Method and apparatus for CDMA demodulation

• US 7,336,640 B2
• Filed: 02/19/2003
• Issued: 02/26/2008
• Est. Priority Date: 02/19/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Wang, Jane, McDonough, John G.
• Primary Examiner(s): MARCELO, MELVIN C
• Application Number:
  US10/370,352
• Publication Number:
  US 20030156593A1
• Time in Patent Office: 1,833 Days
• Field of Search: 370/342, 375/147, 375/148, 375/150
• US Class Current: 370/342
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/70707 Efficiency-related aspects
• CPC Class Codes: H04J 13/0048 Walsh

Abstract

A CDMA receiver (500) minimizes the use of hardware by taking advantage of the fact that Walsh sequences of a predetermined length (e.g., 16) are comprised of inverted and non-inverted versions of smaller length (e.g., 4) sequences. The receiver (500) performs the necessary uncovering operations for example of a Walsh sequence of length 16 by performing uncovering operations using smaller length Walsh sequences such as of length 4 and then performing subsequent summing operations with inverted and non-inverted versions of the results of such uncovering operations.

Claims

1. A code division multiple access (CDMA) receiver, comprising:

an input for receiving an information sequence covered by a Walsh sequence of length N;

a demodulator with an uncovering circuit coupled to the input for uncovering the information sequence using a Walsh code, W^m_o, where M is less than 2^log2<sup>(N)−

1</sup>and having a length N/M when the Walsh length, N, is even, and using a Walsh code, W^M₁, here M is less than 2^log2<sup>(N)−

1</sup> having a length N/M when the Walsh length, N, is odd; and

wherein the CDMA receiver demodulates the information sequence to provide an output from the uncovering circuit to accomplish CDMA communications.

2. A CDMA receiver as defined in claim 1, wherein the uncovering circuit further includes one or more summers for summing non-inverted and/or inverted versions of the result of the uncovering operation using the Walsh code.

3. A CDMA receiver as defined in claim 1, wherein the input receives N information sequences and the CDMA receiver uses M uncovering circuits in order to fully uncover all of the N information sequences.

4. A CDMA receiver as defined in claim 3, wherein the results of the M uncovering circuits are combined.

5. A CDMA receiver as defined in claim 4, wherein the results of the M uncovering circuits are combined using a Maximal Ratio Combining (MRC) circuit.

6. A method for code division multiple access (CDMA) demodulation, comprising the steps of

receiving an information sequence covered by a Walsh sequence of length N;

and

uncovering the information sequence using a Walsh code, W^M₀, where M is less than 2^log2<sup>(N)−

1</sup> and having a length N/M when the original Walsh length, N, is even, and using a Walsh code, W^m₁, here M is less than 2^log2<sup>(N)−

1</sup> and having a length N/M when the original Walsh length, N, is odd;

demodulating the information sequence to provide an output from the uncovering step to accomplish CDMA communications.

7. A method as defined in claim 6, further comprising the step of:

summing non-inverted and/or inverted versions of the result of the uncovering operation using the Walsh code.

8. A method as defined in claim 6, wherein the uncovering is performed by an uncovering circuit and if N information sequences are received, M uncovering circuits are used in order to fully uncover all of the N information sequences.

9. A method as defined in claim 8, wherein the results of the M uncovering circuits are combined.

10. A method as defined in claim 9, wherein the results of the M uncovering circuits are combined using a Maximal Ratio Combining (MRC).

11. A code division multiple access (CDMA) receiver with a demodulator, comprising:

a chip with an input for receiving an information sequence covered by a Walsh sequence of length N;

the demodulator for performing only uncovering operations with an uncovering circuit coupled to the input and using the results of the uncovering operations to generate an output;

wherein the chip demodulates the information sequence to provide the output to accomplish CDMA communications; and

wherein the Walsh sequence of N comprises inverted and non-inverted versions of one of the M Walsh sequences, and uncovering operations is performed on Walsh sequences of M and then subsequent summing operations is performed using inverted and non-inverted versions of the uncovering operations.