Data message bit synchronization and local time correction methods and architectures

• US 20030147457A1
• Filed: 02/11/2003
• Published: 08/07/2003
• Est. Priority Date: 08/16/2001
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: SiRF Technology Holdings Incorporated (Qualcomm, Inc.)
• Inventors: Strother, Troy L., King, Thomas Michael, Geier, George Jeffrey
• Granted Patent: US 6,934,322 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• 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 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/70751 using partial detection H04B1/70758 takes precedence
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 2001/70706 using a code tracking loop, e.g. a delay locked loop

Abstract

Methods and architectures for data message bit synchronization of a spread spectrum signal having a repeating sequence of pseudorandom code bits modulated with data message bits having a data bit time that is an integer number of a repeat time of the pseudorandom code bits. In one embodiment, an adjusted bit sync offset time is determined for each of a plurality of signals for which bit sync offset time is not known based on a corresponding clock error corrected propagation time for each signal, based on a known bit synch offset time and based on a clock error corrected propagation time of the signal for which bit synch offset time is known.

Claims

1. A method in a satellite positioning system receiver, comprising:

receiving a spread spectrum signal;

performing a plurality of coherent correlations between the spread spectrum signal and a replica signal for a time interval corresponding to a data bit time of message bits modulated on the spread spectrum signal;

the plurality of coherent correlations corresponding in number to an integer number of a repeat time of the pseudorandom code bits;

offsetting each of the coherent correlations relative to a previous correlation by the repeat time of pseudorandom code bits of the spread spectrum signal;

generating a plurality of non-coherent sums of magnitudes for each of the plurality of coherent correlations over an interval of at least two data bit times,

the plurality of non-coherent sums of magnitudes corresponding in number to the integer number of the repeat time of the pseudorandom code bits.

2. The method of claim 1, performing the plurality of coherent correlations virtually in parallel by sequentially performing the plurality of coherent correlations at a rate greater than a rate at which pseudorandom code bits of the spread spectrum signal are received.

3. The method of claim 1, confirming bit synchronization by verifying that an integration start time difference between non-coherent sums having minimum and maximum magnitudes is approximately one-half the data bit time, determining a bit synchronization offset time of the message bits as corresponding to an offset time of the non-coherent sum having the maximum magnitude.

4. The method of claim 3, determining an arrival time of a data bit edge of the message bits based on the bit synchronization offset time, determining a local time correction dependent on the arrival time of the data bit edge and a local time of a real-time clock.

5. A method in a satellite positioning system receiver, comprising:

receiving a spread spectrum signal;

performing a plurality of coherent correlations, over a range of code phase uncertainty, between the spread spectrum signal and a replica signal for a time interval corresponding to a data bit time of message bits modulated on the spread spectrum signal,

the plurality of coherent correlations corresponding in number to a integer number of a repeat time of a sequence of pseudorandom code bits of the spread spectrum signal;

offsetting each of the plurality of coherent correlations relative to a previous coherent correlation by the repeat time of the pseudorandom code bits;

generating a plurality of non-coherent sums of magnitudes for each of the plurality of coherent correlations over at least two data bit times,

the plurality of non-coherent sums of magnitudes corresponding in number to the integer number of the repeat time of the pseudorandom code bits.

6. The method of claim 5, performing the plurality of coherent correlations virtually in parallel by sequentially performing the plurality of coherent correlations at a rate greater than a rate at which pseudorandom code bits of the spread spectrum signal are received.

7. The method of claim 5,

determining a code phase delay of the range of code phase uncertainty for which a non-coherent sum has a maximum magnitude,

confirming bit synchronization by verifying that an integration start time difference between a non-coherent sum having minimum and maximum magnitudes for the determined code phase delay is approximately one-half the data bit time,

determining a bit synchronization offset time of the message bit as corresponding to an offset time of the non-coherent sum having the maximum magnitude for the determined code phase delay.

8. A method in a satellite positioning system receiver, comprising:

receiving a spread spectrum signal;

performing a plurality of sequential partial coherent correlations on each of a plurality of sequential signal segments of the spread spectrum signal with a corresponding sequential segment of a replica signal, the plurality of sequential partial coherent correlations corresponding in number to an integer number of a repeat time of pseudorandom code bits of the spread spectrum signal;

summing sequential results of the plurality of sequential partial coherent correlations performed on the plurality of sequential signal segments for a time corresponding to a data bit time of message bits modulated on the spread spectrum signal;

offsetting each of the plurality of summed sequential results relative to another by a distinct multiple of the repeat time of the pseudorandom code bits;

generating a plurality of non-coherent sums of magnitudes for each of the plurality of coherent correlations over at least two data bit times,

the plurality of non-coherent sums of magnitudes corresponding in number to the integer number of the repeat time of the pseudorandom code bits.

9. The method of claim 8, performing the plurality of sequential partial coherent correlations virtually in parallel by sequentially performing the plurality of sequential partial coherent correlations at a rate greater than a rate at which pseudorandom code bits of the spread spectrum signal are received.

10. The method of claim 8,

determining a code phase delay of the range of code phase uncertainty for which a non-coherent sum has a maximum magnitude,

verifying that a difference between a non-coherent sum having minimum and maximum magnitudes for the determined code phase delay is approximately one-half the data bit time,

determining a bit synchronization offset time of the data bit message as corresponding to an offset time of the non-coherent sum having the maximum magnitude for the determined code phase delay.

11. The method of claim 8,

storing results of the sequential partial coherent correlations in a corresponding plurality of memory locations corresponding in number to the integer number of the repeat time;

storing the summed sequential partial correlation results in the plurality of memory locations.

12. A method in a satellite positioning system (SPS) receiver, comprising:

determining a propagation time between the SPS receiver and sources of each of a plurality of signals;

determining a clock error corrected propagation time from an approximate position of the SPS receiver to the source of each of the plurality of signals based on the corresponding propagation times and known corresponding signal source clock correction parameters;

determining an adjusted bit sync offset time for each of the plurality of signals for which bit sync offset time is not known based on the corresponding clock error corrected propagation time for each signal, based on a known bit synch offset time, and based on clock error corrected propagation time of the signal for which bit synch offset time is known.

13. The method of claim 12, the signals are satellite based spread spectrum signals, determining signal source location by derivation thereof from ephemeris data and satellite time.

14. The method of claim 12, the signals are satellite based spread spectrum signals, determining signal source location by derivation thereof from almanac data and satellite time.

15. The method of clam 12, determining the clock error corrected propagation time, PTC[I], for each signal by computing PTC[I]=PT[I]+C[I], where PT(I) is the corresponding propagation time and C(I) is a corresponding signal source clock correction based on the signal source clock correction parameters.

16. The method of claim 15, determine a range, R[I], between the approximate position of the receiver and each of plurality of signal sources, determining the propagation time, PT[I], from the approximate position of the receiver to each of the signal sources by dividing the corresponding range, R[I] by the speed of light.

17. The method of claim 15, determining the adjusted bit sync offset time, BSOT[I], to each of the plurality of signal sources for which bit sync offset time is not known by calculating BSOT[I]=BSOT[K]+(PTC[I]−

PTC[K]), where BSOT[K] is the known bit synch offset time and PTC[K] is the a clock error corrected propagation time for the signal for which bit synch offset time is known.

18. The method of claim 17, coherently integrating each of the plurality of signals for 20 milliseconds, offsetting a start time of each coherent integration in relation to the corresponding bit synch offset time, BSOT[I].