16 research outputs found

    Frequency hopping in wireless sensor networks

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    Wireless sensor networks (WSNs) are nowadays being used to collectively gather and spread information in different kinds of applications, for military, civilian, environmental as well as commercial purposes. Therefore the proper functioning of WSNs under different kinds of environmental conditions, especially hostile environments, is a must and a lot of research currently ongoing. The problems related to the initialization and deployment of WSNs under harsh and resource limited conditions are investigated in this thesis. Frequency hopping (FH) is a spread spectrum technique in which multiple channels are used, or hoped, for communications across the network. This mitigates the worst effects of interference with frequency agile communication systems rather than by brute force approaches. FH is a promising technique for achieving the coexistence of sensor networks with other currently existing wireless systems, and it is successful within the somewhat limited computational capabilities of the sensor nodes hardware radios. In this thesis, a FH scheme for WSNs is implemented for a pair of nodes on an application layer. The merits and demerits of the scheme are studied for different kinds of WSN environments. The implementation has been done using a Sensinode NanoStack, a communication stack for internet protocol (IP) based wireless sensor networks and a Sensinode Devkit, for an IPv6 over low power wireless personal area network (6LoWPAN). The measurements are taken from the developed test bed and channel simulator for different kinds of scenarios. The detailed analysis of the FH scheme is done to determine its usefulness against interference from other wireless systems, especially wireless local area networks (WLANs), and the robustness of the scheme to combat fading or frequency selective fading

    Experimental Characterisation of Body-Centric Radio Channels Using Wireless Sensors

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    PhDWireless sensors and their applications have become increasingly attractive for industry, building automation and energy control, paving the way for new applications of sensor networks which go well beyond traditional sensor applications. In recent years, there has been a rapid growth in the number of wireless devices operating in close proximity to the human body. Wearable sensor nodes are growing popular not only in our normal living lifestyle, but also within healthcare and military applications, where different radio units operating in/on/off body communicate pervasively. Expectations go beyond the research visions, towards deployment in real-world applications that would empower business processes and future business cases. Although theoretical and simulation models give initial results of the antenna behaviour and the radio channel performance of wireless body area network (WBAN) devices, empirical data from different set of measurements still form an essential part of the radio propagation models. Usually, measurements are performed in laboratory facilities which are equipped with bulky and expensive RF instrumentation within calibrated and controllable environments; thus, the acquired data has the highest possible reliability. However, there are still measurement uncertainties due to cables and connections and significant variations when designs are deployed and measured in real scenarios, such as hospitals wards, commercial buildings or even the battle field. Consequently, more flexible and less expensive measurement tools are required. In this sense, wireless sensor nodes offer not only easiness to deploy or flexibility, but also adaptability to different environments. In this thesis, custom-built wireless sensor nodes are used to characterise different on-body radio channels operating in the IEEE 802.15.4 communication standard at the 2.45 GHz ISM band. Measurement results are also compared with those from the conventional technique using a Vector Network Analyser. The wireless sensor nodes not only diminished the effect of semi-rigid or flexible coaxial cables (scattering or radiation) used with the Vector Network Analyser (VNA), but also provided a more realistic response of the radio link channel. The performance of the wireless sensors is presented over each of the 16 different channels present at the 2.45 GHz band. Additionally, custom-built wireless sensors are used to characterise and model the performance of different on-body radio links in dynamic environments, such as jogging, rowing, and cycling. The use of wireless sensors proves to be less obstructive and more flexible than traditional measurements using coaxial cables, VNA or signal generators. The statistical analysis of different WBAN channels highlighted important radio propagation features which can be used as sport classifiers models and motion detection. Moreover, specific on-body radio propagation channels are further explored, with the aim to recognize physiological features such as motion pattern, breathing activity and heartbeat. The time domain sample data is transformed to the frequency domain using a non-parametric FFT defined by the Welch’s periodogram. The Appendix-Section D explores other digital signal processing techniques which include spectrograms (STFT) and wavelet transforms (WT). Although a simple analysis is presented, strong DSP techniques proved to be good for signal de-noising and multi-resolution analysis. Finally, preliminary results are presented for indoor tracking using the RSS recorded by multiple wireless sensor nodes deployed in an indoor scenario. In contrast to outdoor environments, indoor scenarios are subject to a high level of multipath signals which are dependent on the indoor clutter. The presented algorithm is based on path loss analysis combined with spatial knowledge of each wireless sensor

    Modeling and experimental performance analysis of ZigBee-IEEE 802.15.4 for wireless body area networks

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    Dissertação de mestrado integrado em Engenharia de ComunicaçõesThe emerging field of wireless body area networks (WBAN) has the potential to play an important role in everyday life, and there are many industries such as health, sports and entertainment that can take advantage of these networks. The wireless monitoring of users’ physical state, in indoor or outdoor environments, can bring benefits in several application scenarios; for example, it can increase patients’ general well-being and reduce caregivers’ workload by allowing continuous monitoring. This dissertation identifies and analyzes key performance aspects of using the ZigBee and IEEE 802.15.4 protocols in WBAN applications. The main reason behind this work is because these protocols were designed primarily for wireless sensor networks (WSNs) but are also being used in WBAN applications, particularly in the healthcare area. The differences between WSN and WBANs are explained and are used to discuss the usage of the ZigBee and the IEEE 802.15.4 standards in WBANs. The analysis performed in this work consists mainly in the execution of experimental tests with non-beacon enabled ZigBee/IEEE 802.15.4 networks, using widespread hardware and software platforms from Texas Instruments, regarding relevant quality of service (QoS) metrics (maximum throughput, delivery ratio and network delay), as well as the effects of multiple constraints, such as hidden nodes, clock drift and body interference in the network performance. A clock drift model was proposed to estimate when two nodes will interfere with each other. This model was conceived due to the lack of support from the ZigBee to overcome this issue. A solution to overcome the clock drift and the hidden node problems was then designed. A parametric software delay model of ZigBee network devices was also defined and introduced into a simulator so that more accurate simulation results could be obtained. The proposed models were deemed valid since they were thoroughly tested and the predicted results were obtained.As redes de sensores sem fios de área corporal (WBAN) têm o potencial de desempenhar um papel importante no dia-a-dia. Hoje em dia há muitas indústrias, tais como na área da saúde, do desporto e do entretenimento, que podem tirar proveito dessas redes. A monitorização sem fios de sinais fisiológicos, tanto em ambientes fechados como ao ar livre, pode trazer benefícios em vários cenários de aplicação, tais como, aumentar o bem-estar de pacientes que são monitorizados e reduzir a carga de trabalho de médicos, permitindo a monitorização contínua. Esta dissertação identifica e analisa aspetos chave do desempenho das redes ZigBee e IEEE 802.15.4, quando usadas em aplicações típicas das WBAN. A principal motivação para a realização deste trabalho reside no facto de que, apesar de terem sido projetados principalmente para redes de sensores sem fio (WSN), estes protocolos estão também a ser utilizados em aplicações características das WBAN, particularmente na área da saúde. As diferenças entre as WSN e as WBAN são destacadas e usadas para discutir o uso dos protocolos ZigBee e IEEE 802.15.4 nas WBAN. A análise realizada neste trabalho consiste, principalmente, na execução de testes experimentais de redes ZigBee/IEEE 802.15.4 a funcionar no modo non-beacon enabled, usando as plataformas de hardware e software da Texas Instruments. A análise leva em consideração métricas relevantes (o máximo goodput, a taxa de entrega e o atraso da rede) de qualidade de serviço (QoS) e os efeitos de várias condicionantes, como os nós escondidos, o clock drift e a interferência do corpo humano no desempenho da rede. Um modelo para o clock drift foi proposto para estimar quando dois dispositivos irão interferir um com o outro devido a este fenómeno. Este modelo foi concebido devido à falta de capacidade para o ZigBee superar este problema. Posteriormente foi concebida uma solução para ultrapassar os problemas associados ao clock drift e aos nós escondidos. Um modelo paramétrico de atrasos de software em dispositivos de redes ZigBee foi também definido e introduzido num simulador, de modo a que resultados de simulações mais precisos possam ser obtidos. Os modelos propostos foram considerados válidos dado que foram testados e os resultados previstos foram obtidos

    Journal of Telecommunications and Information Technology, 2008, nr 1

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    Performance evaluation of Vehicular Ad Hoc Networks over high speed environment using NCTUns

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    Català: Cada any aproximadament un milió dues-centes mil persones moren en accidents de trànsit. D'aquesta dada es desprèn que els accidents de trànsit són la quarta causa de mortalitat al món. Degut a això, un gran nombre de governs i els majors fabricants de vehicles del món estan invertint temps i diners en recerca i desenvolupament per millorar la seguretat a les carreteres. Amb aquest objectiu, apareix el concepte de VANET: Vehicular Ad-hoc NETwork. Una VANET està basada en vehicles i estacions base intel·ligents que comparteixen informació a través de comunicacions inalàmbriques. Aquest intercanvi de dades podria tenir un gran impacte en la seguretat viària i la qualitat en la conducció però a més a més seria una nova font d' entreteniment mòbil. La millora en seguretat implicaria una reducció en el nombre d'accidents i les comunicacions inalàmbriques usades en mobilitat permetrien una optimització del transport. L'evolució de les VANETs en els últims anys i les seves aplicacions útils a les carreteres són les principals raons per dur a terme aquest projecte. El gran suport a aquest tipus de xarxes inalàmbriques sembla indicar que les VANETs són les xarxes del futur en entorns mòbils. En relació al projecte, el primer problema observat és que el protocol que s'usa específicament en VANETs (802.11p) només està disponible en pocs simuladors de xarxa i està en fase de desenvolupament. Per tant, la majoria de les funcions no estan implementades i això fa que el protocol no sigui madur. En conseqüència, es va triar un protocol àmpliament usat com és 802.11b per fer les proves en el simulador NCTUns. L?objectiu del projecte és avaluar el funcionament de VANETs usant el protocol 802.11b i el protocol d?encaminament AODV en un escenari d?autopista. Ajustant diferents paràmetres com el nombre de cotxes, la seva velocitat i el seu rang de cobertura és possible obtenir variacions en les mesures de pèrdues, throughput i retard extrem-a-extrem en la xarxa. El resultat final és que les mesures permeten saber quines són les comunicacions que es produeixen a la xarxa per cadascuna de les configuracions i la seva incidència en les condicions de conducció.Castellano: Cada año cerca de un millón doscientas mil personas fallecen en accidentes de tráfico. De este dato se desprende que los accidentes de tráfico son la cuarta causa de mortalidad en el mundo. Debido a esto, un gran número de gobiernos y los mayores fabricantes de vehículos del mundo están invirtiendo tiempo y dinero en investigación y desarrollo para mejorar la seguridad en las carreteras. Con este objetivo, aparece el concepto de VANET: Vehicular Ad-hoc NETwork. Una VANET se basa en vehículos y estaciones base inteligentes que comparten información por medio de comunicaciones inalámbricas. Este intercambio de datos podría tener un gran impacto en la seguridad vial y en la calidad de la conducción pero además sería una nueva fuente de entretenimiento móvil. La mejora en la seguridad implicaría una reducción en el número de accidentes y las comunicaciones inalámbricas utilizadas en movilidad permitirían optimizar el transporte. La evolución de las VANETs en los últimos años y sus aplicaciones útiles en las carreteras son las principales razones para llevar a cabo este proyecto. El gran apoyo a este tipo de redes inalámbricas parece indicar que las VANETs son las redes del futuro en entornos móviles. En relación al proyecto, el primer problema observado es que el protocolo específicamente utilizado en VANETs (802.11p) sólo está disponible en pocos simuladores de red y se encuentra en fase de desarrollo. Por lo tanto, la mayoría de funciones no están implementadas y esto hace que el protocolo no sea maduro. En consecuencia, se escogió un protocolo ampliamente utilizado como es 802.11b para realizar las pruebas en el simulador NCTUns. El objetivo del proyecto es evaluar el funcionamiento de VANETs utilizando el protocolo 802.11b y el protocolo de encaminamiento AODV en un escenario de autopista. Ajustando diferentes parámetros como el número de coches, su velocidad y su rango de cobertura es posible obtener variaciones en las medidas de pérdidas, throughput y retardo extremo-a-extremo en la red. El resultado final es que las medidas permiten saber cuáles son las comunicaciones que se producen en la red para cada una de las configuraciones y su incidencia en las condiciones de conducción.English: Every year about 1.2 million people die because of traffic accidents [1]. This means that traffic accidents are the fourth cause of mortality in the world. Therefore, several governments and the most important car manufacturers are investing time and money on research and development in order to improve road safety. At this respect, appears the concept of VANET: Vehicular Ad-hoc NETwork. A VANET is based on smart cars and base-stations that share information via wireless communications. This interchange of data may have a great impact on safety and driving quality but also could be another source of mobile entertainment. This improvement on safety would imply reducing the number of accidents. In addition, the use of wireless communications in mobility would lead to an optimization of transport. The evolution of VANETs in the last years and their useful applications on the road has been the main reason to develop this project. The great support of many people to this type of wireless networks suggests that VANETs are the networks of the future in mobile environments. Regarding the project, the first problem encountered is that the network protocol specially designed for VANETs, IEEE 802.11p, is only available in a few of the network simulators and is on phase of development. This fact means that most of the functions are not implemented so it cannot be considered as a mature protocol. As a consequence, a widely used protocol as IEEE 802.11b was chosen and all the tests were performed on NCTUns simulator. So the purpose of this project is to evaluate the performance of VANETs by using 802.11b protocol and AODV routing protocol in a highway scenario. By adjusting different parameters like number of cars, their speed and their range of coverage, variations on measures of loss ratio, throughput and end-to- end delay were detected on the network. Finally, the measures help to know about network communications for each of the cases and their incidence on driving conditions

    Wireless communication, sensing, and REM: A security perspective

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    The diverse requirements of next-generation communication systems necessitate awareness, flexibility, and intelligence as essential building blocks of future wireless networks. The awareness can be obtained from the radio signals in the environment using wireless sensing and radio environment mapping (REM) methods. This is, however, accompanied by threats such as eavesdropping, manipulation, and disruption posed by malicious attackers. To this end, this work analyzes the wireless sensing and radio environment awareness mechanisms, highlighting their vulnerabilities and provides solutions for mitigating them. As an example, the different threats to REM and its consequences in a vehicular communication scenario are described. Furthermore, the use of REM for securing communications is discussed and future directions regarding sensing/REM security are highlighted

    Routing algorithms for wireless sensor : networks based on the duty cycle of its components

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    [eng] Wireless sensor network is one of the most important topics in the current data transferring. In fact regarding to data gathering and transformation, cost effective is the top topic and optimum point, which every vendors and sector are focusing on it. In the field of petrochemical regarding sensitive processes could not stay out of this scope and start to monitor the gas pipes and processes over the wireless fashion. Therefore some items should have been taking into considerations such as: instant monitoring, nonstop characteristic, long term investing and energy consuming. According to those aforesaid items, we have planned to do an investigation and find the feasibly of how we can to create and distribute a network to have accuracy to measurement , sending data reliability, having long term network life cycle and having minimum energy consuming. Therefore the only technology could help us was IEEE 802.15.4 with mixed of microcontrollers and transceivers, able to manipulate to reach out our objects in maximizing lifetime and minimizing latency in wsn, as an unique routing algorithm in Mobile ad Hoc Network. WSN in fact is a relatively new section of networking technology and nowadays is more popular. The reason of these advantages instead of others is low-power microcontroller and inexpensive sensor usage for any communications and also simple sensor designing. Regarding to network layers, Physical layer for WSN based on IEEE802.15.4 is fundamental of frames and packets transactions. So two main devices which are involving in this project: transceivers such as CC2520 and CC3200 ZigBee/IEEE 802.15.4 RF, managed by microcontrollers. Common controller for those transceivers such as MSP430F1611 16-bit MSP430 family for Texas instrument in the nodes and coordinators ideas were selected. One step more close to the idea, was other layer so called Link layer or in other hand MAC layer. Another advantage of WSN is ability to manipulate MAC layer, because modifications in lower layer always has low Energy consuming than other layers. Therefore according to these circumstances, MAC protocols are able to energy efficiency, also reduce and achieve to zero based of unused time in WSN. So any WSN, energy wasting could be control in MAC sub layer and even though MAC protocols. Other layer in WSN is declared as a Network layer, the logical way which those packets could be find the best way and shortest path in minimum time as possible and reachability to the main point based on node and coordinator. Nodes are programmed in upper layer and have been matched with MAC layer, now it's time to join and stick the frames in a packet and involving to each other. Meanwhile we decided to create a middle layer through MAC and Network layer to play as a bridge, mainly called VRT (Variable Response Time) and FRT (Fixed Response Time) to control the energy consumption in the process of routing in network layer. This algorithm is cooperating with MAC layer in sleep and wake up modes, in fact with VRT, nodes just received their needs and captured the vital packet in wake up mode, sends back the answer, now the task is finished and both sided transaction is done. After that, it's not need to have more listening and capturing packets from the remote nodes as a coordinator therefore, left the transmission process to save more energy for further wireless communication stream in sleep mode. Also FRT is another algorithm in MAC layer, to decrease the energy consumption. This algorithm is switch based energy control, as a same concept in VRT in sleeping and wakeup mode. Finally we have design this algorithm in Simulator and real world. The results correlate quite well results showing as a good agreement between two worlds, also we have obtained better results in battery consumption over network life cycle to other business algorithms.[spa] En este trabajo nos focalizaremos en la minimización del consumo a partir de la minimización del número de transmisiones. Buscamos por tanto aquel algoritmo que nos permita aumentar la probabilidad de aciertos. Esta idea, diseñará el algoritmo de enrutamiento que mejor se ajusta a la red MANET. Una vez simulada la red se diseñará un "testbed" en donde una parte de la red se implementará de forma real, mediante la introducción de sensores inalámbricos y la otra parte se hará de forma simulada, a través de una interfaz que interconecta el mundo real con la simulación de Spyder. Se pretende ver que ambos mundos progresan de forma similar. Con respecto a la capa de OSI en WSN, sería prioritaria la capa física o capa de hardware, por este motivo nuestra proyecto también se centra en el tipo determinado de hardware que debe aplicarse para obtener resultados satisfactorios. Entonces tratamos las características de los dos hardwares, el transceiver y el microcontroller. También se trata en este apartado su concepto lógico de acuerdo con la ficha técnica oficial IEEE802.15.4. La segunda prioridad de la capa OSI se centra en el Medium Access Control (MAC) de la capa. En esta capa nuestro objetivo se logrará mediante la manipulación de las addresses MAC. Los protocolos MAC deben estar orientados a la reducción del consumo de energía y también a la reducción del tiempo no utilizado en WSN, para ello aplicamos algunas políticas para controlar los comportamientos del tráfico en esta capa para cambiar el consumo de energía, la vida útil de la red y evitar el gasto innecesario de recursos, en realidad concentramos a nuestro algoritmo VRT y FRT. Respecto de la idea principal, de controlar los sensores para aumentar la vida útil de la red y disminuir el consumo de energía. En realidad se explica cómo controlar la capa MAC y forzar el hardware para lograr el objetivo principal de este proyecto. De hecho podemos decir que mejoramos el reenvío de paquetes entre los sensores intermedios, buscando el promedio de distancia HOP más corta desde el origen al destino, así como la disminución del consumo de energía en cada sensor

    Real-time wireless networks for industrial control systems

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    The next generation of industrial systems (Industry 4.0) will dramatically transform manyproductive sectors, integrating emerging concepts such as Internet of Things, artificialintelligence, big data, cloud robotics and virtual reality, to name a few. Most of thesetechnologies heavily rely on the availability of communication networks able to offernearly–istantaneous, secure and reliable data transfer. In the industrial sector, these tasks are nowadays mainly accomplished by wired networks, that combine the speed ofoptical fiber media with collision–free switching technology. However, driven by the pervasive deployment of mobile devices for personal com-munications in the last years, more and more industrial applications require wireless connectivity, which can bring enormous advantages in terms of cost reduction and flex-ibility. Designing timely, reliable and deterministic industrial wireless networks is a complicated task, due to the nature of the wireless channel, intrinsically error–prone andshared among all the devices transmitting on the same frequency band. In this thesis, several solutions to enhance the performance of wireless networks employed in industrial control applications are proposed. The presented approaches differ in terms of achieved performance and target applications, but they are all characterized by an improvement over existing industrial wireless solutions in terms of timeliness, reliability and determinism. When possible, an experimental validation of the designed solutions is provided. The obtained results prove that significant performance improvements are already possible, often using commercially available devices and preserving compliance to existing standards. Future research efforts, combined with the availability of new chipsets and standards, could lead to a world where wireless links effectively replace most of the existing cables in industrial environments, as it is already the case in the consumer market

    Remote vital signs monitoring based on wireless sensor networks

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    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

    Towards the efficient use of LoRa for wireless sensor networks

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    Since their inception in 1998 with the Smart Dust Project from University of Berkeley, Wireless Sensor Networks (WSNs) had a tremendous impact on both science and society, influencing many (new) research fields, like Cyber-physical System (CPS), Machine to Machine (M2M), and Internet of Things (IoT). In over two decades, WSN researchers have delivered a wide-range of hardware, communication protocols, operating systems, and applications, to deal with the now classic problems of resourceconstrained devices, limited energy sources, and harsh communication environments. However, WSN research happened mostly on the same kind of hardware. With wireless communication and embedded hardware evolving, there are new opportunities to resolve the long standing issues of scaling, deploying, and maintaining a WSN. To this end, we explore in this work the most recent advances in low-power, longrange wireless communication, and the new challenges these new wireless communication techniques introduce. Specifically, we focus on the most promising such technology: LoRa. LoRa is a novel low-power, long-range communication technology, which promises a single-hop network with millions of sensor nodes. Using practical experiments, we evaluate the unique properties of LoRa, like orthogonal spreading factors, nondestructive concurrent transmissions, and carrier activity detection. Utilising these unique properties, we build a novel TDMA-style multi-hop Medium Access Control (MAC) protocol called LoRaBlink. Based on empirical results, we develop a communication model and simulator called LoRaSim to explore the scalability of a LoRa network. We conclude that, in its current deployment, LoRa cannot support the scale it is envisioned to operate at. One way to improve this scalability issue is Adaptive Data Rate (ADR). We develop two ADR protocols, Probing and Optimistic Probing, and compare them with the de facto standard ADR protocol used in the crowdsourced TTN LoRaWAN network. We demonstrate that our algorithms are much more responsive, energy efficient, and able to reach a more efficient configuration quicker, though reaching a suboptimal configuration for poor links, which is offset by the savings caused by the convergence speed. Overall, this work provides theoretical and empirical proofs that LoRa can tackle some of the long standing problems within WSN. We envision that future work, in particular on ADR and MAC protocols for LoRa and other low-power, long-range communication technologies, will help push these new communication technologies to main-stream status in WSNs
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