An Introduction to Self-Organizing Networks (SON)

An Introduction to Self-Organizing
Networks (SON)
Date: Dec 2013

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2

Parameter Update
What is happening now in operation of typical cellular system?
Performance
analysis
Optimal
parameter
calculation
In field
Remote
Measurement
User Reports
based
Drive test
based
Database
Confidential – Restricted Distribution © eXplanoTech Ltd., 2013 3

How SON will benefit?
Parameter Update
Performance
analysis
Optimal
parameter
calculation
In field
Remote
Measurement
User Reports
based
Drive test
based
Database

SON Architecture: Centralized
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Counters/KPIs Sector-specific settings
SON

SON Architecture: Distributed
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High level reports High level SON policies

SON Architecture: Hybrid
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Counters / KPIs
High level reports
Sector-specific settings
High level SON policies
SON

Three stages of SON
Self-
Configuration
• Plug and Play (PnP)
• Faster Rollout
• Consistency
• Licensees, Hardware Inventory and Software build
• Efficient resource utilization
Self-
Optimization
• Mobility Robustness Optimisation (MRO)
• Mobility Load Balancing (MLB)
• Minimization of Drive Testing (MDT)
• Fast and proactive parameter optimization
• Increased Network performance
Self-
Healing
• Fast, autonomous failure mitigation
• Continuous performance monitoring
• Faster Network maintenance
• More efficient resource utilisation, less effort

SON Features in Release-8
 Release-8 focussed on eNodeB self-configuration.
 The following features have been defined in Rel-8
 Automatic Neighbour Relationship (ANR) management
 Automatic PCI assignment
 Automatic Inventory
 Automatic Software download
 Mobility Load Balancing (MLB)
 ANR and MLB are discussed in detail

eNodeB self-configuration
• When eNodeB is switched on for the first
time, it requires minimal information as
following:
– Domain name of NMS
– Domain name of its MME’s
– Domain name of S-GW
• eNodeB contacts the NMS:
– Downloads the software (if required)
– Download configuration parameters
• TAC, PLMN identities, global cell id, power info
• The Physical cell Id can be assigned or automatic
• Run S1 setup to establish connection with
MME’s
eNB
eNB
DHCP /
DNS server
S-GW
MME

Automatic Neighbour Relationship (ANR)
 Due to the location of the UE, it may be able to
see more cells than the scanner in an eNB
 The UE’s can then report the Cell Id’s in
Measurement report
 This means the NMS does not need to worry
about assigning Neighbour lists to eNB when its
setup.
• This is particularly important in the case of Small cells
whose location can change
 Once a new neighbour cell is identified, the eNB
should setup X2 connection that can be very
useful.

ANR Procedure
Measurement Procedure
RRC Connection Reconfiguration (Meas)
RRC Connection Reconfiguration Complete
Measurement Report (Global Cell Id)
S1-AP: eNB Configuration Transfer
S1-AP: MME Configuration Transfer
S1-AP: eNB Configuration Transfer
S1-AP: MME Configuration Transfer
X2-AP: X2 Setup Request
X2-AP: X2 Setup Response
eNB MMEeNB NeighbourUE

Mobility Load Balancing (MLB)
• eNB’s can co-operate to balance load
between them, thereby increasing
network capacity
• Even though this procedure was
introduced part of Rel-8, there were
enhancements in Rel-9 and Rel-10
that has made this procedure much
more useful.
X2-AP: Resource Status Request
X2-AP: Resource Status Response
X2-AP: Resource Status Update
(Resource block usage,
S1 load, available capacity,
hardware load, etc.)
eNBeNB Neighbour

MLB Enhancements in Rel-9
 Two enhancements have been added in Rel-9:
– The neighbour eNB now reports a fourth field in its Resource
Status Update, the ‘composite available capacity group’, which
indicates the capacity that it has available for load balancing
purposes on the uplink and downlink. The original eNB can use
this information to assist its handover decision.
– There is also a risk that after such a handover that the new base
station will hand the mobile straight back to the old one. To
prevent this from happening, a new X2 procedure, known as
mobility settings change has been introduced. Using this
procedure, a base station can ask a neighbour to adjust the
thresholds that it is using for measurement reporting, by means
of the cell specific offsets. After the adjustment, the mobile
should stay in the target cell, instead of being handed back.

MLB Enhancements in Rel-10
 In Rel-10, using S1 procedure direct information transfer, a base station
can initiate the exchange of radio access network information
management (RIM) information with a UMTS or GSM neighbour. The
information includes the composite available capacity group in the case
of an LTE cell and similar information known as the cell load information
group in the case of the other technologies. In turn, this information can
trigger a load balancing handover to a UMTS or GSM neighbour.
UTRAN
MME
SGSN GGSN
eNB
Iu-PS Gn
S1-MME
S3
RIM Signalling
RIM Signalling
Relaying
RIM Signalling

 Release-9 has been focussed mainly on Network
Optimization procedures.
 The following features have been defined in Rel-9
 Mobility Robustness (MRO) and Handover Optimization (HO)
 RACH Optimization
 Load Balancing Optimization
 Inter-Cell Interference Co-ordination (ICIC)
 Load Balancing Optimization was just discussed
 ICIC is covered as part of Interference Management section

How Self Optimization will work?
User reports
based
Continuous Self Optimization
Parameter Update
Centralized
Autonomous
Distributed
Autonomous
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Self-configuration/Self-optimization support and inter-operability
eNB power on
(or cable connected )
(C) Optimization /
Adaptation
(B) Initial Radio
Configuration
(A) Basic Setup
a-1 : configuration of IP address and
detection of OAM
a- 2 : authentication of eNB/NW
a- 3 : association of aGW
a- 4 : downloading of eNB software
(and operational parameters)
b- 1 : neighbour list configuration
B-2 : coverage/capacity related
parameter configuration
c- 1 : neighbour list optimisation
c- 2 : coverage and capacity control
Self-Configuration
(pre-operational state)
Self-Optimisation
(operational state)

Mobility Robustness Optimization (MRO)
 MRO was introduced in Rel-9
 MRO helps eNB to find the
problems in handover and
then by using this
information, it can adjust the
thresholds
 Three main causes of failures
can be seen in the pictures
C
AB
XX
C
AB
C
AB
HO Request
HO Confirm
Drop
Re-establish
RLF
HO Report
HO Report
X
A
CB A
CB
Drop
Re-establish
RLF
XC
AB
C
AB
C
AB
HO Request
HO Failure
Drop
Re-establish
RLF
HO Report
INTRA-RAT LATE HO TRIGGERING
XC
AB A
CB
Drop
Re-establish
RLF
HO Report
INTRA-RAT EARLY HO TRIGGERING
WRONG CELL HANDOVER (RLF AFTER HO) WRONG CELL HANDOVER (RLF BEFORE HO)

MRO: Late Handover (HO) Triggering
Radio Link Failure
RRC Connection Reestablishment
Handover Procedure On-going
Contention based random access
RRC Connection Reestablishment Complete
UE Information Response
UE Information Request
X2-AP: RLF Indication (old cell ID, C-RNTI, UE Information)
RRC Connection Reestablishment Request
(old Cell Id and C-RNTI)
New eNBOld eNB UE

MRO: Early Handover (HO) Triggering
(new Cell Id and C-RNTI)
Handover to a coverage island of the target cell on new eNB
Radio Link Failure
X2-AP: RLF Indication (new cell ID, C-RNTI, UE Information)
X2-AP: Handover report (handover too early)
New eNBOld eNB UE

MRO: Handover (HO) to Incorrect Cell
(new Cell Id and C-RNTI)
Handover to wrong cell
Radio Link Failure
X2-AP: RLF Indication
X2-AP: Handover report (handover to wrong cell)
(new cell ID, C-RNTI, UE Information)
New eNBOld eNB UE Third eNB

MRO: Release-10 enhancements
 MRO was enhanced in Rel-10 to detect unnecessary inter-
RAT (Radio Access Technology) handover.
 After handover to the other RAT, the new Access Network
can configure LTE measurements for the nearby cells.
 If the power received is sufficiently high, the network can
tell the old eNB that the handover was triggered
unnecessarily.
 This is informed to the old eNB using the S1-AP direct
transfer procedure.

RACH Optimization
• The eNB continuously or periodically performs RACH
optimization based on the UE feedback and knowledge
of neighbouring eNB’s RACH configuration
• An optimized RACH will:
– Reduce connection time
– Help achieve Higher Throughput
– Improve cell coverage
RRC: UE Information Response
RRC: UE Information Request
New eNBUE

RRC UE Information Request message

RRC UE Information Response message

PRACH Configuration in X2-Setup
X2-AP: X2 Setup Response
X2-AP: X2 Setup Request
eNB 1 eNB 2

• Release-10 has been focussed mainly on self-healing
functions.
• The following features have been defined in Rel-10
– Coverage and Capacity Optimization (CCO)
– Minimization of Drive Testing (MDT)
– enhanced ICIC (eICIC)
– Cell outage detection and compensation
– Energy savings
• eICIC is discussed as part of Interference
Management

Example flowchart of Self-Healing process
MONITORING
ALARM
DIAGNOSIS
COMPENSATION
Start
Monitor TCoSH
Trigger self healing
process
Take measurements
and NCL data
Analysis and Diagnosis
False
detection?
Update NCL and begin
compensation action(s)
Performance analysis (faulty
cell and neighbouring cells)
Alarm
cleared?
Monitor, Repair and control
compensating actions
Store alarm
information for
future analysis
Y
N
Y
N
Clustering algorithm classifies to
determine type of fault and
identify necessary
compensating action
Analyse all alarms, alarm
correlation and determine
specific compensating actions(s)
from neighbouring cell(s)
Update Neighbour Cell List (NCL)
and begin compensation action
via specific neighbouring cells
Ensure compensating actions are
relaxed when a faulty node has
been restored
Algorithm continuously
monitors system for alarms that
Trigger Conditions of Self
Healing (TCoSH)
TCoSH
reached?

Coverage and Capacity Optimization (CCO)
• This has traditionally been the key area of optimization.
• This is carried out over a rather long time-scale in the
order of days or weeks by capturing and reacting to
long-term changes in physical environment, load
imbalance, and UL/DL mismatch.
• The network should periodically be automatically able to
adjust the key RF parameters once the cells have been
deployed.
• The key RF parameters are:
– Power of the cell
– Antenna configuration (eg., tilts of the antenna)
• CCO is more of an ‘automatic cell planning’.

CCO Examples

Minimization of Drive Testing (MDT)
• Drive testing is one of the biggest cost of running the
network after the energy usage
• In a traditional network, drive tests have to be done
multiple times on different network loads to get an
accurate picture of the cells coverage and capacity
• To reduce the amount of drive test, MDT feature was
introduced in Release-10
• Two types of MDT are defined:
– Immediate MDT
– Logged MDT
• MDT Measurements can be on Control Plane or User
Plane.

U-plane and C-plane MDT
• The U-plane MDT is
operator specific with
operator deploying an
application on the phone to
do this measurements
• The C-plane MDT is based
on the signalling and would
be standardised across all
devices and form factors.
MDT server MDT server
RANRAN
UEUE

Logged v/s Immediate MDT
Logged MDT
• Measurements in Idle mode
• Logging measurements and
reporting later on
• Optional for the UE to support
Immediate MDT
• Measurement in Connected mode
• Immediate reporting e.g., at RLF
• Mandatory for the UE to support
Log
Coverage
Hole

Logged MDT example
• Same amount of measurements as in normal case
• Periodical logging : 1280ms~61440ms
• logging duration : 10min~120min
IDLE
measurement occasions
Logging
Logging interval
Logging duration
: radio measurements
: detailed location info. (if available)
: time stamp

Immediate MDT example
• UE can discard RLF info 48 hour after the radio link failure is detected
MDT
configuration
RRCConnectionReestablishmentComplete
CONNECTED Re-establishment CONECTECDRLFCoverage
Hole
Logging
Signal strength,
location
measurement occasions
RLF log
indication
Log
retrieval

Procedure for collecting RLF reports by OAM
Trace session activation
MDT server (TCE)
UE information request
UE information response
(RLF report)
Trace record reporting
Cell trace session
started
Connected mode
UE records the
RLF report
Idle mode
Call setup
Include RLF report available indication
Storing RLF report
in trace record
RLF/HOF
eNB UEOAM

RRC UE Information Request message

RRC UE Information Response message

MDT Enhancements for Rel-11
• MDT was enhanced for Rel-11 to collect not only measurements
indicating the network coverage condition but also those indicating
the users’ real-life throughput and connectivity issues.
• For most cases, the battery consumption is not significantly
impacted by MDT. One exception is the ability to request the UE to
activate its GNSS receiver for MDT that is introduced in Rel-11,
which is expected to involve significant battery power consumption.
The operator may choose to handle this by subscription agreements,
and only use requested location for subscribers that have consented
to this.

Cell Outage Detection and Compensation
• Cell Outage Detection and Compensation provides
automatic mitigation of eNB failures especially in the case
where the eNB equipment is unable to recognize being out
of service and has therefore failed to notify OAM of the
outage. Detection and Compensation are two distinct
cases that cooperate to provide a complete solution:
– Cell Outage Detection typically combines multiple separate
mechanisms to determine whether an outage has occurred. This
is needed to detect the latent fault case, often described as
“Sleeping Cell”, where OAM is unaware of the issue.
– Cell Outage Compensation techniques are generally only
applied after standard soft recovery techniques have failed to
restore normal service.

Energy Savings
• Power Amplifiers are the biggest source of power
consumption for an eNB.
• In hotspots where small cells are deployed, they can be
switched off during off-peak hours
– Switching cells off should not create coverage holes
– The eNB is still on, only the transmitter/receiver is switched off
• The active users should be handed over to an overlapping
cell(s)
– It should also inform the cell(s) about the change using X2-AP
eNB Configuration Update message.
• A neighbour can ask at a later stage to the eNB to switch
the cell on using X2-AP Cell Activation Request message.

• Release-11 has been focussed mainly on
Heterogeneous Networks (HetNets).
• The following features have been defined in Rel-11
– UTRAN SON Management
– Inter-RAT Energy saving management
– Automated network management
– Troubleshooting
– Multi-layer, Multi-RAT HetNets
• Will not be covered as part of this training.

An Introduction to Self-Organizing Networks (SON)

An Introduction to Self-Organizing Networks (SON)

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