Enhanced code allocation method for CDMA systems

• US 6,577,671 B1
• Filed: 12/29/1999
• Issued: 06/10/2003
• Est. Priority Date: 12/29/1999
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Vimpari, Markku
• Primary Examiner(s): PHU, PHUONG M
• Application Number:
  US09/474,312
• Time in Patent Office: 1,259 Days
• Field of Search: 375/140, 375/141, 375/146, 375/142, 375/143, 375/130
• US Class Current: 375/146
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04J 13/16 Code allocation

Abstract

A method is taught for assigning spreading codes to mobile stations located within a cell, as is a CDMA communications system that operates in accordance with the method. The method includes steps of (A) assigning a set of spreading codes for use in a particular cell; (B) determining values of entries in a spreading code performance table (fixed or dynamic) based on a weighted combination of cross-correlation factors between individual ones of the spreading codes of the set of spreading codes, and also based on an auto-correlation factor of individual ones of the spreading codes of the set of spreading codes, within a delay spread range that is typical for the particular cell; and (C) assigning a spreading code from the performance table by selecting a spreading code that will cause a least amount of interference with a sub-set of already assigned spreading codes.

Claims

1. A method for assigning spreading codes to mobile stations located within a cell, comprising steps of:

assigning a set of spreading codes for use in a particular cell;

determining entries in a spreading code performance table based on a weighted combination of cross-correlation factors between individual ones of the spreading codes of the set of spreading codes and also an auto-correlation factor of individual ones of the spreading codes of the set of spreading codes, within a delay spread range that is typical for the particular cell; and

assigning a spreading code from the performance table by selecting a spreading code that will cause a least amount of interference with a sub-set of already assigned spreading codes.

2. A method as in claim 1, wherein the step of determining is further based on a consideration of a simultaneous presence of high data rate mobile stations within the delay spread range that is typical for the particular cell.

3. A method as in claim 1, wherein the step of determining establishes a fixed performance table.

4. A method as in claim 1, wherein the step of determining establishes a dynamic performance table.

5. A method as in claim 1, wherein the step of assigning assigns the spreading code to a mobile station by a spreading code handover, wherein an already assigned spreading code is unassigned and replaced by a newly assigned spreading code.

6. A method as in claim 1, wherein data to be transmitted is not scrambled with a scrambling code, but is only spread using the assigned spreading code.

7. A method as in claim 1, wherein the steps of determining and assigning are performed by a base station controller.

8. A method as in claim 1, wherein the steps of determining and assigning are performed by a Radio Resource Management function of a base station controller.

9. A method as in claim 1, wherein the step of assigning assigns the spreading code to a mobile station by a spreading code handover upon an occurrence of a condition wherein an amount of performance improvement that will be experienced by replacing an already assigned spreading code with a new spreading code exceeds a threshold value.

10. A method as in claim 1, wherein the step of assigning assigns a spreading code that is selected to minimize an RMS correlation metric error value for all, already assigned spreading codes.

11. A code division, multiple access wireless communications system, comprising:

at least one base transceiver station (BTS) serving a cell;

a plurality of mobile stations (MSs) within said cell; and

a base station controller (BSC) coupled to said BTS, said BSC comprising a data processor for assigning individual ones of spreading codes selected from a set of spreading codes to mobile stations within said cell, said BSC data processor determining values for entries in a spreading code performance table based on a weighted combination of cross-correlation factors between individual ones of the spreading codes of the set of spreading codes and also an auto-correlation factor of individual ones of the spreading codes of the set of spreading codes, within a delay spread range that is typical for said cell, and for assigning a spreading code from the performance table by selecting a spreading code that will cause a least amount of interference with a sub-set of already assigned spreading codes.

12. A system as in claim 11, wherein said BSC data processor further determines values for said entries based on a consideration of a simultaneous presence of high data rate mobile stations within the delay spread range that is typical for said cell.

13. A system as in claim 11, wherein said BSC data processor establishes a fixed performance table.

14. A system as in claim 11, wherein said BSC data processor establishes a dynamic performance table.

15. A system as in claim 11, wherein said BSC data processor assigns a spreading code to a mobile station by a spreading code handover technique, wherein an already assigned spreading code is unassigned and replaced by a newly assigned spreading code, and wherein a spreading code handover is performed upon an occurrence of a condition wherein an amount of performance improvement that will be experienced by replacing the already assigned spreading code with the newly assigned spreading code exceeds a threshold value.

16. A system as in claim 15, where the threshold value is a static value that remains fixed during the operation of the system.

17. A system as in claim 15, where the threshold value is a dynamic value that varies during the operation of the system.

18. A system as in claim 15, where the value of the threshold is established so as to avoid excessive spreading code handovers.

19. A system as in claim 11, wherein data to be transmitted is not scrambled with a scrambling code, but is only spread using the assigned spreading code.

20. A system as in claim 11, wherein said BSC data processor executes a Radio Resource Management function.

21. A system as in claim 11, wherein the BSC data processor assigns a spreading code that is selected to minimize an RMS correlation metric error value for all, already assigned spreading codes.