• ETRI Journal
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• 제35권5호
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• pp.775-785
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• 2013

Because of their exclusive features, millimeter wave directive mesh networks can be considered for small cell backhaul support in urban environments. For this purpose, a network of closely spaced stations has been considered with very directive line-of-sight links operating in the 60-GHz band. An attempt is made to evaluate channel response and interference behavior in such a network, taking into account the effect of building blockage. A simple grid of building blocks is considered as the propagation environment, and wave propagation is simulated using 2.5-dimensional (2.5D) ray tracing (2D with ground effect) to calculate the received signal at different nodes in the network. The results are compared with free space predictions and used to evaluate interference at all nodes in the channel and describe certain characteristics of links, such as the delay profile and the correlation length.

• 한국통신학회논문지
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• 제42권2호
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• pp.323-330
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• 2017

밀리미터파 대역은 주파수가 30GHz-300GHz이고, 파장이 10mm-1mm인 EHF (Extremely High Frequency) 대역이다. 밀리미터파 대역에서는 장애물이 있는 경우 전파 감쇠가 심하기 때문에 Line-of-Sight (LoS)가 아닌 경우 신호가 잘 잡히지 않는다. 그렇기 때문에 밀리미터파 대역에서 신호 감쇠 측정을 할 경우에 측정 장비가 noise와 구별할 수 없는 신호들이 관찰된다. 이와 같이 감쇠가 심한 환경에서 신호 감쇠 data를 보면 특정한 값에서 제한을 받는 것이 관찰된다. 특정한 값에서 제한 받는 것을 그대로 두고 일반적인 Least square로 추정을 하는 경우에는 감쇠 exponent를 과소평가 할 수도 있다. 본 논문에서는 특정한 값에서 제한을 받아도 정확한 추정이 가능한 Tobit Maximum Likelihood Estimation, Heckman Two-stage Model 그리고 Truncation Regression model의 성능 비교를 하였다.

• ETRI Journal
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• 제42권6호
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• pp.827-836
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• 2020

Measuring the diffraction loss for high frequencies, long distances, and large diffraction angles is difficult because of the high path loss. Securing a well-controlled environment to avoid reflected waves also makes long-range diffraction measurements challenging. Thus, the prediction of diffraction loss at millimeter-wave frequency bands relies on theoretical models, such as the knife-edge diffraction (KED) and geometrical theory of diffraction (GTD) models; however, these models produce different diffraction losses even under the same environment. Our observations revealed that the KED model underestimated the diffraction loss in a large Fresnel-Kirchhoff diffraction parameter environment. We collected power-delay profiles when millimeter waves propagated over a building rooftop at millimeter-wave frequency bands and calculated the diffraction losses from the measurements while eliminating the multipath effects. Comparisons between the measurements and the KED and GTD diffraction-loss models are shown. Based on the measurements, an approximation model is also proposed that provides a simple method for calculating the diffraction loss using geometrical parameters.

• Journal of electromagnetic engineering and science
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• 제18권4호
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• pp.242-247
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• 2018

This paper studies a convenient electromagnetic field (EMF) compliance assessment for base station installations at a millimeter wave (mmW) frequency. We utilize ray-tracing analysis as a numerical method for examining the wave propagation characteristic. Various installation cases are considered and the important parameters with a significant effect on the maximum power density levels are produced. We finally suggest the several scenarios for the convenient assessment of mmW base stations, which allow us to conduct cost effective computational tests compared with the current assessment procedure in the guideline.

• 한국전자파학회논문지
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• 제11권3호
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• pp.410-418
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• 2000

본 논문에서는 27GHz에서 전파환경별 경로손실을 측정하고, 각 수신지점에서 5분간 측정된 경로손실 데이터의 중앙값, 최대값, 최소값을 선형회귀 모델로 모델링하고 분석하였다. 측정 결과를 살펴볼 때, 밀리미터파 대역 가시경로의 경우에도 도심이나 부심 환경에서는 추가의 경로손실을 고려해야 할 것으로 생각된다.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2000년도 종합학술발표회 논문집 Vol.10 No.1
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• pp.233-237
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• 2000

Propagation losses including bath transmission losses and bending losses of the flexible dielectric tube waveguide using commercial polymer substances for a short distance millimeter wave transmission are analytically predicted. The transmission loss and the bending loss are strongly dependent on the power flow distributions in each region. The obtained propagation tosses are compared with those of the commercial metal rigid and flexible waveguides.

• 한국전자파학회논문지
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• 제9권3호
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• pp.410-418
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• 1998

밀리미터파대역의 강우감쇄와 교차편파를 여러 나라의 측정치와 비교하였다. 그리고 국내환경에 적용할 수 있도록 $\tau$분 강우율을 1분 가우율롤 변환할 수 있는 변환모델을 제시하였다. 변환한 국내의 가웅율 데이타를 이요하여, 강우감쇄와 교차편파의 확률분포를 다양한 모델을 이용하여 계산하고, 그 결과를 서로 비교하였다.

• ETRI Journal
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• 제42권1호
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• pp.7-16
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• 2020

Assuming omnidirectional antenna reception, the ITU-R recently developed a new propagation model on building entry loss (BEL) for 5G millimeter-wave frequency sharing and compatibility studies, which is a simplified outdoor-to-indoor path loss model. Considering the utilization of high-gain narrow-beamwidth beamforming, the omnidirectional-based ITU-R BEL model may not be appropriate to predict propagation characteristics for directional beamforming scenarios. This paper studies the effects of beamwidth on the ITU-R BEL model. This study is based on field measurements collected with four different beamwidth antennas: omnidirectional, 10° horn, 30° horn, and 60° horn. The measurement campaigns were conducted at two types of building sites: traditional and thermally efficient buildings. These sites, as well as the measurement scenarios, were carefully chosen to comply with the ITU-R BEL measurement guidelines and the ITU-R building types. We observed the importance of accurate beam alignment from the BEL variation range. We were able to quantify the beamwidth dependency by fitting to a model that is inversely proportional to the beamwidth.

• 한국세라믹학회지
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• 제40권4호
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• pp.350-353
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• 2003

Millimeter-wave dielectric ceramics have been used like applications for ultrahigh speed wireless LAN because it reduces the resources of electromagnetic wave, and Intelligent Transport System (ITS) because of straight propagation wave. For millimeterwave, the dielectric ceramics with high quality factor (Q$.$f), low dielectric constant($\varepsilon$), and nearly zero temperature coefficient of resonant frequency ($\tau$) are needed. No microwave dielectric ceramics with these three properties exist except Ba(Mg$\_$1/3/Ta/sub1/3/)O$_3$ (BMT), which has a little high s: In this paper, alumina (Al$_2$O$_3$) and fosterite (Mg$_2$SiO$_4$), candidates for millimeter-wave applications, were studied with an objective to get high q$.$f and nearly zero $\tau$$\_$f/ For alumina ceramics, q$.$f more than 680,000 GHz was obtained but it was difficult to obtain nearly zero Qf. On the other hand, for forsterite ceramics, q$.$f was achieved from 10,000 GHz of commercial for sterite to 240,000 GHz of highly purified MgO and SiO$_2$ raw materials, and $\tau$$\_$f/ was reduced a few by adding TiO$_2$ with high positive $\tau$$\_$f/.

• ETRI Journal
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• 제38권1호
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• pp.81-89
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• 2016

In this paper, a beam ID preamble (BIDP) technique, where a beam ID is transmitted in the physical layer, is proposed for efficient beam training in millimeter-wave cellular communication systems. To facilitate beam ID detection in a multicell environment with multiple beams, a BIDP is designed such that a beam ID is mapped onto a Zadoff-Chu sequence in association with its cell ID. By analyzing the correlation property of the BIDP, it is shown that multiple beams can be transmitted simultaneously with the proposed technique with minimal interbeam interference in a multicell environment, where beams have different time delays due to propagation delay or multipath channel delay. Through simulation with a spatial channel model, it is shown that the best beam pairs can be found with a significantly reduced processing time of beam training in the proposed technique.