Yasushi Takatori’s research while affiliated with Nippon Telegraph and Telephone and other places

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Publications (159)


Channel reservation scheme for network-controlled IEEE 802.11 wireless LANs
  • Article

January 2025

IEICE Communications Express

Junichi Iwatani

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Hirantha Abeysekera

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Yusuke Asai

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Yasushi Takatori

This paper proposes a priority control method utilizing channel reservation for high-priority access points (APs) in IEEE 802.11 wireless LANs. The proposed algorithms are based on a network-controlled channel allocation scheme called RATOP. Computer simulation results demonstrated the positive effect of the proposed scheme on average and minimum throughput in a large area. This paper also proposes an enhanced algorithm that releases reserved channels to improve throughput. An estimation method based on theoretical analysis provides the number of required reserved channels for a given throughput ratio of high-priority APs to low-priority APs.


Frequency Dependence and Propagation Mechanisms of Path Loss in Indoor Environments

October 2024

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8 Reads

IEEE Antennas and Wireless Propagation Letters

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Minoru Inomata

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Wataru Yamada

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[...]

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Tomoaki Ogawa

This paper presents the frequency dependence of the path loss exponent (PLE) based on measurement results of multiple frequency bands in indoor environments and explains the propagation mechanisms that cause frequency dependence. Path loss measurements from 0.8 GHz to 66.5 GHz in two indoor open office environments were used to derive the parameters of a close-in free space reference distance model (CI model) and an alpha-beta-gamma model (ABG model). We revealed that the PLE of the single-frequency CI model tended to decrease with increasing frequency, while the frequency coefficient of the ABG model was smaller than that of the free space loss (FSPL), indicating a different frequency dependence than FSPL in these environments. Furthermore, the propagation mechanisms of the waveguide effect and the first Fresnel zone shielding cause this frequency dependence. Ray-tracing simulations revealed that the PLE becomes large and small in the low- and high-frequency bands, respectively, when the ceiling height is low, consistent with the measurements. The PLE becomes small regardless of the frequency band when the ceiling height is high, indicating frequency dependence along the propagation mechanism in both the ray-tracing simulation and measurement results.


A Multi-Agent Risk-Averse Reinforcement Learning Method for Reliability Enhancement in Sub-6GHz/mmWave Mobile Networks

October 2024

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4 Reads

IEEE Wireless Communications Letters

The problem of enhancing the reliability of packet transmissions in a multi-Access Point (AP) Sub-6 GHz/mmWave integrated network is investigated. The goal is to improve system reliability in terms of average Packet Loss Rates (PLR), while enabling more IoT devices to satisfy their stringent reliability requirements in terms of individual PLR, under dynamically varying mobile environments and without perfect Channel State Information (CSI) knowledge. For this, we propose a multi-agent framework based on Risk-Averse Averaged Q-Learning (RAQL), where APs share partial information through a Centralized Unit (CU) with which they interact. This enables APs to optimize their interface selection locally, while reinforcing their learning process through a global reward function with minimal overhead. Numerical evaluations demonstrate that the proposed method outperforms benchmark risk-sensitive learning in terms of average PLR, number of satisfied users, and convergence speed.







Deep-learning path loss prediction model using side-view images

October 2023

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8 Reads

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3 Citations

IEICE Communications Express

This paper proposes a path loss prediction model based on a convolutional neural network utilizing side-view images to consider over-rooftop propagation, in addition to the top-view images around the receiving station of the conventional model in the urban macrocell environment. The building profile between the transmitting and receiving stations was used for side-view images. In addition, the scalar parameter of frequency was added to the fully connected neural network part as a proposed method to consider frequency characteristics. The model was learned and validated using the measured data, and the estimation error was compared with the conventional model to evaluate its validity. Our findings showed that the RMS error of 12.1 dB using the conventional model was improved to 4.4 dB by the proposed model.



Citations (55)


... 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. ...

Reference:

Multi-Modal Environmental Sensing Based Path Loss Prediction for V2I Communications
Deep-learning path loss prediction model using side-view images
  • Citing Article
  • October 2023

IEICE Communications Express

... 5G is being rapidly deployed around the world and brings its share of new features with even more throughput, reduced latencies opening new possibilities (autonomous cars, industry 4.0, fine control at a great distance...) and an infrastructure that starts to be aware of its environment by adapting its capacities in real time according to the needs or emergencies [24,25]. ...

Wildlife Detection System Using Wireless LAN Signals
  • Citing Article
  • June 2019

NTT Technical Review

... Furthermore, it should also be considered that in the context of network operators, key features such as radio-related key performance indicators, GPS data, and mobility estimation can also be used for finding out about the network infrastructure as well as user mobility data to improve accuracy. The video player can then leverage information provided by the network leading to higher throughput prediction accuracy as described in Cradio [27]. In this paper, the impact of throughput prediction accuracy on the long-term chunk selection mechanism will be shown by comparing six different baselines with different degrees of accuracy: ...

Multi-radio Proactive Control Technology (Cradio®): A Natural Communication Environment where Users Do Not Need to Be Aware of the Wireless Network
  • Citing Article
  • August 2021

NTT Technical Review

... As a multicarrier modulation technique, orthogonal frequency division multiplexing (OFDM) become the core technique for 4G and 5G mobile communication systems due to its advantages such as robustness to inter-symbol interference [2], [3]. OFDM is widely used in many modern communication scenarios such as visible light communications [4] and multiple-input multiple-output communications [5], [6]. One of the major drawbacks of OFDM is its high peak-to-average power ratio (PAPR). ...

Performance Evaluation of Uplink Multiuser MIMO-OFDM System with Single RF Chain Receiver
  • Citing Article
  • Full-text available
  • January 2022

IEEE Access

... Finally, as consumed energy directly stems from the training process, different DNN architectures and methods should be leveraged. For instance, fully connected layers are known to be more energyefficient than convolutional layers[15]. Besides, DNN compression methods such as energyaware pruning for F-MADRL should be investigated to guarantee a high accuracy while meeting the restricted power-budget of IoT devices.Another improvement direction is to incorporate energy harvesting techniques to enhance communication sustainability. ...

Wireless Multi-Interface Connectivity with Deep Learning-Enabled User Devices: An Energy Efficiency Perspective
  • Citing Article
  • January 2022

IEEE Network

... In the literature, references [8][9][10][11][12][13][14][15][16][17][18][19][20][21] discuss dual connectivity enhancement in cellular networks. Reference [8] introduces a radio resource scheduling method to increase spectrum efficiency and achieve fairness for dual connectivity networks. ...

Resource Allocation for Reconfigurable Intelligent Surface Assisted Dual Connectivity

... The RIS with its elements grouped in blocks assisting multiple users has been formulated, and two heuristics have been proposed to solve them in [7]. The user association strategy with the user mobility for RIS-aided multi-beam transmission systems have been considered in [8], and the ON/OFF selection of RIS in a massive RIS aided wireless communications has been proposed in [9]. The resource allocation of RIS-aided dual connectivity has been presented in [10]. ...

Massive distributed IRS aided wireless communication with ON/OFF selection
  • Citing Article
  • September 2021

ITU Journal on Future and Evolving Technologies

... NTT laboratories are researching and developing Cradio ® to solve this complicated problem and achieve a broader range of optimization by linking with various industries and applications other than wireless [4,5]. Cradio ® is shown in Fig. 5, which, as mentioned above, consists of wireless sensing/visualization technology, wireless-network-quality prediction/estimation technology, and wireless-networkdynamic design/control technology. ...

Wireless Technologies toward Extreme NaaS—Multi-radio Proactive Control Technologies (Cradio®)
  • Citing Article
  • October 2021

NTT Technical Review

... This forward link is considered essential to ensure the coherence and high-speed of the technologies needed for the safety and accuracy of these systems and processes. This research is aimed at achieving these stringent communication requirements by enhancing the network performance to support these applications and advance future technologies in these areas [17]. ...

Distributed user-to-multiple access points association through deep learning for beyond 5G
  • Citing Article
  • June 2021

Computer Networks

... In [16], [17], the authors extended the approach presented in [15] and showed that in addition to satellite, images or vector data obtained from OpenStreetMap, a hybrid approach incorporating a simple path loss model helps the NN with learning and offer improved predictive performance and generalisation as compared to pure data-driven approaches (i.e., without the inclusion of path loss models). The work presented in [18] and [19] also employs a combination of CNN and FCNN for path loss predictions whilst [20] integrates both images and environment related parameters as input features. In [21], the work presented in [22], [23] is extended and a hybrid approach is proposed to improve the path loss estimation accuracy. ...

Evaluation of Characteristics for NN and CNN in Path Loss Prediction
  • Citing Conference Paper
  • January 2021