The work in this thesis is concerned with two complementary aspects of wireless networks research; performance analysis and resource optimization. The first part of the thesis focusses on the performance analysis of IEEE 802.11(e) wireless local area networks. We study the distributed coordination function (DCF) and the enhanced distributed channel access (EDCA) MAC of the IEEE 802.11(e) standard. We consider n IEEE 802.11(e) DCF (EDCA) nodes operating as a single cell; by single cell, we mean that every packet transmission can be heard by every other node. Packet loss is attributed only to simultaneous transmissions by the nodes (i.e., collisions). Using the well known decoupling approximation [19], we characterize the collision behaviour and the throughput performance of the WLAN with a set of fixed point equations involving the backoff parameters of the nodes. We observe that the fixed point equations can have multiple solutions, and in such cases, the system exhibits multistability and short-term unfairness of throughput. Also, the fixed point analysis fails to characterize the average system behaviour when the system has multiple solutions. We then obtain sufficient conditions (in terms of the backoff parameters of the nodes) under which the fixed point equations have a unique solution. For such cases, using simulations, we observe that the fixed point analysis predicts the long term time average throughput behaviour accurately. Then, using the fixed point analysis, we study throughput differentiation provided by the different backoff parameters, including minimum contention window (CWmin), persistence factor and arbitration interframe space (AIFS) of the IEEE 802.11e standard. Finally, we extend the above results to the case where the receiver supports physical layer capture. In the second part of the thesis, we study resource allocation and optimization problems for a variety of wireless network scenarios. For a dense wireless network, deployed over a small area and with a network average power constraint, we show that single cell operation (the channel supports only one successful transmission at any time) is throughput efficient in the asymptotic regime (in which the network average power is made large). We show that, for a realistic path loss model and a physical interference model (SINR based), the maximum aggregate bit rate among arbitrary transmitter-receiver pairs scales only as Θ(log(¯P)), where¯P is the network average power. Spatial reuse is ineffective and direct transmission between source destination pairs is the throughput optimal strategy. Then, operating the network with only a single successful transmission permitted at a time, and with CSMA being used to select the successful transmitter-receiver pair, we consider the situation in which there is stationary spatiotemporal channel fading. We study the optimal hop length (routing strategy) and power control (for a fading channel) that maximizes the network aggregate throughput for a given network power constraint. For a fixed transmission time scheme, we study the throughput maximizing schedule under homogeneous traffic and MAC assumptions. We also characterize the optimal operating point (hop length and power control) in terms of the network power constraint and the channel fade distribution. It is now well understood that in a multihop network, performance can be enhanced if, instead of just forwarding packets, the network nodes create output packets by judiciously combining their input packets, a strategy that is called “network coding.” For a two link slotted wireless network employing a network coding strategy and with fading channels, we study the optimal power control and optimal exploitation of network coding opportunities that minimizes the average power required to support a given arrival rate. We also study the optimal power-delay tradeoff for the network. Finally, we study a vehicular network problem, where vehicles are used as relays to transfer data between a pair of stationary source and destination nodes. The source node has a file to transfer to the destination node and we are interested in the delay minimizing schedule for the vehicular network. We characterize the average queueing delay (at the source node) and the average transit delay of the packets (at the relay vehicles) in terms of the vehicular speeds and their interarrival times, and study the asymptotically optimal tradeoff achievable between them.

Approved for public release, distribution is unlimited / Wireless Local Area Network (WLAN) technologies are becoming widely used since they provide more flexibility and availability. Unfortunately, it is possible for WLANs to be implemented with security flaws which are not addressed in the original 802.11 specification. IEEE formed a working group (TGi) to provide a complete solution (code named 802.11i standard) to all the security problems of the WLANs. The group proposed using 802.1X as an interim solution to the deficiencies in WLAN authentication and key management. The full 802.11i standard is expected to be finalized by the end of 2004. Although 802.1X provides a better authentication scheme than the original 802.11 security solution, it is still vulnerable to denial-of-service, session hijacking, and man-in-the- middle attacks. Using an open-source 802.1X test-bed, this thesis evaluates various session hijacking mechanisms through experimentation. The main conclusion is that the risk of session hijacking attack is significantly reduced with the new security standard (802.11i); however, the new standard will not resolve all of the problems. An attempt to launch a session hijacking attack against the new security standard will not succeed, although it will result in a denial-of-service attack against the user. / Lieutenant Junior Grade, Turkish Navy

Authentication protocols are used for two parties to authenticate each other and build a secure channel over wired or wireless public channels. However, the present standards of authentication protocols are either insufficiently secure or inefficient for light weight devices. Therefore, we propose two authentication protocols for improving the security and user efficiency in wired and wireless environments, respectively. Traditionally, TLS/SSL is the standard of authentication and key exchange protocols in wired Internet. It is known that the security of TLS/SSL is not enough due to all sorts of client side attacks. To amend the client side security, multi-factor authentication is an effective solution. However, this solution brings about the issue of biometric privacy which raises public concern of revealing biometric data to an authentication server. Therefore, we propose a truly three factor authentication protocol, where the authentication server can verify their biometric data without the knowledge of users¡¦ templates and samples. In the major wireless technologies, extensible Authentication Protocol (EAP) is an authentication framework widely used in IEEE 802.11 WLANs. Authentication mechanisms built on EAP are called EAP methods. The requirements for EAP methods in WLANs authentication have been defined in RFC 4017. To achieve user efficiency and robust security, lightweight computation and forward secrecy, excluded in RFC 4017, are desired in WLAN authentication. However, all EAP methods and authentication protocols designed for WLANs so far do not satisfy all of the above properties. We will present a complete EAP method that utilizes stored secrets and passwords to verify users so that it can (1) meet the requirements of RFC 4017, (2) provide lightweight computation, and (3) allow for forward secrecy. In order to prove our proposed protocols completely, we apply two different models to examine their security properties: Bellare¡¦s model, a standard reduction based on computational model, that reduces the security properties to the computationally hard problems and the OFMC/AVISPA tool, a model checking approach based on formal model, that uses the concept of the search tree to systematically find the weaknesses of a protocol. Through adopting Bellare¡¦s model and OFMC/AVISPA tool, the security of our work is firmly established.

Wireless networks have potential applications in wireless Internet connectivity, battlefields, disaster relief, and cyber-physical systems. While the nodes in these networks communicate with each other over the air, the challenges faced by and the subsequent design criteria of these networks are diverse. In this thesis, we study and discuss a few design requirements of these networks, such as efficient utilization of the network bandwidth in IEEE 802.11 infrastructure networks, evaluating utility of sensor node deployments, and security from eavesdroppers. The presence of infrastructure IEEE 802.11 based Wireless Local Area Networks (WLANs) allows mobile users to seamlessly transfer huge volumes of data. While these networks accommodate mobility, and are a cost-effective alternative to cellular networks, they are well known to display several performance anomalies. We study a few such anomalies, and provide a performance management solution for IEEE 802.11 based WLANs. On the other hand, in sensor networks, the absence of infrastructure mandates the use of adhoc network architectures. In these architectures, nodes are required to route data to gateway nodes over a multi-hop network. These gateway nodes are larger in size, and costlier in comparison with the regular nodes. In this context, we propose a unified framework that can be used to compare different deployment scenarios, and provide a means to design efficient large-scale adhoc networks. In modern times, security has become an additional design criterion in wireless networks. Traditionally, secure transmissions were enabled using cryptographic schemes. However, in recent years, researchers have explored physical layer security as an alternative to these traditional cryptographic schemes. Physical layer security enables secure transmissions at non-zero data rate between two communicating nodes, by exploiting the degraded nature of the eavesdropper channel and the inherent randomness of the wireless medium. Also, in many practical scenarios, several nodes cooperate to improve their individual secrecy rates. Therefore, in this thesis, we also study scenarios, where cooperative schemes can improve secure end-to-end data transmission rates, while adhering to an overall power budget. In spite of the presence of voluminous reservoirs of information such as digital libraries and the Internet, asking around still remains a popular means of seeking information. In scenarios where the person is interested in communal, or location-specific information, such kind of retrieval may yield better results than a global search. Hence, wireless networks should be designed, analyzed and controlled by taking into account the evolution of the underlying social networks. This alliance between social network analysis and adhoc network architectures can greatly advance the design of network protocols, especially in environments with opportunistic communications. Therefore, in addition to the above mentioned problem, in this thesis, we have also presented and studied a model that captures the temporal evolution of information in social networks with memory.

As Industry 4.0 keeps approaching, the quality of data communication in industrial scenarios is increasingly important to support a high degree of automation and intelligence in factories. Wi-Fi 6E, the latest advanced wireless local-area network standard, comes with new 6 GHz unlicensed spectrum, a new access method named Orthogonal Frequency Division Multiple Access, and even more features. Accordingly, Wi-Fi 6E can be a promising candidate technology for an industrial wireless network. To fulfill industrial applications, Wi-Fi 6E is challenged with high communication requirements and a massive number of devices to support. Since the cutting-edge Wi- Fi 6E systems have not been widely deployed practically, simulations are required to evaluate the performance of Wi-Fi 6E in industrial scenarios. Based on an event-based simulator from Ericsson, we performed simulations covering not only single access point scenarios with periodic traffic, but also scenarios where multiple applications and generations of Wi-Fi systems coexist. Finally, a large-area industry scenario with frequency planning applied was evaluated. Through simulation results and analysis, we conclude that Wi-Fi 6E performs well in most of our tested scenarios. Compared to legacy Wi-Fi 5,Wi-Fi 6E performs better when subject to uplink traffic, and is more suitable for handling a massive number of devices or high packet rate traffic due to its unique multi-user accessing. However, Wi-Fi 6E can have poor performance when performing multi-user transmission with applications that have complex traffic and millisecond-level latency requirement. In some cases, Wi-Fi 6E performs worse than Wi-Fi 5 while handling multiple applications whose packet sizes vary a lot. Moreover, with the increase in factory scales, Wi-Fi 6E can have a magnificent performance drop, almost 100%, through the regulatory requirements in the new 6 GHz unlicensed band. / När Industri 4.0 fortsätter att närma sig blir datakommunikationens kvalitet i industriella scenarier allt viktigare för att stödja en hög grad av automatisering och intelligens i fabriker. Wi-Fi 6E, den senaste avancerade standarden för trådlöst lokalt nätverk, kommer med ett nytt 6 GHz olicensierat spektrum, en ny åtkomstmetod som heter Orthogonal Frequency Division Multiple Access och ännu fler funktioner. Följaktligen kan Wi-Fi 6E vara en lovande kandidatteknik för ett industriellt trådlöst nätverk. För att uppfylla industriella applikationer utmanas Wi-Fi 6E med höga kommunikationskrav och ett stort antal enheter att stödja. Eftersom de banbrytande Wi-Fi 6E systemen inte har använts i stor utsträckning praktiskt taget, krävs simuleringar för att utvärdera prestandan för Wi-Fi 6E i industriella scenarier. Baserat på en händelsebaserad simulator från Ericsson utförde vi simuleringar som inte bara omfattar enstaka åtkomstpunktsscenarier med periodisk trafik, utan också scenarier där flera applikationer och generationer av Wi-Fi-system samexisterar. Slutligen utvärderades ett storindustriscenario med tillämpad frekvensplanering. Genom simuleringsresultat och analys drar vi slutsatsen att Wi-Fi 6E fungerar bra i de flesta av våra testade scenarier. Jämfört med äldre Wi-Fi 5, fungerar Wi-Fi 6E bättre när den utsätts för upplänkstrafik och är mer lämpad för att hantera ett stort antal enheter eller hög pakettrafik på grund av dess unika åtkomst för flera användare. Wi-Fi 6E kan dock ha dålig prestanda vid överföring av fleranvändare med applikationer som har komplex trafik och krav på latens på millisekundnivå. I vissa fall fungerar Wi-Fi 6E sämre än Wi-Fi 5 när hanterar flera applikationer vars paketstorlekar varierar mycket. Med ökningen av fabriksskalor kan Wi-Fi 6E dessutom ha en fantastisk prestandaförlust, nästan 100%, genom lagkraven för det nya 6 GHz-bandet utan licens.