Mobile Communication
GSM

What is GSM ?
Global System for Mobile (GSM) is a
second generation cellular standard
developed to cater voice services
and data delivery using digital
modulation
d l ti

GSM: History
• Developed by Group Spéciale Mobile (founded 1982) which was an
initiative of CEPT ( Conference of European Post and
Telecommunication )
• Aim : to replace the incompatible analog system
• Presently the responsibility of GSM standardization resides with special
mobile group under ETSI ( European telecommunication Standards
Institute )
• Full set of specifications phase-I became available in 1990
• Under ETSI, GSM is named as “ Global System for Mobile
communication “
• Today many providers all over the world use GSM (more than 135
countries in Asia Africa Europe Australia America)
Asia, Africa, Europe, Australia,
• More than 1300 million subscribers in world and 45 million subscriber in
India.

GSM Services
Tele-services
Bearer or Data S i
B D t Services
Supplementary services

Tele Services
• Telecommunication services that enable voice communication
via mobile phones
• Offered services
- M bil telephony
Mobile t l h
- Emergency calling

Bearer Services
Include various data services for information transfer
between GSM and other networks like PSTN, ISDN etc
at rates from 300 to 9600 bps
Short M
Sh t Message Service (SMS)
Si
up to 160 character alphanumeric data
transmission to/from the mobile terminal
Unified Messaging Services(UMS)
Group 3 fax
Voice mailbox
Electronic mail

Supplementary Services
Call related services :
• Call Waiting- Notification of an incoming call while on the handset
• Call Hold- Put a caller on hold to take another call
• Call Barring- All calls, outgoing calls, or incoming calls
• Call Forwarding- Calls can be sent to various numbers defined by
the user
• Multi Party Call Conferencing - Link multiple calls together
• CLIP – C ll line identification presentation
Caller li id tifi ti t ti
• CLIR – Caller line identification restriction

GSM System Architecture PSTN
ISDN
PDN
BSC
MS BTS
MSC
GMSC
BTS BSC
VLR
MS
EIR
BTS
AUC
MS HLR

GSM System Architecture
Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
( )
Equipment Identity Register (EIR)

System Architecture
Mobile Station (MS)
The Mobile Station is made up of two entities:
Mobile Equipment (ME)
1.
2. Subscriber Identity Module (SIM)

System Architecture
Mobile Station (MS)
Mobile Equipment
Portable,vehicle mounted, hand held device
Uniquely identified by an IMEI (International Mobile
Equipment Identity)
qp y)
Voice and data transmission
Monitoring power and signal quality of surrounding cells for
optimum handover
Power level : 0.8W – 20 W
160 character long SMS.

System Architecture
Mobile Station (MS) contd.
Subscriber Id
S b ib Identity Module (SIM)
i M d l (SIM
Smart card contains the International Mobile
Subscriber Identity (IMSI)
Allows user to send and receive calls and
receive other subscribed services
Encoded network identification details
Protected by a password or PIN
Can be moved from phone to phone –
contains key information to activate the
phone

System Architecture
Base Station Subsystem (BSS)
Base Station Subsystem is composed of two parts that
communicate across the standardized Abis interface allowing
operation between components made by different suppliers
p p y pp
Base Transceiver Station (BTS)
1.
Base St ti Controller (BSC)
B Station C t ll
2.

System Architecture
Base Station Subsystem (BSS)
Base Transceiver Station (BTS):
( )
Encodes,encrypts,multiplexes,modulates and feeds the RF
, yp , p ,
signals to the antenna.
Frequency hopping
Communicates with Mobile station and BSC
Consists of Transceivers (TRX) units

System Architecture
Base Station Subsystem (BSS)
Base Station Controller (BSC)
Manages Radio resources for BTS
Assigns Frequency and time slots for all MS’s in its area
Handles call set up
Transcoding and rate adaptation functionality
Handover for each MS
Radio Power control
It communicates with MSC and BTS

System Archibtecture
Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Heart of the network
Manages communication between GSM and other networks
Call setup function and basic switching
Call routing
Billing information and collection
Mobility management
- Registration
- Location Updating
p g
- Inter BSS and inter MSC call handoff
MSC does gateway function while its customer roams to other
network by using HLR/VLR.

System Architecture
Network S it hi S b t
Nt k Switching Subsystem
Home Location Registers (HLR)
- permanent database about mobile subscribers in a large service
area(generally one per GSM network operator)
- database contains IMSI,MSISDN,prepaid/postpaid,roaming
restrictions,supplementary services.
Visitor Location Registers (VLR)
- Temporary database which updates whenever new MS enters its
area, by HLR database
- Controls those mobiles roaming in its area
g
- Reduces number of queries to HLR

System Architecture
Network Switching Subsystem
Authentication Center (AUC)
- Protects against intruders in air interface
- Maintains authentication ke s and algorithms
a thentication keys
- Generally associated with HLR
Equipment Identity Register (EIR)
Database that is used to track handsets using the
g
-
IMEI (International Mobile Equipment Identity)
- Made up of three sub-classes: The White List, The
Black List d the Gray Li t
Bl k Li t and th G List
- Only one EIR per PLMN

GSM Specifications
RF Spectrum
GSM 900
Mobile to BTS (uplink): 890-915 Mhz
(p )
BTS to Mobile(downlink):935-960 Mhz
Bandwidth : 2* 25 Mhz
GSM 1800
Mobile to BTS (uplink): 1710 1785 Mhz
1710-1785
BTS to Mobile(downlink) 1805-1880 Mhz
Bandwidth : 2 75 Mhz
2*

GSM Specification
Carrier Separation : 200 Khz
Duplex Distance : 45 Mhz
No. of RF carriers : 124
Access Method : TDMA/FDMA
Modulation Method : GMSK
Modulation data rate : 270.833 Kbps

GSM Operation
Speech Speech
Speech decoding
Speech coding
13 Kbps
Channel Coding Channel decoding
22.8 Kbps
Interleaving De-interleaving
22.8 Kbps
Burst Formatting Burst Formatting
33.6 Kbps
Ciphering De-ciphering
33.6 Kbps
Radio Interface
Demodulation
Modulation
270.83 Kbps

Physical Channel

GSM-Frame Structure

Logical Channels
Half t 11 4kb
H lf rate 11.4kbps
Speech
TCH
(traffic) Full rate 22.8kbps
2.4 kbps
Data
4.8 kbps
9.6 kbps
p
FCCH(Frequency correction)
BCH
SCH(Synchronization)
PCH(Paging)
CCCH
RACH(Random Access)
CCH AGCH(Access Grant)
(control)
SDCCH(Stand Alone)
Dedicated
SACCH(Slow-associated)
FACCH(Fast-associated)

GSM Frequency Bands
System Band Uplink Downlink Channel Number
GSM 400 450 450.4 - 457.6 460.4 - 467.6 259 - 293
GSM 400 480 478.8 - 486.0 488.8 - 496.0 306 - 340
GSM 850 850 824.0 - 849.0 869.0 - 894.0 128 - 251
GSM 900 (P-GSM) 900 890.0 - 915.0 935.0 - 960.0 1 - 124
GSM 900 (E-GSM) 900 880.0 - 915.0 925.0 - 960.0 975 - 1023, (0, 1-124)
GSM-R (R-GSM) 900 876.0 - 915.0 921.0 - 960.0 955 - 973, (0, 1-124, 975 - 1023)
DCS 1800 1800 1710.0 - 1785.0 1805.0 - 1880.0 512 - 885
PCS 1900
CS 900 1900
900 1850.0 - 1910.0
850 0 9 0 0 1930.0 - 1990.0
930 0 990 0 5
512 - 810
80
GSM-900, GSM-1800 – Used in most countries (Europe, Middle East, Africa, Asia)

Multi-band and multi-mode
phones
Dual band phones
GSM 900 and 1800 MHz. (Europe, Asia, Australia, Brazil)
GSM 850 and 1900 MHz (North America)
Tri band phones
900, 1800, 1900 (Europe)
850, 1800, 1900 (North America)
Quad band phones
Supports all four major GSM frequency groups.
Multi-mode phones
Can operate on GSM systems as well as on mobile phone
mobile-phone
systems using other technical standards. Often these
phones use multiple frequency bands as well.

Mobile Station
The GSM telephone set and the SIM are the only system elements with which
most users of GSM have direct contact.

Base Station Subsystem

Base Station Subsystem
Via the Air-interface, the BSS provides a
connection between the MSs of a limited
area and the network switching subsystem
(NSS).
The BSS consists of the following elements:
One or more BTSs (base tranceiver station);
One BSC (base station controller);
One TRAU (transcoding rate and adaptation
unit).

Base Transceiver Station
The BTS provides the physical connection of an MS
to the network in form of the Air-interface On the
Air interface.
other side, toward the NSS, the BTS is connected
to the BSC via the Abis-interface.

Transmitte/Receiver M d l
T i /R i Module
The TRX module is, from the perspective of signal processing, the most
important part of a BTS. The TRX consists of a low-frequency part for
digital signal processing and a high-frequency part for GMSK modulation
and demodulation Both parts are connected via a separate or an
demodulation.
integrated frequency hoppingunit. All other parts of the BTS are more or
less associated with the TRXs and perform auxiliary or administrative
tasks.
Operations and Maintenance Module
The operations and maintenance (O&M) module consists of at least one
central unit, which administers all other parts of the BTS. For those
purposes,
purposes it is connected directly to the BSC by means of a specifically
assigned O&M channel. That allows the O&M module to process the
commands from the BSC or the MSC directly into the BTS and to report
the results. Typically, the central unit also contains the system and
operations software of the TRXs. That allows it to be reloaded when
p
necessary, without the need to “consult” the BSC. Furthermore, the O&M
module provides a human-machine interface (HMI),
which allows for local control of the BTS.

Clock Module
Cl k M d l
The modules for clock generation and distribution also are part of
the O&M area. Although the trend is to derive the reference clock
from the PCM signal on the Abis- interface, a BTS internal clock
generation is mandatory. It is especially needed when a BTS has to
be tested in a standalone environment, that is, without a connection
to a BSC or when the PCM clock is not available due to link failure.
Input and Output Filters
Both input and output filters are used to limit the bandwidth of the
received and th t
i d d the transmitted signals. Th i
itt d i l The input filt t i ll i a
t filter typically is
nonadjustable wideband filter that lets pass all GSM 900, all DCS
1800, or all PCS 1900 frequencies in the uplink direction. In
contrast, remote-controllable filters or wideband filters are used for
the downlink direction that limits the bandwidth of the output signal
to
t 200 kHz. When necessary, the O&M center (OMC) controls th
kH Wh th t t l the
settings of the filters, as in the case of a change in frequency.

BTS Configurations
Different BTS configurations, depending on
load, subscriber behavior, and morph
structure,
structure have to be considered to provide
optimum radio coverage of an area. The
most important BTS configurations are,
p g
Standard configuration
Umbrella cell configuration
Sectorized (Collocated) Base Transceiver
Stations

Standard Configuration
All BTSs are
assigned different
cell identities (CIs)
(CIs).
A number of BTSs
(in some cases, a
single BTS) form a
location area.
Figure shows three
location areas with
one, three, and five
BTSs.

Umbrella Cell Configuration
The umbrella cell configuration consists of one BTS with high transmission power and
an antenna installed high above the ground that serves as an “umbrella” for a number
of BTSs with low transmission power and small diameters
The umbrella cell configuration has its merits in certain situations and therefore may
result in relief from load and an improvement of the network
network.
For example, when cars are moving at rather high speeds through a network of small
cells, almost consecutive handovers from one cell to the next are necessary to maintain
an active call. This situation is applicable in every urban environment that features city
highways.
g y
Consequently, the handovers result in a substantial increase of the signaling load for
the network as well as in an unbearable signal quality degradation for the end user. On
the other hand, small cells are required to cope with the coverage demand in an urban
environment.

Sectorized (Collocated) Base
Transceiver Stations
The term sectorized, or
collocated, BTSs refers
to a configuration in
which several BTSs are
collocated at one site but
their antennas cover only
an area of 120 or 180
degrees.
Like the umbrella cell
configuration, this
configuration is used
mostly in highly
populated areas

Base Station Controller
The BSC forms the center of the BSS.
A BSC can, depending on the
manufacturer, connect to many BTSs over
ft tt BTS
the Abis-interface. The BSC is, from a
technical perspective, a small digital
exchange with some mobile-specific
extensions. The BSC was defined with the
intention f
i t ti of removing most of the radio-
i t f th di
related load from the MSC.

Architecture and Tasks of the
Base Station Controller
Switch Matrix
Because the BSC has the functionality of a small digital
exchange, its function is to switch the incoming traffic
channels (A-interface from the MSC) to the correct Abis-
( )
interface channels. The BSC, therefore, comes with a
switch matrix that (1) takes care of the relay functionality
and (2) can be used as the internal control bus

Terminal C t l El
T i l Control Elements of th Abi I t f
t f the Abis-Interface
The connection to the BTSs is established via the Abis-terminal
control elements (TCEs), which, more or less independently from
the BSC’s central unit, provide the control function for a TRX or a
BTS.
The number of Abis TCEs that a BSC may contain depends largely
on the number of BTSs and on the system manufacturer.
Major tasks of the Abis-TCEs are to set up LAPD connections
toward the BTS peers, the transfer of signaling data, and last—but
not least—the transparent transfer of payload
least the payload.
Depending on the manufacturer, the Abis TCEs also may be
responsible for the administration of BTS radio resources.
Database
The BSC is the control center of the BSS. In that capacity, the BSC
BSS capacity
must maintain a relatively large database in which the maintenance
status of the whole BSS, the quality of the radio resources and
terrestrial resources, and so on are dynamically administrated.
Furthermore, the BSC database contains the complete BTS
operations software for all attached BTSs and all BSS specific
information, such as assigned frequencies.

Transcoding Rate and
Adaptation Unit
One f th
O of the most interesting functions in GSM involves the TRAU, which
ti t ti f ti i i l th TRAU hi h
typically is located between the BSC and the MSC.
The task of the TRAU is to compress or decompress speech between the
MS and the TRAU. The used method is called regular pulse excitation–long
term prediction (RPE-LTP).
It is able to compress speech from 64 Kbps to 16 Kbps, in the case of a
fullrate channel and to 8 Kbps in the case of a halfrate channel.
Although speech compression is intended mainly to save resources over the
Air-interface, it also is suitable to save line costs when applied on terrestrial
links

Speech Coding

A-law
A law and µ law
µ-law
Spoken language generally is not linear in its
dynamics, and the human ear is rather sensitive to
soft sounds, but difference in amplitude for loud
sounds cannot be distinguished so easily.
When digitizing speech, one can take advantage of
this it ti
thi situation and code a sufficient-quality sound
dd ffi i t lit d
with relatively few bits.
For this purpose, the A-law and the µ-law were
pp , µ
invented. Both are approximations of the natural
logarithmic function, and both were standardized by
ITU for transmission of digital speech on PCM
transmission lines,

Both methods are used on a per-country basis. The µ-law is used only in
the United States and Japan. All other countries use the A-law.

A-law
A law

µ law
µ-law

Mobile Communication
GSM Network Planning
Nt k Pl i
Dr. Chandimal Jayawardena

Radio Network Planning
Process
The network planning process itself is
not standard.
Though some of the steps may be
common, the process is determined
by the type of project, criteria and
targets. The process has to be applied
case b case.
by

Network Planning Projects
Network planning projects can be divided into three main categories based on
howmuch external planning services the operator is using
using.
No services means simply that the operator is responsible for the network
planning from the very beginning until the end.
This type of comprehensive responsibility for the network planning is more
suitable for traditional network operators, who have extensive knowledge of their
p , g
existing network and previous network planning experience than newcomers in
this technology field. There is risk, however, that if the operator is the only person
responsible for network planning there might be a difficulty in maintaining
knowledge of the latest equipment and features.
The opposite network planning solution is when the network operator buys the
new network with a turnkey agreement.
In this case, the operator is involved only in defining the network planning
criteria. After the network roll-out has been finished and enters the care phase an
agreement about the future has to be made. The care services can be
outsourced as well but the operator might also be interested to take some
well,
portion of the network operations and start to learn the process. An operator
taking all the responsibility after the outsourced planning phase includes some
risk. A better solution is to learn the network operation at a pace agreed with the
network vendor.
The network operator can also buy network planning consultancy services.
In this, the operator performs majority of the planning function and outsource
selected aspects of the job. In this way some special know-how can be bought to
supplement the knowledge of the network planning group. This is generally used
in cases where new technologies need to be introduced in mature networks.

Network Planning Project
Organization

Network Planning Criteria and
Targets
Network planning is a complicated process consisting of several phases. The
final target for the network planning process is to define the network design
design,
which is then built as a cellular network.
A summary of the main factors affecting network planning are listed below:
Market analysis
Competitor analysis
Potential customers
User profiles: services required and usage
Customer requirements
Coverage requirements
Capacity requirements
Quality targets: call setup success, drop call rate, etc.
Financial limitations
Future deployment plans
Environment factors and other boundary conditions
Area topography
Hotspot locations
Available frequency band
Recommended base transceiver station (BTS) locations

Network Planning Process
Steps
The network planning process consists of several phases, which
can be combined at a higher level to main phases that differ
depending on the logics.

Preplanning
The preplanning phase covers the assignments and preparation before the
actual network planning is started
started.
As in any other business it is an advantage to be aware of the current market
situation and competitors.
The network planning criteria is agreed with the customer. As specified earlier,
the requirements depend on many factors, the main criteria being the coverage
and quality targets.
The network planning criteria is used as an input for network dimensioning.
Following are the basic inputs for dimensioning:
coverage requirements, the signal level for outdoor, in-car and indoor with the
coverage probabilities;
b bili i
quality requirements, drop call rate, call blocking;
frequency spectrum, number of channels, including information about possible
needed guard bands;
subscriber information number of users and growth figures;
information,
traffic per user, busy hour value;
services.
The dimensioning gives a preliminary network plan as an output, which is then
supplemented in coverage and parameter planning phases to create a more
detailed plan.

Planning
The planning phase takes input from the dimensioning, initial network
configuration.
config ration This is the basis for nominal planning which means
planning, hich
radio network coverage and capacity planning with a planning tool.
The nominal plan does not commit certain site locations but gives an
initial idea about the locations and also distances between the sites.
The nominal plan is a starting point for the site survey, finding the real
site locations. The nominal plan is then supplemented when it has
information about the selected site locations; as the process proceeds
coverage planning becomes completed.
completed
The final site locations are agreed
The output of the planning phase is the final and detailed coverage
and capacity plans. Coverage maps are made for the planned area
and final site locations and configurations.

Detailed Planning
After the planning phase has finished and the site location and configurations
are known detailed planning can be started
started.
The detailed planning phase includes frequency, adjacency and parameter
planning.
Planning tools have frequency planning algorithms for automatic frequency
planning.
The planning tool can also be utilized in manual frequency planning. The tool
uses interference calculation algorithms and the target is to minimize firstly the
co-channel interference and also to find as low an adjacent channel interference
as possible.
Frequency planning is a critical phase in network planning. The number of
frequencies that can be used is always limited and therefore the task here is to
find the best possible solution.
Neighbour planning is normally done with the coverage planning tool using the
frequency plan information
information.
In the parameter planning phase a recommended parameter setting is allocated
for each network element.
For radio planning the responsibility is to allocate parameters such as handover
control and power control and define the location areas and set the parameters
accordingly.

GSM Network Planning
Criteria
The definition of the radio network planning criteria is
done at the beginning of the network planning process.
The network operator has performance quality targets for
the cellular network and these quality requirements are
also related to how the end user experiences the
network.
Typical network quality targets are as follows:

Radio Network
Dimensioning
Dimensioning is the main part of the preplanning phase. In addition to
the dimensioning parameters the priority of the parameters also needs
to be agreed.
It is imperative to agree the network layout, usage of three sector sites
or a combination of three sector and omni sites with the operator.
One i
O important planning issue i also whether only macro cells are used
t tl ii is l h th l ll d
in the beginning or a combination of macro, micro and pico cells.
The macro cells are used in rural and suburban areas to cover large
areas. The macro cell has a cell range of 1–35 km and is characterised
by
b an outdoor antenna, which covers a l
td t hi h large area. A t
Antennas are above
b
rooftops.
Micro cells are used in city areas to cover areas close by and antennas
are on the walls. The micro cell has a cell range of less than 1 km and
is for
i f outdoor coverage. Th antennas are typically mounted on walls
d The i ll d ll
and below the average rooftop level.
The pico cells are used to cover either very specific hot spot in an
outdoor area or to give indoor coverage. The pico cell has a cell range
less than 500 m and is characterised by antennas mounted low on the
walls, clearly below the rooftop level. They are used for both indoor and
outdoor coverage

Link Budget Calculations
The radio link budget aims to calculate the cell
coverage area.
One of the required parameters is radio wave
propagation t estimate the propagation loss between
ti to ti t th ti l bt
the transmitter and the receiver. The other required
parameters are the transmission power, antenna gain,
cable losses receiver sensitivity and margins.
losses, margins

Link Budget Calculations
cont.
When defining the cell coverage area, the aim is to balance the
uplink and downlink powers.
The links are calculated separately and are different from the
transmission powers
powers.
The BTS transmission power is higher than the MS transmission
power and therefore the reception of the BTS needs to have high
sensitivity.
ii i
The radio signal experiences the same path loss when travelling
from the BTS to the MS as from the MS to the BTS.
The GSM link budget parameters are:
BTS sensitivity Cable and connector losses
MS sensitivity Other equipment loss factors
MS and BTS powers Mast head amplifier (MHA) and
booster
Antenna gains
The interference degradation
Diversity gain
margin

Link Budget Calculations cont.
BTS sensitivity
iti it
Specified on the ETSI GSM recommendation 05.05 and the recommended value
is −106 dBm. This is a general recommendation and therefore when preparing a
link budget with a certain manufacturer’s equipment this vendor’s
recommendations can be used.
MS sensitivity
is also specified in the ETSI recommendation 05.05, where the receiver
sensitivity value is separate for each MS class.
MS class 4, which means GSM 900, the recommended value is −102 dBm.
MS class 1, GSM 1800, the value is −100 dBm.
The MS sensitivity can also be calculated using the information of receiver noise
F and minimum Eb/N0.
The value for the noise is 10 dB and the minimum Eb/N0 is 8 dB, as defined in
the
th ETSI recommendation 03.30. Th receiver sensitivity Si i solved f
d ti 03 30 The i iti it is l d from th the
following equation, where the input noise power Ni is the product of three
parameters: the Boltzman constant k, temperature T0 = 290K and bandwidth W
= 271 kHz (54 dB):

Link Budget Calculations
cont.
MS and BTS powers
MS TX (transmission) power is defined by the MS class in ETSI specifications
specifications.
For MS class 4 (GSM 900) the maximum TX power is 2Wand for class 1 (GSM
1800) 1W.
BTS TX power depends on the BTS type and vendor. The TX power is
adjustable, which enables the link budget to be balanced.
Antenna gains
The BTS antenna gain is dependent on the antenna type and whether the
antenna is omnidirectional or directional. The gain of a directional BTS antenna is
dependent on the horizontal and vertical half power beam widths. It is also
dependent on the physical size of the antenna which in turn has an impact on the
frequency range.
Also frequency range is inversely proportional to the size of the antenna, which is
then connected to the radiating aperture of the antenna.
The antenna gain is around 16–20 dBi when there is a widely used antenna with
60–65◦ horizontal h lf power b
60 6 h i l half beam width and 5–10 vertical h lf power b
id h d 10 i l half beam
width.
In the link budget calculations for the MS antenna the gain is generally 0 dBi. The
actual MS antenna gain is complicated to estimate, because the gain is highly
dependent on the mobile user’s relative location towards the base station when
p
the amount of body loss varies.
Diversity gain
can be used for correcting unbalance between the uplink and downlink. The
typical way to arrange diversity is to have it in the BTS reception. One basic
method is to separate receiver antennas vertically or horizontally; the method is

Link Budget Calculations
cont.
Cable and connector losses
are case specific and need to be measured or calculated separately.
An i di id l
A individual connector gives a l
t i loss of around 0 1 dB b t d
f d 0.1 dB, but depending on
di
the cable installations there can be several in one antenna line.
Other equipment loss factors
consist of isolator, combiner and filter losses.
Two other gain factors, which need to be considered in the link budget if used,
are the mast head amplifier (
p (MHA) and booster.
)
The MHA, which is located close to the antenna in BTS reception, is
used to amplify the received signal. This decreases the unbalance
between the uplink and downlink by giving extra gain in the uplink the
direction. The booster can be used to amplify the BTS transmission
power.
The interference degradation margin
describes the loss due to frequency reuse.

Radio Wave Propagation
Propagation models have been developed to be able
to estimate the radio wave propagation as accurately
as possible.
Models have been created for different environments
to predict the path loss between the transmitter and
receiver.
How much power needs t b t
H h d to be transmitted using th
itt d i the
BTS?
The complexity of the model affects the applicability as
well as the accuracy
accuracy.
Two well-known models are:
Okumura–Hata
Walfish–Ikegami.
W lfi h Ik i

Basic Electromagnetic Wave
Propagation
When the signal has been transmitted in the free space towards the receiver
antenna, the power density S at the distance from the transmitter d can be
written as:
where Pt is the transmitted power and Gt is the gain of the transmission
antenna.
The effective area A of the receiver antenna, which affects the received
power, can be expressed as
where λ is the wavelength and Gr is the gain of the receiver (RX) antenna.
The received power density can also be written as:
Combining these three equations, the received power is given by:

Basic Electromagnetic Wave
Propagation cont.
Free space loss
The free space path loss is the ratio of transmitted and received
power (excluding antenna gains)
Once converted into dB:
where f is the frequency in megahertz a d d is the distance in
e e s t e eque cy ega e t and s t e d sta ce
kilometers.
In reality the radio wave propagation path is normally a non-line-
of-sight situation with surrounding obstacles like buildings and
trees.
trees Therefore the applicability of the free space propagation
loss is limited.
The received signal actually consists of several components,
which have been travelling through different paths facing
g g g
reflection, diffraction and scattering.

Okumura–Hata
Okumura Hata Model
The Okumura–Hata model is a well-known propagation
model, which can be applied for a macro cell environment to
predict median radio signal attenuation.
The Okumura–Hata model is an empirical model, which
means that it is based on field measurements.
Okumura performed the field measurements in Tokyo and
published results in graphical format. Hata applied the
measurement results into equations. The model can be
applied without correction factors for quasi-smooth terrain in
an urban area but in case of other terrain types correction
yp
factors are needed.
The weakness of the Okumura–Hata model is that it does
not consider reflections and shadowing. The parameter
restrictions for this model are:

Okumura–Hata
Okumura Hata Model cont
cont.
The Okumura–Hata model for path loss prediction can by written as where f
is the frequency (MHz), Hb is the base station antenna height (m), a(Hm) is
the mobile antenna correction factor, d is the distance between the BTS and
MS (km) and Lother is an additional correction factor for area type correction.
The correction factor for the MS antenna height is represented as follows for
a small or medium sized city,
and for a large city:
where Hm is the MS antenna height:

Okumura–Hata
Okumura Hata Model cont
cont.
Parameter set for Okumura–Hata calculations
Example: Distance from BTS = 2 km. Transmitter
antenna height = 30 m, Receiver antenna height = 1.5
m,

Okumura–Hata
Okumura Hata Model cont
cont.
The Okumura–Hata model is valid for
frequency ranges 150–1500MHz and 1500–2000
MHz.
base station antenna height - 30 to 200 m
Mobile antenna - 1 to 10 m
cell range, i.e. the distance between the BTS and MS,
from 1 to 20 km.

Walfish–Ikegami
Walfish Ikegami Model
The Walfish–Ikegami model is an empirical
propagation model for an urban area, which is
especially applicable for micro cells but can also be
used for macro cells.
The parameters related to the Walfish–Ikegami model
are:
W = The mean value for street widths (m)
Φ = Road orientation angle (degrees)
hroof = Th mean value for building h i h ( )
The l f b ildi heights (m)
B = The mean value for building separation (m)

Walfish–Ikegami
Walfish Ikegami Model cont
cont.
TheWalfish–Ikegami model separates i
Th W lfi h Ik i dl into
two cases: line-of-sight (LOS) and non-
lineof-sight.
Line-of-sight situation (d in km and f in MHz)
Non-line-of-sight situation
where
Lrts = the rooftop–street diffraction and
scatter loss Lmsd = the multiscreen
d
diffraction loss.

Coverage Planning in GSM
Networks
The t
Th target for coverage planning is to find optimal locations f
tf l i i t fi d ti l l ti for
base stations to build continuous coverage according to the
planning requirements.
The model selection is done according to the planning parameters,
e.g. frequency,
e g frequency macro/microcell environment BTS antenna height
environment, height.
The coverage prediction is based on the map and the model and
therefore the accuracy is dependent on those as well.
As the link budget calculations are created for all the network
configurations, which means different combinations of the planning
parameters, the cell size determination can be started.
The number of different combinations is targeted to be kept as
small as possible, but some different BTS profiles are normally
needed. Sometimes there can be restrictions in the antenna usage,
e.g. only small ones can b used i th city area, and thi creates
l ll be d in the it d this t
different link budgets for urban and rural areas.
The link budget defines the maximum allowed path loss with certain
configurations. Firstly, the theoretical maximum for the cell size is
calculated using the selected basic propagation model.

Capacity Planning in GSM
Networks
In the capacity planning phase a detailed capacity per cell level is
estimated. Th prior task was to select the b
i d The i k l h base station l
i locations and
i d
calculate the coverage area using actual BTS parameters. The capacity
allocation is based on these coverage maps and traffic estimates, which
can be a separate layer on the map of the planning tool.
The amount of traffic is expressed in Erlangs, which is the magnitude of
telecommunications traffic.
An Erlang describes the amount of traffic in one hour. The definition for
Erlang is the following:
g g
Example: 25 users make a phone calls in an hour. Average call duration isthree minutes.
How much traffic are the users creating in Erlangs?
g g

Frequency Planning
The
Th number of carriers per sector can b calculated b di idi th
b f i t be l l t d by dividing the
available bandwidth by the product of the re-use rate and
bandwidth for a single carrier, i.e. dividing the number of channels
by the frequency re-use rate. Using a re-use rate of 12, the number
of TRXs, carriers per sector, is calculated below:
the capacity of the network with 100 BTSs and 600 cells can be
calculated as
The re-use pattern factor K can be calculated geometrically:

Frequency Planning cont
cont.
To enable maximum capacity, the parameter K should
be optimised to be as small as possible when the
system is operational and fulfilling the planning
requirements. Parameter q is the co-channel
interference reduction factor, where the higher the
value of q the smaller is the co-channel interference
The co-channel interference can be calculated as the
ratio of the carrier (C) to the sum of the interferers (In
):
where d describes the distance between the transmitter and the receiver, α is
a constant and γ is the propagation path loss slope.

Frequency Planning cont
cont.
Interference for the first tier is
Assuming all interferers are equally
strong:
g
Interference for the second tier: