VeMAC Protocol Research Articles

An efficient communication scheme for solving merge conflicts in maritime transportation

In researches and applications on maritime transportation, the information is collected by maritime vessels and Underwater Wireless Sensor Networks (UWSNs). The reliable wireless links among maritime vessels are needed to keep the communications efficiency and security. The movements of maritime vessels bring challenges to the reliable and real-time information transmissions, which require proper MAC layer supports of Ship Ad-hoc NETwork (SANET). An improved multi-channel VeMAC protocol based on TDMA, named I-VeMAC, is proposed to meet the transmission requirement on MAC layer. I-VeMAC reduces the time cost of the transmission of service information. In the control channel, time slots are occupied by relay nodes and conflict nodes. In order to solve the merge conflicts in service channels and optimize the transmissions in the control channel, I-VeMAC analyzes the relative positions of time slots. Meanwhile, the service providers provide slot information of nodes within 2 hops to conflict nodes, and recalculate the time slot allocation. It is proved that the hidden terminal problem will be solved without the nearby nodes announcing the time slot information within 2 hops. The simulation results show that the improved method reduces the time cost of solving merge conflict in VeMAC and the transmission delay. I-VeMAC improves the throughput, and it can be used in real-time transmission in SANET for UWSNs data harvesting.

Wireless access technologies for vehicular network safety applications

Road safety is becoming urgent due to a large number of traffic accidents each year and its severe socio-economic impact on a global scale. A promising solution to improve road safety is to deploy VANETs, a technology that can make driving safer by enabling a variety of advanced road safety applications, through broadcasting of safety messages by vehicles and roadside units. This article discusses the ability of existing wireless technologies to provide reliable broadcast of safety messages, which are necessary to realize any road safety application. The wireless technologies under consideration are the IEEE 802.11p standard, the current cellular network standards, and a time-division multiple access protocol, known as VeMAC, recently proposed for VANET safety applications. The performance of the IEEE 802.11p standard is compared with that of the VeMAC protocol via computer simulations in different highway and city scenarios, including a traffic bottleneck situation caused by emergency parking of a vehicle on a highway. We also review recent developments of the VeMAC protocol, including prototype experiments and on-road demonstrations of VeMAC-based safety applications implemented in real cars.

VeMAC: A TDMA-Based MAC Protocol for Reliable Broadcast in VANETs

The need of a medium access control (MAC) protocol for an efficient broadcast service is of great importance to support the high-priority safety applications in vehicular ad hoc networks (VANETs). This paper introduces VeMAC, a novel multichannel TDMA MAC protocol proposed specifically for a VANET scenario. The VeMAC supports efficient one-hop and multihop broadcast services on the control channel by using implicit acknowledgments and eliminating the hidden terminal problem. The protocol reduces transmission collisions due to node mobility on the control channel by assigning disjoint sets of time slots to vehicles moving in opposite directions and to road side units. Analysis and simulation results in highway and city scenarios are presented to evaluate the performance of VeMAC and compare it with ADHOC MAC, an existing TDMA MAC protocol for VANETs. It is shown that, due to its ability to decrease the rate of transmission collisions, the VeMAC protocol can provide significantly higher throughput on the control channel than ADHOC MAC.

Performance Evaluation of VeMAC Supporting Safety Applications in Vehicular Networks

Vehicular ad hoc networking (VANET) is an emerging paradigm that is expected to increase the public safety standards and enhance the safety level of drivers/passengers and pedestrians on roads through a variety of applications. We have recently proposed VeMAC, a medium access control protocol that supports a reliable one-hop broadcast service necessary for high priority safety applications in VANETs. This paper explains how the VeMAC protocol can deliver both periodic and event-driven safety messages in vehicular networks and presents a detailed delivery delay analysis, including queueing and service delays, for both types of safety messages. The probability mass function of the service delay is first derived; then, the D/G/1 and M/G/1 queueing systems are used to calculate the average queueing delay of the periodic and event-driven safety messages, respectively. In addition, a comparison between the VeMAC protocol and IEEE 802.11p standard is presented via extensive simulations using the network simulator ns-2 and the microscopic vehicle traffic simulator VISSIM. A real city scenario is considered and different performance metrics are evaluated, including the network goodput, protocol overhead, channel utilization, protocol fairness, probability of a transmission collision, and message delivery delay.