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Pre-Planned to Self-Organizing and Green Wireless Networks

Disclaimer:Engineers and Mathematicians

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Picture borrowed from:A. Eisenblätter, H.-F. Geerdes, Wireless Network Design: Solution-oriented

Modeling And Mathematical Optimization, IEEE Wireless Communications, December 2006

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Summary

Wireless networks

Radio planning evolution (2G and 3G)

Coverage Planning

Capacity Planning

Self-organizing networks (4G)

Complexity of network management

4G systems (LTE)

Concept of SON

Dynamic resource management

Wireless Green networks

Energy consumption

Green energy management

Conclusion

Phones …

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Mobile phones

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Cellular subscribers vs fixed lines

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0

500

1000

1500

2000

2500

3000

3500

1990 1995 2000 2005 2007 2010

Cellular

Subscribers

Telephone Lines

Source: www.etforecasts.com

Mobile vs fixed vs internet

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60 mobile subscribers per 100 inhabitants

19 fixed lines per 100 inhabitants

23 internet users per 100 inhabitants

9 broadband users per 100 inhabitants

Source: ITU

Data: 2008

Mobile subscribers by country

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Radio planning

The deployment of mobile radio networks required so far HUGE investments

The extension of existing network, new data services, and new technologies are continuing to require a lot of money

This has stimulated mobile operators to use automatic tools for the design and the optimization of their networks

In the last ~15 years the research community has proposed a large number of approaches for designing and optimizing wireless access networks (more than 16000 results in Google Scholar)

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Network planning tools

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Main Planning Tools:

Aircom Asset

Mentum Planet

Atoll FORSK

ATDI

WinProp

EDX Signal Pro

CelPlan

Siradel

Pathloss

Main Optimization Engines

Actix

Capesso

TEMS

What is radio planning?

The basic decisions that must be taken during the radio planning phase are: Where to install base stations (or access points,

depending on the technology) How to configure base stations (antenna type,

height, sectors orientation, tilt, maximum power, device capacity, etc.)

XX

XX

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What is radio planning? This is, however, not enough …

Multiple access techniques are used to define

communication channels on the available radio spectrum

Radio resources for wireless systems are limited and must be reused in different areas (cells)

Resource reuse generates interference

FDMA TDMA CDMA

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Interference

Interference is the key parameter that drives network planning and optimization processes

Interference can be tolerated (good communication quality) if the Signal-to-Interference and Noise Ratio (SINR) is high enough

SIR constraint limits the number of simultaneous communications per cells, i.e. the system capacity

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GOAL:minimize costs

maximize covered traffic

inout

rec

II

PSFSINR

2G Planning

FDMA/TDMA cellular systems adopt a two phases radio planning

Coverage planning

Capacity planning (frequency assignment)

Coverage planning:

Select where to install base stations

Select antenna configurations

s.t. constraints on signal level in the area

Capacity planning:

Define which radio resources can be used by each cell

s.t. SINR (quality) constraints

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Coverage Planning Many different models have been proposed for

the coverage planning

Basically all of them are based on the classical set covering problem

With several specific features that have been added depending on technology and service mix

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min Objective function:

total network cost

Full coverage constraints

One configuration per site

Integrality constraints

Coverage Planning

Example: Cell overlap

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Note that:

zih = 1 if i and h are covered by a same BS

Cell overlap may be required for mobility management

Overlap can negatively affect capacity (e.g. in WLANs)

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Capacity planning(aka frequency assignment)

After coverage planning, capacity planning is in charge of defining which radio resources can be used by each cell

The amount of resources (frequencies) assigned to cells determines system capacity

Frequencies can be reused, but SINR (quality) constraints must be enforced

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F2

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F5

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Frequency assignment

Maximizing the simultaneous transmission with SINR constraints is a key problem is all wireless networks

ij

SINRij>t

However, the most popular models for frequency assignment have been based on compatibility graphs

Frequency assignment problems

are modeled as variants of the

graph coloring problems

i j

cij

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Frequency assignment

Since Graph based models do not consider SINR constrains explicitly the cumulative effect of interference is not accounted for

Compatible?

Minimum Interference Frequency Assignment Problem (MI-FAP) and its variants models directly interference effect

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3G Planning

3rd Generation Systems are based on W-CDMA (UMTS)

Two-phases approach not suitable because:

Channels are shared and there is no frequency planning for CDMA

Coverage depends on SINR values

Joint coverage and capacity planning

SINR constraints make the problem a generalization of the capacitated facility location problems

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Network management & control

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Network configuration and optimization is becoming far too complex for mobile operators

4G – Long Term Evolution

The need to plan, configure, manage a new wireless network from scratch

… with up to 10 times more base stations

… and many more parameters to set

simply worries mobile operators

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4G – Long Term Evolution

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LTE architecture

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eNB

MME / S-GW MME / S-GW

eNB

eNB

S1

S1

S1

S1

X2

X2

X2

E-UTRAN

The radio architecture of LTE is more complex

Base stations (eNodeB) are connected also among them (mesh topology)

and they have computation capability to perform advances functions

The presence of femto-cells can make the network management even more complicated

LTE radio interface

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More similar to 2G than to 3G

Self Organizing Network (SON)

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Self Planning

Self Configuration

Self Optimization and Self Tuning

Self Testing and Self Healing

Self Mantenance

Performance Improvement

Cost reduction

“self-organizing network is a cellular network in which the tasks of configuring, operating, and optimizing are largely automated.”

Self Organizing Network (SON)

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CentralizedArchitecture

DistributedArchitecture

Self Organizing Network (SON)

Most of the SON features are aimed at simplifying preoperational and operational procedures

HW configuration

SW installation and configuration

Radio basic parameters

Transport parameters

Etc.

However, the most interesting issues from our perspective are related to the configuration and management of radio resources

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Automatic carrier

selectionFractional reuse Load balancing

Dynamic assignment

The idea of self-configuring and self-optimizing wireless network is not new!

Several Dynamic Channel Assignment (DCA) schemes have been proposed and analyzed for 2G

Channel/frequency assigned on demand based on compatibility or interference constraints

… but they have never been used in real networks

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Resource assignment in LTE

LTE-advanced offers several instruments to make configuration and dynamic management of radio resources possible

eNBs can make measurements over the radio interface before first resource configuration

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User terminals can provide measurements to eNBsduring system operation to dynamically select resources

Resource assignment in LTE

Defining both centralized and distributed self-configuration and self-optimization models and algorithms for LTE is still an open problem

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Automatic carrier selection

Channel assignment based on position in the cell (fractional reuse)

Load balancing among cells forcing handover

Etc.

Green Wireless Networks

In addition to configuration, energy consumption of wireless network is another issue that concerns of operators

The power consumption of cellular networks infrastructure (base stations and core network) doubles every 4-5 years - to 60 TWh in 2008

Energy consumption of mobile telephony operators in Italy is 0,7% of total national electric consumption, 55% of whole communications sector, with bills of more than 300M€ per year

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Energy consumption

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Radio accessand corenetwork

Base

Stations

80%

Mobile

Stations

Network

90%

User

Terminals

10%

Mobile

Network

20%

Energy consumption

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Traffic load

Wireless access networks are dimensioned for estimated peak demand using dense layers of cell coverage

Traffic varies during the day

Energy consumption is almost constant

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Day 1 Day 2 Day 3

Tra

ffic

Lo

ad

Network capacity

Energy Savings

Significant energy savings can be achieved if parts or all components of some wireless network devices are powered off when traffic is low, and powered on based on the volume and location of user demand

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Energy Savings

It is also possible to partially switch off internal modules of base stations

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Base Station

Cabinet

TRXs

Air

Conditioner

Green Network Management

Switching on and off network elements based on traffic level

Re-planning of the network based on different traffic scenarios

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Green Network Management

Radio Planning models can be “re-used”

But some additional features need to be modeled like:

Coverage and capacity constraints

Cost of network reconfiguration

Performance – Energy trade off

Etc.

Energy saving is one of the issues that is being considered as part of Self Organizing Network by standardization bodies and manufacturers

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Conclusion

The need to plan and manage new generation wireless network in a cost effective way is even more acute now than in the past

Network complexity is increasing

Network re-planning is required more often also for energy saving

New design and management approaches are required

Don’t let engineers play alone with these new challenging problems

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