Correlation Based Cell Search and Measurement for LTE and LTE-A

• US 20130273912A1
• Filed: 04/12/2012
• Published: 10/17/2013
• Est. Priority Date: 04/12/2012
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Mobile Communications GmbH (Intel Corporation)
• Inventors: Xu, Wen, Ma, Xiaojun
• Granted Patent: US 9,066,257 B2
• Time in Patent Office: Days
• US Class Current: 455/434
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic
• CPC Class Codes: H04W 48/12 using downlink control channel
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information

Abstract

Some aspects of the present disclosure relate to a method for accurately detecting and measuring signals received from multiple cells surrounding a user equipment (UE) during a cell search. The method is performed by receiving a composite signal comprising an aggregate of transmissions (e.g., synchronization signals) from a plurality of base stations at a UE. A correlation-based metric describing a cell is generated by performing a cross-correlation of a transmission (e.g., synchronization signal, reference signal, etc.) from the cell with the received composite signal. The correlation-based metric of weaker cells may be modified to generate an equivalent ideal metric, also proportional to the search criteria, in which the impact of interfering signals is suppressed. By suppressing the impact of the interfering signals, the equivalent ideal metric can be used to identify a weaker target signal in light of the eclipsing, stronger signals.

Claims

1. A method for performing a cell search or measurement, comprising:

receiving a composite signal comprising transmissions from at least an interferer cell configured to output at least an interferer signal and from a target cell configured to output a target signal; and

computing a cell search metric or a cell measurement metric of a target cell based upon a cross-correlation between transmissions from the interferer cell and the target cell, or upon the power of the interferer cell, or upon a power ratio of the interferer cell and the target cell.

2. The method of claim 1, wherein the cell measurement metric comprises the reference signal received power (RSRP) or reference signal received quality (RSRQ).

3. The method of claim 1, wherein computing the cell search metric comprises:

generating the cell search metric proportional to a search criterion by performing a cross-correlation of a synchronization signal conveyed by the target signal with the received composite signal; and

generating an equivalent ideal metric proportional to the search criterion by modifying the cell search metric according to the cross-correlation between synchronization signals of interferer and target cells to suppress a component of the interferer signal within the cell search metric so that the equivalent ideal metric can be used to identify the target signal in light of the interferer signal.

4. The method of claim 3, further comprising:

generating equivalent ideal metrics for primary synchronization signals and secondary synchronization signals during a radio frame comprising primary and secondary synchronization signals;

combining results of the equivalent ideal metrics for primary synchronization signals and secondary synchronization signals; and

selecting a subset of signals from the plurality of cells having a strongest signal based upon the combination of results.

21. The method of claim 1, wherein the cell search or measurement metric comprises a received signal strength or power that is proportional to a channel strength or power from a cell to a user equipment.

5. A method for performing a cell search or measurement, comprising:

receiving a composite signal comprising transmissions from a plurality of cells;

generating metrics proportional to a search criterion for the plurality of cells based upon a cross-correlation between transmissions from the plurality of cells and the received composite signal; and

selecting a subset of the plurality of cells having a strongest signal according to the search criterion by comparing the metrics of the plurality of cells.

6. The method of claim 5, where the metrics are based upon a cross-correlation between transmissions from the plurality of cells and the composite signal and the cross-correlation between synchronization signals of an interferer cell and a targeting cell.

7. The method of claim 5,

wherein the composite signal comprises an interferer signal configured to convey first synchronization or reference signal and a target signal configured to convey second synchronization or reference signal overlapping the first synchronization or first reference signal in time;

wherein determining metrics comprises;

generating a correlation-based metric of the target signal, which depends on the interferer signal, by performing a cross-correlation between the second synchronization or reference signal and the received composite signal; and

generating an equivalent ideal metric of the target signal by modifying the correlation-based metric of the target signal according to a cross-correlation between synchronization or reference signal of the interferer and the target cells to suppress the influence of the interferer signal within the correlation-based metric.

8. The method of claim 7, wherein selecting a subset of the plurality of cells comprises comparing an equivalent ideal metrics of the cells.

9. The method of claim 8, wherein the search criterion comprises a synchronization signal received power (SCH_RP) proportional to a received linear average power of resource elements that carry a secondary synchronization signal.

10. The method of claim 9, wherein modifying the correlation-based metric of the target signal comprises subtracting a component contributed by the interferer signal.

11. The method of claim 9, wherein modifying the correlation-based metric of the target signal comprises multiplying the correlation-based metric of the target signal with a weighting factor that suppresses the influence of the interferer signal.

12. The method of claim 11, wherein the weighting factor is inversely proportional to the ratio of the synchronization signal received power of the interferer signal to the synchronization signal received power of the target signal.

13. The method of claim 5, wherein the transmissions comprise primary synchronization signals (PSS), secondary synchronization signals (SSS), cell-specific reference signals, or other reference signals.

14. The method of claim 13, wherein metrics determined by the cross-correlation of the PSS and the cross-correlation of the SSS are combined prior to selecting a subset of the plurality of cells.

15. The method of claim 13, further comprising:

performing a Fourier transform on the received composite signal prior to determining correlation-based metrics corresponding to a search criterion of a secondary synchronization signal or a cell-specific reference signal.

16. A wireless communication apparatus, comprising:

an RF interface configured to receive a composite signal comprising a plurality of transmissions, respectively broadcast by a plurality of communication cells comprising at least an interferer cell configured to broadcast at least an interferer signal and a target cell configured to broadcast a target signal; and

a cell search or measurement element configured to generate a metric proportional to a search or measurement criterion for the plurality of communication cells based upon a cross-correlation between transmissions of the interferer cell and the target cell.

17. The apparatus of claim 16,

wherein the cell search element is configured to:

generate a correlation-based metric of the target signal, which depends on the interferer signal, by performing a cross-correlation between a synchronization signal of the target signal and the received composite signal;

and

generate an equivalent ideal metric of the target signal by modifying the correlation-based metric of the target signal to suppress the influence of the interferer signal within the correlation-based metric.

18. The apparatus of claim 17, wherein the cell search element comprises:

a PSS correlation element configured to generate a second correlation-based metric based upon a cross-correlation between primary synchronization signals (PSS) received from one of the plurality of communication cells the received composite signal; and

a SSS correlation element configured to generate a first correlation-based metric based upon a cross-correlation between secondary synchronization signals (SSS) received from one of the plurality of communication cells and the received composite signal.

19. The apparatus of claim 18, wherein the cell search element further comprises:

a first logic element configured to perform a maximum search on the metrics generated by the PSS correlation element and to determine a first subset of the plurality of communication cells that are broadcasting PSS with the strongest signals according to the search criteria; and

a second logic element configured to perform a maximum search on the metrics generated by the SSS correlation element and to determine a second subset of the plurality of communication cells that are broadcasting SSS with the strongest signals according to the search criteria.

20. The apparatus of claim 19, wherein the cell search element further comprises:

a combining and selection unit configured to receive the first subset and the second subset and to select the subset of the plurality of communication cells therefrom.