Jun-ichi Takada’s research while affiliated with Institute of Science Tokyo and other places

The knife-edge diffraction (KED) model has been widely used to predict the shadowing effect. In addition to the classical Fresnel KED model using the Fresnel integral, in recent years an alternative expression proposed by mobile and wireless communications enablers for the twenty-twenty information society (METIS), i.e., METIS KED model, has also been used. This letter proposes a mathematical derivation to rigorously prove that, the METIS KED model can be seen as an approximated envelope of the Fresnel KED model. Simulated results agree with the proposal that the METIS KED model is identical to the Fresenl KED model with a low error of 0.19 dB in the shadowed region, and the METIS KED model can be seen as an approximated envelope of the Fresnel KED model with a negligible error of 0.01 dB in the lit region. In addition, based on the connection between the Fresnel and METIS KED models, we propose a threshold for the four-state piecewise linear modeling, which can satisfy the modeling of the shadowing effect at a specific frequency or environment and is the closed form.

The broad bandwidth availability of the sub-Terahertz band enables the next generation of mobile communication systems. Since the high-gain antennas are used to compensate for the severe propagation loss, the communication link depends on the line-of-sight (LoS) channel and suffers from a deep fading when the LoS is shadowed by small objects. This paper proposes a method that estimates the diffraction paths from a complex human body as the ones from the cross-section of the human body. The extracted diffraction paths are used for the uniform theory of diffraction (UTD) simulation. The proposal was evaluated by an indoor measurement (3.3 m) of the human body shadowing channel and a simulation based on the modified edge representation and equivalent edge currents (MER-EECs) method. The proposal was found four times more accurate than the conventional point cloud (PC)-based vertical screen model and available for predicting the Doppler frequencies with complex human motions.

Mirror Kirchhoff approximation (MKA) is a technology to quantify the shadowing effect in the 5^th generation mobile communication systems. However, the conventional MKA using equal interval segmentation is inefficient in computation time since it does not consider the change in the slope of the shadowing object. In this letter, the unequal interval mirror Kirchhoff approximation (UMKA) is proposed to reduce computation time. In the proposal, the unequal internal is designed concerning the change in the slope of the object. The proposed method is validated for circular and elliptical conductor cylinders, which are considered to model the cross-section of the human body. The results show that UMKA achieves less computation time than the conventional MKA in the acceptable error range.

The THz band (0.1-10 THz) is emerging as a crucial enabler for sixth-generation (6G) mobile communication systems, overcoming the limitations of current technologies and unlocking new opportunities for low-latency and ultra-high-speed communications by utilizing several tens of GHz transmission bandwidths. However, extremely high spreading losses and other interaction losses pose significant challenges to establishing wide-area communication coverage, while human body shadowing further complicates maintaining stable communication links. Although point-to-point (P2P) fixed wireless access in the THz band has been successfully demonstrated, realizing fully mobile and reliable wireless access remains a challenge due to numerous issues to be solved for highly directional communication. To provide insights into the design of THz communication systems, this article addresses the challenges associated with THz short-range mobile access networks. It offers an overview of recent findings on the environment-dependence of multipath cluster channel properties and the impact of human body shadowing, based on measurements at 300 GHz using a double-directional high-resolution channel sounder and a motion capture-integrated channel sounder.

This paper presents a trajectory tracking algorithm for high-mobility targets using an extended Kalman smoothing (EKS)-based factor graph (FG). Traditional tracking methods often face challenges in maintaining accuracy and computational efficiency when dealing with fast-moving objects. Leveraging the probabilistic framework of factor graphs and robust estimation of EKS' the algorithm enhances tracking precision for fast-moving objects. Extensive simulations across various motion models demonstrate improved accuracy and robustness. The results indicate that this method effectively addresses the limitations of conventional tracking algorithms' providing a promising solution for applications in aviation' autonomous vehicles' and other domains requiring high-mobility tracking.