Off-body Communication Research Articles

Complex Permittivity and Permeability Studies Viewing Antenna Applications of NBR-Based Composites Comprising Conductive Fillers

The work presents studies on the complex permittivity and permeability of composites based on acrylonitrile butadiene rubber containing combinations of conductive fillers which include carbon black and nickel powder. The properties of those composites, containing each of the fillers at the same amount were compared. The permittivity and permeability values of the composites are influenced remarkably by their morphology and structure as well as by the morphological and structural specifics of both fillers. As electron scanning microscopy studies confirm, those parameters are predetermined by the nature of the composites studied—particle size, particles arrangement in the matrix and their tendency to clustering. Last but not least matrix-filler interface phenomena also impact the characteristics in question. The possibilities for applications of the composites in antennae have been studied, in particular, as substrates and insulating layers in flexible antennae for body centric communications (BCCs). The research results allow the conclusion that these materials can find such applications indeed. Composites of higher conductivity can be used where surface waves are generated to provide on-body communications, while composites of lower conductivity may be used for antennae that will be on the body of a person and will transmit to and receive from other antennas that are not on the body of the same person (off-body communications). It is clear that one can engineer the properties of antennae substrates at microwave frequencies by adjusting the filler content and the type of filler and thus control and tailor the antenna performance specific for a particular application.

Off-Body Spatial Diversity Reception Using Circular and Linear Polarization: Measurement and Modeling

A novel circular polarized (CP) spatial diversity reception scheme is proposed to mitigate the human-body-related fading in off-body communication. Compared with the typical linear polarized (LP) diversity receptions, it seems that the proposed scheme can effectively reduce the root mean square delay spread, multi-path component numbers, and their variations over different persons and measured locations. Both the signal-level models of LP and CP diversity receptions which take the polarization misalignment into consideration are mathematically derived with the help of diversity gain and cross polarized discrimination gain factor. The equal-gain-combination signal levels for CP diversity reception are verified to be around 2.1 dB greater than the LP reception, if the polarization mismatch loss is removed. Furthermore, the great signal-level fluctuation caused by the polarization misalignment effect can be mitigated by introducing CP reception when comparing with LP one. The proposed scheme is expected to be useful for designing robust off-body communications.

Security in Wireless Body Area Networks: From In-Body to Off-Body Communications

Wireless body area networks (WBANs) play a vital role in shaping today’s healthcare systems. Given the critical nature of a WBAN in one’s health to automatically monitor and diagnose health issues, security and privacy of these healthcare systems need a special attention. In this paper, we first propose a novel four-tier architecture of remote health monitoring system and then identify the security requirements and challenges at each tier. We provide a concise survey of the literature aimed at improving the security and privacy of WBANs and then present a comprehensive overview of the problem. In particular, we stress that the inclusion of in vivo nano-networks in a remote healthcare monitoring system is imperative for its completeness. To this end, we elaborate on security threats and concerns in nano-networks and medical implants as well as we emphasize on presenting a holistic framework of an overall ecosystem for WBANs, which is essential to ensure end-to-end security. Lastly, we discuss some limitations of current WBANs.

A Mobility Model for Wearable Antennas on Dynamic Users

This paper presents a mobility model for the variations in position and orientation of wearable antennas on dynamic users, considering walking and running motions. Motion is represented as a composition of a linear forward movement plus a periodic component, modeled by a Fourier series with up to two harmonics. The model is simple, yet realistic, as Motion Capture (MoCap) data are used to calculate its parameters. It is suitable for use with a variety of propagation channel models, including deterministic ray-tracing and stochastic geometry-based ones, but can also allow for analytical inference in simplified scenarios. Considering an off-body communication scenario, simulations show that the proposed mobility model provides similar received power as the skeleton-based model with MoCap data, the maximum difference in the considered scenario being below 1 dB. A significant influence of user’s motion on the channel is observed for both free-space and multipath propagation, yielding received power variations up to 28 dB in the considered scenarios.

Impact of Antenna Topology and Feeding Technique on Coupling With Human Body: Application to 60-GHz Antenna Arrays

The 60-GHz band has been identified as an attractive solution for the next-generation mobile networks (5G) as well as for body-centric applications. This paper provides a quantitative comparative analysis of electromagnetic exposure and heating induced by 60-GHz body-mounted antennas. Near-field interaction between representative antenna arrays for off-body communications with three feeding topologies and human body is compared in terms of matching and radiation, as well as in terms of user exposure. The presence of a ground plane results in exposure reduction by more than 70 and 8 times in terms of peak and averaged levels, respectively. Designs allowing to avoid grating lobes allow further reduction of exposure. For considered antenna arrays operating at the maximum allowable power, International Commission on Non-Ionizing Radiation Protection occupational exposure limits are not exceeded. However, only the antennas with a ground plane comply with general public limits. Resulting heating is quantified for on-body millimeter-wave antennas. Detailed analysis is performed for acute and disperse exposures. Numerical results are validated by measurements. Effect of averaging is also investigated. For antennas with a ground plane, heating (typically of several tenths of °C) remains within environmental temperature fluctuations. However, the antennas without a ground plane can induce heating locally exceeding 10 °C.

Communication Challenges in on-Body and Body-to-Body Wearable Wireless Networks—A Connectivity Perspective

Wearable wireless networks (WWNs) offer innovative ways to connect humans and/or objects anywhere, anytime, within an infinite variety of applications. WWNs include three levels of communications: on-body, body-to-body and off-body communication. Successful communication in on-body and body-to-body networks is often challenging due to ultra-low power consumption, processing and storage capabilities, which have a significant impact on the achievable throughput and packet reception ratio as well as latency. Consequently, all these factors make it difficult to opt for an appropriate technology to optimize communication performance, which predominantly depends on the given application. In particular, this work emphasizes the impact of coarse-grain factors (such as dynamic and diverse mobility, radio-link and signal propagation, interference management, data dissemination schemes, and routing approaches) directly affecting the communication performance in WWNs. Experiments have been performed on a real testbed to investigate the connectivity behavior on two wireless communication levels: on-body and body-to-body. It is concluded that by considering the impact of above-mentioned factors, the general perception of using specific technologies may not be correct. Indeed, for on-body communication, by using the IEEE 802.15.6 standard (which is specifically designed for on-body communication), it is observed that while operating at low transmission power under realistic conditions, the connectivity can be significantly low, thus, the transmission power has to be tuned carefully. Similarly, for body-to-body communication in an indoor environment, WiFi IEEE 802.11n also has a high threshold of end-to-end disconnections beyond two hops (approximatively 25 m). Therefore, these facts promote the use of novel technologies such as 802.11ac, NarrowBand-IoT (NB-IoT) etc. as possible candidates for body-to-body communications as a part of the Internet of humans concept.

Dual-Band Dual-Mode Button Antenna for On-Body and Off-Body Communications.

A dual-band dual-mode button antenna for body centric communications is presented. At the lower band, a spiral inverted-F antenna is designed with omnidirectional radiation pattern for on-body communication. At the upper band, the high-order mode of the inverted-F antenna is utilized together with a metal reflector to realize broadside radiation for off-body communication. For demonstration, a prototype is implemented. The measured peak gains on the phantom at the lower and upper bands are -0.6 and 4.3 dBi, respectively. The antenna operating on the phantom has measured efficiencies of 46.3% at the lower band and 69.3% at the upper band. The issue of specific absorption rate (SAR) is studied. The maximum transmitted power under the SAR regulation of 1.6 W/kg is found to be 26.4 dB·m, which is high enough for body centric communications. In addition, the transmission performance between two proposed antennas mounted on the body is investigated by measuring the transmission loss. With an overall miniaturized size, the robust button antenna could be integrated in clothes and be a potential candidate for wireless body area network applications.

Compact, Highly Efficient, and Fully Flexible Circularly Polarized Antenna Enabled by Silver Nanowires for Wireless Body-Area Networks.

A compact and flexible circularly polarized (CP) wearable antenna is introduced for wireless body-area network systems at the 2.4GHz industrial, scientific, and medical (ISM) band, which is implemented by employing a low-loss composite of polydimethylsiloxane (PDMS) and silver nanowires (AgNWs). The circularly polarized radiation is enabled by placing a planar linearly polarized loop monopole above a finite anisotropic artificial ground plane. By truncating the anisotropic artificial ground plane to contain only 2 by 2 unit cells, an integrated antenna with a compact form factor of 0.41λ0 × 0.41λ0 × 0.045λ0 is obtained, all while possessing an improved angular coverage of CP radiation. A flexible prototype was fabricated and characterized, experimentally achieving S 11 <- 15dB, an axial ratio of less than 3dB, a gain of around 5.2dBi, and a wide CP angular coverage in the targeted ISM band. Furthermore, this antenna is compared to a conventional CP patch antenna of the same physical size, which is also comprised of the same PDMS and AgNW composite. The results of this comparison reveal that the proposed antenna has much more stable performance under bending and human body loading, as well as a lower specific absorption rate. In all, the demonstrated wearable antenna offers a compact, flexible, and robust solution which makes it a strong candidate for future integration into body-area networks that require efficient off-body communications.

Dual‐band electrically coupled loop antenna for implant applications

Recent low power implant to off-body communication systems uses both medical implant communication services (MICS) and industrial, scientific, and medical (ISM) frequency bands. In these systems, MICS band and ISM band (2.45 GHz) are dedicated for data transmission and wake-up signal, respectively. This dual band operation which incredibly extends the life time of battery forces designers to use dual band antennas in both implant and off-body sides. In this study, a dual band implant electrically coupled loop antenna is proposed. This antenna as dual of planar inverted-F antenna is a magnetic antenna with inherently low near zone electric field and therefore produces low specific absorption rate (SAR) inside the body. The antenna is miniaturised using a lumped capacitor. In spite of small size of 5 × 5 × 3 mm3, the simulated 1 g average SAR is smaller than reported dual band implant antennas in both frequency bands and makes the proposed antenna a good candidate for implant applications.

Circularly Polarized Rectangular Ring-Slot Antenna with Chamfered Corners for Off-Body Communication at 5.8 GHz ISM Band

Circularly Polarized Rectangular Ring-Slot Antenna with Chamfered Corners for Off-Body Communication at 5.8 GHz ISM Band

A QoS Optimization Approach in Cognitive Body Area Networks for Healthcare Applications.

Wireless body area networks are increasingly featuring cognitive capabilities. This work deals with the emerging concept of cognitive body area networks. In particular, the paper addresses two important issues, namely spectrum sharing and interferences. We propose methods for channel and power allocation. The former builds upon a reinforcement learning mechanism, whereas the latter is based on convex optimization. Furthermore, we also propose a mathematical channel model for off-body communication links in line with the IEEE 802.15.6 standard. Simulation results for a nursing home scenario show that the proposed approach yields the best performance in terms of throughput and QoS for dynamic environments. For example, in a highly demanding scenario our approach can provide throughput up to 7 Mbps, while giving an average of 97.2% of time QoS satisfaction in terms of throughput. Simulation results also show that the power optimization algorithm enables reducing transmission power by approximately 4.5 dBm, thereby sensibly and significantly reducing interference.

Wearable Button Antenna for Dual-Band WLAN Applications With Combined on and off-Body Radiation Patterns

A new type of wearable button antenna for wireless local area network (WLAN) applications is proposed. The antenna is composed of a button with a diameter of circa 16 mm incorporating a patch on top of a dielectric disc. The button is located on top of a textile substrate and a conductive textile ground that are to be incorporated in clothing. The main characteristic feature of this antenna is that it shows two different types of radiation patterns, a monopole type pattern in the 2.4 GHz band for on-body communications and a broadside type pattern in the 5 GHz band for off-body communications. A very high efficiency of about 90% is obtained, which is much higher than similar full textile solutions in the literature. A prototype has been fabricated and measured. The effect of several real-life situations such as a tilted button and bending of the textile ground have been studied. Measurements agree very well with simulations.

Compact EBG-Backed Planar Monopole for BAN Wearable Applications

This paper presents a planar monopole backed with a 2 × 1 array of electromagnetic bandgap (EBG) structures. The reflection phase of a single EBG unit cell has been studied and exploited toward efficient radiation of a planar monopole antenna, intended for wearable applications. The shape of the EBG unit cell and the gap between the ground and the EBG layer are adjusted so that the antenna operates at 2.45 GHz. The proposed antenna retains its impedance matching when placed directly upon a living human subject with an impedance bandwidth of 5%, while it exhibits a measured gain of 6.88 dBi. A novel equivalent array model is presented to qualitatively explain the reported radiation mechanism of the EBG-backed monopole. The proposed antenna is fabricated on a 68 × 38 × 1.57 mm 3 board of semiflexible RT/duroid 5880 substrate. Detailed analysis and measurements are presented for various cases when the antenna is subjected to structural deformation and human body loading, and in all cases, the EBG-backed monopole antenna retains its high performance. The reported efficient and robust radiation performance with very low specific absorption rate, compact size, and high gain make the proposed antenna a superior candidate for most wearable applications used for off-body communication.

Wideband Off-Body Measurements and Channel Modeling at 60 GHz

A wideband indoor channel model between an external base station and a worn receiver on the user body at 60 GHz has been developed based on indoor measurements. The results are presented for three different receiver locations: head, wrist, and belt. A Saleh–Valenzuela impulse response is proposed as numerical model for this scenario. Also, path loss and delay spread results are driven out in order to discuss the node location for assessing an off-body communication.

Channel Characteristics of Dynamic Off-Body Communications at 60 GHz Under Line-of-Sight (LOS) and Non-LOS Conditions

This letter investigates the first-order characteristics of dynamic off-body communications channels at 60 GHz. In particular, we have studied signal propagation from a chest-worn millimeter-wave transmitter as an adult male walked toward and then away from a hypothetical base station. The mobile line-of-sight (LOS) and non-LOS (NLOS) channel measurements have been conducted in a diverse range of environments, including a hallway, an open office, an anechoic chamber, and an outdoor car park. In this study, we have decomposed the received signal into its path loss, large-scale, and small-scale fading components. The large-scale fading has been modeled using the gamma distribution, while the Rice and Nakagami-$m$ distributions have been employed to describe the small-scale fading observed in the LOS and NLOS channel conditions, respectively. The results have shown that the estimated path loss exponents for the anechoic chamber and car park environments were greater than those obtained for the hallway and open office environments for both the LOS and NLOS walking scenarios. Across all environments, it was found that the gamma distribution provided an adequate fit to the large-scale fading. Additionally, the Rice and Nakagami-$m$ distributions were found to well describe the small-scale fading for the LOS and NLOS walking scenarios, respectively.

Shadowed Fading in Indoor Off-Body Communication Channels: A Statistical Characterization Using the $\kappa $ –$\mu $ /Gamma Composite Fading Model

This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz. This is realized with the aid of the $\kappa $ – $\mu $ /gamma composite fading model, which assumes that the transmitted signal undergoes $\kappa $ – $\mu $ fading, which is subject to multiplicative shadowing. Based on this, the total power of the multipath components, including both the dominant and scattered components, is subject to non-negligible variations that follow the gamma distribution. For this model, we present an integral form of the probability density function (PDF) as well as important analytic expressions for the PDF, cumulative distribution function, moments, and moment generating function. In the case of indoor off-body communications, the corresponding measurements were carried out in the context of four explicit individual scenarios, namely: line of sight (LOS), non-LOS walking, rotational, and random movements. The measurements were repeated within three different indoor environments and considered three different hypothetical body worn node locations. With the aid of these results, the parameters for the $\kappa $ – $\mu $ /gamma composite fading model were estimated and analyzed extensively. Interestingly, for the majority of the indoor environments and movement scenarios, the parameter estimates suggested that dominant signal components existed even when the direct signal path was obscured by the test subject’s body. In addition, it is shown that the $\kappa $ – $\mu $ /gamma composite fading model provides an adequate fit to the fading effects involved in off-body communications channels. Using the Kullback-Leibler divergence, we have also compared our results with another recently proposed shadowed fading model, namely, the $\kappa $ – $\mu $ /lognormal LOS shadowed fading model. It was found that the $\kappa $ – $\mu $ /gamma composite fading model provided a better fit for the majority of the scenarios considered in this paper.

Switched Diversity Techniques for Indoor Off-Body Communication Channels: An Experimental Analysis and Modeling

This communication investigates the potential improvement in signal reliability for indoor off-body communications channels operating at 5.8 GHz using switched diversity techniques. In particular, we investi-gate the performance of switch-and-stay combining (SSC), switch-and-examine combining (SEC), and (SECps) schemes, which utilize multiple spatially separated antennas at the base station. During the measurements, a test subject, wearing an antenna on his chest, performed a number of walking movements toward and then away from a uniform linear array. It was found that all the considered diversity schemes provided a worthwhile signal improvement. However, the performance of the diversity systems varied according to the switching threshold that was adopted. To model the fading envelope observed at the output of each of the combiners, we have applied diversity specific equations developed under the assumption of Nakagami- $m$ fading. As a measure of the goodness-of-fit, the Kullback–Leibler divergence between the empirical and theoretical probability density functions (pdfs) was calculated and found to be close to 0. To assist with the interpretation of the goodness-of-fit achieved in this communication, the standard deviation $\sigma $ of a zero-mean, $\sigma ^{2}$ variance Gaussian pdf used to approximate a zero-mean, unit variance Gaussian pdf is also presented. These were generally quite close to 1 indicating that the theoretical models provided an adequate fit to the measured data.

On-Body Characterization of Planar Differential Antennas for Multiple, Wide, and Narrow Bands

This paper reports the results of the on-body experimental tests of a set of four planar differential antennas, originated by design variations of radiating elements with the same shape and characterized by the potential for covering wide and narrow bands. All the antenna designs have been implemented on low-cost FR4 substrate and characterized experimentally through on-body measurements. The results show the impact of the proximity to the human body on antenna performance and the opportunities in terms of potential coverage of wide and narrow bands for future ad hoc designs and implementations through wearable substrates targeting on-body and off-body communication and sensing applications.

Dual-Band Dual-Mode Patch Antenna for On-/Off-Body WBAN Communications

A novel coplanar waveguide (CPW)-fed dual-band dual-mode patch antenna for on-/off-body communications is proposed. The proposed antenna, which comprises a T-shaped patch with parasitic patches, a circular patch, and a CPW feedline, has dimensions of 30×45×3.2 mm 3 The proposed antenna operates in the 2.4-GHz ISM band (2.4-2.485 GHz) for off-body communication, and in the 5.8-GHz ISM band (5.725-5.875 GHz) for on-body communication. The antenna has a patch-like radiation pattern in the 2.4-GHz ISM band and a monopole-like radiation pattern in the 5.8-GHz ISM band.

HILBERT CURVE FRACTAL ANTENNA FOR DUAL ON- AND OFF-BODY COMMUNICATION

We present a Hilbert curve fractal antenna operating at 2.45 GHz ISM and 5.5 GHz WLAN bands. The proposed antenna employs a third-order Hilbert curve and two shorting vias for antenna miniaturization and dual-band/mode operation. At 2.45 GHz, the antenna exhibits a monopole-like radiation pattern, while at 5.5 GHz, it provides a broadside radiation pattern, suitable for simultaneous on- and off-body communication using two distinct frequency bands. The antenna footprint is as small as 25. 5m m× 25.5 mm. Simulation and measurement results demonstrate that the antenna gain is more than 1.9 dBi if the antenna is mounted on a ground larger than 40 mm × 40 mm. The effect of human body presence on antenna performance was investigated by means of full-wave simulations locating the antenna on a human body phantom. It is shown that the proposed antenna is capable of maintaining its free-space performance over the human body phantom except for the gain reduction of 2.5 dBi at 5.5 GHz band.