Method and apparatus for generating non-recursive variable rate orthogonal spreading codes

1. A method comprising:

defining a variable B=SF max /SF min , where SF max is a maximum desired spreading factor and SF min is a minimum desired spreading factor, where SF max and SF min are integer values;

forming B unique base matrices G k of dimension SF min ×SF min , where G i G i T =SF min I min ∀i, where T denotes a matrix transpose and I min is an SF min ×SF min identity matrix;

forming a modulation matrix M of dimension B×B such that MM T =BI B , where I B is a B×B identity matrix;

forming an SF max ×SF max orthogonal variable spread factor (OVSF) code matrix C′ as:

C

′

=

[

M

1

,

1

·

G

1

M

1

,

2

·

G

2

…

M

1

,

B

·

G

B

M

2

,

1

·

G

1

M

2

,

2

·

G

2

…

M

2

,

B

·

G

B

⋮

⋮

⋰

⋮

M

B

,

1

·

G

1

M

B

,

2

·

G

2

…

M

B

,

B

·

G

B

]

,

where M i,j is a scalar from the i-th row and j-th column of the modulation matrix M, G l . . . G B is the k-th base matrix G k and M i,j ·G k denotes the multiplication of the elements of G k by the scalar M i,j , where i, j and k are integer values;

selecting a row of the OVSF code matrix C′ to use as a pseudo-noise (PN) code; and

one of spreading or despreading a signal using the selected PN code, where the steps of defining, forming the B unique base matrices, forming the modulation matrix M, forming the OVSF code matrix C′, selecting and one of spreading or despreading are performed by at least one processor.

2. The method as in claim 1 , where SF max and SF min are measured in chips per modulated symbol.

3. The method as in claim 1 , further comprising: performing at least one constrained column-wise permutation on the OVSF code matrix C′ prior to selection of the row, where the constraint on the at least one constrained column-wise permutation is designed to preserve OVSF properties of the permuted code matrix C′.

4. The method as in claim 1 , where the B unique base matrices G k comprise Hadamard matrices.

5. The method as in claim 1 , where the method is implemented within a multi-rate code division multiple access (CDMA) wireless communication system.

6. The method as in claim 5 , wherein the multi-rate CDMA wireless communication system comprises at least one fixed subscriber unit or at least one mobile subscriber unit.

7. An apparatus comprising:

at least one processor configured to define a variable B=SF max /SF min , where SF max is a maximum desired spreading factor and SF min is a minimum desired spreading factor and where SF max and SF min are integer values; to form B unique base matrices G k of dimension SF min ×SF min , where G i G i T =SF min I min ∀i, where T denotes a matrix transpose and I min is an SF min ×SF min identity matrix; to form a modulation matrix M of dimension B×B such that MM T =BI B , where I B is a B×B identity matrix; to form an SF max ×SF max orthogonal variable spread factor (OVSF) code matrix C′ as:

C

′

=

[

M

1

,

1

·

G

1

M

1

,

2

·

G

2

…

M

1

,

B

·

G

B

M

2

,

1

·

G

1

M

2

,

2

·

G

2

…

M

2

,

B

·

G

B

⋮

⋮

⋰

⋮

M

B

,

1

·

G

1

M

B

,

2

·

G

2

…

M

B

,

B

·

G

B

]

,

where M i,j is a scalar from the i-th row and j-th column of the modulation matrix M, G l . . . G B is the k-th base matrix G k and M i,j ·G k denotes the multiplication of the elements of G k by the scalar M i,j , where i, j and k are integer values; and to select a row of the OVSF code matrix C′ to use as a pseudo-noise (PN) code; and

a transceiver configured to transmit or receive a signal using the selected PN code.

8. The apparatus as in claim 7 , where SF max and SF min are measured in chips per modulated symbol.

9. The apparatus as in claim 7 , where the at least one processor is further configured to perform at least one constrained column-wise permutation on the OVSF code matrix C′ prior to selection of the row, where the constraint on the at least one constrained column-wise permutation is designed to preserve OVSF properties of the permuted code matrix C′.

10. The apparatus as in claim 7 , where the B unique base matrices G k comprise Hadamard matrices.

11. The apparatus as in claim 7 , where the apparatus comprises a unit within a multi-rate code division multiple access (CDMA) wireless communication system.

12. The apparatus as in claim 11 , where the apparatus comprises a fixed subscriber unit or a mobile subscriber unit.

13. The apparatus as in claim 7 , where the apparatus comprises a subscriber unit.

14. The apparatus as in claim 7 , wherein the apparatus comprises a base station.