Method and apparatus for frequency scan in Narrow Band—Internet of Things (NB-IoT) systems

• US 10,455,485 B2
• Filed: 04/25/2018
• Issued: 10/22/2019
• Est. Priority Date: 04/28/2017
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Abedini, Navid, Hsu, Chun-Hao, Mathur, Amit, Uppala, Sathyadev Venkata, Tam, Wingip
• Primary Examiner(s): Holliday, Jaime M
• Application Number:
  US15/963,074
• Publication Number:
  US 20180317161A1
• Time in Patent Office: 545 Days
• CPC Class Codes: H04J 11/0086 Search parameters, e.g. search strategy, accumulation length, range of search, thresholds code acquisition in DSSS H04B1/7075
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 48/18 Selecting a network or a communication service
• CPC Class Codes: H04W 48/20 Selecting an access point
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

Techniques for efficient and accurate frequency scans in Narrow Band-Internet of Things (NB-IoT) systems are provided. In an example, a user equipment (UE) searches for a cell on at least one of a plurality of frequency rasters based on a multi-stage search technique, wherein each stage of the multi-stage search searches the at least one frequency raster based on a different set of search parameters. The UE detects a cell on at least one of the frequency rasters based on the searching.

Claims

1. A method for wireless communication by a User Equipment (UE), comprising:

searching for a cell on a plurality of frequency rasters based on a multi-stage search,

wherein the UE, in each stage of the multi-stage search, is configured to search the plurality of frequency rasters for a different dwell time, the dwell time corresponding to an amount of time the UE searches a frequency raster for, wherein the dwell time for each stage of the multi-stage search is configured to search cells associated with a different range of Signal to Noise Ratios (SNRs), wherein the UE searches the plurality of frequency rasters one stage at a time starting from a stage corresponding to the smallest dwell time and in ascending order of dwell times; and

detecting a cell on at least one of the plurality of frequency rasters based on the searching.

2. The method of claim 1, wherein the UE terminates the searching in response to detecting the cell.

3. The method of claim 1, further comprising:

upon detecting a cell x on frequency raster n in stage k of the multi-stage search, determining if the detected cell x satisfies a performance criterion;

determining that the cell x is correctly detected on raster n, if the detected cell satisfies the performance criterion; and

performing additional processing if the detected cell x fails to satisfy the performance criterion.

4. The method of claim 3, wherein the performance criterion is a function of one or a combination of two or more performance metrics of a set of performance metrics of the detected cell, the set of performance metrics including at least one of:

quality of the detected cell, identity of the detected cell, a raster index of the detected cell, a stage index, timing of the detected cell, or frequency of the detected cell.

5. The method of claim 3, wherein the performance criterion includes a Signal to Noise Ratio (SNR) of the detected cell being higher than a threshold SNR, the threshold SNR being a function of:

a cell identity (ID) of the detected cell, a raster index of the detected cell, a stage index of the stage of the multi-stage search during which the cell was detected, or combinations thereof.

6. The method of claim 5, wherein the cell ID of the detected cell is from a first set of cell IDs assigned a first threshold SNR, the first threshold SNR chosen as the threshold SNR for the performance criterion, wherein the first threshold SNR is different from a second threshold SNR assigned to a second set of cell IDs different from the first set.

7. The method of claim 3, wherein at least one parameter for performing the additional processing is a function of one or more performance metrics of the detected cell.

8. The method of claim 7, wherein the performance metrics include quality of the detected cell, identify of the detected cell, a raster index of the detected cell, a stage index, timing of the detected cell, frequency of the detected cell, or combinations thereof.

9. The method of claim 3, wherein the additional processing includes further searching for a cell on at least one frequency raster adjacent to the frequency raster n, wherein the further searching is limited to at least one of a timing window or a frequency window based on at least one of an estimated timing or an estimated frequency of the detected cell.

10. The method of claim 3, wherein the additional processing includes further searching for a cell on at least one frequency raster adjacent to the frequency raster n, and wherein a dwell time for the further searching is a function of at least one of a stage of the multi-stage search in which the cell was detected or an SNR of the detected cell,

the dwell time corresponding to an amount of time the UE searches a frequency raster for.

11. The method of claim 3, wherein the additional processing includes further searching for a cell on at least one frequency raster adjacent to the frequency raster n, wherein the further searching is limited to a subset of cell identities (IDs) as a function of at least one of a cell ID of the detected cell or an SNR of the detected cell.

12. The method of claim 3, wherein the additional processing comprises:

searching for a cell on at least one frequency raster adjacent to the frequency raster n;

detecting a cell y based on the searching on the at least one adjacent frequency raster;

comparing performance metrics of the cell y with performance metrics of cell x; and

determining cell y or cell x as a correctly detected cell on a corresponding frequency raster, based on the comparison.

13. The method of claim 12, wherein the determining the cell y or cell x comprises designating one of cell y or cell x with a stronger detected SNR as the correctly detected cell.

14. The method of claim 12, wherein the determining the cell y or cell x is a function of cell identities of the cells y and x.

15. The method of claim 12, wherein the determining the cell y or cell x is a function of relative timing of the cells y and x.

16. The method of claim 3, wherein the additional processing comprises:

searching for a cell on at least one frequency raster adjacent to the frequency raster n;

determining that the cell is correctly detected on the frequency raster n, if no cell is detected on the at least one adjacent frequency raster.

17. The method of claim 1, wherein searching the plurality of frequency rasters comprises searching each of the plurality of frequency rasters, and wherein searching each of the plurality of frequency rasters comprises:

processing multiple instances of a synchronization signal received on the frequency raster of the plurality of frequency rasters based on a set of threshold values.

18. The method of claim 17, wherein the set of threshold values includes a threshold value corresponding to each of the multiple instances.

19. The method of claim 18, wherein threshold values in the set are arranged in descending order, the highest threshold value corresponding to a first processing instance.

20. The method of claim 17, wherein the synchronization signal includes at least one of a Primary Synchronization Signal (PSS) or a Secondary Synchronization Signal (SSS).

21. The method of claim 17, wherein processing the multiples instances of the synchronization signal comprises:

for each instance, correlating received samples of the instance with a set of reference signals; and

combining results of the correlating for the multiple instances; and

comparing a result of the combining with one of the set of threshold values.

22. The method of claim 17, wherein each of the multiple instances of the synchronization signal corresponds to a combination of two or more parameters including time, frequency, cell identity, or x msec boundaries.

23. An apparatus for wireless communication by a User Equipment (UE), comprising:

means for searching for a cell on a plurality of frequency rasters based on a multi-stage search,

wherein the means for searching, in each stage of the multi-stage search, is configured to search the plurality of frequency rasters for a different dwell time, the dwell time corresponding to an amount of time a frequency raster is searched for, wherein the dwell time for each stage of the multi-stage search is configured to search cells associated with a different range of Signal to Noise Ratios (SNRs), wherein the means for searching searches the plurality of frequency rasters one stage at a time starting from a stage corresponding to the smallest dwell time and in ascending order of dwell times; and

means for detecting a cell on at least one of the plurality of frequency rasters based on the searching.

24. An apparatus for wireless communication by a User Equipment (UE), comprising:

at least one processor configured to;

search for a cell on of a plurality of frequency rasters based on a multi-stage search,

wherein the at least one processor is configured to, in each stage of the multi-stage search, search the plurality of frequency rasters for a different dwell time, the dwell time corresponding to an amount of time the UE searches a frequency raster for, wherein the dwell time for each stage of the multi-stage search is configured to search cells associated with a different range of Signal to Noise Ratios (SNRs), wherein the plurality of frequency rasters are searched one stage at a time starting from a stage corresponding to the smallest dwell time and in ascending order of dwell times; and

detect a cell on at least one of the plurality of frequency rasters based on the searching; and

a memory coupled to the at least one processor.

25. A non-transitory computer-readable medium for wireless communication by a User Equipment (UE), the computer-readable medium storing instructions which when processed by at least one processor performs a method comprising:

searching for a cell on of a plurality of frequency rasters based on a multi-stage search,

wherein the searching comprises, in each stage of the multi-stage search, searching the plurality of frequency rasters for a different dwell time, the dwell time corresponding to an amount of time a frequency raster is searched for, wherein the dwell time for each stage of the multi-stage search is configured to search cells associated with a different range of Signal to Noise Ratios (SNRs), wherein the plurality of frequency rasters are searched one stage at a time starting from a stage corresponding to the smallest dwell time and in ascending order of dwell times; and

detecting a cell on at least one of the plurality of frequency rasters based on the searching.