International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Sensor network applications typically require continuous monitoring of physical phenomena for extended periods of time under severe energy resource constraints. Accordingly, design considerations for sensor Media Access Control (MAC) protocols depart significantly from those of traditional wireless MAC protocols that largely ignore the energy factor. In this paper, we reexamine the design space of wireless sensor MAC protocols and modify IEEE 802.11 Distributed Coordination Function (DCF) to incorporate energy-adaptive contention mechanisms for prolonging sensor lifetime. Performance of the proposed schemes is evaluated with DCF as a baseline and results indicate the benefits of energy-aware mechanisms for sensor MAC protocols.

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How to improve the radio resource utilization and provide better quality-of-service (QoS) is an everlasting challenge to the designers of wireless networks. As an indispensable element of the solution to the above task, medium access control (MAC) protocols coordinate the stations and resolve the channel access contentions so that the scarce radio resources are shared fairly and efficiently among the participating users. With a given physical layer, a properly designed MAC protocol is the key to desired system performance, and directly affects the perceived QoS of end users. Distributed random access protocols are widely used MAC protocols in both infrastructure-based and infrastructureless wireless networks. To understand the characteristics of these protocols, there have been enormous efforts on their performance study by means of analytical modeling in the literature. However, the existing approaches are inflexible to adapt to different protocol variants and traffic situations, due to either many unrealistic assumptions or high complexity. In this thesis, we propose a simple and scalable generic performance analysis framework for a family of carrier sense multiple access with collision avoidance (CSMA/CA) based distributed MAC protocols, regardless of the detailed backoff and channel access policies, with more realistic and fewer assumptions. It provides a systematic approach to the performance study and comparison of diverse MAC protocols in various situations. Developed from the viewpoint of a tagged station, the proposed framework focuses on modeling the backoff and channel access behavior of an individual station. A set of fixed point equations is obtained based on a novel three-level renewal process concept, which leads to the fundamental MAC performance metric, average frame service time. With this result, the important network saturation throughput is then obtained straightforwardly. The above distinctive approach makes the proposed analytical framework unified for both saturated and unsaturated stations. The proposed framework is successfully applied to study and compare the performance of three representative distributed MAC protocols: the legacy p-persistent CSMA/CA protocol, the IEEE 802.15.4 contention access period MAC protocol, and the IEEE 802.11 distributed coordination function, in a network with homogeneous service. It is also extended naturally to study the effects of three prevalent mechanisms for prioritized channel access in a network with service differentiation. In particular, the novel concepts of ``virtual backoff event'' and ``pre-backoff waiting periods'' greatly simplify the analysis of the arbitration interframe space mechanism, which is the most challenging one among the three, as shown in the previous works reported in the literature. The comparison with comprehensive simulations shows that the proposed analytical framework provides accurate performance predictions in a broad range of stations. The results obtained provide many helpful insights into how to improve the performance of current protocols and design better new ones.

As wireless sensor platforms become less expensive and more powerful, the promise of their wide-spread use for everything from health monitoring to military sensing continues to increase. Like other networks, sensor networks are vulnerable to malicious attack; however, the hardware simplicity of these devices makes defense mechanisms designed for traditional networks infeasible. This work explores the denial-of-sleep attack, in which a sensor node's power supply is targeted. Attacks of this type can reduce sensor lifetime from years to days and can have a devastating impact on a sensor network. This work identifies vulnerabilities in state-of-the-art sensor network medium access control (MAC) protocols that leave them susceptible to denial-of-sleep attack. It then classifies these attacks in terms of an attacker's knowledge of the MAC layer protocol and ability to bypass authentication and encryption protocols. Attacks from each category in the classification are modeled to show the impacts on four current sensor network MAC protocols: S-MAC, T-MAC, B-MAC and G-MAC. To validate the effectiveness and analyze the efficiency of the attacks, implementations of selected attacks on S-MAC and T-MAC are described and analyzed in detail. This research goes on to introduce a suite of mechanisms designed to detect and mitigate the effects of denial-of-sleep attacks on sensor networks. The Clustered Anti Sleep-Deprivation for Sensor Networks, or Caisson, suite includes a lightweight, platform-independent anti-replay mechanism, an adaptive rate-limiter and a jamming detection and mitigation mechanism. These tools are designed to be applied selectively or in concert to defend against denial-of-sleep attacks depending on the specific vulnerabilities in the MAC protocol used in a particular sensor network deployment. This work makes two major contributions to state-of-the-art wireless sensor network research. First, it fully explores the denial-of-sleep attack, to include the implementation of a subset of these attacks on actual sensor devices and an analysis of the efficiency of these attacks. Second, it provides a set of tools by which these attacks are detected and defeated in a lightweight, platform-independent, and protocol-independent way. If sensor networks are to live up to current expectations, they must be robust in the face of newly emerging network attacks, to include denial-of-sleep. / Ph. D.

How to improve the radio resource utilization and provide better quality-of-service (QoS) is an everlasting challenge to the designers of wireless networks. As an indispensable element of the solution to the above task, medium access control (MAC) protocols coordinate the stations and resolve the channel access contentions so that the scarce radio resources are shared fairly and efficiently among the participating users. With a given physical layer, a properly designed MAC protocol is the key to desired system performance, and directly affects the perceived QoS of end users. Distributed random access protocols are widely used MAC protocols in both infrastructure-based and infrastructureless wireless networks. To understand the characteristics of these protocols, there have been enormous efforts on their performance study by means of analytical modeling in the literature. However, the existing approaches are inflexible to adapt to different protocol variants and traffic situations, due to either many unrealistic assumptions or high complexity. In this thesis, we propose a simple and scalable generic performance analysis framework for a family of carrier sense multiple access with collision avoidance (CSMA/CA) based distributed MAC protocols, regardless of the detailed backoff and channel access policies, with more realistic and fewer assumptions. It provides a systematic approach to the performance study and comparison of diverse MAC protocols in various situations. Developed from the viewpoint of a tagged station, the proposed framework focuses on modeling the backoff and channel access behavior of an individual station. A set of fixed point equations is obtained based on a novel three-level renewal process concept, which leads to the fundamental MAC performance metric, average frame service time. With this result, the important network saturation throughput is then obtained straightforwardly. The above distinctive approach makes the proposed analytical framework unified for both saturated and unsaturated stations. The proposed framework is successfully applied to study and compare the performance of three representative distributed MAC protocols: the legacy p-persistent CSMA/CA protocol, the IEEE 802.15.4 contention access period MAC protocol, and the IEEE 802.11 distributed coordination function, in a network with homogeneous service. It is also extended naturally to study the effects of three prevalent mechanisms for prioritized channel access in a network with service differentiation. In particular, the novel concepts of ``virtual backoff event'' and ``pre-backoff waiting periods'' greatly simplify the analysis of the arbitration interframe space mechanism, which is the most challenging one among the three, as shown in the previous works reported in the literature. The comparison with comprehensive simulations shows that the proposed analytical framework provides accurate performance predictions in a broad range of stations. The results obtained provide many helpful insights into how to improve the performance of current protocols and design better new ones.

With the rapid increase in wireless devices, an effective improvement in the demand of efficient spectrum utilisation for gaining better connectivity is needed. Cognitive Radio (CR) is an emerging technology that exploits the inefficient utilisation of the unused spectrum dynamically. Since spectrum sharing is responsible for coordinating channels’ access for Cognitive Users (CUs), the Common Control Channel (CCC) is one of the existing methods used to exchange the control information between CUs. However, the unique characteristics and parameters of Cognitive Radio Networks (CRNs) present several possible threats targeting spectrum sensing, spectrum management, spectrum sharing, and spectrum mobility leading to the deterioration of the network performance. Thus, protection and detection security mechanisms are essential to maintaining the CRNs. This thesis presents a novel decentralised CR MAC protocol that successfully utilises the unused portion of the licensed band. The protocol achieves improved performance; communication time and throughput when compared to two benchmark protocols. Less communication time and higher throughput are accomplished by the protocol due to performing fast switching to the selected available data channel for initiating data transmission. The proposed protocol is then extended to two different versions based on two authentication approaches applied to it; one using Digital Signature and another is based on Shared-Key. The two proposed secure protocols address the security requirements in CRNs leading to subsequent secure communication among CUs. The protocols function effectively in providing defence against several attacks related to the MAC layer such as; Spectrum Sensing Data Manipulation/Falsification, Data Tempering and Modification, Jamming attacks, Eavesdropping, Forgery and Fake control information attacks, MAC address spoofing, and unauthorised access attacks. The associated security algorithms ensure the successful secure communication between CUs in a cooperative approach. Moreover, the security protocols are investigated and analysed in terms of security flows by launching unauthorised access and modification attacks on the transmitted information. The testing results demonstrated that two protocols perform successful detection of threats and ensure secure communication in CRNs.

In this dissertation, the central objective is to achieve fairness in bandwidth sharing amongst selfish users in a distributed system. Because of the inherent contention-based nature of the distributed medium access and the selfishness of the users, the distributed medium access is modeled as a non-cooperative game; designated as the Access Game. A p-CSMA type medium access scenario is proposed for all the users. Therefore, in the Access Game, each user has two actions to choose from: "transmit" and "wait". The outcome of the Access Game and payoffs to each user depends on the actions taken by all the users. Further, the utility function of each user is constructed as a function of both Quality of Service (QoS) and Battery Power (BP). Various scenarios involving the relative importance of QoS and BP are considered. It is observed that, in general the Nash Equilibrium of the Access Game does not result into fairness. Therefore, Constrained Nash Equilibrium is proposed as a solution. The advantage of Constrained Nash Equilibrium is that it can be predicated on the fairness conditions and the solution will be guaranteed to result in fair sharing of bandwidth. However, Constrained Nash Equilibrium is that it is not self-enforcing. Therefore, two mechanisms are proposed to design the Access Game in such a way that in each case the Nash Equilibrium of the Access Game satisfies fairness and maximizes throughput. Hence, with any of these mechanisms the solution of the Access Game becomes self-enforcing.

The low-energy characteristics of Wireless Sensor Networks (WSNs) pose a great design challenge for MAC protocol design. The cluster-based scheme is a promising solution. Recent studies have proposed different cluster-based MAC protocols. We propose an intra-cluster communication bit-map-assisted (BMA) MAC protocol. BMA is intended for event-driven applications. The scheduling of BMA can change dynamically according to the unpredictable variations of sensor networks. In terms of energy efficiency, BMA reduces energy consumption due to idle listening and collisions. In this study, we develop two different analytic energy models for BMA, conventional TDMA and energy efficient TDMA (E-TDMA) when used as intra-cluster MAC schemes. Simulation experiments are constructed to validate the analytic models. Both analytic and simulation results show that in terms of energy efficiency, BMA performance heavily depends on the sensor node traffic offer load, the number of sensor nodes within a cluster, the data packet size and, in some cases, the number of sessions per round. BMA is superior for the cases of low and medium traffic loads, relatively few sensor nodes per cluster, and relatively large data packet sizes. In addition, BMA outperforms the TDMA-based MAC schemes in terms of average packet latency.

The prospect of replacing existing fixed networks with cheap, flexible and evenmobile low-power wireless network has been a strong research driver in recent years.However, many challenges still exist: reliability is hampered by unstable and burstycommunication links; the wireless medium is getting congested by an increasingnumber of wireless devices; and life-times are limited due to difficulties in developingefficient duty-cycling mechanisms. These challenges inhibit the industry to fullyembrace and exploit the capabilities and business opportunities that low-powerwireless devices offer. In this thesis, we propose, design, implement, and evaluateprotocols and systems to increase flexibility and improve efficiency of low-powerwireless communications. First, we present MobiSense, a system architecture for energy-efficient communicationsin micro-mobility sensing scenarios. MobiSense is a hybrid architecturecombining a fixed infrastructure network and mobile sensor nodes. Simulations andexperimental results show that the system provides high throughput and reliabilitywith low-latency handoffs. Secondly, we investigate if and how multi-channel communication can mitigate theimpact of link dynamics on low-power wireless protocols. Our study is motivated bya curiosity to reconcile two opposing views: that link dynamics is best compensatedby either (i) adaptive routing, or (ii) multi-channel communication. We perform acomprehensive measurement campaign and evaluate performance both in the singlelink and over a multi-hop network. We study packet reception ratios, maximumburst losses, temporal correlation of losses and loss correlations across channels.The evaluation shows that multi-channel communication significantly reduces linkburstiness and packet losses. In multi-hop networks, multi-channel communicationsand adaptive routing achieves similar end-to-end reliability in dense topologies,while multi-channel communication outperforms adaptive routing in sparse networkswhere re-routing options are limited. Third, we address the problem of distributed information exchange in proximitybasednetworks. First, we consider randomized information exchange and assess thepotential of multi-channel epidemic discovery. We propose an epidemic neightbordiscoverymechanism that reduces discovery times considerably compared to singlechannelprotocols in large and dense networks. Then, the idea is extended todeterministic information exchange. We propose, design and evaluate an epidemicinformation dissemination mechanism with strong performance both in theory andpractice. Finally, we apply some of the concepts from epidemic discovery to the designof an asynchronous, sender-initiated multi-channel medium access protocol. Theprotocol combines a novel mechanism for rapid schedule learning that avoids perpacketchannel negotiations with the use of burst data transfer to provide efficientsupport of ’multiple contending unicast and parallel data flows. / De senaste åren har forskning inom trådlös kommunikation drivits av önskemåletom att kunna ersätta nuvarande trådbundna kommunikationslänkar med trådlösa lågenergialternativ.Dock kvarstår många utmaningar, såsom instabila och sporadiskalänkar, överbelastning på grund av en ökning i antal trådlösa enheter, hur maneffektivt kan växla duty-cycling mekanismen för att förlänga nätverkens livstid,med flera. Dessa utmaningar begränsar industrin från att ta till sig och utnyttjade fördelar som trådlösa lågenergialternativ kan medföra. I den här avhandlingenföreslår, designar, implementerar och utvärderar vi protokoll och system som kanförbättra de nuvarande trådlösa lågenergialternativen. Först presenterar vi MobiSense, en systemarkitektur för energibesparande kommunikationi mikro-mobila sensorscenarier. MobiSense är en hybridarkitektur somkombinerar ett fast infrastrukturnätverk med rörliga sensornoder. Simulerings- ochexperimentella resultat visar att systemet uppnår en högre överföringskapacitet ochtillförlitlighet samtidigt som överlämnandet mellan basstationer har låg latens. I den andra delen behandlar vi hur effekterna från länkdynamiken hos protokollför lågenergikommunikation kan minskas, och försöker förena idéerna hos två motståendesynsätt: (i) flerkanalskommunikation och (ii) adaptiv routing. Vi analyserarenkanals- och flerkanalskommunikation över en-stegslänkar i termer av andelenmottagna paket kontra andelen förlorade, den maximala sporadiska förlusten avpaket, tidskorrelation för förluster och förlustkorrelation mellan olika kanaler. Resultatenindikerar att flerkanalskommunikation med kanalhoppning kraftigt minskardet sporadiska uppträdandet hos länkarna och korrelationen mellan paketförluster.För flerstegsnätverk uppvisar flerkanalskommunikation och adaptiv routingliknande tillförlitlighet i täta topologier, medan flerkanalskommunikation har bättreprestanda än adaptiv routing i glesa nätverk med sporadiska länkar. I den tredje delen studeras distribuerat informationsutbyte i närhetsbaseradenätverk. Först betraktas det slumpmässiga fallet och vi fastställer potentialen hosflerkanalig indirekt utforskning av nätverket. Vi analyserar ett trestegs protokoll,som möjliggör en snabbare utforskning av nätverket. Sedan föreslår vi en ny algoritmför att upptäcka grannarna i ett flerkanalsnätverk, som kraftigt minskarutforskningstiden i jämförelse med ett enkanalsprotokoll. Vi utökar även problemettill det deterministiska fallet och föreslår en mekanism för informationsspridningsom påskyndar utforskningstiderna för deterministiska protokoll. Utvidgningen hartvå huvudförbättringar som leder till kraftigt ökad prestanda samtidigt som degaranterar att utforskningsprocessen är deterministisk. Till sist applicerar vi koncepten rörande indirekt utforskning för att designa,implementera och evaluera ett asynkront sändare-initierat flerkanals MAC protokollför trådlös lågenergikommunikation. Protokollet kombinerar en ny mekanism försnabbt lärande av tidsschemat, vilket undviker kanalförhandling för varje paket,med sporadisk dataöverföring. Detta möjliggör ett effektivt tillhandahållande avflera konkurrerande och parallella dataflöden. / <p>QC 20151204</p>

It is widely accepted that low energy consumption is the most important requirement when designing components and systems for a wireless sensor network (WSN). The greatest energy consumer of each node within a WSN is the radio transceiver and as such, it is important that this component be used in an extremely energy e±cient manner. One method of reducing the amount of energy consumed by the radio transceiver is to turn it off and allow nodes to enter a sleep mode. The algorithms that directly control the radio transceiver are traditionally grouped into the Medium Access Control (MAC) layer of a communication protocol stack. This thesis introduces the emerging field of wireless sensor networks and outlines the requirements of a MAC protocol for such a network. Current MAC protocols are reviewed in detail with a focus on how they utilize this energy saving sleep mode as well as performance problems that they suffer from. A proposed new method of coordinating the use of this sleep mode between nodes in the network is specifed and described. The proposed new protocol is analytically compared with existing protocols as well as with some fundamental performance limits. The thesis concludes with an analysis of the results as well as some recommendations for future work.