Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Static Beaconing Approaches <s> Nowadays in Europe, USA, Japan and other countries many efforts are being made towards the development and ubiquitous deployment of active vehicular safety systems, which are based on car-to-car and car-to-infrastructure communications. International standard IEEE 802.11p defines low layers protocols for vehicular networks aimed to support Intelligent Transportation Systems (ITS) applications. Periodic broadcasting of short status messages (beacons) is foreseen as one of the key modes, which should be efficiently handled to provide active safety in vehicular networks. This paper presents a simple analytical method to compute the probability of successful message reception and mean message transmission delay in IEEE 802.11p vehicular ad-hoc network with periodic broadcasting of messages. We investigate the influence of beaconing period on the above performance metrics. <s> BIB001 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Static Beaconing Approaches <s> Efficient dissemination of messages in a Vehicular Ad Hoc Network (VANET) still face many challenges in the current research scenario. This paper addresses the problem of redundant forwarding of messages that occur during broad- cast and proposes an adaptive forwarding mechanism which controls the amount of redundant messages thereby improving message dissemination over a VANET. The mechanism will enable a node to efficiently forward a message and at the same time refrain other potential forwarders of the same message in a chosen area to forward the message. The algorithm exploits the density of nodes on the network for its functionality and will make an adaptive sector under which the redundant nodes will be refrained from sending the same message. The area of the sector for a particular node will be proportional to the density of its neighbors that are within the node's communication range. The proposal assumes that the nodes in the VANET are aware of their surroundings up to a certain area by periodic exchange of location information from each of the nodes. The mechanism will enable routing algorithms and/or beaconing systems to consume lesser bandwidth and thereby enhance the efficiency of the algorithm itself. <s> BIB002
The authors in BIB001 proposed an analytical model to calculate the probability of message reception by the packet's receiver and mean packet delay in IEEE 802.11p based vehicular networks. The proposed analytical model considers deterministic beaconing rate fashion rather than Poisson arrival pattern. This attribute of the devised protocol gives uniqueness in comparison to the state of the arts. They also evaluated the proposed analytical model on Matlab simulation model with 802.11p MAC layer. In their simulation, it is observed that the required time delay of a safety-related message can meet the threshold. However, the probability of beacon message reception could not meet the requirement value for critical applications. For instance, beacon message reception probability is 0.7 to 0.5 when Bit Error Rate is 0.0001. Following the trends, Mariyasagayam et al. in BIB002 devised a multi-hop beaconing mechanism that adaptively controls the number of redundant messages during packet dissemination process. The Fig. 9 : Cooperative awareness between vehicles algorithm divides the area falls within the communication range of the source to dynamic backfire sectors. Each sector is dynamic and depends upon the nodes density of nearby the packet source. This adaptive behaviour of each sector suppresses the broadcast of redundant messages. Fig. 9 depicts forwarding of the proposed mechanism where node S would broadcast packet to nearby vehicles (A and B). After receiving the packet, nodes A and B set the waiting time which inversely proportional with the distance between the source (S) and packet receiver (A and B). In this scenario, node A broadcasts the packet since its timer expires first. After the node B receives the same packet form S and A, it drops the packet and thereby node A backfired node B. The performance evaluation is based on the packet level simulator ns-2 [30] in urban vehicular environments. Results show that the proposed dynamics backfire mechanism performs better as compared to constant and no backfire mechanisms of packet forwarding in terms of packet delivery ratio. While radio signals are obstructed by obstacles in urban area, they used unrealistic radio propagation model, which is two ray ground model.