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Introduction
CW test (Continuous Wave test) is an important step of Propagation
Model Tuning. According to the CW test data (including
latitude/longitude and received level) and corresponding Digital
maps, we can get the accurate Propagation Model through
tuning.
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Chapter 2 CW Test Flow
Chapter 3 Analysis of CW Test Data
Chapter 4 Propagation Model Tuning
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Section 3 Purpose of CW Test
Section 4 Basic Principle of CW Test
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Frequencies in different bands have different propagation
characteristics.
The radio waves are distributed in 3Hz ~ 3000GHz. This spectrum is
divided into 12 bands, as shown in the above table. The frequencies
in each specific band present unique propagation features: The
lower the frequency is, the lower the propagation loss will be, the
farther the coverage distance will be, and the stronger the
diffraction capability will be. However, lower-band frequency
resources are stringent and the system capacity is limited, so they
are primarily applied to the systems of broadcast, television and
paging. The higher-band frequency resources are abundant and the
system capacity is large; however, the higher the frequency is, the
higher the propagation loss will be, the shorter the coverage
distance will be, and the weaker the diffraction capability will
be. In addition, the higher the frequency is, the higher the
technical difficulty will be, and the higher the system cost will
be. The band for purpose of the mobile communication system should
allow for both coverage effect and capacity. Compared with other
bands, the UHF band achieves a good tradeoff between the coverage
effect and the capacity, and is hence widely applied to the mobile
communication field. Nevertheless, with the increase of mobile
communication demand, more capacity is required. The mobile
communication system is bound to develop toward the high-frequency
band.
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Magnetic field
Magnetic field
Based on Maxwell equations set:
The variable magnetic field can excite eddy electric field and
variable electric field can also excite eddy magnetic field.
Continuous electromagnetic oscillation (electromagnetic wave) forms
due to mutual excitation of alternating electric and magnetic
field.
The speed of electromagnetic wave only varies with electric and
magnetic characteristics of medium. The propagation speed of
electric microwave in vacuum equals that of light in vacuum.
Light and electromagnetic wave are essentially the same. Light is
electromagnetic wave of a certain wavelength.
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Mountain diffraction wave
Ionosphere refraction wave
(beyond-the-horizon communication path)
Radio wave can be propagated from the transmitting antenna to the
receiving antenna in many ways: perpendicular incidence wave or
ground refraction wave, diffraction wave, troposphere reflection
wave, ionosphere reflection wave, as shown in the diagram. As for
radio wave, the most simple propagation mode between the
transmitter and the receiver is free space propagation. One is
perpendicular incidence wave; the other is ground reflection wave.
The result of overlaying the perpendicular incidence wave and the
reflection wave may strengthen the signal, or weaken the signal,
which is known as multi-path effect. Diffraction wave is the main
radio wave signal source for shadow areas such building interior.
The strength of the diffraction wave is much dependent of the
propagation environment. The higher the frequency is, the weaker
the diffraction signal will be. The troposphere reflection wave
derives from the troposphere. The heterogeneous media in the
troposphere changes from time to time for weather reasons. Its
reflectance decreases with the increase of height. This slowly
changing reflectance causes the radio wave to curve. The
troposphere mode is applicable to the wireless communication where
the wavelength is less than 10m (i.e., frequency is greater than
30MHz).Ionosphere reflection propagation: When the wavelength of
the radio wave is less than 1m (frequency is greater than 300MHz),
the ionosphere is the reflector. There may be one or multiple hops
in the radio wave reflected from the ionosphere, so this
propagation is applicable to long-distance communication. Like the
troposphere, the ionosphere also presents the continuous
fluctuation feature.
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Propagation of Electromagnetic Wave
Ripple in the pond: Energy is propagated around from the source
point and gradually weakens.
Electromagnetic wave is similarly propagated except that (when the
radiation source is isotropically effective ideal point
source):
It is propagated in the form of spherical wave in three-dimension
space.
The propagation media are different, including air, obstacle and
reflector.
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LOS and NLOS
Diffracted wave
Direct wave
NLoS: non-line-of-sight
LoS: line-of-sight
Radio channels vary with user’s position and time.
Multipath scattering and obstruction result in acute changes to
received power.
Slow fading
Shadow: obstructed by barriers
Fast fading
Multipath effect
Fast changes to signal strength at small distance and time
interval
Doppler frequency shift
Explicit diversity
Space diversity
Polarization diversity
Implicit diversity uses signal processing technologies to hide
diversity functions into signals under transmission, such as RAKE
reception technology, interleaving and error code correction.
Regarded as time diversity
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Multipath propagation: Signals on different paths reach the
receiver at different time.
When the receiver fails to distinguish multipath signals,
co-channel interference (CCI) occurs. In the WCDMA system, only the
multipath delay larger than one chip period (0.26µs, 78m) can be
recognized.
Typical value (µs): Open < 0.2, Suburban = 0.5, Urban = 3
Solutions
Example of Doppler effect: A train is passing by you.
Doppler frequency shift in Mobile Communications
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Diffracted wave covers all directions except for barriers.
Diffusion loss is the most serious.
Calculation formula is complicated, varying with different
diffraction constants.
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Indoor signals depend on penetration loss of building.
Signals are different at the indoor window and in the middle of
room.
Building materials have great effect on penetration loss.
The reference angle of electromagnetic wave have great effect
on penetration loss.
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Thick glass: 610dB
Penetration loss of the carriage of the train: 1530dB
Penetration loss of lift: 30dB or so
Loss of thick leaves: 10dB
Penetration Loss
Landform (terrain): mountain, hill, plain, waters, and
vegetation
Clutter: building, road and bridge
Noise: natural noise and artificial noise
Climate: rain, snow and ice (tiny effect on UHF band)
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Type of radio environment
Radio environment is classified as follows, according to ITU-R
P.1411-1 and specific conditions in China.
Propagation environment
Dense urban
Many tall buildings, signals fail to diffract from the roof of
building .
Urban
Signals can diffract from the roof due to low buildings and wide
streets.
Suburban
Mountainous areas
Type of other new cells, such as Mini-cell…
Cell type
Cell type
Micro-cell
Pico-cell
<100m
Installed outdoors or indoors, lower than height of all roofs
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Section 3 Purpose of CW Test
Section 4 Basic Principle of CW Test
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Radio Propagation Model
Propagation model is used to predict the effect of terrain,
obstacle and artificial environment on the path loss.
WCDMA common propagation models
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Common propagation models
Radio Propagation Model
+ K5log(d)×log(HTxeff) + K6(HRxeff) + Kclutterf(clutter)
d: distance between Tx antenna and Rx antenna (m)
K3: multiplier factor of log(HTxeff)
HTxeff: effective height of Tx antenna (m)
K4: multiplier factor of diffraction loss, which must be a positive
value
Diffraction loss: diffraction loss through the path with barriers
(dB)
K5: multiplier factor of log(HTxeff)log(d)
K6: multiplier factor of HRxeff
HRxeff : effective height of Rx antenna (m)
Kclutter: multiplier factor of for f(clutter)
f(clutter): average weighted loss caused by clutter
Model in U-Net:
Section 3 Purpose of CW Test
Section 4 Basic Principle of CW Test
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Purpose of CW Test
Compare CW test data with prediction results, and then tune the
propagation parameters to improve the accuracy of coverage
prediction.
GPS
Section 3 Purpose of CW Test
Section 4 Basic Principle of CW Test
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Typification
The CW test data must represent the characteristic of
electromagnetic wave in this area.
Balance
The CW test data must represent the characteristic of
electromagnetic wave by the proportion of different clutters in
this area.
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Chapter 2 CW Test Flow
Chapter 3 Analysis of CW Test Data
Chapter 4 Propagation Model Tuning
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Section 3 Drive Test
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Principles of site selection
Number of sites: It is usually agreed that a minimum of 5 sites
should be tested in large and dense city, but one site is enough in
normal city, which mainly depends on antenna height and EIRP.
Representation: Site selection should aim to cover all types of
clutter (from the digital map) in the coverage zone.
Multiple models: Define the corresponding zone of each model if the
test environment requires multiple models to describe its
propagation characteristics.
Overlap: Increase measurement overlap area between each site as
much as possible. But reasonable inter-site distance should be
ensured.
Obstacle: The data should be filtered in the subsequent processing
if obvious obstacle exists.
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a. Antenna height should be greater than 20m.
b. The antenna should be 5m higher than the nearest obstacle.
c. The obstacle mainly refers to the highest building on the roof
where the antenna is installed. The building where the site is
located should be higher than average height of surrounding
buildings.
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Section 3 Drive Test
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Tx subsystem: Tx antenna, feeder, high-frequency signal source and
antenna holder
Rx subsystem: test receiver, GPS receiver, test software and
laptop
High frequency signal source
Building Test Platform in Networking
Record the gain of the following parts on signals during
networking:
Tx power of signal source
Loss of RF cable
Gain of Tx antenna
Gain of Rx antenna
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Section 3 Drive Test
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Keep to the following standards to select a test path
Landform: The test route must cover all main landforms in the
area.
Height: The test route must cover landforms with different height
in this area if the landforms are up-and-down.
Distance: The test route must cover different positions from the
site in the area.
Direction: The test points must be consistent on the horizontal and
vertical route.
LengthThe total distance of one CW test should be longer than
60km.
Number of test samples: The more, the better.
Overlap: Overlap the test route in different sites as much as
possible to improve the reliability of models.
Obstacle: Shadow areas behind this wall should be avoided when
antenna signals are obstructed by the wall at a side.
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The maximum vehicle speed: Vmax=0.8λ/Tsample
Delete test results from the sampled data under abnormal
conditions:
Fading over 15~30db without reasonable causes
In tunnels
Under the viaducts
Select test routes from the main lobe coverage area if directional
antennas are adopted for a CW test.
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Chapter 2 CW Test Flow
Chapter 3 Analysis of CW Test Data
Chapter 4 Propagation Model Tuning
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Data to be filtered is as follows:
1. Data tested in the places where GPS is unable to locate
accurately (such as under the overhead rack, in the tunnel).
2. Data obtained when the distance to antenna is too near or
far.
3. Data obtained with too weak signals.
4. Error data caused by inexact AP (antenna pattern).
5. Other data inconsistent with the requirements during the route
design of CW test.
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r(x) = m(x)r0(x)
X: distance
r(x): received signals
r0(x): Raileigh Fading
m(x): local mean value, the combination of long-term fading and
space propagation loss
2L: average length between sampling areas, also called intrinsic
length
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Data Dispersion
The CW test is to obtain the local mean value of each geography
location in some areas as far as possible, i.e. the difference of
r(x) and m(x) should be the minimum value. In this sense, effect of
Raileigh Fading should be excluded.
When the intrinsic length equals 40 wavelength and the number of
sampling points is 50, the difference of test data and actual local
mean value can be less than 1dB according to Lee criteria.
Intrinsic length is average length for binning (2G band is 6 m
long, namely, 40 wavelength)
Since the locating speed of GPS is far lower than the receiving
speed of the receiver, the dispersion processing is required before
the binning.
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Conditions:
There are many test records arranged under each locating point in
time sequence because the receiving speed of the receiver is far
higher than the locating speed of GPS.
The vehicle speed between two locating points is uniform.
The time interval between every two measurement records is the
same.
Processing:
Equally distribute these records to the route section between two
points in time sequence so that there will be sufficient points in
every 6m range on test route.
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Objectives:
Reserve the impact of slow fading but eliminate the fast
fading
Methods:
Method 1: make grids for the whole area with 6m side, perform the
arithmetic average for the data located in each grid, and then take
the grid center as the new location.
Method 2: divide the path into sections in equal interval with 6m
for each, and perform the arithmetic binning for the data in each
section to select some point for the location of mean value.
Tool: CW Data Editor
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Data format imported to UNET is
Format conversion can be implemented manually (saved as .dat
file)
X
Y
CW_Power_List__Freq__Hz
CW_Power_List__Ampl__dBm
Time
Date
X
Y
CW_Power_List__Ampl__dBm
Chapter 2 CW Test Flow
Chapter 3 Analysis of CW Test Data
Chapter 4 Propagation Model Tuning
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Installing network planning software:
UNET is powerful planning and optimization software and model
tuning is only one of its functional modules.
Creating a project
In UNET, perform planning and optimization model tuning based on
each project.
Importing antenna pattern file
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Select the effective antenna height.
Select a calculation method of diffraction loss.
Importing data
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Map correction
GPS locating in CW test usually adopts WGS84 and UTM projection.
However, digital maps in China do not use such projections and
reference plane. Correct digital maps if CW test data does not
correspond to them.
Correction method:
Correct four parameters on rectangular coordinates in a digital map
to realize the optimal match with the test data.
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Setting Filtering
Distance filtering:
Filter the data of which r is less than 150m or r is greater than
3000m.
Signal strength filtering:
Filter the data of which Signal is greater than -40dBm or Signal is
less than -121dB.
Clutter filtering
Filter the Clutter in which sampling points are less than
300.
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Tune such parameters as log(d), log(Heff), Diff, log(d)log(Heff),
Hmeff and Klutter to finally tune SPM propagation model.
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Parameter K
Reference value
Analyze correctness of the acquired model after correction.
Evaluate the correctness of the model with Std Dev, which refer to
the binding degree of the acquired model and actual test
environment.
Make Std Dev less than 8 as much as possible in actual model
tuning, which indicates that the tuned model and actual test
environment are well bound.
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After completing this course, you should be able to master:
Principle and purpose of CW test
Process of CW test
Thank you