The purpose of this research is twofold - the first objective being to develop Markovian models that can be used to analyze the performance of the various medium access control protocols of slotted ring type local area networks.

Wireless sensor network (WSN) technology has gained significant importance due to its potential support for a wide range of applications. Most of the WSN applications consist of a large numbers of distributed nodes that work together to achieve common objects. Running a large number of nodes requires an efficient mechanism to bring them all together in order to form a multi-hop wireless network that can accomplish some specific tasks. Even with recent developments made in WSN technology, numbers of important challenges still stand as vulnerabilities for WSNs, including energy waste sources, synchronisation leaks, low network capacity and self-configuration difficulties. However, energy efficiency remains the priority challenging problem due to the scarce energy resources available in sensor nodes. These concerns are managed by medium access control (MAC) layer protocols. MAC protocols designed specifically for WSN have an additional responsibility of managing radio activity to conserve energy in addition to the traditional functions. This thesis presents advanced research work carried out in the context of saving energy whilst achieving the desired network performance. Firstly the thesis contributes by proposing Overlapped Schedules for MAC layer, in which the schedules of the neighbour clusters are overlapped by introducing a small shift time between them, aiming to compensate the synchronisation errors. Secondly, this thesis proposed a modified architecture derived from S-MAC protocol which significantly supports higher traffic levels whilst achieving better energy efficiency. This is achieved by applying a parallel transmission concept on the communicating nodes. As a result, the overall efficiency of the channel contention mechanism increases and leads to higher throughput with lower energy consumption. Finally, this thesis proposed the use of the Adaptive scheme on Border Nodes to increase the power efficiency of the system under light traffic load conditions. The scheme focuses on saving energy by forcing the network border nodes to go off when not needed. These three contributions minimise the contention window period whilst maximising the capacity of the available channel, which as a result increase network performance in terms of energy efficiency, throughput and latency. The proposed system is shown to be backwards compatible and able to satisfy both traditional and advanced applications. The new MAC protocol has been implemented and evaluated using NS-2 simulator, under different traffic loads and varying duty cycle values. Results have shown that the proposed solutions are able to significantly enhance the performance of WSNs by improving the energy efficiency, increasing the system throughput and reducing the communication delay.

Στην παρούσα διπλωματική εργασία, σκοπός μας είναι η μελέτη, οργάνωση και υλοποίηση πρωτοκόλλων ελέγχου. Το κάθε πρωτόκολλο ελέγχου ευθύνεται για τη διεξαγωγή των ελέγχων στα ιατρικά μηχανήματα. Περιλαμβάνει δε, τα δομικά στοιχεία των ελέγχων, που είναι οι μετρήσεις ελέγχου, καθώς και τις αντίστοιχες ομάδες μηχανημάτων. Στην εργασία μας, για την εκτέλεση των εργασιών, χρησιμοποιήσαμε, κατά βάση, την εφαρμογή PRAXIS, μια εφαρμογή που διαχειρίζεται τη βιοϊατρική τεχνολογία σε νοσοκομειακό επίπεδο. Επίσης, υλοποιήσαμε έναν εναλλακτικό τρόπο διαχείρισης των πρωτοκόλλων/μετρήσεων ελέγχου, μέσω της εφαρμογής ACME, με την οποία παρέχουμε και κάποιες βελτιωτικές δυνατότητες ως προς το PRAXIS. Περιληπτικά η διάρθρωση της εργασίας μας έχει ως εξής: Στο 1ο Κεφάλαιο, εισάγουμε τον αναγνώστη στην επιστήμη της Βιοϊατρικής Τεχνολογίας. Στο 2ο Κεφάλαιο, παρουσιάζουμε τις βασικές αρχές της Κλινικής Μηχανικής, δηλαδή του τομέα εκείνου της Βιοϊατρικής Τεχνολογίας, που είναι υπεύθυνος για τη διαχείριση του ιατρικού εξοπλισμού, στα νοσοκομεία. Αναλύονται τόσο το Τμήμα Κλινικής Μηχανικής (CED), όσο και οι ομάδες ιατρικών μηχανημάτων, μαζί με το πρόγραμμα ελέγχων-συντήρησης IPM. Στο 3ο Κεφάλαιο, αναφερόμαστε στα συστήματα διαχείρισης βιοϊατρικής τεχνολογίας και πιο συγκεκριμένα στην εφαρμογή PRAXIS, στα τεχνικά χαρακτηριστικά, την οργάνωση και τις δυνατότητες που παρέχει. Στο 4ο Κεφάλαιο, παρουσιάζουμε τον τρόπο διαχωρισμού-ομαδοποίησης των μετρήσεων ελέγχου, προβλήματα που αντιμετωπίσαμε και τρόπους επίλυσης και τελικά τη διαδικασία καταχώρησης των μετρήσεων ελέγχου μέσω του PRAXIS. Στο 5ο Κεφάλαιο, καθορίζουμε τους κανόνες που διέπουν τη διασύνδεση μετρήσεων ελέγχου-πρωτοκόλλων ελέγχου-ομάδων μηχανημάτων και τελικά τη διαδικασία υλοποίησης των πρωτοκόλλων ελέγχου μέσω του PRAXIS, παράλληλα με την προσθήκη σε αυτά των αντίστοιχων μετρήσεων ελέγχου και ομάδων μηχανημάτων. Στο 6ο Κεφάλαιο, αναλύουμε την εφαρμογή ACME, μια εφαρμογή που υλοποιήσαμε ως εναλλακτικό τρόπο διαχείρισης, τη συγκρίνουμε με το PRAXIS, παρουσιάζουμε τις δυνατότητές και τις βελτιώσεις της και περιγράφουμε τον τρόπο χρήσης της για την διεκπεραίωση των εργασιών. Στο 7ο Κεφάλαιο, παρέχουμε χρήσιμα περιληπτικά στατιστικά στοιχεία από την όλη μελέτη μας, καταλήγουμε σε συμπεράσματα και κάνουμε προτάσεις. Τέλος, στο Παράρτημα, παραθέτουμε πλήρη εκτυπωμένα παραδείγματα πρωτοκόλλων, τόσο μέσω του PRAXIS, όσο και μέσω της ACME. / -

Wireless networks are less reliable than wired networks because channels are “exposed” to the surrounding environment that is susceptible to interference and noise. To minimize losses of data due to collisions, wireless networks need a mechanism to regulate the access on the transmission medium. Medium Access Control (MAC) protocols control access to the shared communication medium so that it can be used efficiently. In this thesis, we first describe the collision-controlled Dual Prohibition Multiple Access (DPMA) protocol [45]. The main mechanisms implemented in DPMA, such as binary dual prohibition, power control, interference control, and support for differentiated services (DiffServ), are presented in detail. We conducted a thorough simulation study on DPMA protocol from several aspects. First, we conduct simulations to observe the effects of binary competition number (BCN), unit slot length and safe margin on the performance of DPMA. Secondly, the DiffServ capability of DPMA is demonstrated through simulation results. Finally, we compare the DPMA protocol with the CSMA/CA protocol and find that DPMA with optimal configuration has better performance than CSMA/CA under both low and high network density. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-09-28 16:25:02.515

Wireless sensor network (WSN) technology has gained significant importance due to its potential support for a wide range of applications. Most of the WSN applications consist of a large numbers of distributed nodes that work together to achieve common objects. Running a large number of nodes requires an efficient mechanism to bring them all together in order to form a multi-hop wireless network that can accomplish some specific tasks. Even with recent developments made in WSN technology, numbers of important challenges still stand as vulnerabilities for WSNs, including energy waste sources, synchronisation leaks, low network capacity and self-configuration difficulties. However, energy efficiency remains the priority challenging problem due to the scarce energy resources available in sensor nodes. These concerns are managed by medium access control (MAC) layer protocols. MAC protocols designed specifically for WSN have an additional responsibility of managing radio activity to conserve energy in addition to the traditional functions. This thesis presents advanced research work carried out in the context of saving energy whilst achieving the desired network performance. Firstly the thesis contributes by proposing Overlapped Schedules for MAC layer, in which the schedules of the neighbour clusters are overlapped by introducing a small shift time between them, aiming to compensate the synchronisation errors. Secondly, this thesis proposed a modified architecture derived from S-MAC protocol which significantly supports higher traffic levels whilst achieving better energy efficiency. This is achieved by applying a parallel transmission concept on the communicating nodes. As a result, the overall efficiency of the channel contention mechanism increases and leads to higher throughput with lower energy consumption. Finally, this thesis proposed the use of the Adaptive scheme on Border Nodes to increase the power efficiency of the system under light traffic load conditions. The scheme focuses on saving energy by forcing the network border nodes to go off when not needed. These three contributions minimise the contention window period whilst maximising the capacity of the available channel, which as a result increase network performance in terms of energy efficiency, throughput and latency. The proposed system is shown to be backwards compatible and able to satisfy both traditional and advanced applications. The new MAC protocol has been implemented and evaluated using NS-2 simulator, under different traffic loads and varying duty cycle values. Results have shown that the proposed solutions are able to significantly enhance the performance of WSNs by improving the energy efficiency, increasing the system throughput and reducing the communication delay.

No description available.

[pt] Com o rápido crescimento da Internet das Coisas (IoT), surgiram novas tecnologias de comunicação sem fio para atender aos requisitos de longo alcance, baixo custo e baixo consumo de energia exigidos pelos aplicativos de IoT. Nesse contexto, surgiram as redes de longa distância de baixa potência (LPWANs), as quais oferecem diferentes soluções que atendem aos requisitos dos aplicativos de IoT mencionados anteriormente. Entre as soluções LPWAN existentes, o LoRaWAN tem-se destacado por receber atenção significativa da indústria e da academia nos últimos anos. Embora o LoRaWAN ofereça uma combinação atraente de transmissões de dados de longo alcance e baixo consumo de energia, ele ainda enfrenta vários desafios em termos de confiabilidade e escalabilidade. No entanto, devido a sua natureza de código aberto e à flexibilidade do esquema de modulação no qual ele se baseia (Long Range (LoRa) permite o ajuste de fatores de espalhamento e a potência de transmissão), o LoRaWAN também oferece importantes possibilidades de melhorias. Esta dissertação aproveita a adequação dos algoritmos de Aprendizagem por Reforço (RL) para resolver tarefas de tomada de decisão e os utiliza para ajustar dinamicamente os parâmetros de transmissão dos dispositivos finais LoRaWAN. O sistema proposto, chamado RL-LoRa, mostra melhorias significativas em termos de confiabilidade e escalabilidade quando comparado ao LoRaWAN. Especificamente, diminui a taxa de erro de pacote (PER) média do LoRaWAN em 15 porcento, o que pode aumentar ainda mais a escalabilidade da rede. / [en] With the massive growth of the Internet of Things (IoT), novel wireless communication technologies have emerged to address the long-range, lowcost, and low-power consumption requirements of the IoT applications. In this context, the Low Power Wide Area Networks (LPWANs) have appeared, offering different solutions that meet the IoT applications requirements mentioned before. Among the existing LPWAN solutions, LoRaWAN has stood out for receiving significant attention from both industry and academia in recent years. Although LoRaWAN offers a compelling combination of long-range and low-power consumption data transmissions, it still faces several challenges in terms of reliability and scalability. However, due to its open-source nature and the flexibility of the modulation scheme it is based on (Long Range (LoRa) modulation allows the adjustment of spreading factors and transmit power), LoRaWAN also offers important possibilities for improvements. This thesis takes advantage of the appropriateness of the Reinforcement Learning (RL) algorithms for solving decision-making tasks, and use them to dynamically adjust the transmission parameters of LoRaWAN end devices. The proposed system, called RL-LoRa, shows significant improvements in terms of reliability and scalability when compared with LoRaWAN. Specifically, it decreases the average Packet Error Ratio (PER) of LoRaWAN by 15 percent, which can further increase the network scalability.