RECEIVERS, CIRCUITS, AND METHODS TO IMPROVE GNSS TIME-TO-FIX AND OTHER PERFORMANCES

• US 20110187596A1
• Filed: 03/18/2010
• Published: 08/04/2011
• Est. Priority Date: 02/03/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Rao, Sandeep, Tangudu, Jawaharlal, Ramasubramanian, Karthik
• Granted Patent: US 8,441,398 B2
• Time in Patent Office: Days
• US Class Current: 342/357.66
• 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 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• CPC Class Codes: G01S 19/27 creating, predicting or correcting ephemeris or almanac data within the receiver
• CPC Class Codes: G06F 11/10 Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's

Abstract

An electronic circuit (2250) for a satellite receiver (100, 2200). The electronic circuit (2250) includes a correlator circuit (2310) operable to supply a data signal including ephemeris data and a subsequent satellite time datum, and a data processor (2370, 2380) operable to infer satellite time T_S from as few as one of the ephemeris data prior to the satellite time datum. Other circuits, devices, receivers, systems, processes of operation and processes of manufacture are also disclosed.

Claims

1. An electronic circuit for a satellite receiver, the electronic circuit comprising:

a correlator circuit operable to supply a data signal including ephemeris data and a subsequent satellite time datum; and

a data processor operable to infer satellite time from as few as one of the ephemeris data prior to the satellite time datum.

2. The electronic circuit claimed in claim 1 further comprising a circuit operable to provide representations of predicted ephemeris parameters that approximate the ephemeris data in the data signal and the data processor operable to use the representations of the predicted ephemeris parameters to infer satellite time from as few as one ephemeris datum prior to the satellite time datum.

3. The electronic circuit claimed in claim 2 wherein the ephemeris data of the data signal include a received ephemeris datum and said data processor is operable to extract the received ephemeris datum and identify the predicted ephemeris parameter that is closest to it in value, and to use the identified predicted ephemeris parameter to derive the satellite time.

4. The electronic circuit claimed in claim 2 wherein said correlator circuit is operable to supply plural data signals from plural received satellite signals wherein the ephemeris data include a received ephemeris datum from each received satellite signal, and said data processor is operable to perform a matching process comparing each said received ephemeris datum with a set of predicted ephemeris parameters pertaining to ephemeris for the corresponding received satellite signal, and to identify the satellite time as that satellite time common to a most-nearly-matching group of predicted ephemeris parameters pertaining to the same satellite time, one such predicted parameter from each set.

5. The electronic circuit claimed in claim 1 further comprising a local time circuit and wherein the satellite time corresponding to an ephemeris datum is determined by an inference process based on a locally-estimated satellite time.

6. The electronic circuit claimed in claim 1 wherein the ephemeris data include a coarse ephemeris value in an almanac word.

7. The electronic circuit claimed in claim 1 wherein the ephemeris data are received in words and said data processor is operable to do word alignment and then extract a received ephemeris datum from a received word.

8. A process of operating an electronic circuit for satellite signals having ephemeris data and a subsequent satellite time datum, the process comprising inferring satellite time from as few as one of the ephemeris data prior to the satellite time datum.

9. The process claimed in claim 8 further comprising providing representations of predicted ephemeris parameters that approximate the ephemeris data and selecting and using at least one of the representations that is similar to a received ephemeris datum to infer satellite time prior to the satellite time datum.

10. The process claimed in claim 8 wherein the ephemeris data include a received ephemeris datum from each of plural satellite signals, and the process further comprising comparing each such received ephemeris datum with a set of predicted ephemeris parameters pertaining to ephemeris for the corresponding satellite signal, and identifying the satellite time as that satellite time common to a most-nearly-matching group of predicted ephemeris parameters in words having the same satellite time, one such predicted parameter from each set.

11. The process claimed in claim 10 further comprising electronically identifying each of corresponding words having the same satellite time from the plural satellite signals as that word from each such satellite signal that has a time of arrival closest to a received word from one of the satellite signals.

12. A process for operating an electronic circuit for at least one received satellite signal carrying successive satellite transmission parameters according to a predetermined succession, the process comprising:

storing predicted parameters and information defining their positions in the predetermined succession;

extracting a received satellite transmission parameter from at least one received satellite signal;

searching for and identifying the stored predicted parameter that is closest to matching the received satellite transmission parameter; and

using that closest predicted parameter and the information defining its position in the predetermined succession to derive satellite time.

13. The process claimed in claim 12 wherein the extracting and searching are coordinated so that the received satellite signal is extracted according to a series of formats each used as if the received transmission parameter has the same position in the predetermined succession as the stored predicted parameter being searched.

14. The process claimed in claim 12 further comprising generating a coarse time and a time uncertainty estimate and using them to narrow a number of stored predicted satellite transmission parameters subject to the searching.

15. The process claimed in claim 14 wherein the generating includes executing a solve-for-time process on signals from multiple satellites.

16. The process claimed in claim 12 wherein the successive satellite transmission parameters are transmitted in words, and further comprising performing word alignment prior to the extraction.

17. The process claimed in claim 16 further comprising applying a threshold of closeness in the searching and identifying, and if no match is detected then trying another word alignment.

18. The process claimed in claim 16 further comprising applying a threshold of closeness, and if no match is detected then repeating the process on a succeeding word from the received satellite signal.

19. An electronic circuit for a satellite receiver, the electronic circuit comprising:

a correlator circuit operable to acquire one or more satellite signals supplying parameters;

a processor coupled to said correlator circuit;

a memory coupled to said processor and having parameter estimation software and parameter matching software accessible by said processor to determine which estimated parameter matches a received parameter.

20. The electronic circuit claimed in claim 19 wherein said memory includes further software for operating said processor to derive satellite time from pre-stored information reflecting a known sequential order of parameters including a position in that order of the estimated parameter that matches the received parameter.

21. The electronic circuit claimed in claim 19 wherein the determination of a match includes a count of most significant bits (MSBs) representing matching in a magnitude of a difference between an estimated parameter and a received parameter, whereby rollover is accounted for.

22. The electronic circuit claimed in claim 21 wherein the determination of a match further includes a non-linear function of the count of MSBs representing matching.

23. The electronic circuit claimed in claim 19 wherein the parameter matching software includes a similarity metric that is a monotonic function of a closeness function selected from the group consisting of 1) count of most significant bits that match accounting for rollover, 2) cumulative probability distribution, 3) conditional probability function.

24. A power management process for an electronic circuit for use with a satellite system sending ephemeris data and a subsequent satellite time datum, the process comprising:

supplying a data signal at first including a said ephemeris datum; and

operating a circuit to infer satellite time from the ephemeris datum and then perform a position fix and transition to a lower-power mode, whereby less overall energy is consumed.

25. The power management process claimed in claim 24 further comprising determining a value of time and a value of time uncertainty, and using those values to constrain a set of estimated parameters to compare with the ephemeris datum whereupon to infer the satellite time, whereby the constraining leads to less energy consumed.

26. A process for an electronic circuit to supply a more-accurate satellite time based on at least one satellite signal having frames and words in frames and each word having a word duration, the process comprising:

maintaining an approximate time;

computing a word position of a received word as a function of the approximate time when the received word is received; and

supplying the more-accurate satellite time as a second function of at least the word position value.

27. The process claimed in claim 26 wherein the electronic computing of the word position includes electronically forming a representation of a rounded-to-integer ratio of the approximate time divided by the word duration, and said supplying includes electronically forming a further representation of a multiplicative product of the word duration times said rounded ratio.

28. The process claimed in claim 27 further comprising providing an estimated time uncertainty pertaining to the approximate time and conditioning the electronically forming depending on whether that estimated time uncertainty is less than a predetermined fraction of the word duration, and otherwise performing an alternative electronic process to generate the more-accurate satellite time.

29. The process claimed in claim 26 wherein the electronic computing of the word position includes electronically computing an expected grand total word count as a first ratio of the approximate time of the reception divided by the word duration, the ratio rounded to an integer, and storing estimated parameters indexed as a function of grand total word count based on pre-established word positions of ephemeris parameters, and electronically performing similarity metric comparisons of a set of the estimated parameters with the received word and finding the index for the estimated parameter that maximizes the similarity metric, whereby that index corresponds to a true grand total word count as the word position;

and said supplying includes electronically providing the more-accurate satellite time based on the true grand total word count.

30. The process claimed in claim 26 wherein the electronic computing of the word position includes:

computing a word position k_F of a received word based on a highest similarity metric electronically evaluated between predicted words and the received word, thereby signifying that the k_F-th word in a frame is ascertained as the received word;

determining a frame number n_F by electronically adjusting the approximate time of word reception by the word position to a beginning of frame and rounding-to-integer a ratio of that adjusted time divided by a frame duration; and

supplying the more-accurate time based on electronically combining a first product of frame duration times frame number n_F, and a second product of a word duration times word position k_F.

31. A process for an electronic circuit to determine word alignment based on at least one satellite signal having a stream of words having data bits and parity bits in each word and satisfying pre-specified parity relations, the process comprising:

hypothesizing different word alignment possibilities;

parity-checking each of the word alignment possibilities until one of them satisfies parity; and

determining the word alignment as being the hypothesized alignment that satisfies parity.

32. The process claimed in claim 31 wherein said additional parity-checking includes electronically computing the parity check equations on corresponding bits from a second satellite signal.

33. The process claimed in claim 31 wherein the additional parity-checking includes electronically computing the parity check equations on corresponding bits from a second satellite signal and establishing which bits are corresponding bits from the second satellite signal by electronically computing an estimate of a time difference in time of travel from each of the satellites to the receiver, and providing an output identifying as associated bit edges a first bit edge from the first satellite signal that is received relative to a second bit edge from the second satellite signal nearest to having the estimated time difference.

34. A process for an electronic circuit to select for an estimated parameter set a correctly-applicable estimated almanac parameter predictive of an almanac parameter transmitted by one satellite but that can pertain to another satellite, wherein satellites send words in frames, the process comprising:

maintaining an approximate time and providing a time uncertainty of the approximate time;

providing a table of almanac parameters related to word positions in a frame, some of the almanac parameters pertaining to one satellite and other almanac parameters pertaining to another satellite;

establishing low and high range-end word positions whereby to specify a range of an estimated parameter set as a function of the approximate time and the time uncertainty;

electronically providing an actual satellite number S_A as a function of the approximate time and a word position of an almanac parameter in the range; and

accessing the table of almanac parameters and writing from the table the estimated almanac parameter, having that word position in the almanac table for the satellite S_A, as an applicable estimated almanac parameter into the estimated parameter set.

35. The process claimed in claim 34 wherein the electronic providing includes determining a frame number by electronically adjusting the approximate time from that word position to beginning of frame and rounding-to-integer a ratio of that adjusted time divided by a frame duration, and computing, as a function of the frame number, a satellite number of the particular actual satellite S_A to which that word position pertains.

36. A word-position error recovery process for a signal processing circuit wherein a signal carries words, the process comprising:

initially determining an unknown word-position of a received word; and

performing the word-position determining for at least one subsequent received word to determine a subsequent received word position, and if inconsistent word positions result then adopting the more-probable word position.

37. The process claimed in claim 36 wherein the initially determining of the unknown word-position includes comparing estimated parameters with the received word, and the process further comprises a test whether two of the estimated parameters are both about equally similar to the received word and in such case doing the comparing for the subsequent received word.

38. The process claimed in claim 36 further comprising determining the more-probable word position by determining the word position of the estimated parameter with the maximum similarity metric value by comparison with its corresponding word, and with the maximum thus taken across different words respectively predicted by their different estimated parameters.

39. A mobile satellite receiver device comprising:

an antenna;

a front end coupled to said antenna for receiving and converting satellite signals;

a correlator circuit coupled to said front end and operable to supply a data signal including ephemeris data and a subsequent satellite time datum;

a data processor operable to infer satellite time from as few as one of the ephemeris data prior to the satellite time datum and to compute a position fix based on the inferred satellite time;

a wireless modem coupled to said data processor; and

a user interface coupled to said data processor.