Method and apparatus for frequency offset correction

• US 6,363,102 B1
• Filed: 04/23/1999
• Issued: 03/26/2002
• Est. Priority Date: 04/23/1999
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J., Ling, Fuyun, Easton, Kenneth D.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/298,252
• Time in Patent Office: 1,068 Days
• Field of Search: 375/140, 375/142, 375/143, 375/147, 375/148, 375/150, 375/152, 370/203, 370/206, 370/335, 370/342
• US Class Current: 375/147
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04L 2027/003 at baseband only
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

Coherent detection of high-speed digital wireless communications becomes more difficult when the frequencies of the transmitter and receiver oscillators do not coincide. A frequency-locked loop may be used to characterize this frequency offset by processing the samples received on a pilot channel. Rather than using the offset information thus derived to correct the frequency of the received signal, the invention realizes a considerable computational savings by applying a frequency correction to the despread pilot samples instead.

Claims

1. An apparatus for frequency offset correction, comprising:

a phase rotator receiving a pilot and a first phase adjustment value and outputting a rotated pilot, the pilot having a frequency offset and a phase rotation;

a frequency discriminator receiving the rotated pilot and outputting a frequency error value;

a phase calculation and delay unit receiving the frequency error value and outputting the first phase adjustment value and a second phase adjustment value;

a pilot filter receiving the rotated pilot and outputting a channel estimate; and

a phase derotator receiving the channel estimate and the second phase adjustment value and outputting a derotated channel estimate,

wherein the first and second phase adjustment values are complex values, and

wherein the second phase adjustment value is substantially a delayed version of the first phase adjustment value, and

wherein the rotated pilot is substantially the pilot without the frequency offset, and

wherein the channel estimate is substantially a complex value representing the phase rotation.

2. An apparatus according to claim 1, said frequency discriminator comprising a quadricorrelator.

3. An apparatus according to claim 1, said phase calculation and delay unit comprising:

a first integrator receiving a signal based on the frequency error value and outputting a frequency offset value; and

a second integrator receiving the frequency offset value and outputting a phase correction value;

wherein the first phase adjustment value and the second phase adjustment value are based on the phase correction value.

4. An apparatus for frequency offset correction, comprising:

a pilot despreader receiving a plurality of received pilot samples and outputting a plurality of despread pilot samples, said plurality of despread pilot samples having a frequency offset and a phase rotation;

a buffer receiving the plurality of despread pilot samples and outputting a plurality of delayed despread pilot samples;

a phase rotator receiving the plurality of delayed despread pilot samples and a first phase adjustment value and outputting a plurality of rotated pilot samples;

a frequency discriminator receiving the plurality of despread pilot samples and outputting a frequency error value;

a phase calculation and delay unit receiving the frequency error value and outputting the first phase adjustment value and a second phase adjustment value;

a pilot filter receiving the plurality of rotated pilot samples and outputting a channel estimate; and

a phase derotator receiving the channel estimate and the second phase adjustment value and outputting a derotated channel estimate,

wherein the first and second phase adjustment values are complex values, and

wherein the second phase adjustment value is substantially a delayed version of the first phase adjustment value, and

wherein the plurality of rotated pilot samples are substantially the plurality of despread pilot samples without the frequency offset, and

wherein the channel estimate is substantially a complex value representing the phase rotation.

5. A method for frequency offset correction, comprising:

receiving a pilot and a first phase adjustment value and outputting a rotated pilot, the pilot having a frequency offset and a phase rotation;

receiving the rotated pilot and outputting a frequency error value;

receiving the frequency error value and outputting the first phase adjustment value and a second phase adjustment value;

receiving the rotated pilot and outputting a channel estimate; and

receiving the channel estimate and the second phase adjustment value and outputting a derotated channel estimate,

wherein the first and second phase adjustment values are complex values, and

wherein the second phase adjustment value is substantially a delayed version of the first phase adjustment value, and

wherein the rotated pilot is substantially the pilot without the frequency offset, and

wherein the channel estimate is substantially a complex value representing the phase rotation.

6. A method according to claim 5, further comprising:

receiving a signal based on the frequency error value and outputting a frequency offset value; and

receiving the frequency offset value and outputting a phase correction value;

wherein the first phase adjustment value and the second phase adjustment value are based on the phase correction value.

7. A computer readable medium embodying a method for frequency offset correction, the method comprising:

receiving a pilot and a first phase adjustment value and outputting a rotated pilot, the pilot having a frequency offset and a phase rotation;

receiving the rotated pilot and outputting a frequency error value;

receiving the frequency error value and outputting the first phase adjustment value and a second phase adjustment value;

receiving the rotated pilot and outputting a channel estimate; and

receiving the channel estimate and the second phase adjustment value and outputting a derotated channel estimate,

wherein the first and second phase adjustment values are complex values, and

wherein the second phase adjustment value is substantially a delayed version of the first phase adjustment value, and

wherein the rotated pilot is substantially the pilot without the frequency offset, and

wherein the channel estimate is substantially a complex value representing the phase rotation.

8. A computer readable medium according to claim 7, the method further comprising:

receiving a signal based on the frequency error value and outputting a frequency offset value; and

receiving the frequency offset value and outputting a phase correction value;

wherein the first phase adjustment value and the second phase adjustment value are based on the phase correction value.

9. An apparatus for frequency offset correction, comprising:

means for receiving a pilot and a first phase adjustment value and outputting a rotated pilot, the pilot having a frequency offset and a phase rotation;

means for receiving the rotated pilot and outputting a frequency error value;

means for receiving the frequency error value and outputting the first phase adjustment value and a second phase adjustment value;

means for receiving the rotated pilot and outputting a channel estimate; and

means for receiving the channel estimate and the second phase adjustment value and outputting a derotated channel estimate,

wherein the first and second phase adjustment values are complex values, and

wherein the second phase adjustment value is substantially a delayed version of the first phase adjustment value, and

wherein the rotated pilot is substantially the pilot without the frequency offset, and

wherein the channel estimate is substantially a complex value representing the phase rotation.

10. An apparatus according to claim 9, wherein said means for receiving the rotated pilot and outputting a frequency error value comprises a quadricorrelator.

11. An apparatus according to claim 9, further comprising:

means for receiving a signal based on the frequency error value and outputting a frequency offset value; and

means for receiving the frequency offset value and outputting a phase correction value;

wherein the first phase adjustment value and the second phase adjustment value are based on the phase correction value.