FREQUENCY OFFSET ESTIMATION IN A CDMA SYSTEM

• US 20110007644A1
• Filed: 10/24/2008
• Published: 01/13/2011
• Est. Priority Date: 11/06/2007
• Status: Active Grant

• Current Assignee: Icera Inc. (NVIDIA Corporation)
• Original Assignee: Icera Inc. (NVIDIA Corporation)
• Inventors: Walker, Simon Nicholas
• Granted Patent: US 8,737,292 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 7/2125 Synchronisation
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 2027/0048 Frequency multiplication
• CPC Class Codes: H04L 2027/0065 Frequency error detectors H04L2027/0067 takes precedence
• CPC Class Codes: H04L 2027/0087 Out-of-band signals, (e.g. pilots)
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

The present invention provides a method of estimating a frequency offset. The method comprises receiving a wireless signal timed according to a first frequency; generating a local signal timed according to a second frequency; and performing a plurality of synchronization searches, each search comprising obtaining a set of correlation results indicative of a correlation between the wireless signal and the local signal at different timing offsets of the wireless signal relative to the local signal. The method the no comprises finding a series of results, with a result from each of a plurality of the synchronization searches, for which the difference in; timing offset between results from adjacent searches in the series is within a maximum specified value. A frequency off set between the first and second frequencies can be determined from the series.

Claims

1-20. -20. (canceled)

21. A method of estimating a frequency offset, the method comprising:

receiving a wireless signal timed according to a first frequency;

generating a local signal timed according to a second frequency;

performing a plurality of synchronisation searches, each search comprising obtaining a set of correlation results indicative of a correlation between the wireless signal and the local signal at different timing offsets of the wireless signal relative to the local signal;

finding a series of results, with a result from each of a plurality of said synchronisation searches, for which the difference in timing offset between results from adjacent searches in the series is within a maximum specified value; and

determining from said series a frequency offset between the first and second frequencies.

22. The method of claim 21, comprising:

for each synchronisation search, ordering the respective correlation results in order of a corresponding received signal energy.

23. The method of claim 22, wherein said step of finding of said series is performed using only a top portion of the correlation results having the greatest received signal energy from each synchronisation search.

24. The method of claim 21, comprising using said estimation to correct for the frequency offset.

25. The method of claim 21, wherein the step of determining the frequency offset comprises determining the frequency offset from a difference in timing offsets between at least two of the correlation results from different searches in said series.

26. The method of claim 21, wherein the step of determining the frequency offset comprises determining a phase from sums of real and imaginary parts of the correlation results in said series.

27. The method of claim 21, comprising wherein the step of determining the frequency offset is conditional on a magnitude of a sum of real and imaginary parts of the correlation results in said series being above a predetermined threshold.

28. The method of claim 21, wherein the step of receiving the wireless signal comprises receiving a synchronisation channel on which is broadcast a synchronisation code, and the step of generating the local signal comprises generating a local version of the synchronisation code.

29. The method of claim 28, wherein the synchronisation channel is a primary synchronisation channel of a W-CDMA cellular communications system.

30. A wireless receiver, comprising:

reception means arranged to receive a wireless signal timed according to a first frequency;

generation means arranged to generate a local signal timed according to a second frequency;

correlation means arranged to perform a plurality of synchronisation searches, each search comprising obtaining a set of correlation results indicative of a correlation between the wireless signal and the local signal at different timing offsets of the wireless signal relative to the local signal; and

frequency offset estimation means arranged to find a series of results, with a result from each of a plurality of said synchronisation searches, for which the difference in timing offset between results from adjacent searches in the series is within a maximum specified value, and to estimate from said series a frequency offset between the first and second frequencies.

31. The receiver of claim 30, wherein the frequency offset estimation means is arranged, for each synchronisation search, to order the respective correlation results in order of a corresponding received signal energy.

32. The receiver of claim 31, wherein the frequency offset estimation means is arranged to find said series using only a top portion of the correlation results having the greatest received signal energy from each synchronisation search.

33. The receiver of claim 30, wherein the frequency offset estimation means is arranged to determine the frequency offset from a difference in timing offsets between at least two of the correlation results from different searches in said series.

34. The receiver of claim 30, wherein the frequency offset estimation means is arranged to determine the frequency offset from a phase determined from sums of real and imaginary parts of the correlation results in said series.

35. The receiver of claim 30, wherein the frequency offset estimation means is arranged to determining the frequency offset on the condition that a magnitude of a sum of real and imaginary parts of the correlation results in said series is above a predetermined threshold.

36. The receiver of claim 30, comprising automatic frequency correction means for using said estimation to correct for the frequency offset.

37. The receiver of claim 30, wherein the reception means is arranged to receive a synchronisation channel in said wireless signal on which is broadcast a synchronisation code, and the local signal comprises a local version of the synchronisation code.

38. The receiver of claim 37, wherein the synchronisation channel is a primary synchronisation channel of a W-CDMA cellular communications system.

39. A computer program product for estimating frequency offset between a received wireless signal timed according to a first frequency and a generated local signal timed according to a second frequency, the program comprising code which when executed by a processor is configured to perform the steps of:

performing a plurality of synchronisation searches, each search comprising obtaining a set of correlation results indicative of a correlation between the wireless signal and the local signal at different timing offsets of the wireless signal relative to the local signal;

finding a series of results, with a result from each of a plurality of said synchronisation searches, for which the difference in timing offset between results from adjacent searches in the series is within a maximum specified value; and

determining the frequency offset from said series.

40. A wireless cellular communication system comprising:

a base station arranged to transmit a wireless signal timed according to a first frequency, and

a mobile terminal comprising;

reception means arranged to receive said wireless signal;

generation means arranged to generate a local signal timed according to a second frequency;

correlation means arranged to perform a plurality of synchronisation searches, each search comprising obtaining a set of correlation results indicative of a correlation between the wireless signal and the local signal at different timing offsets of the wireless signal relative to the local signal; and

frequency offset estimation means arranged to find a series of results, with a result from each of a plurality of said synchronisation searches, for which the difference in timing offset between results from adjacent searches in the series is within a maximum specified value, and to estimate from said series a frequency offset between the first and second frequencies.