Techniques for Alleviating the Inconveniences Caused by Mobility in Wireless Environments.

摘要

Wireless technology has been through a tremendous revolutionary over the last decade. The adoption of wireless networks has greatly changed people's lifestyle. Wireless has become an essential part of our daily life. Mobility support is one of the most significant benefits of wireless networks. However, such a great convenience doesn't come for granted and for free. While providing user with benefits, mobility also brings essential challenges to wireless network designers. Node mobility causes frequent changes in topology, which means the topology of network changes dynamically. In order to support the mobility for the mobile clients, it is necessary to incorporate special designs in the wireless network protocols that are meant to deal with the problems brought by dynamic network topology and the unpredictable traffic. In this dissertation, we show several technologies for alleviating the inconveniences caused by mobility in wireless environments. The scenarios covered in this dissertation span includes: VoIP services provided in wireless mesh network (WMN), routing and message scheduling in Delay Tolerant Networks (DTN), and message dissemination in Vehicular Ad Hoc Networks (VANET).;In VoIP services provided in wireless mesh network (WMN), client mobility makes mesh node access authentication more difficult when user roams from the range of one Access Point (AP) to the range of another AP. We focus on security issues for supporting VoIP over multi-hop wireless mesh networks. Specifically, we present a solution that provides both client authentication and mutual intermediate mesh node authentication using the individual key of each node.;In Delay Tolerant Networks (DTN), routing and message scheduling is one of the most challenging issues due to the high degree of mobility and continuous movement of ferry nodes. In this dissertation, we propose a novel Look-Ahead Routing and Message Scheduling (ALARMS) scheme in which the ferry nodes inform the gateway nodes about their travel schedule so that the gateway nodes can decide which ferry to use for each message in advance and schedule the message in the queue accordingly. We conduct simulations evaluate and compare ALARMS and other existing routing policies for DTNs. The results show that ALARMS achieves better delivery ratio and shorter delivery delay with much lower overhead.;In Vehicular Ad Hoc Networks (VANET) environment, one of the most important applications is to disseminate emergency notification messages to drivers in order to notify them the occurrence of an accident. The core challenge of message dissemination schemes in VANET is how to select the next forwarding node to further forward the message. However, node mobility in VANET is more dynamic which makes forwarding node selection much harder. In this dissertation, we proposed a Traffic-Aware Geographic forwarding (TAG) protocol for VANET message dissemination. The proposed TAG protocol takes both the real map information and traffic flow information into account to identify the vehicles that are "relevant" to the broadcast packet in question, and selects forwarding nodes accordingly aiming to optimize efficiency and minimize the number of unnecessary transmission. We evaluate the performance of our TAG protocol and compare it with three variations through simulations, and the results show that the TAG forwarding protocol can efficiently forward the message with the lowest number of transmission, the lowest involved vehicles ratio without sacrificing much on coverage.