A Simplified Analytical Urban Propagation Model (UPM) For Use in CJSMPT
Chrysanthos Chrysanthou
US Army RDECOM/CERDEC/S&TCD
Fort Monmouth, NJ 07703
January 2008
Unclassified
6/9/2008 CERDEC-001.2
Urban Propagation ModelUrban Propagation Model
• Need for a fast Urban Propagation Model (UPM) appropriate for the interference and de-confliction analysis in Coalition Joint Spectrum Management Tool (CJSMPT)- Capability to address mobile-to-mobile applications - Capability to use data as input parameters for the UPM
that represents the actual urban environment under analysis
- Minimal computational time and complexity• No commercially available urban propagation models have such capabilities
• This work was a product of collaboration with Penn State University
6/9/2008 CERDEC-001.3
Shortcomings of Current Urban Propagation ModelsShortcomings of Current Urban Propagation Models
• Most of the existing urban propagation models are designed for cellular applications
- Base antennas much higher than rooftops
» Okumura-Hata (Empirical), Walfisch-Ikegami (Semi-Empirical)
- Not applicable for antennas lower than rooftops (mobile to mobile case)
• Urban propagation is primarily influenced by urban parameters such as building heights and road widths
- Different from city to city
- Actual data is not easily accessible
6/9/2008 CERDEC-001.4
Challenges for Urban Propagation Model (UPM)Challenges for Urban Propagation Model (UPM)
• Create a model that is valid for all heights of base antenna relative to rooftop level
- From low-high antennas (mobile) to very high antennas (cellular)
- Implement the software code with minimal computational time and complexity
• Use of actual data that represents the environment under study
6/9/2008 CERDEC-001.5
Input Parameters for UPMInput Parameters for UPM
• UPM requires input parameters such as
- Frequency, transmitter and receiver antenna heights provided from CJSMPT SKR database
- Average values of building height, building separation, and roadwidth» Extracted from Urban Technical Planner (UTP) from US Army
Topographical Engineering Center (TEC) that provides data in shapefiles of key aspects of the urban environment
wBase Antenna
hbs
d
hB
hm
b
ΔhB
ΔhM
Mobile Antenna
6/9/2008 CERDEC-001.6
Methodology for Use of UTP data in UPMMethodology for Use of UTP data in UPM
• A Windows Dynamic Link Library (DLL) is developed in “C” to extract the required data from US Army TEC UTP database for use as primary input parameters for the UPM
• For a given path, described as two WGS-1984 geodetic points, determines appropriate data from the UTP products and computes and returns the UPM primary input parameters for the given path
- Average height of building roofs (meters), average building separation (meters), average road width (meters) and path distance (meters)
hB1w1
b1
w2
b2
hB2
6/9/2008 CERDEC-001.7
Input UTP data into UPM ModelInput UTP data into UPM Model
6/9/2008 CERDEC-001.8
Urban Propagation Model (UPM) ApproachUrban Propagation Model (UPM) Approach
• UPM is based on Bertoni’s book, Radio Propagation for Modern Wireless Systems
- Theoretical approach to determine path loss in urban environments
- Analysis for mobile-to-mobile applications
• Dominant propagation path occurs over rooftops
• Propagation mechanisms that contribute to the path loss
- Free space path loss (PG0)
- Reduction in fields due to multiple diffractions of passed rows of buildings (PG1)
- Reduction due to diffraction from rooftop fields to ground level (PG2)
6/9/2008 CERDEC-001.9
Analysis of Multiple Diffractions over RooftopsAnalysis of Multiple Diffractions over Rooftops
• Three models are used to analyze diffractions over rooftops considering the first Fresnel zone about the ray from the antenna to the last building
• A criterion is used to determine the appropriate model,
- is the width at the first building of the Fresnel zone
bλ• Antenna is above the rooftop level and the first
rooftop is outside the Fresnel zone (gc>1)
- Simplifying formula is usedΔhB
bhg B
cλΔ
=
• Antenna is near the rooftop level and the first rooftop level is within the Fresnel zone (|gc|≤1)- Accurate but complex formula is adopted
• Antenna is below the rooftop level and the Fresnel zone is blocked by the first building (gc>-1)
- Simplifying formula is developed
ΔhB
Fresnel zone
b
bλ
bλ
bλ
6/9/2008 CERDEC-001.10
Modeling PG1 – Transmitter antennas near rooftopsModeling PG1 – Transmitter antennas near rooftops
• A complex formula is used to determine the field reduction factor
• Where M is the number of the buildings
• Then
• At rooftop, QM is 1/M
∑∞
=−=
0,1 )2()2(
!1)(
qqM
qccM Igj
qMgQ π
∑−
=
−−−− −−
+−−
=2
1
1,2,1,1 )1(
)2(2
1)2(2
)1)(1()2(M
n
qnqMqM nM
IM
IM
qMIπ
23
1)2(0,1 MI M =−
∑−
=− −
=1
11,1
23
23 )(
141)2(
M
nM nMn
Iπ
[ ]21 )( cM gQPG =
6/9/2008 CERDEC-001.11
Diffraction losses, PG1, for antenna at rooftopDiffraction losses, PG1, for antenna at rooftop
Rooftop Losses Base antenna height 15 m, RX mobile antenna 2 m,
Building height 15 m, distance between bldgs 50 m, frequency 900 MHz
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
0.1 1 10 100
Distance (km)
Loss
es (d
B)
Ikegami-Walfisch
UPM
6/9/2008 CERDEC-001.12
Modeling PG1 – Transmitter antenna well below rooftopsModeling PG1 – Transmitter antenna well below rooftops
• Mobile-to-mobile scenario where both antennas are below rooftop levels
- Diffraction occurs from transmitter mobile antenna to the first building
hb
d
hB
hm
b
wTransmitter Antenna Mobile Antenna
|θο|
ρoΔhB ΔhM
• A simplifying solution is realized by utilizing the field reduction at the rooftop
• Then
( ) ⎟⎠⎞
⎜⎝⎛
−=
111 22
MDQ o
oe θ
ρ
[ ]22 2 eQPG =
6/9/2008 CERDEC-001.13
Diffraction losses, PG1, for mobile to mobile caseDiffraction losses, PG1, for mobile to mobile case
Rooftop Losses Base antenna height 2m, RX mobile antenna 2 m
Building height 15 m, distance between bldgs 50 m, frequency 900 MHz
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0.1 1 10 100
Distance (km)
Loss
es (d
B) Ikegami-
WalfischUPM
6/9/2008 CERDEC-001.14
Modeling PG1 – Transmitter antennas well above rooftopsModeling PG1 – Transmitter antennas well above rooftops
• A simplifying formula is used to determine the field reduction factor
- Utilized for cellular applications
• Where α is the angle from the horizontal at which an incident plane wave propagates
• Then
32 962.0327.3502.3)( pppp ggggQ +−=
[ ]21 )( pgQPG =
λλα b
dhbg B
pΔ
≈= sin
6/9/2008 CERDEC-001.15
Diffraction losses, PG1, for antenna well above rooftopDiffraction losses, PG1, for antenna well above rooftop
Rooftop Losses Base antenna height 30 m, RX mobile antenna 2 m,
Building height 15 m, distance between bldgs 50 m, frequency 900 MHz
-10.00
-5.00
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
0.1 1 10 100
Distance (km)
Loss
es (d
B)
Ikegami-Walfisch
UPM
6/9/2008 CERDEC-001.16
Construction of UPM Model for Rooftop Losses Building height 15m, distance between bldgs 50m, distance 5km, frequency 900 MHz
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
-15 -10 -5 0 5 10 15
Transmitter Height from Rooftop (m)
Loss
es (d
B)
Below rooftopClose to RooftopAbove rooftopBoundary ConditionBoundary condition
Validation of Multiple Diffraction Analysis in UPMValidation of Multiple Diffraction Analysis in UPM
Fresnel Zone
bλ2
Above RooftopNear Rooftop
Below Rooftop
• Smooth transition from one model to another for the multiple diffraction analysis
- Accurate but complex solution for antennas near the rooftop level
- Simplifying antennas for well below and above the rooftop level
6/9/2008 CERDEC-001.17
Building height 15m, distance between bldgs 50m, distance 5km, frequency 900 MHz
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
-15 -10 -5 0 5 10 15
Transmitter Height from Rooftop (m)
Loss
es (d
B)
UPM ModelIkegami-WalfischDifferences
Comparison of UPM and Ikegami-Walfisch Rooftop LossesComparison of UPM and Ikegami-Walfisch Rooftop Losses
Below Rooftop Near Rooftop Above Rooftop
6/9/2008 CERDEC-001.18
UPM Rooftop Losses vs distanceUPM Rooftop Losses vs distance
RX mobile antenna 2 m, building height 15 m, distance between bldgs 50 m, frequency 900 MHz
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0.1 1 10 100
Distance (km)
Loss
es (d
B)
Antenna at 2 m
Antenna at 15 m
Antenna at 30 m
Losses due to the first rooftop
6/9/2008 CERDEC-001.19
UPM Rooftop Losses vs frequencyUPM Rooftop Losses vs frequency
RX mobile antenna 2 m, distance between antennas 5 km,Building height 15 m, distance between bldgs 50 m
0
10
20
30
40
50
60
70
80
100 300 500 700 900 1100 1300 1500 1700 1900
Frequency (MHz)
Loss
es (d
B)
Antenna at 30m
Antenna at 17m
Antenna at 13m
Antenna at 2m
Antenna at rooftop
Losses due to the first building
6/9/2008 CERDEC-001.20
Diffraction of Rooftop Fields to Ground, PG2Diffraction of Rooftop Fields to Ground, PG2
hB
hm
b
w/2
ρ1
ρ2
ρ4ρ3
• Diffraction down to mobile antenna from buildings immediately near receiver
• Significant contributions are marked 1 – 4 in the illustration below
• Most significant contribution is from diffraction in front of receiver
• Walfisch-Ikegami and Bertoni models are similar for modeling PG2
6/9/2008 CERDEC-001.21
UPM Total Losses vs DistanceUPM Total Losses vs Distance
RX mobile antenna 2 m, Building height 15 m, distance between bldgs 50 m, frequency 900 MHz
80.00
100.00
120.00
140.00
160.00
180.00
200.00
220.00
240.00
0.1 1 10 100
Distance (km)
Loss
es (d
B)
Antenna at 2 m
Antenna at 15 m
Antenna at 30 m
6/9/2008 CERDEC-001.22
Total Losses Difference Between UPM and Ikegami-WalfischTotal Losses Difference Between UPM and Ikegami-Walfisch
RX mobile antenna 2 m, Building height 15 m, distance between bldgs 50 m, frequency 900 MHz
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
0.1 1 10 100
Distance (km)
Loss
es (d
B)
Antenna at 2 m
Antenna at 15 m
Antenna at 30 m
6/9/2008 CERDEC-001.23
Methodology for Selecting the Propagation ModelMethodology for Selecting the Propagation Model
• Software code for selecting automatically the optimal propagation model based on an input flag
- UPM for urban environments and TIREM for rural environments
- Differentiates mixed paths based on input flag• Currently the UPM model is being integrated into CJSMPT under Phase II
6/9/2008 CERDEC-001.24
Flowchart for Selecting the Propagation ModelFlowchart for Selecting the Propagation Model
Is pathin urban area?
NoTIREM Propagation
Model
Retrieve attribute fields that intersect the path
Calculate averageinput parameters
UPM Model
YesUTP Urban Environmental
Data
Calculate Terrain effects
DTEDData
6/9/2008 CERDEC-001.25
Status - Terrain Effects in Urban EnvironmentsStatus - Terrain Effects in Urban Environments
• In collaboration with ACIN Drexel U., a code is currently being developed that considers the impact of terrains effects, e.g., hills, in urban environments using DTED data. The code computes
- The effects of earth curvature and surface along the terrain profile
- Elevations along the given path - Diffraction losses due to isolated edges- Angle of incidence and effective height of base antenna
• The code will be integrated into the UPM
6/9/2008 CERDEC-001.26
ConclusionsConclusions
• The UPM provides the capability for predicting reasonably accurate and fast the path loss in urban environments by- Utilizing data that represents the actual characteristics of
the urban environment- Considering all the suitable scenarios in wireless
networks
