IRAT Failures

IRAT Failure reasons

• This presentation tries to explain some of IRAT handover failure reasons faced during IRAT tuning– Physical channel failure (truncation)– Missing neighbour– T309 expiry (In Actix)

Inter-RAT cell change order from UTRAN

UE UTRAN

CELL CHANGE ORDER FROM UTRAN

UE UTRAN

CELL CHANGE ORDER FROM UTRAN

CELL CHANGE ORDER FROM UTRAN FAILURE

Successful

Un-Successful 3GPP : 25331-3l0

CELL CHANGE ORDER FROM UTRAN message by the UE - Actions

• Start timer T309 and• Establish the connection to the other radio access technology

• The UE regards the procedure as completed when it has received a successful response from the target RAT, e.g. in case of GSM when it received the response to a (PACKET) CHANNEL REQUEST in the new cell.

3GPP : 25331-3l0

• Timer T309 expires prior to the successful establishment of a connection to the target RAT• If the establishment of the connection to the other RAT failed due to other reasons e.g. (random) access failure, rejection due to lack of resources

Cell Change Failure Reason :

Successful Cell Change :

Cell Change UE actions :

Timer used in UE to supervise the time between leaving the UMTS system and entering the GSM system. The timer value is broadcast and used within the UE. The timer is started in UE at reception of the Cell Change Order From Utran. At expiry the UE shall return to the old resources in UTRAN.

Unit: seconds

Default : 5

T309 Wait Timer :

T309:

IRAT failure PS – Physical channel failure

IRAT handover failure due to Physical channel failure

1st Measurement control messagePlease observe IRAT number 24 which is BSIC 37 and BCCH 165

IRAT failure PS – Physical channel failure –MS1

MS1: Message sequence 1

2nd Measurement control messageIRAT number 24 still unchanged

IRAT failure PS – Physical channel failure-MS2

Event 3a messageIRAT number 24 reported with verified BSIC

IRAT failure PS – Physical channel failure-MS3

3rd Measurement control messagePlease observe IRAT number 24 Just before UTRAN cell change command the IRAT 24 is updated to BSIC 73 and BCCH 164 due to active set update and truncation

Active setup date changed the IRAT list

IRAT failure PS – Physical channel failure-MS4

cell change order from UTRAN is to BSIC 73 and BCCH 164 which was different than reported in Event 3a by the UE which was BSIC 37 and BCCH 165.

IRAT failure PS – Physical channel failure-MS5

IRAT handover failed due to Physical channel failure by attempting a handover on a cell which was not even reported by the UE. Solution is to trim down the neighbour list to avoid truncation

IRAT failure PS – T309 Expiry

T309 expired before the Channel request message and was pegged as Handover failure.

T309 expired and was picked as an Handover failure in Actix. It was a successful IRAT Cell Change.

Handover failure occurred on ILU04948 trying to do cell update to IL01993 and the second failure was during cell update to IL01999 close to IL0483 which is not a neighbor. Handover failure was due to “physichalchannelfailure”

IRAT failure PS – Missing Neighbour 1

Handover failure occurred on ILU04948 and ILU04949 trying to do cell update to IL01993 and the second failure was during cell update to IL01999 close to IL0483 which is not a neighbor.

ILU04949 Neighbors ILU04948 Neighbors

Missing Neighbors

IRAT failure PS – Missing Neighbour 1

Handover failure occurred on ILU18338 in SHO withILU14229 trying to do cell update to IL01242 close to IL1834 which is not a neighbor.

IRAT failure PS – Missing Neighbour 2

Missing Neighbors

IRAT failure PS – Missing Neighbour 2