University of Twente Student Theses


Geocasting solution for bluewave services in the context of vehicular communications

Hagos, Ambesagir S. (2010) Geocasting solution for bluewave services in the context of vehicular communications.

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Abstract:There is no doubt that an efficient emergency activity saves lives and reduces damages. BlueWave is an emergency activity in which an emergency vehicle (EV) warns vehicles on its trajectory in order to give it a clear way. The conventional BlueWave activity uses siren and ash light as warning signals. The signaling part of BlueWave has limitations which include the dependence of the ash light on line of sight, the effectiveness of the siren being dependent on driver's situation such as loud music, insulated doors and windows. In addition, the system does not differentiate its target vehicles and fails to assist drivers on how to react even if it does. Many of the solutions available extend the signaling part using radio signals directly from the EV to target vehicles. A common limitation of such technologies is their failure to support multihop communication and well established standards such as IEEE 802.11. In this thesis we designed a system that extends the signaling part, which is cooperative (vehicles share information), support multihop communication, and is based on WAVE (WiFi version for vehicular networks). The PHY and MAC layers of the designed system are based on WAVE standard. In the network, layer a BlueWave protocol is designed to enable vehicles communicate in the BlueWave process. To limit the warning to specific vehicles, a geocasting protocol is designed. In geocasting, vehicles use their geographic location as an address to receive packets. The protocol has basic functionality which is implemented in all involved vehicles. The basic protocol checks if a received message is relevant. A message is said to be relevant if it is not expired, not duplicated and the host is within the ZoR (Zone of Relevance) as defined in the message. Relevant messages are also entitled for dissemination to other vehicles. To disseminate the BlueWave messages within the ZoR, a distance based ooding mechanism called slotted 1-persistent is used. This avoids the broadcast storm problem that may happen if a network is blindly ooded. Moreover, the EV as a source adds extra functionally to enable it broadcast the warning at some rate. To evaluate the performance of the protocol we defined three performance metrics. The first one is Reachability, which measures the number of vehicles that receive at least one message on time. The second metric is Channel utilization, which measures the fraction of time a node uses the medium. The last metric, spam created, which measures the number of unnecessary packets created by the protocol during the BlueWave process. The protocol is implemented in OMNeT++ simulator and experiments are done in a highway scenario of 10km long. The EV moves at its desired speed (as fast as possible) and other vehicles move according to IDM (Intelligent Driver Model). The protocol when using slotted 1-persistent achieves high level of reachability (90%{94%) irrespective of the network density and broadcast rate of the EV. However, the channel utilization and the number of spam packets created increase with density and broadcast rate. The protocol performs better on slow speed scenarios such as urban cases, but this is in the cost of higher channel utilization and more spam created packets. In all, the protocol performs better at lower rates and fulfills most of the requirements of the application.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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