A Clustering-Based Contention-Free MAC Protocol for Vehicular Ad Hoc Networks

Various ongoing research efforts in Vehicular Ad hoc Network (VANET) related to safety and non-safety applications have been published in academia and industry. One of the main areas in VANET that is still lacking of significant research contributions is toward designing reliable Medium Access Control (MAC) protocols. Existing surveys on MAC protocols in VANET mostly discuss general MAC methods, that include contention-based and contention-free MAC protocols. A hybrid MAC protocol that adopts both contention-based and contention-free MAC, proposed to enhance the network performance in VANET, is fruitful to be explored further. Hence, a survey of hybrid MAC protocols for VANET is presented in this paper. The benefits and limitations of the existing hybrid MAC protocols are discussed based on their classification to provide some insights into the recent advancement of high-performance MAC protocols for vehicular networks. Finally, some open research issues are highlighted as part of future research directions that need further investigations.

Vehicular ad hoc networks (VANETs) provide the communication framework for the dissemination of safety-critical messages such as beacons and emergency messages. The communication channel witnesses significant network load generated by frequently exchanged beacons. Under high-density situations, it leads to a serious scalability problem in VANETs. Moreover, contention-based medium access control (MAC) protocols suffer from a great number of packet collisions, and as a result, the reliability and latency of safety messages are severely affected. Because of the periodic nature of beacons, time-division multiple access (TDMA) can be a good choice over contention-based MAC. In this paper, we propose congestion-controlled-coordinator-based MAC (CCC-MAC), which is a time-slot-based medium access protocol that addresses beacons and emergency messages. Basically, the network is virtually partitioned into a number of segments. Within a segment, medium access is accomplished by using a time-slot-scheduling mechanism supervised by a local coordinator vehicle. A significant number of vehicles can be supported under the proposed configuration. In fact, the proposed scheduling mitigates channel congestion by reducing the transmission time of beacons through the use of multiple data rates. Bandwidth utilization is also improved by reusing the unoccupied time slots. Finally, CCC-MAC ensures fast and reliable propagation of emergency messages by employing a pulse-based reservation mechanism. In the simulations, we demonstrate the ability of CCC-MAC to scale well in different vehicular density scenarios. Moreover, it outperforms existing MAC-layer protocols with respect to packet reception probability and latency of safety messages.

Reliability is an important issue for safety-critical broadcast services in vehicular ad hoc networks (VANETs). So far, most investigations of such broadcast networks focus on multihop connectivity, taking all one-hop links for granted. In this paper, four reliability metrics for one-hop broadcast communication in VANETs, including the packet reception rate (PRR), the packet delivery ratio (PDR), the node successful packet delivery probability (PDP), and the effective range (ER), are introduced and evaluated analytically and by simulations. Expressions of these reliability metrics for one-hop broadcast in IEEE-802.11-based 1-D VANETs are derived with consideration of the IEEE 802.11 distributed coordination function (DCF), the hidden terminal problem, and collisions caused by concurrent transmissions. The impacts of network parameters such as distinct transmission, carrier sensing, and interference ranges; the density of nodes in the networks; the distances of receivers to the senders; the message generation rates; the backoff window sizes; and the channel data rates on the reliability of the broadcast communication in VANETs are investigated and discussed. As an example, the proposed model is applied to the evaluation of the dedicated short-range communication (DSRC) safety-critical message propagation in a highway setting. As a result, some important observations to the design and analysis of such communication systems are provided.

International audience

The primary objective of a Medium Access Control (MAC) layer in Vehicular Ad hoc Networks (VANETs) is reliable and rapid broadcast of safety messages. Fast mobility of vehicles, hidden terminal problem, reliability, and congestion control of broadcast channel are challenging issues in VANETs. This paper proposes an R-ALOHA-based channel access mechanism that renders a broadcast channel capable of broadcast failure detection while at the same time maintaining congestion control. The proposal employs a combination of CSMA and TDMA techniques to mitigate the hidden terminal problem and combat fast mobility of vehicles in VANETs. Performance comparison of preexisting TDMA protocols and the proposed protocol - both analytical and in simulation - is also provided. Simulation results validate analytical models and demonstrate significantly improved reliability and increased channel assignment speed to manage the fast mobility of vehicles.

Vehicular ad hoc network (VANET) is an emerging and promising technology, which allows vehicles while moving on the road to communicate and share resources. These resources are aimed at improving traffic safety and providing comfort to drivers and passengers. The resources use applications that have to meet high reliability and delay constraints. However, to implement these applications, VANET relies on medium access control (MAC) protocol. Many approaches have been proposed in the literature using time division multiple access (TDMA) scheme to enhance the efficiency of MAC protocol. Nevertheless, this technique has encountered some challenges including access and merging collisions due to inefficient time slot allocation strategy and hidden terminal problem. Despite several attempts to study this class of protocol, issues such as channel access and time slot scheduling strategy have not been given much attention. In this paper, we have relatively examined the most prominent TDMA MAC protocols which were proposed in the literature from 2010 to 2018. These protocols were classified based on scheduling strategy and the technique adopted. Also, we have comparatively analyzed them based on different parameters and performance metrics used. Finally, some open issues are presented for future deployment.

Medium access control (MAC) is critical for vehicular ad hoc networks (VANET). A real commercial VANET system has not come into the market. Different MAC schemes have been proposed to attempt to achieve the expected performance, such as bounded delay, high packet reception rate, security, etc. Space Division Multiple Access (SDMA) is one of the VANET MAC proposals and has been theoretically investigated. However, it has not been studied whether SDMA is realistically feasible in VANET. In this paper, the suitability of SDMA for VANET is studied. The core mechanisms of the proposed SDMA and of the possible SDMA functions for VANET are analyzed and evaluated. Concerns upon practical implementation issues and theoretical limits are presented, based on which the conclusion of the unsuitability of SDMA for VANET is drawn.

A Vehicular Ad-Hoc NETwork (VANET) consists of a set of vehicles moving along roads, which can communicate with each other through ad hoc wireless devices. VANETs have attracted a great deal of attention in the research community in recent years, with the main focus being on their safety applications. One of the major challenges of vehicular networks is designing an efficient Medium Access Control (MAC) protocol which can cope with the hidden node problem, the high speed of the nodes, the frequent changes in topology, the lack of an infrastructure, and various QoS requirements. Motivated by this observation, we present a fully distributed and location-based TDMA scheduling scheme for VANETs, named DTMAC. The main goal of this work is to propose a MAC protocol that can provide a reliable broadcast service with bounded access delay, while reducing access collisions and merging collisions with various vehicle densities without having to use expensive and complex spectrum mechanisms such as CDMA or OFDMA. An analytical model of the average access collision probability has been derived, which can be used to evaluate the performance of DTMAC and validate the simulation results under different traffic conditions. The simulation results reveal that DTMAC significantly outperforms VeMAC in terms of transmission collisions and broadcast coverage.

Vehicular ad hoc networks (VANET) are also known as intelligent transportation systems. VANET ensures timely and accurate communications between vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) to improve road safety and enhance the efficiency of traffic flow. Due to its open wireless boundary and high mobility, VANET is vulnerable to malicious nodes that could gain access into the network and carry out serious medium access control (MAC) layer threats, such as denial of service (DoS) attacks, data modification attacks, impersonation attacks, Sybil attacks, and replay attacks. This could affect the network security and privacy, causing harm to the information exchange within the network by genuine nodes and increase fatal impacts on the road. Therefore, a novel secure trust-based architecture that utilizes blockchain technology has been proposed to increase security and privacy to mitigate the aforementioned MAC layer attacks. A series of experiment has been conducted using the Veins simulation tool to assess the performance of the proposed solution in the terms of packet delivery ratio (PDR), end-to-end delay, packet loss, transmission overhead, and computational cost.

IEEE 802.11p is a communication protocol which is extended by IEEE 802.11 standard, mainly used in Vehicular Ad-Hoc Networks (VANETs). VANETs generally include the Service Channel (SCH) and Control Channel (CCH). In the traditional 802.11p protocol, the length ratio between CCH and SCHs is fixed. This paper presents a variable SCH interval(VSI) multichannel medium access control (MAC) scheme under the non-saturated channel. Under this scheme, we can control the length of CCH interval and SCH interval. This paper uses three-dimensional Markov chain model to calculate the delay of WAVE service announcement (WSA) frame. We propose a VSI MAC calculation model under unsaturated condition to achieve the maximum throughput. The simulation results indicate that the proposed scheme can help VANETs increase the unsaturated throughput of SCHs and lower the transmission delay of data frames obviously.

The current medium access control (MAC) protocol of the wireless access in vehicular environments (WAVE) system is based on IEEE 802.11 distributed coordination function (DCF) and enhanced distributed channel access (EDCA), which have drawbacks in supporting throughput-sensitive non-safety applications in vehicular ad-hoc network (VANET). In order to address the problem, we propose a novel MAC protocol, namely vehicular MESH network (VMESH), which is specifically designed for the control channel (CCH) and multiple service channels (SCHs) structure of WAVE. A synchronized and distributed beaconing scheme is employed in the VMESH protocol for the purposes of neighborhood awareness and dynamic resource reservation on SCHs. The advantages of the VMESH protocol in supporting the throughput-sensitive non-safety applications in VANET are shown through the theoretical analysis comparing to the current WAVE MAC.

Because of the space and time dynamics of moving vehicles, network connectivity is an important performance metric to affect packet delivery in Vehicular Ad Hoc Networks (VANETs). Grouping vehicles into platoons in VANETs can improve road safety, change the network connectivity, and even reduce channel access collisions. Unfortunately, network connectivity is often ignored in the design of exiting MAC protocols for VANETs. In this paper, we analyze the connectivity probability and present a connectivity-aware Medium Access Control (MAC) protocol for platoon-based VANETs. A multi-priority Markov model is presented to derive the relationship between the connectivity probability and the system saturated throughput. Based on variable traffic status and network connectivity, a multi-channel reservation scheme is adopted to dynamically adjust the length of the Control CHannel (CCH) interval and the Service CHannel (SCH) interval for the improvement of the system performance, in terms of network throughput and the priority packet transmission opportunities for platoons. As a result, some important observations to the design and analysis of such communication systems are provided. © 2015 IEEE

Vehicular Ad Hoc Networks (VANETs) and their diverse applications experience growing interest in both academic and industry. Different types of traffic packets delivered through vehicle-to-vehicle and vehicle-to-infrastructure communications are intended to improve passenger safety and comfort. In this paper, we propose a multiple priority supported Medium Access Control (MAC) protocol for VANETs based on the time slotted p-persistent channel access mechanism. The protocol differentiates the services packets into multi-priority on the Control Channel (CCH). Theoretical analysis based on Markov model is presented to optimize the transmission probabilities of the packets with different priorities, as well as the adjustable intervals of the CCH and the Services Channels (SCHs). Both analytical results and simulation experiments show that the proposed MAC protocol is able to ensure the prioritized transmission of the safety packets and also achieve optimal system performance with respect to saturated throughput.

In Vehicular Ad Hoc Networks (VANETs), efficient use of the control channel affects both safety applications that use the control channel and other applications that use the service channels. Its efficiency deteriorates due the collisions on accessing to the control channel or due to the merging collisions which happen when fast moving vehicles use the same allocated channels. In this paper, we propose an algorithm which predicts the possible merging collisions due to the overtaking of fast vehicles. It predicts the collisions within 2-hops neighborhood and recommends the vehicle to acquire a new time slot in the control channel. Through simulations, it is shown that proposed approach reduces the merging collisions.

This chapter proposes a direction aware cluster-based multichannel MAC (DA-CMAC) protocol for Vehicular Ad-Hoc Networks (VANETs) in which vehicles travelling in the opposite direction may result in a short communication period. Clustering based on the direction of travel can reduce the cost of reconfiguration due to the short communication period. Each cluster consists of Cluster Head (CH), Cluster Members (CMs) and Gateway Vehicles (GV). CH calculates priorities of CMs based on the value of eligibility function that is received from the CM and assign each CM a unique priority based on the future position of CM, CM ID, and eligibility function. The eligibility function is calculated using the number of connected neighbors, average speed deviation, and the average distance between neighbors and itself. Clusters are independently managed and locally reconfigured as vehicles travel. Moreover, the proposed DA-CMAC protocol manages the channel access and allocates time slots to its CMs, reducing access and merging collisions in the channel, by grouping the time slots into two sets based on the direction of movement. Each CMs are allocated with one time slot in both control service channel to achieve fairness in channel access. Simulation results of DA-CMAC are compared with HCA protocol. Simulation results show that the DA-CMAC protocol have higher reliability of packets, fewer CH changes and fewer number of access collisions compared with HCA protocol.