Towards More Reliable MAC and PHY Layer Designs for High QoS Achievements for Safety Messaging in DSRC Systems

Broadcast communications are widely proposed for safety messaging. In the case of highway vehicular networks and constantly communicating safety messages inevitably cause the well-known hidden terminal problem. Three existing leading repetition-based broadcasting protocols have shown to meet the reliability and delay requirements for Dedicated Short Range Communications (DSRC) safety systems. We propose a quantitative model to evaluate the quality of service (QoS) of DSRC systems using these three leading repetition-based protocols under hidden terminals and highway scenarios. The performance of our model is analyzed by means of probability of success and delay performances. We also present three new Medium Access Control (MAC) layer design protocols for safety messaging applications. The main protocol we introduce is known as Passive Cooperative Collision Warning (PCCW) protocol for repetition based vehicular safety message reception reliability improvement in DSRC. The PCCW protocol and jointly proposed Enhanced-PCCW (EPCCW) and emergency-PCCW (ePCCW) protocols variants can work on top of existing repetition protocols for serving as a passive collision warning mechanism in the MAC Layer. A full analytical derivation of the relative reliability and delay performances for all three PCCW, EPCCW and ePCCW protocols are provided, serving as intuitive performance evaluators. EPCCW employs the physical (PHY) layer to create sub-slots for the purpose of further increasing reliability by both avoiding and minimizing probability of collision at slots that would nominally fail. Analytical and simulation results of PCCW and EPCCW agree, and show a significant reduction in message failure rate versus the leading repetition protocols, especially under high collision scenarios up to 40% at optimal, and 80% at higher repetitions. Additionally, an improvement in average timeslots delay is observed, which facilitates improved vehicular safety messaging. ePCCW is particularly useful for emergency vehicle (EV) communications. This enhancement makes meeting stringent quality of service (QoS) requirements particularly prevalent in safety applications of DSRC systems. ePCCW show up to 77% reliability improvement relative to a leading alternative is realized. Additionally, the proposed system is shown to have a decreased average timeslots delay that is well within acceptable delay threshold, and provides the best reliability in its class, which is key to safety messaging. In all our simulation results, we use our accurate Orthogonal Frequency Division (OFDM) MAC and physical (PHY) layer designs. The PHY layer simulator is a new object-oriented simulation environment, and is achieved using high-level design, parallelism and usability for the simulation environment. A high-level design and GUI layouts of the proposed simulator is shown in details. This can serve as a learning/research tool for students or practiced professionals to investigate particular designs. In addition, we provide a simple technique to implement simulation partitioning for increased parallel performance of reconfigurable object-oriented OFDM simulators. This simple technique applies to scenarios where there is disproportionate simulation duration between different OFDM configurations. It is shown to decrease total simulation time considerably. Additionally, we present a study on different demapping schemes at the PHY level. We propose the use of a linear demapper over a recently proposed non-linear demapper. The study is also presented under different decoding schemes of DSRC receivers. We also propose the use of equalization concepts in frequency domain that exploit the frequency domain channel matrix to combat inter-carrier interference (ICI) instead of inter-symbol interference (ISI) in DSRC systems. It is shown that the DSRC system with the frequency-domain equalization scheme achieves a considerable performance enhancement compared to both the conventional and the Viterbi-aided channel estimation schemes that try to combat ISI in terms of both Packet Error Rate (PER) and Bit Error Rate (BER) at relatively high and low velocities

MAC/PHY Cross-Layer Design for Improved Vehicular Safety Messaging Reliability and Simulation Environment Design

In vehicle-to-vehicle safety messaging, periodic safety messages can be used for safety applications. These applications require low latency and high probability of reception, however there can be a problem with unsuccessful reception due to collision of these safety messages when there are sufficiently large amount of vehicles and/or repetitions. Literature proposes repetition based broadcasting to increase reception probability, while decreasing average reception delay; however this increases the probability of packet collision and overall network traffic. In this thesis, we introduce a new cross-layer design, which allows for collision correction of safety message repetitions for further improving probability of reception. We describe our design as well as simulation using various repetition schemes under different packet error rates and compare our cross-layer collision correction method with non-collision correcting performance. Once implemented, this new approach can substantially improve the reception likelihood of safety messages, without loss of latency, and potentially make active vehicle safety applications more responsive

An Adaptation of DSRC Protocol for V2V Communications in Developing Countries: End-to-End Delay Evaluation

Vehicular Ad hoc NETworks (VANETs) help in improving road traffic safety and efficiency. In V2V communications, vehicles exchange kinematic information over a suitable protocol in order, either to warn other vehicles of a dangerous situation or inform them about the current status of the traffic flow. When using Wireless Access in Vehicular Environments (WAVE), also referred to as Dedicated Short Range Communication (DSRC) protocol, kinematic information is called Wave Short Messages (WSM), based on Basic Safety Message (BSM) defined by the SAE J2735 dictionary set. BSM is used for safety advertisement, either in one hop or multi-hop broadcasts. However, DSRC evaluations in many urban and sub-urban environments have shown that this protocol is highly sensitive to transmission conditions such as the density and speed of vehicles, antenna position, interference, etc., which makes it difficult to predict its performance. In this paper, we are interested in evaluating, based on various scenarios, the end-to-end delays when a particular emergency vehicle broadcasts BSM to all its nearby vehicles. The results are obtained by modeling and simulating a modified version of the DSRC protocol to fit the Cameroonian environment. Our results reveal that our adapted version of DSRC protocol performs very well and outperform others proposed protocols

An Emulation Framework for Evaluating V2X Communications in C-ITS Applications

C-ITS enhances transportation systems with advanced communication tech, enabling vehicle-to-vehicle and vehicle-to-infrastructure data exchange for real-time decision-making. The thesis explores C-ITS concepts, DSRC, and C-V2X tech, and proposes a versatile C-ITS framework for app prototyping and communication evaluation. Real-world tests and simulations validate its potential to improve road safety and efficiency, suggesting integration opportunities for stakeholders and promoting a smarter, sustainable transportation ecosystem

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