1 wherein the intended receiver is a satellite, and determining a distance to the intended receiver comprises:

propagating ephemeris data of the intended receiver to determine a spatial location of the intended receiver at the transmission time;

determining a spatial location of the transmitter; and

determining the distance as a difference between the spatial location of the transmitter and the spatial location of the intended receiver.

4. The method of claim 3 wherein the intended receiver is one of a plurality of satellites, the method further comprising prior to determining the distance, selecting the intended receiver from the plurality of satellites.

5. The method of claim 1 further comprising:

determining a relative velocity between the transmitter and the intended receiver;

determining a frequency offset from the relative velocity; and

offsetting a transmission frequency by the frequency offset.

6. The method of claim 1 further comprising:

determining a relative velocity between the transmitter and the intended receiver;

determining a modulation rate offset from the relative velocity; and

offsetting a modulation rate by the modulation rate offset.

7. The method of claim 1 wherein a signal path exists between the transmitter and the intended receiver, the method further comprising:

further offsetting the transmission time as a function of total electron content (TEC) in the signal path.

8. In a transmitter, a method of reducing arrival time uncertainties and arrival frequency uncertainties of a burst transmission at an intended receiver comprising:

determining a time offset from a relative position;

offsetting a timing generator by the time offset, such that the burst transmission is offset in time by the time offset;

determining a Doppler frequency from a relative velocity; and

offsetting a synthesizer frequency by the Doppler frequency such that the burst transmission is offset in frequency by the Doppler frequency.

9. The method of claim 8 wherein:

the burst transmission is scheduled for a future time;

determining the time offset includes storing the time offset for use at the future time; and

determining the Doppler frequency includes storing the Doppler frequency for use at the future time.

10. The method of claim 8 wherein the intended receiver is one of a plurality of satellites, and the method further comprises selecting the intended receiver from the plurality of satellites.

11. The method of claim 8 further comprising:

determining a modulation rate offset from the relative velocity; and

configuring a timing generator to offset a modulation rate by the modulation rate offset.

14. The transmitter of claim 13 wherein the processor is further configured to compute an intended receiver velocity at the future transmission time, the transmitter further including a synthesizer responsive to the processor, wherein the synthesizer is configured to alter a transmission frequency as a function of the intended receiver velocity at the future transmission time.

15. The transmitter of claim 14 wherein the timing generator is further configured to alter a modulation rate as a function of the intended receiver velocity at the future transmission time.

16. The transmitter of claim 14 further comprising an autonomous location unit, wherein the processor, responsive to the autonomous location unit, is configured to compute a transmitter location and a transmitter velocity.

17. The transmitter of claim 16 wherein the autonomous location unit is a global positioning system (GPS) receiver.

18. The transmitter of claim 17 wherein the GPS receiver provides propagation information relating to an intended propagation path, and the processor is configured to further alter the future transmission time as a function of the propagation information.

19. The transmitter of claim 18 wherein the propagation information includes total electron content (TEC).

20. The transmitter of claim 18 further comprising an ephemeris store, the ephemeris store being configured to hold ephemeris data for multiple intended receivers.

21. The transmitter of claim 20 wherein the processor is configured to periodically propagate the ephemeris data to intended transmission times.

12. In a system including multiple burst transmitters and at least one receiver moving relative to the multiple burst transmitters, a method of controlling received signal characteristics comprising:

providing each of the multiple burst transmitters with ephemeris data for the at least one receiver, the multiple burst transmitters being configured to propagate the ephemeris data and compute time offsets and frequency offsets;

restricting guard times between expected burst transmissions; and

restricting frequency guard bands between expected burst transmissions.

13. A transmitter comprising:

a processor responsive to ephemeris data corresponding to an intended receiver, the processor being configured to compute an intended receiver spatial location at a future transmission time; and

a timing generator responsive to the processor, wherein the timing generator is configured to alter the further transmission time as a function of the intended receiver spatial location.