Self-Optimizing Networks The Benefits of SON in LTE

April 2014

Kamakshi Sridhar, PhD

Wireless CTO organization

Alcatel-Lucent

Contributors

This paper has greatly benefitted from the discussions with

and the contributions from various team members

• Alcatel-Lucent - Pantelis Monogioudis, colead

• AT&T – Arun Ghosh, Tom Henderson

• Blackberry – Sophie Vrzic

• Cisco – Jim Seymour, Vladimir Yanover

• CommScope – Tomas Lagerqvist

• Ericsson – Kejia Shi

• NSN – Ejaz Shah

• Qualcomm – Rajat Prakash, Kai Tang, Rao

Yallapragada

• T-Mobile – Pablo Tapia

Drivers for Self-Organizing Networks

RAN complexity: More basestations, More spatial reuse, Multiple technologies Growing QoS variance: Packet loss, latency, throughput, …

More complex policy requirements

Increasing complexity throughout the network: Heterogeneous networks with numerous parameters requiring optimization over a wide range of time scales.

Growing Network Complexity Driven by New Apps & End-User Devices Network complexity will break the present network management paradigm.

Device Proliferation

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Growing diversity of data apps, devices and usage patterns. Rise of the millenials!

Growing device diversity: iPhone, Blackberry, PC, … More diverse applications: Data-intensive (Web, P2P, VoD) vs. Signaling-intensive (M2M)

Explosion in wireless data usage: More data @ lower cost/bit

Universal broadband life: Always on

Mobile Hot spots-Nomadic

Increasing data traffic

Home coverage BB white zones

still wideMobile

Hot spots-Nomadic Increasing data

traffic

Home coverage BB white zones

still wide

Heterogeneous networks: Macros, Picos, Femtos

SON is essential for LTE to help operators realize operational efficiency and improved performance

SELF ORGANIZING Use Cases (3GPP)

1. Self Configuration: Newly deployed nodes (eNBs) are configured by automatic installation procedures

2. Automatic Neighbor Relation: Each eNB should automatically be able to generate and manage its own neighbor relation tables, based on measurement reports from the UEs.

3. Automatic Configuration of Physical Cell ID: automatically select from one of 504 PCIDs.

4. Interference Reduction / ICIC: Inter cell interference coordination to improve throughput at cell edges.

5. Mobility HO Optimization

– Optimization of UE -elated HO parameters

– Detection of problematic cell to cell relationship

– Detection of hot spots leading to ping pong

6. Mobility Load Balancing Optimization

– Intra/Inter carrier load balancing

– Traffic balancing across LTE and 2G/3G

7. Coverage and Capacity Optimization: tilt and power

8. Energy Savings: turn of cells during light loads.

9. RACH (Random Access Channel) Optimization: Random Access procedure performance influences the call setup delay/success rate, handover delay/success rate.

10. Cell Outage Detection and Compensation Cell Outage Compensation is realized through modification of antenna tilt.

SON automation provides operators with a path to maximize their network performance with minimum effort and cost.

NGMN and 3GPP SON

NGMN SON uses cases are defined at a higher level than 3GPP

specifications, and are introduced ahead of them.

• NGMN recommendations provide guidance to the technical standards

being developed for LTE, indicating the key use cases.

• These use cases have been identified by the operators as the typical tasks

that will be performed in day-to-day operations.

• A better system of integration and automation => more efficient utilization

of the operator resources, both material (spectrum, equipment, etc.) and

human (engineering time).

3GPP focus: Support of SON features in multi-vendor networks.

• Defining the appropriate interfaces to allow exchange of common

information which can then be used by each SON algorithm.

• Specifications built over the existing 3GPP network management

architecture, reusing functionality from Release 8.

• Interfaces are defined in a generic manner to leave room for innovation on

different vendor implementations.

SON in multivendor HetNets

Networks are becoming increasingly heterogeneous, multivendor

• Several parameters need to be tuned over a range of timescales

• Automation of parameters (hence SON) is critical

SON usecase coordination aspects

• One parameter affecting multiple usecases

• Multiple usecases interacting with each other over same time scale

• Dynamicity of response of various SON algorithms

• Availability of data needed to make a SON decision

• Impact of collecting the data (bandwidth limitations), signaling

impact , transaction rate limitations of physical hardware

• SON algorithms on different nodes reacting differently to parameter

changes -> conflicts, dependency. Hence, coordination is needed.

Complexities of SON are amplified in multivendor HetNets

CCO COC ES HOO LBO

Antenna parameters

Cell switch On/Off

DL Tx PowerHandover

parameters

SON Functions

Network Parameters

Goals and Summary of white paper

Paper addresses:

• Rel11 SON and multivendor aspects of SON

– challenges, approaches, solutions and tradeoffs

Paper presents:

• Various architecture options and tradeoffs in the

implementation of SON - MRO/MLB, dynamic-eICIC.

– Distributed, Centralized and Hybrid architectures

• Multivendor SON architecture based on X2

• Multivendor SON architecture based on NB interfaces

– An example SON functional architecture is presented along with data

sources needed for execution of SON.

– Harmonization of data schemas and control primitives is addressed to

reduce the integration complexity of SON in wireless networks.

• In the end, we found no “silver bullet” – an optimal

architecture that can provide the best possible performance

and simplicity for all SON usecases.

Multiple tradeoffs in the choice of architecture and solutions

need to be made for multivendor Het-Net SON

3GPP Rel11 SON updates and NGMN SON

3GPP Rel 11 provides enhancements to:

• Automatic Neighbor Relations (UTRAN and IRAT)

• Mobility Load Balancing Optimization

• Handover Optimization

• Coverage and Capacity Optimization

• Energy Savings

• Coordination between various SON Functions

• Minimization of Drive Tests

Rel 11 enhancements address some multivendor aspects.

Work on 3GPP Rel 12 SON is in progress.

NGMN Project Small Cells (2013) -the “Multi-vendor deployment”

work-stream addresses potential interoperability issues in

multi-vendor HetNets with focus on SON features.

SON is an active area of work in 3GPP and NGMN

SON architecture alternatives

• Architecture needs to be decided on a usecase by usecase basis and could co-exist with each other.

• Architecture choices could be phases over time.

• Practical deployments may require partnerships between the infrastructure vendor, the operator and a third party tool company.

Centralized Distributed Hybrid

Distributed SON, Centralized SON, Hybrid SON

Central OAM (NMS)

eNB1

eNB2 X2

EMS

EMS

Commands, Requests, Config Parameters

KPIs,reports, data streams

SON

Central OAM (NMS)

eNB1

eNB2 X2 SON SON

EMS

EMS

Commands, Requests, Config Parameters

KPIs,reports, data streams

SON SON

Distributed SON Centralized SON

Tradeoffs: data availability and validity, responsiveness,

coordination of an algorithm on multiple nodes,

hardware constraints, signaling impact, failure points.

Distributed and Centralized SON could coexist – Hybrid SON

Examples of tradeoffs considered

Traffic is dynamic (geographic, temporal) -> need for Dynamic eICIC

Hybrid architecture: some optimization is done at the eNBs/EMS

while other functions are centrally controlled at NMS.

• Centralized control could provide oversight to the distributed

algorithms. It could intervene to provide configuration parameter

adjustments. However, need to maintain different interface

extensions and extra signaling load.

Distributed Centralized

MRO/MLB Benefits

Information is available faster->

quicker response to congestion

Allows joint optimization of

MRO/MLB parameters for entire

network. More robust to instabilities.

Drawbacks IOT is needed

Slower responsiveness. Increase in

signaling load.

d-eICIC Benefits Faster response

Network wide optimum solution is

possible. Inter-operability is easier.

Drawbacks

Optimization is within each

cluster alone

Slower responsiveness. Certain

degree of IOT is still required in

multivendor. Complexity over Itf-N

needs to be addressed.

Key data source enablers for SON

• PM measurements and KPIs

• Trace Specifications

• Minimization of Drive Tests – Rel 11 enhancements

• Multivendor MDT issues

eNB from one vendor, MME from another vendor.

– Important event information about the call may be missed

Multiple sources of data inputs can be leveraged for SON

“MDT in 3GPP Rel 11”

IEEE communication Nov 2012

Multivendor SON architecture based on X2

Distributed X2 based SON algorithms

Decisions made locally at eNBs in consultation with neighbor eNBs.

• SON algorithms scale well with network growth and densification.

• Distributed SON solutions benefit from direct UE feedback to the

eNB for RACH optimization, MRO, MLB, ANR.

• OAM in the X2 based SON model can set performance targets

and configure boundaries within which the distributed SON

functions can operate.

• Several X2 based SON functions are enabled by the standards.

Dependencies in X2 solutions

• The X2 interface plays a vital role in several SON use cases.

Two aspects of multi-vendor interworking over X2:

• Interpretation of X2 messages and fields by the receiving eNB

• Need for inter-vendor alignment of eNB internal algorithms.

Paper describes X2 interworking for PCI, ANR, ESM,

MLB, MRO building on 2011 4G Americas SON paper

Multivendor SON architecture based on Itf-N

Management interfaces

• Type 2 between Element Manager (EM) and the Network Manager (NM)

• Type 1 between Network Elements (NEs) and the Element Manager (EM)

• The 3GPP management specifications focus on Type 2 primarily.

Paper describes SON mechanisms based on Itf-N for

IDLE and CONNECTED state load balancing CCO, MRO

Summary and Conclusions

• This white paper covers

– Release 11 SON enhancements.

– Multivendor aspects of SON

– Multivendor SON architectures based on X2 and Itf-N

• Choice of best architecture involves various tradeoffs

• Data sources- MDT, Call Trace, PM are SON enablers.

• We expect that SON over the next few years will evolve

towards hybridization to manage complexity

– Some SON use cases, fueled by the industry’s IOT

efforts, will be implemented without OSS involvement.

– Some SON use cases will require a supervisory entity at

the OSS, which itself can be multivendor.

SON architecture and solution space continues to evolve.

Market trends could play a role in architectural choices.