55 research outputs found
Interference mitigation strategy design and applications for wireless sensor networks
The Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 standard presents a very useful technology for implementing low-cost, low-power, wireless sensor networks. Its main focus, which is to applications requiring simple wireless connectivity with relaxed throughout and latency requirements, makes it suitable for connecting devices that have not been networked, such as industrial and control instrumentation equipments, agricultural equipments, vehicular equipments, and home appliances. Its usage of the license-free 2.4 GHz frequency band makes the technique successful for fast and worldwide market deployments. However, concerns about interference have arisen due to the presence of other wireless technologies using the same spectrum. Although the IEEE 802.15.4 standard has provided some mechanisms, to enhance capability to coexist with other wireless devices operating on the same frequency band, including Carrier Sensor Multiple Access (CSMA), Clear Channel Assessment (CCA), channel alignment, and low duty cycle, it is essential to design and implement adjustable mechanisms for an IEEE 802.15.4 based system integrated into a practical application to deal with interference which changes randomly over time. Among the potential interfering systems (Wi-Fi, Bluetooth, cordless phones, microwave ovens, wireless headsets, etc) which work on the same Industrial, Scientific, and Medical (ISM) frequency band, Wi-Fi systems (IEEE 802.11 technique) have attracted most concerns because of their high transmission power and large deployment in both residential and office environments.
This thesis aims to propose a methodology for IEEE 802.15.4 wireless systems to adopt proper adjustment in order to mitigate the effect of interference caused by IEEE 802.11 systems through energy detection, channel agility and data recovery. The contribution of this thesis consists of five parts. Firstly, a strategy is proposed to enable IEEE 802.15.4 systems to maintain normal communications using the means of consecutive transmissions, when the system s default mechanism of retransmission is insufficient to ensure successful rate due to the occurrence of Wi-Fi interference. Secondly, a novel strategy is proposed to use a feasible way for IEEE 802.15.4 systems to estimate the interference pattern, and accordingly adjust system parameters for the purpose of achieving optimized communication effectiveness during time of interference without relying on hardware changes and IEEE 802.15.4 protocol modifications. Thirdly, a data recovery mechanism is proposed for transport control to be applied for recovering lost data by associating with the proposed strategies to ensure the data integrity when IEEE 802.15.4 systems are suffering from interference. Fourthly, a practical case is studied to discuss how to design a sustainable system for home automation application constructed on the basis of IEEE 802.15.4 technique. Finally, a comprehensive design is proposed to enable the implementation of an interference mitigation strategy for IEEE 802.15.4 based ad hoc WSNs within a structure of building fire safety monitoring system.
The proposed strategies and system designs are demonstrated mainly through theoretical analysis and experimental tests. The results obtained from the experimental tests have verified that the interference caused by an IEEE 802.11 system on an IEEE 802.15.4 system can be effectively mitigated through adjusting IEEE 802.15.4 system s parameters cooperating with interference pattern estimation. The proposed methods are suitable to be integrated into a system-level solution for an IEEE 802.15.4 system to deal with interference, which is also applicable to those wireless systems facing similar interference issues to enable the development of efficient mitigation strategies
Interference issues and mitigation method in WSN 2.4GHz ISM band: A survey
Current lifestyles promote the development and advancement in wireless technologies, especially in Wireless Sensor Networks (WSN) due to its several benefits.WSN offers a low cost, low data rate, flexible routing, longer lifetime, and low-energy consumption suitable for unmanned and long term monitoring.Among huge WSN applications, some key applications are smart houses, environmental monitoring, military applications, and other monitoring applications.As a result, ubiquitous increase in the number of wireless devices occupying the 2.4GHz frequency band.This causes a dense wireless connection followed by interference problem to WSN in the 2.4GHz frequency band. WSN is most affected by the interference issue because it has a lower data rate and transmission power compared to WLAN.Despite efforts made by researchers, to the author's knowledge, the interference issue is still a major problem in wireless networks.This paper aims to review the coexistence and interference issues of existing wireless technologies in the 2.4GHz Industrial, Scientific and Medical (ISM) band.Keywords— Coexistence, Frequency Spectrum, IEEE 802.15.4, Interference, WSN, 2.4GHz ISM ban
Innovative energy-efficient wireless sensor network applications and MAC sub-layer protocols employing RTS-CTS with packet concatenation
of energy-efficiency as well as the number of available applications. As a consequence there
are challenges that need to be tackled for the future generation of WSNs. The research work
from this Ph.D. thesis has involved the actual development of innovative WSN applications contributing
to different research projects. In the Smart-Clothing project contributions have been
given in the development of a Wireless Body Area Network (WBAN) to monitor the foetal movements
of a pregnant woman in the last four weeks of pregnancy. The creation of an automatic
wireless measurement system for remotely monitoring concrete structures was an contribution
for the INSYSM project. This was accomplished by using an IEEE 802.15.4 network enabling for
remotely monitoring the temperature and humidity within civil engineering structures. In the
framework of the PROENEGY-WSN project contributions have been given in the identification
the spectrum opportunities for Radio Frequency (RF) energy harvesting through power density
measurements from 350 MHz to 3 GHz. The design of the circuits to harvest RF energy
and the requirements needed for creating a WBAN with electromagnetic energy harvesting and
Cognitive Radio (CR) capabilities have also been addressed. A performance evaluation of the
state-of-the art of the hardware WSN platforms has also been addressed. This is explained by
the fact that, even by using optimized Medium Access Control (MAC) protocols, if the WSNs
platforms do not allow for minimizing the energy consumption in the idle and sleeping states,
energy efficiency and long network lifetime will not be achieved.
The research also involved the development of new innovative mechanisms that tries and solves
overhead, one of the fundamental reasons for the IEEE 802.15.4 standard MAC inefficiency. In
particular, this Ph.D. thesis proposes an IEEE 802.15.4 MAC layer performance enhancement by
employing RTS/CTS combined with packet concatenation. The results have shown that the use
of the RTS/CTS mechanism improves channel efficiency by decreasing the deferral time before
transmitting a data packet. In addition, the Sensor Block Acknowledgment MAC (SBACK-MAC)
protocol has been proposed that allows the aggregation of several acknowledgment responses
in one special Block Acknowledgment (BACK) Response packet. Two different solutions are
considered. The first one considers the SBACK-MAC protocol in the presence of BACK Request
(concatenation) while the second one considers the SBACK-MAC in the absence of BACK Request
(piggyback). The proposed solutions address a distributed scenario with single-destination and
single-rate frame aggregation. The throughput and delay performance is mathematically derived
under both ideal conditions (a channel environment with no transmission errors) and non
ideal conditions (a channel environment with transmission errors). An analytical model is proposed,
capable of taking into account the retransmission delays and the maximum number of
backoff stages. The simulation results successfully validate our analytical model. For more
than 7 TX (aggregated packets) all the MAC sub-layer protocols employing RTS/CTS with packet
concatenation allows for the optimization of channel use in WSNs, v8-48 % improvement in the
maximum average throughput and minimum average delay, and decrease energy consumption
Performance modelling and analysis of multiple coexisting IEEE 802.15.4 wireless sensor networks
With the features of low-power and flexible networking capabilities IEEE 802.15.4 has been widely regarded as one strong candidate of communication technologies for wireless sensor networks (WSNs). It is expected that with an increasing number of deployments of 802.15.4 based WSNs, multiple WSNs could coexist with full or partial overlap in residential or enterprise areas. As WSNs are usually deployed without coordination, the communication could meet significant degradation with the 802.15.4 channel access scheme, which has a large impact on system performance. In this thesis we are motivated to investigate the effectiveness of 802.15.4 networks supporting WSN applications with various environments, especially when hidden terminals are presented due to the uncoordinated coexistence problem. Both analytical models and system level simulators are developed to analyse the performance of the random access scheme specified by IEEE 802.15.4 medium access control (MAC) standard for several network scenarios. The first part of the thesis investigates the effectiveness of single 802.15.4 network supporting WSN applications. A Markov chain based analytic model is applied to model the MAC behaviour of IEEE 802.15.4 standard and a discrete event simulator is also developed to analyse the performance and verify the proposed analytical model. It is observed that 802.15.4 networks could sufficiently support most WSN applications with its various functionalities. After the investigation of single network, the uncoordinated coexistence problem of multiple 802.15.4 networks deployed with communication range fully or partially overlapped are investigated in the next part of the thesis. Both nonsleep and sleep modes are investigated with different channel conditions by analytic and simulation methods to obtain the comprehensive performance evaluation. It is found that the uncoordinated coexistence problem can significantly degrade the performance of 802.15.4 networks, which is unlikely to satisfy the QoS requirements for many WSN applications. The proposed analytic model is validated by simulations which could be used to obtain the optimal parameter setting before WSNs deployments to eliminate the interference risks
Coexistence and interference mitigation for WPANs and WLANs from traditional approaches to deep learning: a review
More and more devices, such as Bluetooth and IEEE 802.15.4 devices forming Wireless Personal Area Networks (WPANs) and IEEE 802.11 devices constituting Wireless Local Area Networks (WLANs), share the 2.4 GHz Industrial, Scientific and Medical (ISM) band in the realm of the Internet of Things (IoT) and Smart Cities. However, the coexistence of these devices could pose a real challenge—co-channel interference that would severely compromise network performances. Although the coexistence issues has been partially discussed elsewhere in some articles, there is no single review that fully summarises and compares recent research outcomes and challenges of IEEE 802.15.4 networks, Bluetooth and WLANs together. In this work, we revisit and provide a comprehensive review on the coexistence and interference mitigation for those three types of networks. We summarize the strengths and weaknesses of the current methodologies, analysis and simulation models in terms of numerous important metrics such as the packet reception ratio, latency, scalability and energy efficiency. We discover that although Bluetooth and IEEE 802.15.4 networks are both WPANs, they show quite different performances in the presence of WLANs. IEEE 802.15.4 networks are adversely impacted by WLANs, whereas WLANs are interfered by Bluetooth. When IEEE 802.15.4 networks and Bluetooth co-locate, they are unlikely to harm each other. Finally, we also discuss the future research trends and challenges especially Deep-Learning and Reinforcement-Learning-based approaches to detecting and mitigating the co-channel interference caused by WPANs and WLANs
Adaptive Resource Allocation for Wireless Body Sensor Networks
The IEEE 802.15.4 standard is an interesting technology for use in Wireless Body Sensor Networks (WBSN), where entire networks of sensors are carried by humans. In many environments the sensor nodes experience external interference for example, when the WBSN is operated in the 2.4 GHz ISM band and the human moves in a densely populated city, it will likely experience WiFi interference, with a quickly changing ``interference landscape''. In this thesis we propose Adaptive Resource Allocation schemes, to be carried out by the WBSN, which provided noticeable performance gains in such environments. We investigate a range of adaptation schemes and assess their performance both through simulations and experimentally
Impulsive Interference Avoidance in Dense Wireless Sensor Networks
ABSTRACT As with all wireless communication devices, wireless sensor networks (WSNs) are subject to interference from other users of the radio-frequency (RF) medium. Such interference is practically never random: originating in applications generally performing some practical and sensible activities, it naturally exhibits various regularities amounting to perceptible patterns, e.g., regularly-spaced short-duration impulses that correlate among multiple WSN nodes. If those nodes can recognize the interference pattern, they can benefit from steering their transmissions around it. This possibility has stirred some interest among researchers involved in cognitive radios, where special hardware has been postulated to circumvent non-random interference. Our goal is to explore ways of enhancing medium access control (MAC) schemes operating within the framework of traditional off-the-shelf RF modules applicable in low-cost WSN motes, such that they can detect interference patterns in the neighbourhood and creatively respond to them mitigating their negative impact on the packet reception rate. In this paper, we describe (a) a method for the post-deployment dynamic characterization of a channel aimed at identifying spiky interference patterns, (b) a way to incorporate interference models into an existing WSN emulator, and (c) the subsequent evaluation of a proof-of-concept MAC technique for circumventing the interference. We found that an interference-aware MAC can improve the packet delivery rates in these environments at the cost of increased latency. Notably, the latter is quite acceptable in the vast majority of WSN applications
Industry 4.0: Industrial IoT Enhancement and WSN Performance Analysis
L'abstract è presente nell'allegato / the abstract is in the attachmen
Remote vital signs monitoring based on wireless sensor networks
Tese de doutoramento em Líderes para as Indústrias TecnológicasGovernmental and private institutions face a major challenge to provide quality
health care to a population consisting of a growing number of elderly and chronically ill
patients. According to the World Health Organization, in 2006, the total global health
expenditures exceeded US$ 4 trillion and are rising in the majority of countries
including Portugal which, during 2006, expended 9.9% of its gross domestic product in
health care.
The use of remote vital signs monitoring systems increases the probability of early
detection of risky situations, allows frequent monitoring of in-patients, elderly and
chronically ill patients, and streamlines the work of health professionals. However, at
present, these systems are expensive, complex and employ obtrusive sensors, which
limit their application to intensive care units and cardiac intermediate care units.
This work is part of a project that aims to design, prototype and evaluate a remote
vital signs monitoring system based on the IEEE 802.15.4 and ZigBee protocols, which
allow the development of small low-power sensors. The prototype system comprises
electrocardiogram/heart rate and axillary thermometer sensors, networking devices and
three informatics applications that collect, process, and exhibit medical data.
The wireless sensors, the networking devices and one of the applications were
developed under this work. Additionally, the wireless sensor network was evaluated
through simulations at the MAC level and experimental and field tests. Field tests were
performed at an in-patient floor of Hospital Privado de Guimarães, a Portuguese
hospital. Finally, questionnaires were used to measure the satisfaction of users and
catalog their critics and suggestions for improvement. Simulations considered different topologies, operation modes and a crescent
number of sensors and hops. Experimental and field tests confirmed most of the results
obtained by simulations, but revealed that networks which did not assign transmission
time slots to electrocardiogram sensors were unable to maintain a high delivery ratio.
Contention between devices, aggravated by the inability of routers in receiving
incoming packets during backoff, and collisions between packets generated by hiddennodes
were responsible for most message losses. On the other hand, beacon-enabled star
IEEE 802.15.4 networks that assigned a guaranteed time slot to sensors were able to
maintain a very high delivery ratio. In contrast, these networks are restricted in terms of
the coverage area and the number of sensors. Also, field tests showed that under low
traffic scenarios ZigBee nonbeacon-enabled networks can achieve a high delivery ratio
even in presence of a high percentage of hidden-nodes.Instituições governamentais e privadas enfrentam um grande desafio para prestar
cuidados de saúde de qualidade a uma população constituída por um número crescente
de idosos e doentes crónicos. Segundo a Organização Mundial de Saúde, em 2006, a
despesa mundial em saúde ultrapassou a quantia de 4 bilhões de dólares americanos e
cresce anualmente na maioria dos países, incluindo Portugal, o qual, em 2006, gastou
9,9% do seu produto interno bruto em cuidados de saúde.
O uso de sistemas de monitorização remota de sinais vitais aumenta a probabilidade
de deteção precoce de situações de risco, permite que doentes internados, idosos ou
doentes crónicos sejam frequentemente monitorizados e agiliza o trabalho dos
profissionais de saúde. No entanto, atualmente, estes sistemas são caros e complexos, o
que limita a sua aplicação a alguns setores dos hospitais, tais como as unidades de
cuidados intensivos e as unidades de cuidados intermédios na área da cardiologia.
O projeto no qual insere-se este trabalho visa a conceção, a prototipagem e a
avaliação de um sistema de monitorização remota de sinais vitais com base nos
protocolos IEEE 802.15.4 e ZigBee, os quais oferecem a possibilidade de construção de
sensores com consumos energéticos muito baixos e reduzidas dimensões. O sistema
consiste em sensores de eletrocardiograma/frequência cardíaca e temperatura axilar,
dispositivos de rede e três aplicações que coletam, processam e apresentam o
eletrocardiograma e os sinais vitais.
No âmbito deste trabalho foram desenvolvidos os sensores sem fios, os dispositivos
de rede e uma das aplicações informáticas. Além disso, foi feita a avaliação do
desempenho da rede de sensores sem fios através da análise de simulações a nível da
camada de acesso ao meio (MAC) e de testes de laboratório e de campo. Os testes de campo da rede de sensores sem fios foram executados em um dos pisos de internamento
do Hospital Privado de Guimarães. Finalmente, foram usados questionários para medir
a satisfação dos utilizadores e recolher críticas e sugestões de melhoria.
As simulações consideraram diferentes topologias e modos de operação, além de
um número crescente de sensores e saltos. Testes experimentais e de campo
confirmaram grande parte dos resultados obtidos por simulação mas, adicionalmente,
revelaram que as redes constituídas por vários sensores de eletrocardiograma e que não
reservaram um intervalo de tempo de transmissão aos sensores não foram capazes de
manter uma elevada taxa de entrega de mensagens. Perdas de mensagens ocorreram
devido a disputas entre sensores pelo acesso ao canal sem fios e devido a ocorrência de
colisões de pacotes transmitidos por nós escondidos. Por outro lado, as redes baseadas
no protocolo IEEE 802.15.4 que atribuíram um intervalo de tempo de transmissão a
cada sensor conseguiram manter uma elevada taxa de entrega. Entretanto, essas redes
são limitadas em termos da área de cobertura e do número de sensores. Adicionalmente,
durante os testes de campo em cenários de tráfego reduzido, as redes ZigBee que não
empregaram beacons atingiram uma elevada taxa de entrega mesmo na presença de uma
grande percentagem de nós escondidos
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