Configuration 2G Planning NOKIA

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Configuration Planning

Training Document

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© Nokia Oyj 1 (39)




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

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Copyright © Nokia Oyj 2003. All rights reserved.

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Table of Contents

Table of Contents

1 Objectives ................................................................................... 4

2 Network elements ...................................................................... 5 2.1 GSM Elements............................................................................. 5 2.1.1 Base Transceiver Station (BTS) .................................................. 6 2.1.2 Nokia BTS.................................................................................... 7 2.2 Antenna Systems....................................................................... 13 2.2.1 Far Field Distance...................................................................... 13 2.2.2 Antenna Types........................................................................... 14 2.2.3 Antenna Characteristics............................................................. 15 2.2.4 Coupling Between Antennas...................................................... 18 2.2.5 Installation Examples................................................................. 18 2.2.6 Nearby Obstacles Requirement................................................. 19 2.3 Diversity Techniques.................................................................. 22 2.3.1 Space Diversity.......................................................................... 23 2.3.2 Polarisation Diversity ................................................................. 24 2.3.3 Combining.................................................................................. 24 2.3.4 Coverage Improvement by Diversity?........................................ 25 2.4 Antenna Cables ......................................................................... 25 2.5 Filters and Combiners................................................................ 26 2.6 MHA and Booster....................................................................... 29 2.6.1 Masthead Preamplifier (MHA).................................................... 29 2.6.2 Downlink Booster (TBU) ............................................................ 30 2.7 Base Station Controller (BSC) ................................................... 30

2.7.1 Nokia BSC ................................................................................. 32 2.8 Transcoder Submultiplexer (TCSM2E)...................................... 32 2.9 Mobile Switching Center (MSC)................................................. 33 2.10 Operation and Maintenance Center (OMC)/ Network

Management System (NMS)...................................................... 33

3 Power Budget........................................................................... 34 3.1 Link Budget Basics .................................................................... 34 3.2 Power Budget Factors ............................................................... 35 3.2.1 Power Budget Powers ............................................................... 36 3.2.2 Power Budget Receiver Sensitivities ......................................... 36 3.2.3 Power Budget Loss Factors....................................................... 36

3.2.4 Power Budget Gain Factors....................................................... 38 3.2.5 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.

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• Describe how to balance uplink and downlink directions in the power

budget.



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 operator’s

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 theadvantages 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 (seeFigure 2) are the 3

rd generation base stations. PrimeSite and MetroSite are 4

th

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 (h x w x 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 -5°C to +45°C

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FlexiTalk +

• 1-2 TRX omni



• Support for Nokia microwave radio

• Portable Site Test Monitor

• Temperature range -33°C to +40°C plus solar load

20°C to +40°C (DC powered) plus solar load

IntraTalk

IntraTalk is 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


• HDSL, ISDN


• Redundant common unit power supply

• Site Test Monitor

• Temperature range -5°C to +45°C

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CityTalk

CityTalk has 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


• HDSL, ISDN


• Redundant common unit power supply

• Site Test Monitor


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


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



• Applications

− IntraTalk, CityTalk and FlexiTalk

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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)



• Applications

− IntraTalk, CityTalk, FlexiTalk and PrimeSite


PrimeSite

Figure 3. PrimeSite

PrimeSite is 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 (h x w x 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

MetroSite is 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 (h x 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 UltrasiteEDGE

Max. TRXs 4 1 1 2 6 6 6

Max. TRXs Special

Cabinet

12 12 108

Max. Sectors 4 1 1 1 4+4+4 4+4+4 36+36+36

Max TX Power

(dBm)

30 38 22 42 42 42 42

Dynamic sensitivity

(dBm) single branch,

RBER2<2%

-106.0 -106.0 -100 -102/-108 -102/-

108

-102/ -

108

-108.5/ -

109

2.2 Antenna Systems

Antennas are the transition points in the communication chain, where the

signal changes from a “wireline” signal to a radio wave propagating signal

and vice-versa.

The signal received at the antenna is the best available signal in terms of

signal-to-noise ratio. Further down the processing chain the signal can only

become more and more corrupted by distortion, noise additions etc. Therefore

every effort shall be taken to make optimum use of the available signal at the

antenna.

2.2.1 Far Field Distance

Electromagnetic energy is transported by constant exchange of energy

between the antenna’s electrical and magnetic field.

The energy density vector (“Poynting-vector”) is calculated by E x H (vector

product). At large distances from the antenna the electrical and magnetic fieldvectors are perpendicular and the energy density vector is a real (as opposed

to complex) vector. The minimum distance in which this can be assumed is

the “far field-distance” which is calculated by (D is largest antenna

dimension)

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r D

R =2 2

λ

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 gain is a measure for the antenna’s 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

π

λ

where A is the mechanical size and w the effective antenna aperture

area.

Note

Catalogues 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 may be 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 downtilting means that the antenna is pointed towards the

ground in the main beam direction. At the same time the back lobe is

uptilted.

Electrical downtilting has 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 cable’s 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 ..10λ 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-power beamwidth, the vertical distance needed for decoupling is also much smaller.

As the rule of thumb, 1λ vertical separation is sufficient in very most cases.

main lobe

5 .. 10 λ

1λ

Figure 10. Horizontal and vertical separation

2.2.5 Installation Examples

Antenna installation configurations depend on the operator’s 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 0 ° up to 6° down tilt

Figure 15. Height clearance versus antenna tilt

If antennas are wall mounted, a safety margin of 15° between 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 multipath propagation is 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 leasttwice (with time delay t)

Transmit the same signal on at leasttwo 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. Antennas must be small and easily

hidden. The amount of physical antenna equipment must be minimised.

Antennas are often placed on lampposts or other existing structures, in which

spatial separation is not possible. On the other hand, arranging the antenna

arrays within one physical antenna doesn’t provide big enough separation

between the arrays. Therefore other means of providing diversity is required

in urban microcellular environment.

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2.3.2 Polarisation Diversity

Uncorrelated signals can be provided without physical separation by applying

different orthogonal linear polarisation at the receiving end. Signals can be

received using for example horizontal and vertical or ±45° slanted polarisationin cross-polarised antennas. The performance of polarisation diversity

technique depends on the environment and the reflections between mobile

station and base station. The more the partial signals reflect and diffract along

the route, the more uncorrelated the signals are at the receiver, and the more

gain can be achieved.

The polarisation diversity gain can be measured as improved bit error rate

(BER) or frame erasure rate (FER) at the receiver. In very dense urban areas,

where narrow streets and high buildings surround the site, more than 5 dB

diversity gain – equal to that of space diversity – has been measured. On the

other hand, in the open areas and LOS situations, signal does not reflect

enough on the way and cross-polarisation would not give any additional gain.This must be taken into account as slightly decreased signal quality with low

field strength levels. Since cross-polarised antennas are small and suitable for

urban areas, cross-polarisation diversity is the preferred diversity method for

microcells.

2.3.3 Combining

Two main combining methods are used to take advantage of the signals in

space or polarisation diversity:

• Selection combining: every antenna signal branch is demodulated, C/Iand bit error rates (BER) are calculated and then all signal branches are

sampled at regular time intervals, always the best signal branch is

selected for further processing. This method passes only a single branch

and rejects all other signals.

• Maximal ratio combining: antenna signals are individually amplified at

the same amplitudes, the signal phasing is assessed. Signal samples are

added (vector addition) with correct phase adjustments. Then the

combined signal is demodulated and further processed. This diversity

method achieves a C/I improvement due to the fact that the wanted

information (carrier signal) from different antenna branches are

strongly correlated, while the additive noise components areuncorrelated (assuming white Gaussian noise process). In the

superposition of both signals the wanted components will

constructively add, while the noise components eliminate each other.

(Note: If antennas are not sufficiently separated from each other, also

the noise processes of both antennas will be correlated and the C/I

improvement therefore decreases to zero.)

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2.3.4 Coverage Improvement by Diversity?

In link budget calculations, antenna diversity brings a signal improvement of

~ 5 dB. Note that this is not a physical improvement, i.e. a signal that is

stronger by 5 dB (physically impossible), but rather an equivalent gain. Theimprovement in signal quality, i.e. in bit error rate, is the same as could be

expected by a signal stronger by 5 dB. It is an “indirect gain”. This higher

equivalent gain allows for a higher tolerable path loss, i.e. a larger

communication range.

One supplier company claims that by 3 dB more allowable path loss they

could provide 20% more coverage range, i.e. 40% more coverage area per

cell. Conclusion was, that therefore they need 40% less base stations to cover

the same area size. This cunningly simple calculation is also stunningly

wrong. It would be in theory true if the environment were infinitely large and

flat, if there were exactly zero overlap between cells and the cells were placed

exactly regularly and there were absolutely no obstacles within the entire area.This obviously is not the case in real life.

• D iversity gain depends on environment

• Is there coverage improvement by diversity ?antenna diversity

equivalent to 5dB more signal strength

more path loss acceptable in link budget

higher coverage range

R

R(div) ~ 1,3 RA 1,7 A ??70% more coverage per cell ??needs less cells in total ??

T rue only (in theory)if envi ronment is infinitely large and flat

Figure 18. Diversity gain is equivalent gain

2.4 Antenna Cables

Coaxial cables of different diameters are usually used to transport the RF

signal from the RX/TX units of the BTS to the antenna itself. Distances are

typically in the range 10..50 m. Thin coax feeder cables are easier to install

(bending radii!), but also cause higher losses per distance unit. Connectors,

6-90199v 1.0





material ageing, jumper cables etc. cause additional losses to the most

valuable RF signal. Typical values are 10 dB/100m for thin cables and 4

dB/100m for thick coax cables.

Typical values for cable losses between BTS and antenna are 3..5 dB. Thismeans that some 50...70% of total signal energy is lost even before it arrives

at the transmitting antenna or the receiver unit! Antenna cables shall therefore

be kept as short as possible.

• Cable types

coaxial cables : 1/2”, 7/8”, 1 5/8”

losses approx. 10 .. 4 dB/ 100m==> power dissipation is exponential withcable length ! !

• Connector losses approx. 1 dB per connection(jumper cables etc..)

• Thick antenna cables lower losses per length

large bending radiimuch more expensive

jumper

(2 m)

4 0 . .

7 0 m

jumper

(2 m)

Keep antenna cables short

Figure 19. Antenna cables

2.5 Filters and Combiners

Antenna Filter Extension (AFE)

AFE is a wideband combiner or receiver multi coupler unit. For the

transmitter combining it has a 3-dB hybrid combiner. One AFE supports 1

TRX (combiner bypassed) or 2 TRXs per sector and has 4 outputs for themain branch (dual duplex use).

Dual Duplexed AFEs (different TRXs are connected to two 2 antennas via

two duplexer filters) support 2 TRXs bypassing the hybrid coupler or 3 or 4

TRXs with 3 dB losses. The Dual Duplex can be used with Intratalk and

Citytalk BTSs.

Standard AFEB configuration:

• AFEB loss 5,2 dB max. (combined)

26 (39) © Nokia Oyj 6-90199v 1.0



• BTS output power +38 dBm guaranteed minimum

• AFEB loss 2,2 dB max. ( no combiner) BTS output power +41 dBm

guaranteed minimum

TX1,TX2

RXdiv1,RXdiv2

RX1,RX2

AF

E

TX1

TX2

RXdiv1

RXdiv2

RX1

RX2

TRX1TX1

RX1RXdiv1

TRX2TX2

RX2RXdiv2

CABINET 1

Figure 20. AFE with X-pol div 2+2+2

CABINET 1

CABINET 2

TX1,TX2,RX1,RX2,RX3,RX4

TX3,TX4,RXdiv1,RXdiv2,RXdiv3,RXdiv4

TRX1TX1

RX1RXdiv1

TRX2TX2

RX2RXdiv2

TRX3TX3

RX3

RXdiv3

TRX4TX4

RX4RXdiv4

AFE

TX1

TX2

RX3

RX4

RX1

RX2

AFE

TX3

TX4

RXdiv3

RXdiv4

RXdiv1

RXdiv2

Figure 21. AFE with X-pol div 4+4+4

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Antenna Filter Twin (AFT)

AFT is a single unit, which supports dual duplexing. It does not have the 3-dB

hybrid coupler. It should be used with masthead LNAs. With an AFT it is

possible to build a 2+2+2 configuration with low transmit path losses.

Upgraded AFTB configuration

• AFTB loss 1,9 dB max.

• BTS output power +41 dBm guaranteed minimum

CABINET 1

TX1,RX1,RX2

TX2, RXdiv1, RXdiv2

2,5 m

AFT

TX1

TX2

RXdiv1

RXdiv2

RX1

RX2

TRX1TX1

RX1RXdiv1

TRX2TX2

RX2RXdiv2

Figure 22. AFT with X-pol div 2+2+2

CABINET 1

TX3

TX4,Rxdiv1,Rxdiv2,RXdiv3,RXdiv4

TX1,RX1,RX2,RX3,RX4

TX2

0.4 m

TRX1TX1

RX1RXdiv1

TRX2TX2

RX2RXdiv2

TRX3TX3RX3RXdiv3

TRX4TX4

RX4RXdiv4

AFT

TX1

TX2

RX3

RX4

RX1

RX2

AFT

TX3TX4

RXdiv3

RXdiv4

RXdiv1

RXdiv2

CABINET 2

Figure 23. AFT with X-pol div 4+4+4

28 (39) © Nokia Oyj 6-90199v 1.0



Remote Tuned Combiner (RTC)

RTC is a narrow-band Remote Tuned Combiner. A separate Receiver

Multicoupler Unit (RMU) is always needed when RTC is used. The

RTC/RMU combination supports up to 6 TRXs per sector. The combining

loss with RTC is lower than with AFE. Synthesised frequency hopping is not

supported with RTC.

CABINET 1

TX1,TX2,TX3,TX4,TX5,TX6

RX1,RX2,RX3,RX4,RX5,RX6

RXdiv1,RXdiv2,RXdiv3,RXdiv4,RXdiv5,RXdiv6

RM

U

RX1RX2RX3RX4RX5RX6RXdiv1RXdiv2RXdiv3RXdiv4RXdiv5RXdiv6

TRX1TX1

RX1RXdiv1

TRX2TX2

RX2RXdiv2

TRX3TX3

RX3RXdiv3

TRX4TX4

RX4RXdiv4

TRX6TX6

RX6RXdiv6

TRX5TX5

RX5RXdiv5

TX2

TX5

TX6

TX3

TX4

RTC

TX1

Figure 24. RTC with X-pol div 6+6+6

2.6 MHA and Booster

2.6.1 Masthead Preampli fier (MHA)

A masthead preamplifier allows for larger pathloss on the uplink. The

masthead preamplifier eliminates the antenna cable loss by amplifying the

received RX-signal near the antenna, in the top of the mast. This increases the

receiver sensitivity at the base station and the cell size increases especially for

hand-held portables, which have a low TX power.

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Figure 25. MastHead Preamplifier (MHA)

2.6.2 Downlink Booster (TBU)

The booster is a power amplifier unit mounted in a TRX slot inside the BTS.

The booster configuration consists of:

• The Booster (PA) Unit (TBU)

• The Booster Filtering Unit (AFH)

• Masthead Preamplifier equipment (MHA)

The output power at the antenna connector can be up to 46,5 dBm (49 dBm

before combining) with roughly 2,5 dB losses (isolator + combiner + filter

(AFH)).

Booster BTS is suitable for all the environments where enhanced coverage or

high output power is needed. Theoretically, cell radius is enhanced up to 60%and the coverage area is roughly tripled.

Figure 26. TRX, downlink booster (TBU) and AFH

2.7 Base Station Controller (BSC)

The Base Station Controller, BSC, is a part of the Base Station sub-system,

BSS. It is responsible for the management of the radio network in the BSS.

30 (39) © Nokia Oyj 6-90199v 1.0



BSC is located between the MSC (TCSM2E, Transcoder Submultiplexer) and

the Base Stations.

BSC Functions:

1. Configuration and Management of the Radio Resources

− BCF, BTS and TRX management

− channel allocation

− channel release

− radio link supervision (measurement handling)

− power control (BTS and MS)

− BCCH (Broadcast Control CHannel)/ CCCH (Common Control

Channel) management− TCH (Traffic CHannel)/SDCCH (Slowly Dedicated Control

CHannel) management

2. Handover management

Handovers in GSM are based for example on the following parameters:

− Signal quality (bad signal quality, up / down link)

− Signal level (weak signal level, up / down link)

− Interference (TS disturbance, up / down link)

− Power budget (max. TX power in BTS and MS)

− Distance (distance > 35 km)

BTSs and MSs measure these values and the measurement data is

stored in the BSC. The BSC is responsible for making the handover

decisions.

3. Frequency hopping management

Frequency hopping improves BTS-MS link quality. There are three

different possibilities for frequency hopping: No frequency hopping,

baseband hopping and synthesised hopping.

4. Measurement and Observation

− traffic measurements

− signalling event observations

− observation of a specific mobile (tracing)

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2.7.1 Nokia BSC

Nokia BSC is based on the DX200 platform. The structure of the DX200

BSC is presented in Figure 27.

BT

GSW

CLS

MSC (TC)

ET ET

BCSU MCMU OMU I/O

MB

Figure 27. Block structure of DX200

2.8 Transcoder Submultiplexer (TCSM2E)

The Transcoder Submultiplexer, TCSM2E, is responsible for the speech

coding in the down link direction, which is then decoded in the Mobile

Station, MS, see Figure 28. The transcoded speech coming from the MS is de-

transcoded in the TCSM2E in the up link direction. Transcoder is always used

between the MSC and the BSC. One TCSM2E (functional unit) can make

transcoding for 90 full rate traffic channels. One time slot in the transcoder is

always through connected and it can be used for the CCS7 signalling between

the MSC and the BSC or digital X.25 between OMC (via MSC) and BSC.X.25 connection between the OMC and the BSC can also be allocated in

another timeslot. The submultiplexing function of the transcoder is used for

reducing the number of the 2 Mbit/s links between the MSC and the BSC.

Three full rate traffic channel 2 Mbit/s links can be submultiplexed into one 2

Mbit/s link.

32 (39) © Nokia Oyj 6-90199v 1.0



TCSM2E

TCSM2E

ET

ET

ET

ET

ET

ET

ET

ET

ET

ET

BSC

Air I/F Abis I/F Ater I/F A I/F

ET

ET

ET

ET

ET

ET

ET

ET

ET

ET

MSCBTS

BIE

MS

Figure 28. Transcoder, TCSM2E in GSM 1800 network

2.9 Mobile Switching Center (MSC)

One MSC (Mobile Switching Center) can typically for serve minimum

150,000 subs. At least one gateway MSC is needed in a network as an

interface to other networks. MSC performs all routing, call control functions,

etc.

2.10 Operation and Maintenance Center (OMC)/

Network Management System (NMS)The Operation and Maintenance Center (OMC) -- also called Network

Management System (NMS) -- performs all fault and alarm monitoring

functions and performance measurements in the network. The OMC has no

direct relevance for the subscriber. It is an observation and management tool

for the operator’s technical staff.

Generic OMC functions are described in the GSM specifications. The

implementation is left open for the manufacturers. The interfaces between

OMC and GSM network are not explicitly specified; therefore it is usually not

possible to supervise infrastructure elements from different suppliers from the

same OMC.In network optimisation tasks the OMC becomes the most important tool for

statistical performance evaluation.

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3 Power Budget

3.1 Link Budget Basics

Link budget calculations are essential in radio network planning. Link budget

calculations consist of two parts:

1. Power budget calculations

2. Cell size evaluations (chapter 6)

The purpose of power budget calculations is to find out what is the maximum

allowable path loss over the air interface between the antennas of BTS and

MS. Also, from these calculations the Tx power of the BTS can be determined

so that the radio link powers are in balance. The calculations may show that

the required BTS Tx power is larger than the maximum power of the BTS, in

this case the radio link is said to be downlink limited.

Power budget calculations have to be made separately for up- and down links.

The path loss over the air interface is reciprocal, i.e. the same in both

directions, but many other factors in these calculations are different for the

two links.

The factors that need to be taken into account in link budget calculations are:

• BTS & MS Tx-powers

• BTS & MS receiver sensitivities

• Loss factors

• Gain factors

• Margins (chapter 5)

The following chapters describe the backgrounds for these factors.

34 (39) © Nokia Oyj 6-90199v 1.0



3.2 Power Budget Factors

path loss = 154 dB

combiner loss = 5 dB

Feeder Loss = 4 dB

Rx Sensitivity

- 102 dBm

Tx power 45 dBm

Gain = 16 dBi

- 102 dBm

52 dBm

36 dBm

40 dBm

Figure 29. Power budget factors downlink

path loss = 154 dBFeeder

Loss = 4 dB

Tx Power

33 dBm

Gain = 16 dBi

Diversity

Gain = 4 dB

33 dBm

- 121 dBm

- 101 dBm

- 105 dBm

Rx sensitivity

-105 dBm

Figure 30. Power budget factors uplink

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3.2.1 Power Budget Powers

ETSI has defined different classes for MS. The Tx power of the MS depends

on the class. For GSM 900 and 1800, the only used classes in practice are

classes 4 & 1. These mean Tx powers of 2W and 1W respectively. These arethe powers on which the calculations have to be based on even though the

specifications allow tolerance of ±2 dB. When doing link budget calculations

for TETRA systems the MS class needs to be taken into account, because

different MS classes are being manufactured.

The Tx power of the BTS depends very much on the BTS type. Normally it is

much higher than of the MS, but lately new low-power BTSs have been

introduced.

3.2.2 Power Budget Receiver Sensit ivi ties

The sensitivities of the BTS and MS used in link budget calculations are

based on the ETSI specifications. The MS sensitivity is –102 dBm for

GSM900, -100 dBm for GSM1800 and –103 dBm for TETRA. In practice

the sensitivities are better than this, but these figures have to be used for link

budget calculations anyway.

For GSM 900 and 1800 BTSs the sensitivities are specified so that certain

performance requirements need to be fulfilled in the specified multipath

environments. These environments are called TU50, RA250 and HT100.

What actually this level is, is subject to change with the development of the

BTSs. Typical value used for this sensitivity is –106dBm.

For TETRA BTSs, the sensitivity level of the BTS is defined to be –106 dBm.

3.2.3 Power Budget Loss Factors

At the BTS end there is several RF equipment needed for combining and

separating two or more TRXs into one feeder. The elements relevant here are:

Isolator prevents the transmitted signal (from TX) being reflected back to the

TX and dispersing it.

Combiner combines the TX outputs after the isolator to one antenna feedercable. The combiner causes the largest individual amount of losses.

Duplex filter is used to combine the transmitted and received signals into a

common antenna feeder. With receive diversity in use, the duplex filter

reduces the number of needed antenna connections from 3 to 2. Duplex or

non-duplex operation is determined by the cable connections during the BTS

installation.

36 (39) © Nokia Oyj 6-90199v 1.0



Typically isolator, combiner and duplex filter are all included in a Coupling

Unit. In Figure 31 one example of combining 4 TRXs into two antennas is

presented.

Isolator

Coupler

D u p l e x f i l t e r

RX FilterLNA S p l i t t e r

Isolator

Coupler

D u p l e x f i l t e r

RX FilterLNA S p l i t t e r

TX

TX

TX

TX

RX main

RX div

RX main

RX div

RX main

RX div

RX main

RX div

MHA

MHA

Coupling Unit 1

Coupling Unit 2

T R X 1

T R X 2

T R X 3

T R X 4

Figure 31. Example of a combining solution.

There are several ways in combining two or more TRXs to one or more

antennas. When doing link budget calculations, one has to take into account

which kind of solution will be used for the case under study. As a typical

example it can be mentioned here that 4+4+4 configuration, 2 antennas per

sector and AFE (Antenna Filtering Equipment) unit for combining, the

expected combiner losses are 5,5 dB. In this case the output power of a

normal BTS can be expected to be around +40 dBm.

Antenna feeders in BTS end contribute some losses depending on the cable

length and thickness. Also cable connectors cause some losses, these are

usually included in feeder losses in link budget calculations.

In the MS end the combiner and cable losses are assumed to be 0dB. This is because there is only one TRX, and extremely short cabling. The effect of

duplex filtering is neglected due to the sake of simplicity and the fact that

there anyway are tolerances in Tx powers of the MS.

Body proximity loss. Based on the assumptions on which the link budget

calculations are to be made a loss factor of this name may be reasonable to be

taken into account. This is due to the fact that the user's body may cause

additional losses depending on the situation. Also the fact that MSs are

typically worn on belt may be reasonable to be taken into account in link

6-90199v 1.0





calculations. In many cases the body proximity loss for a MS on belt can be as

much as 10 dB.

3.2.4 Power Budget Gain Factors

There are basically two gain factors in the link between the BTS ad MS.

These are the antenna gain and diversity gain.

Antenna gain. The antenna by the BTS end can have different gain values.

The gain depends primarily on the beam widths of the antenna. Typically

three-sectored configurations with 65° horizontal half-power beam widths are

used, hence the gain depends on the vertical beamwidth, i.e. the length of the

antenna. Typically the antenna gains are between 15 and 18 dBi. For the MS

end, the antenna gain is much more difficult to determine. Basically there

should not be any reason to have any gain in the MS antenna, because the

receiving part (BTS) would not then necessarily be in the main lobe direction.

Typically therefore the MS antenna gain is assumed to be 0 dB.

Diversity gain. Normally diversity reception by the BTS end is used. There

are several methods for diversity. There may be two receiving antennas or one

cross-polarised antenna. Also how the diversity signals are combined can

vary. The way that the diversity signals are combined in Nokia solutions is

called Maximum Ratio Combining. This is proven to be the most efficient

diversity combining technique, and diversity gain of 4-6 dB can be expected.

3.2.5 Power Budget Calculation

The power budget calculations can be easily made using a spreadsheet

application. In Figure 32 one example of power budget calculations is

presented. In this calculation, which is made for a GSM1800 system, the

approach has been such that the maximum allowable path loss is calculated

for uplink (MS → BTS). After this value of 148 dB has been obtained, the

needed BTS transmitting power is calculated.

Now if the needed BTS transmitting power would be more than what is

available from the BTS, the link is said to be downlink limited. If this value

would turn out to be less than what is possible from the BTS, the link is said

to be uplink limited.Another possible approach to the power budget calculations would be to

assume maximum transmitting powers and to calculate the maximum

allowable path losses to both up- and downlink separately. After these

calculations one could see which direction would allow higher losses and

draw necessary conclusions based on that.

Penetration losses for different indoor environments (building, car, etc.) do

not have any affect on the basic power budget calculations. They are

38 (39) © Nokia Oyj 6-90199v 1.0



considered when evaluating cell sizes. Typical value for building penetration

loss is 10-15 dB; car penetration loss is approximately 8 dB.

RADIO LINK POWER BUDGET MS CLASS: 1

GENERAL INFO

Frequency (MHz): 1800 System: GSM1800

set starting parameters here

RECEIVING END: BS MS

RX RF-input sensitivity dBm -106,00 -100,00 A

Fast fading margin dB 3,00 3,00 B

Cable loss + connector dB 4,00 0,00 C

Rx antenna gain dBi 15,00 0,00 D

Diversity gain dB 4,00 0,00 E

Isotropic power dBm -118,00 -97,00 F=A+B+C-D-E

Field strength dBµV/m 24,00 45,00 G=F+Z*

* Z = 77.2 + 20*log(freq[MHz])

TRANSMITTING END: MS BS

TX RF output peak power W 1,00 25,00

(mean power over RF cycle) dBm 30,00 44,00 K

Isolator + combiner + filter dB 0,00 4,00 L

RF-peak power, combiner output dBm 30,00 40,00 M=K-LCable loss + connector dB 0,00 4,00 N

TX-antenna gain dBi 0,00 15,00 O

Peak EIRP W 1,00 125,90

(EIRP = ERP + 2dB) dBm 30,00 51,00 P=M-N+O

Isotropic path loss dB 148,00 148,00 Q=P-F

path loss shall be balanced

can BS provide

output power needed ?

Figure 32. Example of a power budget (up/downlink) calculation

Date post:	04-Jun-2018
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