122 research outputs found
Wirelessly Powered Backscatter Communication Networks: Modeling, Coverage and Capacity
Future Internet-of-Things (IoT) will connect billions of small computing
devices embedded in the environment and support their device-to-device (D2D)
communication. Powering this massive number of embedded devices is a key
challenge of designing IoT since batteries increase the devices' form factors
and battery recharging/replacement is difficult. To tackle this challenge, we
propose a novel network architecture that enables D2D communication between
passive nodes by integrating wireless power transfer and backscatter
communication, which is called a wirelessly powered backscatter communication
(WP-BackCom) network. In the network, standalone power beacons (PBs) are
deployed for wirelessly powering nodes by beaming unmodulated carrier signals
to targeted nodes. Provisioned with a backscatter antenna, a node transmits
data to an intended receiver by modulating and reflecting a fraction of a
carrier signal. Such transmission by backscatter consumes orders-of-magnitude
less power than a traditional radio. Thereby, the dense deployment of
low-complexity PBs with high transmission power can power a large-scale IoT. In
this paper, a WP-BackCom network is modeled as a random Poisson cluster process
in the horizontal plane where PBs are Poisson distributed and active ad-hoc
pairs of backscatter communication nodes with fixed separation distances form
random clusters centered at PBs. The backscatter nodes can harvest energy from
and backscatter carrier signals transmitted by PBs. Furthermore, the
transmission power of each node depends on the distance from the associated PB.
Applying stochastic geometry, the network coverage probability and transmission
capacity are derived and optimized as functions of backscatter parameters,
including backscatter duty cycle and reflection coefficient, as well as the PB
density. The effects of the parameters on network performance are
characterized.Comment: 28 pages, 11 figures, has been submitted to IEEE Trans. on Wireless
Communicatio
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Leveraging Backscatter for Ultra-low Power Wireless Sensing Systems
The past few years have seen a dramatic growth in wireless sensing systems, with millions of wirelessly connected sensors becoming first-class citizens of the Internet. The number of wireless sensing devices is expected to surpass 6.75 billion by 2017, more than the world\u27s population as well as the combined market of smartphones, tablets, and PCs. However, its growth faces two pressing challenges: battery energy density and wireless radio power consumption. Battery energy density looms as a fundamental limiting factor due to slow improvements over the past several decades (3x over 22 years). Wireless radio power consumption is another key challenge because high-speed wireless communication is often far more expensive energy-wise than computation, storage and sensing. To make matters worse, wireless sensing devices are generating an increasing amount of data. These challenges raise a fundamental question --- how should we power and communicate with wireless sensing devices. More specifically, instead of using batteries, can we leverage other energy sources to reduce, if not eliminate, the dependence on batteries? Similarly, instead of optimizing existing wireless radios, can we fundamentally change how radios transmit wireless signals to achieve lower power consumption? A promising technique to address these questions is backscatter --- a primitive that enables RF energy harvesting and ultra-low-power wireless communication. Backscatter has the potential to reduce dependence on batteries because it can obtain energy by rectifying the wireless signals transmitted by a backscatter reader. Backscatter can also work by reflecting existing wireless signals (WiFi, BLE) when these are available nearby. Because signal reflection only consumes uWs of power, backscatter can enable ultra-low-power wireless communication. However, the use of backscatter for communicating with wireless sensing devices presents several challenges. First, decreasing RF power across distance limits the operational range of micro-powered backscatter devices. This raises the question of how to maintain a communication link with a backscatter device despite tiny amount of harvested power. Second, even though the backscatter RF front-end is extremely power-efficient, the computational and sensing overhead on backscatter sensors limit its ability to operate with a few micro-Watts of power. Such overhead is a negligible factor of overall power consumption for platforms where radio power consumption is high (e.g. WiFi or Bluetooth based devices). However, it becomes the bottleneck for backscatter based platforms. Third, backscatter readers are not currently deployed in existing indoor environments to provide a continuous carrier for carrying backscattered information. As a result, backscatter deployment is not yet widespread. This thesis addresses these challenges by making the following contributions. First, we design a network stack that enables continuous operation despite decreasing harvested power across distance by employing an OS abstraction --- task fragmentation. We show that such a network stack enables packet transfer even when the whole system is powered by a 3cmx3cm solar panel under natural indoor light condition. Second, we design a hardware architecture that minimizes the computational overhead of backscatter to enable over 1Mbps backscatter transmission while consuming less than 100uWs of power, a two order of magnitude improvement over the state-of-the-art. Finally, we design a system that can leverage both ambient WiFi and BLE signals for backscatter. Our empirical evaluation shows that we can backscatter 500bps data on top of a WiFi stream and 50kbps data on top of a Bluetooth stream when the backscatter device is 3m away from the commercial WiFi and Bluetooth receivers
System level simulation of passive and active backscatter devices
Ambient Backscatter is a communications method for batteryless, carrier-powered radio devices which harvest the needed energy from ambient sources and send their information by backscattering the ambient radio signals. An ambient backscatter device sends data bit by bit by either backscattering or not backscattering the received carrier wave. This work studies the operation of an ambient backscatter communication system consisting of a transmitter, a number of ambient backscatter devices and a receiver by simulating it in MATLAB. This thesis aims to answer the research questions: when it is better to use either passive or active ambient backscatter devices and what factors primarily affect the maximum data rate, communication range and susceptibility to interference of the devices. A definite answer to the research questions could not be given, but the thesis results show that active aBS- devices have potential of reaching the same performance figures as passive ones in terms of achievable range
Sensores passivos alimentados por transmissão de energia sem fios para aplicações de Internet das coisas
Nowadays, the Wireless Sensor Networks (WSNs) depend on the battery
duration of the sensors and there is a renewed interest in creating a passive
sensor network scheme in the area of Internet of Things (IoT) and space
oriented WSN systems. The challenges for the future of radio communications
have a twofold evolution, one being the low power consumption
and, another, the adaptability and intelligent use of the available resources.
Specially designed radios should be used to reduce power consumption, and
adapt to the environment in a smart and e cient way. This thesis will focus
on the development of passive sensors based on low power communication
(backscatter) with Wireless Power Transfer (WPT) capabilities used in IoT
applications. In that sense, several high order modulations for the communication
will be explored and proposed in order to increase the data rate.
Moreover, the sensors need to be small and cost e ective in order to be
embedded in other technologies or devices. Consequently, the RF front-end
of the sensors will be designed and implemented in Monolithic Microwave
Integrated Circuit (MMIC).Atualmente, as redes de sensores sem fios dependem da duração da bateria
e,deste modo, existe um interesse renovado em criar um esquema de rede
de sensores passivos na área de internet das coisas e sistemas de redes
de sensores sem fios relacionados com o espaço. Os desafios do futuro
das comunicações de rádio têm uma dupla evolução, sendo um o baixo
consumo de energia e, outro, a adaptação e o uso inteligente dos recursos
disponíveis. Rádios diferentes dos convencionais devem ser usados para
reduzir o consumo de energia e devem adaptar-se ao ambiente de forma
inteligente e eficiente, de modo a que este use a menor quantidade de
energia possível para estabelecer a comunicação. Esta tese incide sobre o
desenvolvimento de sensores passivos baseados em comunicação de baixo
consumo energético (backscatter) com recurso a transmissão de energia sem
fios de modo a que possam ser usados em diferentes aplicações inseridas na
internet das coisas. Nesse sentido, várias modulações de alta ordem para a
comunicação backscatter serão exploradas e propostas com o objectivo de
aumentar a taxa de transmissão de dados. Além disso, os sensores precisam
de ser reduzidos em tamanho e económicos de modo a serem incorporados
em outras tecnologias ou dispositivos. Consequentemente, o front-end de
rádio frequência dos sensores será projetado e implementado em circuito
integrado de microondas monolítico.Programa Doutoral em Engenharia Eletrotécnic
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