Jun-ichi Naganawa

Simulation-Based Scenario-Specific Channel Modeling for WBAN Cooperative Transmission Schemes

Wireless body area networks (WBANs) are an emerging technology for realizing efficient healthcare and remote medicine for the aging society of the future. In order to improve the reliability of WBAN systems and support its various applications, channel modeling and performance evaluation are important. This paper proposes a simulation-based channel modeling for evaluating the performance of WBAN cooperative transmission schemes. The time series of path losses among seven on-body nodes are generated by the finite-difference time-domain method for seven body motions. The statistical parameters of the path loss for all the motions are also obtained. The generated path loss is then applied to the evaluation of the two-hop decode-and-forward relaying scheme, yielding an improvement in transmit power. From the evaluation of body motion, useful insights are obtained such as which relay links are more robust than others. Finally, the proposed approach is validated through comparison with a measurement-based approach.

Antenna De-embedding in FDTD-Based Radio Propagation Prediction by Using Spherical Wave Function

Finite-difference time-domain (FDTD) method is one of the promising approaches for the propagation prediction. However, since the computational domain includes both the antennas and the propagation environment, their coupling prevents evaluating individual contributions to the channel response. As a result, the simulation becomes always specific to the given antenna type or orientation and cannot be reused for other configurations. The simulation also requires the internal structure of the antenna which is often unavailable and/or difficult to be modeled. These problems can be addressed by antenna de-embeddeding which separately models the antenna and the propagation environment, hence the purpose of this paper. In particular, this paper proposes the implementation of spherical-wave-function (SWF) channel modeling using the FDTD method. Instead of modeling the real antenna structures inside the computational domain, the single-mode spherical wave source and the observation points are utilized. The spherical wave source is achieved by a cubical dipole array. The spherical wave source is first validated, including the investigation of the effects of cell and array size. The narrowband channel response synthesized by the proposed approach is then validated numerically through comparison with the transmission formula in free space and the conventional antenna-embedded simulation in the human shadowing environment as well.

FDTD-based antenna de-embedding in WBAN on-body channel modeling

For designing reliable and low-power wireless body area network (WBAN) systems, channel modeling plays an important role. However, coupling between antennas and a human body hinders from separately modeling their individual contributions. Therefore, this paper proposes an antenna de-embedding scheme that is based on the channel modeling by means of spherical wave functions (SWFs). A preliminary validation is also presented.

Antenna Deembedding in WBAN Channel Modeling Using Spherical Wave Functions

Body area network (BAN) is a fundamental technology to realize future ICT-based healthcare services and applications, where channel modeling plays an important role in designing more reliable BAN systems. The greatest challenge of the WBAN channel modeling is that the antennas operate in proximity to the human body. Near-field interactions between the antenna and the human body make it difficult to distinguish the contribution of the antennas within the channel response, i.e., the antennas are embedded in the channel. As a result, the characterized channels had to be always specific to the given antenna, and antenna optimization is difficult. Therefore, this paper proposed antenna deembedding by applying the spherical wave function channel modeling into the on-body channel. The finite-difference time-domain (FDTD) method was utilized to implement the concept. The proposed implementation was validated against the conventional antenna-embedded simulation. Furthermore, the antenna performance evaluation in terms of mean path gain during a specific body motion was demonstrated as an application. The simplified but practical version of the proposed approach, involving only the fundamental modes, was introduced. The obtained mean path gain was compared with the measurement.

Accuracy of approximated WBAN channel by fundamental modes of spherical wave functions

To design sufficiently reliable wireless body area network (WBAN) system for future health-care, channel modeling plays an important role. Especially from the viewpoint of antenna optimization, the channel modeling approach should be able to de-embed the antenna contribution to the channel response. Two modeling approaches using spherical wave functions (SWFs) and orthogonal dipoles (ODs) have been proposed so far for this purpose, and the simplified form of the SWF channel modeling involving only fundamental modes is equivalent to OD channel modeling. Although the modeling by SWF fundamental modes or the ODs is practical, the accuracy of their channel approximation should be clarified in advance, hence the purpose of this paper. For the analysis of the accuracy, deviated dipole is utilized to model the antennas in finite size which can emit the higher modes. Applying the finite-difference time-domain method to the deviated dipole and the animated human body, the approximated and the exact channel response are obtained. The error due to the approximation is then modeled by log-normal distribution, of which statistical parameters are empirically obtained as the function of either the antenna size or residual power.

Development of a tri-polarized dynamic channel sounder for wireless body area network

Wireless body area network (WBAN) is expected to be utilized in various fields such as health-care. One of its vital challenges is that dynamic channels suffer severely from fading. Therefore the characterization of WBAN channel is important and many researches have been done in this area. This paper presents a tri-polarized dynamic WBAN channel sounder to realize 3×3 dynamic channel measurement by applying time division multiplexing (TDM), and by using two tri-polarized dielectric resonator antennas (DRAs) and a multi-port oscilloscope. Due to the tri-polarized property of DRA, this present system can contribute to the antenna polarization dependency of WBAN channel as well as the measurement-based antenna de-embedding. In this paper, system configuration, parameter design, DRA antenna, calibration method, and measurement validation are presented.

Voxel model construction by kinect for propagation channel simulation

Study of the radio propagation channel is essential to design a reliable wireless system, especially in the Body Area Network (BAN) which will be used for medical/healthcare purposes. In the simulation of the BAN channel, various postures and motions of the human body should be examined for robustness. However, generating this motion data consumes time and is costly since experience with 3D animation software or complex motion capture systems with multiple cameras is required. Therefore, this paper proposes the utilization of Kinect, a motion capture gaming device, for the BAN channel simulation. The data from Kinect, namely the series of joints, depth, and image are converted into series of voxel models. Then, finite-difference time-domain (FDTD) simulation using the generated voxel models is performed.