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1Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
Mischa DohlerCTTC, Spain
Manuel Palmowski & Dimitri MarandinmimoOn, Germany
Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved.
LTE/LTE-A SON (for Femtocells)
2Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
System Degrees of Freedom [1/2]
Degrees of Freedom (DOF) / Area: new system DOF = old system DOF x 20‐30 new system density = old system density x 4 new DOF/km2 = old DOF/km2 x 100
1
100
10000
1000000
00000000
1E+10
1E+12
GSM EDGE UMTSHSPA
LTELTE‐A
CELLULAR + WIFI + FEMTO
CELLULAR + WIFI
CELLULAR
3Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
System Degrees of Freedom [2/2]
With femtocells, the DOF increases significantly!
[presented by Interdigital: Globecom’11 – IWM2M, Houston]
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Likelihood of Failure/Outage
Important High‐Level Insides: DOF/area increases failures/outages increase:
loss in revenue if nothing done, and/or very costly if addressed by human labour
[© http://www.scien
cedirect.com
/scien
ce/article/pii/S0951832004000031]
5Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
Importance of SON
Previously Manual Processes: reduce manual intervention for deployment savings automate repetitive processes examples: automatic planning & self‐configuration
Too Fast/Complex Processes: improve run‐time operation based on real‐time data automate optimization of critical network elements example: self‐optimization & self‐healing
SON automation, however, is not new but rather a further evolution of prior automation efforts
6Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
Elements of SON
Important Elements: elements of “autonomous” elements of “distributed” elements of “intelligent/cognitive” elements of “optimality”
SON ≠ SON: despite large DOF, SON has to be (close to) optimal since it makes no sense to have a system with amazing components which however underperforms due to poor “management”
7Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
SON in Cellular Networks
Optimisation/Maintenance
Self Optimisation
Self Healing
Deployment
Planning
Self Configuration
Automated Planning
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Presentation Overview
1. SON in NGMN & 3GPP LTE
2. SON Architectural Elements
3. 3GPP SON Features
4. 3GPP SON Functional Details
5. Conclusions
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1. SON in NGMN & 3GPP LTE
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NGMN’s Input To SON
Next Generation Mobile Networks (NGMN) Alliance: created in 2006 by group of operators business requirements driven often based on use‐cases of daily networking routines
NGMN and SON: SON input to 3GPP since 2006 10 SON use cases have been defined (see right) which input to 3GPP Rx
QoS SON is likely to appear shortly
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3GPP High‐Level Structure
maintenance/developmentof GSM/GPRS/EDGE RAN
maintenance/developmentof UMTS/HSPA/LTE RAN
system architecture, service capabilities, codecs (inc. EPC)
CN interfaces, protocols, interworking, IMS, terminals, SIM
Management!
12Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
SON in 3GPP LTE Release 8
3GPP R8 is about eNB self‐configuration: automatic neighbor relation automatic physical cell ID (PCI) assignment automatic inventory automatic software download
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SON in 3GPP LTE Release 9
3GPP R9 is about network optimization procedures: mobility robustness and handover optimization RACH optimization load balancing optimization inter‐cell interference coordination (ICIC)
14Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
SON in 3GPP LTE‐A Release 10
3GPP R10 is about overlaid networks: coverage & capacity optimization enhanced ICIC cell outage detection and compensation self‐healing functions minimize drive test energy savings
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SON in 3GPP LTE‐A Release 11
3GPP R11 will be about heterogeneous networks: automated network management troubleshooting multi‐layer, multi‐RAT heterogeneous networks among other issues
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3GPP SON Status
PCI_Sel.
ANR
MLB, MRO, RACH
Energy Saving (ES)
Minimize Drive Test (MDT)
SON MgmtSelf‐Healing
MDT
PCI_Selection
Energy Saving
MLB, MRO,CCO
SA5
RAN
Rel9 Rel10Rel8
ANR = Automatic Neighbor RelationPCI = Physical Cell IDMLB = Mobile Load BalancingMRO = Mobility Robustness Opt.RACH = Random Access ChannelCCO = Capacity & Coverage Opt.
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2. SON Architectural Elements
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SON Architecture Approaches [1/2]
Levels of SON Execution: localised: autonomous SON execution based on purely local information at (H)eNB & UE
distributed: autonomous SON execution based on information exchanged with neighbouring (H)eNB (eg via X2 interface)
centralized: decision taking based on (fairly complete) system information (eg at NM/DM/EM levels)
hybrid: any mixture of above
X2
NM
DM/EM
SON
SON
DM/EM
SON SON
SON
NM = Network ManagementDM = Device ManagementEM = Element Management
19Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
SON Architecture Approaches [2/2]
centralized distributed localised hybrid
KPI = Key Performance Indicator
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Key Time Intervals
For Centralised SON, timing is important: Collection Interval: time period during which statistics and data are collected; limited by vendor’s OAM bandwidth; typical 5min (i.e. not at scheduling level!)
Analysis Interval: time period needed to draw decision; typically several collection intervals (filtering effect by considering also prior data history)
Change Interval: time period between executing the changes in the network; typically limited by system’s operational constraints
21Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
Important SON Trade‐Offs
Centralised
multiple cellslong term statisticsuses OAM multi‐vendor/multi‐RAT
self‐configurationcoverage optimisation(load balancing)
Distributed
normally ca. 2 cellsuses X2multi‐vendor (X2)
handover opt.load balancingRACH opt
Localised
adv. RRMsmall impact on ncellsshort term statistics
scheduler optLink adapt. optRACH opt
faster & less prone to “single point of failure”
info from number of cells/RATs
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Coordinated SON Model
very difficult to standardise: lots of different ways to implement a SON function are possible e.g. load balancing (LB) done at NM level but handover (HO) optimization done at eNB level and both want to adjust the same parameter in eNB
practical way around today: if function at NM level, “configure” is standardised at eNB level not standardised currently primary & secondary targets are defined
[based on S5‐102029]
man
agem
ent
decision
taking
execution
feedback
23Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
BeFEMTO HeNB Architecture
SO‐RRIM
MAC
RLC
PDCP
PHYRF
BB
Radio Functions
SON Enabling Functions
Coverage EstimationPositioning …
SO-RRIM Sub-functions
LoadBalancing
Mobility Control
AdmissionControl
EnergySaving
…Scheduler
MAC
IP/IPsec
TCP
PHY
Geo Sublayer
SCTPUDP
RRCHTTPS
SOAP RPC
GTP‐U
S1AP/X2AP
Network /Mgmt Functions
Fault Diag.Probe
Routing
Network Sync
Local NetwElem Agent
Protocol Stacks
S1 / X2 / Type 1C / Rt /Lm interfaces Uu / Un interfaces
Radio SON Coordinator
LocalLocationMgmt.
Perform.Mgmt
IKEv2
EAP‐AKA
NMM
TCP/UDP
Security
ManagementFunctions
NetworkFunctions
ContextLearning
usersnetwork
24Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
3. 3GPP SON Features
25Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
SON in Cellular Networks
Optimisation/Maintenance
Self Optimisation
Self Healing
Deployment
Planning
Self Configuration
Automated Planning
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SON Functions (NGMN & 3GPP)
Self‐Optimisation
Self‐Healing
Self‐Configuration
Automated Planning
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Automated Planning
From “trial & error” to “planning automation”:
[© ICT MOMENTUM]
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Self‐Configuration
Important Self‐Configuration Functions: authentication address allocation secure OAM tunnel setup SW installation inventory management transport parameters setup radio parameters setup self‐test
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Self‐Optimisation
• Automatic Neighbour Relation• Mobility Robustness/Handover Optimisation• (Mobility) Load Balancing• RACH Optimisation• Coverage and Capacity Optimisation• Energy Saving• Interference Coordination• HeNB SON
3GPP
• QoS Optimisation (advanced RRM)• Scheduler• admission control• congestion control• link level/L2/HARQ re‐tx/MIMO parameters
additional from Socrates/NGMN (not discus)
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Self‐Healing
Important Self‐Configuration Functions: failure recovery cell outage compensation
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4. 3GPP SON Functional Details
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eNB Self‐Configuration (Rel. 8)
Benefits: reduction of manual labour faster and cheaper network deployment
Description: detect transport link & establish connection download & upgrade software set up initial configuration parameters perform self‐test go into “operational” mode
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Benefits: keeping centralized neighborhood tables is impossible automating this is one of the most important SON features
Description: keep updated neighborcell(ncell) table through UE obtain ECGI & IP via MME to communicate to target eNB
ECGI = E‐UTRAN Cell Global IdentifierOAM = Operating Administration & MaintenanceMME = Mobility Management EntityRRC = Radio Resource ControlerTCI = Target Cell Identifier
34Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
PCI Selection (Rel 8/9)
Planned/Centralised PCI direct value is assigned (3 x 168 = 504 in total only!)
SON/Distributed PCI selection a range of PCIs is given
eNB will not select cell IDs that arereported by UEsreported over the X2 interface (not for HeNB as of now)acquired through NW listen mode (will not catch all)
select PCI value randomly from the remaining PCIs
PCI collisions: >1 eNB seeing each other choose same ID
PCI = Physical Cell ID
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PCI Selection ‐ Collisions
PCI collision probability depends on the number of PCIs available for such cells
PCI reported belongs to two different ECGI Collision recovery
Number of PCIsavailable for
non-macro eNBs
Percentage of UEs observing collision of
PCIs with random PCI allocation
Percentage of UEs observing collision of PCIs
with random PCI allocation plus downlink receiver (sensitivity at -6
dB)
Percentage of UEs observing collision of PCIs
with random PCI allocation plus downlink receiver
(sensitivity at -8 dB)
10 15.2% 12.2% 11.7%
50 3.3% 2.6% 2.4%
100 1.7% 1.3% 1.2%
200 0.9% 0.7% 0.6%
500 non‐macro eNBs (e.g. HeNBs) dropped randomly in each macro eNB [R3‐091018]
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MRO (Rel‐9, ext Rel‐10)
too early intra‐RAT HO: wrong cell intra‐RAT HO:too late handover (HO):
Mobility Robustness Optimization (MRO) because …… Handovers (HOs) between same (intra) and different (inter) radio access technologies (RATs) can go very wrong:
37Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
MRO (Rel‐9, ext Rel‐10)
Mobility Robustness Optimization detect radio link connection failures due to being too early, too late
handovers or handover to wrong cells caused by not optimised intra/inter‐RAT handover parameters also used for optimising idle mode cell reselection parameters
UE sends Radio Link Failure (RLF) measurement report to eNBwhere UE did re‐establishment
Optimised for Rel‐10 to use also ConnectionRequest
too early handover
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eNB
MRO (Rel‐9, ext Rel‐10)
OAM
MRO
MobilityControl
RRM config examples:Trigger ThresholdTime‐to‐TriggerHysteresis against Ping‐PongSpeed & Neighbour Param.Electric Antenna Tilt
config target:Rate of failures related to HO
monitor KPIs, alarms:Nr of HO eventsNr of HO failuresNr of too early HO
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MLB (Rel‐9)
Mobility Load Balancing Distribute cell load evenly among cells or Transfer part of traffic to other cells so that radio resources remain highly
utilized Optimisation of mobility parameters or handover actions Also includes setting of cell reselection mode for idle mode balancing
Load Reporting the radio resource usage (UL / DL PRB usage) HW and TNL load indicator (UL/DL load: low, mid, high, overload) a cell capacity class indicator and capacity value (UL / DL)
PRB = Physical Resource BlockTNL = Transport Network LayerHW = HardwareUL = uplinkDL = DownlinkRAB = Radio Access Bearer (next slide)
40Copyright © 2009 BeFEMTO– Broadband Evolved FEMTO Network. All Rights reserved
MLB – Active Mode LB
target cell is informed proposed source cell
change proposal for target cell
change
Serving eNB
OAM
MLB
MobilityControl
RRM configHO Trigger‐/+ 10dB (incr/reduce time until HO decision)
config target:‐ RAB setup failure rate due to load‐ Rate of failures related to HO
monitor KPIs, alarms:Nr RAB setup failure due to loadTotal nr of RAB setup failure
Target eNB LOAD INFO
MOBILITY CHANGE
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RACH optimisation (Rel 9)
Optimises the (P)RACH configuration access to internal measurements and access to feedback from UEs (via RRC) and from other (H)eNBs
The setting of RACH parameters that can be optimized are: RACH configuration (resource unit allocation), preamble groups split,
backoff, power control
UEs which receive UEInformationRequest shall feedback:Number of RACH preambles sent until the successful RACH completion (indication of quality of link)
Contention resolution failure (indication of cell load) X2 allows to exchange RACH config between eNBs Rel 10 OAM policy targets: Access Probability and Access Delay
Probability
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Min. Drive Tests (R10 procedure)
Performs logging of available measurements together with location and time for logged measurement configured UEs
Types: Immediate and logged measurements Immediate measurements (UE optional FFS)Reuses normal measurements with addition of location
Enhancement of RLF Report to include location Idle mode logged measurements (UE optional)Input: duration, interval, cell ids and/or tracking areasTime, Location, Cell id, scell/ncell RSRP/Q
Add. eNB meas: eNB RIP and CQI under disc, + PHR and UL SINRMDT activation via OAM per cell/region (not reused at HO) S1 UE specific trace activation (can be cont. on HO)
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Coverage and Capacity Opt (Rel‐10)
Coverage definition“coverage hole” (should cover UL also)
unsuccessful RX of DL control channels and signalling radio bearersdifferent control channels have to be optimised jointly
“weak coverage”: cell‐edge users, minimum service rate not reached
Types of coverage holesother RATs/no radio, coverage too small/too large
CCO detection using MDT/MRO Inputs: UE measurements, Performance measurements,
alarms Outputs: power control, antenna tilt, azimuth
Capacity & Coverage improvements
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Energy Saving
Optimise energy consumption: a cell providing additional capacity can be switched off when its capacity is no longer needed and to be re‐activated when needed
The decision typically based on cell load information Peer eNBs are about the switch‐off over the X2 interface (eNB
Configuration Update procedure) Informed eNBs keep the cell config when a cell is off and may request re‐
activation if needed (X2: Cell Activation procedure) How to select to correct cell to switch‐on? The operators can configure ES function:
enable/disable ES OAM policies for switch‐off and reactivation
open interRAT, overlaid inter‐eNB savings solutions to capacity limited scenario of inter‐eNB energy saving ES in network sharing
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5. Conclusions
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SON Conclusions
Benefits of SON: reduction of human intervention real‐time optimization of network significant CAPEX & OPEX savings!
NGMN & 3GPP: important SON features standardised from R8‐R11 focus shifting from auto‐planning & self‐configurationtowards self‐optimization and self‐healingmost important SON features have been discussed in thispresentation whereas concrete embodiments of SON comes later today