Heterogeneous LTE/ Wi-Fi architecture for intelligent transportation systems

Intelligent Transportation Systems (ITS) make use of advanced technologies to enhance road safety and improve traffic efficiency. It is anticipated that ITS will play a vital future role in improving traffic efficiency, safety, comfort and emissions. In order to assist the passengers to travel safely, efficiently and conveniently, several application requirements have to be met simultaneously. In addition to the delivery of regular traffic and safety information, vehicular networks have been recently required to support infotainment services. Previous vehicular network designs and architectures do not satisfy this increasing traffic demand as they are setup for either voice or data traffic, which is not suitable for the transfer of vehicular traffic. This new requirement is one of the key drivers behind the need for new mobile wireless broadband architectures and technologies. For this purpose, this thesis proposes and investigates a heterogeneous IEEE 802.11 and LTE vehicular system that supports both infotainment and ITS traffic control data. IEEE 802.11g is used for V2V communications and as an on-board access network while, LTE is used for V2I communications. A performance simulation-based study is conducted to validate the feasibility of the proposed system in an urban vehicular environment. The system performance is evaluated in terms of data loss, data rate, delay and jitter. Several simulation scenarios are performed and evaluated. In the V2I-only scenario, the delay, jitter and data drops for both ITS and video traffic are within the acceptable limits, as defined by vehicular application requirements. Although a tendency of increase in video packet drops during handover from one eNodeB to another is observed yet, the attainable data loss rate is still below the defined benchmarks. In the integrated V2V-V2I scenario, data loss in uplink ITS traffic was initially observed so, Burst communication technique is applied to prevent packet losses in the critical uplink ITS traffic. A quantitative analysis is performed to determine the number of packets per burst, the inter-packet and inter-burst intervals. It is found that a substantial improvement is achieved using a two-packet Burst, where no packets are lost in the uplink direction. The delay, jitter and data drops for both uplink and downlink ITS traffic, and video traffic are below the benchmarks of vehicular applications. Thus, the results indicate that the proposed heterogeneous system offers acceptable performance that meets the requirements of the different vehicular applications. All simulations are conducted on OPNET Network Modeler and results are subjected to a 95% confidence analysis

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

Cognitive radio-enabled Internet of Vehicles (IoVs): a cooperative spectrum sensing and allocation for vehicular communication

Internet of Things (IoTs) era is expected to empower all aspects of Intelligent Transportation System (ITS) to improve transport safety and reduce road accidents. US Federal Communication Commission (FCC) officially allocated 75MHz spectrum in the 5.9GHz band to support vehicular communication which many studies have found insufficient. In this paper, we studied the application of Cognitive Radio (CR) technology to IoVs in order to increase the spectrum resource opportunities available for vehicular communication, especially when the officially allocated 75MHz spectrum in 5.9GHz band is not enough due to high demands as a result of increasing number of connected vehicles as already foreseen in the near era of IoTs. We proposed a novel CR Assisted Vehicular NETwork (CRAVNET) framework which empowers CR enabled vehicles to make opportunistic usage of licensed spectrum bands on the highways. We also developed a novel co-operative three-state spectrum sensing and allocation model which makes CR vehicular secondary units (SUs) aware of additional spectrum resources opportunities on their current and future positions and applies optimal sensing node allocation algorithm to guarantee timely acquisition of the available channels within a limited sensing time. The results of the theoretical analyses and simulation experiments have demonstrated that the proposed model can significantly improve the performance of a cooperative spectrum sensing and provide vehicles with additional spectrum opportunities without harmful interference against the Primary Users (PUs) activities

Enhanced snr-based admission control algorithm for vehicular ad-hoc network

Vehicular Ad-hoc Network (VANET) becomes a fundamental subcategory of mobile ad-hoc networks that provides vehicles to communicate with each other and with roadside infrastructure smartly. Data traffic in VANET can be categorized into safety and non-safety, where safety is a very critical point and non-safety is related to entertainment. Various VANET performance challenges are considered in terms of Quality of Service (QoS) which cause performance degradation as performance anomaly where high rates of vehicles wait for the low rates of vehicle transmitting time and starvation problem where some vehicles cannot transfer their data. Three main achievements have been accomplished. Starting with the impact of the increasing vehicle speed on performance anomaly problem consequences has been investigated. Followed by high-speed effects on data delivery is illustrated and how 802.11p has outperformed 802.11 in terms of data delivery is also demonstrated. Lastly, starvation problem is investigated where results showed increased data loss when vehicle nodes unable to deliver data correctly. Finally, a QoS-aware Signal to Noise Ratio (SNR) admission control mechanism (QASAC) is proposed to handle the performance anomaly problem while maintaining the QoS levels for high and low traffics. This can result in wasting throughput and cause data loss. The investigation results show that 802.11p has enhanced the number of dropped packets up to 70%. Also, the 802.11p end to end delay has decreased up to 12% less than the results of the 802.11 MAC protocol. The packet delivery ratio has been enhanced by up to 41% by 802.11p. The starvation problem investigation phase shows that 802.11p perform better than 802.11 which mainly affected by the increased speed of the vehicle. QASAC assigned different SNR values to different vehicles group based on the sending SNR values and in each group. Unlike recently proposed admission control in VANET networks, the proposed architecture differentiate between both high priority and low priority traffic QASAC has been compared against the latest SNR based admission control mechanism. QASAC has enhanced the performance of data delivery up to 23% in terms of data dropping rates for high priority traffic

DSRC Versus LTE-V2X: Empirical Performance Analysis of Direct Vehicular Communication Technologies

Vehicle-to-Vehicle (V2V) communication systems have an eminence potential to improve road safety and optimize traffic flow by broadcasting Basic Safety Messages (BSMs). Dedicated Short-Range Communication (DSRC) and LTE Vehicle-to-Everything (V2X) are two candidate technologies to enable V2V communication. DSRC relies on the IEEE 802.11p standard for its PHY and MAC layer while LTE-V2X is based on 3GPP’s Release 14 and operates in a distributed manner in the absence of cellular infrastructure. There has been considerable debate over the relative advantages and disadvantages of DSRC and LTE-V2X, aiming to answer the fundamental question of which technology is most effective in real-world scenarios for various road safety and traffic efficiency applications. In this paper, we present a comprehensive survey of these two technologies (i.e., DSRC and LTE-V2X) and related works. More specifically, we study the PHY and MAC layer of both technologies in the survey study and compare the PHY layer performance using a variety of field tests. First, we provide a summary of each technology and highlight the limitations of each in supporting V2X applications. Then, we examine their performance based on different metrics