Adaptive selection of signal-detection mode

• US 10,326,633 B2
• Filed: 06/29/2016
• Issued: 06/18/2019
• Est. Priority Date: 06/29/2016
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Reial, Andres, Axnas, Johan, Rune, Johan, Sahlin, Henrik
• Primary Examiner(s): Lai, Andrew
• Assistant Examiner(s): Lee, Andrew C
• Application Number:
  US15/524,471
• Publication Number:
  US 20180278455A1
• Time in Patent Office: 1,084 Days
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals
• CPC Class Codes: H04L 27/2331 wherein the received signal is demodulated using one or more delayed versions of itself
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation

Abstract

A wireless device detects a synchronization signal by obtaining (210), from a received signal, a sequence of samples, and calculating (220) a differentially decoded sequence from the obtained sequence of samples. The wireless device correlates (230) the calculated differentially decoded sequence with a first reference sequence corresponding to the synchronization signal, at each of a plurality of time offsets, and identifies which of the plurality of time offsets results in a largest correlation result. In response to determining (240) that the largest correlation result does not meet a predetermined reliability criterion, the wireless device correlates (250) the obtained sequence of samples with a second reference sequence, at each of a plurality of time and frequency offsets, and identifies which combination of time offset and frequency offset results in a largest correlation result. The first reference sequence comprises a differentially decoded version of the second reference sequence.

Claims

1. A method, in a wireless device, for detecting time and frequency offsets for a synchronization signal in a received signal, the method comprising:

obtaining, from the received signal, a sequence of samples for a first time interval;

calculating a differentially decoded sequence from the obtained sequence of samples, each element of the differentially decoded sequence representing a phase shift between a pair of samples from the obtained sequence of samples;

correlating the calculated differentially decoded sequence with a first reference sequence corresponding to the synchronization signal, at each of a plurality of time offsets, to generate a corresponding plurality of first correlation results, and identifying which of the plurality of time offsets results in a largest one of the first correlation results;

determining that the largest one of the first correlation results does not meet a predetermined reliability criterion; and

in response to said determining, coherently detecting the synchronization signal by correlating the obtained sequence of samples with a second reference sequence, at each of a plurality of time offsets and at each of a plurality of frequency offsets, to generate a corresponding plurality of second correlation results, and identifying which combination of time offset and frequency offset results in a largest one of the second correlation results;

wherein the first reference sequence comprises a differentially decoded version of the second reference sequence.

2. The method of claim 1, wherein determining that the largest one of the first correlation results does not meet a predetermined reliability criterion comprises comparing a magnitude of the largest one of the first correlation results or a scaled magnitude of the largest one of the first correlation results to a threshold value.

3. The method of claim 2, wherein the predetermined reliability criterion comprises one of the following:

the magnitude or scaled magnitude of the largest one of the first correlation results exceeding the threshold value;

the magnitude or scaled magnitude of the largest one of the first correlation results equaling or exceeding the threshold value;

the scaled magnitude of the largest one of the first correlation results being less than the threshold value; and

the scaled magnitude of the largest one of the first correlation results being less than or equal to the threshold value.

4. The method of claim 1, wherein the second reference sequence corresponds to a Zadoff-Chu sequence.

5. The method of claim 4, wherein the synchronization signal in the received signal is a Primary Synchronization Signal in a Long-Term Evolution signal.

6. The method of claim 1, wherein determining that the largest one of the first correlation results does not meet a predetermined reliability criterion comprises:

calculating a ratio of the magnitude of the largest one of the first correlation results to a comparison value; and

determining that the ratio is less than the threshold value, where a ratio greater than the threshold value meets the predetermined reliability criterion.

7. The method of claim 6, wherein the comparison value is one of:

the magnitude of the second-largest one of the first correlation results;

the average magnitude of all of the first correlation results;

the average magnitude of all of the first correlation results other than the largest one of the first correlation results; and

an estimate of noise and interference variance.

8. The method of claim 1, wherein the method further comprises repeating the operations of claim 1 at each of a plurality of periodic intervals.

9. The method of claim 1, wherein the method further comprises, after determining that the largest one of the first correlation results does not meet a predetermined reliability criterion, performing only coherent detection of the synchronization signal during a first time period.

10. The method of claim 9, wherein a length of the first time period is based upon a measure of how far the largest one of the first correlation results is from meeting the predetermined reliability criterion.

11. The method of claim 9, wherein the first time period extends until an estimated signal quality for the received signal exceeds a predetermined signal quality threshold.

12. The method of claim 1, further comprising:

obtaining, from the received signal, a second sequence of samples for a second time interval, the second time interval differing from the first time interval;

calculating a second differentially decoded sequence from the second sequence of samples, each element of the second differentially decoded sequence representing a phase shift between a pair of samples from the second sequence of samples;

correlating the second differentially decoded sequence with the first reference sequence, at each of a plurality of time offsets, to generate a corresponding plurality of third correlation results, and identifying which of the plurality of time offsets results in a largest one of the third correlation results;

determining that the largest one of the third correlation results meets a predetermined reliability criterion; and

estimating a frequency offset by comparing the second differentially decoded sequence to the first reference sequence.

13. A wireless device arranged to detect time and frequency offsets for a synchronization signal in a received signal, the wireless device comprising:

a receiver and sampling circuit configured to obtain, from the received signal, a sequence of samples for a first time interval; and

a processing circuit configured to

calculate a differentially decoded sequence from the obtained sequence of samples, each element of the differentially decoded sequence representing a phase shift between a pair of samples from the obtained sequence of samples,

correlate the calculated differentially decoded sequence with a first reference sequence corresponding to the synchronization signal, at each of a plurality of time offsets, to generate a corresponding plurality of first correlation results, and identify which of the plurality of time offsets results in a largest one of the first correlation results,

determine, that the largest one of the first correlation results does not meet a predetermined reliability criterion, and

in response to said determining, coherently detect the synchronization signal by correlating the obtained sequence of samples with a second reference sequence, at each of a plurality of time offsets and at each of a plurality of frequency offsets, to generate a corresponding plurality of second correlation results, and identify which combination of time offset and frequency offset results in a largest one of the second correlation results;

wherein the first reference sequence comprises a differentially decoded version of the second reference sequence.

14. The wireless device of claim 13, wherein the processing circuit is configured to determine that the largest one of the first correlation results does not meet a predetermined reliability criterion by comparing a magnitude of the largest one of the first correlation results or a scaled magnitude of the largest one of the first correlation results to a threshold value.

15. The wireless device of claim 14, wherein the predetermined reliability criterion comprises one of the following:

the magnitude or scaled magnitude of the largest one of the first correlation results exceeding the threshold value;

the magnitude or scaled magnitude of the largest one of the first correlation results equaling or exceeding the threshold value;

the scaled magnitude of the largest one of the first correlation results being less than the threshold value; and

the scaled magnitude of the largest one of the first correlation results being less than or equal to the threshold value.

16. The wireless device of claim 13, wherein the second reference sequence corresponds to a Zadoff-Chu sequence.

17. The wireless device of claim 16, wherein the synchronization signal in the received signal is a Primary Synchronization Signal in a Long-Term Evolution signal.

18. The wireless device of claim 13, wherein the processing circuit is configured to determine that the largest one of the first correlation results does not meet a predetermined reliability criterion by:

calculating a ratio of the magnitude of the largest one of the first correlation results to a comparison value; and

determining that the ratio is less than the threshold value, where a ratio greater than the threshold value meets the predetermined reliability criterion.

19. The wireless device of claim 18, wherein the comparison value is one of:

the magnitude of the second-largest one of the first correlation results;

the average magnitude of all of the first correlation results;

the average magnitude of all of the first correlation results other than the largest one of the first correlation results; and

an estimate of noise and interference variance.

20. The wireless device of claim 13, wherein the processing circuit is configured to repeat the operations of claim 13 at each of a plurality of periodic intervals.

21. The wireless device of claim 13, wherein the processing circuit is configured to, after determining meets the predetermined reliability criterion, perform only coherent detection of the synchronization signal during a first time period.

22. The wireless device of claim 21, wherein a length of the first time period is based upon a measure of how far the largest one of the first correlation results is from meeting the predetermined reliability criterion.

23. The wireless device of claim 21, wherein the first time period extends until an estimated signal quality for the received signal exceeds a predetermined signal quality threshold.

24. The wireless device of claim 13, wherein the processing circuit is configured to:

obtain, from the received signal, a second sequence of samples for a second time interval;

calculate a second differentially decoded sequence from the second sequence of samples, each element of the second differentially decoded sequence representing a phase shift between a pair of samples from the second sequence of samples;

correlate the second differentially decoded sequence with the first reference sequence, at each of a plurality of time offsets, to generate a corresponding plurality of third correlation results, and identifying which of the plurality of time offsets results in a largest one of the third correlation results;

determine that the largest one of the third correlation results meets a predetermined reliability criterion; and

estimate a frequency offset by comparing the second differentially decoded sequence to the first reference sequence.

25. A non-transitory computer-readable medium comprising, stored thereupon, a computer program product comprising computer program instructions for execution by a wireless device, wherein the computer program instructions are arranged such that, when executed by a processing circuit in the wireless device, the computer program instructions cause the wireless device to detect time and frequency offsets for a synchronization signal in a received signal by:

obtaining, from the received signal, a sequence of samples for a first time interval;

calculating a differentially decoded sequence from the obtained sequence of samples, each element of the differentially decoded sequence representing a phase shift between a pair of samples from the obtained sequence of samples;

correlating the calculated differentially decoded sequence with a first reference sequence corresponding to the synchronization signal, at each of a plurality of time offsets, to generate a corresponding plurality of first correlation results, and identify which of the plurality of time offsets results in a largest one of the first correlation results;

determining that the largest one of the first correlation results does not meet a predetermined reliability criterion; and

in response to said determining, coherently detecting the synchronization signal by correlating the obtained sequence of samples with a second reference sequence, at each of a plurality of time offsets and at each of a plurality of frequency offsets, to generate a corresponding plurality of second correlation results, and identify which combination of time offset and frequency offset results in a largest one of the second correlation results;

wherein the first reference sequence comprises a differentially decoded version of the second reference sequence.