Circularly polarized dual mode wearable implant repeater antenna with enhanced into-body gain

A wearable stripline-fed circularly polarized dual patch antenna structure that exhibits enhanced into-body gain is presented. The antenna is designed for body-surface repeater solutions and it addresses the problem of marginal into-body deep tissue communication links, where power consumption is of the utmost importance and system link efficiency is critical. Under realistic operation conditions the antenna’s circular polarization successfully mitigates implant orientation and polarization mismatch. Polarization loss for linear antennas can be up to 16 dB in anechoic environments and as much as 12:5 dB in a realistic multipath environment, as demonstrated by measured co- and cross-polar forward path gain between implanted and linearly polarized surface antennas. To overcome the body isolating effect of an antenna ground plane and to produce an effective off-body mode, a novel dual aperture stripline feed was developed which also improves the body-mounted antenna radiation efficiency. The antenna provides a 0 dBi off-body gain whilst still maintaining excellent into-body performance. The into-body link was shown to exhibit circular polarization with a maximum isolation of only 1:5 dB between co- and cross-polar measurements in the 2.36–2.4 GHz band. All measurements were carried out using an accurate, next-generation layered phantom tested representative of a wide range of the population

Device-to-device communications: a performance analysis in the context of social comparison-based relaying

Device-to-device (D2D) communications are recognized as a key enabler of future cellular networks which will help to drive improvements in spectral efficiency and assist with the offload of network traffic. Among the transmission modes of D2D communications are single-hop and relay assisted multi-hop transmission. Relay-assisted D2D communications will be essential when there is an extended distance between the source and destination or when the transmit power of D2D user equipments (UEs) is constrained below a certain level. Although a number of works on relay-assisted D2D communications have been presented in the literature, most of those assume that relay nodes cooperate unequivocally. In reality, this cannot be assumed since there is little incentive to cooperate without a guarantee of future reciprocal behavior. Cooperation is a social behavior that depends on various factors, such as peer comparison, incentives, the cost to the donor and the benefit to the recipient. To incorporate the social behavior of D2D relay nodes, we consider the decision to relay using the donation game based on social comparison and characterize the probability of cooperation in an evolutionary context. We then apply this within a stochastic geometric framework to evaluate the outage probability and transmission capacity of relay assisted D2D communications. Through numerical evaluations, we investigate the performance gap between the ideal case of 100% cooperation and practical scenarios with a lower cooperation probability. It shows that practical scenarios achieve lower transmission capacity and higher outage probability than idealistic network views which assume full cooperation. After a sufficient number of generations, however, the cooperation probability follows the natural rules of evolution and the transmission performance of practical scenarios approach that of the full cooperation case, indicating that all D2D relay nodes adopt the same dominant cooperative strategy based on social comparison, without the need for enforcement by an external authority

Onset of Surface-Tension-Driven Benard Convection

Experiments with shadowgraph visualization reveal a subcritical transition to a hexagonal convection pattern in thin liquid layers that have a free upper surface and are heated from below. The measured critical Marangoni number (84) and observation of hysteresis (3%) agree with theory. In some experiments, imperfect bifurcation is observed and is attributed to deterministic forcing caused in part by the lateral boundaries in the experiment.Comment: 4 pages. The RevTeX file has a macro allowing various styles. The appropriate style is "mypprint" which is the defaul

Pedestrian-to-Vehicle Communications in an Urban Environment: Channel Measurements and Modeling

As wireless connectivity becomes increasingly ubiquitous, a greater emphasis will be placed upon the seamless integration of dissimilar networking technologies. One such example of this will occur in urban environments, where wearable devices and vehicular networks will operate in close proximity to one another. Clearly, a natural extension to both types of network is their interconnectivity through vehicle-to-pedestrian (V2P) or equivalently pedestrian-to-vehicle (P2V) communications as part of a much greater vehicle-to-X (V2X) based Intelligent Transportation System (ITS). To this end, we empirically investigate the P2V communications channel at 5.8 GHz for the case of a moving vehicle when a person positioned by the edge of a road was either stationary or walking parallel to the side of the highway. The measurements considered a chest mounted transmitter and four receiver locations on the vehicle covering the front wing mirrors and two positions on the roof, which simultaneously recorded the received signal power. To characterize the propagation mechanisms which are responsible for shaping the received signal in the P2V channel we decomposed it into its path loss, large-scale and small-scale fading components. We first show that although there was evidence of interference caused by multiple rays interacting with one another, the popular Two- Ray ground-reflection path loss model was unable to adequately describe the compounded effects of the vehicle and pedestrian’s body on the signal attenuation in the majority of the considered scenarios. Instead, we found that the overall path loss was well characterized using a dual-slope log-distance model, with lognormal large-scale fading. Due to the often severe small-scale fading that was observed in the P2V channel, we have been able to utilize the kappa-mu Extreme distribution with considerable success to characterize the worse than Rayleigh fading conditions which were encountered

Social comparison based relaying in device-to-device networks

Device-to-device (D2D) communications are recognized as a key component of future wireless networks which will help to improve spectral efficiency and network densification simultaneously. In order to guarantee a quality of service (QoS) to the cellular links, the transmit power of the D2D nodes needs to be restricted, which has lead to a poor link quality over D2D transmission. One viable option to improve the D2D link quality is incorporating cooperative relays into D2D networks. However most of the existing published work in relay assisted D2D networks has assumed that relay nodes cooperate spontaneously. This cannot always be guaranteed and we take this into account by considering a fundamental model on which donation-based cooperation depends. In par- ticular we model relay cooperation as a donation game based on social comparison and characterize cooperation probability in an evolutionary context. When applying this model we evaluate the outage and capacity of relay assisted D2D network using a stochastic geometric framework

A 915 MHz wristwatch-integrated antenna for wireless health monitoring

A compact 915 MHz antenna integrated within a wristwatch wireless sensor device is presented. The antenna is a variant of a planar inverted-F antenna (PIFA) and uses a dual-resonator configuration. The results of simulation and measurement are shown to be in good agreement with the antenna exhibiting desirable impedance and radiation characteristics together with low Specific Absorption Rate (SAR) performance. The antenna is fabricated using a low cost flexible printed circuit and is fully integrated into the watch device. Measurements on the prototype antenna show a -10 dB impedance bandwidth of 30 MHz, a peak realized gain of -4.9 dBi and a peak radiation efficiency of 15.9% at 915 MHz. The antenna also has a low SAR value of 0.003 W/kg making it suitable for a wide range of wrist-worn wireless applications