With the envisioned age of Internet of Things (IoTs), different aspects of Intelligent Transportation System (ITS) will be linked so as to advance road transportation safety, ease congestion of road traffic, lessen air pollution, improve passenger transportation comfort and significantly reduce road accidents. In vehicular networks, regular exchange of current position, direction, speed, etc., enable mobile vehicle to foresee an imminent vehicle accident and notify the driver early enough in order to take appropriate action(s) or the vehicle on its own may take adequate preventive measures to avert the looming accident. Actualizing this concept requires use of shared media access protocol that is capable of guaranteeing reliable and timely broadcast of safety messages. This dissertation investigates the use of Network Coding (NC) techniques to enrich the content of each transmission and ensure improved high reliability of the broadcasted safety messages with less number of retransmissions. A Code Aided Retransmission-based Error Recovery (CARER) protocol is proposed. In order to avoid broadcast storm problem, a rebroadcasting vehicle selection metric η, is developed, which is used to select a vehicle that will rebroadcast the received encoded message. Although the proposed CARER protocol demonstrates an impressive performance, the level of incurred overhead is fairly high due to the use of complex rebroadcasting vehicle selection metric. To resolve this issue, a Random Network Coding (RNC) and vehicle clustering based vehicular communication scheme with low algorithmic complexity, named Reliable and Enhanced Cooperative Cross-layer MAC (RECMAC) scheme, is proposed. The use of this clustering technique enables RECMAC to subdivide the vehicular network into small manageable, coordinated clusters which further improve transmission reliability and minimise negative impact of network overhead. Similarly, a Cluster Head (CH) selection metric F(j) is designed, which is used to determine and select the most suitably qualified candidate to become the CH of a particular cluster. Finally, in order to investigate the impact of available radio spectral resource, an in-depth study of the required amount of spectrum sufficient to support high transmission reliability and minimum latency requirements of critical road safety messages in vehicular networks was carried out. The performance of the proposed schemes was clearly shown with detailed theoretical analysis and was further validated with simulation experiments.

Made available in DSpace on 2014-06-12T15:52:15Z (GMT). No. of bitstreams: 1 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O surgimento de interfaces de rede sem-fio de baixo custo no mercado e o crescimento na demanda por dispositivos móveis (como Smartphones, PDAs, Internet Tablets e Laptops) permitiram a criação de cenários onde serviços de rede para usuários móveis possam existir sem nenhuma infra-estrutrutura pré-configurada. No entanto, a interoperabilidade entre tais redes, que são dinâmicas e heterogêneas, é atualmente objeto de pesquisa. Várias pesquisas na área de redes ad hoc sem-fio tem focado em uma única tecnologia sem-fio, baseada no padrão IEEE 802.11, onde os nós da rede são vistos de maneira plana (2D), ou seja, como elementos homogêneos, identificados apenas por endereços IP, não levando em consideração seus perfis de hardware e tecnologias de rede. Desta forma, pesquisas envolvendo mais de uma tecnologia de rede encontram-se em estágios iniciais. Novas propostas são necessárias para estes cenários, que são cada vez mais comuns, envolvendo múltiplos dispositivos com múltiplas interfaces de rede (multi-homed). Este trabalho propõe o protocolo de roteamento 3D, direcionado a cenários onde há heterogeneidade de dispositivos e tecnologias de rede. O objetivo do protocolo de roteamento proposto é prover mecanismos para a interoperabilidade de redes ad hoc heterogêneas, considerando outra dimensão de informações, aqui denominada de terceira dimensão (3D), que consiste em agregar mais informações, como informações de contexto, recursos dos dispositivos e interfaces de rede, ao processo de roteamento. Para isto, o protocolo considera os seguintes aspectos fundamentais: o processo de bootstrapping da rede heterogênea e dos nós, a construção e disseminação de informações de ciência de contexto entre os nós, e a atribuição de papéis específicos para determinados nós da rede. A avaliação do protocolo é feita através de experimentos em um test-bed real, utilizando um protótipo da implementação do protocolo, num cenário composto de dispositivos móveis como Smartphones OpenMoko, Internet Tablets N810 da Nokia e Laptops, possuindo tecnologias Bluetooth e 802.11, executando versões embarcadas do sistema operacional Linux

No infrastructure, no centralized administration and self-configuration are the main characteristics of MANETs. The primary motivation of MANET deployment is to increase portability, mobility and flexibility. However, this mobility causes an unpredictable change in topology and makes routing more difficult. Many routing algorithms have been proposed and tested over the last few years in order to provide an efficient routing in Ad Hoc networks. In this report we will show our conducted study with AODV (reactive), DSDV (proactive) and ZRP (hybrid) routing protocols. The performance of routing protocols have been evaluated carefully by analyzing the affects of changing network parameters such as, number of nodes, velocity, pause time, workload and flows on three performance metrics: packet delivery ratio, routing cost and average end- to- end delay. All the simulation work has been conducted in NS2. Our simulation results show that AODV gives better performance in all designed simulation models in terms of packets delivery ratio. DSDV shows the second best performance. Performance of ZRP is found average.

Unmanned Aerial Vehicles (UAVs) recently enabled a myriad of new applications spanning domains from personal entertainment and industrial inspection, to criminal surveillance and forest monitoring. A combination of sensor collection, wireless communication and path planning between multiple distributed agents is the natural way to support applications. Several small UAVs working collaboratively can rapidly provide extended reach, at low cost, and efficiently stream sensor information to operators on a ground station. A significant amount of previous work has addressed each of these topics independently, but in this dissertation we propose a holistic approach for joint coordination of networking and topology (placement of mobile nodes). Our thesis is that this approach improves user-interactive control of UAVs for live-streaming applications in terms of throughput, delay and reliability. In order to defend these claims, this dissertation begins by experimentally evaluating and modeling the wireless link between two UAVs, under different conditions. Due to limited link range, and the need for wide-area operation, the model is extended to encompass a multi-hop topology. We show that the performance of such networks using COTS devices is typically poor, and solutions must rely on coordination of network protocol and topology, simultaneously. At the network layer, we introduce a novel Time-division Multiple Access (TDMA) scheme called Distributed Variable Slot Protocol that relies on adaptive slot-length. We prove its convergence as well as its meliorated performance experimentally validated, namely 50% higher packet delivery. In terms of network topology, we show that without node placement control overall performance of the network is severely penalized, due to natural link asymmetries. We propose a novel protocol, named Dynamic Relay Placement, that is able to do both online link quality model-estimation and in a distributed fashion decide the best location for each network node, increasing throughput by 300%. Finally, we demonstrate the end-to-end system in a multi-vehicle monitoring mission. We show that coordination of multiple UAVs increases the sensor sampling rate up to 7 times in wide areas when compared to a naive approach. This work considers environmental constraints such as wind, as well as the intrinsic limitations of the vehicles such as maximum acceleration.

In this thesis, we propose a novel trust management scheme for improving routing reliability in wireless ad hoc networks. It is grounded on two classic autoregression models, namely Autoregressive (AR) model and Autoregressive with exogenous inputs (ARX) model. According to this scheme, a node periodically measures the packet forwarding ratio of its every neighbor as the trust observation about that neighbor. These measurements constitute a time series of data. The node has such a time series for each neighbor. By applying an autoregression model to these time series, it predicts the neighbors future packet forwarding ratios as their trust estimates, which in turn facilitate it to make intelligent routing decisions. With an AR model being applied, the node only uses its own observations for prediction; with an ARX model, it will also take into account recommendations from other neighbors. We evaluate the performance of the scheme when an AR, ARX or Bayesian model is used. Simulation results indicate that the ARX model is the best choice in terms of accuracy.

Opportunistic Routing (OR) is an effective and enhanced routing scheme for wireless multihop environment. OR is an approach that selects a certain number of best forwarders (candidates) at each hop by taking the advantage of the broadcast nature of the wireless medium to reach the destination. When a set of candidates receive the packet, they coordinate with each other to figure out which one has to forward the packet toward the destination. Most of the research in this area has been done in mesh networks where nodes do not have mobility. In this survey, we propose a new OR protocol for mobile ad hoc scenarios called as Enhanced Mobility-based Opportunistic Routing (EMOR) protocol. To deal with the node mobility, we have proposed a new metric which considers the following: geographical position of the candidates; the link delivery probability to reach them; the number of neighboring nodes of candidates; and the predicted position of nodes using the motion vector of the nodes. We have compared EMOR with five other well-known routing protocols in terms of delivery ratio, end-to-end delay, and expected number of transmissions from source to the destination. Our simulation results show that proposed protocol improves delivery ratio and number of expected transmission in terms of different type of mobility models.

Network coding is an emerging technology that intelligently exploits the store/forward nature of routers to increase the efficiency of the network. Though the concept works in theory, the segregation of coding and routing decisions makes them inapplicable in almost any practical environment. Coding-aware routing takes the network coding a step further to lessen its disadvantages by allowing interlayer communication while making routing decisions. However, most of the existing work exploits coding benefits only for fixed wireless networks, making them dependent on the types of network medium, topology and mobility and thus inapplicable for wired and mobile Ad Hoc networks. The aim of this thesis is to present a generalized algorithm that can detect any possible coding opportunity in a network of any medium, topology and mobility while making routing decisions. We have tested and evaluated our algorithm in six different network topology settings i.e. small wired, big wired, small Ad Hoc network with regular trajectories, big Ad Hoc network with regular trajectories, small Ad Hoc with random trajectories and big Ad Hoc with random trajectories. Improved performance in network throughput, mean queue size and mean end-to-end delay confirms the validity of our algorithm.

It is widely believed that the advances of Vehicle-to-Vehicle (V2V) communications will help to remodel the prospect of road transportation systems. By virtue of V2V communications, information generated by the vehicle control system, on-board sensors or passengers can be effectively disseminated among vehicles in proximity, or to vehicles in multiple hops away in a vehicular ad-hoc network (VANET). Without assistance from any built infrastructure, a variety of active road safety applications (e.g., Vehicle-Based Road Condition Warning, Cooperative Collision Warning, Approaching Emergency Vehicle Warning) and traffic efficiency management applications (e.g., Wrong Way Driver Warning) are enabled by inter-vehicle wireless links. The purpose of connecting vehicle technologies is to improve road safety, awareness, and transportation systems efficiency. The Wireless Access for Vehicular Environments (WAVE) technology/Dedicated Short-Range Communications (DSRC) is the main enabling wireless technology for both V2V and vehicle-to-Infrastructure (V2I) communications. From USDOT and stakeholders detailed analysis, it is resolved that WAVE is the only viable option for critical safety and other low latency mobility and environmental applications. WAVE technology has reached to a mature stage and a basic V2V system is expected to be deployed in the next few years. In the late part of 2015, USDOT announce that WAVE is sufficiently robust to proceed with the preparation for deployment of connected vehicle environments. The USDOT has created a roadmap with preliminary plans to guide industries and public agencies implementation efforts. However, there are persisting major concerns regarding the V2V initiative needing more analysis and testing. One of the concerns is the channel congestion. Channel congestion may impact WAVE effectiveness, which may in turn impact the effectiveness of supported safety applications. Suggested solutions to mitigate congestion are focused on supporting adaptive control of the message transmission power. The Institute of Electrical and Electronics Engineers (IEEE), and European Telecommunications Standards Institute (ETSI) have included transmit power component per packet to be used for channel congestion control mechanism. The adjustment of transmission powers has created an environment of vehicles with different transmission powers. Such environment will affect the performance of the proposed protocols to disseminate warning messages. It may also affect the performance of periodic beaconing that is required by most of the safety applications. Thus far, several protocols have been proposed to help identify appropriate relay vehicles. However, such approaches neglect the fact that vehicle transmission ranges are typically heterogeneous due to different transmission power values or dynamic adjustment of power to alleviate congestion. The proper selection of relay nodes governs high delivery ratio, acceptable overall end-to-end delay and efficient bandwidth usage. In this work, area-based relay selection protocols that work in heterogeneous transmission powers are introduced. Mathematical functions are developed for a timer and decision probability to be used by each vehicle receiving the message. The values of the two functions allow the vehicle to determine if it is the next to act as relay node or not. Geometric taxonomy for all possible overlap patterns in wireless environment is constructed with the related math calculations. Moreover, an adaptive expiry time for neighbours-table entries that harmonizes with dynamic beacon scheduling is proposed.

Handheld devices are becoming increasingly common, and they have varied range of resources. Mobile Cloud Computing (MCC) allows resource constrained devices to offload computation and use storage capacities of more resourceful surrogate machines. This enables creation of new and interesting applications for all devices. We propose a scheme that constructs a high-performance de-centralized system by a group of volunteer mobile devices which come together to form a resourceful unit (cloudlet). The idea is to design a model to operate as a public-resource between mobile devices in close geographical proximity. This cloudlet can provide larger storage capability and can be used as a computational resource by other devices in the network. The system needs to watch the movement of the participating nodes and restructure the topology if some nodes that are providing support to the cloudlet fail or move out of the network. In this work, we discuss the need of the system, our goals and design issues in building a scalable and reconfigurable system. We achieve this by leveraging the concept of virtual dominating set to create an overlay in the broads of the network and distribute the responsibilities in hosting a cloudlet server. We propose an architecture for such a system and develop algorithms that are requited for its operation. We map the resources available in the network by first scoring each device individually, and then gathering these scores to determine suitable candidate cloudlet nodes. We have simulated cloudlet functionalities for several scenarios and show that our approach is viable alternative for many applications such as sharing GPS, crowd sourcing, natural language processing, etc.

Video dissemination over Vehicular Ad Hoc Networks (VANETs) is an attractive technology which supports many novel applications. Hence, the merit of this thesis has twofold. Firstly, we evaluate and compare three routing techniques and two error resilience techniques. We select a sender-based routing technique called SUV and compare it with the other two selected receiver-based routing techniques named REACT-DIS and CDS. The results, more specifically, show that the receiver-based solutions outperform the sender-based solution. In addition, only CDS method fulfils the general quality requirements as it is the best that reduces redundancy packets and covers the whole topology. The results also indicate that the video coding scheme, Interleaving, can fix the multiple consecutive packet losses and guarantee reliable video qualities over VANETs. Network Coding, however, fails to provide satisfactory video quality for urban scenarios. This study next combines the selected receiver based routing techniques and the two error resilience techniques. We find the best combination is Interleaving over CDS. Secondly, we design a quality guaranteed video dissemination protocol for urban VANETs scenarios. Based on our comparison result, our protocol selects the CDS and Interleaving as the routing and error resilient techniques. To fix the single packet loses caused by the topology’s intermittent disconnection and collisions, we propose a store-carry-broadcast scheme for the nodes to re-transmit the local buffer saved packets. The results, when compared to the selected techniques and combinations, show that our proposed protocol is the most efficient one in terms of packet delivery, delay, overhead and video quality.