Wataru Yamada's research while affiliated with Nippon Telegraph and Telephone and other places
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Publications (66)
Extreme-high-speed communication exceeding 100 Gbps is one requirement for 6G. To satisfy extreme-high-speed-communication, one solution is to utilize terahertz bands above 100 GHz. To determine the new radio-interface technologies and service frequency bands for 6G, terahertz propagation characteristics above 100 GHz need to be understood. In this...
Extending the frequency range of the Walfisch‐Bertoni (W‐B) model, which is a representative theory‐based model, was investigated. To extend the W‐B model, three changes to the original W‐B model were made: (i) remodeling over rooftop path, (ii) introducing a slant path, and (iii) modeling of multiple reflections between buildings. To validate the...
Path loss in high frequency bands above 6 GHz is the most fundamental and significant propagation characteristic of IMT-2020. To develop and evaluate such high frequency bands, ITU-R SG5 WP5D recently released channel models applicable up to 100 GHz. The channel models include path loss models applicable to 0.5-100 GHz. A path loss model is used fo...
The International Telecommunications Union Radiocommunication Sector (ITU‐R) Study Group 3 identified the need for a number of radio channel models in anticipation of the World Radiocommunications Conference in 2019 when the frequency allocation for 5G will be discussed. In response to the call for propagation path loss models, members of the study...
The user traffic in the mobile communication area has rapidly increased owing to the widespread of smartphones and various cloud services. To handle the increasing traffic, in the fifth-generation mobile communication system (5G), the millimeter-wave multiple-input and multiple-output (MIMO) communication technology is under development. Because th...
This paper proposes a path loss model for crowded outdoor environments that can consider the density of people. Measurement results in an anechoic chamber with three blocking persons showed that multiple human body shadowing can be calculated by using finite width screens. As a result, path loss in crowded environments can be calculated by using th...
This paper presents the characteristics of path loss produced by traffic sign blockage. Multi frequency bands including high frequency bands up to 40 GHz are analyzed on the basis of measurement results in urban microcell environments. It is shown that the measured path loss increases compared to free space path loss even on a straight line-of-sigh...
Before frequencies are allocated to new wireless communication systems, it is important to investigate frequency sharing to avoid interference with existing systems. The International Telecommunication Union Radiocommunication Sector Study Group 3 (ITU-R SG 3) supports activities of other SGs by developing and maintaining recommendations for radiow...
This paper describes analytical results obtained for floor penetration loss characteristics and their frequency dependency by measurements in multiple frequency bands, including those above 6 GHz, in an indoor office environment. Measurement and analysis results confirm that the floor penetration loss depends on two dominant components: the transmi...
NTT Access Network Service Systems Laboratories and NTT DOCOMO have been carrying out joint research and development (R&D) toward construction of the fifth-generation mobile communications system (5G). This article presents a path loss model developed as one of our R&D activities.
Measurement results of path loss characteristics up to 37 GHz band in street microcell environments are described. Ray tracing is used to analyze the effects of building shapes on path loss characteristics at an intersection. A comparison between measured and calculated results clarified the dominant paths in which specular reflection from a chamfe...
This paper proposed that a path loss model for outdoor-to-indoor corridor is presented to construct next generation mobile communication systems. The proposed model covers the frequency range of millimeter wave bands up to 40 GHz and provides three dimensional incident angle characteristics. Analysis of path loss characteristics is conducted by ray...
To design coverage areas for wireless communication systems and evaluate the performance of the systems, it is necessary to develop a path loss model that can be used for the systems' frequency bands. The fifth-generation mobile communication system (5G) is expected to use high frequency bands above 6 GHz. Therefore, developing a path loss model fo...
Regulation is often a key challenge that must be overcome in realizing opportunistic spectrum sharing and white spaces access. The associated nature of spectrum licenses issued to spectrum owners can often constrain the possibility of sharing spectrum in an opportunistic manner, especially if there is no agreement from the "owner" of the spectrum t...
A path loss model based on the Rec. ITU-R P.1411 model, which can cover the frequency range from microwave to millimeter-wave bands, is presented. The path loss characteristics are analyzed on the basis of measurement results obtained using the 2 to 37 GHz band in street microcell environments. It is clarified that the characteristics depend on dis...
In this paper, we report our analysis of path loss variation characteristics in the low millimeter wave band based on measurement results obtained by using 26.365GHz. We analyze the fading scale of the measurement results by applying a wavelet analysis method. It is clarified that a fading of unique scale between the scale of fast fading and shadow...
The aim of this study is to develop an accurate and reliable method to estimate field distributions in train cars so as to advance radio link design of wireless LANs operating inside the cars. This paper describes effects of reflected waves due to tunnel wall and/or train passing on opposite track on propagation characteristics inside the high-spee...
This paper reports the performance analysis of a proposed auto-regressive (AR) model-based linear predictor algorithm with Kalman filtering (KF). The relationship between the optimum AR order and the channel correlation coefficient is investigated by means of the Akaike Information Criterion (AIC). Through our analysis, 2nd-order differential model...
A path loss model for low antenna heights below surrounding buildings in residential areas is presented to contribute to the construction of VHF band wireless systems. The model is constructed on the basis of measurement results at 167.65MHz, near center frequency at VHF band. Path loss characteristics in the middle VHF band are compared to those i...
In this paper, indoor propagation characteristics for TV white space (TVWS) frequency bands are studied. Measurements in the actual indoor environment are performed and described. An indoor propagation model for TVWS is developed, which is useful for evaluating secondary-secondary interference in TVWS scenarios, and its empirical parameters are der...
A new path loss model of interference between mobile terminals in a residential area is proposed. The model uses invertible formulas and considers the effects on path loss characteristics produced by paths having many corners or corners with various angles. Angular profile and height pattern measurements clarify three paths that are dominant in ter...
A new path loss model of interference between mobile terminals in a residential area with a curved road is proposed. On the basis of measurement results, prediction formulas are derived for the attenuation coefficient along a straight road in a non-line-of-sight (NLOS) area. Additional loss resulting from road angles along the curved road is also s...
The applicability to different environment of a proposed path loss model comprising three propagation paths with low antenna height in a residential area is studied. Measurement results show that our model can accurately predict path loss in different building situation.
EMF distributions established in high-speed train cars as experienced by a 5.2 GHz wireless LAN terminal were estimated. Based on field distribution analyses, the energy absorption effects of the passengers' bodies were determined. This absorption cannot be neglected inside train cars. The proposed numerical estimation method can evaluate the degra...
This paper proposes a method for applying interlink correlation to evaluate a multiuser-multiple input multiple output (MU-MIMO) system and describes measurement of a multi-link MIMO propagation channel. The proposed method is validated through comparison of measurement results to those of the conventional MIMO propagation channel model. The result...
When radio areas or systems in wideband wireless communication systems are being planned, a multiple-input multiple-output (MIMO) propagation channel must be considered. This article introduces a technique based on ray tracing that reduces the computational complexity for estimating the MIMO propagation channel. This technique can estimate the MIMO...
This paper presents a propagation model and fading characteristics for a wireless relay system between long-haul train cars under both static and moving conditions. The proposed model is based on the observation results of a measurement campaign using an actual long-haul high-speed train. The measurement results indicate that the propagation loss b...
This paper proposes new techniques to simulate a MIMO propagation channel using the ray-tracing method for the purpose of decreasing the computational complexity. These techniques simulate a MIMO propagation channel by substituting the propagation path between a particular combination of transmitter and receiver antennas for all combinations of tra...
The experimental results of the path loss characteristics for intra-car communications in the 2-GHz band and that for inter-car communications for the 5-GHz band in actual high-speed train cars using the THSR were presented. The measured results for intra-car communications indicated that the path loss in train cars is less than that in free space,...
In this paper, to evaluate the basic performance of MIMO cooperative transmission systems, a simple prediction method which calculation complexity is decreased for evaluating indoor MIMO cooperative transmission is proposed. 5.2 GHz indoor MIMO propagation measurements are carried out in line of sight condition. And the frequency utilization effici...
This paper proposed a novel antenna configuration to achieve 2.4/5 GHz-dual-band WLAN base station antennas with vertically/horizontally dual-polarized omnidirectional radiation pattern in the horizontal plane. The proposed antenna provides a VSWR of 2 in the 2.4-2.5 and 4.9-6-GHz bands and satisfies all the bands required for the IEEE 802.11n stan...
This paper presents a model for the variation in height of the subscriber station (SS) antenna with respect to the path loss for microwave-band wireless access systems. The propagation mechanism that causes the dependency of the height variation characteristics of the received level at an SS on the SS location and operating frequency is clarified i...
The IEEE802.11a standard for indoor wireless LAN systems was released commercially and is wide spread in the marketplace. To achieve higher throughput, IEEE802.11n was proposed and is now undergoing standardization. The MIMO-OFDM technique, which employs multiple antennas for transmission and reception, is the core technology for IEEE802.11n (Foshi...
This paper proposes a novel circular dipole antenna to achieve 2.4/5-GHz dual-band base station antennas with a horizontally-polarized omni-directional radiation pattern in the horizontal plane that satisfies the wide-band requirement for the IEEE 802.11n standard. The structure of the antennas and their fundamental characteristics such as the meas...
It is desirable that the method used for outdoor path loss estimation at microwave frequencies be one for which a worldwide consensus can be obtained through an ITU-R international standard. In this paper, a path loss prediction model for over-rooftop propagation environments is proposed for suburban areas. This model is based on the propagation me...
This paper proposes a 2.4/5-GHz dual-band horizontally-polarized planar antenna for use in a 3-MIMO antenna configuration OFDM wireless LAN (WLAN) system. The proposed antenna provides a voltage standing wave ratio of 2 in the 2.4-2.5 and 4.9-6 GHz bands when printed on a printed circuit board for commercial PCMCIA or WLAN cards and inserted into a...
Wireless LAN cannot give enough throughputs in the non line of sight area. Establishing mesh networking outdoors between access points which covers non line of sight area is one solution that can expand broadband service areas simply and at low cost. The Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) System is...
There have been many studies on the design and development of multi-band antennas for WLAN systems, both in the 2.4 GHz band of IEEE 802.11b/g and in the 5 GHz band of IEEE 802.11a. Many of these studies adopt the approach of using multi-band antennas that support these dual bands, but the bandwidths provided appear to be insufficient. The wide-ban...
Various MIMO-OFDM systems have been studied and various transceiver methods for MIMO systems have been proposed. Most of these systems require estimation of the MIMO channel matrix and calculation of a control parameter to achieve the optimal reception for all sub-carriers. This calculation for all sub-carriers causes an increase in the calculation...
WLAN systems that use the MIMO-OFDM scheme, which enables high-speed transmission of over 100 Mbps, have been developed and are attracting much attention. The paper proposes novel dual-polarized omni-directional antennas as both the base station and personal station antennas for 5.2 GHz-band 2×2 MIMO-OFDM systems. The structure of the proposed ante...
The suitability of a complex multiple-input multiple-output (MIMO) channel matrix for spatial multiplexing (SM) is verified experimentally in terms of the Demmel condition number of the instantaneous MIMO channel matrix. Instantaneous 2×2 MIMO-orthogonal frequency division multiplexing (OFDM) channel measurements in several indoor environments indi...
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...
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 inevitabl...
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 propose...
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...
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.
Citations
... Kuno et al. [49] proposes CNN for the prediction of path loss in communication systems. The propose model applied building side view image and top view image as the typical convention in modeling the path loss. ...
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... • Next-generation video compression techniques that can compress and decompress huge data files in the Metaverse in real time are the need of the hour. The key features of 6G with high bandwidth and URLLC [44] promise is a key enabling technology to realize the high bandwidth requirement of the Metaverse. The use of Edge AI-enabled 6G can also help applications and the Metaverse devices address these issues. ...
Reference: Need of 6G for the Metaverse Realization
... A few deep recurrent networks (DRNN) were found to be used in the prediction of path loss. For example, Sasaki et al. [84] proposed a deep learning method for predicting path loss using the long short-term memory (LSTM) model. The study considered the prediction at frequencies of 2.4, 4.7, and 26.4 GHz. ...
... Because 6G has not been pushing out a wide range of applications and is still in the research stage, there is a vacancy in the next 6G after the success of the development of a wide range of commercial and application. At present, the research direction of 6G mainly includes research on 6G band and bandwidth [1], AI, and 6G communication. This paper mainly studies the application or service industry of 6G in the future by comparing the technical characteristics of 5G. ...
... The modified Warfisch-Bertoni model (W-B model) [13] covering up to millimeter bands is the deterministic model similar to the W-I model, too. This model is also a physical propagation model considering multi-reflective paths between buildings from mainly rear building reflection. ...
... F OR a number of years, the U.S. Federal Communications Commission (FCC) has been investigating opportunities for mid-band spectrum (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) GHz) that would accommodate new broadband technologies [1]. As far back as 2003, the FCC sought stakeholders' comments about a new interference metric to expand unlicensed use in the 6525-6700 MHz band and portions of the 12.75-13.25 ...
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... Nobuaki et al. [59] proposed an AlexNet model of CNN for the prediction of path loss considering diffraction and reflection in an open environment. The model considered transmitter height, the height of the receiver, and distance to the receiver in the nearest line of sight when it is non-line-of-sight. ...
... A model using the Fresnel diffraction method addresses the human body shadowing at 28 GHz [32], and double-edge and multiple-edge methods are applied to calculate the gain in human body shadowing. For a crowded outdoor environment, a body shadowing pathloss [33] is derived from a ray tracing simulation at the frequencies 4.7 GHz and 26.4 GHz. ...
... Most of the time operator demanding signal in shadow fading area is also accounted in this Eq. 1 to observe real signal prediction. Reference distance is another factor to suggest real path loss of signal near the tower for installation engineer [7,8]. Standard deviation is calculated based on received signal strength recorded for different environments using statistical analysis at Mat Lab version 14.6. ...
... A site-specific path loss and clutter loss model was proposed. In [10], an overview of the new developed ITU-R P.2108-0 model was given. Extensive measurements in Aalborg, Gothenburg, and Tokyo were presented. ...
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