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Abstract-Routing protocols developed for ad hoc wireless networks use broadcast transmission to either discover a route or disseminate information. More specifically, reactive routing protocols has to flood the network with a route request (RREQ) message in order to find an optimal route to the destination. Several applications developed for vehicular ad hoc wireless networks (VANET), which is a subset of MANET, rely on broadcast to propagate useful traffic information to other vehicles located within a certain geographical area. However, the conventional broadcast mechanism may lead to the so-called broadcast storm problem.In this paper, we explore how serious the broadcast storm problem is in both MANET and VANET by examining how broadcast packets propagate in a 2-dimensional open area and on a straight road or highway scenarios. In addition, we propose three novel distributed broadcast suppression techniques;i.e., weighted p-persistence, slotted 1-persistence, and slotted ppersistence schemes. Our simulation results show that the proposed schemes can achieve up to 90% reduction in packet loss rate while keeping the end-to-end delay at acceptable levels for most VANET applications. They can also be used together with the route discovery process to guide the routing protocols to select routes with fewer hop counts. I INTRODUCTIONBroadcast transmission is used for at least two very different purposes in MANET. Firstly, many MANET routing protocols broadcasts RREQ messages in order to search for a route to a particular host. In this case, the goal is to propagate the RREQ message to the destination as quickly and efficiently as possible, i.e., RREQ message from the optimal path should be the first one to arrive at the destination. Alternatively, some applications, especially ones that were developed for vehicular ad hoc wireless networks (VANET), may rely on broadcast transmission to disseminate data packet to nodes in a certain geographical area. However, it is well-known that blindly broadcasting the packets may lead to frequent contention, and collisions in transmission among neighboring nodes. This problem is sometimes referred to as the broadcast storm problem.In this paper, we explore how serious the broadcast storm problem is in two very different scenarios; (i) in NIANET where problem rises during the route discovery process, and (ii) in VANET where most applications typically favor broadcast transmissions. While multiple solutions exist to alleviate the broadcast storm problem in a usual MANET environment [1-6], none of these solutions address the problem in the VANET context, nor do they study the impact of broadcast storm on routing decisions.1-4244-0425-8/06/$20.00 ©2006 IEEE While most studies, to the best of our knowledge, focus on improving the performance in terms of latency, overhead, and network reachability, in this paper, we also consider packet loss ratio, route discovery time, and the number of hops chosen by the routing protocols as our performance metrics. More specifically, we propose thr...

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An onboard vehicle-to-vehicle multi-hop wireless networking system has been developed to test the realworld performance of telematics applications. The system targets emergency and safety messaging, traffic updates, audio/video streaming and commercial announcements. The test-bed includes a Differential GPS receiver, an IEEE 802.11a radio card modified to emulate the DSRC standard, a 1xRTT cellular-data connection, an onboard computer and audio-visual equipment. Vehicles exchange data directly or via intermediate vehicles using a multi-hop routing protocol. The focus of the test-bed is to (a) evaluate the feasibility of high-speed inter-vehicular networking, (b) characterize 5.8GHz signal propagation within a dynamic mobile ad hoc environment, and (c) develop routing protocols for highly mobile networks. The test-bed has been deployed across five vehicles and tested over 400 miles on the road. Disciplines Engineering Comments ABSTRACTAn onboard vehicle-to-vehicle multi-hop wireless networking system has been developed to test the realworld performance of telematics applications. The system targets emergency and safety messaging, traffic updates, audio/video streaming and commercial announcements. The test-bed includes a Differential GPS receiver, an IEEE 802.11a radio card modified to emulate the DSRC standard, a 1xRTT cellular-data connection, an onboard computer and audio-visual equipment. Vehicles exchange data directly or via intermediate vehicles using a multi-hop routing protocol. The focus of the test-bed is to (a) evaluate the feasibility of high-speed inter-vehicular networking, (b) characterize 5.8GHz signal propagation within a dynamic mobile ad hoc environment, and (c) develop routing protocols for highly mobile networks. The test-bed has been deployed across five vehicles and tested over 400 miles on the road.