03 WCDMA RNP CW Test and Propagation Model Tuning

1Internal
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
Section 3 Purpose of CW Test
Section 4 Basic Principle of CW Test
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.
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.
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.
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
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.
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)
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
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
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:
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
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.
Section 3 Drive Test
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.
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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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
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.
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.
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.
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.
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
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
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
Select the effective antenna height.
Select a calculation method of diffraction loss.
Importing data
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.
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.
Tune such parameters as log(d), log(Heff), Diff, log(d)log(Heff), Hmeff and Klutter to finally tune SPM propagation model.
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.
After completing this course, you should be able to master:
Principle and purpose of CW test
Process of CW test
Thank you

03 WCDMA RNP CW Test and Propagation Model Tuning

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