272 research outputs found
Empirical Performance Models of MAC Protocols for Cooperative Platooning Applications
Vehicular ad-hoc networks (VANET) enable vehicles to exchange information on traffic
conditions, dynamic status and localization, to enhance road safety and transportation efficiency.
A typical VANET application is platooning, which can take advantage of exchanging information on
speed, heading and position to allow shorter inter-vehicle distances without compromising safety.
However, the platooning performance depends drastically on the quality of the communication
channel, which in turn is highly influenced by the medium access control protocol (MAC). Currently,
VANETs use the IEEE 802.11p MAC, which follows a carrier sense multiple access with collision
avoidance (CSMA/CA) policy that is prone to collisions and degrades significantly with network
load. This has led to recent proposals for a time-division multiple access (TDMA)-based MAC that
synchronize vehicles’ beacons to prevent or reduce collisions. In this paper, we take CSMA/CA
and two TDMA-based overlay protocols, i.e., deployed over CSMA/CA, namely PLEXE-slotted and
RA-TDMAp, and carry out extensive simulations with varying platoon sizes, number of occupied
lanes and transmit power to deduce empirical models that provide estimates of average number of
collisions per second and average busy time ratio. In particular, we show that these estimates can
be obtained from observing the number of radio-frequency (RF) neighbours, i.e., number of distinct
sources of the packets received by each vehicle per time unit. These estimates can enhance the online
adaptation of distributed applications, particularly platooning control, to varying conditions of the
communication channel.info:eu-repo/semantics/publishedVersio
Self-Stabilizing TDMA Algorithms for Dynamic Wireless Ad-hoc Networks
In dynamic wireless ad-hoc networks (DynWANs), autonomous computing devices
set up a network for the communication needs of the moment. These networks
require the implementation of a medium access control (MAC) layer. We consider
MAC protocols for DynWANs that need to be autonomous and robust as well as have
high bandwidth utilization, high predictability degree of bandwidth allocation,
and low communication delay in the presence of frequent topological changes to
the communication network. Recent studies have shown that existing
implementations cannot guarantee the necessary satisfaction of these timing
requirements. We propose a self-stabilizing MAC algorithm for DynWANs that
guarantees a short convergence period, and by that, it can facilitate the
satisfaction of severe timing requirements, such as the above. Besides the
contribution in the algorithmic front of research, we expect that our proposal
can enable quicker adoption by practitioners and faster deployment of DynWANs
that are subject changes in the network topology
Time division multiple access scheduling strategies for emerging vehicular ad hoc network medium access control protocols: a survey
[EN] 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.Tambawal, AB.; Noor, RM.; Salleh, R.; Chembe, C.; Anisi, MH.; Michael, O.; Lloret, J. (2019). Time division multiple access scheduling strategies for emerging vehicular ad hoc network medium access control protocols: a survey. Telecommunication Systems. 70(4):595-616. https://doi.org/10.1007/s11235-018-00542-8S59561670
All-to-all Broadcast for Vehicular Networks Based on Coded Slotted ALOHA
We propose an uncoordinated all-to-all broadcast protocol for periodic
messages in vehicular networks based on coded slotted ALOHA (CSA). Unlike
classical CSA, each user acts as both transmitter and receiver in a half-duplex
mode. As in CSA, each user transmits its packet several times. The half-duplex
mode gives rise to an interesting design trade-off: the more the user repeats
its packet, the higher the probability that this packet is decoded by other
users, but the lower the probability for this user to decode packets from
others. We compare the proposed protocol with carrier sense multiple access
with collision avoidance, currently adopted as a multiple access protocol for
vehicular networks. The results show that the proposed protocol greatly
increases the number of users in the network that reliably communicate with
each other. We also provide analytical tools to predict the performance of the
proposed protocol.Comment: v2: small typos fixe
An Accurate Performance Analysis of Hybrid Efficient and Reliable MAC Protocol in VANET under Non-saturated Conditions
Vehicular Ad Hoc Networks (VANETs) is a technology supporting two types of applications, safety and service applications with higher and lower priorities respectively. Thereby, Medium Access Control (MAC) protocol is designed to provide reliable and efficient data broadcasting based on prioritization. Different from the IEEE 1609.4 (legacy), HER-MAC protocol is a new multi-channel MAC proposed for VANETs, offering remarkable performance with regards to safety applications transmission. This paper focuses on the analysis of packet delivery ratio of the HER-MAC protocol under non-saturated conditions. 1-D and 2-D Markov chains have been developed for safety and non-safety applications respectively, to evaluate mathematically the performance of HER-MAC protocol. The presented work has taken into account the freezing of the backoff timer for both applications and the backoff stages along with short retry limit for non-safety applications in order to meet the IEEE 802.11p specifications. It highlights that taking these elements into consideration are important in modeling the system, to provide an accurate estimation of the channel access, and guarantees that no packet is served indefinitely. More precise results of the system packet delivery ratio have been yield. The probability of successful transmission and collisions were derived and used to compute the packet delivery ratio. The simulation results validate the analytical results of our models and indicate that the performance of our models outperformed the existing models in terms of the packet delivery ratio under different number of vehicles and contention window
DTB-MAC: Dynamic Token-Based MAC Protocol for reliable and efficient beacon broadcasting in VANETs
© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Most applications developed for vehicular environments
rely on broadcasting as the main mechanism to disseminate
their messages. However, in IEEE 802.11p, which is the most
widely accepted MAC protocol for vehicular communications, all
transmissions remain unacknowledged if broadcasting is used.
Furthermore, safety message transmission requires a strict delay
limit and a high reliability, which is an issue for random
access MAC protocols like IEEE 802.11p. Therefore, transmission
reliability becomes the most important issue for broadcast-based
services in vehicular environments. In this paper, we propose a
hybrid MAC protocol, referred as Dynamic Token-Based MAC
Protocol (DTB-MAC). DTB-MAC uses both a token passing
mechanism and a random access MAC protocol to prevent
channel contention as much as possible, and to improve the
reliability of safety message transmissions. Our proposed protocol
tries to select the best neighbouring node as the next transmitter,
and when it is not possible, or when it causes a high overhead,
the random access MAC protocol is used instead. Based on
simulation experiments, we show that the DTB-MAC protocol
can achieve better performance compared with IEEE802.11p in
terms of channel utilization and beacon delivery ratio.This work was partially supported by the Ministerio de Ciencia e Innovación, Spain, under Grant TIN2011-27543-C03-01.Balador, A.; Tavares De Araujo Cesariny Calafate, CM.; Cano Escribá, JC.; Manzoni, P. (2015). DTB-MAC: Dynamic Token-Based MAC Protocol for reliable and efficient beacon broadcasting in VANETs. IEEE. https://doi.org/10.1109/CCNC.2015.7157955
An Analytical Model for Performance Analysis of an Active Signaling-based TDMA MAC Protocol for Vehicular Networks
International audienceIn Vehicular Ad hoc NETworks (VANETs) the vehicles moving along roads 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 support of safety applications. Time Division Multiple Access (TDMA)-based protocols are advantageous in many aspects of VANETs. They can cope with the hidden-terminal problem, and guarantee a strict Quality-of-Service (QoS) to satisfy real-time applications. However, the initial assignment of time-slots to the vehicles can suffer from the access collision problem, which can frequently occur between vehicles trying to access the same time slots. Moreover, a low latency access is not usually possible. That is why we have developed an Active Signaling system (AS-DTMAC : Active Signaling Decentralized Tdma MAC protocol) which operates above the existing DTMAC protocol : a Medium Access Control (MAC) protocol specially devoted to VANETs. AS-DTMAC can drastically reduce the number of access collisions and also offer low latency access. The aim of this article is to provide a complete mathematical analysis of the performance of this scheme, to show its high performances and to validate these results using simulations
Controlo de acesso ao meio em comunicações veiculares de tempo-real
Despite several preventive measures, the number of roadway accidents is still very high, being considered even a problem of public health by some entities. This thesis has as global purpose of contributing to the reduction of that number of accidents, and consequent fatalities, by using safety-related applications that use communication among vehicles. In particular, the primary goal is guaranteeing that communication between users in vehicular environments is done with appropriate time bounds to transfer safety-critical information. In detail, it is studied how to manage the scheduling of message’s transmissions (medium access control - MAC), in order to define precisely who will communicate and when is the appropriate instant. The preferable situation where a communication infrastructure is present with full coverage (RSUs) is also studied, from which medium access control is defined precisely, and vehicles (OBUs) become aware of medium utilization. Also, sporadic situations (e.g., absence of RSUs) are studied in which the communication network is “ad hoc” and solely formed by the current vehicles. It is used the recently WAVE / IEEE 802.11p standard, specific for vehicular communications, and it is proposed a TDMA based solution, with appropriate coordination between RSUs in order to effectively disseminate a critical safety event. It is taken into account two different ways of choosing the instant for the initial broadcast, and both cases are compared. In case there is no infrastructure available, methods are derived to minimize communication medium access collisions, and to maximize the available bandwidth. The results reflect the total end-to-end delay, and show that adequate times are attained, and meet with the requisites for the type of applications being considered. Also, enhancements are obtained when using the alternate choice for the initial broadcast instant.Apesar de diversas medidas preventivas, o número de acidentes rodoviários continua a ser muito elevado, sendo mesmo considerado uma questão de saúde pública por algumas entidades. Esta tese tem como objetivo geral contribuir para a redução desse número de acidentes, e consequentes fatalidades, através da utilização de aplicações de segurança que envolvem comunicação entre veículos. Em particular, o objetivo principal é garantir que a comunicação entre utentes, em ambientes veiculares, seja efetuada com limites temporais apropriados à transferência de informações críticas. De forma mais detalhada, é estudada a gestão do escalonamento das transmissões (controlo de acesso ao meio – MAC) que irá definir quem vai comunicar e quando o pode fazer. São estudadas situações (desejadas) onde há uma infra-estrutura de comunicações com cobertura integral (RSUs), a partir da qual se faz a coordenação do acesso ao meio pelos veículos (OBUs), e situações (esporádicas, por ausência de RSU) em que a rede de comunicação é “ad hoc” e apenas constituída pelos veículos presentes. Utiliza-se a recente norma WAVE / IEEE 802.11p, específica para comunicações veiculares, e propõe-se uma solução baseada em TDMA, com coordenação apropriada entre RSUs para disseminação efetiva de um evento crítico de segurança. A escolha do instante para o broadcast inicial do evento de segurança também é tida em conta, e são comparados dois casos distintos. No caso da ausência de infraestrutura, derivam-se métodos para minimizar colisões no acesso ao meio de comunicação, e maximizar a largura de banda disponível. Os resultados refletem o atraso total end-to-end, mostrando tempos apropriados para os requisitos das aplicações em causa, e evidenciando melhorias aquando da escolha alternativa para o instante do broadcast inicial.Programa Doutoral em Engenharia Eletrotécnic
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