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CHAPTER VII
Radio Aspects, Cell Sites and
Antenna Subsystem
by
Miftadi Sudjai, Ir., MSc., MPhil
Lab. Antena
Jurusan Teknik Elektro
STTTELKOM
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Cellular Radio Access System
MSC
PSTN
Packet/IP
Network
BTS1/cell site 1
BTS1/cell site n
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Radio (Tx & Rx) System
Signal Source: Informasi & Baseband Processing.
Tx-er: Modulator, Channel Encoder, Interleaver, etc.
PA: Power Amplifier. Feedline: Cable, Connector and Jumper.
Pre-Amp: LNA.
Rx-er: Demodulator, Channel Decoder, De-Interleaver, etc.
RxerPASignal
InformationTxer
Signal
Source
(Voice,
data, etc)
propagation
feedlineTx filter Rx filter Pre-Amp
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Structure of Transmitter
BB Processing: to process analog signal into digital signal & other processing
Mod: translate from BB freq. To RF freq depend on type of cellular system beingused e.g. G-MSK modulator for GSM.
Power Amp:- Class A: high linearity
- Class B: greater output power more efficient than Class A, but less linear
- Class AB: combined adv. of class A & B become widely used in wireless.
- Class C: more power efficient widely used in wireless
BB
ProcessingMod PA
Info
Signal
Jumper
Jumper
Cable
Connector
Depend ontype of Mod used
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Transmitting Combiners
Allows multiple transmitters to feedsingle antenna, providing Minimum power loss from transmitter
to antenna
Maximum isolation betweentransmitters
Combiner types Tuned
low insertion loss ~1-3 dB transmitter frequencies must be
significantly separated
Hybrid insertion loss -3 dB per stage
no restriction on transmitter frequencies
Linear amplifier Linearity and intermodulation are
major design and operation issues
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Generic Structure of Rxer
Block diagram of Rxer varies depend on type of modulation, encoder, and/ or baseband processing.
Parameters to be considered are:
- frequency range
- dynamic range
- sensitivity
- distortion
- noise
- tuning speed
1
2
.
.
.
N
Chanel
EncoderPA
Data/
Signal
filter
jumper
Multicoupler/RF Distributor
X IF
LOfeedline
Antenna
IF
Rxer
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Antenna: to convert electromagnetic energy from atmosferelectric energy and transfer it to feed line
Feed line
Receiver Components
Jumper Cable Jumper
Filter & Pre-Amplifier:
- Filter: to pass the wanted signal & attenuated the
interference designed to work according to theintended bands
- Pre-Amplifier is used to increased S/N of receivedsignals.
= Connector
Jumper to ease maintenance and installation
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Receiver Components
Multicoupler:
- used for RF distribution
- many signals/users can share the same receive antenna:
1 : 4
Splitter
1 : 4
Splitter
# 1
# 2
# 3
# 4
1 : 4
Splitter
# 13
# 14
# 15
# 16
RFin
signal
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Performance Criteria of Receivers
Sensitivity:- ability to detect a weak signals, measured by minimum discernible signal (MDS).
- MDS is measured by turning off the AGC, input a signal with correct BW, and
increasing the signal output from generator until S + N = 3 dB higher than 0 when
there is no signal.
- Sensitivity incorporate thermal noise, NF and BW, defined as:
Sen = 10 log (kTB) + 10 log (Channel BW) + NF
where: 10 log (kTB) = -174 dBm/Hz for T = 25oC,
B = 840 MHz and k = 1.38 x 10-23 J/K
Sen = -174 + 10 log(W) + NF
where: W = Channel Bandwidth
e.g. for IS-9 W = 1.23 MHz
S = -174 + 10 log (1.23 x 106) + 4 = 109.1 dBm
GSM W = 200 kHz
S = -174 + 10 log (2 x 105) + 4 = -117 dBm
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Performance Criteria of Receiver
Dynamic Range
- a range of levels of the signal that receiver can handle accurately.
- blocking DR is defined from MDS to 1 dB compression point.
- spurious free DR (SFDR) is defined from MDS to a specified 3rd orderintermodulation level.
Linear operation
Signal slope
Spurious free
dynamic range
Third order
Intercept point
Noise level
Input power, dBm
Input power
causing burnoutOutputpower,dBm
1-dB compression
- e.g. a range from -13 to -104 dBm DR = 91 dB
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Performance Criteria of Receiver
SINAD = signal to noise and distortion:
dBDN
DNSSINAD
Noise = thermal noise + other noises:
affect overall performance of receiver
quantified by Noise Figure, NF:
Selectivity:- a measure of protection from off channel interference.
- depend upon filtering.
- greater selectivity means better rejection to unwanted signal however if
too selective, the signal could be distorted.
NSNS
NF
output
inputlog10
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4 Basic Antenna System
l/2
G=2.14 dBi
Z 73 W
a. Dipole
l/4
G=4 dBi
Z 36 W
b. monopole
Ground plane
c. Loop
Ground plane
conductorFeed point
d. Microstrip/ patch
dielectric l/2
l/2
l
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Base Station Antenna
Use antenna with higher gain
Could be omnidirectional or sectoral depending on cell type
Collinear antenna:
S
2l
2l
4l
feeder
line
OmnidirectionalRadiation
Pattern
boresight
main lobe
side lobe
(elevation)
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Log periodic dipole array (LPDA)
Base Station Antenna
DipolesTransmission
line
- BW is smaller than LPDA
- typical gain 12 14 dB
Reflector Driven element (dipole) Directors
Yagi antenna
Directional Radiation
Pattern
main lobe
main lobeside lobeback lobe
- very wide BW, with constant SWR
- typical gain 10 dBi
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Directional BS Antenna
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Omni AntennasCollinear Vertical Arrays
The family of omni-directionalwireless
antennas:
Number of elements determines Physical size
Gain
Beamwidth, first null angle
Models with many elements have
very narrow beamwidths Require stable mounting and
careful alignment
be sure nulls do not fall in
important coverageareas Rod and grid reflectors are
sometimes added for milddirectivity
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Sector AntennasReflectors And Vertical Arrays
Typical commercial sector antennas
are vertical combinations of dipoles,
yagis, or log-periodic elements with
reflector (panel or grid) backing:
Vertical plane pattern is
determined by number ofvertically-separated elements varies from 1 to 8, affecting
mainly gain and verticalplanebeamwidth
Horizontal plane pattern is
determined by: number of horizontally-spaced
elements
shape of reflectors (is reflector
folded?)
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Example Of Antenna Catalog Specifications
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Antenna Downtilt
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Vertical Depression Angles
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Types Of Downtilt
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Antenna Downtilt:Reduce Interference
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Antenna Downtilt:Avoid Overshoot
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SWR of Antenna
SWR = Vmax/Vmin, define the matching level between antenna and feederline
Reflection coefficient:
11
SWRSWR
2
2log10Re Lossturnwhere represent a percent of reflected power defined by:
SWR of Antenna
Amplitude
Vmax
Vmin
l/2
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Performance Criteria of Antenna
Antenna pattern, defined at azimuth and elevation orientation
either omnior bidirectional antenna
Main lobe & side lobe, the lower side lobe the better resistance tointerference
Input impedance, usually complex matching input ipedance and feeder lineimpedance is very critical to have maximum power transfer from feeder to
antenna Beamwidth, usually defined as angular separation where there is 3 dB
reduction from bore-sight
Directivity & Gain, is ratio of radiation intensity at wanted direction andcoverage radiation intensity over all direction
Bandwidth, define operating range of antenna, limited by SWR. A typicalBW is for SWR 1:1.2 at the band edge.
Polarization, defined by orientation of E
DG .
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Performance Criteria of Antenna
Front to Back Ratio, is ratio between main lobe & back lobe,
very impotant for directional antenna.
Spatial diversity:
Rx2 Rx1
h
d
)(835
11feet
fx
hd
where f is in MHz
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Antenna Installation
a) Tower
Tx
Rx1Rx2
d
b) Roof Top, Edge of Buildingc) Roof Top
d
Rx1
Rx2Tx
d
Rx1
Rx2Tx
d) Wall Mounting
sector 1 Rx1
Rx2
Tx2
3
d
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Antenna Installation Tolerance
Apply to physical oriented & plumbness of its installation
For omnidirectional antenna, it is unnecessary. But for directi-
onal antenna it is very critical
Usually taken +/- 5% from antenna horizontal/azimuth pattern.
Azimuth/Horizontal Pattern Tolerance from Bore Sight
110O +/- 5.5o
92O +/- 4.5o
60O +/- 3.0o
40O +/- 2.0o
Table: Horizontal Antenna Tolerance
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Antenna Isolation
a. vertical
y
Tx
Rx
l
l
ywhere
dBy
VI log4028
c. slant
y
angleslantwhere
dBHIHIVISIo
90
Tx Rx
x
b) horizontal
l
l
10
log2022
xwhere
dBx
HI
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Link Budget
TXer RXer
Txercomponent
Rxer
component
link budget component
path loss
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Link Budget Up Link
Frequency range, MHz
Mobile parameters
- Tx PA output (max)
- Cable loss
- Antenna gain
-------- (Subsc. ERP max, dB)
Environmental margins
- Fading margin
- Environmental attenuation
- Cell overlap
-------------------- (dB)
Base station parameters
- Rx ant. gain Rx jumper loss
- Rx tower top amp gain (net)
- Rx cable loss
- Rx ligthning arrester loss
- Rx duplexer loss
- Rx diversity gain
- Rx coding gain
- Rx sensitivity
------- Up-link budget, dB
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Link Budget Down Link
Frequency range, MHz
Base station parameters
- Tx PA output power
- Tx combiner loss
- Tx duplexer loss
- Tx ligthning arrester loss
- Tx cable loss
- Tx jumper loss
- Tx tower top amp gain
- Tx antenna gain
(Cell ERP, dB)
Environmental margins
- Tx diversity gain- Fading margin
- Environmental attenuation
- Cell overlap
(dB) Mobile parameters
- Antenna gain
- Rx diversity gain
- Antenna cable loss- Coding gain
- Rx sensitivity
---------- Down-link budget, dB
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Type of Cell Site/BTS (1)
Monopole
Rx2Rx1
Tx
Roof Top
Rx2Rx1 Tx
a) Omni cell b) 3 Sectors
Rx12
Tx1
Rx11
Rx21
Tx2
Rx22
Rx32
Tx3
Rx31
1
2
3
120o
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Type of Cell Site/BTS (2)
c) 6 sectors
T
R
R
R
RR
R
RR R
R
R
R
T
T
T
T
T
1
2
3
4
5
6
d) Microcell or picocell
Traffic light
Micro- or pico-cell antenna
60
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Cell Site Design (1)
Site Qualification Test
(SQT)
Planning and
Zoning Board
Site
Accepted?
EMF Compliance
Site activation
Search area
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Cell Site Design (2)
Search Area:
- searching area to place cell site/BTS that meet the specifications
- plot the propagation path, including clearance
- mapping the area for planning & documentation
SQT:
- to assure the area is a viable candidate for a cell site by measurements
- include a sketch of the location, antenna type, height, ERP, path clearance,
and do callibration
Site acceptance:- if SQT is positive then the area is accepted to place a cell site- if not, then area is rejected
- both site acceptance and rejection should be documented
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Cell Site Design (3)
Planning and zoning board:
- why the site is needed
- how the site will improve the network
- drawing the sketch of site
Electromagnetic Force (EMF) Compliance:
- EMF identify the source of EM from the site itself and surrounding area
- to ensure it complies with personal safety and government regulation
- incorporated the type of Txer, power, frequency range, etc
- method for calculating EMF, e.g. IEEE C95.1 1991 standard
Site activation:
- when every steps above is OK, the cell site/BTS could be placed and turn on
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Conclusion
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The End
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