Cellular Network Planning and Optimization

ECEG-6222

Lecture 1
Introduction to Cellular/MobileSystems
Contents
 Basics
 Standardization
 Market share
Characteristics of mobile (cellular)
systems
 From the perspective of a mobile user, the cellular systems are
characterized by:
– Two-way communication between users and the network
– Wide area coverage, where users can connect to the network anywhere at
any time
– Ubiquitous mobility: User services continue smoothly when users move from
one cell to another
 Thus, cellular systems are by nature wireless Wide Area Networks (WANs),
while wireless Local Area Networks (LANs) provide connectivity in a
limited geographical area
 Note that in recent terminology, ”cellular system” has been replaced by
terms like ”mobile networks” or ”mobile systems”
The reasoning behind mobile
communication systems
 Global connectivity and seamless mobility
– User should be able to connect to the network everywhere (i.e., the user should have
service continuity).
– This aspect is very well handled for speech connection, but may sometimes fail in
case of data services (e.g., when user is moving from a 3G coverage area to a 2G
coverage area)

 Global roaming
– User expect to have mobile connectivity (almost) anywhere in
world
– Of course, recent technologies like 3G (or 4G) may provide
coverage only in major cities, but GSM is a truly global system
• 3G is rapidly becoming global as well
– Obstacles for global roaming: lack of a roaming agreement
between operators (usually not an issue) and costs (this is an
issue)
The reasoning behind mobile
communication systems
 Trustworthy authentication and secure connection
– Nowadays, WLANs may also provide secure connectivity but manual
authentication is usually needed.
– However, centralized authentication is employed in mobile networks
– Thus, secure connection and authentication service is available basically
everywhere, without additional manual actions
 Global standards
– Open global standards, designed jointly by industry community, have lead to
global markets for both terminals and networks
– Large production volumes and tight competition have lead to low
equipment prices
The reasoning behind mobile
communication systems
 To sum up,
– Wide area connectivity,
– Mobility,
– Roaming, and
– Centralized authentication
are the main differences between mobile systems and other
communication technologies
 Although WLANs standards are also global in nature, security and
connectivity are usually handled locally by network administrator.
Wide area connectivity and mobility
 Wide area connectivity basically means
that all areas where users may move needs
to be covered by the system
– Thus, numerous equipment providing
connectivity (in practice, a lot of base
stations) are needed
 Wide area connectivity requirement leads
to the so-called cellular structure of the
network, where geographical area is
divided into cells served by different base
stations
 Limitation: Radio spectrum availability is limited
– All users in the network should share the same set of channels
– So, radio resource reuse principle between cells needs to be applied
Cellular network structure
1

 Wide area coverage

(connectivity everywhere) 1 2 3 1
 Cellular structure like honeycomb
2 3 1 2 3

1 2 3 1

 Radio resource reuse 2 3 1 2 3

– Reuse = 1/3 in the figure
 Cells can be split into sectors
2 3
– Three sectors per site in the fig.
 Wide area mobility (handover points marked with blue dots)
Network architecture
 Mobility and global authentication require
the presence of centralized network
elements, connected to other network
elements that provide wireless
connectivity (i.e., BSs)
– Those centralized elements form the Core
Network (CN), while
– Elements handling wireless connectivity
form the Radio Access Network (RAN)

 Global standards ensure compatibility of radio devices produced by

different manufacturers
 However, a legal contract called “roaming agreement” is needed to
ensure reliable authentication & billing
General system architecture
CN-External
Radio interface RAN-CN interface Network interface

RAN CN
Handles all radio Switching, routing,
related functions. security and mobility
User May also handle related functions. External
Terminal some mobility Includes switches, networks
issues. gateways, registers,
Include at least and other controlling
base stations elements

RAN = Radio Access Network; CN = Core Network

Radio spectrum
 Conventionally two types of radio frequency bands have been available for
commercial radio systems:
– Licensed and unlicensed frequency bands
 License for certain frequency band can be granted by national regulator,
which administrates the usage of radio frequencies
– E.g., FCC in the US
 In case of mobile communication systems, license is usually granted for a
certain operator
– Operator then owns the right for exclusive use of the freq. band
 There are also global agreements and guidelines, regarding to the use of
the applied frequencies
– National regulators usually follow these guidelines quite well, to make radio
devices compatible in different countries
Radio spectrum
 The most important unlicensed spectrum covers Industrial, Scientific and Medical
(ISM) radio bands
– These bands were originally reserved internationally for the use by industrial,
scientific and medical purposes
 Currently, one of the most important radio systems (i.e., IEEE 802.11) operates in
this band and provides local connectivity
– Unlicensed freq. bands have also been granted for experimental use
 From a radio system perspective, the important difference between licensed and
unlicensed frequency bands is that licensed spectrum provides resources which
are free from external interference
– Thus, all interference in the network is created by the own system
– So, it is feasible for implementing a radio communication system that
guarantees Quality of Service (QoS) to the served users
Mobility
 As discussed earlier, the user mobility is one of the basic characteristics of a mobile
network
– To ensure a smooth switch of a user connection between neighboring base stations, a
handover operation is needed
– Handover operation is also called hand-off
 The main phases of the handover include:
1) Signal quality measurements by mobile station,
2) Handover decision, usually made at the base station (i.e., from the network side), and
3) Exchange of signaling required to inform to the target base station the control
information regarding the new mobile user
 Handover protocol details are system specific
Mobility

Three phases for mobile assisted handover:

1) Signal quality measurements (@ MS),
2) Handover decision (@ BS/NTW)
3) Exchange of control information (@ NTW)

MS = Mobile Station, BS = Base Station, NTW = Network

Radio Resource Management (RRM)
 The radio resource management (RRM) functions are responsible for efficient
usage of the air interface (physical layer) resources
 In general, RRM is needed to:
– Guarantee QoS for users,
– Maintain the coverage according to network plan, and
– Provide as high system efficiency as possible
 The RRM concept covers usually the following functions:
– Handover control
– Power control
– Admission control, load control, and congestion
control
– Packet scheduling
Radio Resource Management (RRM)
Radio Resource Management Concepts:
 Handover control is used to guarantee the mobility in a
communication in a transparent way (from user’s
perspective)
 Power control is used to keep proper power levels at
the receiver side, to guarantee target QoS
• Power control is also important from interference perspective
 Admission, load and congestion control:
• Aim of these functions is to keep the cell load on feasible level
• In addition, the goal is to resolve overload situations effectively
 Packet scheduling is used to serve mobile users
according to their QoS requirement, so that system
efficiency is maximized
Procedures
 In connection with e.g. 3GPP technologies, an important part of the
system is formed by the so-called Procedures that may cover
– System specific power control,
– Paging procedure,
– Random access procedure,
– Cell search procedure, and other
– Measurement and multi-antenna algorithms
 Procedures are system specific
Network planning
 “Radio network planning” as such could be a course topic itself
 In this presentation, we consider network planning only very briefly, and
focus mostly on link budgets
 Conventionally, network planning is divided into three phases:
(1) Initial planning phase, known as dimensioning
(2) Detailed planning (and implementation)
(3) Network optimization

Phase 1: Dimensioning
 Includes the rough evaluation of the amount of network elements that
are needed to provide coverage in the target service area
 Network element count is obtained through link budget calculations
Network planning
Phase 2: Detailed Planning (and implementation)
 Site locations are selected, system coverage and capacity planning is
carried out in details
 More sophisticated planning and simulation tools are used for this
purpose
Phase 3: Network Optimization
 Not all parameters can be optimally defined during planning phase
 After network implementation, performance measurements are done
− System parameters should can be then optimized, based on
measurement results
 Optimization may be also needed when traffic conditions change, or new
features (like advanced antennas) are introduced
Network planning
Dimensioning Note: We omit core network
150

140

+
Path Loss [dB]
130
EIRP 58dB
120
Margins 23dB
110 Sensitivity -100dB 1000 x 5000 x
100
Allowed PL 135 dB
90
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Distance from BS [km]

Area and propagation information Link budget # Network elements

Detailed planning
TX power 43dBi
Antennas 2
Input from Antenna tilt 5o
Parameter x, y, z
dimensioning

Network planning tools BS Configurations and

System simulations topology plan

Optimization

+
Operating network 30 Optimized system
System performance evaluation
 In addition to network planning, the network performance can be studied
on many levels
 When considering practical networks, sophisticated tools are needed to
model all details of the system.
 Nevertheless, in initial system standardization phases, the mobile system
performances is examined (e.g. 3GPP) using so-called static system
simulators
– In an static simulator, network layout is uniform and physical layer modeling is
kept simple
 Principles for such evaluations are straightforward, and can be understood
based on this course
3GPP family of technologies
 The 3rd Generation Partnership Project (3GPP) unites different standard
development organizations in the field of telecommunications:
– Association of Radio Industries and Businesses (ARIB), Japan
– Alliance for Telecommunications Industry Solutions (ATIS), USA
– China Communications Standards Association (CCSA), China
– European Telecommunications Standards Institute (ETSI), Europe
– Telecommunications Technology Association (TTA), Korea
– Telecommunication Technology Committee (TTC), Japan
 The 3GPP provides their members a stable environment to produce
Reports and Specifications that define 3GPP technologies
3GPP family of technologies
 3GPP has four Technical Specification Groups (TSG)
 Each TSG has a set of Working Groups (WG) which
– Meet regularly few times a year (from four to six times), and
– Are responsible for development of Reports and Specifications that
belong to their area of competence
3GPP family of technologies
 The 3GPP technologies from these groups are constantly evolving
through Generations of commercial cellular/mobile systems
 Although these Generations have become an adequate descriptor for
the type of network under discussion, real progress on 3GPP standards
is measured by the milestones achieved in particular Releases
 New features are ’functionality frozen’ and are ready for
implementation when a Release is completed
 Although this adds some complexity to the work of WGs, such a way of
working ensures that progress is continuous and stable
3GPP family of technologies
3GPP works on a number of Releases in parallel, starting future work well
in advance of the completion of the current Release

2000 2004 2008 2012

Time schedule of 3GPP standards

3GPP Standardization process
 The 3GPP process is such that more topics are started than eventually
end up in the specifications.
 Within the study, only a small set of features is usually entering to
specification.
 Sometimes a study is closed after it is found that there is not enough
gain to justify the added complexity. A change requested in the work
item phase could also be rejected for this same reason.
Mobile network coverage share
Share as of Q1 2016 according to GSA
Mobile subscriptions worldwide - all technologies  7.416
billion  ≥ 100% of the global population

3GPP-family mobile system technologies  6.946 billion

 93.66% market share
 GSM/EDGE3.451 billion subscriptions46.5%
market share
 WCDMA/ HSPA/HSPA+  2.202 billion subscriptions 
29.7% market share
 LTE/LTE-Advanced/LTE-Advanced Pro  1.292 billion
subscriptions 17.4% market share
Mobile connections share
Mobile data traffic growth
Mobile traffic share