Method and apparatus for code phase tracking

• US 20010055330A1
• Filed: 05/11/2001
• Published: 12/27/2001
• Est. Priority Date: 05/13/2000
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Goodings, Christopher J.
• Granted Patent: US 6,931,056 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker

Abstract

A method of code phase tracking for CDMA type communication is disclosed together with apparatus including a GPS receiver (10 to 15) for the same. The method uses a modified early-minus-late correlation function to determine the code phase error between a target pseudorandom noise code of an incoming signal and locally generated replica codes. The early-minus-late correlation function is modified compared to the true function whereby the gradient of the modified function at zero code phase error is increased. This may be achieved my modifying the early-minus-late correlation function after its derivation. Alternatively, it may be modified by modifying variables from which it is derived and in particular, by modifying the either or both of the power spectrums of the subject signal or the early and late replica code signals whereby at least one odd harmonic is reduced in size or removed; at least one even harmonic is increased in size: or the bandwidth is truncating between harmonics so as to excise an adjacent even harmonic.

Claims

1. A method of code phase tracking comprising the steps of:

(a) receiving a subject signal containing a target pseudorandom noise code;

(b) generating a series of signals containing early and late replica codes corresponding to the target code;

(c) correlating the subject signal with the early and late replica code signals and returning respective early and late correlation values; and

(d) determining the code phase error between the target code and the replica codes from a modified early-minus-late correlation function derived from the early and late correlation values, the modified early-minus-late correlation function being such that its gradient at zero code phase error is increased compared to the true early-minus-late correlation function.

2. A method according to

claim 1

wherein the early-minus-late correlation function is modified by modifying either the subject signal, the early and late replica code signals or the early and late correlation values prior to deriving the early-minus-late correlation function.

3. A method according to

claim 2

wherein at least one odd harmonic of the power spectrum of the subject signal is reduced in size or removed.

4. A method according to

claim 2

wherein at least one even harmonic of the power spectrum of the subject signal is increased in size.

5. A method according to

claim 2

wherein the bandwidth of the power spectrum of the subject signal is truncated between harmonics so as to excise an adjacent even harmonic.

6. A method according to

claim 2

wherein at least one odd harmonic of the power spectrum at least one of the early and late replica code signals is reduced in size or removed.

7. A method according to

claim 2

wherein at least one even harmonic of the power spectrum at least one of the early and late replica code signals is increased in size.

8. A method according to

claim 2

wherein the bandwidth of the power spectrum at least one of the early and late replica code signals is truncated between harmonics so as to excise an adjacent even harmonic.

10. A receiver comprising an antenna for receiving a subject signal containing a target pseudorandom noise code;

and a signal processor for implementing a method of code phase correlation according to any preceding claim.

9. A method of code phase tracking substantially as hereinbefore described with reference to the figures.

11. A receiver comprising a signal processor for modifying the power spectrum of a received subject signal containing a target pseudorandom noise code so that the power spectrum of the subject signal has either at least one odd harmonic which is reduced in size or removed;

at least one even harmonic which is increased in size;

or a reduced bandwidth which is truncated between harmonics so as to excise an adjacent even harmonic.

12. A receiver comprising an antenna for receiving a subject signal containing a target pseudorandom noise code and a signal processor, the signal processor comprising a generator for generating a series of signals containing early and late replica codes corresponding to the target code, a correlator for correlating the subject signal with the early and late replica code signals and returning respective early and late correlation values, and means for determining the code phase error between the target code and the replica codes from a modified early-minus-late correlation function derived from the early and late correlation values, such that the gradient of the modified early-minus-late correlation function at zero code phase error is increased compared to the true early-minus-late correlation function.

13. A receiver according to

claim 12

wherein the early-minus-late correlation function is modified by modifying either the subject signal, the early and late replica code signals or the early and late correlation values prior to deriving the early-minus-late correlation function.

14. A receiver according to

claim 13

wherein at least one odd harmonic of the power spectrum of the subject signal is reduced in size or removed.

15. A receiver according to

claim 13

wherein at least one even harmonic of the power spectrum of the subject signal is increased in size.

16. A receiver according to

claim 13

wherein the bandwidth of the power spectrum of the subject signal is truncated between harmonics so as to excise an adjacent even harmonic.

17. A receiver according to

claim 13

wherein at least one odd harmonic of the power spectrum at least one of the early and late replica code signals is reduced in size or removed.

18. A receiver according to

claim 13

wherein at least one even harmonic of the power spectrum at least one of the early and late replica code signals is increased in size.

19. A receiver according to

claim 13

wherein the bandwidth of the power spectrum at least one of the early and late replica code signals is truncated between harmonics so as to excise an adjacent even harmonic.

20. A receiver substantially as hereinbefore described with reference to the figures.