Recent developments and technological advancements in wireless communication, MicroElectroMechanical Systems (MEMS) technology and integrated circuits has enabled low-power, intelligent, miniaturized, invasive/non-invasive micro and nano-technology sensor nodes strategically placed in or around the human body to be used in various applications, such as personal health monitoring. This exciting new area of research is called Wireless Body Area Networks (WBANs) and leverages the emerging IEEE 802.15.6 and IEEE 802.15.4j standards, specifically standardized for medical WBANs. The aim of WBANs is to simplify and improve speed, accuracy, and reliability of communication of sensors/actuators within, on, and in the immediate proximity of a human body. The vast scope of challenges associated with WBANs has led to numerous publications. In this paper, we survey the current state-of-art of WBANs based on the latest standards and publications. Open issues and challenges within each area are also explored as a source of inspiration towards future developments in WBANs.

Wireless Body Area Networks: A Survey

We propose a compact conformal wearable antenna that operates in the 2.36-2.4 GHz medical body-area network band. The antenna is enabled by placing a highly truncated metasurface, consisting of only a two by two array of I-shaped elements, underneath a planar monopole. In contrast to previously reported artificial magnetic conducting ground plane backed antenna designs, here the metasurface acts not only as a ground plane for isolation, but also as the main radiator. An antenna prototype was fabricated and tested, showing a strong agreement between simulation and measurement. Comparing to previously proposed wearable antennas, the demonstrated antenna has a compact form factor of 0.5 λ
 0
 ×0.3 λ
 0
 ×0.028 λ
 0
, all while achieving a 5.5% impedance bandwidth, a gain of 6.2 dBi, and a front-to-back ratio higher than 23 dB. Further numerical and experimental investigations reveal that the performance of the antenna is extraordinarily robust to both structural deformation and human body loading, far superior to both planar monopoles and microstrip patch antennas. Additionally, the introduced metal backed metasurface enables a 95.3% reduction in the specific absorption rate, making such an antenna a prime candidate for incorporation into various wearable devices.

A Compact, Low-Profile Metasurface-Enabled Antenna for Wearable Medical Body-Area Network Devices

In this paper, a reflective metasurface is designed, fabricated, and experimentally demonstrated to generate an orbital angular momentum (OAM) vortexwave in radio frequency domain. Theoretical formula of phase-shift distribution is deduced and used to design the metasurface producing vortexradio waves. The prototype of a practical configuration is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that the vortexwaves with different OAM mode numbers can be flexibly generated by using sub-wavelength reflective metasurfaces. The proposed method and metasurface pave a way to generate the OAM vortexwaves for radio and microwave wireless communication applications.

Design, fabrication, and measurement of reflective metasurface for orbital angular momentum vortex wave in radio frequency domain

This article is a review of wireless body-area network (BAN) channel models, with observations about the selection of the best channel model in terms of both first- and second-order statistics. Particular insight into the dominant factors that affect propagation for body-area networks is given. Important second-order statistical measures are discussed, where coherence times and fade durations are of particular interest. The IEEE 802.15.6 standard is used as a basis for the review, with observations and insights given about body-area networks. In this context, narrowband and ultra-wideband (UWB) models are summarized for different measurement environments and carrier frequencies. On-body, in-body, and off-body propagation models are discussed where appropriate. In general, lognormal fading or gamma fading models of the body-area network channel are most applicable. A goodness-of-fit criterion that directly trades off model error and complexity is presented, which gives a new outlook for channel modeling. By this new outlook it is demonstrated that through significant simplification of individual link propagation models for body-area networks, it is possible to combine link models with only a few parameters. Common misconceptions regarding the appropriateness of applying traditional path-loss measures to these short-range networks are then exposed. Finally, the use of relays, which is an option in IEEE 802.15.6, is shown to be important for maintaining reliability in various body-area-network propagation scenarios.

Propagation Models for Body-Area Networks: A Survey and New Outlook

Mode division multiplexing (MDM) using orbital angular momentum (OAM) is a recently developed physical layer transmission technique, which has obtained intensive interest among optics, millimeter-wave, and radio frequency due to its capability to enhance communication capacity while retaining an ultra-low receiver complexity. In this paper, the system model based on OAM-MDM is mathematically analyzed and it is theoretically concluded that such system architecture can bring a vast reduction in receiver complexity without capacity penalty compared with conventional line-of-sight multiple-in-multiple-out systems under the same physical constraint. Furthermore, a $4\times 4$ OAM-MDM communication experiment adopting a pair of easily realized Cassegrain reflector antennas capable of multiplexing/demultiplexing four orthogonal OAM modes of $l = {-3}$ , −2, +2, and +3 is carried out at a microwave frequency of 10 GHz. The experimental results show high spectral efficiency as well as low receiver complexity.

Mode Division Multiplexing Communication Using Microwave Orbital Angular Momentum: An Experimental Study

A circular phased array antenna that can generate orbital angular momentum (OAM) radio beams in the 10 GHz band is described. The antenna consists of eight inset-fed patch elements and a microstrip corporate feeding network. A full-wave electromagnetic simulator is used to aid the antenna design and theoretical simulations are confirmed by measurements.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/el.2014.2860

Experimental circular phased array for generating OAM radio beams

The performance of a PIFA textile antenna under different crumpling conditions is presented. The PIFA was designed for integration into clothing and other textile applications and the bending and crumpling conditions studied are typical of those found under normal use conditions both on and off body. Input impedance, efficiency and radiation patterns are investigated based on numerical and experimental methods at 2.4 GHz. Crumpling can have a serious effect on the resonant frequency, bandwidth and radiation from textile antennas.

Crumpling of PIFA Textile Antenna

This paper describes the design of an 8-element circular phased patch array antenna which can generate radio beams carrying orbital angular momentum at 10 GHz. Realistic antenna design issues are discussed, including mutual coupling and the array performance when operating in different OAM states.

Generation of orbital angular momentum (OAM) radio beams with phased patch array

A means of encoding and decoding data using wireless orbital angular momentum (OAM) modes is proposed and analysed. Source data symbols are used to select an OAM mode, which is generated using an 8-element circular array. A 2-element array is used to detect the mode by estimating the phase gradient of the received signal, and hence identifying the transmitted data symbol. The results are presented in terms of mode estimation error.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/el.2013.3906

Wireless data encoding and decoding using OAM modes

A study is presented of wireless on-body communication links, with the body in motion. This paper compares simulations and measurements of the path gain (PG) on moving male and female bodies. Simulations using avatars derived from an animation software have been performed at 2.45 GHz. Male and female avatars walking and a male rising from a chair have been simulated and the results are compared with measurements carried out in an anechoic chamber. The results show that good agreement between simulation and measurement of slow fading features can be achieved for a reasonable computational effort.

Qiang Bai

Papers

Experimental circular phased array for generating OAM radio beams

Crumpling of PIFA Textile Antenna

Generation of orbital angular momentum (OAM) radio beams with phased patch array

Wireless data encoding and decoding using OAM modes

Simulation and Measurement of Dynamic On-Body Communication Channels