Handover Measurements in a Mobile Communication System

• US 20110103350A1
• Filed: 11/05/2009
• Published: 05/05/2011
• Est. Priority Date: 11/05/2009
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Lindoff, Bengt
• Granted Patent: US 8,437,308 B2
• Time in Patent Office: Days
• US Class Current: 370/332
• CPC Class Codes: H04W 36/0094 Definition of hand-off measurement parameters
• CPC Class Codes: H04W 56/005 compensating for timing error by adjustment in the receiver

Abstract

A cellular communication system has an air interface divided into frames, each consisting of sub-frames at least two of which are synchronization sub-frames. For each cell, different cell-related synchronization signals are transmitted to user equipments (UEs) in different synchronization signal sub-frames. The UE detects cell identities of first and second cells. Weights then control generation of weighted handover measurements made from the first cell'"'"'s synchronization signals received during synchronization sub-frames, wherein each of the weights is a function of the cell identity of the first cell, the cell identity of the second cell, and which ones of the first and second cells'"'"' cell-related synchronization signals are transmitted in the respective one of the plurality of synchronization sub-frames during which the weight is applied. A filtered handover measurement, upon which a handover decision can be made, is generated from the weighted handover measurements.

Claims

1. A method performed by a user equipment operating in a mobile communication system that comprises equipment for serving a plurality of geographic cells and having an air interface that is divided into sequentially occurring frames, wherein each of the frames consists of a plurality of sub-frames at least two of which are synchronization sub-frames, wherein for each of the cells served by the mobile communication system, a respective one of a plurality of cell-related synchronization signals is transmitted to user equipments in the at least two synchronization signal sub-frames of every frame, the method comprising:

detecting a cell identity of a first cell in the mobile communication system;

detecting a cell identity of a second cell in the mobile communication system;

using a plurality of weights to control generation of a plurality of weighted handover measurements made from the first cell'"'"'s synchronization signals received during a plurality of synchronization sub-frames, wherein the plurality of weights are applied to measurements made for the first cell during respective ones of the plurality of synchronization sub-frames, and wherein each of the weights is a function of the cell identity of the first cell, the cell identity of the second cell, and which ones of the first and second cells'"'"' cell-related synchronization signals are transmitted in the respective one of the plurality of synchronization sub-frames during which the weight is applied;

generating a filtered handover measurement from the weighted handover measurements; and

providing the filtered handover measurement to a handover process that uses the filtered handover measurement to control a handover process involving the user equipment.

2. The method of claim 1, wherein:

each of the cell-related synchronization signals comprises a primary synchronization signal and a secondary synchronization signal, wherein the secondary synchronization signal conveys both a first sequence and a second sequence; and

the plurality of weights to be applied to measurements made for the first cell during respective ones of the plurality of synchronization sub-frames are determined by;

ascertaining whether the primary synchronization signal of the first cell is the same as the primary synchronization signal of the second cell; and

ascertaining at least one of the following;

whether the first sequence conveyed by the secondary synchronization signal of the first cell is the same as the first sequence conveyed by the secondary synchronization signal of the second cell; and

whether the second sequence conveyed by the secondary synchronization signal of the first cell is the same as the second sequence conveyed by the secondary synchronization signal of the second cell.

3. The method of claim 2, comprising:

applying a weight of zero to a measurement made for the first cell during any synchronization sub-frame in which;

both the primary synchronization signals and the first sequences conveyed by the secondary synchronization signals of the first and second cells are the same, and/or both the primary synchronization signals and the second sequences conveyed by the secondary synchronization signals of the first and second cells are the same.

4. The method of claim 3, wherein applying a weight of zero to a measurement made for the first cell comprises:

inactivating a receiver of the user equipment during any synchronization sub-frame in which both the primary synchronization signals and the first sequences conveyed by the secondary synchronization signals of the first and second cells are the same, and/or both the primary synchronization signals and the second sequences conveyed by the secondary synchronization signals of the first and second cells are the same; and

not contributing a weighted handover measurement to the plurality of weighted handover measurements.

5. The method of claim 1, wherein generating the filtered handover measurement from the weighted handover measurements comprises generating an average handover measurement from the weighted handover measurements.

6. The method of claim 1, wherein each of the weights is a function of, for any given one of the synchronization sub-frames, a level of correlation between a cell-related synchronization signal of the first cell communicated during the given synchronization sub-frame and a cell-related synchronization signal of the second cell communicated during the given synchronization sub-frame.

7. The method of claim 6, wherein the weights have values ranging from 0 to 1.

8. The method of claim 1, comprising:

determining a weight to be applied to a measurement made for the first cell during any given one of the synchronization sub-frames by using the cell identity of the first cell and the cell identity of the second cell as indices into a table stored in an addressable memory device, wherein the table is pre-programmed with values related to correlation levels between cell-related synchronization signals of respective different pairs of cells, wherein the higher the correlation level the lower the weight.

9. The method of claim 1, wherein one or more of the weights result in more than none and less than all frequency components of a received synchronization signal contributing to a handover measurement.

10. An apparatus for use in a user equipment operating in a mobile communication system that comprises equipment for serving a plurality of geographic cells and having an air interface that is divided into sequentially occurring frames, wherein each of the frames consists of a plurality of sub-frames at least two of which are synchronization sub-frames, wherein for each of the cells served by the mobile communication system, a respective one of a plurality of cell-related synchronization signals is transmitted to user equipments in the at least two synchronization signal sub-frames of every frame, the apparatus comprising:

circuitry configured to detect a cell identity of a first cell in the mobile communication system;

circuitry configured to detect a cell identity of a second cell in the mobile communication system;

circuitry configured to use a plurality of weights to control generation of a plurality of weighted handover measurements made from the first cell'"'"'s synchronization signals received during a plurality of synchronization sub-frames, wherein the circuitry configured to use the plurality of weights applies the plurality of weights to measurements made for the first cell during respective ones of the plurality of synchronization sub-frames, and wherein each of the weights is a function of the cell identity of the first cell, the cell identity of the second cell, and which ones of the first and second cells'"'"' cell-related synchronization signals are transmitted in the respective one of the plurality of synchronization sub-frames during which the weight is applied;

circuitry configured to generate a filtered handover measurement from the weighted handover measurements; and

circuitry configured to provide the filtered handover measurement to a handover process that uses the filtered handover measurement to control a handover process involving the user equipment.

11. The apparatus of claim 10, wherein:

each of the cell-related synchronization signals comprises a primary synchronization signal and a secondary synchronization signal, wherein the secondary synchronization signal conveys both a first sequence and a second sequence; and

the apparatus comprises circuitry for determining the plurality of weights to be applied to measurements made for the first cell during respective ones of the plurality of synchronization sub-frames by;

ascertaining whether the primary synchronization signal of the first cell is the same as the primary synchronization signal of the second cell; and

ascertaining at least one of the following;

whether the first sequence conveyed by the secondary synchronization signal of the first cell is the same as the first sequence conveyed by the secondary synchronization signal of the second cell; and

whether the second sequence conveyed by the secondary synchronization signal of the first cell is the same as the second sequence conveyed by the secondary synchronization signal of the second cell.

12. The apparatus of claim 11, comprising:

circuitry configured to apply a weight of zero to a measurement made for the first cell during any synchronization sub-frame in which;

both the primary synchronization signals and the first sequences conveyed by the secondary synchronization signals of the first and second cells are the same, and/or both the primary synchronization signals and the second sequences conveyed by the secondary synchronization signals of the first and second cells are the same.

13. The apparatus of claim 12, wherein the circuitry configured to apply a weight of zero to a measurement made for the first cell comprises:

circuitry configured to inactivate a receiver of the user equipment during any synchronization sub-frame in which both the primary synchronization signals and the first sequences conveyed by the secondary synchronization signals of the first and second cells are the same, and/or both the primary synchronization signals and the second sequences conveyed by the secondary synchronization signals of the first and second cells are the same; and

circuitry configured to inhibit contributing a weighted handover measurement to the plurality of weighted handover measurements.

14. The apparatus of claim 10, wherein the circuitry configured to generate the filtered handover measurement from the weighted handover measurements comprises circuitry configured to generate an average handover measurement from the weighted handover measurements.

15. The apparatus of claim 10, wherein each of the weights is a function of, for any given one of the synchronization sub-frames, a level of correlation between a cell-related synchronization signal of the first cell communicated during the given synchronization sub-frame and a cell-related synchronization signal of the second cell communicated during the given synchronization sub-frame.

16. The apparatus of claim 15, wherein the weights have values ranging from 0 to 1.

17. The apparatus of claim 10, comprising:

circuitry configured to determine a weight to be applied to a measurement made for the first cell during any given one of the synchronization sub-frames by using the cell identity of the first cell and the cell identity of the second cell as indices into a table stored in an addressable memory device, wherein the table is pre-programmed with values related to correlation levels between cell-related synchronization signals of respective different pairs of cells, wherein the higher the correlation level the lower the weight.

18. The apparatus of claim 10, wherein one or more of the weights result in more than none and less than all frequency components of a received synchronization signal contributing to a handover measurement.