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LTE UE event Measurement Reporting-Event A1,A2,A3,A4,A5,B1,B2

In LTE system, RRC connection reconfiguration message is used to configure UE measurement reporting. It replaces the measurement control message used in the UMTS system. The stands defines 5 intra-system and 2 inter-system measurement reporting events as described below.

LTE Events A1, A2, A3, A4 and A5 are based upon either RSRP or RSRQ messages. Pls. refer LTE RSRP vs RSRQ for more details. Inter-system LTE events B1 and B2 are based upon CPICH RSCP or CPICH Ec/Io for UMTS system, RSSI for GSM and pilot strength for CDMA2000.

The criteria for triggering and subsequently cancelling each event are evaluated after layer-3 filtering has been applied. The criteria for each event must be satisfied during at least the time to trigger. The time to trigger can be configured independently fpr each reporting event. The values are as follows:
{0,40,64,80,100,128,160,256,320,480,512,640,1024,1280}

Layer-3 filtering is applied prior to evaluate whether or not any measurement reporting events have been triggered.

Fn = (1-a) * Fn-1 + (a * MEASn)

Fn = updated filtered measurement result
Fn-1 = previous filtered measurement result
a = (1/2)^k/4 , where k is appropriate filter coefficient
MEASn = latest measurement result received from PHYSICAL layer

Filter coefficient can be configured independently for LTE RSRP, LTE RSRQ, UMTS CPICH RSCP, UMTS CPICH Ec/Io and GSM RSSI.

LTE Event A1

The LTE Event A1 is triggered when the serving cell becomes better than a threshold. The event is triggered when the following condition is true:

MEAs_serv - Hyst > Threshold

Triggering of the event is subsequently cancelled when the following condition is true:

MEAs_serv + Hyst < Threshold

The hysteresis can be configured with a value between 0 and 30 dB.

Event A2

The LTE Event A2 is triggered when the serving cell becomes worse than a threshold. The event is triggered when the following condition is true:

MEAs_serv + Hyst < Threshold

Triggering of the event is subsequently cancelled when the following condition is true.

MEAs_serv - Hyst > Threshold

The hysteresis can be configured with a value between 0 and 30 dB.

Event A3

The LTE Event A3 is triggered when a neighbouring cell becomes better than the serving cell by an offset. The offset can be either positive or negative. The event is triggered when the following condition is true:

MEAS_neigh + O_neigh,freq + O_neigh,cell - Hyst > MEAS_serv + O_serv,freq + O_serv,cell + Offset

MEAS_neigh + O_neigh,freq + O_neigh,cell + Hyst < MEAS_serv + O_serv,freq + O_serv,cell + Offset

Event A4

The LTE Event A4 is triggered when a neighbouring cell becomes better than a threshold.

MEAS_neigh + O_neigh,freq + O_neigh,cell - Hyst > Threshold

Triggering of the event is subsequently cancelled when the following condition is true:

MEAS_neigh + O_neigh,freq + O_neigh,cell + Hyst <Threshold

Event A5

LTE Event A5 is triggered when the serving cell becomes worse than threshold-1 while a neighbouring cell becomes better than threshold-2. The event is triggered when both of the following consitions are true:

MEAS_serv + Hyst < Threshold-1

MEAS_neigh + O_neigh,freq + O_neigh,cell - Hyst >Threshold-2

Triggering of the event is subsequently cancelled when either of the following conditions are true:

MEAS_serv - Hyst > Threshold-1

MEAS_neigh + O_neigh,freq + O_neigh,cell + Hyst <Threshold-2

LTE Event B1

The LTE Event B1 is triggered when a neighbouring inter-system cell becomes better than a threshold. The event is triggered when the following condition is true:

MEAS_neigh + O_neigh,freq - Hyst > Threshold

Triggering of the event is subsequently cancelled when the following condition is true:

MEAS_neigh + O_neigh,freq + Hyst < Threshold

Event B2

The LTE Event B2 is triggered when the serving cell becomes worse than threshold-1 while a neighbouring inter-system cell becomes better than threshold-2. The event is triggered when both of the following conditions are true:

MEAS_serv + Hyst < Threshold-1

MEAS_neigh + O_neigh,freq - Hyst > Threshold-2

Triggering of the event is subsequently cancelled when either of the following conditions are true:

MEAS_serv - Hyst > Threshold-1

MEAS_neigh + O_neigh,freq + Hyst < Threshold-2

REFERENCE: 3GPP TS 36.331 rel.8

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