Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> A five-layer hierarchy to integrate models, data, and tools is proposed for benefits assessment and requirements development for crash avoidance systems. The framework is known as HARTCAS: Hierarchical Assessment and Requirements Tools for Crash Avoidance Systems. The analysis problem is multifaceted and large-scale. The driving environment is diverse and uncertain, driver behavior and performance are not uniform, and the range of applicable collision avoidance technologies is wide. Considerable real-world data are becoming available on certain aspects of this environment, although the collection of experimental data on other aspects is constrained by technological and institutional issues. Therefore, analyses of collision avoidance systems are to be conducted by collecting data on nominal operating conditions to the greatest extent possible and by using such data to build models for analysis of the rare, abnormal conditions. HARTCAS provides a framework within which to structure the collection and use of... <s> BIB001 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> Broadcasting is a common operation in a network to resolve many issues. In a mobile ad hoc network (MANET) in particular, due to host mobility, such operations are expected to be executed more frequently (such as finding a route to a particular host, paging a particular host, and sending an alarm signal). Because radio signals are likely to overlap with others in a geographical area, a straightforward broadcasting by flooding is usually very costly and will result in serious redundancy, contention, and collision, to which we call the broadcast storm problem. In this paper, we identify this problem by showing how serious it is through analyses and simulations. We propose several schemes to reduce redundant rebroadcasts and differentiate timing of rebroadcasts to alleviate this problem. Simulation results are presented, which show different levels of improvement over the basic flooding approach. <s> BIB002 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> We propose a new power control algorithm capable of managing the topology of a vehicular ad hoc network by adjusting transmission power dynamically. Our algorithm is simple to implement, as it is based only on local information and no exchange of power-related signaling among nodes is required. The algorithm has the objective of making the network operate with both a very low and a very high user density, while maintaining its performance unaltered. This target is obtained by controlling transmission power, so that the number of neighbors of each node is always within a minimum and maximum threshold. In this way, it is possible to cope concurrently with the problems of node isolation and clustering at low load and of excessive competition for radio resources at high load. Finally, the algorithm provides high channel availability for connected users. The algorithm is robust, as performance does not depend on user speed, which has a large variance in a vehicular scenario. <s> BIB003 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> Improving the safety of drivers and passengers by wirelessly exchanging information between vehicles represents a major driving force for the design of vehicular ad hoc networks. In a heavy loaded 802.11-based network, however, safety-related packets might collide frequently and cannot be decoded by a receiver, thus they might not be effective in increasing the safety level on the roads. In this paper, we propose to use transmit power control in order to reduce packet collisions, while taking into account the major design goal of vehicular ad hoc networks, i.e. increasing safety. While previous work has addressed the issue of power control primarily for optimizing network capacity and/or connectivity, the optimization criterion for improving safety has to be built upon the concept of fairness: a higher transmit power of a sender should not be selected at the expense of preventing other vehicles to send/receive their required amount of safety information. In this paper, we propose a fully distributed and localized algorithm called D-FPAV (distributed fair power adjustment for vehicular networks) for adaptive transmit power adjustment which is formally proven to achieve max-min fairness. Furthermore, we investigate the effectiveness and robustness of D-FPAV through extensive simulations based on a realistic highway scenario and different radio propagation models <s> BIB004 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> The main goal of inter-vehicle communication technologies is to provide each vehicle with the required information about its surrounding in order to assist the driver avoiding potential dangers. The required information level, or awareness, can be achieved by the exchange of periodic status messages (beacons) among neighboring vehicles together with the quick dissemination of information about potential hazards. In previous work, we proposed an algorithm (D-FPAV) to control the beaconing load on the medium by adjusting the transmission power in a fair and distributed fashion. In this paper, we adapt a promising position-based message forwarding strategy in order to disseminate time-critical safety information. Moreover, we evaluate its performance when making use of D-FPAV, i.e., limiting the beaconing load on the medium, in a realistic highway environment with probabilistic radio propagation characteristics <s> BIB005 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> Vehicular ad hoc networks have several characteristics that distinguish them from other ad hoc networks. Among those is the rapid change in topology due to traffic jams, which also disturbs the homogeneous distribution of vehicles on the road. For this reason, a dynamic transmission range is more effective in maintaining the connectivity while minimizing the adverse effects of a high transmission power. This paper proposes a scheme that allows vehicles to estimate the local density and distinguish between the free-flow and the congested traffic phases. The density estimate is used to develop a dynamic transmission-range-assignment (DTRA) algorithm that sets a vehicle transmission range dynamically according to the local traffic conditions. Simulations of several road configurations validate the quality of the local density estimation and show that the DTRA algorithm is successful in maintaining the connectivity in highly dynamic networks. <s> BIB006 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> One-hop broadcasting is the predominate form of network traffic in VANETs. Exchanging status information by broadcasting among the vehicles enhances vehicular active safety. Since there is no MAC layer broadcasting recovery for 802.11 based VANETs, efforts should be made towards more robust and effective transmission of such safety-related information. In this paper, a channel adaptive broadcasting method is proposed. It relies solely on channel condition information available at each vehicle by employing standard supported sequence number mechanisms. The proposed method is fully compatible with 802.11 and introduces no communication overhead. Simulation studies show that it outperforms standard broadcasting in term of reception rate and channel utilization. <s> BIB007 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> Problem statement: Vehicular Ad hoc Networks (VANET) is one of the most challenging research area in the field of Mobile Ad Hoc Networks. Approach: In this research we proposed a dynamic power adjustment protocol that will be used for sending the periodical safety message. (Beacon ) based on the analysis of the channel status dependi ng on the channel congestion and the power used for transmission. Results: The Beacon Power Control (BPC) protocol first sensed and examined the percentage of the channel congestion, the result ob tained was used to adjust the transmission power fo r the safety message to reach the optimal power. Conclusion/Recommendations: This will lead to decrease the congestion in the channel and achieve good channel performance and beacon dissemination. <s> BIB008 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> The recently standardised IEEE 802.11p Wireless Access in Vehicular Environment (WAVE) protocol is envisioned to be used for Vehicle-to-Vehicle and Vehicle-to-Infrastructure communications. We provide an analysis of 802.11p's performance when used for the exchange of small status messages known as beacons. These beacons enable vehicles to establish a Cooperative Awareness from which many applications can draw their inputs. Applications have been proposed to increase safety, efficiency and comfort of future road traffic. This paper investigates the impact of adapting settings for the Contention Window (CW) based on the traffic density in order to increase the efficiency of the 802.11p broadcasts w.r.t. reception probability and delay with a focus on real-time vehicle control. In contrast to the literature available on adapting CW settings in unicast, we find that the initial CW value of 15 proposed in the IEEE 802.11p standard performs significantly well under almost all studied circumstances. <s> BIB009 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> In this paper, we present a new scheme for dynamic adaptation of transmission power and contention window (CW) size to enhance performance of information dissemination in Vehicular Ad-hoc Networks (VANETs). The proposed scheme incorporates the Enhanced Distributed Channel Access (EDCA) mechanism of 802.11e and uses a joint approach to adapt transmission power at the physical (PHY) layer and quality-of-service (QoS) parameters at the medium access control (MAC) layer. In our scheme, transmission power is adapted based on the estimated local vehicle density to change the transmission range dynamically, while the CW size is adapted according to the instantaneous collision rate to enable service differentiation. In the interest of promoting timely propagation of information, VANET advisories are prioritized according to their urgency and the EDCA mechanism is employed for their dissemination. The performance of the proposed joint adaptation scheme was evaluated using the ns-2 simulator with added EDCA support. Extensive simulations have demonstrated that our scheme features significantly better throughput and lower average end-to-end delay compared with a similar scheme with static parameters. <s> BIB010 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s> Beaconing Approaches <s> We propose a broadcast algorithm suitable for a wide range of vehicular scenarios, which only employs local information acquired via periodic beacon messages, containing acknowledgments of the circulated broadcast messages. Each vehicle decides whether it belongs to a connected dominating set (CDS). Vehicles in the CDS use a shorter waiting period before possible retransmission. At time-out expiration, a vehicle retransmits if it is aware of at least one neighbor in need of the message. To address intermittent connectivity and appearance of new neighbors, the evaluation timer can be restarted. Our algorithm resolves propagation at road intersections without any need to even recognize intersections. It is inherently adaptable to different mobility regimes, without the need to classify network or vehicle speeds. In a thorough simulation-based performance evaluation, our algorithm is shown to provide higher reliability and message efficiency than existing approaches for nonsafety applications. <s> BIB011
Cooperative awareness demands up-to-date and low delay information exchange between vehicles. This information includes position, movement and acceleration of the vehicles in the vicinity. This can be achieved by broadcasting beacon messages. Recently, European ITS system in  has proposed a fixed beaconing approach which requires every vehicle to establish its cognizance about other nearby vehicles. Furthermore, Cooperative Active Safety System(CASS) utilizes information exchanged between neighbour vehicles in order to provide assistance to drivers. The CASS system may successfully provide this awareness by transmitting vehicular information, at a fixed rate through beacon message, every 100 ms in all vehicular scenarios  BIB001 . This vehicular awareness supports geographical routing and data dissemination. However, since the beacon message size is approximately 400 bytes BIB009 , it requires a profound amount of bandwidth as traffic density increases, leading performance deterioration in the network BIB007 , BIB002 ,  , BIB011 . Fig. 2 shows a vehicular scenario where the source vehicle disseminates the beacon message to nearby vehicles. The problem of beaconing adaptation has been studied in various prospects in VANET. Transmission power control and beacon rate control are two main examples of adaptation approaches. The authors in BIB005 , BIB004 , BIB006 , BIB007 , BIB008 , BIB010 , BIB003 have proposed adaptation approaches to tune transmission power with varying vehicular densities. That is, the purpose is to reduce transmission power in dense vehicular scenarios and hence improve fairness. In addition, adaptation of beaconing can be done by controlling the beacon rate with heterogeneous distribution of vehicles. For the purpose of tuning the contention window size, Van Eenennaam et al. in  proposed a framework to adapt network and MAC-layer parameters in order to mimic the configuration parameters. This adaptive approach can tune MAC layer configurations and beaconing properties to optimal values in the vehicular scenarios. The authors demonstrate the requirement of efficient beaconing approach to increase cooperative awareness between vehicles. Fig. 3 shows that increased distance leads to a lack of cooperative awareness. However, vehicular networks are dynamic, as evidenced by dense rush hours and sparse late night traffic conditions. In designing their model, the aforementioned authors did not take these factors into consideration. 