Investigation of Channel Properties for 28 GHz

Band in Urban Street Microcell Environments

Minoru Inomata, Tetsuro Imai, Koshiro Kitao, and Yukihiko Okumura NTT DOCOMO, INC. 3-6 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-8536, Japan

Email: minoru.inomata.gn@nttdocomo.com

Abstract - In Japan, field trials on the fifth generation mobile communications system (5G) were started in order to create a new market by actualizing 5G. The 28 GHz band is the most promising candidate for commercial 5G systems. When designing the service area, site-specific channel properties in urban areas are required. Therefore, in this paper, we investigate site-specific channel properties for the 28 GHz band in an urban street microcell environments and clarify that the paths affect the channel properties.

Index Terms — 5G mobile communication system, High frequency bands, Channel properties, Street microcell.

1. Introduction

Development of the fifth generation mobile

communications system (5G) has been actively investigated

[1]-[5]. In Japan, 5G field trials were started in order to

create a new market by actualizing 5G [6]. In 5G, high

frequency bands higher than 6 GHz will be used in order to

provide attractive higher bit rates, and the 28 GHz band is

the most promising candidate for commercial 5G systems in

Japan. It is assumed that the main service areas for 5G using

high frequency bands will be in urban areas. In designing

these service areas, since the propagation characteristics is

difference for every environment, it is important to

understand site-specific channel properties for the 28 GHz

band in urban areas. Regarding the channel properties in high

frequency bands, based on the 5G system requirements,

standardized models have been reported by the 3GPP [4] and

ITU-R [5]. These models are useful in evaluating the

performance of technical specifications. However, when

designing the service area, the site-specific channel

properties is required, and since the standardized models are

generated by statistical processing the measurement data

which is acquired in various sites, site specific channel

properties are not clear in standardized models. Therefore,

we investigate site-specific channel properties for the 28

GHz band in urban street microcell environments. In a 5G

field trial we study on the channel models for path loss,

Doppler characteristics, delay profiles and angular profiles.

Therefore, in this paper, we report the path loss and Doppler

characteristics. We first report on the verification results of

the prediction accuracy based on a comparison between

measurements and prediction results using the representative

model, Rep. ITU-R M.2412 [5]. On the basis of the obtained

results, we clarify that the paths affect the channel properties.

2. Measurement Campaign

The channel properties were measured in an urban area

nearby Tokyo Station, Tokyo, Japan. The streets in the area

are surrounded by tall buildings (approximately ten stories or

40 m). In this paper, we report on the path loss and Doppler

characteristics. The path loss measurements are taken along

routes 1 and 2, as shown in Fig. 1. Route 1 includes non-line

of sight (NLOS) and line of sight (LOS) areas. Route 2 is

only a NLOS street. The Doppler measurements are recoded

along route 3. Route 3 is circular route of 2590 m. The

measurements are taken in the 28 GHz bands for a

commercial 5G system. The transmission (Tx) antennas are

set at a height of 10 m. We used them to transmit continuous

waves. A receiver (Rx) antenna is fixed on the roof of a

measurement car whose height is 2.3 m. The Tx and Rx

antenna radiation patterns are omni-directional.

Fig. 1. Measurement routes.

3. Measurement Results

Fig. 2 shows comparison results between the measurement

results on routes 1 and 2, and the predictions for the ITU-R

M.2412 channel model. We calculated the path loss using

channel model B in an urban microcell (UMi). Fig. 2 shows

that the ITU-R model predictions in the LOS environment on

route 1 are relatively accurate. A quantitative evaluation is

given where median prediction errors are calculated. The

error between the prediction results and measurement results

is approximately 2 dB. However, in the NLOS environments

on routes 1 and 2, Fig. 2 shows that the measured path loss

becomes smaller than that for the prediction results. In this

case, the difference is approximately 7.0 dB lower on route 1,

and 10 dB lower on route 2. In order to the analyze the path

which affects the path loss, on route 3 including the street on

routes 1 and 2, we analyzed the propagation path based on

Doppler characteristics. The Doppler frequency shift, Δf, is

calculated using the following equation

∆𝑓 =𝑣

𝜆cos 𝜃 = 𝑓𝐷 cos 𝜃 (1)

Tx240 m 150 m

221 m196 m

Route 1 Route 2

877 m

396 m

926 m

Route 3

①

② ③

④Rx

[WeB1-1] 2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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where the speed of the mobile station is v (m/s), the

wavelength is λ, θ is the angle of the arrival path, and fD is

the maximum Doppler frequency. From (1), the frequency of

paths from the front of the mobile station is + fD. On the

other hand, the frequency of paths from the back of the

mobile station is - fD. Therefore, the direction of the arriving

path from the front or back of the mobile station can be

obtained based on Doppler characteristics. In particular,

when the mobile station passes through the radio wave

source including the transmitter or scattering objects, the

Doppler spectrum shifts from + fD to - fD. Thus, from the

position of the frequency shift Δf = 0, the position of the

source can be obtained. In the following, in order to clarify

the site-specific channel property, we analyze the

propagation paths in an urban area based on the Doppler

characteristics. Fig. 3 shows the measured Doppler spectrum

and the speed of the measurement car. The measurement car

passed by the base station, moved to ①, ②, ③, and ④ as

shown in Fig. 1(b), and returned to the start position. In the

section up to ①, the maximum peak of the Doppler spectrum

varies from + fD to - fD at the moving distance of

approximately 80 m. This path indicates the direct wave

from the base station. Also, around the base station, there are

many paths that vary from + fD to - fD. Since the frequency

shift is continuous, it is assumed that these paths are

scattered by the objects along the street. Furthermore, we

find that the frequency shift of the paths is greater than the

maximum Doppler frequency, fD, and the power of those

paths is greater than the noise level. It is assumed that

because these paths arrive after multiple scattering by a

moving vehicle on the street, the frequency of the paths is

Doppler shifted multiple times. In the section from ① to ②

and from ③ to ④, the peak of the Doppler spectrum is the

same as fD. Therefore, we find that the dominant path in

these sections is a path that propagates along the street from

intersection ① or ④. From these results, in Fig. 2, the reason

why measurements in the NLOS environment are lower than

the predictions is due to the building shape along the street.

In particular, it is assumed that the building shape in the

intersection significantly affects the path loss as described in

[7]. In the section from ② to ③, the peak of the Doppler

spectrum is not the same as fD. This indicates that the arrival

paths do not propagate from intersection ② or ③, and it is

assumed that the dominant path is the path over buildings or

between buildings.

Fig. 2. Comparison results of path loss.

Fig. 3. Measured Doppler spectrum on route 3.

4. Conclusion

This paper investigated site-specific channel properties for

the 28 GHz band in an urban area. We clarified that the paths

affect the channel properties based on the measured path loss

and Doppler spectrum. We find that direct wave and

scattering from fixed or moving objects affect the channel in

a LOS street, paths along the street that propagate from an

intersection affect the channel in a NLOS cross street, and

paths over buildings or between buildings affect the channel

in a parallel NLOS street. Further measurement using

channel sounder and modeling channel properties base on

these results will be future subjects.

Acknowledgment

This paper includes a part of the results from "The

research and examine the technological requirements for 5th

generation wireless systems that can realize a data

communication speed exceeding 10 Gbps in densely

populated areas" commissioned by The Ministry of Internal

Affairs and Communications, Japan.

References

[1] NTT DOCOMO, INC. “DOCOMO 5G white paper, 5G radio access:

Requirements, concept and technologies,” July 2014.

[2] METIS, Deliverable D1.4, METIS Channel Models, Feb. 2015.

(https://www.metis2020.com/.)

[3] Workshop in conjunction with IEEE Globecom’15, White paper on 5G

channel model for bands up to 100 GHz, Dec. 2015.

(http://www.5gworkshops.com/5GCM.html)

[4] 3GPP TR 38. 901 v14. 1. 1, “Study on channel model for frequencies

from 0.5 to 100 GHz (Release 14),” July 2017.

[5] Rep. ITU-R M.2412-0, “Guidelines for evaluation of radio interface

technologies for IMT-2020,” ITU-R, M Series, Oct. 2017.

[6] http://www.soumu.go.jp/menu_news/s-news/01kiban14_02000297.html

(Japanese edition)

[7] M. Inomata, et al., "Effects of building shapes on path loss up to 37 GHz

band in street microcell environments," 2017 ICCEM, Kumamoto, 2017,

pp. 249-251.

80

90

100

110

120

130

140

15050 60 708090100 200 300 400 500

Path

lo

ss (

dB

)

Tx-Rx distance (m)

ITU-R model

Measurements on route 1

Measurements

on route 2

-1500

-1000

-500

0

500

1000

1500

0 500 1000 1500 2000 2500

Fre

quen

cy Δ

f (H

z)

Moving distance (m)

05

10152025303540

Veh

icle

spee

d (

km

/h)

fD

－ fD

① ② ③ ④

Scattering from objects

along the street

Paths along the street

from the front of the car

Paths along the street

from the back of the car

Scattering from moving

objects on the street

Path

gain

(d

B)

Paths over buildings or

between buildings

Direct

wave

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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