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SELF OPTIMIZING NETWORK
Company Confidential | 2
Agenda
RLF
What is RLF ?
How/When/Why will it happen ?
Consequences of RLF
How to identify RLF from UE and X2 logs?
Observations
MRO
What are Too late/Too early and Ho to wrong cell
Test set up
Test case and its procedure
Observations
MLB
Concept of load balancing
MLB algorithm as per 3gpp spec and Samsung work
Test set up, test case and its procedure
Observations
RO
When RACH Occurs ?
PRACH procedures
RACH configuration parameters
Effect of improper RACH Parameters
RACH Optimization parameters
Test plans and Test set up
Observations
RLF - Radio Link Failure
Company Confidential | 4
Radio Link Failure ( RLF )
RLF ?
When/Why/How ?
PHY Layer
MAC Failure
RLC retransmissions reached
Company Confidential | 5
RLF Cont
Consequences:
UE loses its radio link
UE will send RRC Reestablishment Request eNB
Communication over X2
how to identify RLF from UE and X2 logs
UE eNB
RRC Reestablishment Request
Cause RRC Reconfig., Failure
HO Failure
Other
RRC Reestab., Response
X2 logs
RLF Indication
HO Report
Company Confidential | 6
RRC Reestablishment
When Reestablish request occurs , is it mean RLF happened ? No
To confirm ourselves we have started with creating scenarios which can produce Reestablishment message with all
its causes
1. HO Failure:
Set T304 to less value
Make UL to Target eNB to bad level using fader
Now try HO to target cell by making Source cell DL channel bad
UE keep on trying at PRACH for Target eNB; mean while T304 expires and leads to HO Failure
2. RRC Reconfiguration Failure:
Set up DRX or SPS in LSM which doesnt support by UE
3. Other ( RLF , Mobility from EUTRA, PDCP Integrity failure)
As other two are unlikely to come in our lab setup, if we see occurrence of cause other it signifies RLF
happening
We can easily identify RLF on X2 logs with RLF Indication message [explained in later slides]
Company Confidential | 7
Observations
RRC Restablishment : Cause - HO Failure [UE log - QCAT]
Company Confidential | 8
Observations Cont
RRC Reestablishment : Cause Other [UE log - QCAT]
MRO Mobility Robust Optimization
Company Confidential | 10
Mobility Robust Optimization ( MRO )
What is MRO ?
Why MRO ?
How will it help us ?
Too Late : UE is more aggressive than eNB HO parameter
Too Early: eNB is Reacting Slowly compared to UE speed
HO to Wrong Cell: Same as Too Early case with three cells
Company Confidential | 11
MRO Cont
Too Late HO to Wrong Cell
UE eNB A eNB B UE eNB A eNB C eNB B
HO
Re-establishment Request
Re-establishment Reject RRC Re-establishment Request
RLF Indication RRC Re-establishment Reject
RLF Indication
Too Early HO Report
UE eNB A eNB B
HO
Re-establishment Request
Re-establishment Reject
RLF Indication
HO Report
Company Confidential | 12
Test Set Up
Company Confidential | 13
Test Procedure: Too Late
LSM Configuration:
Add two eNBs (eNB A , eNB B) as neighbors to each other
Set N311 to high value and T310, N310 to less
Procedure:
Set RSRPs of both cells to good level and attach UE to eNB A.
Reduce RSRP of eNB A to very low value in very less time using fader.
Observations:
Check UE logs for RRC Reestablishment Request to eNB B with cause as other
RRC Reestablishment Response will be reject
Check X2 logs for RLF indication from eNB B to eNB A
Company Confidential | 14
Test Procedure: Too Early
LSM Configuration:
Add two eNBs as neighbors to each other
Set UE context release timer to high value in eNB A
Set N311 to high value and T310, N310 to less value in eNB B
Procedure:
Set RSRPs of both cells to good level and attach UE to eNB A.
Do successful HO from eNB A to eNB B
Create RLF in eNB B as specified in too late case within the UE context release timer value
Observations:
Check UE logs for
RRC Reconfiguration message from eNB A and Reconfiguration complete to enB B
Reestablishment Request to eNB B A and RRC Reestablishment response as rejected
Check X2 logs for
Successful HO from eNB A to eNB B
RLF INDICATION Message from eNB B A to eNB B
HO REPORT Message from eNB B B to eNB A
Company Confidential | 15
Test Procedure: HO To Wrong Cell
LSM Configuration:
Add two eNBs as neighbors to each other
Set UE context release timer to high value in eNB C
Set N311 to high value and T310, N310 to less value in eNB C
Procedure:
Set RSRPs of eNB A and C to good level and attach UE to eNB A.
Do successful HO from eNB A to eNB C; Reduce RSRP in both eNBs A and C worse than eNB B within UE
context release timer so that RLF will happen in eNB C and will send Reestablishment Request to eNB B
Observations:
Check UE logs for
RRC Reconfiguration from eNB A and Reconfiguration complete to eNB C
Reestablishment Request to eNB B and Reestablishment response as Rejected
Check X2 logs for
Successful HO from eNB A to eNB C
RLF INDICATION from eNB B to eNB C
HO REPORT from eNB C to eNB A
Company Confidential | 16
RLF Indication / HO Report
Company Confidential | 17
Observations
Too Late : RLF INDICATION
Company Confidential | 18
Observations Cont
Too Early: HO Report
Company Confidential | 19
Observations Cont..
Change in parameters :
CIO of eNB A towards eNB B has been incremented by 1 dB
MLB Mobility Load Balancing
Company Confidential | 21
Mobility Load Balancing ( MLB )
Concept: [TS 36.902]
To balance traffic load among eNBs
Minimizing number of HOs and redirections needed to achieve LB
Promising QoS; while taking LB decision
Cell A Cell B
LB Area
Company Confidential | 22
MLB Cont
MLB Procedure:
Resource Status Initiation
Request
Response
Resource Status Update
Resource Status Reporting
Periodicity
T_RESOURCE_STATUS_REPORTING: 1s/2s/5s/10s
Thresholds
PRB Usage or Available Capacity
Decisions
Requesting neighbor eNB for Mobility parameters change ( 3gpp Spec )
Force Handover ( Samsung Implementation )
Company Confidential | 23
Resource Status Request [TS 36.423]
IE/Group Name IE type and reference Semantics description
Message Type 9.2.13
eNB1 Measurement ID INTEGER (1..4095,...) Allocated by eNB1
eNB2 Measurement ID (C) INTEGER (1..4095,...) Allocated by eNB2
Registration Request ENUMERATED(start, stop,
) A value set to stop, indicates a request to stop all cells
measurements.
Report Characteristics (O) BITSTRING
(SIZE(32))
Each position in the bitmap
indicates measurement object
the eNB2 is requested to report.
First Bit = PRB Periodic,
Second Bit= TNL load Ind
Periodic,
Third Bit = HW Load Ind
Periodic,
Fourth Bit = Composite Available
Capacity Periodic.
Bits 5 to 32 shall be ignored by
the eNB2
Cell To Report Cell ID list for which
measurement is needed
>Cell To Report Item
>>Cell ID ECGI
9.2.14
Reporting Periodicity (O) ENUMERATED(1000ms,
2000ms, 5000ms,10000ms, )
Company Confidential | 24
Resource Status Response / Failure [ TS 36.423 ]
IE/Group Name Presence IE type and
reference
Message Type M 9.2.13
eNB1 Measurement ID M INTEGER
(1..4095,...)
eNB2 Measurement ID M INTEGER
(1..4095,...)
Criticality Diagnostics O 9.2.7
IE/Group Name Presence IE type and
reference
Message Type M 9.2.13
eNB1 Measurement ID M INTEGER
(1..4095,...)
eNB2 Measurement ID M INTEGER
(1..4095,...)
Cause M 9.2.6
Criticality Diagnostics O 9.2.7
Company Confidential | 25
Resource Status Update [ TS 36.423 ]
IE/Group Name Presence IE type and reference
Message Type M 9.2.13
eNB1 Measurement ID M INTEGER (1..4095,...)
eNB2 Measurement ID M INTEGER (1..4095,...)
Cell Measurement Result
>Cell Measurement Result Item
>>Cell ID M ECGI
9.2.14
>>Hardware Load Indicator O 9.2.34
>>S1 TNL Load Indicator O 9.2.35
>>Radio Resource Status O 9.2.37
>>Composite Available Capacity Group O 9.2.44
Company Confidential | 26
Test Case
Test Setup
Procedure
LSM
Parameter Description Default Value Value Set
INTRAGROUP _LB_TRIGGER _THRESHOLD
Threshold of load distribution between two cells in the same group of same sector. Only when the radio resource load of source cell is greater than this threshold,
40 10
OVERLOAD_T HRESHOLD_P RB
Threshold of load distribution between two cells in the same group of same sector. Only when the radio resource load of target cell is smaller than this threshold
75 100
T_MEASUREM ENT_COLLECT ION_LB
Period of measurement report collection
1 min 2 min
Company Confidential | 27
Test Set Up
To test Samsung Implementation for MLB
Company Confidential | 28
MLB Cont
As Per 3gpp:
Mobility change request ( Source eNB Target eNB)
Mobility Change Acknowledge ( Target eNB Source eNB)
Change in HO Trigger ( A3-Offset )
IE/Group Name Presence IE type and
reference
Message Type M 9.2.13
eNB1 Cell ID M ECGI
9.2.14
eNB2 Cell ID M ECGI
9.2.14
eNB1 Mobility Parameters O Mobility
Parameters
Information
9.2.48
eNB2 Proposed Mobility
Parameters
M Mobility
Parameters
Information
9.2.48
Cause M 9.2.6
IE/Group Name Presenc
e
IE type and
reference
Message Type M 9.2.13
eNB1 Cell ID M ECGI
9.2.14
eNB2 Cell ID M ECGI
9.2.14
Criticality Diagnostics O 9.2.7
Company Confidential | 29
MLB Cont
Company Confidential | 30
Observations
Resource Status Initiation : Request
Company Confidential | 31
Observations Cont
Resource Status Initiation: Failure
Company Confidential | 32
Observations Cont
Resource Status Update: Reporting
Company Confidential | 33
Observations Cont
HO: Cause MLB Optimization
RO RACH Optimization
Company Confidential | 35
PRACH
When RACH Occurs ?
Initial access from RRC_IDLE;
RRC Connection Re-establishment procedure;
Handover;
DL data arrival during RRC_CONNECTED requiring random access procedure;
UL data arrival during RRC_CONNECTED requiring random access procedure;
For positioning purpose during RRC_CONNECTED requiring random access procedure;
PRACH Procedure
Contention based Non Contention based
1. UE -> eNB: RA Preamble 2. eNB -> UE: RAR 3. UE -> eNB: L2/L3 Msg 4. eNB -> UE: Contention
Resolution
1. eNB -> UE : Dedicated Preamble assignment
2. UE -> eNB: RA Preamble 3. eNB -> UE: RAR
Company Confidential | 36
RACH / PRACH Configuration
Rach -Config Common [SIB2]
Number of RA-Preambles:
Size of RA-Preambles GroupA
Message Size GroupA
Message Power offset GroupB
Power Ramping Step
Preamble Initial Received Target Power
Preamble Trans Max
Ra-Response Window Size
Mac-Contention Resolution Timer
Prach Config Info
Prach-Config Index
High Speed Flag
zero Correlation Zone Config
Prach Frequency Offset
Company Confidential | 37
RACH Optimization
How RO is important ?
Effect of improper RACH Parameters
Call set up delays
Access Delays
HO delays
Wastage of Resources
Company Confidential | 38
Test Plans
Give your Suggestions