Abstract
In vehicular ad-hoc network (VANET), safety services have been proposed to improve driving safely and non-safety services provide comfort for passengers. VANET employs IEEE 802.11p as transmission protocol that provides a control channel (CCH) and six service channels (SCHs). How to use multiple service channels efficiently has significant effects on how many non-safety services can be accommodated in a VANET. IEEE 802.11p MAC is a contention-based protocol that has the drawback that reduces channel utilization. When the traffic flow is heavy, there are collisions and resources wasted. On the other hand, safety applications are the major concern in VANET. One of the important issues of safety-related services is the dissemination of emergency messages. In order to warn the drivers after emergency events, the dissemination of emergency messages should be as fast as possible. This thesis proposes Distributed Channel Assignment Scheme (DCAS) and emergency state transition mechanism to solve these problems. DCAS assigns service channels in a distributed manner and uses service channels efficiently. To avoid hidden terminal problem when assign SCHs, we propose a channel assignment scheme which increases the successful reservation rate so that increases channel utilization. Emergency state transition mechanism has three different states. Through transition among states, our proposed method can update emergency messages efficiently and reduce the latency. Through simulations with ns-3, our approach shows that the utilization of service channels is better and vehicles are able to get slots to transmit safety message and therefore increases driving safety.