On Capacity of Active Relaying in Magnetic Induction based Wireless Underground Sensor Networks

Wireless underground sensor networks (WUSNs) present a variety of new research challenges. Magnetic induction (MI) based transmission has been proposed to overcome the very harsh propagation conditions in underground communications in recent years. In this approach, induction coils are utilized as antennas in the sensor nodes. This solution achieves longer transmission ranges compared to the traditional electromagnetic (EM) waves based approach. Furthermore, a passive relaying technique has been proposed in the literature where additional resonant circuits are deployed between the nodes. However, this solution is shown to provide only a limited performance improvement under practical system design contraints. In this work, the potential of an active relay device is investigated which may improve the performance of the system by combining the benefits of the traditional wireless relaying and the MI based signal transmission.Comment: This paper has been accepted for presentation at IEEE ICC 2015. It has 6 pages, 5 figures (4 colored), and 17 reference

Beamforming for Magnetic Induction based Wireless Power Transfer Systems with Multiple Receivers

Magnetic induction (MI) based communication and power transfer systems have gained an increased attention in the recent years. Typical applications for these systems lie in the area of wireless charging, near-field communication, and wireless sensor networks. For an optimal system performance, the power efficiency needs to be maximized. Typically, this optimization refers to the impedance matching and tracking of the split-frequencies. However, an important role of magnitude and phase of the input signal has been mostly overlooked. Especially for the wireless power transfer systems with multiple transmitter coils, the optimization of the transmit signals can dramatically improve the power efficiency. In this work, we propose an iterative algorithm for the optimization of the transmit signals for a transmitter with three orthogonal coils and multiple single coil receivers. The proposed scheme significantly outperforms the traditional baseline algorithms in terms of power efficiency.Comment: This paper has been accepted for presentation at IEEE GLOBECOM 2015. It has 7 pages and 5 figure

Signals in the Soil: An Introduction to Wireless Underground Communications

In this chapter, wireless underground (UG) communications are introduced. A detailed overview of WUC is given. A comprehensive review of research challenges in WUC is presented. The evolution of underground wireless is also discussed. Moreover, different component of UG communications is wireless. The WUC system architecture is explained with a detailed discussion of the anatomy of an underground mote. The examples of UG wireless communication systems are explored. Furthermore, the differences of UG wireless and over-the-air wireless are debated. Different types of wireless underground channel (e.g., In-Soil, Soil-to-Air, and Air-to-Soil) are reported as well

Zenneck Waves in Decision Agriculture: An Empirical Verification and Application in EM-Based Underground Wireless Power Transfer

In this article, the results of experiments for the observation of Zenneck surface waves in sub GHz frequency range using dipole antennas are presented. Experiments are conducted over three different soils for communications distances of up to 1 m. This empirical analysis confirms the existence of Zenneck waves over the soil surface. Through the power delay profile (PDP) analysis, it has been shown that other subsurface components exhibit rapid decay as compared to the Zenneck waves. A potential application of the Zenneck waves for energy transmission in the area of decision agriculture is explored. Accordingly, a novel wireless through-the-soil power transfer application using Zenneck surface waves in electromagnetic (EM) based wireless underground communications is developed

Fields and coupling between coils embedded in conductive environments

An approximate solution is developed for the mutual inductance of two circular coils enclosed by insulating cavities in a conducting medium. This solution is used to investigate the variation of the mutual inductance upon the conductivity of the background (e.g., soil, seawater or human body), as well as upon other parameters such as the vertical of the coils and the displacement of one of the coils in the horizontal plane. Our theoretical results are compared with full wave simulations and a previous solution valid when a conductive slab is inserted between two coupled resonant coils. The proposed approach can have direct impact on the design and optimisation of magnetoinductive waveguides and wireless power transfer for underground/underwater networks and embedded biomedical systems

A Survey on Subsurface Signal Propagation

Wireless Underground Communication (WUC) is an emerging field that is being developed continuously. It provides secure mechanism of deploying nodes underground which shields them from any outside temperament or harsh weather conditions. This paper works towards introducing WUC and give a detail overview of WUC. It discusses system architecture of WUC along with the anatomy of the underground sensor motes deployed in WUC systems. It also compares Over-the-Air and Underground and highlights the major differences between the both type of channels. Since, UG communication is an evolving field, this paper also presents the evolution of the field along with the components and example UG wireless communication systems. Finally, the current research challenges of the system are presented for further improvement of the WUCs

Magneto-inductive wireless underground sensor networks: novel longevity model, communication concepts and workarounds to key theoretical issues using analogical thinking

This research has attempted to devise novel workarounds to key theoretical issues in magneto-inductive wireless underground sensor networks (WUSNs), founded on analogical thinking (Gassmann & Zeschky 2008). The problem statement for this research can be summarized as follows. There has been a substantial output of research publications in the past 5 years, devoted to theoretically analysing and resolving the issues pertaining to deployment of MI based WUSNs. However, no alternate solution approaches to such theoretical analyses have been considered. The goal of this research was to explore such alternate solution approaches. This research has used the principle of analogical thinking in devising such alternate solution approaches. This research has made several key contributions to the existing body of work. First, this research is the first of its kind to demonstrate by means of review of state-of-the-art research on MI based WUSNs, the largely theoretical genus of the research to the exclusion of alternate solution approaches to circumvent key theoretical issues. Second, this research is the first of its kind to introduce the notion of analogical thinking as a solution approach in finding viable workarounds to theoretical impediments in MI based WUSNs, and validate such solution approach by means of simulations. Third, this research is the first of its kind to explore novel communication concepts in the realm of MI based WUSNs, based on analogical thinking. Fourth, this research is the first of its kind to explore a novel longevity model in the realm of MI based WUSNs, based on analogical thinking. Fifth, this research is also the first to extend the notion of analogical thinking to futuristic directions in MI based WUSNs research, by means of providing possible indicators drawn from various other areas of contemporary research. In essence, the author believes that the findings of this research mark a paradigm shift in the research on MI based WUSNs

Wireless Powered Communication Networks

The limited life time of batteries is a crucial issue in energy-constrained wireless communications. Recently, the radio frequency (RF) wireless energy transfer (WET) technique has been developed as a new practical method to extend the life time of wireless communication networks. Inspired by this, wireless-powered communication network (WPCN) has attracted much attention. Therefore, in this thesis, we consider practical WET and wireless-powered information transmission in WPCNs. First we investigate a WPCN with two nodes, in which an access point (AP) exchanges information with a wireless-powered user. The user is assumed to have no embedded energy supply and needs to harvest energy from RF signals broadcast by the AP. Differing from existing work that focuses on the design of wireless-powered communication with one-way information flow, we deal with a more general scenario where both the AP and the user have information to transmit. Considering that the AP and user can work in either half-duplex or full-duplex mode as well as having two practical receiver architectures at the user side, we propose five elementary communication protocols for the considered system. Moreover, we define the concept of a throughput region to characterize the tradeoff between the uplink and downlink throughput in all proposed protocols. Numerical simulations are finally performed to compare the throughput regions of the proposed five elementary protocols. To further the study on WPCN, we investigate a wireless-powered two-way relay system, in which two wireless-powered sources exchange information through a multi-antenna relay. Both sources are assumed to have no embedded energy supply and thus first need to harvest energy from the radio frequency signals broadcast by the relay before exchanging their information via the relay. We aim to maximize the sum throughput of both sources by jointly optimizing the time switching duration, the energy beamforming vector and the precoding matrix at the relay. The formulated problem is non-convex and hard to solve in its original form. Motivated by this, we simplify the problem by reducing the number of variables and by decomposing the precoding matrix into a transmit vector and a receive vector. We then propose a bisection search, a 1-D search and an iterative algorithm to optimize each variable. Numerical results show that our proposed scheme can achieve higher throughput than the conventional scheme without optimization on the beamforming vector and precoding matrix at the relay. Due to the high attenuation of RF energy over a long distance, RF based wireless-powered communication is usually designed for low-power scenarios, e.g., wireless-powered sensor networks. Recently, magnetic induction (MI) based WET has been proposed to wirelessly transfer a large amount of energy. Inspired by this, we investigate MI based WET in WPCN. Specifically, we study a MI based wireless-powered relaying network, in which a MI source transmits information to a MI destination, with the help of a MI based wireless powered relay. We propose four active relaying schemes, which consider different relaying modes and different energy harvesting receiver architectures at the relay. We then aim to maximize the end-to-end throughput of each scheme by using a bisection search, a water-filling algorithm, a Lagrange multiplier, quasi-convex programming and an iterative algorithm. We compare the proposed active relaying schemes with passive relaying. Numerical results show that the proposed relaying schemes with a decode-and-forward relaying mode significantly improve the throughput over passive relaying