Correlation based cell search and measurement for LTE and LTE-A

• US 9,066,257 B2
• Filed: 04/12/2012
• Issued: 06/23/2015
• Est. Priority Date: 04/12/2012
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Mobile Communications GmbH (Intel Corporation)
• Inventors: Xu, Wen, Ma, Xiaojun
• Primary Examiner(s): Magloire, Vladimir
• Assistant Examiner(s): DONADO, FRANK E
• Application Number:
  US13/445,310
• Publication Number:
  US 20130273912A1
• Time in Patent Office: 1,167 Days
• Field of Search: None
• US Class Current: 1/1
• 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 non-transitory machine readable medium comprising instructions that, when executed, cause a user equipment (UE) to:

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

compute a cell search metric associated with the target cell, wherein the cell search metric is based at least in part on a cross-correlation between the interferer transmission and the target transmission and one or more of the power of the interferer cell and a power ratio of the interferer cell and the target cell, wherein computing the cell search metric comprises;

generating the cell search metric proportional to a search criterion by performing a cross-correlation of a target synchronization signal with the received composite signal, wherein the target transmission comprises the target synchronization signal, and wherein the interferer transmission comprises an interferer synchronization signal, wherein the target synchronization signal comprises a target primary synchronization signal and a target secondary synchronization signal, wherein the interferer synchronization signal comprises an interferer primary synchronization signal and an interferer secondary synchronization signal; and

generating an equivalent ideal metric proportional to the search criterion by modifying the cell search metric according to the cross-correlation between the interferer transmission and the target transmission to suppress a component of the interferer signal within the cell search metric, wherein the equivalent ideal metric identifies the target signal in light of the interferer signal, wherein generating the equivalent ideal metric comprises;

generating a primary equivalent ideal metric based on a cross-correlation of the target primary synchronization signal and the interferer primary synchronization signal;

generating a secondary equivalent ideal metric based on a cross-correlation of the target secondary synchronization signal and the interferer secondary synchronization signal; and

combining the primary equivalent ideal metric and the secondary equivalent ideal metric to obtain the equivalent ideal metric.

2. The non-transitory machine readable medium of claim 1, wherein the cell search metric comprises the reference signal received power (RSRP) or reference signal received quality (RSRQ).

3. The non-transitory machine readable medium 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.

4. A non-transitory machine readable medium comprising instructions that, when executed, cause a user equipment (UE) to:

receive a composite signal comprising transmissions from a plurality of cells that comprise a target cell and an interferer cell;

generate 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, wherein at least one of the metrics is based at least in part on one or more of a cross-correlation between an interferer transmission of the interferer cell and a target transmission of the target cell, the power of the interferer cell, and a power ratio of the interferer cell and the target cell, wherein generating the at least one of the metrics comprises;

generating the at least one of the metrics proportional to a search criterion by performing a cross-correlation of a target synchronization signal with the received composite signal, wherein the target transmission comprises the target synchronization signal, and wherein the interferer transmission comprises an interferer synchronization signal, wherein the target synchronization signal comprises a target primary synchronization signal and a target secondary synchronization signal, wherein the interferer synchronization signal comprises an interferer primary synchronization signal and an interferer secondary synchronization signal; and

generating an equivalent ideal metric proportional to the search criterion by modifying the at least one of the metrics according to the cross-correlation between the interferer transmission and the target transmission to suppress a component of the interferer signal within the cell search metric, wherein the equivalent ideal metric identifies the target signal in light of the interferer signal, wherein generating the equivalent ideal metric comprises;

generating a primary equivalent ideal metric based on a cross-correlation of the target primary synchronization signal and the interferer primary synchronization signal;

generating a secondary equivalent ideal metric based on a cross-correlation of the target secondary synchronization signal and the interferer secondary synchronization signal; and

combining the primary equivalent ideal metric and the secondary equivalent ideal metric to obtain the equivalent ideal metric; 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.

5. The non-transitory machine readable medium of claim 4,

wherein the interferer synchronization signal and the target synchronization signal overlap in time.

6. The non-transitory machine readable medium of claim 5, wherein selecting a subset of the plurality of cells comprises comparing equivalent ideal metrics of the cells.

7. The non-transitory machine readable medium of claim 6, 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.

8. The non-transitory machine readable medium of claim 7, wherein modifying the at least one of the metrics comprises subtracting a component contributed by the interferer transmission.

9. The non-transitory machine readable medium of claim 7, wherein modifying the at least one of the metrics comprises multiplying the correlation-based metric of the target signal with a weighting factor that suppresses the influence of the interferer transmission.

10. The non-transitory machine readable medium of claim 9, wherein the weighting factor is inversely proportional to the ratio of a synchronization signal received power of the interferer transmission to a synchronization signal received power of the target transmission.

11. The non-transitory machine readable medium of claim 4, further comprising:

performing a Fourier transform on the received composite signal prior to generating the metrics.

12. 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 element configured to generate a metric proportional to a search criterion for the plurality of communication cells, wherein the metric is based at least in part upon a cross-correlation between the interferer signal and the target signal,

wherein the cell search element generates the metric proportional to a search criterion by performing a cross-correlation of a target synchronization signal with the received composite signal, wherein the target transmission comprises the target synchronization signal, and wherein the interferer transmission comprises an interferer synchronization signal, wherein the target synchronization signal comprises a target primary synchronization signal and a target secondary synchronization signal, wherein the interferer synchronization signal comprises an interferer primary synchronization signal and an interferer secondary synchronization signal,

wherein the cell search element generates an equivalent ideal metric proportional to the search criterion by modifying the metric according to the cross-correlation between the interferer transmission and the target transmission to suppress a component of the interferer signal within the cell search metric, wherein the equivalent ideal metric identifies the target signal in light of the interferer signal, and

wherein the cell search element generates a primary equivalent ideal metric based on a cross-correlation of the target primary synchronization signal and the interferer primary synchronization signal, generates a secondary equivalent ideal metric based on a cross-correlation of the target secondary synchronization signal and the interferer secondary synchronization signal, and combines the primary equivalent ideal metric and the secondary equivalent ideal metric to obtain the equivalent ideal metric.

13. The apparatus of claim 12,

wherein the equivalent ideal metric is the metric.

14. The apparatus of claim 13, wherein the cell search element further comprises:

a first logic element configured to perform a maximum search on the primary equivalent ideal metric 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 secondary equivalent ideal metric 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.

15. The apparatus of claim 14, 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.