Sunday, 15 November 2015

eNodeB-Interpretation of LTE SRVCC Handover Signaling

Currently, VoLTE relevant functions will soon be enabled for some areas. Apart from basic voice call services, the LTE network employs the SRVCC mode to solve the voice control problem and the voice continuity problem when the network is handed over to the CS network. This case describes briefly about the SRVCC handover signaling.


1. SRVCC’s complete handover signaling:
 

2. MeasurementReport: A2 event
The UE reported the measurement report, in which, “measId=2” corresponds to the A2 event of the “Measurement Control” message in RRC Connection Reconfiguration. The RSRP in this case equals to -80 dBm, the RSRQ corresponds to -3 db. The triggering threshold for the A2 event is met.
3.  Measurement Control Corresponding A2 Event in RRC Connection Reconfiguration.
 
The parameter “threshold_RSRP” in this case indicates the measurement parameter that can be configured on the OMC side.
4.  Measurement Control Corresponding B2 event in RRC Connection Reconfiguration.
The “Measurement Control” message in “RRC Connection Reconfiguration”: The B2 event was delivered. In this case, the switchover threshold of the RSRP is -75 dBm. That is, the RSRP threshold of the service cell equals to or is lower than -75 dBm. You can now determine that the absolute threshold of the service cell “1” is met. As the RSSI of the GSM cell is bigger than -110 dBm, the absolute threshold of the target cell “2” is also met.

 
“Measurement Control” message in RRC Connection Reconfiguration: you can infer from this case that the measurement object is the GSM cell whose starting ARFCN=79.
5.  MeasurementReport: B2 event

The UE reported the measurement report, in which, “measurement ID=5” corresponds to the B2 event of the “Measurement Control” message in “RRC Connection Reconfiguration”. In this case, RSRP=-76 dBm and RSRQ=-3.5 db, which indicates that the B2 event triggering threshold is met.

The reported the measurement report, in which, “measId=5” corresponds to the B2 event of the “Measurement Control” message in “RRC Connection Reconfiguration”. The conditions-met network color code is 6 and the eNodeB color code in the GSM cell is 1 within the GSM cell. The RSSI value is -76 dBm. The triggering threshold of the B2 event is 2.
6.   Handover Required Signaling

 
The eNodeB sent the SRVCC-based handover request to the GSM.

 
 The PLMN of the target cell in the GSM system is 460 00 and the CI=10993.
 
7. Handover Command Signaling
When the GSM system resources are fully prepared, the MME notifies the eNodeB through the S1 interface of triggering the handover from E-UTRAN to GSM.  
8. MobilityFromEUTRACommand Signaling
The eNodeB notifies the UE of the handover execution  from E-UTRAN to GSM.
9. UE Context Release Request Signaling
After the handover is finished, the eNodeB requests the MME to release the UE relevant resources.  
10. UE Context Release Command Signaling
 
The MME responds to the eNodeB’s release request of its UE resources.

Budi Prasetyo

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