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Extended Planning Introduction
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 or means without the prior written permission of Nokia Networks. The document has been
prepared to be used by professional and properly trained personnel, and the customer assumes 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, or performance 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 of this document or the information in it.
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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...................................................19
2.3 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 Budget343.1 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 handover functions 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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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 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 3 rd 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
• 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 -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
• 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 -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
• 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 -33°C to +40°C 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 -33°C to +40°C 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 -33°C to +40°C 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 -33°C to +40°C plus solar load
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
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 field
vectors 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 antennadimension)
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RFCharacteristics Metrosite PrimeSite InSite Flexitalk Intratalk Citytalk UltrasiteEDGE
Max. TRXs 4 1 1 2 6 6 6
Max. TRXsSpecial
Cabinet
12 12 108
Max. Sectors 4 1 1 1 4+4+4 4+4+4 36+36+36
Max TXPower
(dBm)
30 38 22 42 42 42 42
Dynamic sensit ivity
(dBm) singlebranch,
RBER2<2%
-106.0 -106.0 -100 -102/-108 -102/-
108
-102/ -
108
-108.5/ -
109
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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.
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 Characteristics
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
deployment (optical impact!) and apply higher torque to the antenna
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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.
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
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 of the rooftop
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∆hh
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
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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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 polarisation in 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.
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/I
and 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.
• Diversity 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 ??
True only (in theory)if environment 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,
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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 cableslower losses per lengthlarge bending radiimuch more expensive
jumper
(2 m)
4 0 . .
7 0 m
jumper
(2 m)
Keep antenna cables short
Figure 19. Antenna cables
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)
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• 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
A
F
E
TX1
TX2
RXdiv1
RXdiv2
RX1
RX2
TRX1 TX1
RX1RXdiv1
TRX2 TX2
RX2
RXdiv2
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
TRX1 TX1
RX1RXdiv1
TRX2 TX2
RX2RXdiv2
TRX3 TX3
RX3
RXdiv3
TRX4 TX4
RX4RXdiv4
A
F
E
TX1
TX2
RX3
RX4
RX1
RX2
A
F
E
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
CABINET1
TX1,RX1,RX2
TX2, RXdiv1, RXdiv2
2,5 m
A
F
T
TX1
TX2
RXdiv1
RXdiv2
RX1
RX2
TRX1 TX1
RX1RXdiv1
TRX2 TX2
RX2RXdiv2
Figure 22. AFT with X-pol div 2+2+2
CABINET1
TX3
TX4,Rxdiv1,Rxdiv2,RXdiv3,RXdiv4
TX1,RX1,RX2,RX3,RX4
TX2
0.4 m
TRX1 TX1
RX1RXdiv1
TRX2 TX2
RX2RXdiv2
TRX3 TX3RX3RXdiv3
TRX4 TX4
RX4RXdiv4
A
F
T
TX1
TX2
RX3
RX4
RX1
RX2
A
F
T
TX3
TX4
RXdiv3
RXdiv4
RXdiv1
RXdiv2
CABINET 2
Figure 23. AFT with X-pol div 4+4+4
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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
TRX1 TX1
RX1RXdiv1
TRX2 TX2
RX2RXdiv2
TRX3 TX3
RX3RXdiv3
TRX4 TX4
RX4RXdiv4
TRX6 TX6
RX6RXdiv6
TRX5 TX5
RX5RXdiv5
TX2
TX5
TX6
TX3
TX4
R TC
TX1
Figure 24. RTC with X-pol div 6+6+6
2.6 MHA and Booster
2.6.1 Masthead Preamplifier (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)
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
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.
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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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Nokia BSC
Nokia BSC is based on the DX200 platform. The structure of the DX200
BSC is presented in Figure 27.
BTS
GS
CLS
MSC (TC)
ET ET
BCSU MCMU OMU I/O
MB
Figure 27. Block structure of DX200
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.
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T C S M 2 E
T C S M 2 E
E T
E T
E T
E T
E T
E T
E T
E T
E T
E T
B S C
A i r I / FA b i s I / FA t e r I / FA I / F
E T
E T
E T
E T
E T
E T
E T
E T
E T
E T
M S CB T S
B I E
M S
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
Link Budget Basics
Link budget calculations are essential in radio network planning. Link budget
calculations consist of two parts:
5. Power budget calculations
6. 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.
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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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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.
Power Budget Receiver Sensitivities
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.
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 feeder cable. 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.
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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
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calculations. In many cases the body proximity loss for a MS on belt can be as
much as 10 dB.
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 thereceiving 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.
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
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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 hereRECEIVING END: BS MS
RX RF-input sensitivity dBm -106,00 -100,00 A
Fast fading margin dB 3,00 3,00 BCable loss + connector dB 4,00 0,00 C
Rx antenna gain dBi 15,00 0,00 D
Diversity gain dB 4,00 0,00 EIsotropic 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 provideoutput power needed ?
Figure 32. Example of a power budget (up/downlink) calculation
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