When performing an intra-frequency, inter-frequency or inter-RAT handover the UE has to do certain measurements in order to know if the target cell is suitable to be camped on. This is done with the help of Measurement procedure which consists of RRC Connection Reconfiguration and Measurement Report. The RRC Connection Reconfiguration message is always sent by the network which consists of some parameters for one or many events. The Measurement Report is always sent by the UE to the network. Only when a certain condition for a specific event is satisfied, the UE sends Measurement Report.​​

LTE Measurement Events

 

1. Measurement Configuration

Measurement configuration is sent in RRC Connection Reconfiguration message. The measurement configuration includes the following parameters:

  • Measurement objects: The objects on which the UE shall perform the measurements, i.e. what to measure.​

  • Reporting configurations: A list of reporting configurations which consists of:

    • Reporting criteria: The criteria that trigger the UE to send a measurement report. This can either be periodical or a single event description.

    • Reporting format: The quantities that the UE includes in the measurement report and associated information (e.g. number of cells to report).

  • Measurement identities

  • Each measurement identity links one measurement object with one reporting configuration. By configuring multiple measurement identities it is possible to link more than one measurement object to the same reporting configuration, as well as to link more than one reporting configuration to the same measurement object.

  • Quantity configurations

    • The quantity configuration defines the measurement quantities and associated filtering used for all event evaluation and related reporting of that measurement type.

  • Measurement gaps

    • Periods that the UE may use to perform measurements, i.e. when no UL and DL transmissions are scheduled.

 

2. Measurement Events

  • LTE Event A1 is triggered when the serving cell becomes better than a threshold.

 

  • LTE Event A2 is triggered when the serving cell becomes worse than a threshold.

 

  • LTE Event A3 is triggered when a neighboring cell becomes better than the serving cell by an offset.

 

  • LTE Event A4 is triggered when a neighboring cell becomes better than a threshold. 

 

  • Event A5 is triggered when the serving cell becomes worse than threshold-1 and neighboring cell becomes better than threshold-2. 

 

  • Event A6 is triggered when the Intra Frequency Neighbor becomes offset better than Scell (Introduced in Rel 10 for CA).

 

  • LTE Event B1 is triggered when a neighboring inter-RAT cell becomes better than a threshold.

 

  • LTE Event B2 is triggered when the serving cell becomes worse than threshold-1 and neighboring inter-RAT cell becomes better than threshold-2.

Calculation of threshold for triggering event A2

Check the "RRC Connection Reconfiguration" message IE: [reportConfigToAddModList] for event A2 and calculate the threshold as follows.

Threshold = -140 + [a2 threshold-RSRP]

Hysteresis = IE*0.5

Consider that the [a2 threshold-RSRP] is set to 37 and Hysteresis(IE) is set to 4 in RRC Connection Reconfiguration. We should calculate it as,

Threshold = -140 + [a2 threshold-RSRP]
                 = -140 + 37
                 = -103 dBm

Hysteresis = IE*0.5
        = 4 x 0.5
        = 2

A2 Threshold = Threshold - Hysteresis
                       = -103 - 2
                       = -105 dBm

 

This means that UE will send measurement report for event A2 when it measures serving cell RSRP below -105 dBm.

Calculation of threshold for triggering event A4

Check the "RRC Connection Reconfiguration" message IE: [reportConfigToAddModList] for event A4 and calculate the threshold as follows.

Threshold = -140 + [a4 threshold-RSRP]

Hysteresis = IE*0.5

Consider that the [a4 threshold-RSRP] is set to 40 and Hysteresis(IE) is set to 4 in RRC Connection Reconfiguration. We should calculate it as,

Threshold = -140 + [a4 threshold-RSRP]
                 = -140 + 40
                 = -100 dBm

Hysteresis = IE*0.5
        = 4 x 0.5
        = 2

A4 Threshold = Threshold - Hysteresis
                       = -100 - 2
                       = -102 dBm

 

This means that UE will send measurement report for event A4 when it measures serving cell RSRP above -102 dBm.

Calculation of threshold for triggering event B1

Check the "RRC Connection Reconfiguration" message IE: [reportConfigToAddModList] for event B1 and calculate the threshold as follows.

Threshold = -115 + [b1 threshold-RSCP]

Hysteresis = IE*0.5

Consider that the [b1 threshold-RSCP] is set to 12 and Hysteresis(IE) is set to 2 in RRC Connection Reconfiguration. We should calculate it as,

Threshold = -115 + [b1 threshold-RSCP]
                 = -115 + 12
                 = -103 dBm

Hysteresis = IE*0.5
        = 2 x 0.5
        = 1

B1 Threshold = Threshold - Hysteresis
                       = -103 - 1
                       = -102 dBm

This means that UE will send measurement report for event B1 when it measures 3G cell RSCP above -102 dBm.

 

NOTE: In case of handover to a 2G cell, [b1 threshold-GERAN] is sent by the network in RRC Connection Reconfiguration like the [b1 threshold-RSCP] which is for a 3G cell.