arXiv subjects

Kenichi Takizawa

Publications and source records attributed to Kenichi Takizawa.

7 recordsLinked to original sources

arXiv2026

A Two-Element Capsule Antenna for Near-Field Polarization MIMO in Wireless Capsule Endoscopy

Multiple-Input-Multiple-Output (MIMO) technology is considered to be a viable method for spectral efficiency and data rate enhancement in wireless communications. This article presents a two-element capsule antenna with orthogonal current distributions for polarization multiplexing in a wireless capsule endoscopy (WCE) application at 915 MHz. The proposed antenna was evaluated in a MIMO link where it served as the transmitter and an existing on-body antenna was the receiver. The performance was assessed in two distinct environments: an anatomically accurate human body model using full-wave (FW) simulations, and a homogeneous liquid tissue phantom, using both FW simulations and measurements. The former was used to evaluate the performance in a realistic environment and to demonstrate the superiority of the proposed capsule antenna against existing two-element antennas in the literature, while the latter aimed at verifying the antenna design by comparison of simulated and measured MIMO links. We studied channel capacity and eigenvalues for the comparisons. The MIMO link with the proposed antenna provided nearly doubled median channel capacity relative to a baseline single-input-single-output link, consistently in the simulations and measurements. Our results prove the suitability of the proposed antenna for polarization multiplexing and, in terms of channel capacity, establish it as the best conformal two-element capsule antenna design at 915 MHz.

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arXiv2026

Propagation models for IEEE 802.15.6 standardization of implant communication in body area networks

A body area network is a radio communication protocol for short-range, low-power, and highly reliable wireless communication for use on the surface, inside, or in the peripheral proximity of the human body. Combined with various biomedical sensors, BANs enable realtime collection and monitoring of physiological signals. Therefore, it is regarded as an important technology for the treatment and prevention of chronic diseases, and health monitoring of the elderly. The IEEE 802 LAN/MAN Standards Committee approved Task Group TG15.6 in December 2007. As a result of more than four years of effort, in February 2012, TG15.6 published the first international standard for BANs, IEEE Std 802.15.6. Throughout the development of this standard, ample collaboration between the standardization group and the research community was required. In particular, understanding the radio propagation mechanisms for BANs demanded the most research effort. Technical challenges were magnified for the case of implant communication because of the impossibility of conducting in-body measurements with human subjects. Therefore, research in this field had to make use of intricate computer simulations. This article outlines some of the research that has been done to obtain accurate propagation models supporting the standardization of implant communication in BANs. Current research to enhance the channel models of IEEE Std 802.15.6 through the use of ultra wideband signals for implantable devices along with physical measurements in animals is also presented.

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arXiv2022

Experimental Demonstration of Delay-Bounded Wireless Network Based on Precise Time Synchronization

Low latency and reliable information transfer are highly demanded in fifth generation (5G) and beyond 5G wireless communications. A novel delay-bounded wireless media access control (MAC) protocol called Carrier Sense Multiple Access with Arbitration Point (CSMA/AP) was established to strictly ensure the upper boundary of communication delay. CSMA/AP enables collision-free and delay-bounded communications with a simple arbitration mechanism exploiting the precise time synchronization achieved by Wireless Two-Way Interferometry (Wi-Wi). Experimental demonstration and proving the feasibility in wireless environments are among the most critical steps before any further discussion of CSMA/AP and extension to various applications can take in place. In this work described in this paper, we experimentally demonstrated the fundamental principles of CSMA/AP by constructing a star-topology wireless network using software-defined radio terminals combined with precise time synchronization devices. We show that CSMA/AP was successfully operated, even with dynamic changes of the spatial position of the terminal or the capability to accommodate mobility, thanks to the real-time adaption to the dynamically changing environment by Wi-Wi. We also experimentally confirmed that the proposed CSMA/AP principle cannot be executed without Wi-Wi, which validates the importance of precise time synchronization. This study paves the way toward realizing delay-bounded wireless communications for future low-latency and highly reliable critical applications.

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arXiv2018

Range Variation Monitoring with Wireless Two-Way Interferometry (Wi-Wi)

We demonstrated a simple technique for monitoring range variation with millimeter-precision between two remote sites using off-the-shelf wireless communication modules. The need for the flexible positioning of wireless devices is significantly increasing as more devices are being connected and new services are being developed that require devices to collaborate with one another. We showed that one can monitor the distance variation by analyzing the propagation delay of the wireless communication signal between devices. We previously reported a technique for synchronizing clocks with picosecond precision by monitoring the time variation of two rubidium clocks located at remote sites. Precise measurement of the propagation time variation was necessary for precise synchronization of the clocks, and we used this information to estimate the distance with high precision. In a localized situation, our technique makes it easy to implement a millimeter-precision measurement system. Furthermore, it is less complex in terms of system design and can be a low-cost alternative to existing systems that require precise position measurement. We envision that this demonstrated protocol will be implemented in wireless communication chips and microprocessing units.

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arXiv2015

Reflective Network Tomography Based on Compressed Sensing

Network tomography means to estimate internal link states from end-to-end path measurements. In conventional network tomography, to make packets transmissively penetrate a network, a cooperation between transmitter and receiver nodes is required, which are located at different places in the network. In this paper, we propose a reflective network tomography, which can totally avoid such a cooperation, since a single transceiver node transmits packets and receives them after traversing back from the network. Furthermore, we are interested in identification of a limited number of bottleneck links, so we naturally introduce compressed sensing technique into it. Allowing two kinds of paths such as (fully) loopy path and folded path, we propose a computationally-efficient algorithm for constructing reflective paths for a given network. In the performance evaluation by computer simulation, we confirm the effectiveness of the proposed reflective network tomography scheme.

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arXiv2014

Multi-Dimensional Wireless Tomography with Tensor-Based Compressed Sensing

Wireless tomography is a technique for inferring a physical environment within a monitored region by analyzing RF signals traversed across the region. In this paper, we consider wireless tomography in a two and higher dimensionally structured monitored region, and propose a multi-dimensional wireless tomography scheme based on compressed sensing to estimate a spatial distribution of shadowing loss in the monitored region. In order to estimate the spatial distribution, we consider two compressed sensing frameworks: vector-based compressed sensing and tensor-based compressed sensing. When the shadowing loss has a high spatial correlation in the monitored region, the spatial distribution has a sparsity in its frequency domain. Existing wireless tomography schemes are based on the vector-based compressed sensing and estimates the distribution by utilizing the sparsity. On the other hand, the proposed scheme is based on the tensor-based compressed sensing, which estimates the distribution by utilizing its low-rank property. We reveal that the tensor-based compressed sensing has a potential for highly accurate estimation as compared with the vector-based compressed sensing.

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arXiv2014

Synchronization-Free Delay Tomography Based on Compressed Sensing

Delay tomography has so far burdened source and receiver measurement nodes in a network with two requirements such as path establishment and clock synchronization between them. In this letter, we focus on the clock synchronization problem in delay tomography and propose a synchronization-free delay tomography scheme. The proposed scheme selects a path between source and receiver measurement nodes as a reference path, which results in a loss of equation in a conventional delay tomography problem. However, by utilizing compressed sensing, the proposed scheme becomes robust to the loss. Simulation experiments confirm that the proposed scheme works comparable to a conventional delay tomography scheme in networks with no clock synchronization between source and receiver measurement nodes.

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