41 research outputs found
Energy Harvesting Communication System with SOC-Dependent Energy Storage Losses
The popularity of Energy Harvesting Devices (EHDs) has grown in the past few
years, thanks to their capability of prolonging the network lifetime. In
reality, EHDs are affected by several inefficiencies, e.g., energy leakage,
battery degradation or storage losses. In this work we consider an energy
harvesting transmitter with storage inefficiencies. In particular, we assume
that when new energy has to be stored in the battery, part of this is wasted
and the losses depend upon the current state of charge of the device. This is a
practical realistic assumption, e.g., for a capacitor, that changes the
structure of the optimal transmission policy. We analyze the throughput
maximization problem with a dynamic programming approach and prove that, given
the battery status and the channel gain, the optimal transmission policy is
deterministic. We derive numerical results for the energy losses in a capacitor
and show the presence of a \emph{loop effect} that degrades the system
performance if the optimal policy is not considered.Comment: In Proc. IEEE Twelfth Int. Symposium on Wireless Communication
Systems (ISWCS), pp. 406-410, Aug. 201
On the Effects of Battery Imperfections in an Energy Harvesting Device
Energy Harvesting allows the devices in a Wireless Sensor Network to recharge
their batteries through environmental energy sources. While in the literature
the main focus is on devices with ideal batteries, in reality several
inefficiencies have to be considered to correctly design the operating regimes
of an Energy Harvesting Device (EHD). In this work we describe how the
throughput optimization problem changes under \emph{real battery} constraints
in an EHD. In particular, we consider imperfect knowledge of the state of
charge of the battery and storage inefficiencies, \emph{i.e.}, part of the
harvested energy is wasted in the battery recharging process. We formulate the
problem as a Markov Decision Process, basing our model on some realistic
observations about transmission, consumption and harvesting power. We find the
performance upper bound with a real battery and numerically discuss the novelty
introduced by the real battery effects. We show that using the \emph{old}
policies obtained without considering the real battery effects is strongly
sub-optimal and may even result in zero throughput.Comment: In Proc. IEEE International Conference on Computing, Networking and
Communications, pp. 942-948, Feb. 201
Joint Transmission and Energy Transfer Policies for Energy Harvesting Devices with Finite Batteries
One of the main concerns in traditional Wireless Sensor Networks (WSNs) is
energy efficiency. In this work, we analyze two techniques that can extend
network lifetime. The first is Ambient \emph{Energy Harvesting} (EH), i.e., the
capability of the devices to gather energy from the environment, whereas the
second is Wireless \emph{Energy Transfer} (ET), that can be used to exchange
energy among devices. We study the combination of these techniques, showing
that they can be used jointly to improve the system performance. We consider a
transmitter-receiver pair, showing how the ET improvement depends upon the
statistics of the energy arrivals and the energy consumption of the devices.
With the aim of maximizing a reward function, e.g., the average transmission
rate, we find performance upper bounds with and without ET, define both online
and offline optimization problems, and present results based on realistic
energy arrivals in indoor and outdoor environments. We show that ET can
significantly improve the system performance even when a sizable fraction of
the transmitted energy is wasted and that, in some scenarios, the online
approach can obtain close to optimal performance.Comment: 16 pages, 12 figure
Achievable Secrecy Rates of an Energy Harvesting Device
The secrecy rate represents the amount of information per unit time that can
be securely sent on a communication link. In this work, we investigate the
achievable secrecy rates in an energy harvesting communication system composed
of a transmitter, a receiver and a malicious eavesdropper. In particular,
because of the energy constraints and the channel conditions, it is important
to understand when a device should transmit and to optimize how much power
should be used in order to improve security. Both full knowledge and partial
knowledge of the channel are considered under a Nakagami fading scenario. We
show that high secrecy rates can be obtained only with power and coding rate
adaptation. Moreover, we highlight the importance of optimally dividing the
transmission power in the frequency domain, and note that the optimal scheme
provides high gains in secrecy rate over the uniform power splitting case.
Analytically, we explain how to find the optimal policy and prove some of its
properties. In our numerical evaluation, we discuss how the maximum achievable
secrecy rate changes according to the various system parameters. Furthermore,
we discuss the effects of a finite battery on the system performance and note
that, in order to achieve high secrecy rates, it is not necessary to use very
large batteries.Comment: Accepted for publication in IEEE Journal on Selected Areas in
Communications (Mar. 2016
Joint Optimization of Energy Efficiency and Data Compression in TDMA-Based Medium Access Control for the IoT - Extended Version
Energy efficiency is a key requirement for the Internet of Things, as many
sensors are expected to be completely stand-alone and able to run for years
without battery replacement. Data compression aims at saving some energy by
reducing the volume of data sent over the network, but also affects the quality
of the received information. In this work, we formulate an optimization problem
to jointly design the source coding and transmission strategies for
time-varying channels and sources, with the twofold goal of extending the
network lifetime and granting low distortion levels. We propose a scalable
offline optimal policy that allocates both energy and transmission parameters
(i.e., times and powers) in a network with a dynamic Time Division Multiple
Access (TDMA)-based access scheme.Comment: 8 pages, 4 figures, revised and extended version of a paper that was
accepted for presentation at IEEE Int. Workshop on Low-Layer Implementation
and Protocol Design for IoT Applications (IoT-LINK), GLOBECOM 201
Achievable Secrecy Rates of an Energy Harvesting Device with a Finite Battery
In this paper, we investigate the achievable secrecy rates in an Energy Harvesting communication system composed of one transmitter and multiple receivers. In particular, because of the energy constraints and the channel conditions, it is important to understand when a device should transmit or not and how much power should be used. We introduce the Optimal Secrecy Policy in several scenarios. We show that, if the receivers demand high secrecy rates, then it is not always possible to satisfy all their requests. Thus, we introduce a scheme that chooses which receivers should be discarded. Also, we study how the system is influenced by the Channel State Information and, in particular, how the knowledge of the eavesdropper's channel changes the achievable rates
Stochastic Optimization of Energy Harvesting Wireless Communication Networks
Energy harvesting from environmental energy sources (e.g., sunlight) or from man-made
sources (e.g., RF energy) has been a game-changing paradigm, which enabled the possibility
of making the devices in the Internet of Things or wireless sensor networks operate
autonomously and with high performance for years or even decades without human
intervention. However, an energy harvesting system must be correctly designed to achieve
such a goal and therefore the energy management problem has arisen and become a critical
aspect to consider in modern wireless networks. In particular, in addition to the hardware
(e.g., in terms of circuitry design) and application point of views (e.g., sensor deployment),
also the communication protocol perspective must be explicitly taken into account; indeed,
the use of the wireless communication interface may play a dominant role in the energy
consumption of the devices, and thus must be correctly designed and optimized. This
analysis represents the focus of this thesis.
Energy harvesting for wireless system has been a very active research topic in the past
decade. However, there are still many aspects that have been neglected or not completely
analyzed in the literature so far. Our goal is to address and solve some of these new
problems using a common stochastic optimization setup based on dynamic programming.
In particular, we formulate both the centralized and decentralized optimization problems
in an energy harvesting network with multiple devices, and discuss the interrelations
between these two schemes; we study the combination of environmental energy harvesting
and wireless energy transfer to improve the transmission rate of the network and achieve a
balanced situation; we investigate the long-term optimization problem in wireless powered
communication networks, in which the receiver supplies wireless energy to the terminal
nodes; we deal with the energy storage inefficiencies of the energy harvesting devices,
and show that traditional policies may be strongly suboptimal in this context; finally, we
investigate how it is possible to increase secrecy in a wireless link where a third malicious
party eavesdrops the information transmitted by an energy harvesting node
Studio ed elaborazione di dati sulla propagazione acustica sottomarina
In questa tesi si studia il canale acustico sottomarino. Tale studio è motivato dall'interesse a migliorare le prestazioni delle comunicazioni acustiche sottomarine per la trasmissione dati. Tali comunicazioni rendono possibili diverse utili applicazioni militari e civili. Si sono quindi trattate inizialmente le caratteristiche principali del canale acustico sottomarino. In seguito, si sono stimate le risposte impulsive di canale ottenute dalla rielaborazione di registrazioni di segnali acustici trasmessi sott'acqua. Tale analisi dei dati ha evidenziato delle discrepanze tra i modelli di canale presentati nel primo capitolo della tesi e la struttura delle risposte impulsive stimate nei dati sperimentali. Per questo motivo il problema del modello di canale è stato riconsiderato da una diversa prospettiva. Infatti, si è data un'interpretazione della struttura dei tempi di interarrivo dei cammini multipli nella risposta impulsiva del canale, attraverso un modello geometrico a raggi. Infine, si accenna a considerazioni utili per il successivo sviluppo di modelli per il canale acustico sottomarinoope