Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> The inter-vehicle communications (IVC) is one of the most important technologies to realize advanced intelligent transport systems (ITS). Conventional IVC is vehicle-to-vehicle communication through line of sight communication by millimeter wave in a narrow area. Here, we deal with more progressive IVC in a wide area. In this paper, we propose Dynamic Integrated Transmission Control (DITRAC) for IVC. DITRAC optimizes transmission power and transmission interval of vehicles according to the fluctuation of the communications circumstance of the ad-hoc vehicular communications network. In order to estimate the fluctuation of the neighboring communications, we present an effective and simple method, the road-weight with receiving history (WH) method. The simulations are conducted to show the validity of DITRAC for IVC. <s> BIB001 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> This study presents narrow-band measurements of the mobile vehicle-to-vehicle propagation channel at 5.9 GHz, under realistic suburban driving conditions in Pittsburgh, Pennsylvania. Our system includes differential Global Positioning System (DGPS) receivers, thereby enabling dynamic measurements of how large-scale path loss, Doppler spectrum, and coherence time depend on vehicle location and separation. A Nakagami distribution is used for describing the fading statistics. The speed-separation diagram is introduced as a new tool for analyzing and understanding the vehicle-to-vehicle propagation environment. We show that this diagram can be used to model and predict channel Doppler spread and coherence time using vehicle speed and separation. <s> BIB002 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <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> BIB003 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> We consider the problem of adjusting transmission power for vehicle-to-vehicle broadcast safety communication in vehicular ad hoc networks. Given a target communication range designated by a vehicle safety application, the power control algorithm is designed to select a transmission power no greater than necessary for the targeted range. The power control algorithm results in higher communication reliability since collisions are minimized for safety communications. Our main idea is to add a power tuning feedback beacon during each safety message exchange. Our simulation results show that the power control algorithm can reduce the transmission power significantly to achieve higher packet reception rate than the case without any power control. This algorithm is mainly applied to communications-based vehicle safety applications but could be useful for other applications as well. <s> BIB004 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> Vehicular networking is an enabling technology for Intelligent Transportation Systems (ITS). Different types of vehicular traffic applications are currently being investigated. In this paper we briefly introduce the communication requirements of a Co-operative Adaptive Cruise Control (C-ACC) vehicular traffic efficiency application. Furthermore, we propose a Channel Busy Time model to evaluate the solution space of a vehicular beaconing system designed to communicate information both vital and sufficient for vehicular traffic applications and in particular for C-ACC. We identify that the solution space is three-dimensional. These dimensions being based on the number of nodes (or vehicles), the beacon generation rate of the nodes and the size (or duration) of a beacon message. Based on the Channel Busy Time model we derive boundaries and ranges of parameters within which the beaconing system can be adapted to meet the requirements of the C-ACC application. <s> BIB005 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> This paper presents a class of routing protocols called road-based using vehicular traffic (RBVT) routing, which outperforms existing routing protocols in city-based vehicular ad hoc networks (VANETs). RBVT protocols leverage real-time vehicular traffic information to create road-based paths consisting of successions of road intersections that have, with high probability, network connectivity among them. Geographical forwarding is used to transfer packets between intersections on the path, reducing the path's sensitivity to individual node movements. For dense networks with high contention, we optimize the forwarding using a distributed receiver-based election of next hops based on a multicriterion prioritization function that takes nonuniform radio propagation into account. We designed and implemented a reactive protocol RBVT-R and a proactive protocol RBVT-P and compared them with protocols representative of mobile ad hoc networks and VANETs. Simulation results in urban settings show that RBVT-R performs best in terms of average delivery rate, with up to a 40% increase compared with some existing protocols. In terms of average delay, RBVT-P performs best, with as much as an 85% decrease compared with the other protocols. <s> BIB006 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> Optimizing vehicular communication strategies is important for an efficient usage of the available wireless bandwidth and also critical for the success of VANETs. In this paper we address the fundamental and practical question whether the load on the wireless channel can be reduced if periodic beacon messages are transmitted over multiple hops with reduced transmit power instead of being transmitted over one hop with high transmit power. In particular, we look at the possible bandwidth savings that can be achieved by piggybacking forwarded messages into the own next beacon transmission. For that matter, we first propose an analytical model to compute a lower bound for the resulting channel load when single- or multi-hop dissemination of beacons is performed. In this model we assume optimal channel conditions and perfect relaying and piggybacking decisions to show that a reduction of the load by multi-hop is possible and closely related to piggybacking. Further, we show that the possible savings depend on the ratio between the size of the header and the payload of a beacon and that a reduction of the load is theoretically possible if the header is larger than the payload - what would be the case in VANETs if security overheads are considered part of the header. We then perform a simulative comparison of single- and multi-hop beaconing to evaluate the impact of effects such as packet collisions and channel fading. We show that the possible savings of multi-hop beaconing are difficult to exploit under non-perfect channel conditions and suboptimal relaying decisions. <s> BIB007 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> In the future intervehicle communication will make driving safer, easier, and more comfortable. As a cornerstone of the system, vehicles need to be aware of other vehicles in the vicinity. This cooperative awareness is achieved by beaconing, the exchange of periodic single-hop broadcast messages that include data on the status of a vehicle. While the concept of beaconing has been developed in the first phase of research on VANETs, recent studies have revealed limitations with respect to network performance. Obviously, the frequency of beacon messages directly translates into accuracy of cooperative awareness and thus traffic safety. There is an indisputable trade-off between required bandwidth and achieved accuracy. In this work we analyze this trade-off from different perspectives considering the consequences for safety applications. As a solution to the problem of overloading the channel, we propose to control the offered load by adjusting the beacon frequency dynamically to the current traffic situation while maintaining appropriate accuracy. To find an optimal adaptation, we elaborate on several options that arise when determining the beacon frequency. As a result, we propose situation-adaptive beaconing. It depends on the vehicle's own movement and the movement of surrounding vehicles, macroscopic aspects like the current vehicle density, or microscopic aspects. <s> BIB008 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> Intelligent transportation systems could improve transportation safety, driving assistance and traffic management system. Vehicular Ad hoc Network (VANET) is an emerging field of technology, embedding wireless communication networks into vehicles to achieve intelligent transportation systems. The development of such systems pose many unique challenges like designing routing protocols that not only forward packets with good end to end delay but also take into consideration the reliability and progress in data packets forwarding. In this article, we begin by presenting a review of recent unicast, geocast and broadcast routing protocols for message transmission. We then outline a novel Delay and Reliability aware Routing (DR 2 ) protocol that addresses these challenges (forwarding packets with low latency, high reliability and fast progress toward destination). Furthermore, our DR 2 protocol uses cross layer communication between MAC (Medium Access Control) and network layer. That is, the MAC layer observes the Signal to Noise (SNR), delay and velocity vector difference metrics for all paths of neighboring nodes, network layer then could select the best preferable path based on fuzzy inference system. We also used H∞ technique to optimize the membership functions and then tune it with rapid changing topology of VANET. To achieve a fair comparison with other routing protocols, we have implemented the proposed DR 2 protocol in Network Simulator 2 (NS 2). The preliminary results show that the proposed DR 2 protocol is able to improve end- to-end delay in sparse traffic conditions and packet delivery ratio in error prone urban vehicular scenarios. <s> BIB009 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> We present Adaptive Traffic Beacon (ATB), a fully-decentralized car-to-X protocol built around the central ideas of delay sensitivity and congestion awareness. From previous research findings, we see that centralized solutions, VANETs, and broadcasting based approaches each show benefits and drawbacks depending on traffic density, penetration, network utilization, and other parameters; intelligent transportation systems are therefore tuned for specific settings. In order to overcome this limitation, we developed a broadcast-based solution that has been designed to carefully use only the remaining capacity of the wireless channel. Thus, it will not influence other applications using the same radio network. ATB is adaptive in two dimensions: First, the beacon interval is adapted dynamically according to the channel quality and the importance of messages in the local knowledge base, and, secondly, the protocol can dynamically make use of available infrastructure elements. Simulation experiments demonstrate that ATB performs well in a broad range of settings. It maintains a non-congested wireless channel to prevent collisions during the data exchange. <s> BIB010 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> Proxy Mobile IPv6 (PMIPv6) was standardized by the Internet Engineering Task Force (IETF) NetLMM WG as a Network-based Mobility management protocol, this protocol allows the Mobile Node (MN) to maintain service connectivity while moving within the PMIPv6 domain. PMIPv6 mobility management is different from the Host-based Mobility management protocols; where the mobility signaling management is controlled by the serving network on behalf of the MN. PMIPv6 introduced new network entities to handle the signaling on behalf of the MN. However, PMIPv6 protocol can only manage the MN’s reachability within a local domain (intra-domain). If the MN moves beyond the perimeter of PMIPv6 domain, the mobility support will be lost. To provide MN continuous support across domains, PMIPv6 needs to be developed to support interconnect neighboring PMIPv6 domains. In this paper we propose an inter-domain handover scheme. The proposed scheme uses the Media Independent Information Service (MIIS) to help the vehicle store information about the network that it is attached with. In addition the Local Mobile Anchor (LMA) will use Fully Qualified Domain Name (FQDN). <s> BIB011 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <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> BIB012 </s> Beaconing Approaches in Vehicular Ad Hoc Networks: A Survey <s>  <s> Abstract Some public transport vehicles embed devices that allow passengers to connect to Internet while traveling. These vehicles are true mobile Internet access zones inside public paths. These zones could be used by other vehicles moving close to them in order to have Internet access. At the same time, other vehicles in the influence area could be used as relay nodes which would increase this access area. In this paper, we present a group-based protocol and mobility model for vehicular ad hoc networks (VANETs) where each public transport vehicle forms a group of vehicles. They can access and allow access to Internet though the public transport vehicle. Each vehicle is moving inside the group and can leave and join any group at will, while all groups are moving. First, we will show the algorithm and protocol to achieve our purpose. Then, we will study the probability of having Internet access in order to demonstrate that it is a feasible proposal. Finally, we simulate a study case based on real values in order to obtain the performance of our proposal in terms of several network parameters such as the number of hops per route, the network traffic, the page response time, network delay, network load and so on. <s> BIB013
: Taxonomy of the literature on beaconing approaches. between vehicles. In addition, in the near future, more vehicles will be embedded with devices that facilitate communication between vehicles, such as IEEE 802.11p, called Wireless Access in Vehicular Environment (WAVE)  . The WAVE wireless technology is extended from the IEEE standard of 802.11a and adopted service differentiation of IEEE 802.11e to support multimedia applications. When vehicles are equipped with WAVE, they can synchronize and handshake via beacons. In this way, a vehicle exchanges beacon messages periodically, sharing its mobility characteristics with its neighbours, thereby building cooperative awareness. The main purpose of mobile ad hoc networks (MANET) is to maximize lifetime and capacity of the wireless networks. In contrast to MANET, vehicular networks are emerged to improve traffic safety related applications through beacon (periodic) and event-driven messages BIB002 . Beacon messages are crucial to enable safety applications. Each vehicle broadcasts periodic beacon messages to inform neighbour nodes about their address, location and other relevant information. This status messages can be used to detect abnormal situation on the highway and urban scenarios. On the other hand, dangerous situations like car accidents will trigger event-driven messages to be disseminated with highest priority to nearby vehicles. In this proactive neighbourhood awareness, each vehicle should maintain the up-to-date list of neighbour nodes. Otherwise, the outdated information problem of the neighbour list leads to miss the next candidate node or the node that has been chosen will move out the radio range. However, rapid changes in traffic density from sparse to heavy, as well as periodic beaconing between vehicles, can cause the wireless channel between vehicles to promptly become congested, resulting in a high degree of performance degradation of vehicular network BIB005 , BIB003 , BIB013 . The reason for this channel congestion is that each vehicle periodically broadcasts beacons at a fixed rate. This also leads to high channel overloading and hence packet loss. In short, the higher the frequency of beacon rate, the higher the bandwidth overload in dense traffic conditions BIB006 . On the other hand, the solution to channel overloading does not involve simply reducing the frequency of beacon generation. As the frequency of beacon generation is reduced, the error will increase between the current physical position and the last reported position. For instance, in geographical routing protocols, reducing beacon rate would lead to the inaccuracy of the exchanged position coordinates between vehicles. This would negatively affect the performance of routing protocols. In short, reducing the beacon rate leads to the exchange of out-of-date information. To tackle this issue, the authors in BIB001 , BIB008 ,  , BIB009 , BIB007 BIB010 considered conditional update approach in which a vehicle adapts its beacon rate based on various parameters. In addition, due to fast movement of vehicles link life time will last very soon in VANET. Increasing radio coverage of the vehicle is counted as a method of increasing the link life time when vehicles are sparsely deployed. But, the increase of transmission range might negatively affect the VANET performance when vehicles are densely deployed. This is due to higher interference and overhead. Thus, dynamic transmission power adaptation is an imperative need in such bipolar traffic distribution environment BIB004 , BIB011 . On the other hand, quality of service differentiation of various applications are very important in VANET since vehicles might expose to different incidents BIB012 . In this article, a concise description of the background of beaconing approaches will be presented first, followed by an elaboration of the main types of adaptive beaconing approaches, and the differences between them. The overall taxonomy of beaconing approaches are depicted in Fig. 1 . Then, the classification of each type of VANET's beaconing approaches will be demonstrated and their implementation are explored. That is, adaptation of beacon transmission power with respect to the heterogeneous vehicular traffic distribution, adjustment of beacon rate and hybrid adaptive beaconing approaches. After that, it provides a survey of recent state of the art beaconing approaches, the motivation behind their design and trace the influence of mobility model on these beaconing approaches. At the end of the paper, we summarize the beaconing approaches as shown in Table 1 . We finally conclude this paper by discussing important open issues and research directions in VANET.