Lte mobility optimization

1. LTE Mobility Optimization
Mahedi MAHALAL

2. Introduction
- Two principal parts in LTE Mobility:
● RRC_Idle: UE moves among sites in Idle mode and triggering cells
reselection (PLMN, cells,…….).
● RRC_Connected: UE moves among sites in connected mode and
initiates Handover to camp from cell to cell.
- These slides are going to focus on Mobility Optimization in LTE, mainly
when a UE is in connected mode.

3. LTE MOBILITY
RRC_Connected
Mobility Mode.
RRC_Idle
Mobility Mode.
Cell reselection:
- PLMN selection.
- Cell selection.
- Cell reselection.
HandOver

4. Both of RRC Connected/Idle Modes may trigger:
1. Intra LTE Mobility: moving from E-NB to E-NB in order to maintain LTE
connectivity. This could happen among sectors of the same site ‘Intra-eNB
Handover’ or between adjacent sites through X2 or S1 interfaces ‘Inter-eNB
Handover’.

5. 2. Inter LTE Mobility: usually called IRAT-handover ‘Inter-radio access
technology handover’, UE connectivity decays to 3G or 2G to guarantee
continuity of service and load balance, this also could happen in the same site or
between other sites.

6. To dig a bit deeper, these two pictures from Sharetechnote could illustrate
Handover and cell reselection techniques on Intra/inter LTE.

8. HandOver Phases
Handover contains 3 main continuous phases:
- Measurement and Reporting.
- Preparation.
- Execution.
1. Measurement and Reporting:
This phase is controlled by E-NB parametres, it forwards to the UE a configuration message contains:
● RSRP Thresholds to start measurement.
● Cells/frequency target.
● Reporting mode: periodically or eventually.
Fine-tuning these parameters leads to avoid many problems as Pingpong between cells, Energy consumption, UE battery
life … .

9. 2. Preparation phase:
● In this phase the source E-NB exchanges information with the target E-
NB if UE receives better RSRP level from target cell (RSRPTarget + CIO >
RSRPSOURCE), When CIO (negative value) is an offset added to target
measurement to initiate a robust handover.
● Possibility that the UE camps in the target cell, then Data Forwarding
process starts.
● This phase should success promptly because at the same time the UE
meets a bad channel conditions in the source cell.

10. 3. Execution phase:
● In this phase E-NB sends message to order the UE to change the cell or
to trigger the handover with the target cell.
● LTE handover is a hard handover.

11. - To study handover’ KPIs, a deep understanding of handover procedure
will be crucial.
- Two pictures from LTE optimization engineering handbook give us the
whole procedure of X2 and S1 handover based.