Method for locating and tracking communication units in a synchronous wireless communication system

• US 20040109475A1
• Filed: 12/04/2002
• Published: 06/10/2004
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Elam, Daryl B.
• Granted Patent: US 7,289,541 B2
• Time in Patent Office: Days
• US Class Current: 370/508
• CPC Class Codes: G01S 11/08 using synchronised clocks
• CPC Class Codes: G01S 19/18 Military applications
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04W 56/0065 using measurement of signal travel time

Abstract

A method for locating and tracking communication units in a synchronous wireless communication system allows for system synchronization and communication unit location when usable GPS signals are not available or are being jammed. Communication units communicate within frames that are synchronized with a timing-reference signal. The timing-reference signal may be generated from GPS signals when available or generated from TOA and trajectory extrapolations when the GPS signals are not available. A disciplined oscillator may be used to maintain substantial synchronization over a few seconds of a frame. In one embodiment, propagation delays of received signals within the frame are determined and provided to other communication units allowing one or more communication units to calculate locations of the communication units. The location information may be reported to the other communication units for use in the self-synchronization.

Claims

1. A method for maintaining substantial synchronization among a plurality of communication units that communicate therebetween using synchronous wireless communications, wherein the communication units are substantially synchronized with other units by an internally generated synchronization signal, the synchronization signal indicating a beginning of a communication frame, the method comprising:

receiving communications from other communication units within the frame, each communication unit transmitting during a preassigned time-slot of the frame;

determining propagation delays from the received communications for at least some of the other communication units;

calculating a location of at least one of the communication units from the propagation delays; and

generating a timing-reference signal for frame synchronization from the location.

2. The method of claim 1 wherein the timing-reference signal is derived from GPS signals received by the communication units when the GPS signals are available, the timing-reference signal being substantially synchronized for each of the communication units.

3. The method of claim 1 wherein the timing-reference signal is based on a previously determined location for at least one of the communication units and trajectory extrapolations for the communication units, the timing-reference signal being substantially synchronized for each of the communication units to indicate the beginning of the communication frame.

4. The method of claim 3 wherein the method includes the communication units generating the self-synchronization signal when GPS signals are not available.

5. The method of claim 1 wherein the determined propagation delays are based on a time-delay between the beginning of the frame and receipt of the communication from at least some of the other communication units.

6. The method of claim 1 further comprising receiving propagation delays at a current communication units from at least some of the other communication units and calculating locations of at least some of the communication units using the received propagation delays, wherein calculating includes calculating a location for the current communication unit.

7. The method of claim 1 further comprising reporting the propagation delays to at least some of the other communication units.

8. The method of claim 6 further comprising sending the calculated locations to at least one of the other communication units.

9. The method as claimed in claim 1 further comprising correcting a timing reference for the communication units for zero propagation time from a system-wide local coordinate system origin.

10. A synchronous wireless communication system comprising a plurality of communication units synchronized with an internally generated timing-reference signal wherein the communication units receive communications from other communication units within preassigned time-slots of a synchronized communication frame, determine propagation delays for the other communication units, exchange location information with at least some of the other communication units, and generate the timing-reference signal for frame synchronization based on the location information.

11. The system of claim 10 wherein the location information includes propagation delays, and wherein the communication units include guided projectiles and/or missiles, and wherein target information for at least one of the communication units is updated by a controlling communication unit based on the location information for the one communication unit.

12. The system of claim 11 wherein the communication units correct a timing reference for zero propagation time from a system-wide local coordinate system origin.

13. A communication unit to operate as part of a synchronous wireless communication system, the communication unit comprising:

a data receiver/transmitter to communicate data packets with other communication units within preassigned time-slots of a synchronized communication frame;

a time of arrival (TOA) determinator to determine propagation delays associated with communications received from the other communication units within time-slots assigned to the other communication units; and

a self-synchronization signal generator to generate a timing-reference signal for frame synchronization with the other communication units,

wherein propagation delays of received communications are exchanged with the other communication unit and the timing-reference signal is generated based on the propagation delays received from the other communication units.

14. The communication unit of claim 13 further comprising a synchronization element that includes a disciplined oscillator responsive to the timing-reference signal to generate a clock signal during the duration of the synchronized communication frame.

15. The communication unit of claim 14 further comprising a GPS receiver to generate the timing-reference signal when GPS signals are received by the communication unit, and wherein the self-synchronization signal generator refrains from generating the timing-reference signal when usable GPS signals are received.

16. The communication unit of claim 13 wherein the communication unit is two-way portable radio.

17. The communication unit of claim 13 wherein the communication unit is located on a guided projectile, missile or aircraft, and the other communication units include a ground station, other guided projectiles, missiles or aircraft.

18. An article comprising a storage medium having stored thereon instructions, that when executed by a computing platform, result in:

maintaining substantial synchronization among a plurality of communication units that communicate therebetween using synchronous wireless communications, wherein the communication units are substantially synchronized with other units by an internally generated synchronization signal, the synchronization signal indicating a beginning of a communication frame;

receiving communications from other communication units within the frame, each communication unit transmitting during a preassigned time-slot of the frame;

determining propagation delays from the received communications for at least some of the other communication units;

calculating a location of at least one of the communication units from the propagation delays; and

generating a timing-reference signal for frame synchronization from the location.