Relays in communication networks is a well-researched topic. Historically, relays were used in analog radio and television to extend the coverage. Using relays in wireless data networking applications is a more recent problem. In the early 2000s, relays were introduced for Micro-cellular and Wi-Fi deployments. Recently it has been considered for sensor networks and Vehicular Ad-hoc Networks (VANETs) applications. In this dissertation we present a novel approach to determine the optimal bounds for the Medium Access Control (MAC) throughput at the target receiver in a multi-hop multirate wireless data network. For a given relationship between the throughput and the distance, and a given distance between the access point and the target receiver, there is a minimum number of nodes that provides the maximum throughput to the target receiver. It is always desirable to optimize the deployment from various aspects. These aspects are application dependent and they range from energy conservation in sensor networks to throughput and coverage maximization in data networks. We apply this novel approach to vehicular ad-hoc network (VANET) scenarios. Using multi-hop relays, we show how to determine the optimum throughput for communciation between two vehicles. The optimal number of relays is chosen to maximize the throughput for point-to-point communication between a source and a destination as well as broadcast among all vehicles in the coverage area of the source. Additionally, in the physical layer, performance issues arise from the effects of interference and fading. The physical layer performance will in turn impact medium access control performance, effectively reducing the network throughput. We evaluate the ii performance of dense small cells for wireless local area networks (WLAN) and femto cells for data applications under the effects of interference and fading. We assume the network is fully saturated. We use the throughput-distance relationship to take into consideration the effects of interference, fading as well as the medium access control overheads. Using this model, we show that under certain conditions, the medium access control throughput for WLANs can outperform that of femto cells.

This research devises a unified method for the distribution of pseudonyms in hybrid ephemeral vehicular networks (VNs), which are often referred to as vehicular ad hoc networks (VANETs), for the purposes of refill, intra-regional, and inter-regional movement. This work addresses a significant impediment to the use of pseudonyms, which has been almost universally accepted (and is on the verge of being standardized by the Institute for Electrical and Electronic Engineers (IEEE) and the Society for Automotive Engineers (SAE) as the best means to balance attribution and privacy to maximize the value of infrastructure deployment and citizen acceptability (i.e. use). The results include a pseudonym distribution protocol that maximizes ease of use while not compromising the security or privacy pseudonyms afford. These results contribute to the solution, in a scalable, adaptive, and bandwidth efficient manner, one of the remaining impediments to the adoption of VANETs. The new method shows improved performance compared to a baseline pseudonym distribution method that does not take these factors into consideration.

As roadside and in-vehicle sensors are deployed under the Connected Vehicle Research program (formerly known as Vehicle Infrastructure Integration initiative and Intellidrive), an increasing variety of traffic data is becoming available in real time. This real time traffic data is shared among vehicles and between vehicles and traffic management centers through wireless communication. This course of events creates an opportunity for mobile computing and online traffic simulations. However, online traffic simulations require faster than real time running speed with high simulation resolution, since the purpose of the simulations is to provide immediate future traffic forecast based on real time traffic data. However, simulating at high resolution is often too computationally intensive to process a large scale network on a single processor in real time. To mitigate this limitation an online ad hoc distributed simulation with optimistic execution is proposed in this study. The objective of this study is to develop an online traffic simulation system based on an ad hoc distributed simulation with optimistic execution. In this system, data collection, processing, and simulations are performed in a distributed fashion. Each individual simulator models the current traffic conditions of its local vicinity focusing only on its area of interest, without modeling other less relevant areas. Collectively, a central server coordinates the overall simulations with an optimistic execution technique and provides a predictive model of traffic conditions in large areas by combining simulations geographically spread over large areas. This distributed approach increases computing capacity of the entire system and speed of execution. The proposed model manages the distributed network, synchronizes the predictions among simulators, and resolves simulation output conflicts. Proper feedback allows each simulator to have accurate input data and eventually produce predictions close to reality. Such a system could provide both more up-to-date and robust predictions than that offered by centralized simulations within a single transportation management center. As these systems evolve, the online traffic predictions can be used in surface transportation management and travelers will benefit from more accurate and reliable traffic forecast.

The topic of the research is granting privacy and authentication in Mobile Ad Hoc Networks (MANETs) that are under the authority of a certificate authority (CA) that is often not available. Privacy is implemented in the form of an anonymous identity or pseudonym, and ideally has no link to the real identity. Authentication and privacy are conflicting tenets of security as the former ensures a user's identity is always known and certified and the latter hides a user's identity. The goal was to determine if it is possible for a node to produce pseudonyms for itself that would carry the authority of the CA while being traceable by the CA, and would be completely anonymous. The first part of the dissertation places Vehicular Ad Hoc Networks (VANETs) into context, as this is the application of MANETs considered. This is followed by a detailed survey and analysis of the privacy aspects of VANETs. Thereafter, the solution is proposed, documented and analysed. Lastly, the dissertation is concluded and the contributions made are listed. The solution implements a novel approach for making proxies readily available to vehicles, and does indeed incorporate privacy and authentication in VANETs such that the pseudonyms produced are always authentic and traceable. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Mobile Ad-hoc Network (MANET) is a group of mobile devices that can form a network, interconnect and share resources without the use of any fixed network infrastructure or centralised management. MANET is exposed to security attacks because of its fundamental characteristics such as open medium, dynamic topology and lack of central monitoring. The black hole attack is one example of the attacks MANET is exposed to. In black hole attack, a malicious node misleadingly claims to have an updated route to the destination node, absorbs and drops the packets that are supposed to be forwarded to the destination node. The common MANET reactive routing protocols are Ad-hoc on-demand Distance Vector (AODV) and Dynamic Source Routing (DSR). These protocols are easily attacked by the black hole during the route discovery process. This research therefore studies black hole attack in detail and assesses the performance of AODV and DSR under black hole attack. The work is achieved by simulating the two protocols under regular operation and under black hole attack using Network Simulator 2 (NS-2). The protocols are analysed using packet delivery ratio, throughput and end-to-end delay as performance metrics. The research further compares the black hole attack solutions that have been previously proposed and determines the solution that performs better than others. The simulation results show that MANET under normal operating environment out performs MANET attacked by black hole, and that AODV is more vulnerable to black hole attack than DSR. The comparison study of the existing black hole attack solutions show that SAODV is the best effective black hole attack removal technique. But when considering the solution that brings no negative impact to the normal operation of the network, IDSAODV is the best solution. / Computing / M. Sc. (Computer Science)

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis explores two key aspects of wireless ad hoc networks. The first aspect concerns the topic of stimulating cooperation between nodes in a wireless ad hoc network. The functionality of a wireless ad hoc network depends entirely on the willingness of nodes to relay messages on behalf of other nodes. Network functionality depends on ensuring cooperation between nodes, so that each node benefits from continued participation in the network. This suggests an important question: how can cooperation among individual nodes be managed to improve overall wireless ad hoc network performance? The second aspect explored in this thesis concerns the concept of optimal resource utilisation. Wireless ad hoc networks are characterised by limited bandwidth and energy resources, which facilitates deployment in situations in which traditional infrastructure based networks are not practical. This suggests another important question: how can the use of the limited energy and bandwidth resources of wireless ad hoc networks be optimised? This research relies on the concept of a credit-based market economy. Nodes in simulated ad hoc networks use credits to pay for the cost of sending their own traffic and earn credits by forwarding traffic on behalf of other nodes. We show that a credit-based market economy approach can be employed to stimulate and regulate cooperation between nodes in a wireless ad hoc network. We show that this approach can be implemented in a simple decentralised manner and that it has several variants depending on which node is considered to be paying for the service, what the price of each service should be and how we route packets around the network using information derived from the credit-based economy. This thesis demonstrates that several variants of a credit-based scheme can be implemented in a packet based simulator and that these variants result in the stable operation of the network and improve the overall performance. The credit-based mechanisms also show significant improvement to network performance in resource constrained conditions and represent an effective means for optimising limited energy and bandwidth resource. The effectiveness of the credit-based mechanisms increases as the load on the networks increases. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek twee belangrike aspekte van draadlose ad hoc-netwerke. Die eerste aspek het betrekking op die onderwerp van 'n stimulerende samewerking tussen die nodusse in 'n draadlose ad hoc-netwerk. Dat die network funksioneer hang daarvan af om samewerking tussen die nodusse te verseker sodat elke nodus voordeel put uit voortgesette deelname in die netwerk. Dit dui op 'n belangrike vraag: Hoe kan die samewerking tussen die individuele nodusse bestuur word om die prestasie van 'n draadlose ad hoc-netwerk te verbeter? Die tweede aspek wat in hierdie tesis ondersoek word, behels die konsep van optimale hulpbronbenutting. Draadlose ad hoc-netwerke word gekenmerk deur beperkte bandwydte- en energie-hulpbronne, wat ontplooiing bewerkstellig in situasies waar tradisionele infrastruktuur-gebaseerde netwerke nie practise moontlik is nie. Dit dui op 'n ander belangrike vraag: Hoe kan die gebruik van die beperkte energie- en bandwydte-hulpbronne van draadlose ad hoc-netwerke optimaal bestuur word? Hierdie navorsing berus op die konsep van 'n krediet-gebaseerde markekonomie. Nodusse in gesimuleerde ad hoc-netwerke gebruik krediete om te betaal vir die versending van hul eie verkeer en nodusse verdien krediete deur die verkeer van ander nodusse aan te stuur. Ons wys dat die benadering van 'n krediet-gebaseerde markekonomie gebruik kan word om die samewerking tussen die nodusse in 'n draadlose ad hoc-netwerk te stimuleer en te reguleer. Ons wys dat hierdie benadering geïmplementeer kan word op 'n eenvoudige gedesentraliseerde wyse. Ons ondersoek verskeie variasies van die benadering, na gelang van watter nodus oorweeg word om vir die diens te betaal, wat die prys van elke diens moet wees en hoe inligting afgelei van die krediet-gebaseerde ekonomie gebruik kan word om pakkies in die netwerk te roeteer. Hierdie tesis toon dat verskeie variante van 'n krediet-gebaseerde skema geïmplementeer kan word in 'n netwerksimulator en dat hierdie variante die stabiele bedryf van en algehele verbetering in die prestasie van die network tot gevolg het. Die krediet-gebaseerde meganismes toon 'n beduidende verbetering in hulpbronbenutting en netwerkprestasie in omgewings met beperkte hulpbronne en verteenwoordig 'n doeltreffende manier om die beperkte energie- en bandwydte-hulpbronne optimaal te benut. Laastens, die doeltreffendheid van die krediet-gebaseerde meganismes word verhoog as die las op die netwerke word verhoog.

Vehicular Ad hoc Networks (VANET) is a wireless ad-hoc network that includes two types of communications, Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I). In VANET there are two types of messages. The first type is the event-driven messages that are only triggered in case of emergency. The second type is the periodical messages named beacons that are exchanged frequently between vehicles. A beacon message contains basic information about the sending vehicle such as id, location and velocity. Beacons are frequently exchanged to increase the cooperative awareness between vehicles. Increasing beacon frequency helps increasing neighborhood awareness and improving information accuracy. However, this causes more congestion in the network, specially when the number of vehicles increases. On the other hand, reducing beacon frequency alleviates network congestion, but results in out-dated information. In this dissertation, we address the aforementioned challenges and propose a number of smart beaconing protocols and evaluate their performance in di↵erent environments and network densities. The four adaptive beaconing protocols are designed to increase the cooperative awareness and information freshness, while alleviating the network congestion. All the proposed protocols take into account the most important aspects, which are critical to beaconing rate adaptation. These aspects include channel status, traffic conditions and link quality. The proposed protocols employ fuzzy logic-based techniques to determine the congestion rank, which is used to adjust beacon frequency. The first protocol considers signal to interference-noise ratio (SINR), number of neighboring nodes and mobility to determine the congestion rank and adjust the beacon rate accordingly. This protocol works well in sparse conditions and highway environments. The second protocol works well in sparse conditions and urban environments. It uses channel busy time (CBT), mobility and packet delivery ratio (PDR) to determine the congestion rank and adjust the beacon rate. The third protocol utilizes CBT, SINR, PDR, number of neighbors and mobility as inputs for the fuzzy logic system to determine the congestion rank and adjust the beacon rate. This protocol works well in dense conditions in both highway and urban environments. Through extensive simulation experiments, we established that certain input parameters are more e↵ective in beacon rate adaptation for certain environments and conditions. Based on this, we propose a high awareness and channel efficient scheme that adapts to di↵erent environments and conditions. First, the protocol estimates the network density using adaptive threshold function. Then, it looks at the spatial distribution of nodes using the quadrat method to determine whether the environment is highway or urban. Based on the density conditions and nodes distribution, the protocol utilizes the appropriate fuzzy input parameters to adapt the beaconing rate. In addition, the protocol optimizes the performance by adapting the transmission power based on network density and nodes distribution. Finally, an investigation of the impact of adaptive beaconing on broadcasting is conducted. The simulation results confirm that our adaptive beaconing scheme can improve performance of the broadcast protocols in terms of reachability and bandwidth consumption when compared to a fixed rate scheme. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

The United States has been going through a road accident crisis for many years. The National Safety Council estimates 40,000 people were killed and 4.57 million injured on U.S. roads in 2017. Direct and indirect loss from tra c congestion only is more than $140 billion every year. Vehicular Ad-hoc Networks (VANETs) are envisioned as the future of Intelligent Transportation Systems (ITSs). They have a great potential to enable all kinds of applications that will enhance road safety and transportation efficiency. In this dissertation, we have aggregated seven years of real-life tra c and incidents data, obtained from the Florida Department of Transportation District 4. We have studied and investigated the causes of road incidents by applying machine learning approaches to this aggregated big dataset. A scalable, reliable, and automatic system for predicting road incidents is an integral part of any e ective ITS. For this purpose, we propose a cloud-based system for VANET that aims at preventing or at least decreasing tra c congestions as well as crashes in real-time. We have created, tested, and validated a VANET traffic dataset by applying the connected vehicle behavioral changes to our aggregated dataset. To achieve the scalability, speed, and fault-tolerance in our developed system, we built our system in a lambda architecture fashion using Apache Spark and Spark Streaming with Kafka. We used our system in creating optimal and safe trajectories for autonomous vehicles based on the user preferences. We extended the use of our developed system in predicting the clearance time on the highway in real-time, as an important component of the traffic incident management system. We implemented the time series analysis and forecasting in our real-time system as a component for predicting traffic flow. Our system can be applied to use dedicated short communication (DSRC), cellular, or hybrid communication schema to receive streaming data and send back the safety messages. The performance of the proposed system has been extensively tested on the FAUs High Performance Computing Cluster (HPCC), as well as on a single node virtual machine. Results and findings confirm the applicability of the proposed system in predicting traffic incidents with low processing latency. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Vehicular Ad hoc Networks (VANETs) have the potential to enable various kinds of applications aiming at improving road safety and transportation efficiency. These applications require uni-cast routing, which remains a significant challenge due to VANETs characteristics. Given VANET dynamic topology, geographic routing protocols are considered the most suitable for such network due to their scalability and low overhead. However, the optimal selection of next-hop nodes in geographic routing is a challenging problem where the routing performance is highly affected by the variable link quality and bandwidth availability. In this dissertation, a number of enhancements to improve geographic routing reliability in VANETs are proposed. To minimize packet losses, the direction and link quality of next-hop nodes using the Expected Transmission Count (ETX) are considered to select links with low loss ratios. To consider the available bandwidth, a cross-layer enchantment of geographic routing, which can select more reliable links and quickly react to varying nodes load and channel conditions, is proposed. We present a novel model of the dynamic behavior of a wireless link. It considers the loss ratio on a link, in addition to transmission and queuing delays, and it takes into account the physical interference e ect on the link. Then, a novel geographic routing protocol based on fuzzy logic systems, which help in coordinating di erent contradicting metrics, is proposed. Multiple metrics related to vehicles' position, direction, link quality and achievable throughput are combined using fuzzy rules in order to select the more reliable next-hop nodes for packet forwarding. Finally, we propose a novel link utility aware geographic routing protocol, which extends the local view of the network topology using two-hop neighbor information. We present our model of link utility, which measures the usefulness of a two-hop neighbor link by considering its minimum residual bandwidth and packet loss rate. The proposed protocol can react appropriately to increased network tra c and to frequent topology dis-connectivity in VANETs. To evaluate the performance of the proposed protocols, extensive simulation experiments are performed using network and urban mobility simulation tools. Results confirm the advantages of the proposed schemes in increased traffic loads and network density. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Mi, Wengang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 80-85). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Path loss and fading channel --- p.2 / Chapter 1.2 --- Relay Channel --- p.4 / Chapter 1.3 --- Power allocation --- p.6 / Chapter 1.4 --- Network coding --- p.8 / Chapter 1.5 --- Outline of the thesis --- p.8 / Chapter 2 --- Background Study --- p.10 / Chapter 2.1 --- Cooperative communication --- p.10 / Chapter 2.1.1 --- User cooperation diversity --- p.11 / Chapter 2.1.2 --- Cooperative diversity --- p.14 / Chapter 2.1.3 --- Coded cooperation --- p.18 / Chapter 2.2 --- Power control and resource allocation in cooperative communication --- p.19 / Chapter 2.3 --- Network coding --- p.21 / Chapter 3 --- Power allocation in DF system --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- System Model --- p.25 / Chapter 3.3 --- BER analysis with power allocation --- p.27 / Chapter 3.3.1 --- BER analysis of single relay system --- p.27 / Chapter 3.3.2 --- Generalization for N-relay cooperation system --- p.30 / Chapter 3.4 --- Approximation --- p.31 / Chapter 3.5 --- Conclusion --- p.37 / Chapter 4 --- Network coding cooperation --- p.38 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- System model --- p.39 / Chapter 4.3 --- Performance analysis --- p.44 / Chapter 4.3.1 --- Network coding cooperation --- p.47 / Chapter 4.3.2 --- Conventional repetition cooperation --- p.48 / Chapter 4.3.3 --- Simulation result --- p.49 / Chapter 4.4 --- More nodes with network coding --- p.52 / Chapter 4.4.1 --- System model: to be selfish or not --- p.53 / Chapter 4.4.2 --- Performance analysis --- p.56 / Chapter 4.4.3 --- Simulation result --- p.62 / Chapter 4.5 --- Further discussion --- p.63 / Chapter 5 --- Conclusion --- p.64 / Chapter A --- Equation Derivation --- p.66 / Chapter A.l --- Proof of proposition 1 --- p.66 / Chapter A.2 --- Generalized solution --- p.68 / Chapter A.3 --- System outage probability of generous scheme --- p.69 / Chapter A.4 --- System outage probability of selfish scheme --- p.74 / Bibliography --- p.79