742 research outputs found
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
Overlap-Minimization Scheduling Strategy for Data Transmission in VANET
The vehicular ad-hoc network (VANET) based on dedicated short-range
communication (DSRC) is a distributed communication system, in which all the
nodes share the wireless channel with carrier sense multiple access/collision
avoid (CSMA/CA) protocol. However, the competition and backoff mechanisms of
CSMA/CA often bring additional delays and data packet collisions, which may
hardly meet the QoS requirements in terms of delay and packets delivery ratio
(PDR). Moreover, because of the distribution nature of security information in
broadcast mode, the sender cannot know whether the receivers have received the
information successfully. Similarly, this problem also exists in no-acknowledge
(non-ACK) transmissions of VANET. Therefore, the probability of packet
collisions should be considered in broadcast or non-ACK working modes. This
paper presents a connection-level scheduling algorithm overlaid on CSMA/CA to
schedule the start sending time of each transmission. By converting the object
of reducing collision probability to minimizing the overlap of transmission
durations of connections, the probability of backoff-activation can be greatly
decreased. Then the delay and the probability of packet collisions can also be
decreased. Numerical simulations have been conducted in our unified platform
containing SUMO, Veins and Omnet++. The result shows that the proposed
algorithm can effectively improve the PDR and reduce the packets collision in
VANET.Comment: 6 pages,7 figure
A Centralized TDMA based Scheduling Algorithm for Real-Time Communications in Vehicular Ad Hoc Networks
International audience—As wireless technologies inside smart cars are increasing , Vehicular Ad hoc NETworks (VANETs) are becoming a promising way to enhance driver and passenger safety by enabling each vehicle to provide a warning in real time when a critical event is predicted. These applications require reliable broadcast schemes with minimum access delay and transmission collisions, which thus increase the need for an efficient Medium Access Control (MAC) protocol. However, the design of an efficient MAC protocol in VANET networks is a challenging task due to the high speed of the nodes, the frequent changes in network topology and various QoS requirements. Motivated by this observation, in this paper we present a Centralized TDMA based MAC protocol named CTMAC for real-time communications in VANETs. In our solution, Road Side Units (RSUs) are used as central coordinators to schedule and maintain time slot assignment for the vehicles in their coverage areas. In this work, we will show how interference between vehicles in the overlapping regions can be avoided without using any complex spectrum mechanisms such as CDMA or OFDMA. The simulation results reveal that CTMAC significantly outperforms the VeMAC and ADHOC MAC protocols. in terms of transmission collisions and the overhead required to create and maintain the TDMA schedules
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 nĂşmero de acidentes rodoviários continua a ser muito elevado, sendo mesmo considerado uma questĂŁo de saĂşde pĂşblica por algumas entidades. Esta tese tem como objetivo geral contribuir para a redução desse nĂşmero de acidentes, e consequentes fatalidades, atravĂ©s da utilização de aplicações de segurança que envolvem comunicação entre veĂculos. Em particular, o objetivo principal Ă© garantir que a comunicação entre utentes, em ambientes veiculares, seja efetuada com limites temporais apropriados Ă transferĂŞncia de informações crĂticas. De forma mais detalhada, Ă© estudada a gestĂŁo do escalonamento das transmissões (controlo de acesso ao meio – MAC) que irá definir quem vai comunicar e quando o pode fazer. SĂŁo 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 veĂculos (OBUs), e situações (esporádicas, por ausĂŞncia de RSU) em que a rede de comunicação Ă© “ad hoc” e apenas constituĂda pelos veĂculos presentes. Utiliza-se a recente norma WAVE / IEEE 802.11p, especĂfica para comunicações veiculares, e propõe-se uma solução baseada em TDMA, com coordenação apropriada entre RSUs para disseminação efetiva de um evento crĂtico de segurança. A escolha do instante para o broadcast inicial do evento de segurança tambĂ©m Ă© tida em conta, e sĂŁo comparados dois casos distintos. No caso da ausĂŞncia de infraestrutura, derivam-se mĂ©todos para minimizar colisões no acesso ao meio de comunicação, e maximizar a largura de banda disponĂvel. 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 EletrotĂ©cnic
Low-latency Networking: Where Latency Lurks and How to Tame It
While the current generation of mobile and fixed communication networks has
been standardized for mobile broadband services, the next generation is driven
by the vision of the Internet of Things and mission critical communication
services requiring latency in the order of milliseconds or sub-milliseconds.
However, these new stringent requirements have a large technical impact on the
design of all layers of the communication protocol stack. The cross layer
interactions are complex due to the multiple design principles and technologies
that contribute to the layers' design and fundamental performance limitations.
We will be able to develop low-latency networks only if we address the problem
of these complex interactions from the new point of view of sub-milliseconds
latency. In this article, we propose a holistic analysis and classification of
the main design principles and enabling technologies that will make it possible
to deploy low-latency wireless communication networks. We argue that these
design principles and enabling technologies must be carefully orchestrated to
meet the stringent requirements and to manage the inherent trade-offs between
low latency and traditional performance metrics. We also review currently
ongoing standardization activities in prominent standards associations, and
discuss open problems for future research
TDMA scheduling strategies for vehicular ad hoc networks: from a distributed to a centralized approach
International audienceVehicular Ad hoc NETworks, known as VANETs, are deployed to reduce the risk of road accidents as well as to improve passenger comfort and safety by allowing vehicles to exchange different kinds of data. Medium Access Control protocols, namely those that are based on TDMA technique play a primary role in providing bounded transmission delay while minimizing data packet loss. However, due to mobility constraints and frequent changes in topology, slot scheduling is a more challenging task in VANETs than in other networks. Many MAC protocols based on TDMA for vehicular networks have been proposed to date. Among them, CTMAC is a centralized scheduling mechanism, while DTMAC, VeMAC and AD-HOCMAC are three distributed TDMA based MAC protocols. In this paper, we evaluate and analyze the performance these four protocols. The scenarios used in the simulation experiments take into account density variation factor that influences protocol performance. We use the MOVE and SUMO tools to generate realistic mobility scenarios. Performance metrics such as access collision, merging collision rate, packet loss and overhead are evaluated using NS-2.34
Robotic Wireless Sensor Networks
In this chapter, we present a literature survey of an emerging, cutting-edge,
and multi-disciplinary field of research at the intersection of Robotics and
Wireless Sensor Networks (WSN) which we refer to as Robotic Wireless Sensor
Networks (RWSN). We define a RWSN as an autonomous networked multi-robot system
that aims to achieve certain sensing goals while meeting and maintaining
certain communication performance requirements, through cooperative control,
learning and adaptation. While both of the component areas, i.e., Robotics and
WSN, are very well-known and well-explored, there exist a whole set of new
opportunities and research directions at the intersection of these two fields
which are relatively or even completely unexplored. One such example would be
the use of a set of robotic routers to set up a temporary communication path
between a sender and a receiver that uses the controlled mobility to the
advantage of packet routing. We find that there exist only a limited number of
articles to be directly categorized as RWSN related works whereas there exist a
range of articles in the robotics and the WSN literature that are also relevant
to this new field of research. To connect the dots, we first identify the core
problems and research trends related to RWSN such as connectivity,
localization, routing, and robust flow of information. Next, we classify the
existing research on RWSN as well as the relevant state-of-the-arts from
robotics and WSN community according to the problems and trends identified in
the first step. Lastly, we analyze what is missing in the existing literature,
and identify topics that require more research attention in the future
TDMA-based MAC Protocols for Vehicular Ad Hoc Networks: A Survey, Qualitative Analysis and Open Research Issues
International audience—Vehicular Ad-hoc NETworks (VANETs) have attracted a lot of attention in the research community in recent years due to their promising applications. VANETs help improve traffic safety and efficiency. Each vehicle can exchange information to inform other vehicles about the current status of the traffic flow or a dangerous situation such as an accident. Road safety and traffic management applications require a reliable communication scheme with minimal transmission collisions, which thus increase the need for an efficient Medium Access Control (MAC) protocol. However, the design of the MAC in a vehicular network is a challenging task due to the high speed of the nodes, the frequent changes in topology, the lack of an infrastructure, and various QoS requirements. Recently several Time Division Multiple Access (TDMA)-based medium access control protocols have been proposed for VANETs in an attempt to ensure that all the vehicles have enough time to send safety messages without collisions and to reduce the end-to-end delay and the packet loss ratio. In this paper, we identify the reasons for using the collision-free medium access control paradigm in VANETs. We then present a novel topology-based classification and we provide an overview of TDMA-based MAC protocols that have been proposed for VANETs. We focus on the characteristics of these protocols, as well as on their benefits and limitations. Finally, we give a qualitative comparison, and we discuss some open issues that need to be tackled in future studies in order to improve the performance of TDMA-based MAC protocols for vehicle to vehicle (V2V) communications
- …