Page 55 - ITU Journal: Volume 2, No. 1 - Special issue - Propagation modelling for advanced future radio systems - Challenges for a congested radio spectrum

ITU Journal: ICT Discoveries, Vol. 2(1), December 2019

netic (EM) propagation. In our RTS, we set the build- 4. RAY TRACING SIMULATIONS FOR DACM
ing material as one-layer concrete and the terrain as wet
earth. For simplicity, we consider a lat terrain and ne-
glect the afforestation, which is acceptable since it is a typ- A ray tracing simulator, Wireless InSite , is used for the
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ical urban environment. As for the building layout, we fol- radio propagation modeling in this paper. It predicts
low the Recommendation document proposed by the In- radio frequency (RF) signal propagation, as well as EM
ternational Telecommunication Union (ITU) [22]. Three ield in a speci ic environment and offers a list of output
parameters, , , and detailed in Table 1 are used results, including propagation paths between each pair

to generate a virtual random city model. The PDF of the of transmitter and receiver, received signal power, mag-
building height follows a Rayleigh distribution [22] nitude and phase of E- ield, DOA, DOD etc. The major
ray propagation mechanisms are line-of-sight(LoS), re-
ℎ exp( −ℎ 2 2 ) lection and diffraction. Scattering is neglected due to the
(ℎ) = 2 (1)
h
2 building layout and transmission parameters in this case.
Since radio propagation mainly interacts with buildings
where ℎ is the building height in meters. and terrain in the urban environment, the transmission
through objects is also neglected for simplicity. It is rea-
sonable because we are not interested in indoor propaga-
Table 1 – Parameters for generating a virtual random city model
tion, nor indoor-to-outdoor propagation. As a result, our
simulation involves a mixture of LoS and non-line-of-sight
Ratio of land area covered by buildings to total

land area (dimensionless) (NLoS) propagation. Fig. 3 shows a pair of BS and MS in
Mean number of buildings per unit area Melbourne CBD from the ray tracing simulator as an ex-
(buildings/km ) ample. Cubes shaded blue at various height represent the
2
A variable scaling the building height PDF, de- buildings, and the dark green layer at the bottom is the
ined by a Rayleigh distribution given by (1) (di- terrain. The green and red cubes are the BS and the MS re-

mensionless) spectively. In this case, the MS is 600 m away from the BS.
The colorful lines are the propagation paths (rays) from
Fig. 2 shows a Manhattan grid layout for the software- BS to MS. Such colors indicate the power level of each ray.
generated city. Cubic buildings are uniformly distributed Since ℎ MS is identical for all the MS and the terrain is rel-
within a square area with side length m. All buildings atively lat in our environment, there is little variation in
2
share the same square cross-section, × m , and ixed the elevation angle. As a result, we focus more on the az-
street width m. Both and can be obtained from imuth angle . The MS itself is the pole of the local angular
and as = 1000√ , and = 1000 − [23]. coordinate system. The LoS direction from the MS to the

BS is de ined as the angular axis at = 0°, and increases
√
counterclockwise from -180° to 180°.
50
45
60 40
Building Height [m] 40 35
20
30
500 0 25
20
400
15
300
500 10
200 400
300 5
X Axis [m]
100 200
100 Y Axis [m] 0
0
0
Fig. 2 – A virtual random city generated based on ITU-R parameters.
Fig. 3 – The local coordinate system in the ray tracing simulator (simu-
In this paper, we consider not only software-generated lation environment: Melbourne CBD).
virtual city models but also real urban footprints. The
RTS in a real urban environment can give us more prac- TheoutputdatafromRTSisfurtherprocessedbyMatlab .
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tical and reliable insights into the results. We export the We quantify the parameters for the proposed channel
footprints and terrain map of the central business district model from curve itting. The inal veri ication is given by
(CBD) area in Melbourne, Australia from online databases the ray tracing results as well as the numerical results by
[24, 25]. The Melbourne CBD scenario is used for the veri- Matlab Monte-Carlo simulations. A brief process of the
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ication of our proposed directional channel model in sec- methodology of our DACM is shown in Fig. 4.
tion 8.

© International Telecommunication Union, 2019 39