7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 1/54
Table of Contents
Chapter 4 Application of Antenna Feeder System .................................................................... 2
4.1 Overview........................................................................................................................... 2
4.2 Antenna Basics................................................................................................................. 3
4.2.1 Types...................................................................................................................... 3
4.2.2 Working Principles.................................................................................................. 4
4.2.3 Important Technology Characteristics.....................................................................5
4.2.4 Antenna diversity..................................................................................................13
4.2.5 Relationship between antenna lobe width and antenna gain................................17
4.3 Antenna Tilt Planning......................................................................................................184.3.1 Antenna Tilt design............................................................................................... 19
4.3.2 Application............................................................................................................23
4.4 Antenna Selection........................................................................................................... 26
4.4.1 Problems Present in Antenna Selection................................................................26
4.4.2 Principles for Selecting Base Station Antenna in Urban Areas.............................26
4.4.3 Principles for Selecting Base Station Antenna in Suburban Areas........................27
4.4.4 Principles for Selecting Base Station Antenna in Rural Areas..............................28
4.4.5 Principles for Selecting Base Station Antenna along Highroads...........................28
4.4.6 Other Considerations for Antenna Selection.........................................................30
4.4.7 Antenna Selection Reference............................................................................... 30
4.5 Combiner and Divider Unit.............................................................................................. 32
4.5.1 Principles..............................................................................................................32
4.5.2 Configuration of Combiner and Divider Unit......................................................... 35
4.6 Tower Amplifier................................................................................................................ 37
4.7 Feeder............................................................................................................................. 38
4.8 Distributed Antenna System............................................................................................ 39
4.8.1 Composition Principle of a Distributed Antenna System.......................................39
4.8.2 Types of Distributed Antenna Systems.................................................................40
4.8.3 Key Technical Indexes for Antenna Components..................................................434.9 New Antenna Technology—Smart Antenna Overview.....................................................47
4.9.1 Smart antenna...................................................................................................... 47
4.9.2 Smart Antenna Application.................................................................................... 51
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 2/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Χηαπτερ 4 Application of Antenna Feeder System
4.1 Overview
In a wireless telecommunication system, the antenna provides the interface between
base transceiver station (BTS) and outside propagation mediums. One set of antenna
can both radiate and receive radio waves. When radiating radio waves, it converts
high frequency current into electromagnetic wave; when receiving radio waves, it
converts the electromagnetic wave into high frequency current.
During network planning, the right antenna is selected according to the radio
environment of the BTS. The parameters, such as antenna height, antenna azimuth
angle, tilt angle, are decided based on the selected antenna.
Antenna is directly related to uplink and downlink converges, so are the radio
frequency (RF) components, such as feeder cable, combiner, and duplexer.
Figure 1.1 shows the composition of an antenna feeder system
Figure 1.1 Composition of an antenna feeder system
6/27/2013 All rights reserved Page2 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 3/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
4.2 Antenna Basics
4.2.1 Types
Generally, antennas for mobile communication are passive. Table 1.1 lists the
antenna types in terms of different division standards.
Table 1.1 Antenna type and division standard
Division standard Type
Radiation direction Omni-directional antenna
Directional antenna
Structural feature Linear antenna
Dish antenna
Cap antenna
Polarization way Vertical polarization antenna (unipolarization antenna)
Cross polarization antenna (dual polarization antenna)
Figure 1.2 shows the antennas commonly used in mobile communication. They are
directional antenna, omni antenna, and indoor cap antenna from left to right.
Figure 1.2 Antennas commonly used in mobile communication
6/27/2013 All rights reserved Page3 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 4/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
4.2.2 Working Principles
According to Maxwell equation, electromagnetic wave radiation can be generated if
alternate current is present in the conductor. The radiation capability is related to the
length and shape of the conductor.
Figure 1.1 shows the principles of antenna radiation
Figure 1.1 Principles of antenna radiation
As shown in Figure 1.1 (a), when the distance of the two conductors is short, the
induced electromotive force generated on the ideal conductors will offset the effect of
each other, so only a small amount of energy is radiated beyond the two conductors.
As shown in Figure 1.1 (b), there is a flare angle between the two conductors.
Because the current is generated in the same direction, the induced electromotive
6/27/2013 All rights reserved Page4 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 5/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
force is generated in the same direction. In this case, a larger amount of energy is
radiated beyond the two conductors.
As shown in Figure 1.1 (c), when the flare angle is wide enough to match wavelength,
the amount of current flowing through the conductors will be greatly increased. Thus
intensive radiation is generated.
Generally, the direct conductor that can generate intensive radiation is called dipole. If
the length of the two arms of a dipole is 1/4 wavelength, the dipole is called
symmetrical half-wave dipole.
The symmetrical half-wave dipole is a basic element of a mobile telecommunication
antenna. As shown in Figure 1.2, an actual antenna consists of multiple dipoles.
Figure 1.2 Composition of an actual antenna
4.2.3 Important Technology Characteristics
I. Antenna gain
The antenna is passive equipment, so the concept of antenna gain is different from
6/27/2013 All rights reserved Page5 of 54
Unit dipole
Feeding networkFeedingnetwork
Antenna connector Antenna connector
Unit dipole
Feeding network
Directional antenna Omni-directional antenna
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 6/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
that of the power amplifier gain. The power amplifier can amplify power, but the
antenna does not increase the energy for radiated signals. It concentrates the energy
into a certain direction by changing the feeding mode of antenna dipoles throughassembling the antenna dipoles.
Antenna gain is an important antenna index, indicating the antenna capability (the
directional antenna) of concentrating energy into a certain direction.
The dBi and dBd are two units of antenna gain, and the relationship between the two
is as follows:
15.2+= dBd dBi
Where,
The dBi indicates the energy concentration capability of the antennas withdirections (including omni antennas) as compared with that of the isotropic
antennas. “i” stands for “isotropic”.
The dBd indicates that the energy concentration capability of the antennas with
directions (including omni antennas) as compared with that of the symmetrical
dipole antennas. “d” stands for “dipole”.
Figure 1.1 shows the relationship between dBi and dBd.
Isotropic antenna
Symmetrical dipole
antenna Actual antenna
dBd
dBi
2.15d
B
Figure 1.1 Relationship between dBi and dBd
The dBi indicates the gain of actual antennas as compared with that of isotropic
antennas; the dBd indicates the gain of actual antennas as compared with that of
half-wave dipole antennas.
II. Directional diagram
The radiation intensity is related to radiation direction. If the relationship between the
two is drawn according to relative scale, it is an antenna directional diagram, or
6/27/2013 All rights reserved Page6 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 7/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
radiation diagram.
Three relative scales are available for drawing a directional diagram. They are:
Linearity (power directional diagram)
Square root (field strength diagram)
Decibel
The decibel scale is more often used among the three, because it expresses the side
lobe level in a simpler way.
The antenna directional diagram is space solid figure, but the one in common use is a
directional diagram within two principle planes perpendicular to each other, known as
plane directional diagram. For the linear antenna, since the ground effect is great, it
adopts the vertical plane and horizontal plane as its principle plane. For the planeantenna, it adopts two principles planes, namely, E plane and H plane.
Essentially, the dipole arrangement and the change of the feeding phase of each
dipole work together to determine antenna direction, and the principle of which is
similar to that of the light interference effect. Therefore, the energy in some directions
is amplified, but the energy in other directions is weakened. In this case, lobes (or
beams) and zero points are formed. The lobe with the fullest energy is the major lobe.
The lobe with the second fullest energy lobe is the first side lobe, and so on. For the
directional antenna, it has a back lobe.
Figure 1.1 shows a horizontal plane and a vertical plane of a directional antenna.
Figure 1.1 Directional diagram of the directional antenna (horizontal plane and
vertical plane)
6/27/2013 All rights reserved Page7 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 8/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Table 1.1 list the parameters related to the antenna directional diagram.
Table 1.1 Parameters related to the antenna directional diagram
Parameter Description
Zero
power
point lobe
width
It refers to the included angle
between the zero radiation
directions on both sides of the
maximum major lobe.
Half
power
point lobe
width
It refers to the included angle after
the maximum electrical field falls by
0.707 points (if power falls by half,
the gain falls by 3dB).
It is divided into two types:
horizontal half power point lobe
width and vertical half power lobe
width.
Side lobe
suppressi
on ratio
It refers to the ratio of the maximum
major lobe to the maximum side
lobe.
Front-to-
back ratio
—
Electric tilt
angle
—
III. Polarization
Polarization is a radiation feature describing the space direction for the field strength
vector of electromagnetic wave. Generally, the space direction of the field strength
vector works as the polarization direction of the electromagnetic wave.
The electromagnetic wave with the space direction of the electric field vector
unchanged at any time is called straight line polarized wave. If the land is taken as a
reference, the direction of the electric field vector parallel to the land is called
horizontal polarized wave; the direction of the electric field vector perpendicular to the
land is called vertical polarized wave. The space direction of the electric field vector is
changeable. If the trace of the electric field vector end is a circle, the electromagnetic
wave is called circular polarized wave; if the trace is an ellipse, the electromagnetic
wave is called ellipse polarized wave. Both the circular polarized wave and ellipse
have a feature, which is rotating phase.
The electromagnetic waves of different bands are transmitted by different polarization
6/27/2013 All rights reserved Page8 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 9/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
modes. Generally, the vertical polarization is used in mobile communication; the
horizontal polarization is used in broadcasting systems; and the ellipse polarization is
used in satellite communication.
The GSM antenna can be divided into two types, namely, single polarization antenna
and dual polarization antenna. With the help of polarization diversity technology, a
dual polarization antenna can promise BTS to receive good signals through reducing
the multi-path effect in mobile communication. Two specifications, 0°/90° and ±45°
are available to the dual polarization antenna. Because GSM bands are more
favorable to the horizontal polarized wave than to the vertical polarized wave, the
0°/90° cross polarization antenna is seldom used at present.
IV. Antenna tilt
Antenna tilt is commonly used to enhance the signal level for the serving cell and
reduces the signal interference on other cells. Table 1.1 lists the antenna tilt type and
related descriptions.
Table 1.1
Antenna type Description
Mechanical tilt It is set by lowering the antenna to a required position
through adjusting antenna mount.
Electrical tilt It is controlled by changing the phase of antenna dipole.
Note:
In actual project implementation, electrical tilt and mechanical tilt can be used
together to control the antenna tilt angle.
The tilt angel of an electrical tilt antenna is fixed, known as preset tilt. The latest
technology enables an electrical tilt antenna to adjust its tilt angles, and this kind of
electrical tilt antenna is called electrical adjustment antenna.
V. Voltage standing wave ratio (VSWR)
For VSWR of the base station antenna in a mobile communication cellular system, its
maximum value must be equal to or less than 1.5:1. If Z A stands for antenna input
impedance, and Z 0 stands for antenna standard characteristic impedance, the
reflection coefficient is:
6/27/2013 All rights reserved Page9 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 10/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
|Г | =
| Z A− Z 0|
| Z A+ Z 0|,VSWR =
1+|Г |
1−|Г |, where
Z 0is 50 ohm. The return loss can also
indicate the match characteristic of the port, that is, R. L.(dB
) =20 lglg|
Г
| if VSWR =1.5:1 and R.L. = -13.98dB.
When antenna input impedance is inconsistent with its characteristic impedance, the
reflection wave and incident wave will overlap on feeder cable to form standing wave.
The ratio of the maximum to minimum value of neighbor is the VSWR.
If the ratio is too large, the radiation power will be reduced because part of the power
transmitted into the antenna is reflected back to the power amplifier. Furthermore, the
cable loss is measured when VSWR=1 (it means full match), so the reflection power
increases the cable loss. In addition, the transmitter output power cannot reach the
designed rated value.
The factors in the previous paragraph will decrease coverage area. Moreover, the
reflection power will return to the power amplifier of the transmitter. If the power is too
high, it will damage the power tube. In this case, the communication system cannot
work normally.
At present, however, the transmitter output power can reach the rated power under
certain mismatch conditions (for example, when VSWR < 1.7 or 2.0). Related
calculation shows that compared with the power loss when VSWR = 1.3, the power
loss is decreased by only 0.23dB when VSWR=1.5, which can be neglectedaccording to mobile communication fading. If the VSWR is too low, however, it will
increase antenna manufacturing cost. Therefore, the balance between the cost and
VSWR must be emphasized.
VI. Front-to-back ratio (F/B)
The difference between the level of the side lobes within back 180°±30° and the
maximum beam is indicated by positive value. Generally, the antenna front-to-back
ratio ranges from 18 dB to 45dB. For densely populated areas, to reduce the
interference generated by back lobes, the antenna with greater front-to-back ratioshould be used.
VII. Port isolation
For the antenna with multiple ports, such as dual polarization antenna and dual-band
dual polarization antenna, the isolation between the ports for both transmission and
reception must be greater than 30dB.
6/27/2013 All rights reserved Page10 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 11/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
VIII. Power capacity
Power capacity refers to the average power capacity. The antenna contains coupling
devices, such as match, balance, and phase shift, so the power it can bear is limited.
Suppose the power of a single carrier is 20W, if one antenna port can input up a
maximum of six carriers, the total input power of the antenna is 120W. Therefore, the
power capacity of the antenna single port must be greater than 200W when
environmental temperature is 65 degree Celsius.
IX. Zero point filling
To make the radiation level within service areas more even, the first zero point of the
lower side lobe needs to be filled by using the shaped-beam design. Generally, when
the zero depth is -20dB greater than the main beam, it means that the zero point
filling is present in antenna.
It is recommended that the zero point filling technology should be applied to high gain
antennas with great height (for example, the antenna height is 100 meters) to improve
nearby coverage and avoid the unequal coverage caused by signal fluctuation.
X. Upper side lobe suppression
For a cellular system, to reduce the interference between neighbor cells, the base
station antenna should reduce the side lobes aiming at the interference cells. In this
case, the upper side lobe suppression ratio can be enhanced and the ratio of garbagesignals to useful signal (D/U) of the coverage area is improved. The level of the first
upper lobe must be smaller than -18dB relative to the maximum gain of the major
lobe. There is no such requirement for the antenna of macro cell base station.
XI. Antenna inout interface
To improve the reliability of passive intermodulation and RF connection, the input
interface of base station antenna adopts 7/16DIN-Female. Before the antenna is
available, a cover must be installed at the antenna port to prevent oxide and
contamination.
XII. Passive intermodulation (PIM)
It is the inermodulation effect caused by the non-linearity present in the passive
components, such as connector, antenna, feeder, and filter, working under high power
signals of multiple carriers.
Generally, it is granted that passive components are of linearity. Under high power
condition, nonlinearity is present in passive components to some extent mainly due to
the following causes:
6/27/2013 All rights reserved Page11 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 12/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Metals of different materials are contacted together.
The contact surface of the same materials is rough.
The components are not tightly connected. Magnetic substances are present.
Intermodulation products will disturb the communication system; especially the
intermodulation products falling within the receiving band have a remarkable negative
effect on the system receptivity. Therefore, the requirements on the passive
components, such as the connector, feeder, antenna, are strict in a GSM system.
Generally, the value of the antenna passive intermodulation index must reach
-150dBc.
XIII. Antenna size and weight
If all electric indicators are met, the antenna should be as small as possible in size
and as light as possible in weight for storage, transport, installation, and security
purposes.
Now carriers have higher requirements on antenna size, weight, and shape.
Therefore, both technical indicators and the previous non-technical factors must be
emphasized in antenna selection. Generally, the antenna installed in urban area
should be small, light, and eye catching.
XIV. Wind loading
The base station antenna must be installed on the top of high buildings and towers. In
coastal areas, where the wind is strong all the year around, so it is required that the
antenna can work normally against the wind at the speed of 36m/s and are not
damaged when the wind speed reaches 55m/s.
The antenna itself can stand strong wind. In areas where the wind is strong, the
antenna is damaged mainly because the tower or the supporting bar is damaged.
XV. Work temperatire and humidity
The base station antenna works normally when environment temperature ranges
-40°C to +65°C and environmental relative humidity ranges from 0 to 100%.
XVI. Lightning protection
All RF input ports of the base station antenna are required to be directly grounded
through direct current.
6/27/2013 All rights reserved Page12 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 13/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
XVII. “Three proof” capability
The base station antenna must have “three proof” capability, that is, moisture proof,
salt atmosphere proof, and mildew proof. For the omni antenna, it can be installed in
reverse direction according to installation instructions and the “three proof”
requirements.
4.2.4 Antenna diversity
I. Diversity features
Signal fading in mobile radio environment will give rise to serious problems. With the
movement of the mobile station, the Raleigh fading varies rapidly with signal
instantaneous value, while the logarithm normal fading varies with signal average
value (median value). The two values will deteriorate receiving signals greatly, so they
are the main factors that attributed to unstable receiving signal in mobile
communication.
Though signal stability can be improved through increasing transmitting power,
antenna size and height, such methods cost much in mobile communication, and they
are sometimes far beyond reality.
This problem can be solved, however, with the help of diversity technology. The
diversity technology enables antenna to receive the signals with little dependencies
but carrying the same information on several tributaries. After that, the antenna
combines the signals from each tributary and output the combined signal. In this
case, the deep fading probability can be greatly reduced at the receiving end.
Generally, diversity technology is applied at base station side.
The diversity can be divided into two types, namely, explicit diversity and implicit
diversity. The implicit diversity implies the diversity function in the signals to be
transmitted through signal processing technologies, such as RAKE receiving
technology, channel interleaving technology, anti-fading error correction technology,
and so on, but only the explicit diversity technology is introduced hereunder. The
explicit diversity can also be divided into two types, namely, base station explicit
diversity and common explicit diversity.
According to base station explicit diversity, several base stations distributed in space
fully or partially cover the same area. Because multiple signals are available, the
effect of signal fading can be greatly reduced. Because electric waves are transmitted
on different paths and the shadow effect of landforms and ground objects varies, the
multiple slow fading signals transmitted via independent fading paths are irrelevant to
each other.
6/27/2013 All rights reserved Page13 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 14/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Because each signal is not likely to undergo deep fading simultaneously, if the
diversity combination is used to select the tributary with the best signal-to-noise ratio
from all tributaries, namely, the base station and mobile station with the best signalare selected to establish the communication, the shadow effect and other geographic
effect can be eased. Therefore, base station explicit diversity is also called multiple
base station diversity.
Generally, the explicit diversity is used for suppressing Raleigh fading. The
suppression ways include:
Traditional space diversity
Frequency diversity
Polarization diversity
Direction diversity Time diversity
Field component diversity
If the space diversity, polarization diversity, and direction diversity are used, at least
two set of receiving antennas are needed at the diversity receiving side; if the
frequency diversity, field component diversity, and time diversity are used, only one
set of receiving antenna is enough.
The explicit diversity, however, improves the uplink signal quality only. For the mobile
station is restricted in terms of size, price, and battery capacity, and so on, the space
diversity of multiple antenna cannot be realized.
To improve the transmitting quality of downlink signals, you can employ the reciprocity
principle for linear system to equally shift the diversity technology of the mobile station
receiving end to base station transmitting end. And this technology is called transmit
diversity technology.
For the transmit diversity technology, one problem is present. That is, the reciprocity
principle is applicable only when a mobile channel is simplified to an approximately
linear time-variant system. Moreover, when the reciprocity principle for reception and
transmission of the linear system is applicable, the signals must be transmitted andreceived on the same band so that the fading features of the signals are the same.
In fact, frequency division duplex (FDD) are more often used in a mobile
communication system, where the interval between reception and transmission is far
greater than coherence bandwidth. To prevent FDD from deteriorating the transmit
diversity, you can realize the transmit diversity through controlling the closed loop.
In 3G, the transmit technology is widely used.
6/27/2013 All rights reserved Page14 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 15/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
II. Diversity and synthesis
The relevant coefficients between the quantity of the diversity tributaries and the
receiving diversity determine diversity features. If the relevant coefficients of each
tributary are identical, various diversity solutions can realize the same relevant
performances. In addition, we must consider how to synthesize the multiple signals
received through the diversity technology because proper synthetic technology can
bring forth desirable performance.
For example, if the Q multiple diversity is adopted, the Q signals before synthesis are
S 1(t ),S 2(t ), ...S q(t ). Because the synthesis can be performed at the baseband output
end between each diversity antenna and receiver and behind the intermediate
frequency output end of the receiver and the detection, the S i(t ) here can be
understood as a general form of the high frequency signal, intermediate frequency
signal and baseband signal. The synthesis concerns how to combine and sum up the
S i(t ). The synthesized signal is expressed as follows:
S (t ) = k 1S 1(t ) + k 2S 2(t ) + ... + k qS q(t )
Where k 1, k 2, ..., k q indicates weighting coefficient. If different weighting coefficients are
selected, different synthesis methods are produced.
The four synthetic techniques commonly used are as follows:
Maximum ratio compound (MRC)
Equal gain compound (EGC)
Selective compound (SEC)
Switch compound (SWC)
Where the MRC is defined as follows:
After weighting the voltage amplitude of the useful signals, perform relevant synthesis
for the signals and non-relevant synthesis for noise power. When the weighting
coefficient is equal to the signal-to-noise ratio of each signal, the maximum
synthesized signal-to-noise ratio of the synthesized signals is equal to the sum of the
signal-to-noise ratio of each tributary signal. In this case, the MRC is present.
For the details of the previous synthesis technologies, they are not introduced in thistextbook. In mobile communication, the space diversity and polarization diversity are
commonly used. The diversity gain designed in a project in about 3.5dB. The
following three sections introduce the space diversity and polarization diversity in
detail.
III. Space diversity
It is performed using the random change of the field intensity in space. In mobile
communication, any space change will result in great change of the field intensity. The
6/27/2013 All rights reserved Page15 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 16/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
larger the space distance, the less relevance of the signals transmitted on multi-paths
is and the less likely for the deep fading to occur simultaneously, so the space
technology can reduce the effect of the deep fading to the minimum. For this purpose,the antenna space distance must be determined. Generally, the space distance
between two receiving antennas ranges from 12λ to 18λ.
In actual project implementation, the horizontal distance between diversity antennas
should be 0.11 times higher than the valid height of the antenna. If is used to
indicate this parameter, the relationship between and the actual antenna height (h)
is=h D
. For antennas placed horizontally, when ≤ 10, two signal can be irrelevant
to each other. For example, if the antenna is 30 meters in height, a good space
diversity gain can be obtained when the antenna distance is about 3 meters.
IV. Polarization diversity
At present, dual polarization antenna is widely used in actual projects. Theoretically,
because the medium does not give rise to coupling effect, no mutual interference is
present when a frequency carries the signal with two polarization modes. In actual
mobile communication, however, the coupling effect is always present. This means
that after the signals are transmitted via mobile radio mediums, the energy of thevertical polarized wave will leak into the horizontal wave, and vice versa. Compared
with the amount of the main energy, however, the amount of the leaked energy is
little. Therefore, good diversity gain can still be obtained with the help of polarization
diversity.
Because the effect of the ±45° polarization antenna is better than that of the 0°/90°
polarization antenna, the communication networks now mainly use the ±45°
polarization antenna. The greatest advantage of the polarization antenna is that one
set of polarization antenna can meet the requirements, thus reducing the installation
cost.
V. Comparison between space diversity and polarization diversity
The greatest advantage of the polarization diversity is to save installation space. For
the space diversity, it is realized by two set of receiving antennas with a certain
distance. For the polarization diversity, however, it can be realized by only one set of
antenna, which contains two groups of dipoles.
When the transmitting antenna of the mobile station declines, the polarization
diversity obtains better relevant statistics than the space diversity. Apart from some
6/27/2013 All rights reserved Page16 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 17/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
special performances of space diversity antenna the polarization diversity antenna
has, the polarization diversity antenna is affected by the local radio transmitting or
scattering.
The environment measurement performed in urban area shows that the diversity gain
of a ±45° dual polarization antenna equals the space diversity gain, but the diversity
gain of a 0°/90° dual polarization is 1dB lower than the space diversity gain. In the
open areas, such as suburban areas, the diversity gain needs to be further measured.
In addition, any group of dipoles of the ±45° dual polarization diversity antennas can
transmit signals, but only the vertical polarized dipoles of the 0°/90° dual polarized
antenna can transmit signals.
4.2.5 Relationship between antenna lobe width and antenna gain
One function of the antenna is concentrating energy, so if the radiation intensity in
some direction is strong; the radiation intensity in other direction is weak. Generally,
the radiation intensity in a direction can be enhanced through reducing the width of
the lobes on the horizontal plane. When the antenna gain is certain, the antenna
horizontal half power angle is reversely proportional to the vertical half power angle,
and the relationship between the two is as follows:
β θ ⋅≈
32400log10
aG
Where,
Ga is antenna gain, in the unit of dBi.
is vertical half power angle, in the unit of degree.
is horizontal half power angle, in the unit of the degree.
According to the formula, when the gain and horizontal half power angle is known, the
vertical half power angle can be obtained.
For example, there is an omni antenna. If the antenna gain is 11dBi, and the
horizontal half power angle is 360°, the vertical half power angle is
°=⋅
≈ 15.710360
3240010/11
β .
Due to the difference of antenna design and manufacturing, slight difference is
present for the vertical half power angle of the actual omni antenna. And such
difference is determined by the focus and implementation ways of the electrical
design.
6/27/2013 All rights reserved Page17 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 18/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.1 shows the relationship of the antenna gain, vertical half power angle and
horizontal half power angle.
Figure 1.1 Relationship of the antenna gain, vertical half power angle and horizontal
half power angle.
As shown in Figure 1.1, when the antenna gain is small, the vertical half power angle
and horizontal half power angle are large; when the antenna gain is large, the vertical
half power angle and horizontal half power angle are small.
In addition, the antenna gain depends on dipole quantity. The larger the dipole
quantity, the larger the antenna gain is, and the larger the antenna aperture (effectiveantenna receiving area) is. For example, for a 900MHz omni antenna, if the antenna
gain increases by 3dB, the antenna length doubles. Generally, therefore, the gain of
the omni antenna does not exceed 11dBi, and the antenna length now is about 3
meters.
4.3 Antenna Tilt Planning
In cellular communication, coverage theory, frequency multiplexing theory and BSS
functional algorithm are all based on regular cellular layout. The design of project
6/27/2013 All rights reserved Page18 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 19/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
parameters is the main factor that affects the cellular layout in radio network planning.
In a wireless network system, the macro-BTS layout and the actual location of each
base station, antenna height, lobe width, direction, tilt angle, and EIRP together forma specific cellular network.
Generally, the performance indexes of the antenna itself are selected according to the
radio networking characteristics, such as the base station density and macro
coverage goal. Once the location of a base station is determined, it seldom changes.
For the antenna height, direction and tilt angle, however, they are finally determined
according to the parameters specified previously and the actual coverage goal of a
cell.
Hereunder is the analysis of the relationship among antenna height, direction, tilt
angle, and coverage goal (suppose that the cell radius is R), and the antenna tilt
angel is finally recommended according to this analysis. The propagation of radio
signals is closely related to the environment. For example, dense buildings and the
reflection caused by mountains, water surface, or huge glass walls will affect radio
propagation. Therefore, it is not necessarily that all the environments are favorable to
radio propagation. However, the regularity of cellular structure and the coverage area
and goal of a cell are the foundation for a good network, so they must be carefully
considered during network planning.
4.3.1 Antenna Tilt design
The following factors must be considered in antenna tilt design:
Antenna height
Azimuth angle
Antenna gain
Vertical half power angle
Expected coverage area
For the base stations distributed in urban areas, when the antenna has no tilt angle or
the angle is very small, the serving area of each cell is determined by the antennaheight, azimuth angle, antenna gain, transmit power, landforms and ground objects.
In this case, the coverage radius can be calculated by the commonly-used
propagation module formulas, such as Okumura-Hata and COST231.When the tilt
angle of the antenna is large, the coverage radius cannot be calculated out because
the angle is not considered in the previous formulas. If accurate propagation module
and digital map are provided, however, the coverage radius can be calculated out by
planning software. In this case, the antenna vertical half power angle and tilt angle
helps to calculate the coverage radius directly based on the triangle geometry formula
as follows:
6/27/2013 All rights reserved Page19 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 20/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
If the needed coverage radius is D (m), the antenna height is H (m), the tilt angle is
, and the vertical half power angle is , the relationship between the beams of the
major antenna lobe and the ground is shown in Figure 1.1.
Figure 1.1 Relationship between the beams of the major antenna lobe and the
ground
As shown in this figure, when the antenna tilt is 0 degrees, the beams of the major
antenna lobe, or the major energy, radiate horizontally; when the antenna tilt angle is
, the extension line of the major lobe and the ground will ultimately intersect at one
point (point A). Because a beam width is present in the vertical direction for the
antenna, intense radiation is present in the area form point A to point B.
According to the technical performance of the antenna, the antenna gain decreases
slowly within half power angle, but it decreases sharply beyond the half power angle,
especially for the upper lobe. Therefore, when the antenna tilt angle is considered,
the scope between the extension line of the half power angle to intersection point
(point B) can be taken as the actual coverage area of the antenna.
Based on the previous analysis and the principles of triangle geometry, the
relationship between the antenna height, tilt angle and coverage distance can be
obtained as follows:
= arctanarctanarctanarctanarctanarctan (H/D) + /2
This formula can calculate the coverage distance after the adjustment for tilt angle.
Actual results of on-site optimization projects show that this formula is of great
significance. However, the application of this formula meets limited conditions. It can
be applied when the tilt angle is 1.5 times greater than the half power angle, and the
6/27/2013 All rights reserved Page20 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 21/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
distance (D) must be less than the distance calculated by the previous formula when
no tilt angle is present. For the width of vertical beams in the previous formula, it is
provided in the specific antenna technical indexes.
Figure 1.2 shows the relationship between coverage distance and antenna tilt angle
when the vertical beam width of the antenna is 17 degrees. (The antenna height is 40
meters.)
Figure 1.2 Relationship between coverage distance and tilt angle (The width of the
vertical beam is 17 degrees, and the antenna height is 40 meters.)
6/27/2013 All rights reserved Page21 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 22/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.3 shows the relationship between coverage distance and antenna tilt angle
when the vertical beam width of the antenna is 6.5 degrees. (The antenna height is
40 meters.)
Figure 1.3 Relationship between coverage distance and tilt angle (The width of the
vertical beam is 17 degrees, and the antenna height is 40 meters.)
The previous two figures shows the relationship between the coverage distance and
the width of the antenna vertical beams when antenna height and tilt angle are
certain. The smaller the width of the vertical beam, the shorter the coverage distance
is. Therefore, if the cross coverage are effectively controlled, the antennas with
smaller vertical beam width and with the zero point filling function should be selected
during the planning phase. In this case, the cross interference can be controlled and
the indoor coverage near the base station.
However, if the vertical beam width grows smaller, the horizontal lobe will grow wider
or the antenna gain will grows larger. In this case, new cross interference is caused
and the cross coverage area between neighbor cells is too large. Therefore, the
antennas of medium gain are often selected in urban areas. For example, if the
antenna of 65 degrees and 15dBi is selected for a GSM 900MHz base station, the
vertical beam width is about 13 degrees to 15 degrees.
6/27/2013 All rights reserved Page22 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 23/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Note:
The adjustment of the tilt angle can serve to control the cross coverage and to
improve the indoor coverage near the base station, but the coverage far from the
base station will get worse.
4.3.2 Application
For the purpose of application and necessary overlaps of adjacent cells, the distance
(D) from the base station in populated urban areas to the target coverage area can be
simplified as the designed cell radius (R). The antenna height (H) refers to the relative
height from the base station and target coverage area. This textbook introduces the
application of antenna tilt planning in the areas similar to plains.
Antenna tilt can be divided into mechanical tilt and electrical tilt, and their effect on
coverage is almost the same. Because electrical tilt antennas are expensive,
mechanical antennas are more often used. Emulation shows that if the mechanical tilt
is greater than 10 degrees, the lobes are distorted, which will cause unexpected
interference against other cells. Therefore, it is better to keep the mechanic tilt within
10 degrees.
If only for the convenience of controlling network quality, the adaptation of the
electrical adjustment antenna will win more advantages. Because the electricaladjustment antennas are expensive, electrical antennas with a certain preset tilt angle
(for example, 6 degrees to 7 degrees) are more often used in actual networking.
When the network needs to be expanded and optimized, the electrical tilt antenna
and the mechanical tilt antenna work together to set the tilt angles greater than 10
degrees.
According to the previous analysis and in combination with the common antenna
height (25 meters to 50 meters), the reference tilt angles can be provided for the cells
whose radius is 250 meters, 500 meters, 800 meters, and 1000 meters in populated
urban areas. The case is the same for other situations.
Table 1.1 lists the reference tilt angles for antennas in populated urban areas.
Table 1.1 Reference tilt angles for antennas in populated urban areas
Antenna model Vertical half
power angle
Cell radius
R(m)
Antenna
height (m)
Tilt angle
(degree)
65 degrees, a gain of 15 dBi 15 200 25 15
65 degrees, a gain of 15 dBi 15 200 25 13
6/27/2013 All rights reserved Page23 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 24/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
65 degrees, a gain of 15 dBi 15 250 30 14
65 degrees, a gain of 15 dBi 15 250 35 15
65 degrees, a gain of 15 dBi 15 250 40 17
65 degrees, a gain of 15 dBi 15 500 25 10
65 degrees, a gain of 15 dBi 15 500 30 11
65 degrees, a gain of 15 dBi 15 500 35 12
65 degrees, a gain of 15 dBi 15 500 40 12
65 degrees, a gain of 15 dBi 15 800 30 10
65 degrees, a gain of 15 dBi 15 1000 30 2
According to the table, when the cell radius is small, the coverage area cannot be
effectively controlled even through mechanically tilting the antenna. In this case, the
coverage area can be controlled through lowering the antenna height only. If it is hard
for the antenna height to be lowered, the antenna electrical tilt together with the
antenna mechanical tilt must be used.
The previous methods for calculating tilt angles are mainly applicable for the densebase station networking with the distance within 1200 meters (that is, R = 800 meters)
between stations.
When the distance from the base station to the coverage target is greater than 800
meters, large area coverage is still being emphasized. In this case, it is unnecessary
for you to consider the effect of the vertical half power angle when estimating the
antenna tilt angle. Generally, the tilt angle now is 1 degree to 4 degrees. In special
cases, such as the base station has already been installed at a high position, the tilt
angle may also be large.
However, because the environment around the base station is rather complicated, the
reflection caused the nearby mountains, water surface, huge glass walls has an effect
on antenna tilt angle. The reflection of this kind will easily cause unexpected
interference against the neighbor frequencies and time dispersion effect. In addition,
the shadow effect caused by building roofs, front dense buildings and mountains must
be also considered. In actual networking, however, geographic environment, such as
the barrier of high buildings and mountains, around the base station can be used to
control coverage area.
When a network is implemented in a populated urban area, the major lobe of the
6/27/2013 All rights reserved Page24 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 25/54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 26/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
4.4 Antenna Selection
The antenna selection is a very important part in a mobile communication network.
The antenna must be selected according to the actual conditions, such as coverage
requirement, traffic volume, interference, and the quality of service of the network. A
proper antenna can enlarge coverage area, reduce interference, and improve the
quality of service.
Because antenna selection is closely related to coverage requirement, the antenna
application environment can be divided into four types according to landforms or
traffic distribution. They are: urban area, suburban area, rural area, and highroad.
4.4.1 Problems Present in Antenna Selection
This section introduces the problem present in antenna application from the following
perspectives:
The antenna is selected only based on the covered traffic distribution, but little
consideration is given to the relationship between landforms and antenna
directional diagram. For example, if all antennas used in a network are of the
same type, when the antenna is installed at a high position, the phenomenon of
"blind under tower” will be present because the width of the beams in vertical
plane is narrow.
Too large antenna mechanical tilt angle results in the distortion of the directional
diagram. In this case, coverage problem or interference problem will occur.
Emulation shows that the restrictions on tilt angles must vary in accordance with
the antennas with different gains.
Too much attention is focused on the high gain performance of the antenna but
little attention is given to its drawbacks. As a result, the gains of almost all the
antennas used in a network are quite high. A high gain antenna has many
drawbacks, including large size, great weight, high side lobe, deep zero lobe,
and narrow vertical beams. No consideration is given to the difference between the vertical polarization
antenna and dual polarization antenna in terms of application. The dual
polarization antenna is selected from the perspective of installation.
4.4.2 Principles for Selecting Base Station Antenna in Urban Areas
Base stations are densely distributed in urban areas. Therefore, it is required that the
coverage area of each base station is as small as possible so as to reduce cross
coverage and interference among base stations, and enhance frequency reuse rate
6/27/2013 All rights reserved Page26 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 27/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
as well. In this case, an antenna must meet the following requirements in principle.
I. Selection of antenna horizontal half power beam width
Because a large number of base stations are distributed in urban areas, overlapping
coverage and frequency interference rises as serious problems in a network. To
reduce the overlapping areas of neighbor sectors and the interference between base
stations, you can set the beam width of the antenna horizontal half power to a smaller
value. Generally, antennas whose horizontal half power beam width is 65° are
selected, but antennas whose horizontal half power beam width is above 90° are not
selected.
II. Selection of antenna gain
The base stations in urban areas are not required to cover a large area, so the
antennas with medium gain are recommended. Thus the antenna vertical beam can
be wider, which can improve the coverage quality within the areas to be covered. In
addition, the size and weight of the antenna with medium gain are small, which is
helpful for installing the antenna and reducing cost. According to present antenna
specifications, antennas with a gain of 15dBi (900MHz) and 15-18 dBi (1800 MHz)
are recommended in urban areas.
For the base stations on the outskirt of a city, if it is required to cover a large distance,
you can select the antennas with higher gains, such as 17dBi and 18dBi.
In principle, when designing base station coverage in urban areas, you should select
the antennas with a fixed electrical tilt angle. The degrees of the electrical tilt angle
can be set according to actual conditions (the recommended value is 6° to 9°).
In urban areas, to enhance frequency reuse rate and reduce cross interference, you
can select the shaped-beamed antenna with the first upper side lobe suppressed and
the lower side lobe filled.
Because space restriction is present in the antenna installation in urban areas, the
dual polarization antenna is recommended. And it is better to select the antenna with
a smaller size when the electrical specifications of the antennas are the same or
nearly the same.
4.4.3 Principles for Selecting Base Station Antenna in Suburban Areas
Because the environment is suburban areas are largely different from that in urban
areas, antennas used in suburban areas can be selected according to the required
coverage area. Generally, in suburban areas, an antenna can be selected according
6/27/2013 All rights reserved Page27 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 28/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
to the following principles:
The antennas whose horizontal half power beam width is 65° or 90° can be
selected according to actual conditions. If base stations are sparsely distributed,the antennas whose horizontal half power beam width is 90° is first considered.
If the base stations are densely distributed, the antennas are selected by
referring to the principles for selecting base station antenna in urban areas.
Omni antennas are not recommended for the purpose of smooth expansion in
the future.
4.4.4 Principles for Selecting Base Station Antenna in Rural Areas
In rural areas, traffic volume is small and base station are sparsely distributed, so
some base stations are required to cover a large area. In this case, the antennas are
selected based on the following principles:
Considering the construction cost, you are recommended to select an omni
antenna for the base stations whose coverage area is small and traffic volume is
low. However, because the gain of the omni antenna is low, the coverage of an
omni antenna is shorter than that of a directional antenna. When the base station
is required to cover a long distance, the directional antenna must be selected to
realize the coverage. Generally, a high gain vertical polarization antenna whose
horizontal half power beam width is 90° is recommended.
One point needs to be noted. That is, if the base station antenna is installed at ahigh position, but the area needs to be covered lies in a low location (the
depression angle is greater than 5°), when an omni antenna is used, the kind
with a preset tilt angle or with zero point filling function are recommended to
improve the coverage quality of this area. In this case, the phenomenon of “blind
under tower” and the signal fluctuation caused by uneven coverage can be
avoided.
4.4.5 Principles for Selecting Base Station Antenna along Highroads
The principles for selecting antennas along highroads are as follows:
For the base stations designed to cover the areas along railways and highroads,
a directional antenna with narrow beams can be selected.
For the base station designed to cover the highroads and the villages scattered
around the highroads, an omni antenna can be selected.
For the base station designed to cover highroads only, an 8-shaped antenna can
be selected, because the 8-shaped antenna help realize the highroad coverage
with only a few base stations.
6/27/2013 All rights reserved Page28 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 29/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
For the base station designed to cover the highroads and the towns on both
sides of the highroads, the antenna whose horizontal half power beam width is
210° can be selected according to actual conditions. It is recommended to givethe priority to the 8-shaped antenna and the 210°antenna for highroads
coverage.
Figure 1.1 shows the application of a 210° antenna.
Figure 1.1 Application of a 210° antenna
Figure 1.2 shows the application of an 8-shaped antenna
6/27/2013 All rights reserved Page29 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 30/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.2 Application of an 8-shaped antenna
4.4.6 Other Considerations for Antenna Selection
Apart from the basic principles for selecting the antenna in different places areprovided in the previous parts, other factors, such as system expansion and
equipment performance, must be considered for antenna selection.
Hereunder is an example:
If the 210° antenna and used to cover the highroads nearby a small town, and only a
cell is used to promise the coverage requirements, you should consider whether the
traffic of this area will increase in the future and whether to meet the expansion
requirements by adding carriers. Generally, once a carrier is added to the base
station, the combiner loss will increase, so the coverage distance will decrease after
the expansion. Therefore, when selecting an antenna, you should consider these
problems beforehand and work out a good plan for the selection of antenna gain and
base station type.
4.4.7 Antenna Selection Reference
Table 1.1 lists the antenna selection references.
6/27/2013 All rights reserved Page30 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 31/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Table 1.1 Antenna selection reference
Landform Station type Reference
Urban areas Directional
station
Generally, select the antennas with low
or medium gains and preset electrical tilt
angle depending on base station density.
An electrical adjustment antenna or
mechanical tilt angle can be selected.
Suburban
areas
Directional
station
Generally, select the antennas with high
gain; both electrical adjustment tilt
antenna and mechanical tilt antenna are
ok.
Plains &
Rural areas
Directional
station
Generally, select the 90° antennas; but
the best choice is the vertical signal
polarization antennas.
Directional
station
Select the antennas with zero point filling
first regardless of tilt angle.
Expressways Directional
station
First select the 8-shaped antennas, and
then consider using the power splitter of
0.5/0.5 configuration; it is preferred to
have zero point filling function.
Directional
station + Omni
station
First consider the 210° antennas, and
then consider using the directional
antenna and omni antenna together.
Mountain
areas
Omni station First consider the antennas with zero
point filling function, and then consider
the antennas with low gain; the antenna
tilt angel is considered last.
Directional
station
First consider the antennas with low gain
and wide vertical beams, and then
consider adding tile angle.
6/27/2013 All rights reserved Page31 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 32/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
4.5 Combiner and Divider Unit
The functions of the combiner and divider unit include: Transmitting and receiving signals
Combining and filtering transmitting signals
Filtering receiving signals
Amplifying and dividing low noise
Providing feeding feeders for tower amplification
Therefore, the combiner and divider unit enables multiple transmitting signals and
receiving signals to share the same antenna unit.
4.5.1 Principles
The combiner and dividing unit has the following detection and alarm functions:
Standing wave detection
When it detects that the standing wave exceeds the preset threshold (1.5:1 or
2.5:1), it gives out alarm signals and indications, thus monitoring the feeder
status.
Low noise amplifier fault alarm
If fault signals are taken from the supporting current of the low noise amplifier, it
generates alarm signals when the current exceeds a certain limit or no current is
generated.
Tower amplification alarm
When the tower amplifier is working, if fault signals are taken from the supporting
current of the tower amplifier, it generates alarm signals when the current
exceeds a certain limit or no current is generated.
Control function
It can control the power attenuation over the major reception path and the
diversity reception paths (the dynamic is 15 dB and step length is 1 dB); it can
drop out the feeder for the tower amplification configuration; and it can select the
feed current for different tower amplifiers.
Take Huawei equipment for example, it can provide three modules for the combiner
and divider unit. They are CDU, SCU, and EDU.
The schematic diagram of CDU is shown in Figure 1.1.
6/27/2013 All rights reserved Page32 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 33/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.1 Schematic diagram of CDU
The schematic diagram of SCU is shown in Figure 1.2.
6/27/2013 All rights reserved Page33 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 34/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.2 Schematic diagram of SCU
The schematic diagram of EDU is shown in Figure 1.3.
6/27/2013 All rights reserved Page34 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 35/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.3 Schematic diagram of EDU
The loss of different combiner and divider unit varies, and it is configured based on
the configuration of actual station types. Theoretically, the insertion loss is 3dB for
each two-in-one combination; and the duplexer insertion loss is about 1dB.
4.5.2 Configuration of Combiner and Divider Unit
This section takes Huawei equipment as an example to explain the configuration of
various combiner and divider units. For details, see Table 1.1.
6/27/2013 All rights reserved Page35 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 36/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Table 1.1 Configuration of combiner and divider unit (take Huawei equipment as an
example)
Number of
carriers for
each cell
Normal
configuration
plan
Large
coverage
configuration
plan
Remark
7 – 8 TRXs 2 CDUs + 2
SCUs
- Large station; mainly
located in urban areas;
seldom applied to large
coverage.
5 - 6TRXs CDU + CDU+ SCU
CDU + CDU +SCU
Applicable to largecoverage configuration
plans; it works when
combined with Huawei
concentric circle
technology.
3 - 4TRXs CDU + SCU 2 CDUs -
1 - 2TRXs CDU EDU or 2
CDUs
Applicable to the sector
with no more than 2
carriers; it will be
replaced during system
expansion.
Note:
The large converge plan is not implemented through adding the number of antennas
and feeders to a cell. In actual networking, according to the coverage and capacity
requirements of different base stations and when the conditions of uplink anddownlink balance are met, you can perform the configuration flexibly and combine the
actual BSC software algorithms to enable the coverage quality to reach the best. For
example, you can adopt the configuration of {feeder + amplifier (40W, 60W, or 80W)},
and adopts the concentric circle control technology applicable to the situation when
the coverage of each carrier in a cell is inconsistent.
6/27/2013 All rights reserved Page36 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 37/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
4.6 Tower Amplifier
In terms of technical principle, a tower amplifier is used to reduce the noise coefficientof the base station receiving system, thus improve the sensitivity of the base station
receiving system.
The contribution of the tower amplifier to uplinks is distinguished according to the low
noise amplifier performance of the tower amplifier itself but not according to its gain
only. If a tower amplifier is installed, the uplink and downlink must be modified and
calculated according to the methods for testing the tower amplifier sensitivity. In
addition, the sub band tower amplifier or the all band tower amplifier should be
selected according to different bands.
The tower amplifier indexes include band, gain, noise coefficient, insertion loss, and
so on.
4.5.2 I. 1Table 1.1 shows the principles of a triplex tower amplifier. This tower
amplifier transmits and receives signals using one feeder, and the bypass function is
present. (Automatic bypass is present when faults occur, and the receiving gain at
this time is about -2dB.)
Figure 1.1 Principles of a triplex tower amplifier
6/27/2013 All rights reserved Page37 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 38/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
4.7 Feeder
The feeder selection is rather important for the whole design of a cellular system.Because the feeder is exposed to outdoors, it must stand the rough environments.
Both the foam and air can be pressed into the feeder as insulation medium. If the air
is used as the insulation medium, short circuit can easily occur, so the air is seldom
used.
I. Feeder selection
Two types of feeders are in common use, namely, 7/8" feeder and 5/4" feeder. They
are selected as follows:
For GSM 900MHz
If the required feeder length is shorter than 80 meters, use the 7/8" feeder;
otherwise use the 5/4" feeder.
For GSM 1800 MHz
If the required feeder length is shorter than 50 meters, use the 7/8" feeder;
otherwise use the 5/4" feeder.
II. Feeder technical indexes
Table 1.1 Technical indexes for feeders in common use
Feeder type 100-meter attenuation (dB) Standing
wave
(Any
length)
- 890MHz 1000MHz 1700MHz 2000MHz -
SYFY-50-22 (7/8") 4.03 - 5.87 6.46 1.15
LDF5-50A (7/8") 4.03 4.3 5.87 6.46 1.15
LDF6-50 (5/4") 2.98 3.17 4.31 4.77 1.15
M1474A (7/8") - 4.3 - 6.6 1.15
HFC22D-A (7/8") - 4.47 - 6.7 1.15
FSJ4-50B (1/2") 11.2 11.9 16.1 17.7 1.15
III. Feefer installation
The feeders to be selected must be the shortest and are easy for installation and
maintenance. The curvature of the feeder must comply with the specifications
6/27/2013 All rights reserved Page38 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 39/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
required by the manufacturers. When the feeder enters the equipment room, its
external conductor must be well grounded regardless of the installation position of the
antenna.
4.8 Distributed Antenna System
With the development of the mobile communication, users have higher requirements
on the quality of service. They hope they can make successful calls anywhere and
anytime. In some places, such as in large buildings, tunnels, underground railways,
where the environments are rather complicated, only outdoor base stations cannot
promise the coverage, which will result in blind spots and conversation break.
Moreover, in some areas where high buildings are densely distributed, the strong
signals from base stations will cause frequent MS handover (ping pong effect) and
remarkable interference. In this case, the conversation may be broken.
To solve the previous problems, you can adopt a distributed antenna system. With the
help of the distributed antenna system, the capacity of abundant cells can be
transferred to other cells; thus the system capacity is well allocated.
4.8.1 Composition Principle of a Distributed Antenna System
Figure 1.1 shows the composition principle of a distributed antenna system. In terms
of function, it is equal to one set of signal polarization antenna connected to a base
station.
Figure 1.1 Composition principle of a distributed antenna system
6/27/2013 All rights reserved Page39 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 40/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
As shown in this figure, the downlink signal from the base station first enters the
distributed antenna system through an interface. Then the power splitter divides the
signal into several tributaries, and the end of each tributary connects to a miniantenna, which has a certain coverage capacity. When a signal is not strong enough,
the bilateral amplifier amplifies the antenna gain. On the contrary, the downlink
signals form each tributary enters the base station through the mini antenna, power
splitter, and bilateral amplifier.
In this system, signals can be transmitted and distributed by one of the following
mediums:
Coaxial cable and RF power splitter
Optical transmission link
Leaky feeder
4.8.2 Types of Distributed Antenna Systems
I. Coaxial cable
The coaxial cable distributed antenna system is often used for indoor coverage. The
design of this type is flexible, the cost is effective and the installation is convenient.
The attenuation of coaxial cable is relatively small, so the antenna selection depends
on coverage area and installation restrictions.
Figure 1.1 shows the coaxial cable distributed antenna system
6/27/2013 All rights reserved Page40 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 41/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.1 Coaxial cable distributed antenna system
II. Leaky feeder
It is better to use leaky cable in narrow and long coverage areas, but load matching (it
can be either load or antenna) is required at the end of the leaky feeder.
Leaky feeder looks like the continuous transverse antenna, so its coverage mainly
depends on its route. The coverage of the leaky feeder is realized by the small
windows provided on coaxial cables, because the signals are radiated to the
coverage areas through these windows.
Figure 1.1 shows the leaky feeder distributed antenna system.
Figure 1.1 Leaky feeder distributed antenna system
Compared to other antenna systems, the leaky feeder antenna system has the
following advantages:
The possibility of signal shadow and barrier is small. For example, if a distributed
antenna is used in a complicated tunnel, the distance between the mobile station
and an antenna may be barred; thus the coverage cannot be promised.
The signal fluctuation is slight. If the leaky feeder is used, the signal fluctuation is
slight in complicated environment.
The multiple service coverage can be provided. The leaky feeder had a wide
working band, so several radio systems can share a leaky feeder. For example,
some radio systems, such as paging system, alarm system, broadcasting
system, and mobile phone system, are often used in tunnels, because these
systems can share a leaky feeder, the antenna installation is simplified greatly.
Compared with the coaxial cable, both the equipment cost and installation
expenditure of the leaky feeder are higher.
6/27/2013 All rights reserved Page41 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 42/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
III. Optical fiber
The fiber distributed antenna system can replace the coaxial distributed antenna
system in some complicated environments where the transmission distance is large.
Generally, the fiber distributed antenna system is more applicable to the base station
designed to cover underground areas such as tunnels, because the space for RF
feeder installation is rather limited.
Figure 1.1 shows the fiber distributed antenna system. The fiber distributed antenna
systems provided by different carriers may be different.
Figure 1.1 Fiber distributed antenna system
The fiber distributed antenna system has the following advantages:
The number of feeders is small for indoor installation.
Thinner feeders are applicable.
Optical fibers can be used to reduce electromagnetic interference.
The design in complicated network is more flexible.
Compared with the coaxial feeder, the transmission loss of the fiber is lower in a short
distance, but the cost is more and it requires local power and automatic detection
equipment.
IV. Summary
The comparison of the previous three types of distributed antenna system is
summarized in Table 1.1.
6/27/2013 All rights reserved Page42 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 43/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Table 1.1 Comparison of distributed antenna systems
Type Advantage Disadvantage
Coaxial cable Flexible design
Cost effective
Realizable
Great loss
Leaky feeder Flexible design High cost
Optical fiber Low loss
Easily installed
High cost
Inflexible design
Power required
4.8.3 Key Technical Indexes for Antenna Components
I. Two-in-one combiner (3dB mixed bridge)
Table 1.1 lists the technical indexes for the combiner.
Table 1.1 Technical indexes for a two-in-one combiner
Index GSM900MHz GSM1800MHz
Working band 890 – 960MHz 1710 – 1880MHz
Port imbalance 0.25dB
Insertion loss 3.6dB
Port standing wave 1.5dB
Power capacity 20W
II. Equal power distributor
The equal power distributor distributes the energy of the base station to several
tributaries. For the purpose of simplifying project design, only two types of equal
power distributor is used in the system. For the technical indexes, see Table 1.1.
6/27/2013 All rights reserved Page43 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 44/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Table 1.1 Technical indexes for an equal power distributor
Index 1-to-2 1-to-4
Working band 800 – 2500MHz
Power distribution
ratio
1:1 1:1:1:1
Insertion loss 3.5dB 6.5dB
Port standing wave 1.5dB
Connector type N_Female
Note:
The insertion loss in this table includes distribution loss.
III. Power coupler
The coupler here refers to bilateral coupler, or unequal power distributor. The coupler
specifications must be selected according to actual project design. For the purposes
of even coverage and energy saving, as more base station signals as possible must
be distributed to each antenna as more as possible.
Table 1.1 lists the technical indexes for the 7dB coupler, 10dB coupler, and 15dB
coupler.
Table 1.1 Technical indexes for a power coupler
Indexes 7dB
coupler
10dB
coupler
15dB coupler
Working band 800 – 2500MHz
Coupling degree 7dB 10dB 15dB
Insertion loss 1.2dB 0.5dB 0.3dB
Port standing wave 1.5
Connector type N_Female
6/27/2013 All rights reserved Page44 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 45/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
For the small-sized indoor coverage, the three types of couplers in this table can meet
the project design requirements. For large scale indoor converge, the truck amplifier
must be used.
IV. Indoor antenna
The antennas used in the distributed antenna system are required to have a low gain
and eye-catching appearance. When selecting an indoor antenna, you should select
the wideband antenna and consider whether it is possible for multiple systems to
share a distributed antenna system.
In tunnels, to enlarge coverage area as much as possible, you can use a directional
antenna along the tunnel direction. Two types of antennas are available. They are
bidirectional antenna and unidirectional antenna.
In tunnels, the advantage of the bidirectional antenna is that it can cover the distance
along the two directions of the tunnel as compared with the unidirectional antenna if
their gain is the same. If you intend to use two unidirectional antennas to cover the
distance along two directions, you should add a power splitter. Therefore, the
bidirectional antenna (8-shaped antenna) is recommended) because this kind of
antenna is cost effective and brings no extra loss.
V. Coaxial connector
Because the length of the feeders used for the indoor distributed antenna system is
determined according on-site requirement, coaxial connectors must be designed for
the feeders. The system uses two types of coaxial connectors.
Table 1.1 lists the technical indexes for a coaxial connector
Table 1.1 Technical indexes for a coaxial connector
Type N type N type
Description Coaxial connector-N type
connector-50Ω/right
angle/male-nut installation-
configured with SYV-50-7-1
Coaxial connector-N type
connector-50Ω/right
angle/female-configured with
7/8”LDF5-50A cable
Feeder
specification
SYV-50-7-1 7/8"
Impedance 50Ω
Standing 1.2
6/27/2013 All rights reserved Page45 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 46/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
wave
VI. Leaky feeder
Hereunder a 7/8" leaky feeder is taken as an example to explain the technical indexes
for a leaky feeder. For details, see Table 1.1.
Table 1.1 Technical indexes for a leaky feeder
Index Description
Characteristic
impedance
50Ω
Attenuation
constant
900MHz: 0.051dB/m; 1800MHz: 0.076dB/m
Coupling loss 900MHz: 72dB; 1800MHz: 84dB; (the loss 2 meters away from
the coupling hole with an error of ±10dB)
Feeder structure
specification
7/8"
Type of supporting
connector
14040121
Fire-proof
performance
Be proof against flames and ultraviolet
VII. Coaxial cable (feeder)
When designing a distributed antenna system, you should use the feeder to connect
all the antenna components. Table 1.1 lists two specifications of feeders in common
use. For the SYV-50-7-1 specification, the cost is low and it is flexible, but the loss is
great; for the LDF5-50A-7/8" specification, the loss is less, but the cost is high and it
is inflexible. The former feeder is more applicable to the tributary connection from
power splitter to antenna, and the later feeder is more applicable to the trunk
connection from one power splitter to another power splitter.
Table 1.1 Technical indexes for a coaxial cable
Index SYV-50-7-1 LDF5-50A-7/8"
6/27/2013 All rights reserved Page46 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 47/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Characteristic
impedance
50Ω 50Ω
Attenuation constant 900MHz; 0.22dB/m
1800MHz; 0.31dB/m
1000MHz: 0.0446dB/m
2000MHz: 0.0659dB/m
Type of supporting N
connector
14040184 14040121
Flexibility Good Poor
VIII. Load
When the leaky feeder is used, a small antenna can be used as the load for its ends,
or the load can be directly used as a match. Table 1.1 lists the technical indexes for
the load.
Table 1.1 Technical indexes for load
Working band 0 to 2GHz
Characteristic impedance 50Ω
Port standing wave < 1.15
Connector type N_Male
Power capacity 2W
4.9 New Antenna Technology—Smart Antenna Overview
4.9.1 Smart antenna
With the rapid development of global communication services, the wireless mobile
communication as the major means of individual communication in the future attracts
people’s great attention. How to eliminate co-channel interference (CCI), multiple
access interference (MAI) and the effect of multi-path effect is a major consideration
on how to improve the performance of a wireless mobile communication system.
The smart antenna adopts the digital signal processing technologies, such as the
switched beam technology and adaptive spatial digital processing technology, to
6/27/2013 All rights reserved Page47 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 48/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
produce space directional beams so that the antenna major beam can aim at the
direction where user signals arrive and the side lobes or zero lobes can aim at the
direction where interference signals arrive. In this case, the mobile used signals canbe efficiently used and the interference signals can be effectively removed and
suppressed.
The smart antenna is mandatory for TD-SCDMA; for WCDMA and CDAM2000, the
smart antenna is optional.
The greatest disadvantage of a traditional base station is that it wastes much radio
signal energy. Therefore, only a small amount of signal energy can reach the
receiving part. Moreover, apart from useful signals, the signals received by a base
station contain interference noises. For the smart antenna, however, it listens to users
signals more effectively and uses signal energy sent to them.Different from the traditional CDAM, FDMA, or CDMA, the smart antenna introduces
SCDMA, which is a four-dimensional multiple access. The SCDMA technology
enables a user to distinguish signals according to their space propagation paths
under same timeslot, same frequency or same address code.
The smart antenna is similar to a space filter, which can reduce the interferences
among user signals remarkably when it is controlled by the parallel antenna beams
aiming at different users. To be specific, the smart improves the performance of the
future mobile communication system in terms of the following aspects:
Enlarge coverage area Reduce interference and enhance system capacity
Enhance spectrum utilization ratio
Improve base station sensitivity
Reduce base station transmit power
Reduce electromagnetic environment pollution
The smart antenna is divided into two types: switched beam antenna and adaptive
antenna, between which the adaptive antenna is the major type.
For realization reasons, the smart antenna is mainly used at base station side.
I. Multiple-beam antenna
The multiple-beam antenna selects the beam that is directed towards a fixed
direction. The base station side selects the beams that can best improve signal
quality and suppress restriction to communicate with the mobile station. The beam
width is determined by the number of array elements.
When a user moves in a cell, the base station selects different beams so as to make
the signals received strongest. Because the user is not necessarily at the center of
the fixed beams, the received signal is poor when the user is at the beam edge. In
6/27/2013 All rights reserved Page48 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 49/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
addition, because, the multiple-beam antenna often selects a beam according to the
maximum receiving power, it cannot adapt itself to adjust the zero suppression
interference of the beams. Therefore, the multiple-beam antenna always cannotreceive the best signals. Compared with the adaptive antenna, however, the multiple-
beam antenna has some advantages, such as its structure is simple and it needs not
judge the arriving direction of user signals.
Figure 1.1 shows the schematic diagram of a multiple-beam antenna.
Figure 1.1 Schematic diagram of a multiple-beam antenna
A multiple-beam antenna consists of a group of low gain antenna array elements,
BFW, and switched beam logical circuit.
II. Adaptive antenna
An adaptive antenna is an antenna array that can change the antenna directional
diagram dynamically according to noise, interference and multi-path effect. It can
monitor users and adjust itself to suppress the zero point interference of the beams
through changing the directional diagram so that it can receive the signal-interference
ratio to the maximum.
Figure 1.1 shows the schematic diagram of an adaptive antenna (for single user).
6/27/2013 All rights reserved Page49 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 50/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.1 Schematic diagram of an adaptive antenna (for single user)
This figures shows the schematic diagram of an adaptive antenna when only one
user is present. When multiple users are present, the situation is far more
complicated. An adaptive antenna consists of the following four parts:
Antenna array
The number (N) and list way of antenna array elements is directly related to the
performance of the adaptive antenna.
Generally, the antenna arrays are listed in three ways: linear equal spacing (LES),
circle equal spacing (CES), and plane equal spacing (PES), among which the LES is
in common use.
The number of array elements is 8 or 16 in actual application.
Analog-to-digital conversion or digital-to-analog conversion
On downlinks, this part converts analog signals to digital signals; on uplinks, this part
converts digital signals to analog signals
BFW
Adaptive digital signal processor
An adaptive antenna can identify the arriving direction of user signals and form a
major beam in this direction. In Figure 1.1, W stands for weight vector, y (t) stands for
output. The y (t) is expressed by the following equality:
6/27/2013 All rights reserved Page50 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 51/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
∑−
=
++=1
1
)()()()( M
j
T
j
T
k
T t nW t S W t S W t y
Where, Sk (t) is the arriving signals of the expected users from the direction θ (k); S j (t)
is the arriving interference signals of other users from the direction θ(j), with the total
number of M-1; n (t) is noise vector; and W is weighting vector.
The adaptive digital signal processor amplifies the expected signal and suppresses
the interference signals and noise signals through selecting a proper weighting vector.
There are two tasks leave for the smart antenna. One is identifying arriving direction
of user signals; the other is realizing the digital matrix. The representative algorithms
for the smart antenna to identify the direction of arrival (DOA) of the signals are Musicalgorithm, RSPRIP algorithm, and maximum likelihood algorithm. The adaptive
beams are shaped for obtaining the best weighting coefficient through adaptive
algorithms.
For which algorithm is selected, adaptive rules must be considered, and the rules in
common use include SINR, MMSE, minimum variance, and maximum likelihood. It
has been proved that the four rules can help the adaptive antenna to obtain the best
weighting coefficient value which has the same stale solution (Wiener solution).
The adaptive algorithms in common use are direct sampling covariance matrix
inversion algorithm (DMI), various minimum mean square algorithms (LMS), recursion
least square algorithm (RLS), and constant model algorithm (CMA).
4.9.2 Smart Antenna Application
I. Omni-directional beam and shaped beam
The functions of the smart antenna are realized through transmitting and receiving
shaped-beams adaptively. A smart antenna transmits and receives shaped-beams
based on the geometric structure of the base station and the user signals required
and received by the system.
In a mobile communication system, the smart antenna adopts shaped-beams on the
uplink signals of each user, which serves to improve the performance of the system
directly. However, if the user is in receiving status and in idle mode, it is impossible for
the base station to know the location of the user. In this case, the base station
performs the transmission using the omni directional beams. For example, the
physical channels, such as the pilot channel, synchronization channel, broadcast
channel and paging channel are available for the omni directional beams.
6/27/2013 All rights reserved Page51 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 52/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
Figure 1.1 shows a base station with the omni directional coverage, and the beams
transmitted on different channels are different. Therefore, the base station must
provide both the omni directional and directional shaped-beams. In this case, theomni directional channels requires much higher transmit power (the possible
maximum transmit power required by the omni directional channels is 101gN dB
higher than that required by dedicated channels, where N stands for the number of
antenna array elements). And this must be considered in system design.
Figure 1.1 Coverage area required by different channels
II. Shared downlink channel and discontinuous
In the mobile communication systems providing IP data services, the multiple user
shared downlink and uplink channels are designed and the discontinuous
transmission technologies are applied between base stations and user terminals.
For the base station using smart antennas, it cannot know the location of the user due
to the user movement. In this case, therefore, the base station can adopt the omni
directional beams only. In addition, the base station can also perform directional
transmission for each user by adding on more access process. Both the two methods
can be used because each method has advantages.
III. Smart antenna alignment
The real time and automatic alignment technology must be applied to the smart
antenna when it is in use. For actual base stations, however, the radio link of each
path cannot necessarily be the same and its performance changes with the time,
working level and environment. If real time and automatic alignment are not
6/27/2013 All rights reserved Page52 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 53/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
performed, downlink shaped-beams will be seriously affected. In this case, the
advantages of the smart antenna are inapplicable, or even the communication failure
will occur.
IV. Frame structure and physical layer technolgy
The application of the smart antenna has no special requirement on the physical layer
technologies of a mobile communication system. Furthermore, the basic payer
technologies, such as modulation and demodulation, spectrum spreading,
interleaving, error correction, and data multiple connection, are completely the same.
If the smart antenna is used, however, the physical layer can be designed in a more
effective way. For example, in a TD-SCDMA system, if the synchronization CDMA
technology is adopted, the receiver can be simplified; if a specified uplink anddownlink pilot timeslots are designed for the physical layer timeslots, the interference
against cell search and random access is reduced. Therefore, all the previous
technologies enable the functions of the smart antenna to be fully played.
V. Combination of the smart antenna with other anti-interference
technologies
At present, the balance between the complexity and the real time realization
possibility of antenna algorithms must be emphasized. Therefore, the practical smart
antenna algorithms can neither handle the multi-path interference, whose delay
excels the width of one chip, nor overcome the channel deterioration caused by the
Doppler Effect.
When the multi-path effect is great, desirable results can be obtained only through
applying the anti-interference digital processing technologies to the smart antenna.
These digital signal processing technologies include joint detection, interference
cancellation, rake receiver. Currently, there are practical algorithms for the
combination of the smart antenna and the technologies of joint detection and
interference cancellation, but the algorithms for the combination of the smart antenna
and the rake receiver technology are still in research.
VI. Problems of beam shapping speed
Due to the mobility of user terminals, mobile communication is time-variable channel.
For the smart antenna, its received signals shape the uplink and downlink beams, so
the TDD period cannot be too long. For example, when a user terminal moves at the
speed of 100km/h higher, the Doppler shift is near to 200Hz, and the location change
reaches 28cm in 10ms. In this case, the location change will be greater than one
6/27/2013 All rights reserved Page53 of 54
7/28/2019 Chapter 4 of GSM RNP&RNO Application of Antenna Feeder System-20060327-A-1.0
http://slidepdf.com/reader/full/chapter-4-of-gsm-rnprno-application-of-antenna-feeder-system-20060327-a-10 54/54
GSM Radio Network Planning and OptimizationChapter 4 Application of Antenna Feeder System
For internal use only
wavelength at 2GHz band, which will cause great error against shaping the downlink
beams. Therefore, the TDD period is expected to be reduced at least by half so that
the interval between transmission and reception can be controlled within 2-3ms. Inthis case, the smart antenna can work normally. If the terminals in this system are
required to move at a higher speed, the TDD uplink and downlink switching period
must be further reduced.
VII. Considerations for equipment complication
The performance of the smart antenna is improved with the increase of the number of
antenna array elements, but the greater the number of antenna array elements, the
more complicated the system is. In this case, the amount of the baseband digital
signals to be processed will increase geometrically. Nowadays, especially becausethe CDMA system is more in favor of wideband, the chip rate is already quite high,
stricter requirements are put forward to microelectronic technologies due to the
complication of baseband processing. As a result, the number of antenna array
elements will not be too great. Currently, the number ranges from 6 to 16.
In addition, the complication of the mobile communication environment causes other
problems for the smart antenna; such as the multi-path effect is great and message
sources generally outnumber antenna array elements.
Due to the characteristic of multiple sources and multiple paths, the followings must
be considered in the research and development of the smart antenna.
Thoroughly understand the mobile communication environment, especially the
space characteristics. To achieve this, you need to rebuild the models for mobile
communication and obtain great experimental results.
Based on the understanding of the characteristics of the mobile environments,
develop new algorithms. And these algorithms must seamlessly cooperate with
mobile communication systems and other radio technologies.
Research the cooperation between the smart antenna and the technologies,
such as power control, multiple user detection, synchronization technology, and
rake receiver technology.
These previous factors must be considered for the purpose of eliminating
interference, balancing, utilizing and improving system performance.