Methods, mobile stations and systems for acquiring global positioning system timing information

• US 6,295,023 B1
• Filed: 01/21/2000
• Issued: 09/25/2001
• Est. Priority Date: 01/21/2000
• Status: Expired due to Term

• Current Assignee: IDTP Holdings Incorporated (InterDigital, Inc.)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Bloebaum, Leland Scott
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/489,108
• Time in Patent Office: 613 Days
• Field of Search: 342/357.06, 342/357.12, 342/352, 701/213
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/254 relating to Doppler shift of satellite signals
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 2205/008 using a mobile telephone network

Abstract

Methods, systems and mobile stations are provided which determine GPS timing by collecting energy from transmitted signals from one and preferably more acquired satellites to determine a single timing value, which may increase sensitivity. In addition, the receiver devices may use the entire navigation message from each satellite to obtain timing information which may further improve sensitivity and possibly remove latency from having to wait for the time-of-week (TOW) field to be received in the GPS satellite transmission. This is preferably accomplished by maximizing a single delay metric created based on expected (known in advance from some source) and actual (received) navigation symbols from the acquired satellites. As a result, position fixes may possibly be obtained under disadvantaged conditions where the signal quality from the GPS satellites is poor. Furthermore, the timing information obtained pursuant to the present invention does not require a timing relationship between GPS and communication network time.

Claims

1. A method for acquiring GPS timing information at a mobile station including a GPS receiver comprising the steps executed at the mobile station of:

receiving assistance information from a communication network;

acquiring a plurality of GPS satellites using the received assistance information;

determining expected fields in navigation messages [information] associated with at least one of the plurality of acquired GPS satellites based on the received assistance information;

correlating actual information received from the at least one of the plurality of acquired GPS satellites with the associated determined expected fields in navigation messages for a plurality of delays to provide a quality indication for each of the plurality of delays; and

determining the GPS timing information based on the quality indications.

2. A method according to claim 1 further comprising the steps of:

adjusting a timing of the GPS receiver based on the determined GPS timing information; and

determining a position of the GPS receiver based on the timing of the GPS receiver.

3. A method according to claim 1 wherein the step of determining expected fields in navigation messages further comprises the step of determining expected fields in navigation messages for at least two of the plurality of GPS satellites and wherein the step of receiving assistance information from a communication network comprises the step of receiving the assistance information from a wireless communication network.

4. A method according to claim 3 wherein assistance information includes ephemeris information and wherein the step of determining expected fields in navigation messages further comprises the step of determining expected fields in navigation messages associated with each of the at least two of the plurality of GPS satellites based on the received ephemeris information.

5. A method according to claim 4 wherein the step of determining expected fields in navigation messages further comprises the step of determining expected fields in navigation messages associated with each of the at least two of the plurality of GPS satellites based on time-of-week information known to the mobile station.

6. A method for acquiring GPS timing information at a mobile station including a GPS receiver comprising the steps of:

receiving assistance information from a communication network;

acquiring a plurality of GPS satellites using the received assistance information;

determining expected information associated with at least one of the plurality of acquired GPS satellites;

correlating actual information received from the at least one of the plurality of acquired GPS satellites with the associated determined expected information for a plurality of delays to provide a quality indication for each of the plurality of delays;

determining the GPS timing information based on the quality indications; and

wherein the step of determining expected information associated with at least one of the plurality of acquired GPS satellites further comprises the step of determining expected fields in navigation messages associated with each of at least two of the plurality of GPS satellites based on calculated parity bit information.

7. A method for acquiring GPS timing information at a mobile station including a GPS receiver comprising the steps of:

receiving assistance information from a communication network;

acquiring a plurality of GPS satellites using the received assistance information;

determining expected fields in navigation messages associated with at least two of the plurality of acquired GPS satellites;

correlating actual information received from the at least two of the plurality of acquired GPS satellites with the associated determined expected fields in the navigation messages for a plurality of delays to provide a quality indication for each of the plurality of delays;

determining the GPS timing information based on the quality indications; and

wherein the step of correlating actual information further comprises the steps of;

receiving the navigation messages from the at least two of the plurality of GPS satellites;

demodulating the received navigation messages at the plurality of delays to provide delay received fields for each of the plurality of delays;

correlating the delay received fields with the expected fields to provide the quality indication for each of the plurality of delays; and

wherein the step of determining the GPS timing information comprises the step of selecting one of the plurality of delays as the GPS timing information based on the quality indications.

8. A method according to claim 7 wherein the assistance information includes an assistance time reference and wherein the step of demodulating is preceded by the step of determining the plurality of delays based on an expected maximum delay time for receipt of the assistance time reference at the mobile station.

9. A method according to claim 7 wherein the step of correlating the delay received fields includes the steps of:

establishing a buffer of expected current and upcoming symbols for each of the at least two of the plurality of GPS satellites from the corresponding expected fields;

initializing a correlation register for each of the at least two of the plurality of GPS satellites with an expected n most recent symbols for the respective GPS satellite, wherein the expected n most recent symbols are obtained from the corresponding buffer of expected current and upcoming symbols for the respective GPS satellite;

correlating coherent samples of the received navigation messages with the expected n most recent symbols for each of the at least two of the plurality of GPS satellites to provide a coherent correlation result for each of the plurality of delays;

shifting a next expected symbol into each of the correlation registers; and

repeating the steps of initializing, correlating coherent samples and shifting for a first accumulation period while accumulating the coherent correlation results for each of the plurality of delays to provide the quality indication for each of the plurality of delays.

10. A method according to claim 9 wherein the repeating step is followed by the steps of:

converting the coherent correlation results to power values associated with each of the plurality of delays;

resetting the accumulated coherent correlation results; and

repeating the steps of repeating the steps of initializing, correlating coherent samples and shifting for a first accumulation period, converting the coherent correlation results to power values and resetting the accumulated coherent correlation results for a second accumulation period while accumulating the power values associated with each of the plurality of delays to provide the quality indication for each of the plurality of delays.

11. A method according to claim 7 further comprising the steps of:

adjusting a timing reference of the GPS receiver based on the GPS timing information; and

determining a position of the mobile station based on the timing reference of the GPS receiver.

12. A method according to claim 7 wherein the step of acquiring a plurality of GPS satellites further comprises the steps of:

receiving transmissions from the plurality of GPS satellites;

synchronizing a timing of the GPS receiver with a boundary of a navigation message of a first acquired one of the plurality of GPS satellites based on the received transmissions to provide a first timing synchronization reference;

adjusting an expected timing for others of the plurality of GPS satellites based on the first timing synchronization reference; and

acquiring the others of the plurality of GPS satellites based on their respective expected timing.

13. A method according to claim 12 wherein the assistance information includes an assistance time reference and ephemeris information and wherein the step of synchronizing a timing of the GPS receiver is preceded by the steps of:

initializing the timing of the GPS receiver based on the assistance time reference;

determining GPS satellite acquisition parameters based on the ephemeris information and the assistance time reference; and

acquiring the first acquired one of the plurality of GPS satellites based on the GPS satellite acquisition parameters.

14. A mobile station comprising:

a first receiver that receives communication signals including assistance information for GPS satellite acquisition from a wireless communication network;

a GPS receiver that receives signals associated with fields in navigation messages from GPS satellites, the GPS receiver including a local reference timer;

a correlation circuit that generates a quality indication for each of a plurality of delays based on the received signals associated with fields in the navigation messages from GPS satellites and expected symbol values for the fields in the navigation messages; and

a timing adjustment circuit that adjusts the local reference timer responsive to the correlation circuit.

15. A mobile station comprising:

a first receiver that receives communication signals including assistance information for GPS satellite acquisition from a wireless communication network;

a GPS receiver that receives signals from GPS satellites, the GPS receiver including a local reference timer;

a correlation circuit that generates a quality indication for each of a plurality of delays based on the received signals from GPS satellites;

a timing adjustment circuit that adjusts the local reference timer responsive to the correlation circuit; and

wherein the correlation circuit further comprises;

a plurality of correlation bank circuits, each of the correlation bank circuits comprising;

a correlation shift register that receives expected symbol values; and

a plurality of accumulator circuits, each of the accumulator circuits being associated with one of the plurality of delays and outputting a delay quality indication, wherein each of the plurality of accumulator circuits receives as inputs the expected symbol values from the correlation shift register and the received signals from the GPS satellite; and

a combiner circuit coupled to each of the plurality of correlation bank circuits that outputs the quality indication for each of the plurality of delays based on the delay quality indications from the plurality of accumulator circuits of each of the plurality of correlation bank circuits.

16. The mobile station of claim 15 further comprising a plurality of expected symbol buffer arrays, each of the expected symbol buffer arrays being associated with one of the plurality of correlation bank circuits to provide the expected symbol values to the corresponding correlation shift register.

17. The mobile station of claim 16 further comprising a expected symbol buffer initialization circuit that generates expected symbol values for storage in the expected symbol buffer arrays based on the assistance information.

18. The mobile station of claim 17 wherein the GPS receiver further comprises a position calculation circuit that determines a position of the mobile station based on the received signals and the local reference timer.

19. The mobile station of claim 15 wherein each of the accumulator circuits further comprises:

a coherent accumulation circuit having an I accumulation circuit and a Q accumulation circuit, the coherent accumulation circuit having a reset input;

a power calculation circuit responsive to the coherent accumulation circuit that calculates a power; and

a second accumulation circuit responsive to the power calculation circuit that sums the calculated power, the second accumulation circuit having a reset input.

20. The mobile station of claim 19 wherein at least one of the I accumulation circuit and the Q accumulation circuit further comprise an adder and at least one of a multiplier and an exclusive-OR (XOR).

21. The mobile station of claim 19 further comprising a reset circuit that resets the coherent accumulation circuit after a first accumulation period and resets the second accumulation circuit after a second accumulation period, the first accumulation period and the second accumulation period being measured based on symbol count.

22. The mobile station of claim 21 wherein the combiner circuit further comprises a plurality of adders, each of the adders being associated with one of the plurality of delays.

23. A system for acquiring GPS timing information at a mobile station including a GPS receiver comprising the following positioned in the mobile station:

means for receiving assistance information from a communication network;

means for acquiring a plurality of GPS satellites using the received assistance information;

means for determining expected fields in navigation messages associated with at least one of the plurality of acquired GPS satellites based on the received assistance information;

means for correlating actual information received from the at least one of the plurality of acquired GPS satellites with the associated determined expected fields in navigation messages for a plurality of delays to provide a quality indication for each of the plurality of delays; and

means for determining the GPS timing information based on the quality indications.

24. A system according to claim 23 further comprising:

means for adjusting a timing of the GPS receiver based on the determined GPS timing information; and

means for determining a position of the GPS receiver based on the timing of the GPS receiver.

25. A system according to claim 23 wherein the means for determining expected fields in navigation messages further comprises means for determining expected fields in navigation messages for at least two of the plurality of GPS satellites and wherein the means for receiving assistance information from a communication network comprises means for receiving the assistance information from a wireless communication network.

26. A system according to claim 25 wherein assistance information includes ephemeris information and wherein the means for determining expected fields in navigation messages further comprises means for determining expected fields in navigation messages associated with each of the at least two of the plurality of GPS satellites based on the received ephemeris information.

27. A system according to claim 26 wherein the means for determining expected fields in navigation messages further comprises means for determining expected fields in navigation messages associated with each of the at least two of the plurality of GPS satellites based on time-of-week information known to the mobile station.

28. A system for acquiring GPS timing information at a mobile station including a GPS receiver comprising:

means for receiving assistance information from a communication network;

means for acquiring a plurality of GPS satellites using the received assistance information;

means for determining expected information associated with at least one of the plurality of acquired GPS satellites;

means for correlating actual information received from the at least one of the plurality of acquired GPS satellites with the associated determined expected information for a plurality of delays to provide a quality indication for each of the plurality of delays;

means for determining the GPS timing information based on the quality indications; and

wherein the means for determining expected information associated with at least one of the plurality of GPS satellites further comprises means for determining expected fields in navigation messages associated with each of the at least two of the plurality of GPS satellites based on calculated parity bit information.

29. A system for acquiring GPS timing information at a mobile station including a GPS receiver comprising:

means for receiving assistance information from a communication network;

means for acquiring a plurality of GPS satellites using the received assistance information;

means for determining expected fields in navigation messages associated with at least two of the plurality of acquired GPS satellites;

means for correlating actual information received from the at least two of the plurality of acquired GPS satellites with the associated determined expected information for a plurality of delays to provide a quality indication for each of the plurality of delays;

means for determining the GPS timing information based on the quality indications; and

wherein the means for correlating actual information further comprises;

means for receiving the navigation messages from the at least two of the plurality of GPS satellites;

means for demodulating the received navigation messages at the plurality of delays to provide delay received fields for each of the plurality of delays;

means for correlating the delay received fields with the expected fields to provide the quality indication for each of the plurality of delays; and

wherein the means for determining the GPS timing information comprises means for selecting one of the plurality of delays as the GPS timing information based on the quality indications.

30. A system according to claim 29 wherein the assistance information includes an assistance time reference and further comprising means for determining the plurality of delays based on an expected maximum delay time for receipt of the assistance time reference, at the mobile station.

31. A system according to claim 29 wherein the means for correlating the delay received fields further comprises:

means for establishing a buffer of expected current and upcoming symbols for each of the at least two of the plurality of GPS satellites from the corresponding expected fields;

means for initializing a correlation register for each of the at least two of the plurality of GPS satellites with an expected n most recent symbols for the respective GPS satellite, wherein the expected n most recent symbols are obtained from the corresponding buffer of expected current and upcoming symbols for the respective GPS satellite;

means for correlating coherent samples of the received navigation messages with the expected n most recent symbols for each of the at least two of the plurality of GPS satellites to provide a coherent correlation result for each of the plurality of delays;

means for shifting a next expected symbol into each of the correlation registers; and

means for accumulating the coherent correlation results for each of the plurality of delays over a first accumulation period to provide the quality indication for each of the plurality of delays.

32. A system according to claim 31 further comprising:

means for converting the coherent correlation results to power values associated with each of the plurality of delays;

means for resetting the accumulated coherent correlation results; and

means for accumulating the power values associated with each of the plurality of delays over a second accumulation period to provide the quality indication for each of the plurality of delays.

33. A system according to claim 29 further comprising:

means for adjusting a timing reference of the GPS receiver based on the GPS timing information; and

means for determining a position of the mobile station based on the timing reference of the GPS receiver.

34. A system according to claim 29 wherein the means for acquiring a plurality of GPS satellites further comprises:

means for receiving transmissions from the plurality of GPS satellites;

means for synchronizing a timing of the GPS receiver with a boundary of a navigation message of a first acquired one of the plurality of GPS satellites based on the received transmissions to provide a first timing synchronization reference;

means for adjusting an expected timing for others of the plurality of GPS satellites based on the first timing synchronization reference; and

means for acquiring the others of the plurality of GPS satellites based on their respective expected timing.

35. A system according to claim 34 wherein the assistance information includes an assistance time reference and ephemeris information and further comprising:

means for initializing the timing of the GPS receiver based on the assistance time reference;

means for determining GPS satellite acquisition parameters based on the ephemeris information and the assistance time reference; and

means for acquiring the first acquired one of the plurality of GPS satellites based on the GPS satellite acquisition parameters.