Method and apparatus for assigning variable length walsh codes in a spread spectrum system

• US 6,317,413 B1
• Filed: 05/18/1998
• Issued: 11/13/2001
• Est. Priority Date: 05/18/1998
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Honkasalo, Zhi-Chun
• Primary Examiner(s): Nguyen, Chau
• Assistant Examiner(s): Nguyen, Phuongchau Ba
• Application Number:
  US09/080,908
• Time in Patent Office: 1,275 Days
• Field of Search: 370/209, 370/204, 370/208, 370/320, 370/335, 370/342, 370/441, 375/130, 375/140, 375/136, 375/1
• US Class Current: 370/209
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/70703 using multiple or variable rates
• CPC Class Codes: H04J 13/0044 OVSF [orthogonal variable spreading factor]
• CPC Class Codes: H04J 13/20 having an orthogonal variable spreading factor [OVSF]

Abstract

A method and apparatus for assigning Walsh codes in a direct sequence spread spectrum (DS-SS) telecommunications system. Walsh code sets are each generated from a different Walsh code C_x of length N. Each of the code sets is mutually disjoint to one another, i.e., each is generated from a different Walsh code C_x of length N, and each Walsh code C_x is from the same Walsh code matrix W. Each code set may be used to support a set of parallel CDMA channels. Because the codes of each Walsh code set are generated from the same C_x, a number of least significant bits from the code indexes of the codes in the set are equal and identical to the code index for the C_x used to generate the set. Assignment messages may be reduced in length by preassigning the code index of C_x to selected channels and then transmitting only the additional information necessary to specify the index of the assigned codes from the general code set generated from the C_x.

Claims

1. A method of assigning Walsh codes to a plurality of CDMA channels, said method comprising the steps of:

determining a plurality of M-bit codes from an N-bit code, said N-bit code having an I-bit index and each of said M-bit codes having an n-bit index, wherein at least one significant bit of said n-bit index for said M-bit code is equal to said I-bit index;

transmitting said I-bit index to each of a plurality of receivers in a first message, each of said plurality of receivers for receiving on at least one of said plurality of CDMA channels;

assigning each of said plurality of M-bit codes to one of the plurality of CDMA channels;

transmitting each one of a plurality of n-I bit fields to a separate one of said plurality of receivers, wherein the number of bits in each of said plurality of n-I bit fields is equal to the number of bits in said n-bit index minus the number of bits of said I-bit index, each of said plurality of n-I bit fields comprising data bits, which are combined with said I-bit index to indicate an index of one of said plurality of M-bit codes.

2. The method of claim 1, wherein said plurality of CDMA channels comprises a first plurality of CDMA channels, said I-bit index comprises a first I-bit index, said N-bit code comprises a first N-bit code, and wherein said method further comprises the steps of:

determining a plurality of variable length codes from a second N-bit code, said second N-bit code having a second I-bit index;

transmitting said second I-bit index to each of said plurality of receivers in a third message;

assigning a selected code of said plurality of variable length rate codes to each of a second plurality of CDMA channels; and

transmitting each one of a plurality of variable length fields to a separate one of said plurality of receivers, each one of said plurality of variable length fields comprising data bits which are combined with said second I-bit index to indicate an index of one of said plurality of variable length codes.

3. The method of claim 2, wherein N=16, n=8, M=256 and I=4.

4. The method of claim 2, wherein said first plurality of CDMA channels comprises a plurality of fundamental channels and said second plurality of CDMA channels comprises a plurality of supplemental channels.

5. The method of claim 2, wherein each of said plurality of variable length fields comprises bits indicating a data rate.

6. The method of claim 5, wherein each of said plurality of variable length fields further comprises at least one bit indicating additional code index information.

7. The method of claim 1, wherein N=16, n=8, M=256 and I=4.

8. The method of claim 1, wherein said plurality of CDMA channels comprises a first plurality of CDMA channels, said I-bit index comprises a first I-bit index, said N-bit code comprises a first N-bit code and wherein said method further comprises the steps of:

assigning each of a plurality of identifiers to one of a plurality of variable length code configurations, each of said variable length code configurations comprising at least one of a plurality of variable length codes generated from a second N-bit code, said second N-bit code having a second I-bit index;

transmitting a selected identifier of said plurality of identifiers to a receiver; and

transmitting a signal to said receiver on a CDMA channel, said channel spread by at least one variable rate code assigned to said selected identifier.

9. The method of claim 8, wherein N=16, n=8, M=256 and I=4 and wherein said plurality of identifiers comprises 30 identifiers.

10. An apparatus for assigning Walsh codes to a plurality of CDMA channels, said apparatus comprising:

means for determining a plurality of M-bit codes from an N-bit code, said N-bit code having an I-bit index and each of said M-bit codes having an n-bit index, wherein at least one significant bit of said n-bit index for said M-bit code is equal to said I-bit index;

means for transmitting said I-bit index to each of a plurality of receivers in a first message, each of said plurality of receivers for receiving on at least one of said plurality of CDMA channels;

means for assigning each of said plurality of M-bit codes to one of the plurality of CDMA channels;

means for transmitting each one of a plurality of n-I bit fields to a separate one of said plurality of receivers, wherein the number of bits in each of said plurality of n-I bit fields is equal to the number of bits in said n-bit index minus the number of bits of said I-bit index, each of said plurality of n-I bit fields comprising data bits, which are combined with said I-bit index to indicate an index of one of said plurality of M-bit codes.

11. The apparatus of claim 10, wherein said plurality of CDMA channels comprises a first plurality of CDMA channels, said I-bit index comprises a first I-bit index, said N-bit code comprises a first N-bit code, and wherein said apparatus further comprises:

means for determining a plurality of variable length codes from a second N-bit code, said second N-bit code having a second I-bit index;

means for transmitting said second I-bit index to each of said plurality of receivers in a third message;

means for assigning a selected code of said plurality of variable length rate codes to each of a second plurality of CDMA channels; and

means for transmitting each one of a plurality of variable length fields to a separate one of said plurality of receivers, each one of said plurality of variable length fields comprising data bits which are combined with said second I-bit index to indicate an index of one of said plurality of variable length codes.

12. The apparatus of claim 11, wherein N=16, n=8, M=256 and I=4.

13. The apparatus of claim 11, wherein said first plurality of CDMA channels comprises a plurality of fundamental channels and said second plurality of CDMA channels comprises a plurality of supplemental channels.

14. The apparatus of claim 11, wherein each of said plurality of variable length fields comprises bits indicating a data rate.

15. The apparatus of claim 14, wherein each of said plurality of variable length fields further comprises at least one bit indicating additional code index information.

16. The apparatus of claim 10, wherein N=16, n=8, M=256 and I=4.

17. The apparatus of claim 10, wherein said plurality of CDMA channels comprises a first plurality of CDMA channels, said I-bit index comprises a first I-bit index, said N-bit code comprises a first N-bit code and wherein said apparatus further comprises:

means for assigning each of a plurality of identifiers to one of a plurality of variable length code configurations, each of said variable length code configurations comprising at least one of a plurality of variable length codes generated from a second N-bit code, said N-bit code having a second I-bit index;

means for transmitting a selected identifier of said plurality of identifiers to a receiver; and

means for transmitting a signal to said receiver on a CDMA channel, said channel spread by at least one variable rate code assigned to said selected identifier.

18. The apparatus of claim 10, wherein N=16, n=8, M=256 and I=4, and wherein said plurality of identifiers comprises 30 identifiers.

19. A method of assigning Walsh codes to a plurality of CDMA channels, said method comprising the steps of:

determining at least one M-bit code from an N-bit code, said N-bit code having an I-bit index and said at least one M-bit code having an n-bit index, wherein at least one least significant bit of said n-bit index for said at least one M-bit code is equal to said I-bit index;

transmitting said I-bit index to at least one receiver in a first message, said at least one receiver for receiving on at least one of said plurality of CDMA channels;

assigning each of said at least one M-bit code to one of the plurality of CDMA channels; and

transmitting each of at least one n-I bit field to a separate one of said at least one receiver, wherein the number of bits in each of said at least one n-I bit field is equal to the number of bits in said n-bit index minus the number of bits of said I-bit index, each of said at least one n-I bit field comprising data bits, which are combined with said I-bit index to indicate said n-bit index of one of said at least one M-bit code.

20. An apparatus for assigning Walsh codes to a plurality of CDMA channels, said apparatus comprising:

means for determining at least one M-bit code from an N-bit code, said N-bit code having an I-bit index and said at least one M-bit code having an n-bit index, wherein at least one least significant bit of said n-bit index for said at least one M-bit code is equal to said I-bit index;

means for transmitting said I-bit index to at least one receiver in a first message, said at least one receiver for receiving on at least one of said plurality of CDMA channels;

means for assigning each of said at least one M-bit code to at least one of the plurality of CDMA channels;

means for transmitting each of said at least one n-I bit field to a separate one of said at least one receiver, wherein the number of bits in each of said at least one n-I bit field is equal to the number of bits in said n-bit index minus the number of bits of said I-bit index, each of said at least one n-I bit field comprising data bits, which are combined with said I-bit index to indicate said n-bit index of one of said at least one M-bit code.