Wataru Yamada’s research while affiliated with Nippon Telegraph and Telephone and other places

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Publications (85)


Wideband characteristics of Demmel condition number for 2 x 2 MIMO-OFDM channels
  • Article

May 2004

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18 Reads

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2 Citations

IEICE Transactions on Communications

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W. Yamada

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A. Sato

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S. Uwano

The suitability of a complex MIMO channel matrix for spatial multiplexing is verified experimentally in terms of the Demmel condition number. The instantaneous 2 × 2 MIMO-OFDM channel measurements in several indoor environments indicate the location dependency of the condition number. Wideband frequency characteristics are also analyzed to evaluate the applicability of spatial multiplexing.


Propagation studies for wireless IP access system

January 2002

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7 Reads

Since the line-of-sight path condition between AP (Access Point) and WT (Wireless Terminal) is necessary to provide reliable telecommunication services in WIPAS (Wireless IP Access System), path visibility in a residential area, which is a main service area, is a fundamental parameter for radio zone designing. Effects of precipitation are inevitable for evaluating availability because of its quasi-millimeter band. This paper presents the path visibility that is estimated by ray-tracing techniques using real data from detailed building and terrain databases first. Then, a user capacity is estimated by using the visibility. Secondly, it discusses vegetation attenuation and a building blockage with some measured results. The effectiveness of a reflector plate is demonstrated as an improvement for those shadowed regions by a numerical simulation. For reconsidering the precipitation effect, the nationwide AMeDAS data is analyzed in a viewpoint of rain fade event number and an evaluation method based on a day-unit is discussed. Lastly, building entry loss characteristics are made clear by measurement and computer simulation.


NEW METHOD FOR PREDICTING THE PATH LOSS IN OVER-ROOFTOP PROPAGATION ENVIRONMENTS IN THE MICROWAVE BAND

19 Reads

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Kiyohiko Itokawa

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Wataru Yamada

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[...]

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Hironobu Watanabe

A new method for predicting the path loss in over-rooftop propagation environments in the microwave band is proposed. The path loss due to distance can be divided into three regions in terms of the dominant wave at a mobile station. These regions are the direct wave, reflected wave, and diffracted wave dominant regions, and they compose the proposed path loss model. The method can also deal with polarization. The validity of the model is tested by measuring the path loss at 2.2 GHz and 5.2 GHz (CW) in suburban areas in Tokyo.


Experimental Study on Characteristics of Direction of arrival (DOA) at subscriber station in Non-Line-of-Sight (NLOS) Environment for 5GHz Band Fixed Wireless Access (FWA) Systems

4 Reads

The microwave band fixed wireless access (FWA) systems are expected to operate in non-line-of-sight (NLOS) environments in order to loosen the restrictions on antenna installation at a subscriber station (SS). In addition, it is planning to adopt array antenna at a SS in the next generation FWA. In this case, Direction of arrival (DOA) is a one of the important propagation parameters. We carried out some measurements to obtain characteristics of DOA at SS in suburban area for NLOS-FWA systems. In this paper, we present these measurement results and propose a DOA model for microwave band FWA in NLOS environment.


Path Loss Model with Over-Roof Propagation Paths between Mobile Terminals in a Residential Area
  • Article
  • Full-text available

15 Reads

We propose a path loss model with an over-roof propagation path between mobile terminals in residential areas. A double knife-edge diffraction model shows that over-roof propagation loss can be accurately estimated. Measurement results confirm the estimation accuracy of the new model.

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Citations (45)


... This setup fails to capture the omnidirectional multipath characteristics, where significant multipath rays can arrive from 360° in the azimuth plane, as demonstrated in this study. An exception is the work in [24], which conducted measurements in a real office desk environment within the 110 [31]. However, these studies typically focused on longer-range communications, such as cellular or WLAN-type communications, where the propagation characteristics differ significantly from those in personal office desk environments. ...

Reference:

105 GHz Multipath Propagation Measurement and Comparison with 60 GHz in Office Desk Environment for Ultra-High Speed Sub-THz WPAN Systems
Analysis of Propagation Channel Characteristics in an Indoor Office Environment at 160 GHz
  • Citing Conference Paper
  • June 2024

... The authors of [17] developed a sub-THz massive multipleinput multiple-output (MIMO) channel sounder using 896 antenna elements, offering a high time-spatial channel resolution. The developed channel sounder could determine how many pathways arrived with a lower received power in real time. ...

Sub-Terahertz MassiveMIMO Channel Sounder for 6G Mobile Communication Systems
  • Citing Conference Paper
  • March 2024

... The authors of [7] utilized visual data obtained from multi-view sensing cameras to predict path loss. The authors of [8] utilized side-view images between the transmitter and receiver, along with frequency information, to predict path loss. The work in [9] employed 2D satellite images of the target area as input to a deep neural network to predict path loss distributions at various UAV altitudes. ...

Deep-learning path loss prediction model using side-view images
  • Citing Article
  • October 2023

IEICE Communications Express

... For DOA measurement, methods using array antennas with super-resolution algorithms [4,5] and methods using physically rotating large aperture antennas [6,7] are employed. For frequencies beyond 100 GHz, the first method is not easy to prepare array antennas. ...

Measurement of Multipath Waves at 160 GHz and 300 GHz in an Indoor Conference Room
  • Citing Conference Paper
  • March 2023

... In next-generation mobile communications, the proactive use of millimeter-wave (mm-wave) and terahertz-wave (THz-wave) frequencies, which can secure a wide frequency bandwidth, is anticipated to achieve further high-speed and large-capacity communications. Various studies have reported on the characteristics of path-loss, delay, and direction-of-arrival (DOA) for these frequencies in different scenarios [1][2][3]. ...

Path-loss Characteristics and Modeling for 2-300-GHz bands in Urban Microcell Environment
  • Citing Conference Paper
  • March 2023

... In [74] the imaging method, a variant of ray tracing, is approached with a quantum annealer. Given a number of VOLUME 11, 2023 interactions N and a set of M interaction objects, the problem to be solved is to find the dominant propagation path, i.e., the path that experiences exactly N reflections or diffractions and has minimal propagation loss (PL). ...

Radio Propagation Analysis Using Quantum Annealing
  • Citing Conference Paper
  • December 2022

... Several applications of DNN for the next generation of wireless communication systems (e.g., 6G) have recently emerged [3]. Models utilizing this technique have been proposed for path loss estimation, which is essential for the cell and system design of wireless communications [4,5,6,7]. These models use the convolutional neural network (CNN) as the DNN [5,7], which enables feature quantities (e.g., building profile) to be automatically and internally extracted from input images and utilized for estimation. ...

Deep Learning-Based Path Loss Prediction Using Side-View Images in an UMa Environment
  • Citing Conference Paper
  • March 2022

... Despite promising features, major challenges in the effective usage of higher frequency bands include high free space path loss (FSPL), atmospheric attenuation in gasses and rainfall, and non-line of sight (NLOS) propagation issues, that lead to the degradation of signal-to-noise ratio (SNR) and data rates [11][12][13][14][15]. To solve these issues, high-gain and highly-directive antennas have been commonly used; however, as a result, the beam coverage has become quite narrow, limiting the practicality of such systems. ...

Sub-terahertz propagation characteristics up to 150 GHz for 6G mobile communication systems

International Journal of Microwave and Wireless Technologies

... 10 to 100 times of the current 5G peak rate [4]. The other characteristics encompass remarkable penetrability [5], the capacity to traverse non-metallic materials without inflicting any damage, and the low energy levels that minimize harm to living organisms, thereby facilitating non-destructive testing. ...

Terahertz Propagation Characteristics for 6G Mobile Communication Systems
  • Citing Conference Paper
  • March 2021

... Against the previous methods, Sotiroudis et al. [19] developed a long short-term memory neural network for the prediction of PL with the frequency of 2-26 GHz. Other relevant works adopted DL or ML to predict PL over a channel [20]- [22]. Some of the methods are support vector machine (SVM) [23], random forest [24], and K-nearest neighbors (KNN) [25]. ...

Deep Learning Based Channel Prediction at 2–26 GHz Band using Long Short-Term Memory Network
  • Citing Conference Paper
  • March 2021