SUCCESSIVE DETECTION AND CANCELLATION FOR CELL PILOT DETECTION

• US 20100029213A1
• Filed: 07/31/2009
• Published: 02/04/2010
• Est. Priority Date: 08/01/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Wang, Michael M.
• Granted Patent: US 9,237,515 B2
• Time in Patent Office: Days
• US Class Current: 455/63.100
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

Techniques for performing cell detection with successive detection and cancellation (SDC) are described. For SDC, pilots from stronger cells may be canceled from a received signal at a user equipment (UE) so that weaker cells may be detected as a result of reduced interference from the stronger cells. In one design, a UE processes a received signal to detect for a cell and determines whether the detected cell is sufficiently strong. If the cell is sufficiently strong, then the UE cancels the interference due to the detected cell from the received signal and further processes an interference-canceled signal to detect for another cell. The UE may detect for cells in a set of cells in a sequential order, from the strongest cell to the weakest cell. The UE may terminate detection when a cell not sufficiently strong is detected or when all cells in the set are detected.

Claims

1. A method of detecting for cells in a wireless network, comprising:

processing a received signal to detect for a cell;

determining whether the detected cell is sufficiently strong; and

if the detected cell is sufficiently strong,

canceling interference due to the detected cell from the received signal to obtain an interference-canceled signal, and

processing the interference-canceled signal to detect for another cell.

2. The method of claim 1, wherein the processing the received signal comprises processing the received signal to detect for a strongest cell in a set of cells.

3. The method of claim 2, wherein the processing the interference-canceled signal comprises

processing the interference-canceled signal to detect for a second strongest cell in the set of cells,

determining whether the second strongest cell is sufficiently strong, and

if the second strongest cell is sufficiently strong,

canceling interference due to the second strongest cell from the interference-canceled signal to obtain a second interference-canceled signal, and

processing the second interference-canceled signal to detect for a next strongest cell in the set of cells.

4. The method of claim 2, wherein the cells in the set are detected in a sequential order, from the strongest cell to a weakest cell, and wherein detection terminates when a cell not sufficiently strong is detected or when all cells in the set have been detected.

5. The method of claim 1, further comprising:

skipping interference cancellation for the detected cell if not sufficiently strong.

6. The method of claim 1, wherein the processing the received signal comprises

performing correlation on the received signal at different time offsets to identify channel taps for the cell, and

detecting for the cell based on the identified channel taps.

7. The method of claim 1, wherein the determining whether the detected cell is sufficiently strong comprises

determining a metric for the detected cell,

comparing the metric against a threshold, and

declaring the cell to be sufficiently strong if the metric exceeds the threshold.

8. The method of claim 7, wherein the metric comprises a signal-to-noise-and-interference ratio (SINR) of the cell.

9. The method of claim 7, wherein the metric comprises received energy of the cell.

10. The method of claim 7, wherein the determining the metric for the detected cell comprises determining the metric for the cell based on a strongest channel tap for the cell.

11. The method of claim 7, wherein the determining the metric for the detected cell comprises determining the metric for the cell based on all sufficiently strong channel taps identified for the cell.

12. The method of claim 11, wherein the determining the metric for the detected cell further comprises determining whether a channel tap is sufficiently strong based on a second metric for the channel tap and a second threshold.

13. The method of claim 11, wherein channel taps for the detected cell are identified in a sequential order, from a strongest channel tap to a weakest channel tap, and wherein processing for the detected cell terminates when an identified channel tap is not sufficiently strong.

14. The method of claim 13, further comprising:

performing interference cancellation after each sufficiently strong channel tap for the detected cell is identified.

15. The method of claim 1, wherein the canceling interference due to the detected cell comprises

deriving a channel estimate for the detected cell based on the received signal,

generating a pilot signal for the detected cell,

estimating interference due to the detected cell based on the pilot signal and the channel estimate for the detected cell, and

canceling the estimated interference from the received signal.

16. The method of claim 1, wherein the received signal is processed to detect for common pilots transmitted by cells with a reuse factor of one.

17. The method of claim 1, wherein the received signal is processed to detect for low reuse pilots transmitted by cells with a reuse factor greater than one.

18. The method of claim 1, further comprising:

obtaining time measurements for multiple detected cells; and

obtaining a location estimate for a user equipment (UE) based on the time measurements for the multiple detected cells, the location estimate having improved accuracy due to a higher number of detected cells with interference cancellation.

19. The method of claim 1, further comprising:

identifying multiple detected cells; and

obtaining a location estimate for a user equipment (UE) based on identities of the multiple detected cells, the location estimate having improved accuracy due to a higher number of detected cells with interference cancellation.

20. An apparatus for wireless communication, comprising:

means for processing a received signal to detect for a cell;

means for determining whether the detected cell is sufficiently strong;

means for canceling interference due to the detected cell from the received signal to obtain an interference-canceled signal if the detected cell is sufficiently strong; and

means for processing the interference-canceled signal to detect for another cell if the detected cell is sufficiently strong.

21. The apparatus of claim 20, wherein the means for processing the received signal comprises means for processing the received signal to detect for a strongest cell in a set of cells, and wherein the means for processing the interference-canceled signal comprises

means for processing the interference-canceled signal to detect for a second strongest cell in the set of cells,

means for determining whether the second strongest cell is sufficiently strong,

means for canceling interference due to the second strongest cell from the interference-canceled signal to obtain a second interference-canceled signal if the second strongest cell is sufficiently strong, and

means for processing the second interference-canceled signal to detect for a next strongest cell in the set of cells if the second strongest cell is sufficiently strong.

22. The apparatus of claim 21, wherein the cells in the set are detected in a sequential order, from the strongest cell to a weakest cell, and wherein detection terminates when a cell not sufficiently strong is detected or when all cells in the set have been detected.

23. The apparatus of claim 20, wherein the means for determining whether the detected cell is sufficiently strong comprises

means for determining a metric for the detected cell,

means for comparing the metric against a threshold, and

means for declaring the cell to be sufficiently strong if the metric exceeds the threshold.

24. The apparatus of claim 23, wherein the means for determining the metric for the detected cell comprises means for determining the metric for the cell based on all sufficiently strong channel taps identified for the cell.

25. An apparatus for wireless communication, comprising:

at least one processor configured to process a received signal to detect for a cell, to determine whether the detected cell is sufficiently strong, to cancel interference due to the detected cell from the received signal to obtain an interference-canceled signal if the detected cell is sufficiently strong, and to process the interference-canceled signal to detect for another cell if the detected cell is sufficiently strong.

26. The apparatus of claim 25, wherein the at least one processor is configured to process the received signal to detect for a strongest cell in a set of cells, to process the interference-canceled signal to detect for a second strongest cell in the set of cells, to determine whether the second strongest cell is sufficiently strong, to cancel interference due to the second strongest cell from the interference-canceled signal to obtain a second interference-canceled signal if the second strongest cell is sufficiently strong, and to process the second interference-canceled signal to detect for a next strongest cell in the set of cells if the second strongest cell is sufficiently strong.

27. The apparatus of claim 26, wherein the at least one processor is configured to detect for the cells in the set in a sequential order, from the strongest cell to a weakest cell, and to terminate detection for the cells when a cell not sufficiently strong is detected or when all cells in the set have been detected.

28. The apparatus of claim 25, wherein the at least one processor is configured to determine a metric for the detected cell, to compare the metric against a threshold, and to declare the cell to be sufficiently strong if the metric exceeds the threshold.

29. The apparatus of claim 28, wherein the at least one processor is configured to determine the metric for the cell based on all sufficiently strong channel taps identified for the cell.

30. A computer program product, comprising:

a computer-readable medium comprising;

code for causing at least one computer to process a received signal to detect for a cell,

code for causing the at least one computer to determine whether the detected cell is sufficiently strong,

code for causing the at least one computer to cancel interference due to the detected cell from the received signal to obtain an interference-canceled signal if the detected cell is sufficiently strong, and

code for causing the at least one computer to process the interference-canceled signal to detect for another cell if the detected cell is sufficiently strong.