Method and apparatus for canceling pilot interference in a CDMA communication system

• US 6,680,727 B2
• Filed: 09/27/2001
• Issued: 01/20/2004
• Est. Priority Date: 10/17/2000
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Jou, Yu-Cheun, Zhang, Haitao, Butler, Brian K., Bender, Paul E.
• Primary Examiner(s): Ghayour, Mohammad H.
• Application Number:
  US09/966,256
• Publication Number:
  US 20020131479A1
• Time in Patent Office: 845 Days
• Field of Search: 375/147, 375/144, 375/148, 375/346
• US Class Current: 375/144
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation

Abstract

Techniques for canceling pilot interference in a wireless (e.g., CDMA) communication system. A received signal typically includes a number of signal instances (i.e., multipaths). For each multipath desired to be processed, the other multipaths act as interference on the desired multipath. If the pilot is generated based on a known data pattern (e.g., all zeros) and covered with a known channelization code (e.g., a Walsh code of zero), then the pilot in an interfering multipath may be estimated as the spreading sequence at a time offset corresponding to the arrival time of that multipath. The pilot interference from each interference multipath may be estimated based on the spreading sequence for the interfering multipath and the despreading sequence for the desired multipath. The total pilot interference from a number of interfering multipaths may be subtracted from the data component in the desired multipath to provide pilot-canceled data having improved performance.

Claims

1. In a wireless communication system, a method for canceling pilot interference at a receiver unit that receives first and second pilot signals and first and second data signals, comprising:

generating a first PN sequence corresponding to the first pilot signal;

despreading the first PN sequence with a second PN sequence corresponding to the second pilot signal;

multiplying the despread first PN sequence with an estimated gain and phase of the first pilot signal to generate a first multiplied signal; and

subtracting the first multiplied signal from the second data signal.

2. The method of claim 1, further comprising:

despreading the second PN sequence with the first PN sequence;

multiplying the despread second PN sequence with an estimated gain and phase of the second pilot signal to generate a second multiplied signal; and

subtracting the second multiplied signal from the first data signal.

3. The method of claim 2, further comprising:

receiving a modulated signal comprised of a plurality of signal instances, wherein a first signal instance includes the first pilot signal and the first data signal and a second signal instance includes the second pilot signal and the second data signal.

4. The method of claim 2, further comprising:

decovering each of the first and second despread PN sequence, wherein the decovering for each despread PN sequence includes

multiplying the despread PN sequence with a channelization code, and

accumulating the multiplied PN sequence over an integer multiple of a channelization code length.

5. A system for canceling pilot interference in a receiver unit that receives first and second pilot signals and first and second data signals, comprising:

a first PN generator configured to generate a first PN sequence corresponding to the first pilot signal;

a first despreader configured to despread the first PN sequence with a second PN sequence corresponding to the second pilot signal;

a first multiplier configured to multiply the despread first PN sequence with an estimated gain and phase of the first pilot signal to generate a first multiplied signal; and

a first adder configured to subtract the first multiplied signal from the second data signal.

6. The system of claim 5, further comprising:

a second PN generator configured to generate the second PN sequence;

a second despreader configured to despread the second PN sequence with the first PN sequence;

a second multiplier configured to multiply the despread second PN sequence with an estimated gain and phase of the second pilot signal to generate a second multiplied signal; and

a second adder configured to subtract the second multiplied signal from the first data signal.

7. The system of claim 6, further comprising:

a first decoverer configured to decover the despread first PN sequence; and

a second decoverer configured to decover the despread second PN sequence.

8. The system of claim 7, wherein each of the first and second decovers includes

a multiplier configured to multiply the despread PN sequence with a channelization code, and

an accumulator configured to accumulate the multiplied PN sequence over a channelization code length.

9. In a wireless communication system, a pre-processor for canceling pilot interference in a receiver unit that receives first and second pilot signals and first and second data signals, comprising:

a first PN generator configured to generate a first PN sequence corresponding to the first pilot signal;

a second PN generator configured to generate a second PN sequence corresponding to the second pilot signal; and

a first despreader configured to despread the first PN sequence with the second PN sequence corresponding to the second pilot signal.

10. The pre-processor of claim 9, further comprising:

a second despreader configured to despread the second PN sequence with the first PN sequence.

11. The pre-processor of claim 10, further comprising:

a first decoverer configured to decover the despread first PN sequence; and

a second decoverer configured to decover the despread second PN sequence.