Timing acquisition and mode and guard detection for an OFDM transmission

• US 8,315,191 B2
• Filed: 03/28/2006
• Issued: 11/20/2012
• Est. Priority Date: 09/20/2005
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Glazko, Serguei A., Patel, Shimman, Reeves, Jonathan R.
• Primary Examiner(s): Thier, Michael
• Assistant Examiner(s): Alia, Curtis A
• Application Number:
  US11/392,266
• Publication Number:
  US 20070086329A1
• Time in Patent Office: 2,429 Days
• Field of Search: 370203-208, 370310-350, 455/403, 455/73, 455/88, 455/550.1, 455/553.1, 455/561, 455/562.1, 375/219, 375/295, 375/299, 375/345
• US Class Current: 370/310
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window
• CPC Class Codes: H04L 27/2666 Acquisition of further OFDM parameters, e.g. bandwidth, subcarrier spacing, or guard interval length
• CPC Class Codes: H04N 21/2383 Channel coding or modulation of digital bit-stream, e.g. QPSK modulation arrangements for detecting or preventing errors in the information received by adapting the channel coding H04L1/0009; analogue front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 21/4382 Demodulation or channel decoding, e.g. QPSK demodulation analog front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002

Abstract

Techniques for detecting mode and guard length and estimating timing offset for an OFDM transmission are described. Multiple hypotheses for different combinations of mode and guard length that might have been used for the OFDM transmission are evaluated. For each hypothesis, correlation is performed on received samples for a hypothesized guard interval to obtain correlation results. The energy of the hypothesized guard interval is determined. A first metric is derived based on the correlation results and the energy. The first metric may be filtered, e.g., averaged. Noise is estimated, e.g., based on a set of elements for the filtered first metric at locations determined by an estimated timing offset for the hypothesis. A second metric is derived based on the filtered first metric and the estimated noise. The second metric for all hypotheses may be used to determine the mode, guard length, and timing offset for the OFDM transmission.

Claims

1. An apparatus comprising:

at least one processor configured to;

perform correlation for a hypothesized guard interval in a transmission received from a transmitter to obtain correlation results for the transmission, to estimate noise, to derive a metric by combining the correlation results and the estimated noise, and to use the metric for detection of at least one parameter for the transmission; and

determine energy for the hypothesized guard interval, to derive a first metric based on the correlation results and the energy, to filter the first metric, to estimate the noise based on a set of elements for the filtered first metric, and to derive the metric based on the filtered first metric and the estimated noise; and

a memory coupled to the at least one processor;

wherein an actual length of a guard interval used by the transmitter for the transmission is unknown at said apparatus.

2. The apparatus of claim 1, wherein the at least one processor is configured to determine energy for the hypothesized guard interval and to derive the metric further based on the energy.

3. A method comprising:

performing correlation for a hypothesized guard interval in a transmission received from a transmitter to obtain correlation results for the transmission;

estimating noise;

deriving a metric by combining the correlation results and the estimated noise; and

using the metric for detection of at least one parameter for the transmission;

determining energy for the hypothesized guard interval to derive a first metric based on the correlation results and the energy;

filtering the first metric to estimate the noise based on a set of elements for the filtered first metric; and

deriving the metric based on the filtered first metric and the estimated noise;

wherein an actual length of a guard interval used by the transmitter for the transmission is unknown during performance of said method.

4. The method of claim 3, further comprising:

determining energy for the hypothesized guard interval, and wherein the deriving the metric comprises deriving the metric based on the correlation results, the energy, and the estimated noise.

5. An apparatus comprising:

means for performing correlation for a hypothesized guard interval in a transmission received from a transmitter to obtain correlation results for the transmission;

means for estimating noise;

means for deriving a metric by combining the correlation results and the estimated noise; and

means for using the metric for detection of at least one parameter for the transmission;

means for determining energy for the hypothesized guard interval to derive a first metric based on the correlation results and the energy;

means for filtering the first metric to estimate the noise based on a set of elements for the filtered first metric; and

means for deriving the metric based on the filtered first metric and the estimated noise;

wherein an actual length of a guard interval used by the transmitter for the transmission is unknown at said apparatus.

6. The apparatus of claim 5, further comprising:

means for determining energy for the hypothesized guard interval, and wherein the means for deriving the metric comprises means for deriving the metric based on the correlation results, the energy, and the estimated noise.

7. A non-transitory processor readable media for storing instructions operable on a processor to:

perform correlation for a hypothesized guard interval in a transmission received from a transmitter to obtain correlation results for the transmission;

estimate noise;

derive a metric based on by combining the correlation results and the estimated noise; and

use the metric for detection of at least one parameter for the transmission; and

determine energy for the hypothesized guard interval to derive a first metric based on the correlation results and the energy;

filter the first metric to estimate the noise based on a set of elements for the filtered first metric; and

further derive the metric based on the filtered first metric and the estimated noise;

wherein an actual length of a guard interval used by the transmitter for the transmission is unknown to the processor.

8. The processor readable media of claim 7, and further for storing instructions operable to:

determine energy for the hypothesized guard interval, and wherein the deriving the metric comprises deriving derive the metric based on the correlation results, the energy, and the estimated noise.

9. An apparatus comprising:

at least one processor configured to derive at least one metric by combining at least one of noise information and energy information associated with an OFDM transmission with correlation results associated with samples of the OFDM transmission, to detect a mode and a guard length for the OFDM transmission based on the at least one metric, and to process the samples in accordance with the detected mode and guard length, wherein the mode indicates the duration of a useful portion of each OFDM symbol in the OFDM transmission and the guard length indicates the duration of a guard interval for each OFDM symbol, wherein an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown to said apparatus prior to said detection, and wherein the OFDM transmission is received from a transmitter via a communication channel; and

a memory coupled to the at least one processor;

wherein the at least one processor is further configured to;

determine energy for at least one hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission to derive a first metric based on the correlation results and the energy;

filter the first metric to estimate the noise based on a set of elements for the filtered first metric; and

derive the at least one metric based on the filtered first metric and the estimated noise.

10. The apparatus of claim 9, wherein the at least one processor is configured to derive the at least one metric for multiple hypotheses, each hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission, to identify a most likely hypothesis based on the at least one metric, and to provide the mode and guard length for the identified hypothesis as the detected mode and guard length for the OFDM transmission.

11. The apparatus of claim 10, wherein for each of the multiple hypotheses the at least one processor is configured to perform correlation for a guard interval for the hypothesis to obtain correlation results for the hypothesis, to estimate noise for the hypothesis, and to derive the at least one metric for the hypothesis based on the correlation results and the estimated noise for the hypothesis.

12. The apparatus of claim 11, wherein for each of the multiple hypotheses the at least one processor is configured to determine energy of the guard interval for the hypothesis and to derive the at least one metric for the hypothesis further based on the energy.

13. The apparatus of claim 9, wherein the at least one processor is configured to estimate a timing offset for the OFDM transmission based on the at least one metric, and to process the samples further based on the estimated timing offset.

14. A method comprising:

deriving at least one metric by combining at least one of noise information and energy information associated with an OFDM transmission with correlation results associated with samples of the OFDM transmission, wherein the OFDM transmission is received from a transmitter via a communication channel;

detecting a mode and a guard length for the OFDM transmission based on the at least one metric, the mode indicating the duration of a useful portion of each OFDM symbol in the OFDM transmission and the guard length indicating the duration of a guard interval for each OFDM symbol, wherein an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown during performance of said method prior to said detecting; and

processing the samples in accordance with the detected mode and guard length; and

further comprising

determining energy for at least one hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission to derive a first metric based on the correlation results and the energy;

filtering the first metric to estimate the noise based on a set of elements for the filtered first metric; and

deriving the at least one metric based on the filtered first metric and the estimated noise.

15. The method of claim 14, wherein the deriving the at least one metric comprises deriving the at least one metric for multiple hypotheses, each hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission, and wherein the detecting the mode and the guard length comprises

identifying a most likely hypothesis based on the at least one metric, and

providing the mode and guard length for the identified hypothesis as the detected mode and guard length for the OFDM transmission.

16. The method of claim 14, wherein the deriving the at least one metric comprises

performing correlation for a guard interval for the hypothesis to obtain correlation results for the hypothesis,

estimating noise for the hypothesis, and

deriving the at least one metric for the hypothesis based on the correlation results and the estimated noise for the hypothesis.

17. An apparatus comprising:

means for deriving at least one metric by combining at least one of noise information and energy information associated with an OFDM transmission with correlation results associated with samples of the OFDM transmission, wherein the OFDM transmission is received from a transmitter via a communication channel;

means for detecting a mode and a guard length for the OFDM transmission based on the at least one metric, the mode indicating the duration of a useful portion of each OFDM symbol in the OFDM transmission and the guard length indicating the duration of a guard interval for each OFDM symbol, wherein an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown to said apparatus prior to said detecting; and

means for processing the samples in accordance with the detected mode and guard length; and

further comprising;

means for determining energy for at least one hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission to derive a first metric based on the correlation results and the energy;

means for filtering the first metric to estimate the noise based on a set of elements for the filtered first metric; and

means for deriving the at least one metric based on the filtered first metric and the estimated noise.

18. The apparatus of claim 17, wherein the means for deriving the at least one metric comprises means for deriving the at least one metric for multiple hypotheses, each hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission, and wherein the means for detecting the mode and the guard length comprises

means for identifying a most likely hypothesis based on the at least one metric, and

means for providing the mode and guard length for the identified hypothesis as the detected mode and guard length for the OFDM transmission.

19. The apparatus of claim 17, wherein the means for deriving the at least one metric comprises

means for performing correlation for a guard interval for the hypothesis to obtain correlation results for the hypothesis,

means for estimating noise for the hypothesis, and

means for deriving the at least one metric for the hypothesis based on the correlation results and the estimated noise for the hypothesis.

20. An apparatus comprising:

at least one processor configured to derive a first metric for each of multiple hypotheses based on samples for an OFDM transmission received from a transmitter via a communication channel, each hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission, to estimate a timing offset of the OFDM transmission for each hypothesis based on the first metric for the hypothesis, to derive a second metric for each hypothesis by combining the first metric and the estimated timing offset for the hypothesis, and to detect a mode and a guard length for the OFDM transmission based on the second metric, wherein an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown to said apparatus prior to said detection;

for each of the multiple hypotheses the at least one processor is configured to filter the first metric for the hypothesis, to estimate noise for the hypothesis based on the filtered first metric and the estimated timing offset for the hypothesis, and to derive the second metric for the hypothesis based on the filtered first metric and the estimated noise for the hypothesis; and

a memory coupled to the at least one processor.

21. The apparatus of claim 20, wherein for each of the multiple hypotheses the at least one processor is configured to perform correlation for a guard interval for the hypothesis to obtain correlation results for the hypothesis, to determine energy of the guard interval for the hypothesis, and to derive the first metric for the hypothesis based on the correlation results and the energy for the hypothesis.

22. The apparatus of claim 21, wherein for each of the multiple hypotheses the at least one processor is configured to estimate a timing offset for the hypothesis, and to estimate the noise for the hypothesis based on a set of elements for the filtered first metric at locations determined by the estimated timing offset for the hypothesis.

23. The apparatus of claim 20, wherein the at least one processor is configured to estimate a timing offset for the OFDM transmission based on the second metric.

24. An apparatus comprising:

means for deriving a first metric for each of multiple hypotheses based on samples for an OFDM transmission received from a transmitter via a communication channel, each hypothesis corresponding to a different combination of mode and guard length hypothesized for the OFDM transmission;

means for estimating a timing offset of the OFDM transmission for each hypothesis based on the first metric for the hypothesis;

means for deriving a second metric for each hypothesis by combining the first metric and the estimated timing offset for the hypothesis; and

means for detecting a mode and a guard for the OFDM transmission based on the second metric;

means for filtering the first metric for the hypothesis,

means for estimating noise for the hypothesis based on the filtered first metric and the estimated timing offset for the hypothesis, and

means for deriving the second metric for the hypothesis based on the filtered first metric and the estimated noise for the hypothesis;

wherein an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown to said apparatus prior to said detecting.

25. The apparatus of claim 24, wherein the means for deriving the first metric comprises

means for performing correlation for a guard interval for the hypothesis to obtain correlation results for the hypothesis,

means for determining energy of the guard interval for the hypothesis, and

means for deriving the first metric for the hypothesis based on the correlation results and the energy for the hypothesis.

26. An apparatus comprising:

at least one processor configured to compute at least one parameter for each of multiple hypotheses based on samples for an OFDM transmission received from a transmitter via a communication channel, wherein each hypothesis corresponds to a different combination of mode and guard length hypothesized for the OFDM transmission, and to derive a metric for each of the multiple hypotheses based on the at least one parameter for the hypothesis, wherein for at least one hypothesis a fraction of the samples is used to compute the at least one parameter or a fraction of elements available for the metric is stored, and wherein for each of the at least one hypothesis the at least one processor is configured to perform correlation using a fraction of samples available for the hypothesis, and an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown to said apparatus; and

wherein the metric for at least one hypothesis of the multiple hypotheses may be further derived by;

determining energy for a hypothesized guard interval to derive a first metric based on the correlation results and the energy;

filtering the first metric to estimate the noise based on a set of elements for the filtered first metric; and

deriving the metric based on the filtered first metric and the estimated noise; and

a memory coupled to the at least one processor.

27. The apparatus of claim 26, wherein for each of the at least one hypothesis the at least one processor is configured to perform correlation using a fraction of samples taken from across a hypothesized guard interval for the hypothesis.

28. The apparatus of claim 26, wherein the multiple hypotheses cover at least two different guard lengths, and wherein the at least one processor is configured to perform correlation on equal number of samples for the multiple hypotheses.

29. The apparatus of claim 26, wherein for each of the at least one hypothesis the at least one processor is configured to derive the metric for a fraction of timing offsets possible for the hypothesis.

30. The apparatus of claim 26, wherein for each of the at least one hypothesis the at least one processor is configured to derive the metric with equal time resolution relative to OFDM symbol size for the multiple hypotheses.

31. An apparatus comprising:

means for computing at least one parameter for each of multiple hypotheses based on samples for an OFDM transmission received from a transmitter via a communication channel, wherein each hypothesis corresponds to a different combination of mode and guard length hypothesized for the OFDM transmission, and further including means for performing correlation using a fraction of samples available for the hypothesis; and

means for deriving a metric for each of the multiple hypotheses based on the at least one parameter for the hypothesis, wherein for at least one hypothesis a fraction of the samples is used to compute the at least one parameter or a fraction of elements available for the metric is stored, and wherein an actual mode and an actual guard length used by the transmitter for the OFDM transmission are unknown to said apparatus; and

wherein the means for deriving the metric further comprises;

means for determining energy for a hypothesized guard interval to derive a first metric based on the correlation results and the energy;

means for filtering the first metric to estimate the noise based on a set of elements for the filtered first metric; and

means for deriving the metric based on the filtered first metric and the estimated noise.

32. The apparatus of claim 31, wherein the means for deriving the metric comprises means for deriving the metric for a fraction of timing offsets possible for the hypothesis.

33. An apparatus comprising:

at least one processor configured to perform correlation on samples for an OFDM transmission received from a transmitter via a communication channel to obtain first correlation results for a first hypothesis with a first guard length, and to combine the first correlation results to obtain second correlation results for a second hypothesis with a second guard length that is longer than the first guard length; and

the at least one processor configured to compute energies for a first guard interval for the first hypothesis, and to combine the energies for the first guard interval to obtain energies for a second guard interval for the second hypothesis; and

a memory coupled to the at least one processor;

wherein an actual guard length used by the transmitter for the OFDM transmission is unknown to said apparatus.

34. The apparatus of claim 33, wherein the second guard length is twice as long as the first guard length.

35. The apparatus of claim 33, wherein the at least one processor is configured to combine the second correlation results to obtain third correlation results for a third hypothesis with a third guard length that is longer than the second guard length.