199 research outputs found
Improved Signal Detection for Ambient Backscatter Communications
In ambient backscatter communication (AmBC) systems, passive tags connect to
a reader by reflecting an ambient radio frequency (RF) signal. However, the
reader may not know the channel states and RF source parameters and can
experience interference. The traditional energy detector (TED) appears to be an
ideal solution. However, it performs poorly under these conditions. To address
this, we propose two new detectors: (1) A joint correlation-energy detector
(JCED) based on the first-order correlation of the received samples and (2) An
improved energy detector (IED) based on the p-th norm of the received signal
vector. We compare the performance of the IED and TED under generalized noise
modeled using the McLeish distribution and derive a general analytical formula
for the area under the receiver operating characteristic (ROC) curves. Based on
our results, both detectors outperform TED. For example, the probability of
detection with a false alarm rate of 1% for JCED and IED is 14% and 5% higher,
respectively, compared to TED. These gains are even higher using the direct
interference cancellation (DIC) technique, with increases of 16% and 7%,
respectively. Overall, our proposed detectors offer better performance than the
TED, making them useful tools for improving AmBC system performance.Comment: This paper has got Major Revision by IEEE TGC
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
Generic wireless sensor network for dynamic monitoring of a new generation of building material
Existing testing methods for building materials before deployment include a series of
procedures as stipulated in British Standards, and most tests are performed in a controlled
laboratory environment. Types of equipment used for measurements, data logging, and
visualisation are commonly bulky, hard-wired, and consume a significant amount of
power. Most of the off-the-shelf sensing nodes have been designed for a few specific
applications and cannot be used for general purpose applications. This makes it difficult
to modify or extend the sensing features when needed. This thesis takes the initiative of
designing and implementing a low-powered, open-source, flexible, and small-sized
Generic wireless sensor network (GWSN) that can continuously monitor the building
materials and building environment, to address the limitations of the conventional
measurement methods and the technological gap.
The designed system is comprised of two custom-made sensor nodes and a gateway, as
well as purpose designed firmware for data collection and processing. For the proof of
concept and experimental studies, several measurement strategies were designed, to
demonstrate, evaluate, and validate the effectiveness of the system. The data was
collected from selected case study areas in the School of Energy, Geoscience,
Infrastructure and Society (EGIS) laboratories by measuring and monitoring building
structures and indoor environment quality parameters using the designed GWSN. The
measured data includes heat flux through the material, surface and air temperatures on
both sides of the material/structure, moisture variation, ambient temperature, relative
humidity, carbon dioxide, volatile organic compounds, particulate matter, and
sound/acoustic levels.
The initial results show the potential of the designed system to become the new
benchmark for tracking the variation of building materials with the environment and
investigating the impact of variation of building materials on indoor environment quality.
Based on the estimates of the thermal performance data, the sample used in the
experiment had a typical U-value between 4.8 and 5.8 W/m2K and a thermal resistance
value of 0.025m2
·K/W[1][2]. Thermal resistance values from the GWSN real-time
measurement were between 0.025 and 0.03 m2K/W, with an average of 0.025 m2K/W,
and thermal transmission values varied between 4.55 and 5.11 W/m2K. Based on the data
obtained, the results are within the range of typical values[3]. For thermal comfort measurements, the results of humidity and temperature from GWSN
were compared to values in the Kambic climatic chamber in the EGIS laboratory, and the
accuracies were 99 % and 98 % respectively. For the IAQ measurements, the values of
CO2 and TVOCs were compared to the commercial off-the-shelf measuring system, and
the accuracies were 98 %, and 97 %. Finally, the GWSN was tested for acoustic
measurements in the range of 55 dB to 106 dB. The results were compared to class one
Bruel & Kjaer SLM. The accuracy of GWSN was 97 %. The GWSN can be used for in lab and in-situ applications, to measure and analyse the thermal physical properties of
building materials/building structures (thermal transmittance, thermal conductivity, and
thermal resistance). The system can also measure indoor air quality, thermal comfort, and
airborne sound insulation of the building envelope. The key point here is to establish a
direct link between how building materials vary with the environment and how this
impacts indoor environment quality. Such a link is essential for long-term analysis of
building materials, which cannot be achieved using current methods.
Regarding increasing the power efficient of the implemented GWSN as well as its
performance and functionality, a new sensing platforms using backscatter technology
have been introduced. The theory of modulation and spread spectrum technique used in
backscattering has been explored. The trade-off between hardware complexity/power
consumption and link performance has been investigated.
Theoretical analysis and simulation validation of the new sensing technique, using
backscatter communication, has been performed. A novel multicarrier backscatter tag
compatible with Wireless Fidelity has been implemented and an IEEE 802.11g OFDM
preamble was synthesized by simulation. The tag consists of only two transistors with
current consumption no larger than 0.2 μA at voltage of less than 0.6 V.
Novel harmonic suppression approaches for frequency-shifted backscatter
communication has been proposed and demonstrated. The proposed approaches
independently manipulate mirror harmonics and higher order harmonics whereby;
specified higher order harmonics can be removed by carefully designing the real-valued
(continuous and discrete) reflection coefficients-based backscatter tags.
When successfully implemented, the backscatter system will reduce sensor node power
consumption by shifting the power-consuming radio frequency carrier synthesis functions
to carrier emitters.Engineering and Physical Sciences Research
Council (EPSRC) Funding EP/H009612/
RIScatter: unifying backscatter communication and reconfigurable intelligent surface
Backscatter Communication (BackCom) nodes harvest energy from and modulate information over an external electromagnetic wave. Reconfigurable Intelligent Surface (RIS) adapts its phase shift response to enhance or attenuate channel strength in specific directions. In this paper, we show how those two seemingly different technologies (and their derivatives) can be unified to leverage their benefits simultaneously into a single architecture called RIScatter. RIScatter consists of multiple dispersed or co-located scatter nodes, whose reflection states can be adapted to partially engineer the wireless channel of the existing link and partially modulate their own information onto the scattered wave. This contrasts with BackCom (resp. RIS) where the reflection pattern is exclusively a function of the information symbol (resp. Channel State Information (CSI)). The key principle in RIScatter is to render the probability distribution of reflection states (i.e., backscatter channel input) as a joint function of the information source, CSI, and Quality of Service (QoS) of the coexisting active primary and passive backscatter links. This enables RIScatter to softly bridge, generalize, and outperform BackCom and RIS; boil down to either under specific input distribution; or evolve in a mixed form for heterogeneous traffic control and universal hardware design. For a single-user multi-node RIScatter network, we characterize the achievable primary-(total-)backscatter rate region by optimizing the input distribution at the nodes, the active beamforming at the Access Point (AP), and the backscatter detection regions at the user. Simulation results demonstrate RIScatter nodes can exploit the additional propagation paths to smoothly transition between backscatter modulation and passive beamforming
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