Method of despreading a spread spectrum signal

• US 20010043644A1
• Filed: 05/15/2001
• Published: 11/22/2001
• Est. Priority Date: 05/16/2000
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Yule, Andrew T., Dooley, Saul R.
• Application Number:
  US09/855,595
• Publication Number:
  US 20010043644A1
• Time in Patent Office: Days
• US Class Current: 375/150
• 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 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A method of despreading a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message is disclosed. The method comprises the steps of providing data message information relating to the timing of an epoch of at least one data bit; and performing a correlation of the target signal and a replica signal containing corresponding PRN code sequences using the data message information to minimise degradation of the correlation caused by variations in the PRN code sequences in the target signal attributable to modulation by the data message.

The correlation may be timed so as to substantially avoid continuous correlation over an epoch of a data bit. Alternatively, the data message information may further comprise bit information wherein the correlation is modified as a function of the data message information. In particular, where data bit modulation of the PRN code sequences in the target signal is the same as or equivalent to exclusive-or modulation, the polarity of PRN code sequences in the replica signal may be selectively reversed.

Claims

1. A method of despreading a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message comprising the steps of:

providing data message information relating to the timing of an epoch of at least one data bit of the target signal; and

performing a correlation of the target signal and a replica signal containing corresponding PRN code sequences using the data message information to minimise degradation of the correlation caused by variations in the PRN code sequences in the target signal attributable to modulation by the data message.

2. A method according to

claim 1

wherein the correlation is timed so as to substantially avoid continuous correlation over an epoch of a data bit.

3. A method according to

claim 2

wherein the correlation is timed so as to occupy more than 80% but less than 100% of the data bit width.

4. A method according to

claim 2

or

claim 3

wherein a correlation output is provided as a function of the sum of correlation values returned for a series of individual, continuous correlations.

5. A method according to

claim 1

wherein the data message information further comprises data bit information relating to at least part of the data message;

and wherein the correlation is modified as a function of the data message information.

6. A method according to

claim 5

wherein a continuous correlation occurs over a time period in which an epoch of a data bit occurs separating data bits of differing polarity.

7. A method according to claims 5 or 6 wherein a continuous correlation occurs over a time period greater than the transmission period of a single data bit.

8. A method according to

claim 7

in which continuous correlation occurs over a time period 10 times greater than the transmission period of a single data bit.

9. A method according to

claim 8

in which continuous correlation occurs over a time period 50 times greater than the transmission period of a single data bit.

10. A method according to any of claims 5 to

claim 9

wherein data bit modulation of the PRN code sequences in the target signal is the same as or equivalent to exclusive-or modulation;

and wherein the polarity of PRN code sequences in the replica signal is selectively reversed as a function of the data message information.

11. A method according to any of the preceding claims wherein pseudorandom noise (PRN) code sequences of the target spread spectrum signal are modulated by a data message, at least part of which is cyclically repeated, and wherein at least some of the data bit information is predicted based on a previous data message.

12. A method according to

claim 11

wherein data bit information based on a previous data message is known to be substantially constant from one message to the next.

13. A method according to

claim 12

wherein upon the identification of data bit information having a likelihood of being incorrect, alternative correlations are performed based on other possible formulations of the data bit information.

14. A method according to

claim 13

wherein the viterbi algorithm is used in order to establish the most likely data bit sequence.

15. A method according to

claim 14

wherein upon the identification of data bit information having a likelihood of being incorrect, the correlation reverts from a continuous correlation over data epochs to summing the moduli of individual correlations timed between data epochs.

16. A method according to any of the preceding claims wherein the target signal is a GPS signal and is received by a mobile unit;

and wherein the data message information is provided from another GPS spread spectrum signal which has already been received and acquired at the mobile unit (hereafter “

the reference signal”

).

17. A method according to

claim 16

wherein the data message information relating to the timing of an epoch of at least one data bit of the target signal is derived from the timing of an epoch of at least one data bit of the reference signal.

18. A method according to

claim 17

wherein the data message information relating to the timing of an epoch of at least one data bit of the target signal is derived from the timing of an epoch of at least one data bit of the reference signal using GPS ephemeris data.

19. A method according to any of

claims 16

to

18

wherein the dwell time for each code check made whilst attempting to acquiring the target signal is greater than that previously used to acquire the reference signal.

20. A method according to any of

claims 16

to

19

wherein the data message information further comprises data bit information relating to at least part of the data message of the target signal which is derived from corresponding data bit information of the reference signal.

21. A method according to any of

claims 1

to

15

wherein the target signal is received by a mobile unit, and the data message information is provided at a base station.

22. A method according to

claim 21

wherein the base station comprises a transmitter and the mobile unit comprises a receiver adapted for communication with the base station whereby the data message information is transmitted from the base station to the mobile unit;

and wherein the correlation is performed within the mobile unit.

23. A method according to

claim 22

wherein predicted data bit information is transmitted to the mobile unit in advance of the mobile unit receiving the corresponding portion of the data message in the target signal.

24. A method according to

claim 22

or

claim 23

wherein the base station and the mobile unit each comprise a transmitter and a receiver adapted for two-way communication with each other;

wherein the target signal is a GPS signal; and

wherein position information relating to the position of the mobile unit is transmitted from the mobile unit to the base station.

25. A method according to

claim 24

wherein the mobile unit is mobile cellular telephone and the base station is one of a plurality of such base stations used in a cellular telephone network and situated at respective geographical locations to define a corresponding plurality of overlapping service areas constituting one or more regions.

26. A method according to

claim 21

wherein the base station comprises a receiver and the mobile unit comprises a transmitter adapted for communication with the base station, and wherein the target signal received by the mobile unit is transmitted to the base station.

27. A method according to

claim 26

wherein the correlation is performed at the base station.

29. A mobile unit for despreading a spread spectrum signal by a method according to

claims 16

to

20

and

claims 22

to

25

.

43. A base station for despreading a spread spectrum signal by a method according to

claim 27

.

28. A method of despreading a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message as hereinbefore described with reference to the accompanying figures.

30. A mobile unit comprising a receiver for receiving a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message, and a signal containing data message information relating to the timing of an epoch of at least one data bit;

and a processor for generating a replica signal containing PRN code sequences corresponding to those of the target signal and performing a correlation of the target signal and the replica signal;

wherein the data message information is used to reduce degradation of the correlation caused by variations in the PRN code sequences in the target signal attributable to modulation by the data message.

31. A mobile unit according to

claim 30

wherein the correlation is timed so as to substantially avoid continuous correlation over an epoch of a data bit.

32. A mobile unit according to

claim 31

wherein a correlation output is provided as a function of the sum of correlation values returned for a series of individual, continuous correlations.

33. A mobile unit according to

claim 30

wherein the data message information further comprises data bit information relating to at least part of the data message, and wherein the correlation is modified as a function of the data message information.

34. A mobile unit according to

claim 33

wherein a continuous correlation occurs over a time period in which an epoch of a data bit occurs separating data bits of differing polarity.

35. A mobile unit according to

claim 33

or

claim 34

wherein data bit modulation of the PRN code sequences in the target signal is the same as or equivalent to exclusive-or modulation;

and wherein the polarity of PRN code sequences in the replica signal is selectively reversed as a function of the data message information.

36. A mobile unit according to any of

claims 30

to

35

wherein the data message information is provided from another spread spectrum signal which has already been received and acquired at the mobile unit (hereafter “

the reference signal”

).

39. A mobile unit according to any of

claims 36

to

38

wherein the dwell time for each code check made whilst attempting to acquiring the target signal is greater than that previously used to acquire the reference signal.

40. A mobile unit according to any of

claims 36

to

39

wherein the data message information further comprises data bit information relating to at least part of the data message of the target signal which is derived from corresponding data bit information of the reference signal.

41. A mobile unit according to

claim 30

to 35 in the form of a cellular telephone for use with a cellular telephone network and comprising a GPS receiver, wherein the signal containing data message information is provided from a cellular telephone network base station.

51. The combination of a mobile unit according to any of

claims 30

to

35

and a base station, wherein the target signal is received by the mobile unit, and the data message information is provided at a base station.

37. A mobile unit according to

claim 37

wherein the data message information relating to the timing of an epoch of at least one data bit of the target signal is derived from the timing of an epoch of at least one data bit of the reference signal.

38. A mobile unit according to

claim 37

in the form of a GPS receiver wherein the target signal is a GPS signal;

and wherein the data message information relating to the timing of an epoch of at least one data bit of the target signal is derived from the timing of an epoch of at least one data bit of the reference signal and GPS ephemeris data.

42. A mobile unit for despreading a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message as hereinbefore described with reference to the accompanying figures.

44. A base station comprising a receiver for receiving from a mobile unit a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message received by the mobile unit, means for providing data message information;

and a processor for generating a replica signal containing PRN code sequences corresponding to those of the target signal and performing a correlation of the target signal and the replica signal;

wherein the data message information is used to reduce degradation of the correlation caused by variations in the PRN code sequences in the target signal attributable to modulation by the data message.

45. A base station according to

claim 44

wherein the correlation is timed so as to substantially avoid continuous correlation over an epoch of a data bit.

46. A base station according to

claim 45

wherein a correlation output is provided as a function of the sum of correlation values returned for a series of separate, continuous correlations.

47. A base station according to

claim 44

wherein the data message information further comprises data bit information relating to at least part of the data message, and wherein the correlation is modified as a function of the data message information.

48. A base station according to

claim 47

wherein a continuous correlation occurs over a time period in which an epoch of a data bit occurs separating data bits of differing polarity.

49. A base station according to

claim 47

or

claim 48

wherein data bit modulation of the PRN code sequences in the target signal is the same as or equivalent to exclusive-or modulation;

and wherein the polarity of PRN code sequences in the replica signal is selectively reversed as a function of the data message information.

52. The combination of a mobile unit and a base station according to any of

claims 44

to

50

.

50. A base station for despreading a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message as hereinbefore described with reference to the accompanying figures.

53. A combination of a mobile unit and a base station for despreading a target spread spectrum signal containing pseudorandom noise (PRN) code sequences modulated by a data message as hereinbefore described with reference to the accompanying figures.