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LTE Intra-Frequency Handover Call Flow

call-flow LTE | Mobility | Same EARFCN | RRC | X2 | S1AP

LTE intra-frequency handover moves the UE between LTE cells on the same carrier layer. It is one of the most common connected mobility paths in live networks because the UE stays inside the same LTE frequency plan while the serving cell changes.

This page focuses on the same-frequency case, where the target decision is still measurement-driven but the UE does not have to change to another LTE carrier layer.

Introduction

The flow starts after same-frequency neighbor measurements show that another LTE cell should become the serving cell. The preparation, command, target access, and path-switch pattern remains close to the baseline intra-LTE handover path.

The main nodes are the UE, source eNB, target eNB, and later the MME and SGW for continuity handling.

What Is Intra-Frequency Handover in Simple Terms?

What starts the procedure: A connected UE sees a better LTE cell on the same frequency layer and the network chooses to move it.
What the UE and network want to achieve: Change the serving LTE cell without leaving the current LTE carrier layer.
What success looks like: The UE moves to the target cell and traffic continues there with normal continuity.
What failure means: The same-frequency move breaks during execution or later continuity handling.

Why this procedure matters

This page separates same-frequency mobility from inter-frequency cases. It is useful when the mobility problem is cell-specific rather than layer-specific.

Quick Fact Sheet

Procedure name	LTE Intra-Frequency Handover
Domain	Connected LTE mobility within one EARFCN layer
Main trigger	Neighbor-cell improvement on the same LTE frequency
Start state	UE is in RRC_CONNECTED on the source cell
End state	UE is connected on the target LTE cell on the same frequency layer
Main nodes	UE, source eNB, target eNB, MME, SGW
Main protocols	RRC, X2AP or S1AP, GTP-U
Main success outcome	Serving cell changes without leaving the current LTE carrier
Main failure outcome	Interrupted same-frequency connected mobility
Most important messages	Measurement Report, handover command, Path Switch Request
Main specs	TS 36.331, TS 36.300, TS 23.401

LTE Intra-Frequency 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.

Measure neighbors to Finish continuity. The serving path is fully transferred to the target cell.

Preconditions

The UE is already connected on LTE.
Same-frequency neighbor relations are configured.
The target same-layer cell is admitted and available.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Reports same-frequency measurements and executes the move.
Source eNB	Triggers the same-layer move and delivers the handover command.
Target eNB	Admits the UE and becomes the new serving LTE cell.
MME	Handles later path-switch control updates.
SGW	Maintains user-plane continuity after the target side becomes active.

Interfaces used

Interface	Path	Role
LTE Uu	UE <-> eNB	Carries same-frequency measurement and execution signaling.
X2 or S1-MME	Source side <-> target side / MME	Carries target preparation and later EPC continuity handling.
S1-U	eNB <-> SGW	Carries user-plane continuity after the move.

End-to-End Call Flow

UE          Source eNB         Target eNB           MME
|--Measurement Report->|                 |                 |
|                      |--HO preparation>|                 |
|                      |<--HO ack--------|                 |
|<--HO command---------|                 |                 |
|==== same-frequency target access ======================>|
|                      |                 |--Path Switch--->|
|                      |<--Release source context---------|

Major Phases

Phase	What happens
1. Same-layer trigger	Measurement results show a better LTE cell on the same frequency.
2. Preparation	The target same-frequency cell receives UE context and reserves resources.
3. Execution	The UE leaves the source side and accesses the target.
4. Continuity update	The target side becomes the full serving path and the source is released.

Step-by-Step Breakdown

Step 1: Same-frequency measurement

Sender -> receiver: UE -> source eNB

Message(s): Measurement Report

Purpose: Show that a same-layer LTE neighbor is the best target.

State or context change: The UE stays connected to the source cell while the decision is made.

Note: This is where A3-style neighbor dominance usually appears.

Step 2: Target preparation

Sender -> receiver: Source eNB -> target eNB

Message(s): Handover Request and acknowledgement

Purpose: Prepare target resources before moving the UE.

State or context change: The target same-frequency cell becomes ready for access.

Note: Admission rejection here prevents a bad move before execution starts.

Step 3: Command and move

Sender -> receiver: Source eNB -> UE -> target eNB

Message(s): RRC Connection Reconfiguration and target access

Purpose: Move the UE to the target same-frequency cell.

State or context change: The serving radio path changes cell while staying on the same layer.

Note: The frequency stays the same even though the serving cell changes.

Step 4: Path switch

Sender -> receiver: Target eNB -> MME

Message(s): Path Switch Request

Purpose: Finalize control and bearer continuity through the target side.

State or context change: Traffic follows the target LTE cell.

Note: A successful radio move still needs a successful EPC update.

Important Messages

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
Measurement Report	RRC	UE -> source eNB	Shows that a same-frequency target should be chosen.	Check the reported neighbor and event result.
RRC Connection Reconfiguration	RRC	source eNB -> UE	Carries the handover command.	Check that the target information matches the intended same-layer cell.
Path Switch Request	S1AP	target eNB -> MME	Completes the EPC side of the same-frequency move.	Inspect the target eNB identity and bearer continuity.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
EARFCN	The LTE carrier layer used before and after the move.	Measurement and target data	Confirms this is a same-frequency case.	Accidental misclassification as inter-frequency.
PCI	Source and target physical cell identities.	Measurement report and handover command	Separates cell change from frequency change.	Wrong target cell interpretation.
Event result	Measurement trigger used for the move.	Measurement Report	Explains why the handover started.	Threshold mismatch or oscillation.
Bearer continuity	Target-side bearer mapping after the move.	Path switch handling	Shows whether service followed the cell move.	Partial bearer carry-over.
Timing	Spacing between measurement, command, and target access.	Full trace	Helps explain late or rushed same-layer moves.	Ping-pong or stale command timing.

Successful Completion

Success means the UE changes serving cell on the same LTE frequency, the target side becomes active, and the bearer path follows the move.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Ping-pong behavior	The same-layer target choice is unstable.	Back-to-back measurement and command history.	Measurement Report, handover command	LTE Uu	Check the measurement trigger and neighbor relation quality.
Move breaks during target access	Execution failed after the source released the active path.	Command timing and target access branch.	RRC Connection Reconfiguration, later recovery	LTE Uu	Move into handover recovery.

What to Check in Logs and Traces

Verify that source and target share the same EARFCN.
Check that the target PCI in the command matches the intended same-layer neighbor.
Confirm whether the EPC path switch followed the radio move.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

Notes

Intra-frequency handover is still a full handover. The UE keeps the same LTE carrier layer, but the serving cell and bearer path still change.

FAQ

What is intra-frequency handover?

It is an LTE handover between cells that use the same LTE carrier frequency.

How is it different from inter-frequency handover?

The target cell stays on the same LTE frequency layer instead of moving the UE to another LTE carrier.