Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Early mental stress detection can prevent many stress related health problems. This study aimed at using a wearable sensor system to measure physiological signals and detect mental stress. Three different stress conditions were presented to a healthy subject group. During the procedure, ECG, respiration, skin conductance, and EMG of the trapezius muscles were recorded. In total, 19 physiological features were calculated from these signals. After normalization of the feature values and analysis of correlations among these features, a subset of 9 features was selected for further analysis. Principal component analysis reduced these 9 features to 7 principal components (PCs). Using these PCs and different classifiers, a consistent classification accuracy between stress and non stress conditions of almost 80% was found. This suggests that a promising feature subset was found for future development of a personalized stress monitor. <s> BIB001 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Pervasive healthcare is a promising field of research as small and unobtrusive on-body sensors become available. However, despite considerable advances in the field, current systems are limited in terms of the pathologies they can detect, particularly regarding mental disorders. In this work we propose wearable eye tracking as a new method for mental health monitoring. We provide two reviews: one of the state-of-the-art in wearable eye tracking equipment and a second one of the work in experimental psychology and clinical research on the link between eye movements and cognition. Both reviews show a significant potential of wearable eye tracking for mental health monitoring in daily life settings. This finding calls for further research on unobtrusive sensing equipment and novel algorithms for automated analysis of long-term eye movement data. <s> BIB002 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Visible Light Positioning (VLP) provides a promising means to achieve indoor localization with sub-meter accuracy. We observe that the Visible Light Communication (VLC) methods in existing VLP systems rely on intensity-based modulation, and thus they require a high pulse rate to prevent flickering. However, the high pulse rate adds an unnecessary and heavy burden to receiving devices. To eliminate this burden, we propose the polarization-based modulation, which is flicker-free, to enable a low pulse rate VLC. In this way, we make VLP light-weight enough even for resource-constrained wearable devices, e.g. smart glasses. Moreover, the polarization-based VLC can be applied to any illuminating light sources, thereby eliminating the dependency on LED. This paper presents the VLP system PIXEL, which realizes our idea. In PIXEL, we develop three techniques, each of which addresses a design challenge: 1) a novel color-based modulation scheme to handle users? mobility, 2) an adaptive downsampling algorithm to tackle the uneven sampling problem of wearables? low-cost camera and 3) a computational optimization method for the positioning algorithm to enable real-time processing. We implement PIXEL?s hardware using commodity components and develop a software program for both smartphone and Google glass. Our experiments based on the prototype show that PIXEL can provide accurate realtime VLP for wearables and smartphones with camera resolution as coarse as 60 pixel x 80 pixel and CPU frequency as low as 300MHz. <s> BIB003 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> A review of the market landscape and System-on-Chip (SoC) technical trends in the area of wearable sports and fitness technology. Wearable solutions such as smart clothing and equipment embedded sensors are presented. Technical topics include trends in low-power secure computing. <s> BIB004 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Supporting high data rate wireless connectivity among wearable devices in a dense indoor environment is challenging. This is primarily due to bandwidth scarcity when many users operate multiple devices simultaneously. The millimeter-wave (mmWave) band has the potential to address this bottleneck, thanks to more spectrum and less interference because of signal blockage at these frequencies. In this paper, we explain the potential and challenges associated with using mmWave for wearable networks. To provide a means for concrete analysis, we present a system model that admits easy analysis of dense, indoor mmWave wearable networks. We evaluate the performance of the system while considering the unique propagation features at mmWave frequencies, such as human body blockages and reflections from walls. One conclusion is that the non-isotropy of the surroundings relative to a reference user causes variations in system performance depending on the user location, body orientation, and density of the network. The impact of using antenna arrays is quantified through analytic closed-form expressions that incorporate antenna gain and directivity. It is shown that using directional antennas, positioning the transceiver devices appropriately, and orienting the human user body in certain directions depending on the user location result in gigabits-per-second achievable ergodic rates for mmWave wearable networks. <s> BIB005 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> A wearable RGB-D camera based indoor navigation system for the blind is proposed.Egomotion estimation is performed using both sparse features and dense point clouds.Probabilistic mapping and traversability analysis for path planning is presented.The system stores and reloads maps to expand coverage area of navigation.The system improves mobility performance complementing the white cane. In this paper, a novel wearable RGB-D camera based indoor navigation system for the visually impaired is presented. The system guides the visually impaired user from one location to another location without a prior map or GPS information. Accurate real-time egomotion estimation, mapping, and path planning in the presence of obstacles are essential for such a system. We perform real-time 6-DOF egomotion estimation using sparse visual features, dense point clouds, and the ground plane to reduce drift from a head-mounted RGB-D camera. The system also builds 2D probabilistic occupancy grid map for efficient traversability analysis which is a basis for dynamic path planning and obstacle avoidance. The system can store and reload maps generated by the system while traveling and continually expand the coverage area of navigation. Next, the shortest path between the start location to destination is generated. The system generates a safe and efficient way point based on the traversability analysis result and the shortest path and updates the way point while a user is constantly moving. Appropriate cues are generated and delivered to a tactile feedback system to guide the visually impaired user to the way point. The proposed wearable system prototype is composed of multiple modules including a head-mounted RGB-D camera, standard laptop that runs a navigation software, smart phone user interface, and haptic feedback vest. The proposed system achieves real-time navigation performance at 28.6Hz in average on a laptop, and helps the visually impaired extends the range of their activities and improve the orientation and mobility performance in a cluttered environment. We have evaluated the performance of the proposed system in mapping and localization with blind-folded and the visually impaired subjects. The mobility experiment results show that navigation in indoor environments with the proposed system avoids collisions successfully and improves mobility performance of the user compared to conventional and state-of-the-art mobility aid devices. <s> BIB006 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Wearable Health Devices (WHDs) are increasingly helping people to better monitor their health status both at an activity/fitness level for self-health tracking and at a medical level providing more data to clinicians with a potential for earlier diagnostic and guidance of treatment. The technology revolution in the miniaturization of electronic devices is enabling to design more reliable and adaptable wearables, contributing for a world-wide change in the health monitoring approach. In this paper we review important aspects in the WHDs area, listing the state-of-the-art of wearable vital signs sensing technologies plus their system architectures and specifications. A focus on vital signs acquired by WHDs is made: first a discussion about the most important vital signs for health assessment using WHDs is presented and then for each vital sign a description is made concerning its origin and effect on heath, monitoring needs, acquisition methods and WHDs and recent scientific developments on the area (electrocardiogram, heart rate, blood pressure, respiration rate, blood oxygen saturation, blood glucose, skin perspiration, capnography, body temperature, motion evaluation, cardiac implantable devices and ambient parameters). A general WHDs system architecture is presented based on the state-of-the-art. After a global review of WHDs, we zoom in into cardiovascular WHDs, analysing commercial devices and their applicability versus quality, extending this subject to smart t-shirts for medical purposes. Furthermore we present a resumed evolution of these devices based on the prototypes developed along the years. Finally we discuss likely market trends and future challenges for the emerging WHDs area. <s> BIB007 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Technology has become ubiquitous, it is all around us and is becoming part of us. Togetherwith the rise of the Internet of Things (IoT) paradigm and enabling technologies (e.g., Augmented Reality (AR), Cyber-Physical Systems, Artificial Intelligence (AI), blockchain or edge computing), smart wearables and IoT-based garments can potentially have a lot of influence by harmonizing functionality and the delight created by fashion. Thus, smart clothes look for a balance among fashion, engineering, interaction, user experience, cybersecurity, design and science to reinvent technologies that can anticipate needs and desires. Nowadays, the rapid convergence of textile and electronics is enabling the seamless and massive integration of sensors into textiles and the development of conductive yarn. The potential of smart fabrics, which can communicate with smartphones to process biometric information such as heart rate, temperature, breathing, stress, movement, acceleration, or even hormone levels, promises a new era for retail. This article reviews the main requirements for developing smart IoT-enabled garments and shows smart clothing potential impact on business models in the medium-term. Specifically, a global IoT architecture is proposed, the main types and components of smart IoT wearables and garments are presented, their main requirements are analyzed and some of the most recent smart clothing applications are studied. In this way, this article reviews the past and present of smart garments in order to provide guidelines for the future developers of a network where garments will be connected like other IoT objects: the Internet of Smart Clothing. <s> BIB008 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> As wearable devices become more ingrained in our daily lives, traditional communication networks primarily designed for human-being-oriented applications are facing tremendous challenges. The forthcoming fifth-generation (5G) wireless systems look to support unprecedented high capacity, low latency, and massive connectivity. In this article, we examine key challenges facing wearable communication devices. A cloud/edge communication architecture that integrates the cloud radio access network (CRAN), software-defined network (SDN), device-to-device (D2D) communications, and cloud/edge technologies is presented. Computation offloading enabled by this multilayer communications architecture can offload computation-excessive and latency-stringent applications to nearby devices through D2D communications or to nearby edge nodes through cellular or other wireless technologies. Critical issues faced by wearable communications, e.g., short battery life, limited computing capability, and stringent latency, can be greatly alleviated by this cloud/edge architecture. Together with the presented architecture, current transmission and networking technologies [including nonorthogonal multiple access (NOMA), mobile edge computing (MCE), and energy harvesting] can greatly enhance the performance of wearable communications in terms of spectral efficiency, energy efficiency, latency, and connectivity. <s> BIB009 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> A. Significance of Wearable Technologies <s> Numerous antenna design approaches for wearable applications have been investigated in the literature. As on-body wearable communications become more ingrained in our daily activities, the necessity to investigate the impacts of these networks burgeons as a major requirement. In this study, we investigate the human electromagnetic field (EMF) exposure effect from on-body wearable devices at 2.4 GHz and 60 GHz, and compare the results to illustrate how the technology evolution to higher frequencies from wearable communications can impact our health. Our results suggest the average specific absorption rate (SAR) at 60 GHz can exceed the regulatory guidelines within a certain separation distance between a wearable device and the human skin surface. To the best of authors' knowledge, this is the first work that explicitly compares the human EMF exposure at different operating frequencies for on-body wearable communications, which provides a direct roadmap in design of wearable devices to be deployed in the Internet of Battlefield Things (IoBT). <s> BIB010
Mobile wearable communications devices are rapidly making inroads thanks to advancements in miniature electronics fabrication, wireless communications, batteries, and data analytics. The initial driver of the mobile electronics market was fitness and healthcare gadgets BIB005 . The convergence of wearables, such as smartwatches and activity trackers, has initiated the growth of smart technology in healthcare-e.g., wireless blood pressure/respiratory rate wristbands or patches for home diagnosis BIB007 . Today, we evidence a remarkable expansion of wearable technologies in the mobile device market [3] . September 2009 can be considered as the defining moment when iconic wearable technologies like Nike+ and Fitbit became commercialized  , which further expanded the industry and led to an unprecedented variety of applications: e.g., smartwatches, wristbands, smart sunglasses, smart jewelry, electronic clothing, skin patches, etc BIB008 . Data obtained from these wearables creates opportunities that will improve the quality of life that S. Kim The work shown in Section VI of this paper was presented in this paper was presented in IEEE MILCOM 2019 BIB010 . existing mobile technologies (e.g., smartphone) alone could not easily achieve  . Not only for personal life, wearable devices are also used to provide a wider range of value-added services such as indoor positioning and navigation BIB003 BIB006 , financial payments   , physical and mental health monitoring BIB002 BIB001 , sports analytics BIB004 , and medical insurance analytics  . Wearable devices can provide easier access to information and more convenience for their users. They have varying form factors, from low-end health and fitness trackers to high-end virtual reality (VR) devices, augmented reality (AR) helmets, and smartwatches BIB009 .