VanDung Nguyen

HER-MAC: A Hybrid Efficient and Reliable MAC for Vehicular Ad Hoc Networks

Vehicular Ad hoc Networks (VANETs) should provide the vehicles with reliable safety message broadcasts and efficient non-safety message transmissions. The IEEE 1609.4 MAC is designed for VANETs to support multi-channel operations, but the safety message broadcast is not much reliable and the Service Channel (SCH) resources are not fully utilized. In this paper, we propose a new multi-channel MAC for VANETs, named HER-MAC, which supports both TDMA and CSMA multiple access schemes. The HER-MAC allows vehicle nodes to send safety messages without collision on the Control Channel (CCH) within their reserved time slots and to utilize the SCH resources during the control channel interval (CCHI) for the non-safety message transmissions. Compared to the current IEEE 1609.4, the proposed HER-MAC protocol is more reliable in the safety message broadcast, efficient in the service channel utilization.

An Efficient Time Slot Acquisition on the Hybrid TDMA/CSMA Multichannel MAC in VANETs

The multichannel MACs increase the throughput and reduce the collision probability compared to the single-channel MACs. However, coordination of multiple nodes across multichannels is nontrivial. Recently, a multichannel MAC, called HER-MAC, uses both TDMA and CSMA schemes to improve reliability in broadcasting safety messages and efficiency in service channel utilization. Nevertheless, HER-MAC suffers a high collision probability for a large number of vehicle nodes. In this letter, we propose a hybrid TDMA/CSMA multichannel MAC protocol for VANETs that allows efficient broadcasting of messages and increases throughput on the control channel. Furthermore, our proposed MAC eliminates unnecessary control packet such as HELLO and SWITCH packets in HER-MAC. Analysis and simulation results show that the proposed MAC can provide faster time slot acquisition on the control channel than HER-MAC.

e-VeMAC: An enhanced vehicular MAC protocol to mitigate the exposed terminal problem

The VeMAC, a TDMA-based MAC protocol for Vehicular Ad-hoc NETworks (VANET), assigns disjoint sets of the time slots to vehicles moving in opposite directions and to road side units. So the VeMAC protocol reduces the access and merging collisions. Moreover, the VeMAC protocol employs slot release prevention condition which avoids unnecessarily releasing time slots when a node just enters the communication range of each other. Although VeMAC supports reliable and efficient transmission, it is still not full applicable for VANET in parallel transmission. In this paper, we propose an e-VeMAC protocol: an enhanced vehicular MAC protocol to mitigate the exposed terminal problem. The simulation results show that the e-VeMAC protocol supports more parallel transmissions than the VeMAC protocol.

An Efficient and Fast Broadcast Frame Adjustment Algorithm in VANET

Designing MAC protocol for vehicle ad hoc networks (VANETs) is challenging because of quick topology changes, high vehicle mobility, and different quality of service requirements. One promising approach is to employ both TDMA and CSMA hybrid access schemes in the control channel interval. These protocols can adjust the length of TDMA frame (also called broadcast frame) to adapt itself to different vehicle conditions and provide efficient non-safety message transmission. To improve the efficiency of the hybrid MAC mechanism in VANET, we propose an efficient and fast broadcast frame adjustment algorithm, called EFAB based on the three-hop neighbor information. By adjusting the broadcast frame length quickly, MAC protocol using EFAB can support efficient broadcast services on the control channel. Simulation results show that the hybrid MAC protocol using EFAB can provide faster broadcast frame adjustment and higher packet delivery ratio of safety packets on the control channel than using the existing algorithms.

Application of the lowest-ID algorithm in cluster-based TDMA system for VANETs

To gather data of a larger area and improve the capability in the system, vehicles in Vehicular Ad-hoc NETworks (VANETs) are organized into clusters. Moreover, the effectiveness of application in VANET depends on performance of Medium Access Control (MAC) protocol. In addition, cluster-based MAC protocols can avoid or limit channel contention, provide fairness to channel access, increase radio network capacity management by reusing the spatial network and effectively controlling the topology of the network. This paper proposes a cluster-based TDMA system using the lowest-ID algorithm for Vehicular Ad hoc NETworks (VANETs). Using the lowest-ID algorithm, the analytical and simulated results show that not only the average number of time slots for electing a vehicle head but also total number of time slots before data can be successfully transmitted is less than the existing cluster-based TDMA system and IEEE 802.11p.

A reliable multi-hop safety message broadcast in Vehicular Ad hoc Networks

Vehicular Ad hoc NETworks (VANETs) should provide the reliable safety message broadcasts and the efficient non-safety message transmissions to vehicles. The IEEE 1609.4 MAC, which supports multi-channel operations in VANETs, is not reliable enough for the safety message broadcast and not efficient in the Service CHannel (SCH) resources utilization. In this paper, we propose a MAC protocol which supports a Reliable Multi-hop Safety message Broadcast (RMSB-MAC) in VANETs. Each Multi-hop Forwarder (MF) collects the safety messages from the neighbor vehicle nodes, and then the MF uses its reserved time slot to broadcast them to all vehicle nodes in its transmission range as well as to forward them to the next MF. Moreover, by allowing vehicle nodes to exchange non-safety messages during the Control CHannel Interval (CCHI), the RMSB-MAC utilizes the SCH resources more efficiently.

ECCT: an efficient-cooperative ADHOC MAC for cluster-based TDMA system in VANETs

In VANETs, a clustering algorithm can be used to partition the network into smaller segments. Therefore, the clustering algorithms provide not only limited channel contention but also fair channel access within the cluster. In addition, they also increase spatial reuse in VANETs and efficient control for the network topology. The main concern in the clustering algorithm is the cluster stability. The major challenge is to elect a cluster head and to maintain the membership of member nodes in a highly dynamic and a fast-changing topology. Therefore, the major criterion for cluster formation is to form a stable cluster. In this paper, a clustering algorithm to affect organization and cooperative ADHOC MAC for cluster-based TDMA system in VANETs (ECCT) is proposed. The cooperation is used to help a cluster head update each neighbor clusters information which helps each cluster head to avoid collision when two clusters move into each others clusters transmission range. This efficiently utilizes a time slot. We use the lowest-ID algorithm to achieve organization. The analytical and simulated results show that not only the average number of time slots for electing a cluster head but also total number of time slots before data can be successfully transmitted is less than the existing cluster-based TDMA system and IEEE 802.11p.

Improving time slot acquisition through RSU's coordination for TDMA-based MAC protocol in VANETs

Vehicles and Road Side Units (RSUs) are essential units to create a dynamic network, called Vehicular Ad hoc NETwork (VANETs). An RSU plays a role of collecting and analyzing traffic data given from vehicles. RSUs and vehicles have to assign time slots to broadcast service applications on the control channel in VANETs. One of MAC protocol versions named VeMAC is proposed. VeMAC protocol can decrease the rate of transmission collisions and increase the throughput on the control channel. However, VeMAC protocol did not consider to special properties of an RSU in VANETs. In this paper, we propose an improvement of time slot acquisition through RSUs coordination for TDMA-based MAC protocol in VANET, called RCMAC protocol. In our protocol, RSUs exploit time slots assignment and disseminate control information. Hence, RCMAC protocol reduces the rate transmission collisions due to all nodes on the control channel receive a control information from an RSU. Simulation results show that RCMAC protocol outperforms both VeMAC and ADHOC-MAC protocols in term of average of number of frames that all nodes successfully acquire a time slot and average number of access collisions until all nodes successfully acquire a time slot.

Finding realistic shortest path in road networks with lane changing and turn restriction

Most existing work on path computation has been focused on the shortest-path problem, which is to find the optimal path between an origin and destination pair. To get an optimal route, they usually consider travel time moving forward on the road and distance from a source to a target as crucial factors to value and select a path. However, it is not sufficient for real life traffic. Firstly, when we drive on the road, the road driving time includes the duration of moving forward on the road section, going through an intersection and performing lane changes. Secondly, it is not possible, in practice, to go on any road section. Some road sections have restricted rules. Turn restrictions are commonly restricted in a real network to reduce disruption to traffic. Therefore, in our work, we direct to find not only the shortest path but also realistic or feasible path. Both lane changes and turn restrictions are considered in our work. Simulation results show that two these additional constraints are necessarily considered to achieve a realistic shortest path. In addition, our proposal is not only giving a practical path but also a satisfied path for each individual car.

An efficient and reliable Green Light Optimal Speed Advisory system for autonomous cars

An autonomous car is a self-driving car that is to keep the human being out of the car and to relieve them from the task of driving. An autonomous car can make more convenient, safer, and less energy intensive. In addition, Green Light Optimal Speed Advisory (GLOSA) systems reduce the travel time and CO2 emission. In this paper, we propose a novel GLOSA, called R-GLOSA system to support to autonomous cars. We assume that an autonomous car can access to all traffic light schedules that it will encounter on its route. The route is divided into each segment according to traffic lights. In each segment, an autonomous car can communicate to Road Side Units (RSUs) distributed among the road. An autonomous car collects the road information transmitted by an RSU and then, it optimizes speed in order to arrive at the intersection when the light is green. The R-GLOSA system provides an autonomous car with speed advisory for each RSUs coverage. The simulation results show that an autonomous car using R-GLOSA system outperforms in terms of travel time and waiting time compared to using single-segment and multi-segment GLOSA system.