Connectivity and Data Transmission over Wireless Mobile Systems

We live in a world where wireless connectivity is pervasive and becomes ubiquitous. Numerous devices with varying capabilities and multiple interfaces are surrounding us. Most home users use Wi-Fi routers, whereas a large portion of human inhabited land is covered by cellular networks. As the number of these devices, and the services they provide, increase, our needs in bandwidth and interoperability are also augmented. Although deploying additional infrastructure and future protocols may alleviate these problems, efficient use of the available resources is important. We are interested in the problem of identifying the properties of a system able to operate using multiple interfaces, take advantage of user locations, identify the users that should be involved in the routing, and setup a mechanism for information dissemination. The challenges we need to overcome arise from network complexity and heterogeneousness, as well as the fact that they have no single owner or manager. In this thesis I focus on two cases, namely that of utilizing "in-situ" WiFi Access Points to enhance the connections of mobile users, and that of establishing "Virtual Access Points" in locations where there is no fixed roadside equipment available. Both environments have attracted interest for numerous related works. In the first case the main effort is to take advantage of the available bandwidth, while in the second to provide delay tolerant connectivity, possibly in the face of disasters. Our main contribution is to utilize a database to store user locations in the system, and to provide ways to use that information to improve system effectiveness. This feature allows our system to remain effective in specific scenarios and tests, where other approaches fail

A Distributed Algorithm for Constructing a Generalization of de Bruijn Graphs

De Bruijn graphs possess many characteristics that make them a suitable choice for the topology of an overlay network. These include constant degree at each node, logarithmic diameter and a highly-regular topology that permits nodes to make strong assumptions about the global structure of the network. We propose a distributed protocol that constructs an approximation of a de Bruijn graph in the presence of an arbitrary number of nodes. We show that the degree of each node is constant and that the diameter of the network is no worse than 2logN, where N is the number of nodes. The cost of the join and the departure procedures are O(logN) in the worst case. To the best of our knowledge, this is the first distributed protocol that provides such deterministic guarantees

Virtual Access Points for Vehicular Networks

ABSTRACT This paper introduces the concept of Virtual Access Points (VAPs) for wireless Vehicular Ad-hoc Networks (VANETS). This new technique allows data dissemination among vehicles, thus extending the reach of roadside access points to uncovered road areas. Each vehicle that receives a message from an Access Point (AP) stores this message and rebroadcasts it into non covered areas. This extends the network coverage for non time critical messages. The VAP role is transparent to the connected nodes, and designed to avoid interference since each operates on a bounded region outside any AP. The experiments show the presented mechanism of store and forward at specific positions present a gain, in term of all the evaluated parameters

System for 802.11 connectivity at high speed

Measurements and ongoing research have shown that WLAN connection for moving vehicles is feasible. However none of the previous work suggests a solution addressing a complete array of the challenges in vehicular WLAN communications. To amend this we designed a system that provides wireless connection roaming at high velocities transparent to user level applications, and does not impose additional requirements to existing infrastructures. It offers simple deployment, security, and scalability. It remains efficient under ­ intermittent connectivity conditions and supports heterogeneous network mediums for increased robustness

PEGASUS: 802.11 connectivity at high speed

Measurements and ongoing research have shown that WLAN connection for moving vehicles is feasible. However none of the previous works suggests a solution addressing a complete array of the challenges in vehicular WLAN communications. Our system, PEGASUS amends this by providing wireless connection roaming at high velocities. To the best of our knowledge, it is the first system that operates over “in situ” wifi networks, while at the same time offers transparency to user level applications by allowing a single IP address per user, and does not impose additional requirements to existing infrastructures. PEGASUS offers simple deployment, improved scalability, and is the first able to operate over secure “in situ” networks. It remains efficient under intermittent connectivity conditions and supports heterogeneous network mediums for increased robustness