The objective of this research is to enhance the network performance under realistic mobile ad-hoc networks environments without modification of the standard. Overview of this research is summarized as follows: First, a packet-fragmentation technique to improve network throughput under the worst channel conditions is proposed. While the conventional packet-fragmentation technique research focuses only on random-bit errors, the proposed technique employs both random bit errors and hidden-node collisions. The analytical models based on Markov-chain model shows that the optimal fragmentation technique can effectively reduce the number of retransmissions caused by both collisions from hidden nodes and corrupted packets by random bit errors, and eventually improving throughput in noisy VANETs channels. As a second contribution, a dynamic service-channel allocation (DSCA) scheme is proposed to maximize the network throughput by dynamically assigning different service channels to the users. The theoretical analysis in this thesis will consider wireless access in the vehicular environment (WAVE) protocol, which is the main characteristic of the vehicular ad-hoc networks standard (the IEEE 802.11p). To summarize, the main contribution of this research is that two schemes will improve the network throughput significantly without modification of the standard. Therefore, there is no implementation issue to deploy the proposed schemes in real devices.

With the proliferation of mobile devices and wireless connectivity technologies, mobile social communities offer novel opportunities for targeted marketing by service or product providers. Unfortunately, marketers are still unable to realize the full potential of these markets due to their inability to effectively target right audiences. This thesis presents a novel middleware for identifying spontaneous social communities (SSCs) of mobile users in ad hoc networks in order to facilitate marketers' advertisements. The contributions of the presented work are two fold; the first is a novel model for SSCs that captures their unique dynamic nature, in terms of community structure and interest in different \textit{hot-topics} over time. These time-varying interests are represented through an inferred \textit{community profile prototype} that reflects dominant characteristics of community members. This prototype is then employed to facilitate the identification of new potential members. The selected community prototypes are also used by marketers to identify the right communities for their services or products promotions. The second contribution of this paper is novel distributed techniques for efficient calculation of the community prototypes and identification of potential community links. In contrast to traditional models of detecting fixed and mobile social networks that rely on pre-existing friendships among its members to predict new ones, the proposed model focuses on measuring the degree of similarity between the new user's profile and the profiles of members of each community in order to predict new users' relationships in the community. The adopted model of SSCs can foster many existing and new socially-aware applications such as recommender systems for social events and tools for collaborative work. It is also an ideal target for business-oriented applications such as short-message-service (SMS) advertisement messages, podcasting news feeds in addition to location/context-aware services. The performance of the proposed work was evaluated using the NetLogo platform where obtained experimental results demonstrate the achieved high degree of stability in the resulting communities in addition to the effectiveness of the proposed middleware in terms of the reduction in the number of routing messages required for advertisements.

Broadcast communications is critically important in vehicular networks. Many safety applications need safety warning messages to be broadcast to all vehicles present in an area. In this thesis, we propose a novel repetition-based broadcast protocol based on ``optical orthogonal codes.'' Optical orthogonal codes are used because of their ability to reduce the possibility of collision. We present a detailed mathematical analysis for obtaining the probability of success and the average delay. Furthermore, we propose to use coding to increase network throughput, and ``adaptive elimination'' of potentially colliding transmissions to further increase reliability. We show, by analysis and simulations, that the proposed protocol outperforms existing repetition-based ones and provides reliable broadcast communications and can reliably deliver safety messages under load conditions deemed to be common in vehicular environments. We also show that the proposed protocol is able to provide different levels of quality of service.

Broadcast communications is critically important in vehicular networks. Many safety applications need safety warning messages to be broadcast to all vehicles present in an area. In this thesis, we propose a novel repetition-based broadcast protocol based on ``optical orthogonal codes.'' Optical orthogonal codes are used because of their ability to reduce the possibility of collision. We present a detailed mathematical analysis for obtaining the probability of success and the average delay. Furthermore, we propose to use coding to increase network throughput, and ``adaptive elimination'' of potentially colliding transmissions to further increase reliability. We show, by analysis and simulations, that the proposed protocol outperforms existing repetition-based ones and provides reliable broadcast communications and can reliably deliver safety messages under load conditions deemed to be common in vehicular environments. We also show that the proposed protocol is able to provide different levels of quality of service.

An ad hoc network is a collection of mobile wireless devices that cooperate with each other to route packets amongst themselves. The main difficulty in designing routing algorithms for such a network is the large number of topology changes that the network undergoes due to device movement. Selective flooding is a routing technique that is more resilient to topology changes than traditional algorithms but is more bandwidth efficient than pure flooding. An on-demand selective flooding algorithm has been designed and tested on the ns-2 simulator. In scenarios involving a large number of topology changes, selective flooding outperforms other ad hoc network routing techniques. Unfortunately, selective flooding is much more bandwidth hungry and is unable to scale to handle reasonable traffic loads. Interestingly, the analysis of selective flooding reveals major problems with traditional ad hoc networking techniques. Many current algorithms demonstrate shortcomings when dealing with bursty traffic, and current wireless hardware cannot handle ad hoc networking traffic in an efficient manner. These issues need to be addressed before ad hoc networking technology can become feasible for widespread use.

Over the past decade or so, there has been rapid growth in wireless and mobile applications technologies. More recently, an increasing emphasis has been on the potential of infrastructureless wireless mobile networks that are easy, fast and inexpensive to set up, with the view that such technologies will enable numerous new applications in a wide range of areas. Such networks are commonly referred to as mobile ad hoc networks (MANETs). Exchanging sensitive information over unprotected wireless links with unidentified and untrusted endpoints demand the deployment of security in MANETs. However, lack of infrastructure, mobility and resource constraints of devices, wireless communication links and other unique features of MANETs induce new challenges that make implementing security a very difficult task and require the design of specialized solutions. This thesis is concerned with the design and analysis of security solutions for MANETs. We identify the initial exchange of authentication and key credentials, referred to as pre-authentication, as well as authentication and key exchange as primary security goals. In particular, the problem of pre-authentication has been widely neglected in existing security solutions, even though it is a necessary prerequisite for other security goals. We are the first to classify and analyze different methods of achieving pairwise pre-authentication in MANETs. Out of this investigation, we identify identity-based cryptographic (IBC) schemes as well-suited to secure MANET applications that have no sufficient security solutions at this time. We use pairing-based IBC schemes to design an authentication and key exchange framework that meets the special requirements of MANETs. Our solutions are comprised of algorithms that allow for efficient and secure system set up, pre-authentication, mutual authentication, key establishment, key renewal, key revocation and key escrow prevention. In particular, we present the first fully self-organized key revocation scheme for MANETs that does not require any trusted third party in the network. Our revocation scheme can be used to amend existing IBC solutions, be seamlessly integrated in our security framework and even be adopted to conventional public key solutions for MANETs. Our scheme is based on propagated accusations and once the number of received accusations against a node reaches a defined threshold, the keys of the accused nodes are revoked. All communications are cryptographically protected, but unlike other proposed schemes, do not require computationally demanding digital signatures. Our scheme is the first that efficiently and securely enables nodes to revoke their own keys. Additionally, newly joining nodes can obtain previous accusations without performing computationally demanding operations such as verifying digital signatures. Several security and performance parameters make our scheme adjustable to the hostility of the MANET environment and the degree of resource constraints of network and devices. In our security analysis we show how security parameters can be selected to prevent attacks by colluding nodes and roaming adversaries. In our proposed security framework, we utilize special properties of pairing-based keys to design an efficient and secure method for pairwise pre-authentication and a set of ID-based authenticated key exchange protocols. In addition, we present a format for ID-based public keys that, unlike other proposed formats, allows key renewal before the start of a new expiry interval. Finally, we are the first to discuss the inherent key escrow property of IBC schemes in the context of MANETs. Our analysis shows that some special features of MANETs significantly limit the escrow capabilities of key generation centers (KGCs). We propose a novel concept of spy nodes that can be utilized by KGCs to increase their escrow capabilities and analyze the probabilities of successful escrow attacks with and without spy nodes. In summary, we present a complete authentication and key exchange framework that is tailored for MANET applications that have previously lacked such security solutions. Our solutions can be implemented using any pairing-based IBC scheme. The component design allows for the implementation of single schemes to amend existing solutions that do not provide certain functionalities. The introduction of several security and performance parameters make our solutions adjustable to different levels of resource constraints and security needs. In addition, we present extensions that make our solutions suitable for applications with sporadic infrastructure access as envisioned in the near future.

As a result of the recent advances in the computation and communications industries, wireless communications-enabled computing devices are ubiquitous nowadays. Even though these devices are introduced to satisfy the user’s mobile computing needs, they are still unable to provide for the full mobile computing functionality as they confine the user mobility to be within certain regions in order to benefit from services provided by fixed network access points. Mobile ad hoc networks (MANETs) are introduced as the technology that potentially will make the nowadays illusion of mobile computing a tangible reality. MANETs are created by the mobile computing devices on an ad hoc basis, without any support or administration provided by a fixed or pre-installed communications infrastructure. Along with their appealing autonomy and fast deployment properties, MANETs exhibit some other properties that make their realization a very challenging task. Topology dynamism and bandwidth limitations of the communication channel adversely affect the performance of routing protocols designed for MANETs, especially with the increase in the number of mobile hosts and/or mobility rates. The Connected Dominating Set (CDS), a.k.a. virtual backbone or Spine, is proposed to facilitate routing, broadcasting, and establishing a dynamic infrastructure for distributed location databases. Minimizing the CDS produces a simpler abstracted topology of the MANET and allows for using shorter routes between any pair of hosts. Since it is NP-complete to find the minimum connected dominating set, MCDS, researchers resorted to approximation algorithms and heuristics to tackle this problem. The literature is rich of many CDS approximation algorithms that compete in terms of CDS size, running time, and signaling overhead. It has been reported that localized CDS creation algorithms are the fastest and the lightest in terms of signaling overhead among all other techniques. Examples of these localized CDS algorithms are Wu and Li algorithm and its Stojmenovic variant, the MPR algorithm, and Alzoubi algorithm. The designers of each of these algorithms claim that their algorithm exhibits the highest degree of localization and hence incurs the lowest cost in the CDS creation phase. However, these claims are not supported by any physical or at least simulation-based evidence. Moreover, the cost of maintaining the CDS (in terms of the change in CDS size, running time, and signaling overhead), in the presence of unpredictable and frequent topology changes, is an important factor that has to be taken into account -a cost that is overlooked most of the time. A simulation-based comparative study between the performance of these algorithms will be conducted using the ns2 network simulator. This study will focus on the total costs incurred by these algorithms in terms of CDS size, running time, and signaling overhead generated during the CDS creation and maintenance phases. Moreover, the effects of mobility rates, network size, and mobility models on the performance of each algorithm will be investigated. Conclusions regarding the pros and cons of each algorithm will be drawn, and directions for future research work will be recommended.

This thesis contributes toward the design of a quality-of-service (QoS) aware network layer for wireless ad hoc networks. With the lack of an infrastructure in ad hoc networks, the role of the network layer is not only to perform multihop routing between a source node and a destination node, but also to establish an end-to-end connection between communicating peers that satisfies the service level requirements of multimedia applications running on those peers. Wireless ad hoc networks represent autonomous distributed systems that are infrastructure-less, fully distributed, and multi-hop in nature. Over the last few years, wireless ad hoc networks have attracted significant attention from researchers. This has been fueled by recent technological advances in the development of multifunction and low-cost wireless communication gadgets. Wireless ad hoc networks have diverse applications spanning several domains, including military, commercial, medical, and home networks. Projections indicate that these self-organizing wireless ad hoc networks will eventually become the dominant form of the architecture of telecommunications networks in the near future. Recently, due to increasing popularity of multimedia applications, QoS support in wireless ad hoc networks has become an important yet challenging objective. The challenge lies in the need to support the heterogeneous QoS requirements (e.g., data rate, packet loss probability, and delay constraints) for multimedia applications and, at the same time, to achieve efficient radio resource utilization, taking into account user mobility and dynamics of multimedia traffic. In terms of research contributions, we first present a position-based QoS routing framework for wireless ad-hoc networks. The scheme provides QoS guarantee in terms of packet loss ratio and average end-to-end delay (or throughput) to ad hoc networks loaded with constant rate traffic. Via cross-layer design, we apply call admission control and temporary bandwidth reservation on discovered routes, taking into consideration the physical layer multi-rate capability and the medium access control (MAC) interactions such as simultaneous transmission and self interference from route members. Next, we address the network-layer resource allocation where a single-hop ad hoc network is loaded with random traffic. As a starting point, we study the behavior of the service process of the widely deployed IEEE 802.11 DCF MAC when the network is under different traffic load conditions. Our study investigates the near-memoryless behavior of the service time for IEEE 802.11 saturated single-hop ad hoc networks. We show that the number of packets successfully transmitted by any node over a time interval follows a general distribution, which is close to a Poisson distribution with an upper bounded distribution distance. We also show that the service time distribution can be approximated by the geometric distribution and illustrate that a simplified queuing system can be used efficiently as a resource allocation tool for single hop IEEE 802.11 ad hoc networks near saturation. After that, we shift our focus to providing probabilistic packet delay guarantee to multimedia users in non-saturated IEEE 802.11 single hop ad hoc networks. We propose a novel stochastic link-layer channel model to characterize the variations of the IEEE 802.11 channel service process. We use the model to calculate the effective capacity of the IEEE 802.11 channel. The channel effective capacity concept is the dual of the effective bandwidth theory. Our approach offers a tool for distributed statistical resource allocation in single hop ad hoc networks, which combines both efficient resource utilization and QoS provisioning to a certain probabilistic limit. Finally, we propose a statistical QoS routing scheme for multihop IEEE 802.11 ad hoc networks. Unlike most of QoS routing schemes in literature, the proposed scheme provides stochastic end-to-end delay guarantee, instead of average delay guarantee, to delay-sensitive bursty traffic sources. Via a cross-layer design approach, the scheme selects the routes based on a geographical on-demand ad hoc routing protocol and checks the availability of network resources by using traffic source and link-layer channel models, incorporating the IEEE 802.11 characteristics and interaction. Our scheme extends the well developed effective bandwidth theory and its dual effective capacity concept to multihop IEEE 802.11 ad hoc networks in order to achieve an efficient utilization of the shared radio channel while satisfying the end-to-end delay bound.

The increasing usage of information technology in military affairs raises the need for robust high capacity radio networks. The network will be used to provide several different types of services, for example group calls and situation awareness services. All services have specific demands on packet delays and packet losses in order to be fully functional, and therefore there is a need for a Quality of Service (QoS) mechanism in the network. In this master thesis we examine the possibility to provide a QoS mechanism in Ad Hoc networks by using priority queues. The study includes two different queuing schemes, namely fixed priority queuing and weighted fair queuing. The performance of the two queuing schemes are evaluated and compared with respect to the ability to provide differentiation in network delay, i.e., provide high priority traffic with lower delays than low priority traffic. The study is mainly done by simulations, but for fixed priority queuing we also derive a analytical approximation of the network delay. Our simulations show that fixed priority queuing provides a sharp delay differentiation between service classes, while weighted fair queuing gives the ability to control the delay differentiation. One of those queuing schemes alone might not be the best solution for providing QoS, instead we suggest that a combination of them is used.

This thesis involved a research of mechanisms of MAC layer in the ad-hoc networks environment, the ad-hoc networks in the terminology of the standard are called IBSS Independent Basic Service, these type of networks are very useful in real situation where there are not the possibility of display a infrastructure, when there isn’t a network previous planning. The connection to a new network is one of the different with the most common type of Wireless Local Area Networks (WLAN) that are the ones with infrastructure. The connection is established without the presence of a central station, instead the stations discover the others with broadcast messages in the coverage area of each station. In the context of standard 802.11 networks the communication between the stations is peer to peer, only with one hop. To continue with initiation process is necessary the synchronization between the different stations of his timers. The other capital mechanism that is treated is the medium access mechanism, to hold a shared and unreliable medium, all the heavy of this issue goes to the distributed coordination function DCF. In this moment there is an emergent technology, WIMAX or standard IEEE 802.16, like the standard 802.11 is a wireless communication protocol. Some comparison between the MAC layer mechanisms would be realized between these two standards