Pilot frequency acquisition based on a window of data samples

• US 20030143951A1
• Filed: 01/30/2003
• Published: 07/31/2003
• Est. Priority Date: 01/31/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Patel, Shimman, Challa, Raghu, Roh, Mark Charles
• Granted Patent: US 6,912,244 B2
• Time in Patent Office: Days
• US Class Current: 455/20
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 2027/0055 single phase
• CPC Class Codes: H04L 2027/0095 in a preamble or similar structure
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

Techniques to acquire the frequency of a signal instance based on a window of data samples covering a time period shorter than the time needed to achieve frequency lock. The window of data samples is initially captured and stored to a sample buffer. A segment of data samples is then retrieved from the sample buffer for processing. The retrieved data samples are rotated by a current frequency error estimate to provide frequency-translated data samples, which are further processed to provide one or more pilot symbols. An updated frequency error estimate for the frequency-translated data samples is then derived based on the pilot symbols using a frequency control loop. The window of data samples is processed for a number of iterations until frequency acquisition is achieved for the signal instance or termination is reached. For each iteration, one segment is processed at a time and typically in sequential order.

Claims

1. A device operable to acquire frequency of a signal instance received in a wireless communication system, comprising:

a rotator operative to receive a segment of data samples and rotate the data samples by a current frequency error estimate to provide frequency-translated data samples, wherein the segment of data samples is a portion of a window of data samples having included therein the signal instance; and

a frequency control loop operative to derive an updated frequency error estimate based on the frequency-translated data samples, wherein the rotator and frequency control loop are operative to process the window of data samples a plurality of times until frequency acquisition is achieved for the signal instance or termination is reached.

2. The device of claim 1, wherein the duration of time covered by the window of data samples is shorter than the duration of time required by the frequency control loop to acquire the frequency of the signal instance.

3. The device of claim 1, wherein the window of data samples is processed one segment at a time and in a sequential order, from start to end of the window, for each of the plurality of times.

4. The device of claim 1, further comprising:

a despreader operative to process the data samples in the segment to recover a pilot for the signal instance, and wherein the updated frequency error estimate is derived based on the recovered pilot.

5. The device of claim 1, wherein the frequency control loop includes

a frequency discriminator operative to determine a frequency error metric based on one or more pilot symbols obtained for the segment of data samples, and

a loop filter operative to filter the frequency error metric to provide the updated frequency error estimate.

6. The device of claim 1, further comprising:

a frequency acquisition detector operative to detect for frequency acquisition based on the frequency-translated data samples.

7. The device of claim 6, wherein the frequency acquisition detector includes a received signal strength indicator (RSSI).

8. The device of claim 1, further comprising:

a sample buffer operative to store the window of data samples.

9. The device of claim 1, wherein the frequency-translated data samples are stored back in place of the corresponding data samples.

10. The device of claim 1, wherein the wireless communication system is a CDMA system.

11. The device of claim 1, wherein the window of data samples covers a paging indicator (PI) bit for a quick paging channel.

22. The device of claim 1, wherein the means for deriving includes

means for determining a frequency error metric based on one or more pilot symbols obtained for the segment of data samples, and

means for filtering the frequency error metric to provide the updated frequency error estimate.

12. A device operable to acquire a parameter of a signal instance received in a wireless communication system, comprising:

a processing unit operative to receive a segment of data samples and process the data samples in accordance with a current error estimate to provide corrected data samples, wherein the segment of data samples is a portion of a window of data samples having included therein the signal instance; and

a control loop operative to derive an updated error estimate based on the corrected data samples, wherein the processing unit and control loop are operative to process the window of data samples a plurality of times until acquisition of the parameter is achieved for the signal instance or termination is reached.

13. The device of claim 12, wherein the parameter to be acquired is frequency.

14. The device of claim 12, wherein the parameter to be acquired is sample timing.

15. The device of claim 12, wherein the duration of time covered by the data sample window is shorter than the duration of time required by the control loop to acquire the parameter.

16. An integrated circuit comprising:

a rotator operative to receive and rotate a segment of data samples in accordance with a current frequency error estimate to provide frequency-translated data samples, wherein the segment of data samples is a portion of a window of data samples having included therein a signal instance to be processed; and

a frequency control loop operative to derive an updated frequency error estimate based on the frequency-translated data samples, wherein the rotator and frequency control loop are operative to process the window of data samples a plurality of times until frequency acquisition is achieved for the signal instance or termination is reached.

17. The integrated circuit of claim 16, further comprising:

a sample buffer operative to store the window of data samples.

18. The integrated circuit of claim 16, further comprising:

a frequency acquisition detector operative to provide an indication of frequency acquisition based on the frequency-translated data samples.

19. The integrated circuit of claim 18, wherein the frequency acquisition detector includes a received signal strength indicator (RSSI).

20. An apparatus in a wireless communication system, comprising:

means for rotating a segment of data samples in accordance with a current frequency error estimate to provide frequency-translated data samples, wherein the segment of data samples is a portion of a window of data samples having included therein a signal instance whose frequency is to be acquired; and

means for deriving an updated frequency error estimate based on the frequency-translated data samples, wherein the means for rotating and means for deriving are configured to operate on the window of data samples a plurality of time until frequency acquisition is achieved for the signal instance or termination is reached.

21. The apparatus of claim 20, further comprising:

means for storing the window of data samples.

23. A method of acquiring frequency of a signal instance received in a wireless communication system, comprising:

receiving a segment of data samples for processing, wherein the segment of data samples is a portion of a window of data samples having included therein the signal instance;

rotating the data samples in accordance with a current frequency error estimate to provide frequency-translated data samples;

deriving an updated frequency error estimate based on the frequency-translated data samples; and

repeating the receiving, rotating, and deriving a plurality of times through the window of data samples until frequency acquisition is achieved for the signal instance or termination is reached.

24. The method of claim 23, wherein the deriving includes

processing the data samples to provide one or more pilot symbols,

determining a frequency error metric based on the one or more pilot symbols, and

filtering the frequency error metric to provide the updated frequency error estimate.

25. The method of claim 23, further comprising:

determining frequency acquisition based on the frequency-translated data samples.

26. A method of acquiring frequency of a signal instance in a CDMA communication system, comprising:

receiving a segment of data samples for processing, wherein the segment of data samples is a portion of a window of data samples having included therein the signal instance, and wherein the duration of time covered by the window is shorter than the time required to achieve frequency acquisition;

rotating the data samples in accordance with a current frequency error estimate to provide frequency-translated data samples;

processing the frequency-translated data samples to provide one or more pilot symbols;

deriving an updated frequency error estimate based on the one or more pilot symbols; and

repeating the receiving, rotating, processing, and deriving a plurality of times through the window of data samples until frequency acquisition is achieved for the signal instance or termination is reached, wherein the window of data samples is processed one segment at a time and in a sequential order, from start to end of the window, for each of the plurality of times.

27. A method of recovering a paging indicator (PI) bit for a quick paging channel in a CDMA communication system, comprising:

storing a window of data samples covering the PI bit;

acquiring frequency of a signal instance by processing the window of data samples a plurality of times until frequency acquisition is achieved for the signal instance; and

processing frequency-corrected data samples for the signal instance to recover the PI bit.

28. The method of claim 27, further comprising:

powering down front-end circuitry after the window of data samples have been stored.

29. The method of claim 28, wherein the frequency acquisition and the recovery of the PI bit are performed offline with the front-end circuitry powered down.

30. A memory communicatively coupled to a digital signal processing device (DSPD) capable of interpreting digital information to:

receive a segment of data samples for processing, wherein the segment of data samples is a portion of a window of data samples having included therein a signal instance having a frequency to be acquired;

rotate the data samples in accordance with a current frequency error estimate to provide frequency-translated data samples;

derive an updated frequency error estimate based on the frequency-translated data samples; and

repeat processing of the window of data samples a plurality of times until frequency acquisition is achieved for the signal instance or termination is reached.

31. A computer program product for acquiring a frequency of a signal instance received in a wireless communication system, comprising:

code for receiving a segment of data samples for processing, wherein the segment of data samples is a portion of a window of data samples having included therein the signal instance;

code for rotating the data samples in accordance with a current frequency error estimate to provide frequency-translated data samples;

code for deriving an updated frequency error estimate based on the frequency-translated data samples;

code for repeating the receiving, rotating, and deriving a plurality of times through the window of data samples until frequency acquisition is achieved for the signal instance or termination is reached; and

a computer-usable medium for storing the codes;

32. A device in a wireless communication system, comprising:

a sample buffer operative to store a window of data samples for a received signal; and

a digital signal processor including

a rotator operative to receive and rotate a segment of data samples in accordance with a current frequency error estimate for a signal instance in the received signal to provide frequency-translated data samples, wherein the segment of data samples is a portion of the window of data samples, and

a frequency control loop operative to derive an updated frequency error estimate based on the frequency-translated data samples, wherein the rotator and frequency control loop are operative to process the window of data samples a plurality of times until frequency acquisition is achieved for the signal instance or termination is reached.

33. The device of claim 32, further comprising:

a front-end unit operative to process the received signal to provide the window of data samples.

34. The device of claim 33, wherein the front-end unit is powered down after the window of data samples has been obtained, and wherein the digital signal processor is operative to perform frequency acquisition offline with the front-end unit powered down