Human Body Communication System Research Articles

EQS-Band Human Body Communication through frequency hopping and MCU-Based transmitter

Human Body Communication (HBC) is an emerging technology that uses the human body as a communication channel. It offers significant advantages over traditional RF techniques in terms of power consumption and security. In recent developments, Electro-quasistatic HBC (EQS-HBC) in the frequency band below 1 MHz has been employed to enable communication without signal radiation beyond the body, effectively turning the body into a wired communication medium. This paper delves into the application of the EQS band for HBC. Experimental results show the determinantal effect of intermittent noise that sporadically disrupts communications across the band of interest. To address this challenge, we introduce an innovative frequency-hopping transceiver system, which allows the transmitter to seamlessly adapt to different frequencies. In addition, we present a miniature transmitter design, incorporating a simplified micro-controller unit (MCU) to facilitate the implementation of HBC. Furthermore, to validate this proposed design, we present a fully functional prototype of an HBC system that effectively employs frequency hopping techniques for practical applications.

Comprehensive review of the human body communication system for wireless body area network applications

Comprehensive review of the human body communication system for wireless body area network applications

Signal transmission analysis in implantable human body communication for abdominal medical devices

Implantable medical devices, such as neurostimulators, need to be wirelessly controlled from outside the body. Many of these devices use high-frequency signals in the 400 MHz, 900 MHz, and 2.45 GHz bands to communicate with external devices. However, high-frequency bands can suffer from signal attenuation in biological tissues and from electromagnetic interference with surrounding devices. In contrast, human body communication (HBC) uses relatively low frequencies in the 3–30 MHz band, which can alleviate signal attenuation and prevent emissions outside the body during communication. In this study, we investigated the use of HBC for implantable medical devices in the abdomen using electromagnetic field simulations. The results showed that the transmission between the transmitter inside the body and the receiver outside the body was adequate for stable communication. However, when the receiver was detached from the skin surface, the transmission characteristics rapidly decreased. Moreover, when the receiver and skin were separated by 1 mm, the transmission degraded by 34 dB, indicating that electromagnetic interference between the implanted transmitter and surrounding devices (including other medical devices) is rare. Finally, we evaluated the proposed system from the perspective of medical electromagnetic compatibility and human safety. The simulation results demonstrated that the radiated emissions and human exposure of the HBC system meet international standards.

Physically Secure Wearable–Wearable Through-Body Interhuman Body Communication

Human body communication (HBC) has recently emerged as an alternative method to connect devices on and around the human body utilizing the electrical conductivity properties of the human body. HBC can be utilized to enable new interaction modalities between computing devices by enhancing the natural interaction of touch. It also provides the inherent benefit of security and energy-efficiency compared to a traditional wireless communication, such as Bluetooth, making it an attractive alternative. However, most state-of-the-art HBC demonstrations show communication between a wearable and an Earth ground–connected device, and there have been very few implementations of HBC systems demonstrating communication between two wearable devices. Also, most of the HBC implementations suffer from the problem of signal leakage out of the body which enables communication even without direct contact with the body. In this article, we present BodyWire which uses an electro-quasistatic HBC (EQS-HBC) technique to enable communication between two wearable devices and also confine the signal to a very close proximity to the body. We characterize the human body channel loss under different environment (office desk, laboratory, and outdoors), posture, and body location conditions to ascertain the effect of each of these on the overall channel loss. The measurement results show that the channel loss varies within a range of 15dB across all different posture, environmental conditions, and body location variation, illustrating the dynamic range of the signal available at the input of any receiver. Leakage measurements are also carried out from the devices to show the distance over which the signal is available away from the body to illustrate the security aspect of HBC and show its effect on the channel loss measurements. For the first time, a through-body interhuman channel loss characterization is presented. Finally, a demonstration of secure interhuman information exchange between two battery-operated wearable devices is shown through the BodyWire prototype, which shows the smallest form factor HBC demonstration according to the authors’ best knowledge.

Nearest Neighbor Classification of Binary Channel States for Secure Human Body Communication

Human body communication (HBC) is a short-range communication technique in which the human body is used as a data transmission channel. Although the HBC was originally proposed for connecting multiple mobile devices, it is also useful for quickly linking mobile and fixed devices. The latter feature can be applied to smart identification of persons. The HBC channel is formed by a capacitive coupling among the body, mobile and fixed devices, and earth. Consequently, if an outsider approaches the HBC system, that person inevitably becomes involved in the system because of the capacitive coupling. In this situation, a mobile device of the outsider accidentally transmits data signals and misidentification occurs. This is a serious problem in terms of communication system security. An effective approach for resolving this problem is to predict whether the outsider is involved in the HBC system based on signal information received by the fixed device. In this paper, we present a method for correctly predicting the existence of the outsider involved in the HBC system based on channel gain features detected by the fixed device. As the problem can be viewed as a binary classification problem, we adopted <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -nearest neighbor method ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -NN), which is a supervised machine learning algorithm, for solving it. A key to correctly execute and evaluate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -NN is to obtain the reliable channel gain data for training and evaluation. We utilized optical devices for correctly measuring the HBC channel gain and acquired 360 samples of the channel gain data. It was demonstrated that error-free classification was possible with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -NN classifier for the 360 samples. We obtained three key findings for reducing classification errors. First, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 1 is best for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -NN classifiers. Second, 1-norm is better than 2-norm for calculating error functions of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -NN classifiers. Third, the preprocessing that include partition and normalization of channel gain data is highly effective.

Spiking Neural Networks-Inspired Signal Detection Based on Measured Body Channel Response

Spiking neural networks (SNNs) are inspired by biological behavior in the neural system processing information by the rate or delay components of discrete spiking signals in a massively parallel manner. Sparse and asynchronous spikes allow event-driven information processes, leading to low power consumption and fast inference. By exploiting these advantageous features of the SNNs, this paper presents a signal detection method for human body communication (HBC), which has recently emerged as an innovative alternative for wireless body area networks using the human body as a signal transmission medium. In particular, binary spike signaling in the SNNs is highly appropriate for application in the digital signal transmission-based HBC systems. The experiments of body channel response measurements using digital training signals show that the body channel characteristics vary with changes in body posture and device location, especially in wearable environments requiring small-sized devices powered by batteries. The proposed SNN structures can enhance communication performance from signal distortions, stemming from the effects of the time-dispersive body channel and bandwidth-limited receive-filter. The proposed SNN-based transmission symbol code detector (STD) can improve about 3.53 dB carrier-to-noise ratio (CNR) at a bit-error-rate (BER) of 10^-6 for a data rate of 1.3125 Mbps, compared to that of a conventional maximum likelihood detector. In addition, the proposed SNN-based preamble detector can secure an approximately 150 wider threshold range than that of a conventional correlator to achieve a detection probability higher than 99% of the frame existence at a CNR of approximately 0dB required for achieving a BER of 10^-6 by the STD.

Toward Understanding the Return Path Capacitance in Capacitive Human Body Communication

Human Body Communication (HBC) utilizes the human body as a conductive channel to enable ultra-low-power secure communication between devices on and around the body. In Capacitive HBC, although the body provides the forward path for communication, the closed loop return path is formed through parasitic coupling of the device's ground plane with the environment. This return path capacitance (CG) is a critical factor in determining the overall HBC channel response. Hence an indepth understanding CG and the key factors affecting its value will enable optimized design of HBC systems. In this brief we provide a detailed analysis of the return path capacitance for wearable devices of different shapes (disc, rectangular) through derivations, simulations as well as experiments. FEM simulation results show that the parasitic capacitance is almost equal to the self capacitance found through theoretical derivations, when the distance of the device to earth's ground is significantly larger than the device dimensions. Independent experiments using an LCR meter and wearable devices, show close correspondence with theory and simulations. The return path capacitance (CG) value, which is in the range of a few pFs for a watch sized wearable, is primarily dependent on the size of the device and almost independent of the distance from earth's ground.

Investigating on the Interferences on Human Body Communication System Induced by Other Wearable Devices.

Human body communication (HBC) has become one of the most energy-efficient candidates for wireless body area network (WBAN) as it uses higher conductivity of human body as transmission media to reduce transmission loss. The use of medical electrodes instead of bulky antennas makes it suitable for biomedical sensors. The IEEE 802.15.6 standard has reserved only one communication channel for HBC centering at 21 MHz with 5.25 MHz bandwidth, which enlarges the probability of the collision and interference when multiple wearable devices locate on the human body. As a result, the error vector magnitude (EVM) of HBC will be affected by the various states of the interference sources. However, none of the previous works has studied the effects of interferences in HBC. In this paper, the interference factors in HBC WBAN systems assisted by actual measurement on human body are investigated. The HBC signal EVM under different interference states are studied, including frequency, power, modulation scheme, symbol rate, and apart distance between interference source and receiver of HBC. Based on the result and analysis, we propose a possible communication scheme for other body nodes to avoid the collision with HBC.

Efficient Autoencoder-Based Human Body Communication Transceiver for WBAN

Human Body Communication (HBC), which utilizes the human body as a communication channel, is a promising communication method for wireless body area networks. In this paper, we use the deep-learning based approach to design and implement a new optimized architecture for HBC system with scalable date rates feature. The proposed transceiver is completely implemented using two deep neural networks, one represents the autoencoder for the transmitter and receiver, and the other for frame synchronization. The proposed autoencoder-based HBC improves block error rate by $2~dB$ compared to the conventional HBC design. In addition, low complexity modules for CRC encoder and decoder, Scrambler and Descrambler, and Preamble/SFD generator are proposed. Implemented under 45nm CMOS technology, the core size of the proposed design is $0.116~mm^{2}$ , and the estimated power is 1.468 mW with a peak data rate of 5.25 Mbps. The energy efficiency ( $E_{b}$ ) of the proposed design is 280 pJ/b that is over 3.5x better than the conventional HBC designs in literature.

A Review on Human Body Communication: Signal Propagation Model, Communication Performance, and Experimental Issues

Human body communication (HBC), which uses the human body tissue as the transmission medium to transmit health informatics, serves as a promising physical layer solution for the body area network (BAN). The human centric nature of HBC offers an innovative method to transfer the healthcare data, whose transmission requires low interference and reliable data link. Therefore, the deployment of HBC system obtaining good communication performance is required. In this regard, a tutorial review on the important issues related to HBC data transmission such as signal propagation model, channel characteristics, communication performance, and experimental considerations is conducted. In this work, the development of HBC and its first attempts are firstly reviewed. Then a survey on the signal propagation models is introduced. Based on these models, the channel characteristics are summarized; the communication performance and selection of transmission parameters are also investigated. Moreover, the experimental issues, such as electrodes and grounding strategies, are also discussed. Finally, the recommended future studies are provided.

Investigation and Modeling of Capacitive Human Body Communication.

This paper presents a systematic investigation of the capacitive human body communication (HBC). The measurement of HBC channels is performed using a novel battery-powered system to eliminate the effects of baluns, cables and instruments. To verify the measured results, a numerical model incorporating the entire HBC system is established. Besides, it is demonstrated that both the impedance and path gain bandwidths of HBC channels is affected by the electrode configuration. Based on the analysis of the simulated electric field distribution, an equivalent circuit model is proposed and the circuit parameters are extracted using the finite element method. The transmission capability along the human body is also studied. The simulated results using the numerical and circuit models coincide very well with the measurement, which demonstrates that the proposed circuit model can effectively interpret the operation mechanism of the capacitive HBC.

Channel Modeling of Miniaturized Battery-Powered Capacitive Human Body Communication Systems.

The purpose of this contribution is to estimate the path loss of capacitive human body communication (HBC) systems under practical conditions. Most prior work utilizes large grounded instruments to perform path loss measurements, resulting in overly optimistic path loss estimates for wearable HBC devices. In this paper, small battery-powered transmitter and receiver devices are implemented to measure path loss under realistic assumptions. A hybrid electrostatic finite element method simulation model is presented that validates measurements and enables rapid and accurate characterization of future capacitive HBC systems. Measurements from form-factor-accurate prototypes reveal path loss results between 31.7 and 42.2 dB from 20 to 150 MHz. Simulation results matched measurements within 2.5 dB. Comeasurements using large grounded benchtop vector network analyzer (VNA) and large battery-powered spectrum analyzer (SA) underestimate path loss by up to 33.6 and 8.2 dB, respectively. Measurements utilizing a VNA with baluns, or large battery-powered SAs with baluns still underestimate path loss by up to 24.3 and 6.7 dB, respectively. Measurements of path loss in capacitive HBC systems strongly depend on instrumentation configurations. It is thus imperative to simulate or measure path loss in capacitive HBC systems utilizing realistic geometries and grounding configurations. HBC has a great potential for many emerging wearable devices and applications; accurate path loss estimation will improve system-level design leading to viable products.

Bit error rate degradation model for time‐delay parameter of co‐channel interference occurring in human body communication

Human body communication (HBC) is a new technology for mobile and wearable devices operating over body area networks. In HBC, the body is used as a medium for transmitting data between devices to replace wired and wireless technologies. This study examines the bit error rate (BER) degradation experienced by HBC systems under the presence of co-channel interference. A degradation model is proposed to estimate the change in BER, and a selective simulation method is proposed to obtain the BER performance with a small exceedance probability and a small number of BER samples.

Empirical Channel Model for Human Body Communication

In this letter, an empirical channel model for human body communication (HBC) is presented based upon impulse response. For a channel model over a wide range of frequencies between 5 and 80 MHz, the amplitude of an impulse response is modeled with a random variable at each sampling point; the random variable is found using empirically obtained impulse responses with respect to multiple subjects of 70 human subjects. This empirical channel model is obtained when a signal transmitter and receiver are located on opposite hands. However, it provides a practical way to estimate the performance of HBC systems within an environment of multiple users and various devices.