The increasing popularity of wireless networks over the last years indicates that there will be a demand for communicating devices providing high capacity communication together with QoS requirements. There are two types of wireless networks, infrastructure and Ad Hoc networks. The variation of topology caused by the mobility of hosts in the Ad Hoc networks results in a long latency, large jitter and low throughput. In infrastructure wireless networks, a base station (BS) or an Access Point (AP) is in charge of the data transmission. Therefore, the wireless hop can be considered as another hop of the transmission path. With the rapid growth of wireless traffics, the future wireless network is expected to provide services for heterogeneous data traffics with different quality of service requirements. Most proposed schemes do not have mechanisms to adapt to environment changes. In real situation, bandwidths, error rates, and loss rates of wireless links vary frequently. The QoS issues are very important in modern networks. There are many proposed service models and mechanisms to support QoS in wireline networks. Most of these QoS mechanisms are not suitable for direct application to the wireless network because of the characteristics of wireless communication which includes: 1) high error rates and bursty errors, 2) location-dependent and time-varying wireless channel capacity, 3) scarce bandwidth, 4) user mobility, and 5) power constraints of the mobile hosts. All of these above characteristics make the development of QoS in wireless networks very difficult and challenging. We try to cope with the bandwidth variations caused by the high error rate and bursty errors in wireless links, and the location-dependent and time-varying natures of wireless channel capacity. Furthermore, we expect to utilize the scarce wireless bandwidth more efficiently. In our proposed scheme, the higher priority flow is capable of broadcasting a message to inform the lower priority flows to change their priorities to adapt to environment variations. We will base on the differentiated service model and propose a Wireless Differentiation (WD) scheme for UDP flows and a Wireless Differentiation with Prioritized ACK (WDPA) scheme for connections with TCP flows which provide QoS support for IEEE 802.11b and do not change the basic access mechanism of IEEE 802.11b.

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.

Το ζήτημα της κατανάλωσης ενέργειας σε ασύρματα ad hoc δίκτυα αποτελεί ένα ερευνητικό πεδίο το οποίο έχει λάβει ιδιαίτερη προσοχή τα τελευταία χρόνια. Οι σταθμοί σε ένα ασύρματο ad hoc δίκτυο λειτουργούν επί το πλείστον με μπαταρίες με αποτέλεσμα η εξοικονόμηση ενέργειας στο δίκτυο να αποτελεί πρώτιστο στόχο για την βιωσιμότητα των σταθμών του δικτύου και την αξιόπιστη παραλαβή των πακέτων δεδομένων από τους παραλήπτες τους. Μέχρι σήμερα, έχουν αναπτυχθεί διάφορα ενεργό-αποδοτικά πρωτόκολλα τα οποία μπορούν να υιοθετηθούν σε ένα ασύρματο ad hoc δίκτυo. Τα πρωτόκολλα αυτά λειτουργούν σε διαφορετικό επίπεδο το καθένα (ελέγχου πρόσβασης στο μέσο, δικτύου, υψηλότερα). Η παρούσα εργασία συντάχθηκε με σκοπό την μελέτη αυτών των ενεργό-αποδοτικών πρωτοκόλλων που μπορούν να υιοθετηθούν σε ασύρματα ad hoc δίκτυα, την καταγραφή των ιδιαίτερων χαρακτηριστικών κάθε πρωτοκόλλου καθώς και την ανάπτυξη ενός νέου πρωτοκόλλου ελέγχου της ισχύος μετάδοσης σε ασύρματα ad hoc δίκτυα με κύριο στόχο την περαιτέρω μείωση της κατανάλωσης ενέργειας στο δίκτυο με παράλληλη αύξηση του throughput του δικτύου. Συγκεκριμένα, στην παρούσα μελέτη, αναλύονται και παρουσιάζονται τα ακόλουθα ζητήματα. Στο Κεφάλαιο 1 παρουσιάζονται οι στόχοι της παρούσας εργασίας καθώς και η συνεισφορά της στο ζήτημα της κατανάλωσης ενέργειας στα ασύρματα ad hoc δίκτυα. Στο Κεφάλαιο 2 αρχικά πραγματοποιείται μία εισαγωγή στην αρχιτεκτονική των ασυρμάτων ad hoc δικτύων και ακολούθως παρουσιάζονται οι διάφορες κατηγορίες των ασυρμάτων ad hoc δικτύων, δίνοντας ιδιαίτερη έμφαση στην 802.11 τεχνολογία και πρωτόκολλα. Στο Κεφάλαιο 3 παρουσιάζονται υπάρχοντα ενεργό-αποδοτικά πρωτόκολλα τα οποία μπορούν να χρησιμοποιηθούν σε ασύρματα ad hoc δίκτυα. Τα πρωτόκολλα αυτά παρουσιάζονται ταξινομημένα ανάλογα με το επίπεδο στο οποίο το καθένα λειτουργεί (επίπεδο ελέγχου πρόσβασης στο μέσο, επίπεδο δικτύου, υψηλότερα επίπεδα). Στο Κεφάλαιο 4 περιγράφεται το προτεινόμενο MAC πρωτόκολλο ελέγχου της ισχύος μετάδοσης το οποίο μπορεί να χρησιμοποιηθεί σε ασύρματα ad hoc δίκτυα. Παρουσιάζεται η λειτουργία του πρωτοκόλλου, περιγράφοντας το χαρακτηριστικό της αργής εκκίνησης που το προτεινόμενο πρωτόκολλο υιοθετεί για την μετάδοση των RTS πλαισίων, καθώς και τον CTS μηχανισμό που χρησιμοποιείται. Στο τέλος του κεφαλαίου, πραγματοποιείται μια σύγκριση της λειτουργίας του προτεινόμενου ενεργό-αποδοτικού πρωτοκόλλου με υπάρχοντα πρωτόκολλα MAC επιπέδου που παρουσιάστηκαν στο Κεφάλαιο 3. Στο Κεφάλαιο 5 πραγματοποιείται αξιολόγηση της απόδοσης του προτεινόμενου πρωτοκόλλου. Η αξιολόγηση της απόδοσης του προτεινόμενου πρωτοκόλλου πραγματοποιείται μέσω της εκτέλεσης πειραμάτων με την βοήθεια του εξομοιωτή δικτύων network simulator 2. Η αξιολόγηση του προτεινόμενου πρωτοκόλλου πραγματοποιείται ως προς διάφορες παραμέτρους – κατανάλωση ενέργειας στο δίκτυο, διασπορά της καταναλόμενης ενέργειας, μέση καθυστέρηση παραλαβής των πακέτων, throughput του δικτύου, πλήθος συγκρούσεων RTS πλαισίων, λόγος ληφθέντων προς απεσταλμένα πακέτα – έχοντας ως βάση το πρόβλημα της εκκένωσης των πακέτων στο δίκτυο και για την περίπτωση δύο διαφορετικών προσεγγίσεων. Μία στην οποία κάθε σταθμός χρησιμοποιεί στατική ισχύ για τις μεταδόσεις του και μία στην οποία κάθε σταθμός ρυθμίζει την ισχύ μετάδοσής του στην ελάχιστη απαιτούμενη τιμή για την ορθή παραλαβή των πακέτων από τους παραλήπτες τους. Τέλος στο Κεφάλαιο 6 παρουσιάζονται τα συμπεράσματα που προκύπτουν από την παρούσα εργασία καθώς και διάφορα ανοιχτά ζητήματα προς περαιτέρω έρευνα. / Power consumption at wireless ad hoc networks has received last years much attention. Mobile stations in a wireless ad hoc network operate in the most cases with batteries, so power conservation at the network is a major objective for the viability of the mobile stations of the network and the reliable delivery of packets to their destinations. Till today, various power-aware protocols have been developed for wireless ad hoc networks. Each one of these protocols operates at different layer (medium access control, network, higher layers). The main objectives of this study are the review of the power-aware protocols that can be used at wireless ad hoc networks, the detection of the special characteristics of each protocol, and the development of a new power control MAC-layer protocol for wireless ad hoc networks. The main objective of this new protocol is the farther reduction of the power consumption in the network, with parallel increment at network throughput. More specifically speaking, in this study, the following points are represented and analyzed: in Chapter 1 the various objectives of this study are represented as the contribution of the study in point of power consumption at wireless ad hoc networks. In Chapter 2, initially an introduction at the architecture of wireless ad hoc networks is performed, while afterwards the various categories of wireless ad hoc networks are represented, by emphasizing the 802.11 technology and protocols. In Chapter 3 various energy-aware protocols for wireless ad hoc networks are represented. These protocols are represented categorized by the layer at which every one operates (medium access control layer, network layer and higher layers). In Chapter 4 the proposed power control MAC protocol for mobile ad hoc networks is represented. The operation of the protocol is represented, by describing the slow start mechanism used for RTS frames transmissions, and the CTS mechanism used. At the end of Chapter 4, a comparison between the operation of the proposed power-aware protocol and previous MAC-layer power aware protocols is performed. In Chapter 5, the performance evaluation of the proposed protocol is performed. The performance evaluation of the proposed protocol was done via execution of experiments with network simulator 2. The performance parameters that were measured are: the power consumption in the network, the variance of the consumed energy, the average delay for packets delivery, the network throughput, the number of RTS frames collisions and the received-to-sent packets ratio. The performance of the proposed protocol was evaluated in the setting of the evacuation problem and for two different approaches. One in which every node uses static power for its transmissions and one in which every node adjusts its transmission power at the minimum required value for coherent reception of the packets from the recipients. Finally in Chapter 6 are represented the results that are derived from this study and various open issues for further investigation.

Dans un contexte de besoins croissants de moyens de communication pour augmenter la sécurité des vols et répondre aux attentes des compagnies et des passagers, le monde de l'aviation civile cherche de nouveaux systèmes de communication pouvant répondre à ces objectifs. Les systèmes de communication sol-bord existants, que ce soit les solutions par satellites en bande L (SATCOM, ...) ou les solutions cellulaires par liaison directe avec le sol (HF, VHF, ...), présentent des limites en terme de capacité, de couverture et de coût.La proposition avancée dans le cadre de cette thèse est d'utiliser les avions comme relais afin de propager les données jusqu'à une station sol. Ce système peut être vu comme un réseau ad hoc mobile dont les nœuds sont les avions civils en vol. Grâce à plusieurs sauts successifs au travers d'avions relais, chaque avion doit pouvoir joindre le sol sans être à portée directe d'une station. Le réseau ad hoc ainsi formé peut ensuite être utilisé pour différentes classes de communications : contrôle aérien, services pour les compagnies aériennes ou pour les passagers. Une telle solution permettrait d'améliorer la couverture des solutions cellulaires classiques en zone continentale. Elle est également applicable en zone océanique où les seuls moyens disponibles sont actuellement le satellite et la HF. On peut imaginer que les coûts de déploiement et de maintenance seraient relativement bas puisque l'infrastructure sol est limitée.Dans cette thèse, nous avons étudié la faisabilité puis les performances qui peuvent être attendues pour ce système de communication aéronautique innovant.

Information on the location of mobile nodes in Mobile Ad-hoc Networks (MANETs) has the potential to significantly improve network performance. This thesis uses node location information to develop new techniques for route discovery in on-demand routing protocols such as the Ad-hoc On-Demand Distance Vector (AODV), thus making an important contribution to enhancing the experience of using mobile networks. A Candidate Neighbours to Rebroadcast the Route Request (CNRR) approach has been proposed to reduce the deleterious impact, known as the broadcast storm, of RREQ packets flooding in traditional on-demand routing protocols. The main concept behind CNRR is specifying a set of neighbours which will rebroadcast the received RREQ. This is a departure from the traditional approach of all receiving nodes rebroadcasting RREQs and has the effect of reducing the problem of redundancy from which mobile networks suffer. The proposed protocol has been developed in two phases: Closest-CNRR and Furthest-CNRR. The simulation results show that the proposed algorithms have a significant effect as they reduce the routing overhead of the AODV protocol by up to 28% compared to the C-CNRR, and by up to 17.5% compared to the F-CNRR. Notably, the proposed algorithms simultaneously achieve better throughput and less data dropping. The Link Stability and Energy Aware protocol (LSEA) has been developed to reduce the overhead while increasing network lifetimes. The LSEA helps to control the global dissemination of RREQs in the network by eliminating those nodes that have a residual energy level below a specific threshold value from participation in end-to-end routes. The proposed LSEA protocol significantly increases network lifetimes by up to 19% compared with other on-demand routing protocols while still managing to obtain the same packet delivery ratio and network throughput levels. Furthermore, merging the LSEA and CNRR concepts has the great advantage of reducing the dissemination of RREQs in the network without loss of reachability among the nodes. This increases network lifetimes, reduces the overhead and increases the amount of data sent and received. Accordingly, a Position-based Selective Neighbour (PSN) approach has been proposed which combines the advantages of zoning and link stability. The results show that the proposed technique has notable advantages over both the AODV and MAAODV as it improves delivery ratios by 24.6% and 18.8%, respectively.

Hop count, i.e., the number of wireless hops a packet has to go through to reach the destination, is a fundamental metric in multi-hop wireless ad-hoc networks. Network performance, such as throughput, end-to-end delay, energy consumption, and so on, depends critically on hop count. Previous work on modeling hop count is limited in making unrealistic simplifying assumptions either at the physical or network, or both layers of the communication protocol stack. A key contribution of this thesis is to present an analytical model to derive the probability distribution of hop count under realistic assumptions at both physical and network layers. Specifically, the model considers a log-normal shadowing radio propagation capable of accommodating the random signal fading observed in most wireless communication environments, and the widely used geographic routing at the network layer. Validation of the model is achieved by a comprehensive set of simulation experiments including a trace driven simulation of a real-word vehicular ad-hoc network. The model reveals that the presence of randomness in radio propagation reduces the required number of hops to reach a given destination significantly. To demonstrate the utility of the proposed hop count model, the thesis proposes three new applications which address some of the key challenges in multi-hop wireless networks. The first application derives the per-node packet forwarding load in multi-hop wireless sensor networks and reveals that the nodes in the vicinity of the base station has a significantly less forwarding load than previously thought under simplifying radio propagation and routing assumptions. The second application demonstrates that using hop count as a measure of distance traveled by a data packet, geocasting can be achieved in multi-hop wireless networks in situations when some of the network nodes do not have access to reliable location information. Finally, the proposed hop count model is used to evaluate the performance of the third application which demonstrates that the overhead of geographic routing can be reduced significantly by embracing a position update philosophy which adapts to the mobility and communication patterns of the underlying ad-hoc network.

Hop count, i.e., the number of wireless hops a packet has to go through to reach the destination, is a fundamental metric in multi-hop wireless ad-hoc networks. Network performance, such as throughput, end-to-end delay, energy consumption, and so on, depends critically on hop count. Previous work on modeling hop count is limited in making unrealistic simplifying assumptions either at the physical or network, or both layers of the communication protocol stack. A key contribution of this thesis is to present an analytical model to derive the probability distribution of hop count under realistic assumptions at both physical and network layers. Specifically, the model considers a log-normal shadowing radio propagation capable of accommodating the random signal fading observed in most wireless communication environments, and the widely used geographic routing at the network layer. Validation of the model is achieved by a comprehensive set of simulation experiments including a trace driven simulation of a real-word vehicular ad-hoc network. The model reveals that the presence of randomness in radio propagation reduces the required number of hops to reach a given destination significantly. To demonstrate the utility of the proposed hop count model, the thesis proposes three new applications which address some of the key challenges in multi-hop wireless networks. The first application derives the per-node packet forwarding load in multi-hop wireless sensor networks and reveals that the nodes in the vicinity of the base station has a significantly less forwarding load than previously thought under simplifying radio propagation and routing assumptions. The second application demonstrates that using hop count as a measure of distance traveled by a data packet, geocasting can be achieved in multi-hop wireless networks in situations when some of the network nodes do not have access to reliable location information. Finally, the proposed hop count model is used to evaluate the performance of the third application which demonstrates that the overhead of geographic routing can be reduced significantly by embracing a position update philosophy which adapts to the mobility and communication patterns of the underlying ad-hoc network.

Wireless communication has grown very popular, and communication is the key to success in many situations. However, most of the common technologies today rely on infrastructure and in disaster situations infrastructure might be lost or get severely overloaded. This master thesis concerns intermittently connected mobile ad hoc networks. A network in which the devices may move freely in any direction and still be able to communicate. To be able to demonstrate a network protocol called random-walk gossip-based manycast (RWG) my assignment has been to implement this protocol using off-the-shelf hardware and software. RWG is a multi-hop and partition-tolerant mobile ad hoc manycast network protocol. Multi-hop refers to information being able to hop between more than two nodes in a network and partition-tolerant means that the protocol works even though a network is partitioned. Manycast means that the information should be successfully delivered to K of all the potential nodes in the area. The RWG protocol makes use of four different packet types, request to forward (REQF), ac- knowledgement (ACK), ok to forward (OKTF) and be silent (BS). The actual data being sent is carried by REQFs, and is referred to as messages. When a message is sent it takes what could be described as a random walk among the nodes in the network, hence the name. The implementation of the RWG protocol resides in user-space and depends on the IEEE 802.11b standard and the raw socket that is specified in the BSD socket API. It is written in C and was developed on a machine running Ubuntu. It runs on systems that use Linux 2.6 kernels and it supports cross-compiling for ARM based devices such as the Nokia N810 internet tablet and the Android dev phone 1. To be able to demonstrate the protocol I developed my own client application. Moreover, an already existing application for Android, Portable Open Search and Identification Tool (POSIT), was successfully extended to run on top of the RWG implementation. The extension was developed by people in the POSIT project and tested in a physical experiment covering five devices. The report covers the RWG protocol, the system choice, the implementation and the testing of the implementation.

A multi-hop ad hoc network requires no infrastructure, like base stations or routers to function. This means that it can quickly be deployed and in movement, making it ideal for scenarios like natural disasters or battlefield communication. A single-frequency network (SFN) is the idea that transmitters can cooperate to send the same signals simultaneously over the same frequency channel, such that the signals are amplified. It was previously proposed that SFNs could be created in multi-hop ad hoc networks. According to simulations, this could improve the energy consumption, signal reachability, and data transfer rate. As this has only been simulated, the purpose of this project is to experimentally verify that SFN is attainable in a multi-hop ad hoc network, and to assess what the difficulties are of an actual implementation. The method involved synchronizing the transmission of two devices operating under the 802.11a standard. A multi-hop ad hoc network was created by changing the settings of the network interface cards. The devices used were mainly laptops and transmissions were monitored in Wireshark. The laptops were forced to send on one frequency channel to make interference possible, and identical packets were sent. Experiments were made to assess whether SFN was attained. The packet loss rate and distance were used to evaluate the results. The results suggest that a synchronized transmission off by less than 2 μs was attained. However, the error of these measurements were neither known nor approximable. This meant it was hard to know when a SFN was formed. The results indicate that SFN was attained, as the packet loss rate decreased significantly when employed. The effectiveness of SFN was hard to assess because the results were not comparable with the simulation values. The difficulty of an actual implementation is deemed to be the synchronization of transmissions.

This dissertation presents novel approaches to modeling and analyzing security and resource allocation in mobile ad hoc networks (MANETs). The research involves the design, implementation and simulation of different models resulting in resource sharing and security’s strengthening of the network among mobile devices. Because of the mobility, the network topology may change quickly and unpredictably over time. Moreover, data-information sent from a source to a designated destination node, which is not nearby, has to route its information with the need of intermediary mobile nodes. However, not all intermediary nodes in the network are willing to participate in data-packet transfer of other nodes. The unwillingness to participate in data forwarding is because a node is built on limited resources such as energy-power and data. Due to their limited resource, nodes may not want to participate in the overall network objectives by forwarding data-packets of others in fear of depleting their energy power. To enforce cooperation among autonomous nodes, we design, implement and simulate new incentive mechanisms that used game theoretic concepts to analyze and model the strategic interactions among rationale nodes with conflicting interests. Since there is no central authority and the network is decentralized, to address the concerns of mobility of selfish nodes in MANETs, a model of security and trust relationship was designed and implemented to improve the impact of investment into trust mechanisms. A series of simulations was carried out that showed the strengthening of security in a network with selfish and malicious nodes. Our research involves bargaining for resources in a highly dynamic ad-hoc network. The design of a new arbitration mechanism for MANETs utilizes the Dirichlet distribution for fairness in allocating resources. Then, we investigated the problem of collusion nodes in mobile ad-hoc networks with an arbitrator. We model the collusion by having a group of nodes disrupting the bargaining process by not cooperating with the arbitrator. Finally, we investigated the resource allocation for a system between agility and recovery using the concept of Markov decision process. Simulation results showed that the proposed solutions may be helpful to decision-makers when allocating resources between separated teams.