Method of generating a time shifted signal

• US 20020061055A1
• Filed: 09/24/2001
• Published: 05/23/2002
• Est. Priority Date: 09/23/2000
• Status: Active Grant

• Current Assignee: Fox Digital, Intel Corporation, Intel IP Corporation (Intel Corporation), ST Wireless SA
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Yule, Andrew T., Young, Bryan D., Sarkar, Amites, Wilcox, Martin S.
• Granted Patent: US 7,010,021 B2
• Time in Patent Office: Days
• US Class Current: 375/149
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A method of generating a time shifted replica signal (SLS) from a reference signal (SPS) comprising a series of samples (A to K) describing bits of a data message in which the sampling rate is at least twice the data message bit rate is disclosed. The method comprising the steps of determining the phases of the reference signal samples with respect to virtual epochs (41) of the data message bits of the reference signal (SPS); and composing the time shifted replica signal (SLS) from the reference signal samples as a function of the phases of the reference signal samples.

Also disclosed is method comprising the step of composing the time shifted replica signal (SLS) from the reference signal samples (A to K), wherein the sampling rate of the replica signal (SLS) is the same as that of the reference signal (SPS), and wherein at least one reference signal sample (A to K) is not present in the time shifted replica signal (SLS).

Claims

1. A method of generating a time shifted replica signal from a reference signal comprising a series of samples describing bits of a data message in which the sampling rate is greater than the data message bit rate, the method comprising the steps of determining the phases of the reference signal samples with respect to virtual epochs of the data message bits of the reference signal;

and composing the time shifted replica signal from the reference signal samples as a function of the phases of the reference signal samples.

2. A method according to claim 1 wherein the phases of the reference signal samples are used to determine which signal samples are to be used to compose the time shifted replica signal.

3. A method according to claim 1 or claim 2 wherein the phases of the reference signal samples are determined using a numerical controlled oscillator.

4. A method according to any of the preceding claims wherein the sampling rate of the replica signal is the same as that of the reference signal.

5. A method according to any of the preceding claims wherein at least one reference signal sample is not present in the time shifted replica signal.

7. A method according to any of the preceding claims wherein at least one reference signal sample is replicated twice in succession in the time shifted replica signal.

8. A method according to any of the preceding claims wherein at least one pair of adjacent replica signal samples positioned either side of a virtual data bit epoch in the time shifted replica signal correspond to a pair of non-adjacent reference signal samples positioned either side of the virtual data bit epoch in the reference signal.

9. A method according to any of the preceding claims wherein the time shifted replica signal is time shifted from the reference signal by an amount not equal to an integer multiple of the time period between adjacent samples.

10. A method according to claim 9 wherein the time shifted replica signal is time shifted from the reference signal by an amount less than the time period between adjacent samples.

11. A method according to any of the preceding claims wherein, to 95% accuracy, a fraction having the data message bit rate as the numerator and the sampling rate as the denominator can be expressed by a continued fraction expansion in which the largest integer is less than or equal to 12.

12. A method according to any of claims 1 to 11 wherein, to 95% accuracy, the fraction having the data message bit rate as the numerator and the sampling rate as the denominator can be expressed as a continued fraction expansion in which the largest integer is less than or equal to 26.

13. A method according to any of claims 1 to 11 wherein, to 99% accuracy, the fraction having the data message bit rate as the numerator and the sampling rate as the denominator can be expressed as a continued fraction expansion in which the largest integer is less than or equal to 26.

14. A method according to any of the preceding claims wherein the reference signal samples describe a pseudorandom noise (PRN) code and the data message bits correspond to the PRN code chips.

16. A signal generator for generating a time shifted replica signal from a reference signal by a method according to any of the preceding claims.

17. A method of despreading a target spread spectrum signal containing a pseudorandom noise (PRN) code comprising the steps of generating a reference signal comprising a series of samples describing a PRN code corresponding to that contained in the target signal and in which the sampling rate is at least twice the PRN code chipping rate;

generating time shifted, early and late replica signals from the reference signal by a method in accordance with claim 14; and

correlating the target signal with the time shifted, early and late replica signals.

18. A method according to claim 17 further comprising the steps of measuring the code phase of the target spread spectrum signal when acquired using the generated time shifted, early and late replica signals;

and adjusting the code phase measurement to compensate for error in the generated time shifted, early and late replica signals compared to respective ideal early and late replica signals.

20. A spread spectrum signal receiver for despreading a target spread spectrum signal containing a pseudorandom noise (PRN) code by a method according to any of claims 17 to 19.

21. A spread spectrum signal receiver for despreading a spread spectrum signal comprising a receiver for receiving a target spread spectrum signal containing a pseudorandom noise (PRN) code;

a signal generator for generating a reference signal comprising a series of samples describing a PRN code corresponding to that contained in the target signal and in which the sampling rate is at least twice the PRN code chipping rate, and generating time shifted, early and late replica signals from the reference signal by a method in accordance with claim 14; and

a correlation processor for correlating the target signal with the time shifted, early and late replica signals.

22. A spread spectrum signal receiver according to claim 21 wherein the correlation processor is adapted to measure the code phase of the target spread spectrum signal when acquired using the generated time shifted, early and late replica signals, and further adapted to adjust the code phase measurement to compensate for error in the generated time shifted, early and late replica signals compared to respective ideal early and late replica signals.

23. A spread spectrum signal receiver according to claim 21 or claim 22 wherein the signal generator comprising a code NCO, a code generator for generating the reference signal, and early and late processing units for generating time shifted, early and late replica signals from the reference signal as outputted by the code generator;

wherein the early and late processing units receive early and prompt, and prompt and late signals from the code generator respectively, and determine which of the early or prompt, and prompt or late signal samples are used to generate the time shifted, early and late replica codes respectively, both as a function of the residual code phase measurement of the NCO.

24. A spread spectrum signal receiver according to claim 23 wherein the correlation processor is adapted to measure the code phase of the target spread spectrum signal when acquired using the generated time shifted, early and late replica signals, and further adapted to adjust the code phase measurement to compensate for error in the generated time shifted, early and late replica signals compared to respective ideal early and late replica signals using an output from at least one of the early and late processing units.

6. A method of generating a time shifted replica signal from a reference signal comprising a series of samples describing bits of a data message in which the sampling rate is greater than the data message bit rate, the method comprising the step of composing the time shifted replica signal from the reference signal samples, wherein the sampling rate of the replica signal is the same as that of the reference signal, and wherein at least one reference signal sample is not present in the time shifted replica signal.

15. A method of generating a time shifted replica signal from a reference signal substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of despreading a target spread spectrum signal containing a pseudorandom noise (PRN) code substantially as hereinbefore described with reference to the accompanying drawings.

25. A spread spectrum signal receiver for despreading a target spread spectrum signal containing a pseudorandom noise (PRN) code substantially as hereinbefore described with reference to the accompanying drawings.