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5/26/2018 Training NSN- All
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GSM Standardisation andTechnology
Training Document
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GSM Standardisation and TechnologyThe information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been
prepared to be used by professional and properly trained personnel, and the customerassumes full responsibility when using it. Nokia Networks welcomes customer comments aspart of the process of continuous development and improvement of the documentation.
The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered bindingbut shall be defined in the agreement made between Nokia Networks and the customer.However, Nokia Networks has made all reasonable efforts to ensure that the instructionscontained in the document are adequate and free of material errors and omissions. NokiaNetworks will, if necessary, explain issues which may not be covered by the document.
Nokia Networks' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL ORCONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use ofthis document or the information in it.
This document and the product it describes are considered protected by copyrightaccording to the applicable laws.
NOKIA logo is a registered trademark of Nokia Corporation.
Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.
Copyright Nokia Oyj 2003. All rights reserved.
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Table of ContentsTable of Contents
1 Objectives ................................................................................... 4
2 Technologies .............................................................................. 52.1 Why Digital?................................................................................. 52.2 Standardisation ............................................................................ 52.2.1 European Telecommunications Standard Institute
(ETSI)........................................................................................... 5
3 GSM Overv iew ............................................................................ 7
4 Radio Access ............................................................................. 94.1 Multiple Access Techniques ........................................................ 9
4.2 Frequency Division Multiple Access (FDMA)............................... 94.2.1 Time Division Multiple Access (TDMA)........................................ 94.2.2 Code Division Multiple Access (CDMA)..................................... 104.2.3 Space Division Multiple Access (SDMA) ................................... 104.3 Channel Types........................................................................... 11
5 Modulation ................................................................................ 135.1 Modulation ................................................................................. 135.1.1 Complex Signals........................................................................ 135.1.2 Fourier Transformation .............................................................. 145.1.3 The Radio Engineers Dilemma ................................................. 145.1.4 GMSK Spectrum........................................................................ 15
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GSM Standardisation and Technology
1 Objectives
At the end of this module the participant will be able to:
Describe GSM architecture and main elements
List radio access technologies
Describe the principles of GMSK modulation
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2 Technologies
Second generation cellular systems on a fully digital basis are the systems
belonging to the GSM family. GSM900 and its twin sister GSM1800(formerly DCS1800) are in worldwide use in over 100 countries on all
continents now.
In the USA a GSM derivative (GSM1900) is being promoted as a competitor
to US-based CDMA (Code Division Multiple Access) systems. GSM1900 is
very similar to GSM900/1800, but uses a different voice coding system. This
is more a political issue rather than a technical issue.
2.1 Why Digital?During transmission through the entire communication chain signals become
distorted by noise, non-linearity in amplifiers, interference from other
transmitters, etc. Analogue signals may take any given waveform. Therefore
distortions are undetectable since any signal form is valid. Digital signals have
two distinct states, 1 and 0. At any intermediate stage, a digital signal can
be regenerated to its ideal state. Error correction algorithms can be applied to
detect transmission errors (bit errors). Such, a digital signal can be carried
clean all the way from source to destination and be converted to an audible
(analogue) signal only at the receiving users ear.
As opposed to analogue, digital signals can be: ideally and error-free regenerated
packaged
compressed
stored
reproduced identically
easily de-/ and encrypted
2.2 Standardisation
2.2.1 European Telecommunications Standard Institute (ETSI)
ETSI (European Telecommunications Standard Institute) was founded by the
former CEPT (Confrence Europene des Postes et Tlcommunications).
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GSM Standardisation and Technology
ETSIs task is to elaborate unified standards for telecommunicationsequipment in Europe.
ETSI is financed by the European Union (EU) and contributions of its
members. It is a co-operation between all the major telecommunication
suppliers and operator companies.
Presently standards issued by ETSI include:
Cellular: GSM 900 (Global System for Mobile Communications), GSM
1800, GSM 1900, GPRS (Generalized Packet Radio Services), UMTS
(Universal Mobile Telecommunication System)
Cordless Telephony: DECT (Digital European Cordless Telephone)
Paging: ERMES (European Radio Messaging System)
Trunked Radio: TETRA (Trans-European Trunked Radio System)
ETSI is located in the Sophia Antipolis technology park (French SiliconValley) near Nice in Southern France.
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3 GSM Overview
The principle of the GSM System architecture is shown in the illustration
below:
other MSC
other BTSs
VLR HLREIR
AuCOMC
Figure 1. GSM architecture
A site (=BS) can have several sectors (=cell). Each sector consists of a
number of TRXs.
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GSM Standardisation and Technology
Channel spacing 200kHz
Usual bandwidth values (GSM900):5 ..8 MHz per operator in one or more sub-bands
1880
GSM 900 :
25 MHz
GSM 1800 :
75 MHz 1710 1785 1805
duplex distance : 95 MHz
890 915 935 960
duplex distance : 45 MHz
GSM 1900 :
2 x 60 MHz at channel spacing 200kHz = ~300channels
Band subdivided by FCC into subbands A..F
sub-bands A, B, C : 2 x 15 MHz spectrum
sub-bands D, E, F : 2 x 5 MHz
1850 1910 1930 1990
duplex distance : 80 MHz
Figure 2. GSM frequency bands
GSM 900 and GSM 1800 are twins. There are no major differences betweenthem except the operating frequency:
GSM 900 GSM 1800
Frequency band 890...960 MHz 1710...1880 MHz
Number of channels 124 372
Channel spacing 200 kHz 200 kHz
Access technique TDMA/FDMA TDMA/FDMA
Mobile power 0,8 / 2 / 5 W 0,25 / 1 W
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4 Radio Access
4.1 Multiple Access Techniques
In order for several radio links to be in progress simultaneously in the same
geographical area without mutual interference, arrangements have to be made
to avoid system degradation due to mutual interference. This is known as
multiple access to a common transmission medium. Several multiple access
techniques exist:
Frequency Division Multiple Access (FDMA)
Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)
Space Division Multiple Access (SDMA)
4.2 Frequency Division Multiple Access (FDMA)
FDMA systems allocate one frequency band continuously (in time) to one
specific user, who is the only one transmitting and receiving on this
frequencies during his time of transaction. Each radio resource (radio channel)is identified with the carrier frequency and relative bandwidth. In the GSM
900-case the carrier frequencies are in the 900 MHz band and the single
channel bandwidth available for one user is 200 kHz.
4.2.1 Time Division Multip le Access (TDMA)
TDMA systems operate with time slots, short periods of time. Each user is
assigned to a specific timeslot for his transaction. Within a specific radio
channel (frequency channel) several users are served. They share the channel
sequentially in time. The time slots are of very short duration, the user,however, perceives a continuous speech stream due to appropriate
compression and expansion techniques at transmitter and receiver.
TDMA is the choice mainly in digital systems. From a bandwidth perspective,
FDMA and TDMA provide the same spectral efficiency (measured in kHz per
user). Figure 3 illustrates the TDMA principle.
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GSM Standardisation and Technology
T = Allocated time
t
A
Slot for user 1
Slot for user 2
Slot for user 3
Slot for user 5
Slot for user 7
Slot for user 8
Slot for user 4
Slot for user 6
Figure 3. Time division multiple access principle
4.2.2 Code Division Multip le Access (CDMA)
CDMA follows the idea of many users using one single physical radio
channel (spread spectrum approach). Coding each stream with orthogonalcoding sequences separates user data streams. Orthogonality thereby provides
(ideally) a cross-correlation of zero; i.e. each stream can be extracted error-
free by correlation.
Multiplying each user data bit with a spreading sequence increases the used
bandwidth considerably (spread spectrum). Since the signals of all users are
by nature then co-channel interferers to any other users signals, resistance
against interference needs to be provided by the achievable coding gain of the
spreading sequence. More coding gain can be achieved by longer sequences,
which in turn increases the bandwidth used. Sets of orthogonal (cross-
correlation = 0!) and long sequences are difficult to find. A cross-correlation
other than zero means that the signal cannot be extracted uninfluenced byother signals, i.e. bit errors remain.
4.2.3 Space Division Multip le Access (SDMA)
SDMA follows the idea of separating users by their location in space (or in
angle). By transmitting and receiving signals only into the direction where the
user/basestation signals are coming from, interference to other users is
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reduced considerably. SDMA requires "smart"/adaptive antennas, which in
turn require a certain physical space. Therefore smart antennas are especially
to be deployed at the base station. SDMA is a technique which become
popular recently, but it still will take some time to be deployed in commercial
systems.
4.3 Channel Types
In mobile communications different types of physical radio channels can be
distinguished (see Figure 4):
Simplex channel:The generic channel type. A specific radio frequency is
allocated to each party (FDMA). The channel is permanently allocated to the
user. Usage: e.g. amateur radio, walkie-talkie
FDMA/TDD:(TDD Time Division Duplex) The same radio channel is
used alternatingly for direction A-to-B, then B-to-A, etc. Usage: e.g. cordless
phones (half-duplex channel)
TDMA/TDD:Timeslots on same radio channel are used for both uplink and
downlink direction. Usage: e.g. DECT
FDMA/ TDMA:A timeslot on a radio channel is allocated to a specific user.
Different users are on the same frequency channel and another timeslot or on
another frequency channel and another timeslot. There exist several frequency
channels in parallel. Uplink and downlink directions operate on different radio
frequencies (FDD Frequency Division Duplex). Usage: e.g. GSMCDMA/FDMA:Users on the same frequency channel are separated by
different codes. There exist several frequency channels in parallel. Uplink and
downlink directions operate on different radio frequencies (FDD). Usage: e.g.
UMTS
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A to B
B to A
f1
f2
f3f4
FDMA : e.g. walkie-talkie
A to B B to A A to B B to A
X to Y Y to X X to Y Y to X
C to D D to C C to D D to CM to N N to M N to M M to N
f1
f2
f3f4
FDMA/TDD : e.g. CT2-system
f1
f2
f3
f4
1 2 3 4 5 6 ... 1 2 3 4 5 6
TDMA/TDD : e.g. DECT
f1
f2
f3
f4
1 2 3 4 5 6 ... 1 2 3 4 5 6
3 4 5 6 ... 1 2 3 4 5 6 .. 1
FDMA/ TDMA: e.g. GSM
Figure 4. Channel types
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5 Modulation
5.1 Modulation
Regardless of the technology used, in radio link there is always a carrier
frequency, which is being modified by the information signal. There are
several ways to modulate the carrier. Regardless of the technology of the
information signal (analogue or digital), the result modulated carrier signalis always analogue.
Where is the information?
Amplitude modulation
Frequency modulation
Phase modulation
equidistant sampling points
Figure 5. Modulation types
5.1.1 Complex Signals
While unipolar or bipolar signals (0 / 1 or -1 / +1) can be displayed inone dimension, complex signals span out a signal plane (2-dimensional
signals). The distance of the signal point from the origin represents the signal
amplitude (energy); the angle of the sample represents the value of the
symbol. Such, multi-level signals can be represented with a single signal
sample. This pie-slices principle is referred to also as angular modulation.
In microwave radio links multilevel QAM signals are used, thereby providing
a very efficient modulation scheme. In mobile radio the transmission path
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GSM Standardisation and Technology(air) is very variant and unreliable, therefore on four signal points in the
complex plane are used to minimise error probability.
I
Q
I
Q
Multiplying the user data stream with two orthogonal signals generates
complex signals (simplest case: sine and cosine wave). By superposition of
both partial streams a complex (2-dimensional) signal is created.
For details on modulation schemes refer to theory books.
5.1.2 Fourier Transformation
In signal theory there is a duality of time and frequency. The Fourier
transform provides the means to equivalently transform a signal
representation in time domain into frequency domain and vice versa.
-3 -2 -1 0 1 2 3
k/a
w(x)
-3 -2 -1 0 1 2 3
k/a
w(x)
2 3 4-2-3-4 0
kx/a
W(kx)
2 3 4-2-3-4 0
kx/a
W(kx)
W k w x e dxxjk xx( ) ( )=
1
2
Figure 6. Fourier transformation
5.1.3 The Radio Engineers Dilemma
As seen from Fourier transform properties, an instant signal change in time
domain (e.g. a binary signal changing from 1 to 0) causes an infinite
signal in frequency domain. Since bandwidth of any system is strictly limited
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this means that any system with a certain bandwidth can only support a
certain modulation speed. In other words: bandwidth * modulation speed =
constant.
The radio engineers dilemma is that either we can have fast modulation ORnarrow bandwidth, but not both. Since we would like to optimise both
contradictory parameters, it seems well have to settle for a compromise,
allowingprettyfast modulation at an acceptablynarrow bandwidth.
5.1.4 GMSK Spectrum
In search of a modulation scheme providing an acceptable compromise of
both parameters, the GSM community has decided to use a Gaussian
Minimum Shift Keying (GMSK) modulation with properties B*T = 0,3.
The Gaussian stands for a filtered modulation signal with limited signalslopes (time domain), which in turn guarantees limited bandwidth in
frequency domain. Minimum Shift keying is a modulation scheme featuring
a continuous phase trajectory, i.e. no sudden jumps of the signal vector.
The combination of both allows GSM to perform at a modulation speed of
approx. 271 kb/s within a modulation bandwidth of 162 kHz (allowing a
channel spacing of 200 kHz)
Figure 7. Digital modulation spectrum
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Radio Propagation Channel
Training Document
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Radio Propagation ChannelThe information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been
prepared to be used by professional and properly trained personnel, and the customerassumes full responsibility when using it. Nokia Networks welcomes customer comments aspart of the process of continuous development and improvement of the documentation.
The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered bindingbut shall be defined in the agreement made between Nokia Networks and the customer.However, Nokia Networks has made all reasonable efforts to ensure that the instructionscontained in the document are adequate and free of material errors and omissions. NokiaNetworks will, if necessary, explain issues which may not be covered by the document.
Nokia Networks' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL ORCONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use ofthis document or the information in it.
This document and the product it describes are considered protected by copyrightaccording to the applicable laws.
NOKIA logo is a registered trademark of Nokia Corporation.
Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.
Copyright Nokia Oyj 2003. All rights reserved.
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Table of ContentsTable of Contents
1 Objectives ................................................................................... 4
2 Reflections, Dif fract ions and Scattering.................................. 52.1 Calculation in dB.......................................................................... 52.2 Propagation Mechanisms ............................................................ 6
3 Mult ipath and Fading ................................................................. 73.1 Fading.......................................................................................... 8
4 Propagation Slope and Different Environments ................... 114.1 Propagation Loss....................................................................... 124.1.1 Plane Earth Approximation and Path Loss Breakpoint.............. 14
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Radio Propagation Channel
1 Objectives
At the end of this module the participant will be able to:
Describe basic propagation mechanisms
Describe multi path propagation
Describe the difference between fast and slow fading
Describe factors of path loss
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2 Reflections, Diffractions andScattering
2.1 Calculation in dB
Decibel (dB) is a relative, logarithmic scale commonly used in
communications theory. dB always refers to a reference value, e.g. the
isotropic radiator in antenna context (dBi) or militates in link budget
calculations (dBm). As a rule of thumb: 3 dB is linear factor 2, and 10 dB is a
linear factor of 10.
Calculations in dB (deci-Bel) logarithmic, relative scale
Always with respect to a referencedBW : dB above Watt
dBm : dB above mWatt
dBi : dB above isotropic
dBd : dB above dipole
dBV/m: dB above V/m
rule-of-thumb: +3 dB = factor 2
+7 dB = factor 5
+10 dB = factor 10
-30 dBm = 1 W-20 dBm = 10 W-10 dBm = 100 W-7 dBm = 200 W-3 dBm = 500 W 0 dBm = 1 mW
+3 dBm = 2 mW
+7 dBm = 5 mW
+10 dBm = 10 mW
+13 dBm = 20 mW
+20 dBm = 100mW
+30 dBm = 1 W
+40 dBm = 10W
+50 dBm = 100W
Power
Voltages
Conversion factorE(dBV/m) = P(dBm) + 106,4 + antenna factor
antenna factor = 20 log(f [MHz]) -29,8 - ant_gain + cable_lossantenna factor for
900 MHz : ~ 29 dB1800 MHz : ~ 35 dB
dBP
PPlin
P dB
=
=10 10
0
10log [ ].( )
dBE
EElin
E dB
=
=20 10
0
20log [ ].( )
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Radio Propagation Channel2.2 Propagation Mechanisms
Free- space propagation
Signal strength decreasesexponentially with distance
specular reflection
diffuse reflection
Reflection
Specular Reflection
amplitude: A --> *A (< 1)
phase : --> -
polarisation: material dependant phase shift
Diffuse Reflection.amplitude: A --> *A (< 1)
phase : --> random phase
polarisation : random
D
Absorption
heavy amplitudeattenuation materialdependant phase shiftsdepolarisation
Diffraction
wedge- model
knife edge
multiple knife edges
A A - 5..30 dB
Figure 1. Propagation mechanisms
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3 Multipath and Fading
The radio channel is reciprocal in field-strength. This means that a signal
propagating from A to B will experience the same path losses and attenuationwhen propagating from B to A. This is an important fact to remember when
considering link budgets. Reciprocity is true for field-strength, but not for
interference conditions. These may be greatly different at the mobiles
location as opposed to the base station location.
The mobile radio channel features time dispersion as a result of multipath
propagation. Partial signals take different paths to the mobile and
consequently arrive with different time delays in the order of some
microseconds. At velocity of light (c = 3 10^8 m/s) 1 sec delay correspondsto a path difference of approx. 300m.
GSM specifies an equaliser with a time window of 16 sec to be used in thereceiver. This means that all partial waves arriving within this time windoware valid contributions to the received signal. Signals with excessive delay act
counter-productive as co-channel interference.
Equalisers are specified to cope with standardised delay profiles
TU3: typical urban environment at 3 km/h (pedestrians)
TU50: typical urban at 50 km/h (cars)
HT100: hilly terrain at 100 km/h (road vehicles)
RA250: rural area at 250 km/h (highways, trains)
Note that there is no hard limitation at the speed of 250 km/h (130 km/h forGSM1800), despite of some discussions on this topic. Bit error rates may
under certain conditions exceed the specifications at higher speeds, but this
does not necessarily cut the connection. The limit --if at all-- is a very soft
limit. In fact, GSM900 has been successfully performing within specification
at speeds above 400 km/h and a German operator has conducted performance
tests of GSM1800 in high-speed trains travelling at 250 km/h.
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Radio Propagation Channel
equaliser window 16 s
amplitude
delay time
echos
direct path
Figure 2. Equaliser window
3.1 Fading
There are several fading mechanisms to be distinguished in mobile radio
environment:
Slow fading:This is due to shadowing by terrain structures and large
obstacles. It is in the order of 10s of wavelengths. The slow fading can be
described mathematically by the Gaussian distribution.
Figure 3. Gaussian distribution
Rayleigh or fast fading:This phenomenon is due to multipath propagation of
the signal. Signals with same amplitudes and opposite phase shifts
superimpose and eliminate each other. This creates local very distinguished
fading dips in the order of fractional wavelengths. The Rayleigh fading
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process is applicable to obstructed propagation paths (non-line-of-sight
conditions) and can be mathematically modelled by the Rayleigh distribution.
Figure 4. Rayleigh distribution
Rician fading:This is a combination of the upper two conditions: Rayleigh
fading in the presence of a direct (line-of-sight wave). The ratio of direct to
indirect signal energy is the Rice factor. This fading type is applicable to
partly obstructed propagation paths. It is modelled mathematically by the
Rician distribution
K = 0
(Rayleigh)
K = 1
K = 5
Figure 5. Rician distribution, K = 0:Rayleigh; K >>1: Gaussian
In mobile environment the received signal generally is not received via the
direct line-of-sight path (which often doesnt even exist), but by a variety of
different independent propagation paths (multipath propagation).
The received signal can be seen as a superposition ofseveral superimposed
individual partial signals having a certain amplitude and phase (complex
signals). Each partial signal corresponds to a certain propagation path. Each
signal has experienced several reflections and diffractions, each causing
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Radio Propagation Channelamplitude attenuation and a random phase shift. The resulting signal vector is
composed by vector addition of its components, see Figure 6. In every instant
the partial waves take different (complex) values, thereby also influencing the
resulting vector.
A1
A2
A3
A4
A5
Aresult
1
2
3
4
5
result
Figure 6. Phasor diagram
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4 Propagation Slope and DifferentEnvironments
It can be easily shown that in free space signal power decreases with the
square of distance from the antenna. This simplified illustration shall explain
the basic mechanism:
Free space loss proportional to 1/ d^2Simplified case: isotropic antenna
Which part of total radiated power is foundwithin surface s ?
Simplified case (perfectly isotropic antenna) :Power density = P / Stotal power within surface s : P = P/S *s
assume R=100m: ==> P = P/ 7,96*10e-6==> -51 dB
(coupling loss at ref. distance)
Power density reduces with square of distance==> received power per area unit reduces at same rate==> free space loss proportional to 1/d^2
R
Surface S = 4* R^2
assume surface
s = 1m^2
2d
4d
A = 4*A
A = 16*A
A
d
Figure 7. Free space loss
Radio wave signals attenuate with the square of distance in the best case. This
is pure law of physics and valid for all frequency bands and modulation types.
In mobile communication, signal levels decrease with 3rd to 4th power of
distance, depending on terrain.
Signal attenuation is often expressed in dB per decade or dB per octave
(meaning: doubling the distance). A decade has 3.32 octaves (Solve equation:
2 ^x = 10).
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Radio Propagation Channel Power density by the
receiving end:
Effective antennaarea:
Received power
Mobile environments: )5...5,2( == withdCGGPP rssr
Reff GA
4
2
=
Pr= S Aeff
SP G
d
s s=4
2
P
P G G d
r
ss r=
4
2
Ps
As
Gs
Pr
Ar
Gr
d
2
4
Figure 8. Signal propagation formulas
In radar technology received power is inversely proportional to the 4th power
of distance, since the signal traverses distance twice.
In mobile communications distance is traversed only once, but the
propagation path is not free-space (line-of-sight), but heavily obstructed in
most cases, causing considerable loss. Received signal levels are inversely
proportional to the 2nd ...5th power of distance, depending on the
environment between transmitter and receiver.
4.1 Propagation Loss
Radio wave propagation losses are usually calculated in a logarithmic scale, in
dB. Losses are exponential with distance. Propagation loss formulas are based
on the free-space loss formula with additional empirical correction factors.
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Bas ic los s formula
C lutte r loss fac tors land-usage classesus ually stated in dB /deca dee.g. :
L L d= +0 log( )
loss at reference point (e.g. 1km)
losses are exponential with distance
free s pace 20 dB /dec
ope n countrys ide 25 dB /de c
suburban areas 30 dB /dec
urban area 40 dB /dec
h is to ric c ity c entre >45dB/dec
0,1km 10km1km
EIRP level
coupling loss
= L0
reference
distance
20 dB/dec
30 dB/dec40 dB/dec
Figure 9. Propagation loss
Signal levels attenuate differently in different environment (land usage
classes). Typical signal attenuation rates are 20 ..45 dB/decade.
25 dB/dec
30 dB/dec20 dB/dec
40 ..50 dB/decpath l
Figure 10. Signal attenuation in different environments
The radio signal attenuation depends on the environment the signal passes
though. A rise in signal strength can be observed despite of increasing
distance, when the receiver re-enters open area after passing through urban
environment, causing a higher attenuation exponent. Since the received signal
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Radio Propagation Channelstrength depends on the close environment of the receiver, there is no abrupt
rise in signal strength but a gradual increase, as the mobile enters open area.
urban: 40 ..50 dB/decopen: 25 dB/dec open: 25 dB/dec
open area curveurban curve
actualsignal level
signallevel
distance
Figure 11. Mixed path loss
4.1.1 Plane Earth Approximation and Path Loss Breakpoint
The so-called plane earth approximation is used for studying radio wave
propagation mathematically. In this approximation, the earth is assumed to becompletely flat and smooth. Hence, the received signal is a result of exactly
two signals; the direct (LOS) signal and once ground-reflected signal, see
Figure 12.These signals sum up constructively or destructively, depending on
their phases. The phases of the received signal components depend on the
path length differences and reflection coefficient. For very small angles of
incidence (measured from the ground) the reflection coefficient is 1 for both
polarisations, hence the two signals tend to compensate each other as distance
increases. This leads to a path loss exponent of 4 after a certain distance. This
distance is called "the breakpoint distance".
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Figure 12. Propagation over plane earth
The formula for break point distance calculation is
,4 21
hhB =
where h1and h2are the transmitting and receiving antenna heights.
Real environments are, of course, totally different from the plane earth
approximation. However, in practical field strength measurements a path loss
breakpoint is usually really detectable. If one would be able to determine the
path loss breakpoint exactly, it would be a great benefit in network planning;
the serving cell would be the region up to the breakpoint distance and less
interference would be generated for the other area.
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Radio Network Planning Process
Training Document
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Radio Network Planning Process
The information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been
prepared to be used by professional and properly trained personnel, and the customerassumes full responsibility when using it. Nokia Networks welcomes customer comments aspart of the process of continuous development and improvement of the documentation.
The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered bindingbut shall be defined in the agreement made between Nokia Networks and the customer.However, Nokia Networks has made all reasonable efforts to ensure that the instructionscontained in the document are adequate and free of material errors and omissions. NokiaNetworks will, if necessary, explain issues which may not be covered by the document.
Nokia Networks' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL ORCONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use ofthis document or the information in it.
This document and the product it describes are considered protected by copyrightaccording to the applicable laws.
NOKIA logo is a registered trademark of Nokia Corporation.
Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.
Copyright Nokia Oyj 2003. All rights reserved.
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Table of Contents
Table of Contents
0 Objectives ................................................................................... 4
1 Introduction and Pre-planning .................................................. 51.1 Network Planning Competence ................................................... 51.2 Network Characteristics............................................................... 51.3 Scope of Network Planning.......................................................... 61.4 Cellular Planning Process............................................................ 61.5 Input Data for a Planning Process ............................................... 81.6 Key Dimensioning Quantities....................................................... 9
2 Detailed Planning ..................................................................... 102.1 Coverage Planning .................................................................... 102.1.1 Coverage Planning Process ...................................................... 102.2 Coverage Requirements ............................................................ 11
3 Site Select ion ........................................................................... 133.1 Site Locations ............................................................................ 133.1.1 Bad Site Location....................................................................... 133.1.2 Good Site Location .................................................................... 133.1.3 Site Selection Criteria ................................................................ 143.2 Site Building Process................................................................. 153.3 Site Information.......................................................................... 15
4 Post -Planning ........................................................................... 17
5 Documentation ......................................................................... 18
6 Signal Measurements .............................................................. 196.1 Measurement Types .................................................................. 196.1.1 Measurement Methods .............................................................. 196.1.2 Choice of Routes ....................................................................... 206.1.3 Interpretation of Results............................................................. 20
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1 Objectives
At the end of this module the participant will be able to:
Describe the radio network planning process
Describe the major tasks in the planning process
Describe the planning tools for the different phases
Describe the input and output documents (data)
Describe the planning environment
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2 Introduction and Pre-planning
2.1 Network Planning Competence
Traditional network operators (old PTTs) tend to do their very own network
planning following their internal structures. The advantage is detailed
knowledge of their network; disadvantages are often low efficiency and no
up-to-date knowledge of new techniques and features.
New network operators often come from a non-telecom background and
have no or little resources capable of doing network planning. Therefore this
task is often subcontracted to other companies.
Some infrastructure suppliers also offer network planning in more or less
detail. They usually require the use of their own equipment and have good
knowledge of internal limitations and undocumented features of the
equipment.
Many consulting companies also offer network planning services. Their main
advantage is independence from manufacturers. This makes them the natural
choice for operators in the license-tendering phase. It is difficult for
consulting companies to stay up-to-date with the latest information
concerning equipment capabilities of different suppliers.
2.2 Network Characteristics
Each operators network will have different characteristics. These strategic
intentions of the operator shall also be reflected in the network topology in
order to tailor a network according to the needs. The first operator in a
country could for example aim for plain coverage, whereas the second
operator could target for competitive pricing. The strategy of the third
operator could be replacing the wireline phones.
The following factors should also be taken into account when making the
planning:
Expected roamer numbers and locations
Existing international regulations at border areas
Are microwave links or leased lines the preferred solution?
Each network philosophy calls for a different planning approach.
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2.3 Scope of Network Planning
Network Planning is a complex task involving interactions with many
different functions within the operators organisations. Some tasks areiterative, therefore rather time and resource consuming.
Figure 1 shows the main dependencies and interactions within the scope of
network planning.
Network planning team
data acquisition
site survey and selection
field measurement evaluation
NW design and analysis
transmission planningNetwork design
number and configuration of B Santenna systems specificationsBS S topologydimensioning of transmission lines frequency plan
network evolution strategy
Network performance
grade of service (blocking)outage calculations interference probabilities
quality observation
Customer requirements
coverage requirementsquality of service recommended sites subscriber forecasts
External information sources
topo- & morphological datapopulation databandwidth available frequency co-ordination
constraints
Interactions with
external subcontractors
site hunting teams
measurement teams
operator
switch planning engineers
Figure 1. Scope of network planning
2.4 Cellular Planning Process
Coverage planning is an iterative and time-consuming task. It involves rounds
of discussions and decisions with site acquisition people. Figure 2belowshows the main process stream.
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external inputs:(traffic, subs. forecast,coverage requirements...)
Initial NW dimensioning
TRX?, cells, sites
bandwidth needed NW topology
nominal cellplansuggestions for
site locations cell parameters
coverage achieved
coverage prediction
signal strength
multipath propagation
Sitepre-validation
site inspection
site accepted ?
real cellplanfield measurements
planningcriteria fulfilled?
N
N
N
create cell
data forBSC
go tofrequencyplanning
field measurements
Figure 2. Coverage planning
Inputs from operators marketing and business planning departments are
considered for the initial network design. Then follows the very iterative
process of coverage planning. Aim of the transmission plan is to minimise the
costs for transmission over the networks life cycle. This then decides the
final network topology.
Frequency and interference calculations are iterated to the stage of acceptance
from the customer. This includes detailed inputs about traffic volumes anddistributions expected in the network.
Parameter planning and tuning increases the network performance.
Figure 3. Cellular planning process
CoveragePlanning andSite Selection
CoveragePlanning andSite Selection
ParameterPlanningParameterPlanning
PropagationmeasurementsCoverageprediction
SiteacquisitionCoverageoptimization
PropagationmeasurementsCoverageprediction
SiteacquisitionCoverageoptimization
External InterferenceAnalysisExternal InterferenceAnalysis
NetworkConfigurationandDimensioning
NetworkConfigurationandDimensioning
PRE-PLANNING
DETAILED PLANNING
Traffic distribution
Service distributionAllowed blocking/queuingSystem features
IdentificationAdaptationIdentificationAdaptation
Area / Cellspecific
Handoverstrategies
Maximumnetworkloading
Other RRM
NetworkOptimizationNetworkOptimization
POST-PLANNING
Surveymeasurements
Statisticalperformanceanalysis
QualityEfficiencyAvailability
Capacity Requirements
Requirementsand strategyfor coverage,quality andcapacity,
per service
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marketing
business
plan
traffic
assumptions
initial NW
dimensioning
freq. & inter-
ference plan
transmission
plan
final NW
topology
parameter
planning
coverage
plan
Figure 4. Cellular planning principles
2.5 Input Data for a Planning Process
Demographic Data:Demographic data are useful for estimating traffic
densities and distributions. Population distributions are valuable information
for placement of base stations, probable routing possibilities for terrestrial
lines etc.
Topographic Data: Before starting the coverage planning task, some
elementary topographic data need to be collected to get a first impression of
the countrys characteristics. Useful sources of data are a close study of maps
and local knowledge obtainable from residents.
Map informationincludes e.g.
location of main cities
important roads
location of mountain ranges
inhabited area
shore lines
Local knowledgeincludes
typical formation of city skylines
typical building architectures used
structures of city
local peoples habits (phone habits, normal working hours,
conversation styles...).
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2.6 Key Dimensioning Quantities
Some essential dimensioning figures for network design include:
number of base stations needed for coveragereasons
number of base stations needed for trafficreasons
acceptable outage probabilities
balance of interference level and acceptable frequency re-use rate
bandwidth available
Note that design goals are interdependent. A network can only be optimised
with respect to a single parameter. The overall optimum is always a trade-
off and compromise between different aspects.
Design goals and rules must be clearly agreed with the customer beforestarting the planning procedure.
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3 Detailed Planning
3.1 Coverage Planning
Coverage planning is the first (and also most visible) step in the actual
network planning process.
3.1.1 Coverage Planning Process
The coverage planning process is a major portion of network planning. Itinvolves several iteration loops with respect to site selection, site negotiation
and measurements. Coverage Planning is a quite resources and time-
consuming task.
external inputs:(traffic, subs. forecast,
coverage requirements...)
Initial NW dimensioning
TRX?, cells, sites
bandwidth needed
NW topology
nominal cellplansuggestions for
site locations
cell parameters
coverage achieved
coverage prediction
signal strength
multipath propagation
Site
pre-validation
site inspection
site accepted ?
real cellplanfield measurements
planning
criteria fulfilled?
N
N
N
create cell
data for
BSC
go to
frequency
planningfield measurements
Figure 5. Coverage planning process
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3.2 Coverage Requirements
The early and clean definition of coverage requirements is a fundamental
basis for network planning. This, of course, is on the traditional borderline oftechnical and marketing departments. Experience shows that this border is
seldom trespassed. However, the operators that have functioning co-operation
between technical and marketing staff are also the more successful operators.
The agreed targets should include:
Roll-out phases & time schedules
Coverage level requirements, i.e. coverage thresholds
Agree on min. levels for outdoor coverage
Indoor coverage area
Mobile classes to plan for
Operators cell deployment strategies
Omni-cells in rural areas?
3-sector cells in urban areas?
Minimum of 2 TRX per cell?
phase 1
NW launch
rollout
phase 2
rollout
phase 3
Figure 6. Rollout phases
Coverage thresholds affect the cell size as shown in Figure 7.In a hilly area
the surrounding mountains have more effect on the cell size than what the
coverage thresholds do.
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Figure 7. Coverage thresholds define the cell range in a flat open area
Full coverage of an area can never be guaranteed. Outages (see Figure 8)due
to coverage gaps and interference will always occur. The total location
probability in a cell is a function of the probability for no coverage and
interference:
(1- Pno_cov) * (1- PIf)Common values for the total location probability are between 90%-95% (time
and location probabilities).
Pno_covPif
Figure 8. Outage areas
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4 Site Selection
4.1 Site Locations
Proper site location determines usefulness of its cells. Sites are expensive,
long-term investments. Site acquisition is a slow process and hundreds of sites
are needed per network. Hence a base station site is a valuable long-term asset
for the operator. That's the reason that planners need to visit each site.
4.1.1 Bad Site Location
Hilltop locations for BS sites should be avoided as they cause:
uncontrolled interference
interleaved coverage
awkward HO behaviours
but: good location for microwave links!
wanted cell
boundary
uncontrolled, strong
interferences
interleaved coverage areas:weak own signal, strong foreign signal
Figure 9. Bad site location
4.1.2 Good Site Location
Sites off the hilltops are preferable as:
hills can be used to separate cells
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contiguous coverage area
only low antenna heights are needed if sites are slightly elevated above
valley bottom
wanted cell
boundary
Figure 10. Good site location
4.1.3 Site Selection Criteria
Radio criteria for site selection:
good view in main beam direction
no surrounding high obstacles
good visibility of terrain
room for antenna mounting
LOS to next microwave site
short cabling distances
Non-radio criteria for site selection:
space for equipment
availability of leased lines or microwave link
power supply
access restrictions?
house owner
rental costs
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4.2 Site Building Process
issue search area
& requirements
find suitablesite candidates
calculate coverage range
of each candidate
propagationmeasurements
needed ?
transmission
links available? sign contract
with site owner
get building permit
construction work
installing & testing
on air!
Figure 11. Site building process
Site acquisition is a slow process and hundreds of sites are needed per
network. Hence a base station site is a valuable long-term asset for theoperator. Therefore it is important to select good sites. They cannot be
changed easily.
4.3 Site Information
Collect all necessary information about site details. The necessary information
should include:
site co-ordinates, height above sea level, exact address house owner
type of building
building materials (photo)
possible antenna heights
360 degree photo (clearance view)
neighbourhood, surrounding environment
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drawing sketch of rooftop
antenna mounting conditions
access possibilities (truck?, road, roof)
BS location, approximate feeder lengths.
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5 Post-Planning
In post-planning verification, monitoring and optimisation tasks are carried
out in order to reach maximum capacity and quality from the radio network.
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6 Documentation
All the information that is needed to rebuild a site has to be documented to a
site folder database. Also measurement results and e.g. traffic history shouldbe documented.
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7 Signal Measurements
7.1 Measurement Types
Signal measurements can be divided into three different types. The different
types have different goals and are used in different phases of network
planning and optimisation.
7.1.1 Measurement Methods
Propagation measurements:
Purpose:
check coverage area of site
propagation model tuning
site candidate evaluations
Method:
test transmitter, mast, omni/directional antennas
CW- signal
Time:
planning phase
Functional test:
Purpose:
after commissioning of site, verify complete BS installation (incl.
antennas)
verify basic parameter settings (HO, power control )
Method:
coverage audit, real antenna types, ant. directions & tilting
use test mobile to check settings & record results
Time:
pre-opening phase
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Performance measurements:
Purpose:
check the users perspective of live network performance
secondary input to OMC information
identify problem areas in network
Method:
drive tests
real network under live conditions
Time:
commercial phase
7.1.2 Choice of Routes
Propagation measurements
stay within coverage area of cell
model tuning: preferably stay within a single land usage class
Functional tests
radial from site into neighbouring cells
check handovers in & out of cell
Performance measurements
define a random route once
drive repeatedly (comparable results!)
7.1.3 Interpretation of Results
Propagation measurements
signal averaging
Lees criterion: min. 50 samples per 40
estimate accuracy of prediction
database resolution
model tuning
Functional tests
identify incorrect parameter settings
check missing HO relations
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Performance measurements
detect misbehaviour of network
calculate call success rate
key performance indicators
evaluate network behaviour under nominal conditions (subscribers
view).
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Configuration Planning
Training Document
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Configuration Planning
The information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been
prepared to be used by professional and properly trained personnel, and the customerassumes full responsibility when using it. Nokia Networks welcomes customer comments aspart of the process of continuous development and improvement of the documentation.
The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered bindingbut shall be defined in the agreement made between Nokia Networks and the customer.However, Nokia Networks has made all reasonable efforts to ensure that the instructionscontained in the document are adequate and free of material errors and omissions. NokiaNetworks will, if necessary, explain issues which may not be covered by the document.
Nokia Networks' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL ORCONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use ofthis document or the information in it.
This document and the product it describes are considered protected by copyrightaccording to the applicable laws.
NOKIA logo is a registered trademark of Nokia Corporation.
Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.
Copyright Nokia Oyj 2003. All rights reserved.
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Table of Contents
Table of Contents
1 Objectives ................................................................................... 4
2 Network elements ...................................................................... 52.1 GSM Elements............................................................................. 52.1.1 Base Transceiver Station (BTS) .................................................. 62.1.2 Nokia BTS.................................................................................... 72.2 Antenna Systems....................................................................... 132.2.1 Far Field Distance...................................................................... 132.2.2 Antenna Types........................................................................... 142.2.3 Antenna Characteristics............................................................. 152.2.4 Coupling Between Antennas...................................................... 182.2.5 Installation Examples................................................................. 182.2.6 Nearby Obstacles Requirement................................................. 192.3 Diversity Techniques.................................................................. 222.3.1 Space Diversity.......................................................................... 232.3.2 Polarisation Diversity ................................................................. 242.3.3 Combining.................................................................................. 242.3.4 Coverage Improvement by Diversity?........................................ 252.4 Antenna Cables ......................................................................... 252.5 Filters and Combiners................................................................ 262.6 MHA and Booster....................................................................... 292.6.1 Masthead Preamplifier (MHA).................................................... 292.6.2 Downlink Booster (TBU) ............................................................ 302.7 Base Station Controller (BSC) ................................................... 30
2.7.1 Nokia BSC ................................................................................. 322.8 Transcoder Submultiplexer (TCSM2E)...................................... 322.9 Mobile Switching Center (MSC)................................................. 332.10 Operation and Maintenance Center (OMC)/ Network
Management System (NMS)...................................................... 33
3 Power Budget........................................................................... 343.1 Link Budget Basics .................................................................... 343.2 Power Budget Factors ............................................................... 353.2.1 Power Budget Powers ............................................................... 363.2.2 Power Budget Receiver Sensitivities ......................................... 363.2.3 Power Budget Loss Factors....................................................... 36
3.2.4 Power Budget Gain Factors....................................................... 383.2.5 Power Budget Calculation.......................................................... 38
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1 Objectives
At the end of this module, the participant will be able to:
List the different elements used in the GSM network.
Calculate the power budget.
Describe how to balance uplink and downlink directions in the power
budget.
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2 Network elements
2.1 GSM Elements
Terminals are mostly hand-held, lightweight offering voice & data services.
Today (1999) the majority of users utilizes only voice services.
The SIM card holds all subscriber relevant information: identities, codes,
algorithms needed to identify the subscriber towards the network. The SIM
card is issued by the operator and may be transferred between mobiles, which
in turn then take the properties and access rights as defined on the SIM card.
Antennas are the most visible element of the infrastructure chain. Dependingon site configuration, 1..6 antennas are needed per site. Antennas increasingly
cause discussions about possible health hazards of mobile phones. To avoid
unnecessary spreading of this kind of "electrophobia", antennas should be
placed inconspicuously, hidden as much as possible from public view.
Antennas can be e.g. integrated into house facades or as a minimum the
antenna case can be painted in the same colour as the background.
Base Stations are the actual counterpart to the users mobile in terms of radio
transmission and reception. Base Stations are becoming increasingly more
compact in size. Presently BS are approx. the size of a TV-set. BS come as
outdoor or indoor versions in ranges from typically 2..12 TRX.
The Base Station Controller (BSC) controls radio resources and handoverfunctions of its associated base stations. Typically some 50 ...100 BS are
connected to a BSC, depending on network topology and the operators
design philosophy.
The Mobile Switching Center (MSC) is the termination point for all protocols
between mobile station and the network. The MSC performs all routing, call
control functions, Supplementary Services and provides connection to
external networks (Gateway-MSC)
The Base Station Subsystem (BSS) as defined in GSM, consists of the Base
Transceiver Stations (BTS's), the Base Station Controller (BSC) and the
Transcoder (TC) unit. The transcoder is usually physically located at the MSC
site, logically it belongs to the BSS. This physical separation has the
advantages that the transmission lines (typically many 10 km) between BSC
and Transcoder can be used much more efficiently (by factor 3..4) when voice
signals are transported in the compact GSM format, before being expanded
into the normal ISDN-type format in the transcoder. This brings great savings
in transmission resources.
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2.1.1 Base Transceiver Station (BTS)
The main tasks of a BTS are presented in Figure 1.
Base station transceiver maintain synchronisation to MS
GMSK modulation
RF signal processing (combining,filtering, coupling...)
diversity reception
radio interface timing detect access attempts of
mobiles
de-/ encryption on radio path
channel de-/ coding & interleaving on radio path
perform frequency hopping
forward measurement data to BSC
typ. 1..4 TRX1..3 sectorsavg. 7,5 traffic channels per TRXsupports typ. 300 users
typ. 1..4 TRX1..3 sectorsavg. 7,5 traffic channels per TRXsupports typ. 300 users
Figure 1. Tasks of BTS
Main entities of a BTS are
Transmitter and receiver unit
Frequency Hopping unit
RF combiners and filters
Signal processing units, channel coding, demodulation...
Alarm collecting units, clocks and timing
OMU: remote operation and maintenance transmission interfaces towards Abis interface
Power supply, heat exchangers....
See BTS product documentation for more details.
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2.1.2 Nokia BTS
Nokia base stations have different generations: Talk-family base stations (see
Figure 2)are the 3rd
generation base stations. PrimeSite and MetroSite are 4th
generation base stations.
Citytalk6 TRX
Extratalk, SiteSupport System
Flexitalk2 TRX
Flexitalk+2 TRX
Intratalk6 TRX
Figure 2. Talk-family base stations
FlexiTalk
Nokia FlexiTalk (MiniSite) is a 3rd
generation base station with 1-2 TRX in
one cell. It can be mounted on a wall, on a free-standing plinth indoors, or at
street level. The physical size of the base station is about equal to a television
set: 0,51m x 0,59m x 0,50m (hx wx d), weight 40 kg. The max TX output
power is 20 W.
FlexiTalk can be used in microcells, especially when indoor penetration and
coverage is needed. There is an option for fixed line transmission but no
possibilities for microwave radios without a cabin.
1-2 TRX omni
AC or DC power supply
Up to 3 coaxial or twisted pair 2M links
Support for Nokia microwave radio
Portable Site Test Monitor
Temperature range -5C to +45C
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FlexiTalk +
1-2 TRX omni
AC or DC power supply
Up to 3 coaxial or twisted pair 2M links
Support for Nokia microwave radio
Portable Site Test Monitor
Temperature range -33C to +40C plus solar load
20C to +40C (DC powered) plus solar load
IntraTalk
IntraTalkis the indoor version of the Talk-family BTS. It offers from 1-6
TRX omni or up to 6+6 or 4+4+4 in a sectored configuration. The base station
size is 1,60m high, 0,6m wide and 0,48m deep. Empty weight is 132 kg.
Omni directional 6 TRX and sectored up to 4+4+4 TRX
Integrated radio links
Up to 4 coaxial or twisted pair 2M links
HDSL, ISDN
AC or DC power supply
Redundant common unit power supply
Site Test Monitor
Temperature range -5C to +45C
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CityTalk
CityTalkhas been designed primarily for outdoor environments and rooftop
installations. The cabinet is small enough to be transported within buildings,
through standard size doors and in elevators (height: 1,36m, width: 0,77m,
depth: 0,88m, weight: 102kg). Two versions are available; the standard
cabinet with heat exchanger and the all climate cabinet with air conditioner.
Like the Nokia Intratalk, the first cabinet has a capacity up to 6 TRX with the
extension cabinet taking the BTS up to its maximum of 12 TRX.
Omni directional 6 TRX and sectored up to 4+4+4 TRX
Close-circuit internal airflow
Integrated radio links
Up to 4 coaxial or twisted pair 2M links
HDSL, ISDN
AC or DC power supply
Redundant common unit power supply
Site Test Monitor
Temperature range -33C to +40C plus solar load
ExtraTalk, Site Support System, support extension
Space for Line Terminal Equipment
19, 20U height sub-rack
Applications
IntraTalk, CityTalk and FlexiTalk
Alone or co-located with AC/DC or AC/AC cabinet
Temperature range -33C to +40C plus solar load
ExtraTalk; Site Support System AC/DC
Battery back-up
AC input, DC output
Typical back-up time 1 hour (tri-sector 1+1+1 TRX)
Redundant rectifier
Space for Line Terminal Equipment
19, 6U height sub-rack
Applications
IntraTalk, CityTalk and FlexiTalk
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Temperature range -33C to +40C plus solar load
ExtraTalk, Site Support System AC/AC
Battery back-up
AC input, AC output
DC feed for Line Terminal Equipment
Typical back-up time 1 hour (tri-sector 1+1+1 TRX)
Space for Line Terminal Equipment
19, 6U height sub-rack
Applications
IntraTalk, CityTalk, FlexiTalk and PrimeSite
Temperature range -33C to +40C plus solar load
PrimeSite
Figure 3. PrimeSite
PrimeSiteis a compact base station with 1 TRX. It includes an integratedcircularly polarised antenna, but there is a possibility for an external antenna.
The physical size of the base station is 0,65m x 0,38m x 0,14m (hx wx d),
weight 23 kg. The base station can be installed on a wall or pole. The
maximum transmitting output power is 8 W; therefore PrimeSite is useful in
microcells with high transmitting powers and relatively low capacity. It can be
used to fill coverage gaps or to provide indoor coverage and capacity.
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MetroSite Concept
MetroSiteis a new concept for microcells, including all equipment needed for
a microcell site: base station, (microwave) radio transmission equipment,
transmission node and a battery backup, see Figure 4.MetroSite suits
networks, where microcells with low transmission powers and very high
capacity are required.
MetroSite Base Station, MetroHub transmission node and MetroSite battery
backup have in addition to the same physical appearance also the same
mounting options and kits for vertical and horizontal wall mounting and pole
mounting.
Nokia MetroSite
Base Station
Connected to FXC RRI or
FC RRI indoor unit.
Connected to FXC RRI or
FC RRI indoor unit.
Nokia
MetroHopper Radio
Nokia MetroHub
Transmission Node
Nokia FlexiHopper
Microwave Radio
Nokia MetroSite
Battery Backup
Nokia MetroSite
Antennas
Figure 4. MetroSite concept
MetroSite Base Station is the core element of the MetroSite solution. It has 1-4 TRX, which can be freely divided to any combinations of omni or sectored
cells. It can be used in GSM 900, GSM 1800, GSM 1900 systems or as a
GSM 900 / GSM 1800 Dual Band base station. The base station is small:
0,84m x 0,31m x 0,22m (hx w x d) and relatively lightweight: 40 kg.
Therefore it is likely to make site acquisition and implementation easier.
Maximum transmitting power is 1 W. There are no internal combiners in the
base station. Base station supports RF hopping and later on also baseband
hopping. MetroSite BTS is easy to set up with the new autoconfiguration
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feature and the commissioning wizard of the MetroSite Manager local
management tool.
As the transmission media, microwave radio, fixed lines or 58 GHz radio can
be used with Nokia MetroSite BTS. The transmission units for wire linetransmission are FC E1/T1 and FXC E1/T1, whereas FC RRI and FXC RRI
are the microwave transmission units. The latter two are compatible with
Nokia MetroHopper and Nokia FlexiHopper microwave radios.
UltraSite
Nokia UltraSite EDGE BTS has many features and benefits, such as:
Nokia UltraSite EDGE BTS is light weight and compact and, with its
fullfrontal accessibility, can be installed just about anywhere.
The modular design of Nokia UltraSite EDGE BTS guarantees smooth
expansion and upgrades of base station equipment with minimal disturbanceto network operation. In addition, the BTS supports hot insertion of plug-in
units, which means that most units can be replaced during operation without
disrupting the BTS functions.
Nokia UltraSite EDGE BTS cabinets can be installed side by side and in
corners, which means less space is required.
Nokia UltraSite EDGE BTS fits into the corresponding Nokia Talk-family
BTS footprints. The operator does not need to alter any previous plans for
expansion. In addition, the BTS can be co-sited with Nokia Talk-family as an
upgrade cabinet.
Figure 5. UltraSite
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Table 1. Nokia base station features, summary
RF Characteristics Metrosite PrimeSite InSite Flexitalk Intratalk Citytalk UltE
Max. TRXs 4 1 1 2 6 6
Max. TRXs Special
Cabinet
12 12 1
Max. Sectors 4 1 1 1 4+4+4 4+4+4 36+
Max TX Power
(dBm)
30 38 22 42 42 42
Dynamic sensitivity
(dBm) single branch,
RBER2
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rD
R =2 2
E- field
H- field
Figure 6. Electrical and magnetic field vectors
At distances less than the far field distance (antenna near field), no reliable
signal measurements can be performed, since the electromagnetic field hasnot yet settled to its final and stable state. Signal strength measurements
therefore always are relative to an arbitrary reference point (e.g. 10m, 100m, 1
km...) from the antenna. The difference between signal power measured at the
reference point and the signal power input to the antenna is called the
minimum coupling loss. Typical values for coupling loss are in the order of 50
dB at 5..10m distance from the antenna.
Energy in an antenna only partly converts to electromagnetic waves.
Therefore the received energy is only a fraction of the radiated energy. The
received energy can only be measured at a reference distance from the
antenna. This distance is agreed to be the far field distance. The coupling
losses are approximately 50-60 dB for the first few meters. After that freespace propagation can be used.
2.2.2 Antenna Types
Many different types and mechanical forms of antennas exist. Each is
specifically designed for special needs.
In mobile communications the two main categories to consider are:
omnidirectional antennas:radiate with same intensity to all directions
(in azimuth) directional antennas:main radiation energy is concentrated to certain
directions
Omnidirectional antennas are useful in rural areas, while directional beam
antennas are preferable in urban areas. They provide a more controllable
signal distribution and energy concentration.
The most common antenna types are:
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Dipoles:the basic antenna type. Simple design, low gain,
omnidirectional radiation pattern.
Arrays:combination of many elementary arrays. High achievable
gains, special radiation pattern can be engineered. Active arrays usemany actively fed dipole elements. Passive arrays merely use the
reflecting properties of array elements.
Yagi antenna:Very popular passive array antenna. Widespread use as
TV-reception antenna. Very high gain and good directional effects.
Parabolic antenna:Used for microwave links, optical antennas and
satellite links. Very high gains and extremely narrow beamwidth. Most
commonly used for line-of-sight propagation paths. (satellites,
microwave links)
2.2.3 Antenna Characteris tics
Antennas can be characterised with a number of attributes:
Radiation pattern:the main characteristic of antennas is the radiation
pattern. The horizontal pattern (H-plane) describes azimuth
distribution of radiated energy. The vertical pattern (E-plane)
describes the energy distribution in elevation angle.
Figure 7. Horizontal and vertical antenna radiation patterns
Antenna gainis a measure for the antennas efficiency. Reference
antenna configuration to compare with is by convention the isotropic
antenna. Gain is measured usually in decibel above isotropic (dBi) or
in decibel above Hertz dipole (dBd). Hertz dipole has a gain of 2.2
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dB compared to the isotropic antenna, therefore dBd + 2.2 = dBi.
Antenna gain depends on the mechanical size of the antenna, the
effective aperture area, the frequency band and the antenna
configuration. Antennas for GSM1800 can achieve some 5...6 dB more
antenna gain than antennas for GSM900 while maintaining the samemechanical size. Antenna gain can be estimated by the formula:
G A w=4
2
where A is the mechanical size and w the effective antenna aperture
area.
NoteCatalogues usually show dBi values, since they are higher numerical values and
therefore look more impressive...
Antenna lobes:main lobe, side-lobes; ratio of main lobe to max. side
lobe is a measure for quality of radiation pattern
Half-power beamwidth:3-dB beamwidth; the angle (in both azimuth
and elevation plane), at which the radiated power has decreased by 3
dB with respect to the main lobe. Narrow angles mean good focusing of
radiated power (= larger communication distances possible)
Antenna downtilt(mechanical or electrical): directional antennas maybe tilted either mechanically or electrically in order to lower the main
radiation lobe.
By downtilting the antenna radiation pattern, field strength levels from
this antenna at larger distances can be reduced substantially. Therefore
antenna downtilting reduces interference to neighbouring cells while
improving spot coverage also. Two types of downtilting exist:
Mechanical downtiltingmeans that the antenna is pointed towards the
ground in the main beam direction. At the same time the back lobe is
uptilted.
Electrical downtiltinghas the advantage that the antenna pattern isshaped so that the main beam and the back lobe are downtilted. In order
to be able to control the interference situation it is better to use
electrical down tilting.
With omnidirectional antennas, mechanical downtilting is not
applicable, but only electrical. Electrical downtilting is performed by
internal slight phase shifts in the feeder signals to the elementary
dipoles of the antenna system.
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Figure 8. Radiation pattern of an antenna with electrical downtilt
5..8 deg
Figure 9. Mechanical downtilting
Polarisation:polarisation plane is the propagation plane of the
electrical field vector (by definition). Antennas are usually vertically
polarised. Cross-polarised antennas achieve some dB gain in signal
quality in environments where the radio wave is subjected to
polarisation shifts, e.g. by multipath propagation and reflection on
dielectric materials.
Antenna bandwidth:defined as the bandwidth, within which the VSWR
(Voltage Standing Wave ratio) is less than 1:2. Typical values for
antenna bandwidths are approx. 10% of the operating frequency.
Antenna impedance:maximum power coupling into antennas can be
achieved when the antenna impedance matches the cables impedance.
Antenna impedance depends on the design used. Impedance can be
trimmed to practically any value by micro strip stubs, coils and
capacitors. This is done by the antenna supplier and not relevant to the
network planner. Typical value is 50 Ohm.
Mechanical size:mechanical size is related to achievable antenna gain.
Large antennas provide higher gains, but also need more care in
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deployment (optical impact!) and apply higher torque to the antenna
mast (static). Wind load and icing of antennas in winter may cause
static problems to the mast. Usual values for wind velocities are
assumed at 150 km/h or 200 km/h.
2.2.4 Coupling Between Antennas
Antenna radiation pattern will become superimposed when distance between
antennas becomes too small. This means the other antenna will mutually
influence the individual antenna patterns.
As a rule of thumb, 5 ..10 horizontal separation provides sufficient
decoupling of antenna patterns. The exact distance needed depends on the
individual radiation patterns.
As vertical radiation patterns often have very much narrower half-powerbeamwidth, the vertical distance needed for decoupling is also much smaller.
As the rule of thumb, 1vertical separation is sufficient in very most cases.
main lobe
5 .. 10
1
Figure 10. Horizontal and vertical separation
2.2.5 Installation Examples
Antenna installation configurations depend on the operators preferences, if
any. It is important to keep sufficient decoupling distances between antennas.
If TX and RX direction use separated antennas, it is advisable to keep a
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horizontal separation between the antennas in order to reduce the TX signal
power at the RX input stages.
Recommended decoupling
TX - TX: ~20dB
TX - RX: ~40dB
Horizontal decoupling distance depends on
antenna gain
horizontal rad. pattern
Omnidirectional antennas
RX + TX with vertical separation (Bajonett)
RX, RX div. , TX with vertical separation (fork)
Vertical decoupling is much more effective
0,2m
omnidirectional.: 5 .. 20mdirectional : 1 ... 3m
Figure 11. Antenna coupling
Figure 12. Antenna installation examples
2.2.6 Nearby Obstacles Requirement
Nearby obstacles are those reflecting or shadowing materials that can obstruct
the radio beam both in horizontal and vertical planes. When mounting the
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antenna system on a roof top, the dominating obstacle in the vertical plane is
the roof edge itself and in the horizontal plane, obstacles further away, e.g.
surrounding buildings, can act as reflecting or shadowing material.
It is possible that the antenna beam will be distorted if the antenna is too closeto the roof. In other words, the antenna must be mounted at a minimum height
above the rooftop or other obstacles. As a practical planning / installation rule,
the first Fresnel zone (vertical plane) must be kept clear. The clearance is
between the bottom of the antenna and the most dominant obstacles. As a rule
of thumb, in the horizontal plane the 3dB beamwidth must be clear within
150m.
Figure 13. Required height clearance from the antenna to the edge ofthe rooftop
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h h
Figure 14. Antenna tilting near an edge of the rooftop
Antenna downtilt affects previous results. The following graph shows how the
clearance requirement changes when antenna downtilt varies from 0 to 6
degree.
Height Clearance vs Antenna Tilt
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
5 10 15 20 25 30 35 40 45 50
Distance to the roof edge d (m)
h (m)
From 0up to 6
down tilt
Figure 15. Height clearance versus antenna tilt
If antennas are wall mounted, a safety margin of 15between the reflecting
surface and the 3-dB lobe should be guaranteed, see Figure 16.
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Figure 16. Horizontal clearance
2.3 Diversity Techniques
Diversity techniques are based on the fact that receiving multiple uncorrelated
copies of the same signal, at the same or delayed time, can reduce fast fading
dips. When two received signals are combined, the achieved signal quality is
better than either of the partial signals separately.There are different diversity reception schemes (see Figure 17): both the base
station and the mobile station implement time diversity already by
interleaving. Frequency diversity can be achieved with frequency hopping:
since fast fading is frequency dependent, many frequencies are quickly and
cyclically hopped so that if one frequency is in a fading dip, it is just for a
very brief time. Traditionally two base station receiver antennas have been
separated horizontally (usually) or vertically (seldom) to create space
diversity. In urban environment, the same diversity gain can be achieved by
using polarisation diversity: signals are received using two orthogonal
polarisations at the reception end.
In the mobile radio channel multipathpropagationis present. The delayedand attenuated signal copies can be combined in a proper way to increase the
level of the received signal (multipath diversity). In GSM it is performed by
an equaliser, while in W-CDMA (Wideband-CDMA) a so called "rake
receiver" is utilized.
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Time diversity
Frequency diversity
Space diversity
Polarisation diversity
Multipath diversity
Transmit the same signal at leastwice (with time delay t)
Transmit the same signal on at ltwo different frequency bands
multiple antennas
crosspolar antennas
equaliser,rake receiver
t
f
Figure 17. Diversity techniques
The most used methods in cellular network planning are space and
polarisation diversity, as far as base station antennas are concerned.
2.3.1 Space Diversity
Space diversity is a traditional diversity method, especially used in
macrocells. Spatial antenna array separation causes different multipath lengths
between a mobile station and a base station. Partial signals arrive at the
receiving end in different phases. The two antenna arrays must be separated
horizontally in order to achieve uncorrelated signals. Space diversity performs
very well with macrocells in all environments, giving diversity gain of about
4-5 dB.In microcells, the large antenna configurations are not often possible due to
site acquisition and environmental reasons. An