Coexistence of RF-powered IoT and a Primary Wireless Network with Secrecy Guard Zones

This paper studies the secrecy performance of a wireless network (primary network) overlaid with an ambient RF energy harvesting IoT network (secondary network). The nodes in the secondary network are assumed to be solely powered by ambient RF energy harvested from the transmissions of the primary network. We assume that the secondary nodes can eavesdrop on the primary transmissions due to which the primary network uses secrecy guard zones. The primary transmitter goes silent if any secondary receiver is detected within its guard zone. Using tools from stochastic geometry, we derive the probability of successful connection of the primary network as well as the probability of secure communication. Two conditions must be jointly satisfied in order to ensure successful connection: (i) the SINR at the primary receiver is above a predefined threshold, and (ii) the primary transmitter is not silent. In order to ensure secure communication, the SINR value at each of the secondary nodes should be less than a predefined threshold. Clearly, when more secondary nodes are deployed, more primary transmitters will remain silent for a given guard zone radius, thus impacting the amount of energy harvested by the secondary network. Our results concretely show the existence of an optimal deployment density for the secondary network that maximizes the density of nodes that are able to harvest sufficient amount of energy. Furthermore, we show the dependence of this optimal deployment density on the guard zone radius of the primary network. In addition, we show that the optimal guard zone radius selected by the primary network is a function of the deployment density of the secondary network. This interesting coupling between the two networks is studied using tools from game theory. Overall, this work is one of the few concrete works that symbiotically merge tools from stochastic geometry and game theory

Tight Lower Bounds on the Contact Distance Distribution in Poisson Hole Process

In this letter, we derive new lower bounds on the cumulative distribution function (CDF) of the contact distance in the Poisson Hole Process (PHP) for two cases: (i) reference point is selected uniformly at random from $\mathbb{R}^2$ independently of the PHP, and (ii) reference point is located at the center of a hole selected uniformly at random from the PHP. While one can derive upper bounds on the CDF of contact distance by simply ignoring the effect of holes, deriving lower bounds is known to be relatively more challenging. As a part of our proof, we introduce a tractable way of bounding the effect of all the holes in a PHP, which can be used to study other properties of a PHP as well.Comment: To appear in IEEE Wireless Communications Letter

Joint Uplink and Downlink Coverage Analysis of Cellular-based RF-powered IoT Network

Ambient radio frequency (RF) energy harvesting has emerged as a promising solution for powering small devices and sensors in massive Internet of Things (IoT) ecosystem due to its ubiquity and cost efficiency. In this paper, we study joint uplink and downlink coverage of cellular-based ambient RF energy harvesting IoT where the cellular network is assumed to be the only source of RF energy. We consider a time division-based approach for power and information transmission where each time-slot is partitioned into three sub-slots: (i) charging sub-slot during which the cellular base stations (BSs) act as RF chargers for the IoT devices, which then use the energy harvested in this sub-slot for information transmission and/or reception during the remaining two sub-slots, (ii) downlink sub-slot during which the IoT device receives information from the associated BS, and (iii) uplink sub-slot during which the IoT device transmits information to the associated BS. For this setup, we characterize the joint coverage probability, which is the joint probability of the events that the typical device harvests sufficient energy in the given time slot and is under both uplink and downlink signal-to-interference-plus-noise ratio (SINR) coverage with respect to its associated BS. This metric significantly generalizes the prior art on energy harvesting communications, which usually focused on downlink or uplink coverage separately. The key technical challenge is in handling the correlation between the amount of energy harvested in the charging sub-slot and the information signal quality (SINR) in the downlink and uplink sub-slots. Dominant BS-based approach is developed to derive tight approximation for this joint coverage probability. Several system design insights including comparison with regularly powered IoT network and throughput-optimal slot partitioning are also provided

Wideband P-Shaped Dielectric Resonator Antenna

A novel P-shaped dielectric resonator antenna (DRA) is presented and investigated for wideband wireless application. By using P-shaped resonator, a wideband impedance bandwidth of 80% from 3.5 to 8.2 GHz is achieved. The antenna covers all of wireless systems like C-band, 5.2, 5.5 & 5.8 GHz-WLAN & WiMax. The proposed antenna has a low profile and the thickness of the resonator is only 5.12 mm, which is 0.06-0.14 free space wavelength. A parametric study is presented. The proposed DRA is built and the characteristics of the antenna are measured. Very good agreement between numerical and measured results is obtained

Joint Energy and SINR Coverage in Spatially Clustered RF-powered IoT Network

Owing to the ubiquitous availability of radio-frequency (RF) signals, RF energy harvesting is emerging as an appealing solution for powering IoT devices. In this paper, we model and analyze an IoT network which harvests RF energy and receives information from the same wireless network. In order to enable this operation, each time slot is partitioned into charging and information reception phases. For this setup, we characterize two performance metrics: (i) energy coverage and (ii) joint signal-to-interference-plus-noise (SINR) and energy coverage. The analysis is performed using a realistic spatial model that captures the spatial coupling between the locations of the IoT devices and the nodes of the wireless network (referred henceforth as the IoT gateways), which is often ignored in the literature. In particular, we model the locations of the IoT devices using a Poisson cluster process (PCP) and assume that some of the clusters have IoT gateways (GWs) deployed at their centers while the other GWs are deployed independently of the IoT devices. The level of coupling can be controlled by tuning the fraction of total GWs that are deployed at the cluster centers. Due to the inherent intractability of computing the distribution of shot noise process for this setup, we propose two accurate approximations, using which the aforementioned metrics are characterized. Multiple system design insights are drawn from our results. For instance, we demonstrate the existence of optimal slot partitioning that maximizes the system throughput. In addition, we explore the effect of the level of coupling between the locations of the IoT devices and the GWs on this optimal slot partitioning. Particularly, our results reveal that the optimal value of time duration for the charging phase increases as the level of coupling decreases.Comment: To appear in IEEE Transactions on Green Communications and Networkin

Stochastic Geometry-Based Comparison of Secrecy Enhancement Techniques in D2D Networks

This letter presents a performance comparison of two popular secrecy enhancement techniques in wireless networks: 1) creating guard zones by restricting transmissions of legitimate transmitters whenever any eavesdropper is detected in their vicinity, and 2) adding artificial noise to the confidential messages to make it difficult for the eavesdroppers to decode them. Focusing on a noise-limited regime, we use tools from stochastic geometry to derive the secrecy outage probability at the eavesdroppers as well as the coverage probability at the legitimate users for both these techniques. Using these results, we derive a threshold on the density of the eavesdroppers below which no secrecy enhancing technique is required to ensure a target secrecy outage probability. For eavesdropper densities above this threshold, we concretely characterize the regimes in which each technique outperforms the other. Our results demonstrate that guard zone technique is better when the distances between the transmitters and their legitimate receivers are higher than a certain threshold

Effect of Cell-Selection on the Effective Fading Distribution in a Downlink K-Tier HetNet

This letter characterizes the statistics of effective fading gain in multi-tier cellular networks with strongest base station (BS) cell association policy. First, we derive the probability of association with the n-th nearest BS in the k-th tier. Next, we use this result to derive the probability density function of the channel fading gain (effective fading) experienced by the user when associating with the strongest BS. Interestingly, our results show that the effective channel gain distribution solely depends upon the original channel fading and the path-loss exponent. Moreover, we show that in the case of Nakagami-m fading channels (Gamma distribution), the distribution of the effective fading is also Gamma but with a gain of (α/2) in the shape parameter, where α is the path-loss exponent

ANTIOXIDANT AND ANTIRADICAL ACTIVITY OF GREEN TEA (Camellia sinensis) AQUEOUS EXTRACT AND ITS CAPABILITY TO RETARDATION OF RATS LIVER CIRRHOSIS

he aim of the present study was to optimize the extraction conditions of green tea aqueous extract [green tea concentration (G) and extraction temperature (T)]. Response surface methodology was applied to determine the highest radical scavenging activity (RSA), Ferric reducing antioxidant power (FRAP) and reducing power (RP) of the prepared green tea extract. Effect of green tea aqueous extract prepared using the optimal conditions on the liver cirrhosis retardation in rats was also investigated. Two-factors central composite design was established to determine the effects of G or T and radical scavenging holding time as independent variables on RSA, FRAP and RP as dependent variables. The optimum G, T and holding time with maximum RSA were 1.0 %, 88.7 °C for 25 min, with a predicted RSA of 81.3 % (r2=0.9115) compared to the BHT, which had a scavenging value of 87.4 % at concentration 150 ppm and holding time 30 min The same predicted concentration and temperature obtained with the highest FRAP and RP were 2.566 and 1.687 with r2 0.9780 and 0.9550, respectively. The phenolic and flavonoid contents were 81.2 mg gallic acid equivalent and 33.5 mg quercetin equivalent per 100 ml green tea extract. The extract prepared at optimal conditions was used for treatment of cirrhotic rats by CCl4. Insignificant (P≥0.05) differences were observed between the green tea group and control group in obtained total protein or albumin values. Total protein and albumin were dramatically decreased in the group treated by CCL4.  The same trend was observed with studying the transaminase enzymes. Histopathological sections appeared the effect of green tea extract on the retardation of liver cirrhosis in rats

An E-band Compact Frequency Division Duplex Radio Front-end Based on Gap Waveguide Technology

A compact module consisting of a novel integration of an antenna, a diplexer, and millimeter-wave active circuits for low latency wireless backhaul links working at E-band is presented in this paper. The proposed radio front-end module is built by four distinct layers which are vertically stacked with no electrical contact requirement between them based on gap waveguide technology. A 16 716 corporate-fed slot array antenna is successfully integrated 7 with a 5th order diplexer, as well as a transmitter (Tx) and a receiver (Rx) monolithic microwave integrated circuits (MMICs) in one package with a novel architecture and a compact form. The integrated radio front-end is able to simultaneously send and receive data by using a frequency division duplex (FDD) transmission scheme at 71-76 GHz and 81-86 GHz bands. A wireless data transmission is successfully demonstrated showing a data rate of 6 Gbit/s using 64 quadrature amplitude modulated (QAM) signal with a spectral efficiency of 4.4 bit/s/Hz. The proposed radio front-end provides the advantages of low loss, high efficiency, compact integration, and a simple mechanical assembly, which makes it a suitable solution for small cell backhaul links