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LTE Measurement-Controlled Handover Call Flow

call-flow LTE | Measurements | Mobility | RRC

LTE measurement-controlled handover is the decision path that turns measurement configuration and Measurement Report results into a real handover command. It sits between measurement logic and mobility execution.

This page focuses on how the network decides to start a handover, not only on the later execution steps.

Introduction

The procedure starts when the eNB configures measurements, the UE reports event-based results, and the source side uses those results to choose whether a target cell should take over. The later mobility branch can become intra-frequency, inter-frequency, or inter-RAT.

The main nodes are the UE and source eNB, with later target-side nodes depending on the mobility type selected.

What Is Measurement-Controlled Handover in Simple Terms?

What starts the procedure: The source side configures measurements and the UE begins reporting event results.
What the UE and network want to achieve: Decide whether connected mobility should start and which target should be chosen.
What success looks like: Measurement results lead to a valid mobility decision and the right handover branch starts.
What failure means: Bad measurement interpretation leads to no move, wrong target selection, or unstable mobility.

Why this procedure matters

This page explains why many handovers start when they do. It is the right reference when the mobility issue begins before the handover command is even sent.

Quick Fact Sheet

Procedure name	LTE Measurement-Controlled Handover
Domain	Measurement-to-mobility decision path
Main trigger	Configured measurement events reach their handover condition
Start state	UE is connected and measurement configuration is active
End state	A specific handover branch starts or is intentionally not started
Main nodes	UE, source eNB, later target nodes
Main protocols	RRC
Main success outcome	Measurement results produce the correct mobility action
Main failure outcome	Wrong move timing, wrong target, or no move when needed
Most important messages	Measurement Control, Measurement Report, RRC Connection Reconfiguration
Main specs	TS 36.331 and mobility policy implementation

LTE Measurement-Controlled Handover call flow — Click the diagram to open the full-size in a new tab.

Handover Concept

This illustration shows the basic handover concept used in this procedure: the UE leaves the serving side after the mobility decision and continues on the target side once the target path is ready.

Configure measurements to Start mobility. The decision phase ends when a real mobility execution branch starts.

Preconditions

The UE is already in connected LTE service.
Measurement configuration has been delivered.
Neighbor or target data is available for mobility decisions.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Applies measurement rules and reports results.
Source eNB	Configures measurements and decides whether to start mobility.
Target decision logic	Represents the policy layer that chooses the next mobility branch.

Interfaces used

Interface	Path	Role
LTE Uu	UE <-> source eNB	Carries measurement control and measurement reports.

End-to-End Call Flow

UE                Source eNB
|<--Measurement Control--|
|--Measurement Report--->|
|       decision         |
|<--handover command-----|

Major Phases

Phase	What happens
1. Configure	The source side sets up measurement rules.
2. Report	The UE sends event-based results.
3. Decide	The source side evaluates whether mobility should start.
4. Launch the chosen branch	A concrete handover procedure begins.

Step-by-Step Breakdown

Step 1: Measurement setup

Sender -> receiver: source eNB -> UE

Message(s): Measurement Control

Purpose: Tell the UE which events and cells to monitor.

State or context change: Measurement supervision becomes active in connected mode.

Note: Wrong setup here can mislead every later handover decision.

Step 2: Measurement report

Sender -> receiver: UE -> source eNB

Message(s): Measurement Report

Purpose: Return the event result that may trigger mobility.

State or context change: The source side can now evaluate a real target decision.

Note: This is the highest-value message for early mobility analysis.

Step 3: Decision

Sender -> receiver: source eNB

Message(s): Mobility policy evaluation

Purpose: Choose whether to hand over, wait, or reject the move.

State or context change: The source side either starts a handover or keeps the UE on the serving cell.

Note: A bad decision here can look like a later handover problem even when execution is fine.

Step 4: Start the branch

Sender -> receiver: source eNB -> UE and target side

Message(s): RRC Connection Reconfiguration or related handover start

Purpose: Convert the measurement decision into a real mobility branch.

State or context change: The page now hands off to the chosen mobility procedure.

Note: At this point you should move into the exact handover type page.

Important Messages

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
Measurement Report	RRC	UE -> source eNB	Carries the result that often triggers mobility.	Inspect event type, target identity, and measurement timing.
RRC Connection Reconfiguration	RRC	source eNB -> UE	Shows that the measurement decision became a real mobility command.	Check whether the selected target matches the report.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Event type	The measurement condition that was met.	Measurement Report	Explains why the move started.	Wrong threshold or unstable trigger.
Target identity	The candidate cell or RAT named by the report.	Measurement Report	Shows which target won the decision.	Mismatch between report and command.
Hysteresis and time-to-trigger	Decision-stability controls behind the event.	Measurement configuration	Help explain late, early, or oscillating moves.	Ping-pong or delayed mobility.
Decision timing	Delay between the report and the command.	Trace timing	Useful for spotting stale or rushed decisions.	Command sent too late.
Chosen branch	Whether the result became intra-frequency, inter-frequency, or inter-RAT mobility.	Later mobility start	Links the measurement stage to the right call-flow page.	Wrong follow-up procedure chosen.

Successful Completion

Success means the measurement logic leads to the correct mobility branch at the correct time and the selected target matches the intended policy.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Handover starts too early or too late	Measurement conditions or policy timing are not tuned correctly.	Measurement report timing and configuration values.	Measurement Report	LTE Uu	Review event thresholds and decision delay.
Wrong target is chosen	Neighbor relation or decision logic did not match the strongest intended target.	Measurement report target versus handover command target.	Measurement Report, handover command	LTE Uu	Compare the reported target with the target carried in the command.

What to Check in Logs and Traces

Start with the measurement report, not the handover command.
Check whether the target named in the report matches the target later chosen.
Confirm whether the selected branch became intra-LTE or inter-RAT.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

Notes

Measurement-controlled handover is the decision stage. If the target choice is wrong here, a later execution trace can still look technically correct.

FAQ

What is measurement-controlled handover?

It is the decision path that turns measurement results into a specific handover action.