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As society ages, wireless body area networks (WBANs) are expected to increasingly improve the quality of life of the elderly and disabled. One promising WBAN technology is human body communication (HBC), which utilizes part of the human body as a transmission medium. Communication between head-mounted wearable devices, such as hearing aids, is a potential HBC application. To clarify the HBC transmission mechanism between head-mounted wearable devices, this study analyzes the input impedance characteristics of the transceiver electrodes, transmission characteristics, and electric field distributions around and through a detailed head model. The investigation was performed via an electromagnetic field simulation. The signal frequency had less effect on the transmission characteristics and electric field distributions at 10, 20, and 30 MHz. However, the transmission mechanism between the head-mounted wearable devices was influenced by the number of electrodes in the transceiver. Moreover, the transmission characteristics between two-electrode transceivers were improved by impedance matching. Finally, the availability of the proposed system was evaluated from power consumption and human safety perspectives.

In human body communication (HBC) systems, radio-frequency signals are excited in the human body through a wearable antenna comprised of electrodes that are in contact with the surface of the body. The input impedance characteristics of these antennas are important design parameters for increasing transmission efficiency and reducing signal reflection, similar to other wireless circuits. In this study, we discuss variations of input impedance characteristics of a wearable antenna prototype caused by differences among real human subjects. A realistic human arm model is used for simulations, and the analytical results obtained are compared to measured data obtained from real human subjects, in a range from 1 to 100 MHz. The simulations of input impedance characteristics from antennas worn on the wrists of male and female models with dry and wet skin conditions show that the impedance variation between genders is small. The moisture condition of the skin has little influence on frequencies exceeding several MHz. Measurements with a proto-type wearable antenna and 22 real human subjects reveal that HBC is robust against the variations of individual users from the viewpoint of the voltage standing wave ratio. Moreover, a simplified rectangular prism model is proposed to analyze the thickness of body tissues. Comparisons of measured input impedances indicate that individual differences in impedance are mainly due to differences in the thickness of skin and fat layers. The model also enables us to design the antenna prototype without multiple subject experiments.

Human body communication (HBC) is a signal transmission method that uses the human body as a part of the transmission path. The incoming signal through the receiver electrode can be modeled as a signal from a signal source, which consists of the equivalent signal source voltage and output impedance. These values are important parameters for analyzing the transmission characteristics of HBC as well as for designing the front-end circuit of the receiver. In this paper, an equivalent circuit model of signal transmission from a transmitter on the human body to an off-body receiver touched by a finger was constructed. The ground electrode of the transmitter was in contact with the human body. This is a different configuration compared to capacitive HBC configurations that leave the ground electrode floating. The relationship between the received signal voltage and the distance between the transmitter's electrodes, the size of the receiver ground, and the transmitter-receiver distance were evaluated. Results were analyzed by using the equivalent circuit model. The transmitter-receiver distance and the distance between the transmitter's electrodes were both independently related to the equivalent signal source voltage. The receiver ground size which was related to the capacitive coupling between the receiver ground and the human body was related to the equivalent output impedance.

Daily and continuous measurement of glycemia is vital for managing diabetes. To improve a patient's quality of life, we propose non-invasive glycemia monitoring based on bioimpedance. This study aims to investigate the optimal frequency band for bioimpedance-measurement to estimate the blood-glucose level. We clarify the frequency characteristics of the correlation coefficient between blood-glucose level and bioimpedance from the subject experiment. It is found that the frequency band below 40 kHz is a candidate for stable estimation.

Electromagnetic simulation of human body communication (HBC) was conducted to clarify the electric field distribution and signal transmission paths. Signal transmission from a transmitter to a receiver attached on the same person was analyzed by inspecting the distribution of electric field vector. Contribution of the floor was evaluated by comparing the signal transmission with/without the floor. Electric field was analyzed by using not only the vertical but also the horizontal planes for the observation plane in order to better understand the three dimensional distribution. These simulation results show the major signal transmission path in commonly adopted configuration of HBC.

Herein, we studied a multiuser human body communication system that uses multiple human bodies as a transmission channel when assuming data sharing among users. We evaluated electric field distributions around human bodies and transmission characteristics between wearable transceivers through electromagnetic field simulation using whole-body human models. Simulation results showed that the electric field strongly propagates between human bodies via physical contact; however, the contact area between two users has little influence on the electric field. In addition, the dominant control on the transmission characteristics is the position of the receiver.

In this study, a set of transmitter/receiver modules was designed to facilitate human body communication (HBC) between pairs of users. The modules, which use a direct digital synthesizer (DDS) to produce frequency shift keying (FSK) modulated signals at arbitrary frequencies, are compatible with a wide range of systems through the use of a USB port interface. The proposed method was tested by implementing an LED color control system where the HBC modules were paired with a smartphone to successfully transmit color information between a pair of users.

In the fifth generation mobile communication systems, various wireless communication services such as massive machine-type communications (mMTC), ultra-reliable low latency communications (URLLC), and enhanced mobile broadband (eMBB) will be supported. The physical channels (service channels) dedicated to these respective wireless communication services will be multiplexed in a shared system frequency band and these services will have different requirements regarding spectrum efficiency and fairness among terminals. Therefore, appropriate frequency bandwidth assignment to each service channel considering the service requirement, number of terminals, and their channel conditions for all wireless communication services is important to maximize the system performance. In this paper, we define different forms of system throughput for the respective service channels considering different service requirements. Based on a definition of the integrated system throughput that combines the system throughput levels of all service channels, this paper proposes the optimum frequency bandwidth allocation method among service channels to maximize the integrated system throughput. Computer simulation results show the effectiveness of the proposed method.

This paper proposes a low latency hybrid automatic repeat request (HARQ) method that uses the channel state information before channel decoding to address the increased transmission latency resulting mainly from the delay time required for the channel decoding in HARQ. We focus on applying the proposed method to ultra-reliable low latency communication. The proposed method reduces the transmission latency by requesting early retransmission before the channel decoding process is completed. We consider two metrics for deciding the early retransmission request: (1) mutual information (MI) calculated from the signal-to-noise ratio of the received packet and (2) the a priori log-likelihood ratio (LLR) of the coded bits obtained from the signal detection results of the received packet. Simulation results show that the proposed method successfully reduces the transmission latency at the cost of a very small loss in throughput. Between these two metrics, the MI-based method achieves a slightly better tradeoff between the throughput and transmission latency than the LLR-based method.

Human body communication (HBC) is a wireless communication method that uses human body as part of the transmission medium. It uses electrodes instead of antennas to generate electric field around the human body. This electric field forms capacitive couplings between transmitter, receiver, human body, and surrounding environment. Transmission from a transmitter on user's wrist to an off-body receiver touched by the user was investigated. The human body wearing a transmitter was modeled as a signal source connected to the receiver input. The equivalent output impedance is composed of impedance of the human body and the capacitance of the capacitive coupling that is affected by the surrounding environment and the transmitter arrangement. Equivalent output impedance was estimated by maximizing the received signal power by adjusting input resistance of the receiver and by inserting inductance. Three types of transmitter electrodes and two types of receiver stands (wood and steel) were used to evaluate influences on the equivalent output impedance.