Pseudorandom noise code acquisition in direct sequence spread spectrum systems

• US 8,300,721 B2
• Filed: 03/14/2007
• Issued: 10/30/2012
• Est. Priority Date: 03/14/2007
• Status: Active Grant

• Current Assignee: Keysight Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Law, Wai Kwok
• Primary Examiner(s): NGUYEN, LEON VIET Q
• Application Number:
  US11/686,270
• Publication Number:
  US 20080225928A1
• Time in Patent Office: 2,057 Days
• Field of Search: 375/148, 375/134, 375/136, 375/144, 375/265, 375/329, 375/340, 370/235, 370/329
• US Class Current: 375/265
• CPC Class Codes: H04B 1/7075 with code phase acquisition

Abstract

A method for receiving spread spectrum signals and for initial code acquisition from the received signals comprises de-spreading the received signals, based on code phase synchronization, to produce a de-spread signal; and performing a modulation detection based on a change of time-domain characteristic of the de-spread signal.

Claims

1. An initial code acquisition method, comprising:

receiving a spread spectrum signal including symbols;

de-spreading the received spread spectrum signal based on code phase synchronization to produce a de-spread signal; and

detecting a modulation format of the received spread spectrum signal based on a change of a time-domain characteristic of the de-spread signal,

wherein the change of a time-domain characteristic comprises a magnitude variation in a despread symbol in the de-spread signal.

2. A method as recited in claim 1, wherein the de-spreading is based on frequency offset and code phase synchronization.

3. A method as recited in claim 2, wherein:

a range of code phase to be searched is determined by a propagation delay of the spread spectrum signal; and

a range of frequency offset to be searched is determined by a Doppler frequency shift of the spread spectrum signal.

4. A method as recited in claim 1, where the de-spreading includes de-scrambling.

5. A method as recited in claim 4, wherein the de-scrambling employs a scrambling sequence that is a function of a code phase.

6. A method as recited in claim 1, wherein the de-spreading includes de-spreading at one of a set of code channels, each of the code channels being based on a respective one of a set of orthogonal functions.

7. A method as recited in claim 6, wherein:

the set of orthogonal functions includes a set of Walsh functions, each of the orthogonal functions comprising a respective one of the Walsh functions; and

the de-spreading includes de-scrambling and de-spreading at a predetermined Walsh code channel that corresponds with the respective one of the Walsh functions.

8. A method as recited in claim 7, wherein the de-spreading includes:

generating a scrambling sequence based on a code phase and a frequency offset;

multiplying the received signal by the scrambling sequence to produce a product thereof; and

multiplying the product by the respective one of the Walsh functions.

9. A method as set forth in claim 1, wherein detecting the modulation format of the received spread spectrum signal includes

recognizing a modulation format from among a plurality of possible modulation formats for the spread spectrum signal;

and

detecting a threshold activity at the recognized modulation format.

10. A method as recited in claim 9, wherein recognizing the modulation format includes recognizing based on Walsh code channels.

11. A method as recited in claim 1, wherein:

the received spread spectrum signal is modulated with one of a plurality of possible modulation formats; and

detecting the modulation format of the received spread spectrum signal includes;

(i) calculating a metric for each of the possible modulation formats,

(ii) comparing the calculated metric for the modulation format to a threshold, and

(iii) detecting the presence of a given one of the modulation formats based on the comparison with the threshold.

12. A method as recited in claim 11, wherein the calculating a metric includes calculating the magnitude variation in the de-spread signal.

26. A non-transitory computer-readable medium encoded with a computer program, for directing a processing system to perform initial code acquisition for received spread spectrum signals, the computer-readable medium comprising:

software program code, provided on the computer-readable medium, for directing the processing system to perform a method as recited in any of claims 1-12.

13. An initial code acquisition system, comprising:

de-spreading circuitry for de-spreading a received spread spectrum signal based on code phase synchronization to produce a de-spread signal comprising symbols; and

a modulation detector for detecting a modulation format of the received spread spectrum signal based on a change of a time-domain characteristic of the de-spread signal,

wherein the change of a. time-domain characteristic comprises a magnitude variation in a despread symbol in the de-spread signal.

14. A system as recited in claim 13, wherein the de-spreading circuitry includes circuitry that is operable based on frequency offset and code phase synchronization.

15. A system as recited in claim 14, wherein:

a range of code phase to be searched is determined by a propagation delay of the spread spectrum signal; and

a range of frequency offset to be searched is determined by a Doppler frequency shift of the spread spectrum signal.

16. A system as recited in claim 13, where the de-spreading circuitry includes de-scrambling circuitry,

17. A system as recited in claim 16, wherein the de-scrambling circuitry employs a scrambling sequence that is a function of a code phase.

18. A system as recited in claim 13, wherein the de-spreading circuitry includes de-spreading circuitry for de-spreading at one of a set of code channels, each of the code channels being based on a respective one of a set of orthogonal functions.

19. A system as recited in claim 18, wherein:

the set of orthogonal functions includes a set of Walsh functions, each of the orthogonal functions comprising a respective one of the Walsh functions; and

the de-spreading circuitry includes circuitry for de-scrambling and de-spreading at a predetermined Walsh code channel that corresponds with the respective one of the Walsh functions.

20. A system as recited in claim 19, wherein the de-spreading circuitry includes:

scrambling sequence generating circuitry that is operable based on a code phase and a frequency offset;

first multiplying circuitry for multiplying the received signal by the scrambling sequence to produce a product thereof; and

second multiplying circuitry for multiplying the product by the respective one of the Walsh functions.

21. A system as set forth in claim 13, wherein the modulation detector includes:

circuitry for recognizing a modulation format from among a plurality of possible modulation formats for the spread spectrum signal; and

circuitry for detecting a threshold activity at the recognized modulation format.

22. A system as recited in claim 21, wherein the circuitry for recognizing includes circuitry for recognizing based on Walsh code channels.

23. A system as recited in claim 21, wherein:

the received spread spectrum signal is modulated with one of a plurality of possible modulation formats; and

the modulation detection circuitry includes;

(i) circuitry for calculating a metric for each of the possible modulation formats,

(ii) circuitry for comparing the calculated metrics to a threshold, and

(iii) circuitry for detecting the presence of a given one of the modulation formats based on the comparison with the threshold.

24. A system as recited in claim 23, wherein the circuitry for calculating a metric includes circuitry for calculating the magnitude variation in the de-spread signal.

25. A system as recited in any of claims 13-24, wherein circuitry recited therein is implemented as a processor and software for performing the operation of the recited circuitry.