PN generators for spread spectrum communications systems

• US 6,661,833 B1
• Filed: 01/31/2000
• Issued: 12/09/2003
• Est. Priority Date: 01/31/2000
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J., Padovani, Roberto, Weaver, Lindsay A. Jr.
• Primary Examiner(s): Ghebretinsae, Temesghen
• Application Number:
  US09/494,838
• Time in Patent Office: 1,408 Days
• Field of Search: 375/130, 375/367, 375/147, 708/250, 370/335
• US Class Current: 375/147
• CPC Class Codes: H03K 3/84 Generating pulses having a predetermined statistical distribution of a parameter, e.g. random pulse generators
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker
• CPC Class Codes: H04J 13/10 Code generation

Abstract

Techniques to improve the acquisition process in a spread spectrum environment. The signals from different CDMA systems are spread with different sets of PN sequences, with the PN sequences in each set being uncorrelated to the PN sequences in the other sets. By using uncorrelated PN sequences, the likelihood of detecting a pilot signal from an undesired system is reduced or minimized, and the mean time to acquisition of the pilot signal from the desired system is improved. The mobile station can attempt to acquire the pilot signal by processing the received signal with a first set of PN sequences corresponding to a first hypothesis of the particular signal being acquired. If acquisition of the pilot signal fails, a second set of PN sequences corresponding to a second hypothesis is selected and used to process the received signal. The PN sequences in the second set are uncorrelated to the PN sequences in the first set. The PN sequences for the first set can be generated based on the characteristic polynomials defined by IS-95-A, and the PN sequences for the second set can be the reverse of the PN sequences for the first set.

Claims

1. A method for acquiring a particular one of a plurality of spread spectrum signals, wherein the particular spread spectrum signal is spread with a particular set of pseudo-random noise (PN) sequences, the method comprising:

identifying a first set of PN sequences corresponding to a first hypothesis of the particular spread spectrum signal being acquired;

processing a received signal with the identified set of PN sequences to extract a pilot signal;

computing a metric for the extracted pilot signal;

determining whether the pilot signal has been acquired based, in part, on the computed metric; and

if the pilot signal is determined to not be acquired,

selecting a second set of PN sequences corresponding to a second hypothesis of the particular spread spectrum signal being acquired, wherein the PN sequences in the second set are uncorrelated to the PN sequences in the first set, and

repeating the processing, computing, and determining steps.

2. The method of claim 1, wherein the PN sequences for the second set are the reverse of the PN sequences for the first set.

3. The method of claim 2, wherein the PN sequences for the first set are stored in a memory unit, the method further comprising:

accessing the memory unit in a first direction to retrieve the PN sequences for the first set; and

accessing the memory unit in a second direction to retrieve the PN sequences for the second set.

4. The method of claim 1, wherein the PN sequences for the first set are generated based on the following characteristic polynomials:

5. The method of claim 4, wherein the PN sequences for the second set are generated based on the following characteristic polynomials:

 

P_1,2=x¹⁵+x¹⁰+x⁸+x⁷+x⁶+x²+1, and

6. The method of claim 1, wherein the PN sequences for the first and second sets each has a length of 2¹⁵.

7. The method of claim 1, wherein the metric for the extracted pilot signal is an energy measurement computed over a particular time interval.

8. The method of claim 1, wherein the particular spread spectrum signal is generated in accordance with IS-95-A standard.

9. The method of claim 1, wherein the particular spread spectrum signal includes a pilot signal that is gated in time.

10. A receiver unit configurable to acquire a particular one of a plurality of spread spectrum signals, the receiver unit comprising:

a receiver configured to receive and condition a received signal to provide a conditioned signal, wherein the received signal includes the particular spread spectrum signal;

a demodulator coupled to the receiver, the demodulator configured to demodulate the conditioned signal to provide baseband signals;

a despreader coupled to the demodulator, the despreader configured to despread the baseband signals with a first set of PN sequences to provide despread signals;

a PN generator coupled to the despreader and configured to provide the first set of PN sequences, wherein the first set of PN sequences is selected from among a plurality of sets of PN sequences and corresponds to a first hypothesis of the particular spread spectrum signal being acquired;

a processing unit coupled to the despreader, the processing unit configured to process the despread signals to extract a pilot signal and to compute a metric for the extracted pilot signal; and

a controller coupled to the PN generator and the processing unit, the controller configured to determine whether the pilot signal has been acquired based, in part, on the computed metric and, if the pilot signal is determined to not be acquired, direct the PN generator to provide a second set of PN sequences corresponding to a second hypothesis of the particular spread spectrum signal being acquired, wherein the PN sequences in the second set are uncorrelated to the PN sequences in the first set.

11. The receiver unit of claim 10, wherein the PN sequences for the second set are reverse of the PN sequences for the first set.

12. The receiver unit of claim 10, wherein the PN sequences for the first set are generated based on the following characteristic polynomials:

13. The receiver unit of claim 12, wherein the PN sequences for the second set are generated based on the following characteristic polynomials:

14. The receiver unit of claim 10, wherein the PN generator includes a memory unit configured to store the first set of PN sequences.

15. The receiver unit of claim 14, wherein the memory unit is accessed in a first direction to retrieve the first set of PN sequences and accessed in a second direction to retrieve the second set of PN sequences.

16. The receiver unit of claim 10, wherein the PN generator includes a set of linear feedback shift registers configured to implement a set of characteristic polynomials that define the PN sequences in the first and second set.

17. The receiver unit of claim 10, wherein the particular spread spectrum signal conforms to IS-95-A standard.