Wireless sensor networks suffer from limited power resources. Therefore, managing the energy constraints and exploring new ways to minimize the power consumption during the operation of the nodes are critical issues. Conventional MAC protocols deal with this problem without considering the internal properties of the sensor nodes’ batteries. However, recent studies about battery modeling and behaviour showed that the pulsed discharge mechanism and the charge recovery effect may have a significant impact on wireless communication in terms of power saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these factors to save more energy and to prolong the lifetime of the nodes/network without affecting the throughput. In both protocols we measure the remaining battery capacity of the node and use that measurement in the back-off scheme. The first protocol gives the nodes with higher remaining battery capacity more priority to access the medium, while the other one provides more medium access priority to the nodes with lower remaining battery capacity. The objective is to investigate, through simulations, which protocol reduces the power consumption of the nodes, improve the lifetime of the network, and compare the results with the CSMA-CA protocol.

Target tracking using Wireless Sensor Networks (WSNs) has drawn lots of attentions after the recent advances of wireless technologies. Target tracking aims at locating one or several mobile objects and depicting their trajectories over time. The applications of Object Tracking Sensor Networks (OSTNs) include but not limited to environmental and wildlife monitoring, industrial sensing, intrusion detection, access control, traffic monitoring, patient monitoring in the health-related studies and location awareness in the battle eld. One of the most rewarding applications of target tracking is wildlife monitoring. Wildlife monitoring is used to protect the animals which are endangered to extinction. Road safety applications are another popular usage of wildlife monitoring using WSNs. In this thesis, the issues and challenges of energy-efficient wildlife monitoring and target tracking using WSNs are discussed. This study provides a survey of the proposed tracking algorithms and analyzes the advantages and disadvantages of these algorithms. Some of the tracking algorithms are proposed to increase the energy e ciency of the tracking algorithm and to prolong the network lifetime; while, other algorithms aim at improving the localization accuracy or decreasing the missing rate. Since improving the energy efficiency of the system provides more alive sensors over time to locate the target; it helps to decrease the missing rate as the network ages. Thus, this study proposes to adjust the sensing radius of the sensor nodes in real-time to decrease the sensing energy consumption and prolong the network lifetime. The proposed VAriable Radius Sensor Activation (VARSA) mechanism for target tracking using wireless sensor networks tackles the energy consumption issues due to resource constraints of the WSNs. VARSA reduces the radio covered area of each sensor node to only cover the Area of Interest (AoI) which is the location of the target in tracking applications. Thus, VARSA aims at decreasing the sensing energy consumption which leads to encreasing the network life time. In addition, VARSA decreases the missing rate over time as it provides more alive sensors to detect the target compared to previous activation algorithms as the network ages. VARSA is compared to PRediction-based Activation (PRA) and Periodic PRediction-based Activation (PPRA) algorithms which are two of the most promising algorithms proposed for sensor activation. The simulation results show that VARSA outperforms PRA and PPRA. VARSA prolongs the lifetime of the network and decreases the missing rate of the target over time.

In order to implement wireless sensing and monitoring services at large scale, Internet connection is highly desirable. Particularly, TCP is indispensable for end-to-end connection orientated communication. It is well known that low power and low rate IEEE802.15.4 based Wireless Sensor Networks (WSNs) are vulnerable to the interference from collocated Wireless Local Area Networks (WLAN) utilizing the same un-licensed 2.4GHz frequency band. Such coexistence interference seriously deteriorates the performance of TCP/IPv6 over WSN, resulting in packet losses, disconnections, reduced throughput and so on. This thesis focuses on experimental research on the performance evaluation and improvement of TCP/IPv6 over IEEE 802.15.4 based WSN. In this research, a versatile testbed has been developed and implemented, which consists of off-the-selves and custom built hardware, open source and in-house developed firmware and software. A periodical monitoring/sensing application that uses TCP to transmit data over WSN has been developed and used for performance evaluation when there is various Wi-Fi interference close by. Based on the observations and analysis of our experimental results, several important parameters that impact the TCP packet transmission performance have been identified. Performance improvement technique is proposed to effectively adjust these parameters so as to support periodic monitoring/sensing application with substantial better performance. Extensive experiments have been performed in the testbed to evaluate the performance of WSN packets transmission via TCP over WSN when subjected to different Wi-Fi interference.

Wireless sensor networks (WSNs) are an emerging area of technology that have applications across many domains. By adding a mobile platform to the WSN we can increase its capabilities. One such scenario involves a mobile platform relocating sensors to fill sensing holes that are the result of sensor failure. We examine this problem, known as robot-assisted sensor relocation (RASR), and propose our own, multi-objective version, that we call reliable robot-assisted sensor relocation. We solve this problem using a set of state-of-the-art evolutionary multi-objective optimization algorithms. Additionally, we examine the multi-robot model, which we christen reliable multiple robot-assisted sensor relocation (RMRASR). The works collected within define these problems as well as provide empirical insight into the performance of well-known algorithms using these problems as a test-bed.

In Wireless Sensor and Robot Networks (WSRNs), static sensors report event information to one of the robots. In the k nearest neighbour query processing problem in WSRNs, the robot receives event report needs to find exact k nearest robots (KNN) to react to the event, among those connected to it. We are interested in localized solutions, which avoid message flooding to the whole network. Several existing methods restrict the search within a predetermined boundary. Some network density-based estimation algorithms were proposed but they either result in large message transmission or require the density information of the whole network in advance which is complex to implement and lacks robustness. Algorithms with tree structures lead to the excessive energy consumption and large latency caused by structural construction. Itinerary based approaches generate large latency or unsatisfactory accuracy. In this thesis, we propose a new method to estimate a search boundary, which is a circle centred at the query point. Two algorithms are presented to disseminate the message to robots of interest and aggregate their data (e.g. the distance to query point). Multiple Auction Aggregation (MAA) is an algorithm based on auction protocol, with multiple copies of query message being disseminated into the network to get the best bidding from each robot. Partial Depth First Search (PDFS) attempts to traverse all the robots of interest with a query message to gather the data by depth first search. This thesis also optimizes a traditional itinerary-based KNN query processing method called IKNN and compares this algorithm with our proposed MAA and PDFS algorithms. The experimental results followed indicate that the overall performance of MAA and PDFS outweighs IKNN in WSRNs.

This thesis, entitled Wireless Sensor Networks in Hostile RF Environments, was submitted to the The University of Manchester by Mr Dominic James Patrick Crutchley on 30th April 2012 for the degree Doctor of Philosophy (PhD). This thesis considers two different but related aspects of wireless communication in Wireless Sensor Networks (WSNs) operating in hostile environments. Using grain as an example of a hostile environment, the influence of hostile, attenuating media on Radio Frequency (RF) communications was considered. Further to this the implications of a hostile environment for protocol stacks were considered, and a cross-layer, cross-application framework was proposed to help future protocol designers address these issues. To achieve both these aims, the software for a bespoke WSN node was designed and implemented. The node was characterised to ensure a good understanding of its RF behaviour and practical experiments were then conducted in a small-scale grain silo to gain an understanding of attenuation and data communications within grain. Finally, a real world implementation of the proposed cross-layer, cross-application framework was produced and a small example cross-layer protocol was demonstrated running on the WSN node. It was shown that a WSN can be used to characterise communications within a hostile medium and also that data communications are achievable within grain. It was also shown that a small cross-layer, cross-application framework could ease the development of cross-layered protocols in WSN software.

To achieve greater performance in computing networks, a setup of critical computing aspects that ensures efficient network operation, needs to be implemented. One of these computing aspects is, Quality of Service (QoS). Its main functionality is to manage traffic queues by means of prioritizing sensitive network traffic. QoS capable networking allows efficient control of traffic especially for network critical data. However, to achieve this in Wireless Sensor Networks (WSN) is a serious challenge, since these technologies have a lot of computing limitations. It is even difficult to manage networking resources with ease in these types of technologies, due to their communication, processing and memory limitations. Even though this is the case with WSNs, they have been largely used in monitoring/detection systems, and by this proving their application importance. Realizing efficient network control requires intelligent methods of network management, especially for sensitive network data. Different network types implement diverse methods to control and administer network traffic as well as effectively manage network resources. As with WSNs, communication traffic and network resource control are mostly performed depending on independently employed mechanisms to deal with networking events occurring on different levels. It is therefore challenging to realize efficient network performance with guaranteed QoS in WSNs, given their computing limitations. Software defined networking (SDN) is advocated as a potential paradigm to improve and evolve WSNs in terms of capacity and application. A means to apply SDN strategies to these compute-limited WSNs, formulates software defined wireless sensor networks (SDWSN). In this work, a resource-aware OpenFlow-based Active Network Management (OF-ANM) QoS scheme that uses SDN strategies is proposed and implemented to apply QoS requirements for managing traffic congestion in WSNs. This scheme uses SDN programmability strategies to apply network QoS requirements and perform traffic load balancing to ensure congestion control in SDWSN. Our experimental results show that the developed scheme is able to provide congestion avoidance within the network. It also allows opportunities to implement flexible QoS requirements based on the system’s traffic state. Moreover, a QoS Path Selection and Resource-associating (Q-PSR) scheme for adaptive load balancing and intelligent resource control for optimal network performance is proposed and implemented. Our experimental results indicate better performance in terms of computation with load balancing and efficient resource alignment for different networking tasks when compared with other competing schemes. / Thesis (PhD)--University of Pretoria, 2019. / National Research Foundation / University of Pretoria / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

The advancement of wireless technology has led to an increase in the employment of wireless sensor networks (WSNs). Traditionally, WSNs are powered by batteries. However, the high power consump- tion and the need to change the batteries regularly has made these networks costly to maintain. The nodes in the WSNs are increasingly strained as power consumption increases and the batteries are depleted faster. This has consequently decreased the overall lifetime of the WSNs. Although many energy-conserving techniques exist, for example energy-efficient medium access control and energy-efficient routing protocols, energy consumption remains one of the significant constraints in the development of WSNs. A natural solution to this constraint is harvesting energy from the environment. However, unlike conventional energy, energy harvested from the environment is random in nature, making it challenging to realise energy-harvesting transmission schemes. Although energy harvesting might be considered a solution to many problems, it brings about new challenges with regard to the usage and management of the energy harvested. Some of these challenges include uneven consumption of power in the network, resulting in dead nodes in some portion of the network and the batteries used in the network are being affected negatively by the energy usage; they may consequently sustain the nodes for long or short periods. To analyse the usage and consumption of energy, a number of techniques have been proposed, namely; information theory, game theory and queueing theory. By this time, the performance of the sensor nodes in WSNs has been analysed making use of a queueing-theoretic model for each sensor. The aforementioned model inadequately expresses the physical constraints, namely, the energy drawing process and the finite battery capacity. This research focuses on developing a model that captures the harvesting, accumulation and dissipation of energy, utilising queueing theory. A rechargeable battery with a finite storage capacity will be used. To ensure that the battery does not lose its capability to store charge after being recharged repeatedly, the leaky bucket model is proposed to check the network data flow as the harvested energy in the WSN is analysed. To capture real-world WSNs with energy harvesting in which there is energy leakage, the energy- harvesting sensor node performance is analysed with two assumptions: data transmission and energy leakage occurring and the token buffer being subjected to a threshold. The system had finite buffers for the data and energy. To make it possible to have some influence over the system performance measures a threshold is imposed on the token buffer. Four models are developed: a basic model, a basic model with leakage incorporated, a basic model with leakage and priority incorporated and a basic model with leakage, priority and threshold incorporated. The developed models are simulated and results for the performance measures are obtained. / Dissertation (MEng (Computer Engineering))--University of Pretoria, 2021. / BWMC, NRF / Electrical, Electronic and Computer Engineering / MEng (Computer Engineering) / Unrestricted

Wireless sensor networks have become increasingly popular in many applications such as environment monitoring and law enforcement. Data aggregation is a method used to reduce network traffic but cannot be used together with conventional encryption schemes because it is not secure and introduces extra overhead. Homomorphic encryption is an encryption scheme that allows data processing on encrypted data as opposed to plaintext. It has the benefit that each intermediate node does not have to decrypt each packet, but the resulting cyphertext is usually much larger than the original plaintext. This could negatively affect system performance because the energy consumption of each node is directly proportional to the amount of data it transmits. This study investigates the benefits and drawback of using homomorphic encryption in the aggregation process particularly in the context of scalable networks. It was found that conventional encryption outperforms the homomorphic encryption for smaller networks, but as the network size grows, homomorphic encryption starts outperforming conventional encryption. It was also found that the homomorphic encryption scheme does significantly reduce the performance of plaintext aggregation. This performance reduction will however be acceptable for most applications where security is a concern. / Draadlose sensornetwerke raak toenemend meer gewild vir heelwat verskillende toepassings, soos byvoorbeeld opgewingsmonitering en wetstoepassing. Data-aggregasie is n metode wat gebruik word om netwerkverkeer te verminder, maar kan nie gebruik word saam met konvensionele enkripsie-skemas nie, omdat dit nie veilig is nie en oorhoofse koste verhoog. Homomorfiese enkripsie is n enkripsie-skema wat dataverwerking toelaat op geënkripteerde in teenstelling met gewone-teks. Dit het die voordeel dat elke intermediêre nie nodig het om elke pakkie te dekripteer nie, maar die resulterende kodeteks is gewoonlik heelwat groter as die gewone-teks. Dit kan die stelselgedrag negatief beÏnvloed omdat die energieverbruik van elke node eweredig is aan die hoeveelheid data wat dit versend. Hierdie studie ondersoek die voor- en nadele van homomorfiese enkripsie in die aggregasieproses, veral in die konteks van skaleerbare netwerke. Daar is gevind dat konvensionele enkripsie beter vaar as homomorfies enkripsie in kleiner netwerke. Die omgekeerde is waar vir groter netwerke. Dit is ook gevind dat homomorfiese enkripsie gewone-teks-aggregasie negatief beÏnvloed, maar dit word as aanvaarbaar beskou vir toepassings waar sekuriteit belangrik is. / Dissertation (MEng)--University of Pretoria, 2015. / Electrical, Electronic and Computer Engineering / Meng / Unrestricted

Wireless sensor networks, networks of nodes communicating wirelessly with sensing capabilities, are becoming more popular and are utilized by an increasing number of applications. Some wireless sensor networks are implemented because the usual network solutions of an always connected network could not be applied. Specifically this thesis is concerned with the case when the connection between the end-user and the network is not always available, i.e., there is only intermittent connectivity. This masters thesis gives an introduction and provides some background knowledge concerning wireless sensor networks, specifically focusing on disconnected operation. A set of building blocks will be presented to help programmers deal with programming disconnected operations. Examples to demonstrate our solution is implemented as shell commands using the Contiki operating system. Our solution was tested in the field and compared against a common, monolithic, programming approach. This practical example shows the potential significance of this thesis project in real world applications and allowed an evaluation of both the qualitative and quantitative aspects of our solution. The results of our evaluation prove that our solution offers an easier interface for the programmer to work with at the cost of possible less memory space. / Trådlösa sensornätverk, nätverk med noder som kommunicerar trådlöst och har sensorer, blir mer populära och används av i ett ökande antal applikationer. Några trådlösa sensornätverk används för att en vanlig nätverkslösning med ständigt uppkopplade noder inte går att genomföra. Det här examensjobbet är specifikt inriktat på fall när en uppkoppling mellan slutanvändaren och nätverket inte alltid är tillgängligt, t.ex. när det bara är tillfällig uppkoppling. Detta examensarbete ger en introduktion och bakgrund till trådlösa sensornätverk med fokus på programmering av frånkopplade operationer. Ett antal byggstenar har tagits fram för att hjälpa programmerare att programmera frånkopplade operationer. Exempel för att styrka vår lösning i vår rapport kommer att implementeras som shellkommandon i operativsystemet Contiki. Vår lösning kommer att testas i verkligheten och jämföras med ett vanligt, monolitisk, programmeringsangreppssätt. Detta praktiska exempel kommer visa den potentiella nyttan av detta examensarbete i verkliga applikationer och tillåta utvärdering av kvalitativa och kvantitativa aspekter på vår lösning. Resultaten från vår utvärdering bevisar att vår lösning erbjuder ett enkelt gränssnitt för programmeraren att arbeta med till en kostnad av möjligen mindre minnesplats.