Impact of using CSS PHY and RTS/CTS Combined with Frame Concatenation in the IEEE 802.15.4 Non-beacon Enabled Mode Performance

This paper studies the performance improvement of the IEEE 802.15.4 non-beacon-enabled mode originated by the inclusion of the Request-To-Send/Clear-To-Send (RTS/CTS) handshake mechanism resulting in frame concatenation. Under IEEE 802.15.4 employing RTS/CTS, the backoff procedure is not repeated for each data frame sent but only for each RTS/CTS set. The maximum throughput and minimum delay performance are mathematically derived for both the Chirp Spread Spectrum and Direct Sequence Spread Spectrum Physical layers for the 2.4 GHz band. Results show that the utilization of RTS/CTS significantly enhances the performance of IEEE 802.15.4 applied to healthcare in terms of bandwidth efficiency.This work was supported by FCT/MCTES through national funds and when applicable co-funded EU funds under the project UIDB/50008/2020, COST CA20120 INTERACT, Fundación Carolina and Grupo Tordesillas short stay grant in UC3M, SNF Scientific Exchange - AISpectrum (project 205842), ORCIP (22141- 01/SAICT/2016) and TeamUp5G. TeamUp5G project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie project number 813391.info:eu-repo/semantics/acceptedVersio

Performance enhancement of IEEE 802.15.4 by employing RTS/CTS and frame concatenation

IEEE 802.15.4 has been widely accepted as the de facto standard for wireless sensor networks (WSNs). However, as in their current solutions for medium access control (MAC) sub-layer protocols, channel efficiency has a margin for improvement, in this study, the authors evaluate the IEEE 802.15.4 MAC sub-layer performance by proposing to use the request-/clear-to-send (RTS/CTS) combined with frame concatenation and block acknowledgement (BACK) mechanism to optimise the channel use. The proposed solutions are studied in a distributed scenario with single-destination and single-rate frame aggregation. The throughput and delay performance is mathematically derived under channel environments without/with transmission errors for both the chirp spread spectrum and direct sequence spread spectrum physical layers for the 2.4 GHz Industrial, Scientific and Medical band. Simulation results successfully verify the authors’ proposed analytical model. For more than seven TX (aggregated frames) all the MAC sub-layer protocols employing RTS/CTS with frame concatenation (including sensor BACK MAC) allow for optimising channel use in WSNs, corresponding to 18–74% improvement in the maximum average throughput and minimum average delay, together with 3.3–14.1% decrease in energy consumption.info:eu-repo/semantics/publishedVersio

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 Evaluation of Class A LoRa Communications

Recently, Low Power Wide Area Networks (LPWANs) have attracted a great interest due to the need of connecting more and more devices to the so-called Internet of Things (IoT). This thesis explores LoRa’s suitability and performance within this paradigm, through a theoretical approach as well as through practical data acquired in multiple field campaigns. First, a performance evaluation model of LoRa class A devices is proposed. The model is meant to characterize the performance of LoRa’s Uplink communications where both physical layer (PHY) and medium access control (MAC) are taken into account. By admitting a uniform spatial distribution of the devices, the performance characterization of the PHY-layer is studied through the derivation of the probability of successfully decoding multiple frames that were transmitted with the same spreading factor and at the same time. The MAC performance is evaluated by admitting that the inter-arrival time of the frames generated by each LoRa device is exponentially distributed. A typical LoRaWAN operating scenario is considered, where the transmissions of LoRa Class A devices suffer path-loss, shadowing and Rayleigh fading. Numerical results obtained with the modeling methodology are compared with simulation results, and the validation of the proposed model is discussed for different levels of traffic load and PHY-layer conditions. Due to the possibility of capturing multiple frames simultaneously, the maximum achievable performance of the PHY/MAC LoRa scheme according to the signal-to-interference-plus-noise ratio (SINR) is considered. The contribution of this model is primarily focused on studying the average number of successfully received LoRa frames, which establishes a performance upper bound due to the optimal capture condition considered in the PHY-layer. In the second stage of this work a practical LoRa point-to-point network was deployed to characterize LoRa’s performance in a practical way. Performance was assessed through data collected in the course of several experiments, positioning the transmitter in diverse locations and environments. This work reports statistics of the received packets and different metrics gathered from the physical-layer

Design of a wireless monitoring system based on the ZigBee protocol for photovoltaic systems

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.This work deals with the possibility of using the promising technology of wireless sensor networks (WSN) in the field of photovoltaic (PV) plant supervising and monitoring. The knowledge of the status and good working condition of each PV module separately as well as of any component of the PV system will guide in a more efficient way of power management. This work will concentrate on monitoring and controlling as well as healthy operation control of PV panels separately. Data logging will be also available and can be used for reference or statistical purposes. The nature of wireless sensor networks (WSN) offers several advantages on monitoring and controlling applications over other traditional technologies including self-healing, self-organization, and flexibility. The versatility, ease of use, and reliability of a mesh network topology offered by the ZigBee technology that is based on the IEEE 802.15.4 standard, are used in this work to offer the maximum of its capabilities on the system being presented. A set of sensors attached on each PV panel are connected to a wireless ZigBee module. Each PV panel has its own ZigBee device located at its back side. All ZigBee devices forms a network with all the necessary devices of the ZigBee protocol included, such as end devises (RFD), a router (FFD), and a coordinator (COO). An extra ZigBee device might optionally be used to serve the whole system as an Ethernet gateway for making the system able to be connected to the internet. The factors that are being monitored are the panel‟s temperature, the output voltage, and output current. At the router device that operates as a parent for all the end devices, extra monitored factors are the air dust concentration, current irradiance and also the angle of the PV array (in the case of tracking system use).Two controlling outputs (relays) are located at the router device offering the capability of controlling the motors or the actuators of a tracking system

Comunicações sem-fios de tempo-real para ambientes abertos

Doutoramento em Engenharia InformáticaWireless communication technologies have become widely adopted, appearing in heterogeneous applications ranging from tracking victims, responders and equipments in disaster scenarios to machine health monitoring in networked manufacturing systems. Very often, applications demand a strictly bounded timing response, which, in distributed systems, is generally highly dependent on the performance of the underlying communication technology. These systems are said to have real-time timeliness requirements since data communication must be conducted within predefined temporal bounds, whose unfulfillment may compromise the correct behavior of the system and cause economic losses or endanger human lives. The potential adoption of wireless technologies for an increasingly broad range of application scenarios has made the operational requirements more complex and heterogeneous than before for wired technologies. On par with this trend, there is an increasing demand for the provision of cost-effective distributed systems with improved deployment, maintenance and adaptation features. These systems tend to require operational flexibility, which can only be ensured if the underlying communication technology provides both time and event triggered data transmission services while supporting on-line, on-the-fly parameter modification. Generally, wireless enabled applications have deployment requirements that can only be addressed through the use of batteries and/or energy harvesting mechanisms for power supply. These applications usually have stringent autonomy requirements and demand a small form factor, which hinders the use of large batteries. As the communication support may represent a significant part of the energy requirements of a station, the use of power-hungry technologies is not adequate. Hence, in such applications, low-range technologies have been widely adopted. In fact, although low range technologies provide smaller data rates, they spend just a fraction of the energy of their higher-power counterparts. The timeliness requirements of data communications, in general, can be met by ensuring the availability of the medium for any station initiating a transmission. In controlled (close) environments this can be guaranteed, as there is a strict regulation of which stations are installed in the area and for which purpose. Nevertheless, in open environments, this is hard to control because no a priori abstract knowledge is available of which stations and technologies may contend for the medium at any given instant. Hence, the support of wireless real-time communications in unmanaged scenarios is a highly challenging task. Wireless low-power technologies have been the focus of a large research effort, for example, in the Wireless Sensor Network domain. Although bringing extended autonomy to battery powered stations, such technologies are known to be negatively influenced by similar technologies contending for the medium and, especially, by technologies using higher power transmissions over the same frequency bands. A frequency band that is becoming increasingly crowded with competing technologies is the 2.4 GHz Industrial, Scientific and Medical band, encompassing, for example, Bluetooth and ZigBee, two lowpower communication standards which are the base of several real-time protocols. Although these technologies employ mechanisms to improve their coexistence, they are still vulnerable to transmissions from uncoordinated stations with similar technologies or to higher power technologies such as Wi- Fi, which hinders the support of wireless dependable real-time communications in open environments. The Wireless Flexible Time-Triggered Protocol (WFTT) is a master/multi-slave protocol that builds on the flexibility and timeliness provided by the FTT paradigm and on the deterministic medium capture and maintenance provided by the bandjacking technique. This dissertation presents the WFTT protocol and argues that it allows supporting wireless real-time communication services with high dependability requirements in open environments where multiple contention-based technologies may dispute the medium access. Besides, it claims that it is feasible to provide flexible and timely wireless communications at the same time in open environments. The WFTT protocol was inspired on the FTT paradigm, from which higher layer services such as, for example, admission control has been ported. After realizing that bandjacking was an effective technique to ensure the medium access and maintenance in open environments crowded with contention-based communication technologies, it was recognized that the mechanism could be used to devise a wireless medium access protocol that could bring the features offered by the FTT paradigm to the wireless domain. The performance of the WFTT protocol is reported in this dissertation with a description of the implemented devices, the test-bed and a discussion of the obtained results.As tecnologias de comunicação sem fios tornaram-se amplamente adoptadas, surgindo em aplicações heterógeneas que vão desde a localização de vítimas, pessoal médico e equipamentos em cenários de desastre à monitorização da condição física de máquinas em ambientes industrials. Muito frequentemente, as aplicações exigem uma resposta limitada no tempo que, geralmente, em sistemas distribuídos, é substancialmente dependente do desempenho da tecnologia de comunicação utilizada. Estes sistemas tendem a possuir requisitos de tempo-real uma vez que a comunicação de dados tem de ser conduzida dentro de limites temporais pré-definidos que, quando não cumpridos, podem comprometer o correcto funcionamento do sistema e resultar em perdas económicas ou colocar em risco vidas humanas. A potencial adopção de tecnologias sem-fios para um crescente número de cenários traduz-se num aumento da complexidade e heterogeneidade dos requisitos operacionais relativamente às tecnologias cabladas. A acompanhar esta tendência verifica-se uma crescente procura de sistemas distribuídos, caracterizados quer por uma boa relação custo-eficácia, quer pela simplicidade de instalação, manutenção e adaptação. Ao mesmo tempo, estes sistemas tendem a requerer flexibilidade operacional, que apenas pode ser assegurada se a tecnlogia de comunicação empregue supportar transmissões de dados dispoletadas quer por eventos (event-triggered), quer por tempo (timetriggered) e se, ao mesmo tempo, em funcionamento, permitir a alteração dos parâmetros de comunicação correspondentes. Frequentemente, as aplicações com comunicações sem fios caracterizam-se por exigências de instalação que apenas podem ser endereçadas usando alimentação através de baterias e/ou mecanismos de recolha de energia do ambiente envolvente. Estas aplicações têm tipicamente requisitos exigentes de autonomia e de tamanho, impedindo o recurso a baterias de grande dimensão. Dado que o suporte de comunicações pode representar uma parte significativa dos requisitos de energia da estação, o uso de tecnologias de comunicação de elevado consumo não é adequado. Desta forma, nestas aplicações, as tecnologias de comunicação de curto-alcance tornaram-se amplamente adoptadas uma vez que, apesar de se caracterizarem por taxas de transmissão inferiores, consomem apenas uma fracção da energia das tecnologias de maior alcance. resumo Em geral, os requisitos de pontualidade da comunicação de dados podem ser cumpridos através da garantia da disponibilidade do meio no instante em que qualquer estação inicie uma transmissão. Em ambientes controlados esta disponibilidade pode ser garantida, na medida em que existe um controlo de quais as estações que foram instaladas na área e qual a sua função. Contrariamente, em ambientes abertos, tal controlo é difícil de garantir uma vez que não existe conhecimento a priori de que estações ou tecnologias podem competir pelo meio, tornando o suporte de comunicações de temporeal um desafio difícil de implementar em cenários com estações de comunicação não controladas. As comunicações de baixo consumo têm sido o foco de um esforço de investigação bastante amplo, por exemplo, no domínio das redes de sensores sem fios. Embora possam permitir uma maior autonomia a estações baseadas em baterias, estas tecnologias são reconhecidas como sendo negativamente influenciadas por tecnologias semelhantes competindo pelo mesmo meio e, em particular, por tecnologias que utilizem níveis de potência de transmissão mais elevados em bandas de frequências comuns. De forma cada vez mais acentuada, a banda industrial, científica e médica (ISM) dos 2.4 GHz tem-se tornado mais saturada com tecnologias que competem entre si pelo acesso ao meio tais como, por exemplo, Bluetooth e ZigBee, dois padrões de comunicação que são a base de vários protocolos de tempo-real. Apesar destas tecnologias aplicarem mecanismos para melhorar a sua coexistência, são vulneráveis a transmissões de estações não controladas que usem as mesmas tecnologias ou que usem tecnologias com níveis de potência de transmissão mais elevados, impedindo, desta forma, o suporte de comunicações de tempo-real fiáveis em ambientes abertos. O protocolo de comunicação sem fios flexível disparado por tempo (WFTT) é baseado numa arquitectura mestre/múltiplo escravo alavancado na flexibilidade e pontualidade promovidas pelo paradigma FTT e na captura e manutenção determinística do meio suportadas pela técnica de bandjacking (captura de banda). Esta tese apresenta o protocolo WFTT e argumenta que este permite suportar serviços de comunicação de tempo-real com requisitos elevados de fiabilidade em ambientes abertos onde várias tecnologias de comunicação baseadas em contenção disputam o acesso ao meio. Adicionalmente, esta tese reivindica que é possível suportar comunicações sem-fios simultaneamente flexíveis e pontuais em ambientes abertos. O protocolo WFTT foi inspirado no paradigma FTT, do qual importa os serviços de alto nível como, por exemplo, o controlo de admissão. Após a observação da eficácia da técnica de bandjacking em assegurar o acesso ao meio e a correspondente manutenção, foi reconhecida a possibilidade de utilização deste mecanismo para o desenvolvimento de um protocolo de acesso ao meio, capaz de oferecer as funcionalidades do paradigma FTT em meios de comunicação sem-fios. O desempenho do protocolo WFTT é reportado nesta tese com uma descrição dos dispositivos implementados, da bancada de ensaios desenvolvida e dos resultados obtidos

Reliable LoRaWAN links: performance analysis

Nowadays the IoT paradigm is attracting interest in the scientific and commercial fields. This thesis focuses on the solution combining LoRa and LoRaWAN and on its performance when reliable communication is employed. The discussion presents the implementation of LoRaWAN reliable communication in the ns-3 simulator and proposes a mathematical model for performance evaluation. The performance of the system and the validity of the proposed model are evaluated by means of simulations

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

Energy efficiency in short and wide-area IoT technologies—A survey

In the last years, the Internet of Things (IoT) has emerged as a key application context in the design and evolution of technologies in the transition toward a 5G ecosystem. More and more IoT technologies have entered the market and represent important enablers in the deployment of networks of interconnected devices. As network and spatial device densities grow, energy efficiency and consumption are becoming an important aspect in analyzing the performance and suitability of different technologies. In this framework, this survey presents an extensive review of IoT technologies, including both Low-Power Short-Area Networks (LPSANs) and Low-Power Wide-Area Networks (LPWANs), from the perspective of energy efficiency and power consumption. Existing consumption models and energy efficiency mechanisms are categorized, analyzed and discussed, in order to highlight the main trends proposed in literature and standards toward achieving energy-efficient IoT networks. Current limitations and open challenges are also discussed, aiming at highlighting new possible research directions