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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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yc
j
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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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F2
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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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