<p>Accident statistics indicate that every year a significant number of casualties and extensive property losses occur due to traffic accidents. Consequently, efforts are directed towards developing passive and active safety systems that help reduce the severity of crashes, or prevent vehicles from colliding with one another. To develop these systems, technologies such as sensor systems, computer vision and vehicular communication have been proposed. Safety vehicular communication is defined as the exchange of data between vehicles with the goal of providing in-vehicle safety systems with enough information to permit detection of traffic dangers. Inter-vehicle communication is a key safety technology, especially as a complement to other technologies such as radar, as the information it provides cannot be gathered in any other way. However, due to the specifics of the traffic environment, the design of efficient safety communication systems poses a series of major technical challenges.</p><p>In this thesis we focus on the design and development of a safety communication system that provides support for active safety systems such as collision warning and collision avoidance. We begin by providing a method for designing the support system for active safety systems. Within our study, we investigate different safety aspects of traffic situations. For performing traffic investigations, we have developed ECAM, a temporal reasoning system for modeling and analyzing accident scenarios.</p><p>Next, we focus on the communication system design. We investigate approaches that can be applied to implement safety vehicular communication, as well as design aspects of such systems, including networking techniques and transmission procedures. We then propose a new solution for vehicular communication in the form of a distributed communication protocol that allows the vehicles to organize themselves in virtual clusters according to their common interest in traffic safety. To disseminate the information used for organizing the network and for assessing dangers in traffic, we develop an anonymous context-based broadcast protocol. This protocol requires the receivers to determine whether they are the intended destination for sent messages based on knowledge about their current situation in traffic. This communication system is then augmented with a reactive operation mode, where warnings can be issued and forwarded by vehicles. A vehicular communication platform that provides an implementation framework for the communication system, and integrates it within a vehicle, is also proposed. Experiments have been conducted, under various conditions, to test communication performance and the system’s ability to reduce accidents. The results indicate that that the proposed communication system can efficiently provide the exchange of safety information between vehicles.</p>

Accident statistics indicate that every year a significant number of casualties and extensive property losses occur due to traffic accidents. Consequently, efforts are directed towards developing passive and active safety systems that help reduce the severity of crashes, or prevent vehicles from colliding with one another. To develop these systems, technologies such as sensor systems, computer vision and vehicular communication have been proposed. Safety vehicular communication is defined as the exchange of data between vehicles with the goal of providing in-vehicle safety systems with enough information to permit detection of traffic dangers. Inter-vehicle communication is a key safety technology, especially as a complement to other technologies such as radar, as the information it provides cannot be gathered in any other way. However, due to the specifics of the traffic environment, the design of efficient safety communication systems poses a series of major technical challenges. In this thesis we focus on the design and development of a safety communication system that provides support for active safety systems such as collision warning and collision avoidance. We begin by providing a method for designing the support system for active safety systems. Within our study, we investigate different safety aspects of traffic situations. For performing traffic investigations, we have developed ECAM, a temporal reasoning system for modeling and analyzing accident scenarios. Next, we focus on the communication system design. We investigate approaches that can be applied to implement safety vehicular communication, as well as design aspects of such systems, including networking techniques and transmission procedures. We then propose a new solution for vehicular communication in the form of a distributed communication protocol that allows the vehicles to organize themselves in virtual clusters according to their common interest in traffic safety. To disseminate the information used for organizing the network and for assessing dangers in traffic, we develop an anonymous context-based broadcast protocol. This protocol requires the receivers to determine whether they are the intended destination for sent messages based on knowledge about their current situation in traffic. This communication system is then augmented with a reactive operation mode, where warnings can be issued and forwarded by vehicles. A vehicular communication platform that provides an implementation framework for the communication system, and integrates it within a vehicle, is also proposed. Experiments have been conducted, under various conditions, to test communication performance and the system’s ability to reduce accidents. The results indicate that that the proposed communication system can efficiently provide the exchange of safety information between vehicles.

Vehicular Ad-Hoc Network (VANET)s are a key element of Intelligent Transport System (ITS)s. One of the challenges in VANETs is dealing with awareness and congestion due to the high amount of messages received from the vehicles in communication range. As VANETs are used in critical applications, congestion on the receiver side caused by the buffering of the packets is a safety hazard. In this thesis, we propose a stream-wise queuing system on the receiver side and show how it improves the timeliness of the messages received and main- tains the awareness of the system in a congestion situation.

Vehicular communication has been an emerging topic among current wireless research. The vehicular communication can be classified to Inter-Vehicle Communication (IVC) and Road-to-Vehicle Communication (RVC). IVC and RVC support applications mainly on two aspects: safety applications aiming to reduce dangers on the road, and data applications aiming to provide information and entertainment to people on traveling. Vehicles nearby form Vehicular Ad hoc Networks (VANETs) without any fixed infrastructures. Due to the characteristics of vehicular networks such as quickly changing and unstable network topology, IVC has special requirements to the network protocols. Several MAC protocols have been appeared or improved based on previous work for IVC. But these protocols are designed either for QoS guaranteed data service or for reliable message broadcast. There is not a protocol including both application requirements and inexpensive to implement as well. MAC protocol for vehicular communication hasn’t been finalized. In this thesis, an overlay token ring protocol (OTRP) is proposed which can work on MAC layer with broadcast function and taking into the IVC features into consideration. In OTRP, vehicles are grouped to overlapped rings with a token passed in each ring as the sole right for transmission. The ring is dynamically updated in a distributed manner based on smart algorithm at each node. OTRP provides bounded delay by assigning maximum token holding time for each node. It also reduces collisions by decreasing the number of contention nodes by times of ring size. Fair and high throughput is obtained as well. Furthermore, it provides reliable and prompt broadcast of emergency messages by pre-emptively transmitting while applying the token as an acknowledgement. The time nodes reliably receive the message is within limit. Theoretical analysis is provided and simulation results are given to evaluate the performance of OTRP under saturated traffic conditions both in safety and data applications.

Vehicular communication has been an emerging topic among current wireless research. The vehicular communication can be classified to Inter-Vehicle Communication (IVC) and Road-to-Vehicle Communication (RVC). IVC and RVC support applications mainly on two aspects: safety applications aiming to reduce dangers on the road, and data applications aiming to provide information and entertainment to people on traveling. Vehicles nearby form Vehicular Ad hoc Networks (VANETs) without any fixed infrastructures. Due to the characteristics of vehicular networks such as quickly changing and unstable network topology, IVC has special requirements to the network protocols. Several MAC protocols have been appeared or improved based on previous work for IVC. But these protocols are designed either for QoS guaranteed data service or for reliable message broadcast. There is not a protocol including both application requirements and inexpensive to implement as well. MAC protocol for vehicular communication hasn’t been finalized. In this thesis, an overlay token ring protocol (OTRP) is proposed which can work on MAC layer with broadcast function and taking into the IVC features into consideration. In OTRP, vehicles are grouped to overlapped rings with a token passed in each ring as the sole right for transmission. The ring is dynamically updated in a distributed manner based on smart algorithm at each node. OTRP provides bounded delay by assigning maximum token holding time for each node. It also reduces collisions by decreasing the number of contention nodes by times of ring size. Fair and high throughput is obtained as well. Furthermore, it provides reliable and prompt broadcast of emergency messages by pre-emptively transmitting while applying the token as an acknowledgement. The time nodes reliably receive the message is within limit. Theoretical analysis is provided and simulation results are given to evaluate the performance of OTRP under saturated traffic conditions both in safety and data applications.

Vehicular ad hoc networks (VANETs) are instances of mobile ad hoc networks with the aim to enhance the safety and efficiency of road traffic. The basic idea is to allow arbitrary vehicles to broadcast ad hoc messages (e.g. traffic accidents) to other vehicles and remind drivers to change their route immediately or slow down to avoid dangers. However, some concerns of security and privacy are also raised in this environment. Messages should be signed and verified before they are trusted while the real identities of vehicles should not be revealed to guarantee the source privacy, but it still has to be traceable to prevent any abuse of VANETs (e.g. sending a fake message). Many related works have been presented in the literature so far. They can be generally divided into two constructions, where one is based on pseudonymous authentication and the other is based on group signatures. However, both of the two constructions have some drawbacks. Consequently, in this thesis, we come up with a provably secure and strong privacy preserving protocol based on the blind signature technique to guarantee privacy and fulfill other essential security requirements in the vehicular communication environment. Besides, compared with other similar works, we offer an efficient tracing mechanism to trace and revoke the vehicles abusing the VANETs. In addition, considering the real environment, we also provide simulation results to show that our scheme is more practical, efficient and suitable for VANETs under a real city street scenario with high vehicle density. Finally, we also demonstrate the security of the proposed protocol by formal proofs.

Vehicular communication systems rely on temporary anonymous identities, i.e. pseudonyms, in order to establish security and at the same time avoid the possibility of tracking vehicles. If a vehicle uses only one pseudonym, an adversary would be able to follow the vehicle by observing and linking messages, signed under that pseudonym. Therefore, the vehicles acquire a set of pseudonyms from the VPKI, i.e. infrastructure of the communication system, and switches pseudonym frequently. If a vehicle would be unable to acquire these pseudonyms, it would not be able to utilize the communication system without compromising its privacy. A vehicle is able to create its own pseudonyms using group signatures, i.e. the so-called Hybrid scheme. However, a pseudonym issued by the VPKI and a pseudonym created with a group signature would look different to an observer. If only one vehicle used pseudonyms created with group signature, it would easily be singled out and tracked. This thesis proposes a solution to this problem, but not the broader problem of linking messages by other means, e.g. the content of the message. In the solution, a vehicle is able to generate its own pseudonyms, using the Hybrid scheme, and make them unlinkable at the cost of computational overhead for itself and the vehicles around it, since group signatures are costly. The vehicle achieves this by aligning the lifetime of the pseudonym with other pseudonyms and asking neighboring vehicles to alternate randomly between using pseudonyms issued by the VPKI and pseudonyms created with group signatures. This alternation by neighboring vehicles decreases the linkability of pseudonyms created with group signature without increasing the linkability of pseudonyms created by the VPKI. This results in a trade off between reasonable computational overhead and acceptable linkability for pseudonyms. A short paper, presenting the scheme and results of this thesis, has been accepted to the IEEE Vehicular Networking Conference in Torino, Italy, 27-29 November, 2017 [1]. / Fordonskommunikation utnyttjar temporära identiteter, dvs. pseudonymer, för att etablera säkerhet och samtidigt undvika möjligheten att spåra fordon. Om ett fordon skulle använda endast ett pseudonym så skulle en observatör kunna följa fordonet genom att observera och länka meddelanden signerade under det pseudonymet. Varje fordon erhåller därför ett set pseudonymer från kommunikationssystemet och byter pseudonym regelbundet. Om ett fordon inte kan erhålla dessa pseudonymer från systemet, så skulle fordonet inte kunna utnyttja kommunikationssystemet utan att förkasta sin integritet. Ett fordon skulle kunna skapa sina egna pseudonymer genom att använda gruppsignaturer, dvs. det så kallade Hybrid scheme. Problemet är att ett pseudonym som är erhållet från kommunikationssystemet och ett pseudonym som är genererat med en gruppsignatur, ser olika ut för en observatör. Om endast ett fordon skulle använda pseudonymer med gruppsignaturer, så skulle det enkelt filtreras ut och spåras. Den här avhandlingen föreslår en lösning på detta problem, men inte till det större problemet att länka meddelanden på andra sätt, exempelvis använda informationen i själva meddelandet. I lösningen kan fordonetgenerera egna pseudonymer, genom att använda gruppsignaturer, dvs. Hybrid scheme, och göra dem olänkbara till priset av extra beräkningstid för sig själv och fordonen omkring sig, eftersom gruppsignaturer är kostsamma. Fordonet uppnår det genom att synkronisera pseudonymernas livslängd med de andra pseudonymerna och fråga fordonen i närheten om de kan slumpmässigt växla mellan att använda pseudonymer från systemet och pseudonymer som de skapat med gruppsignaturer. Om fordon i närheten växlar mellan pseudonymer från systemet och pseudonymer genererade med gruppsignaturer så minskar länkbarheten av pseudonymer baserade på gruppsignaturer utan att öka länkbarheten av pseudonymer från kommunikationssystemet. Det resulterar i en avvägning mellan beräkningstid och acceptabel länkbarhet av pseudonymer. Ett konferens papper, som presenterar protokollet och resultatet av denna avhandling, har blivit accepterat till IEEE Vehicular Networking Conference i Torino, Italien, 27-29 November 2017 [1].

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第23549号 / 情博第779号 / 新制||情||133(附属図書館) / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 原田 博司, 教授 大木 英司, 准教授 山本 高至 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DGAM

Vehicle-related communications are a key application to be enabled by Fifth Generation (5G) wireless systems. The communications enabled by the future Internet of Vehicles (IoV) that are connected to every wireless device are referred to as Vehicle-to-Everything (V2X) communications. A major application of V2X communication systems will be to provide emergency warnings. This thesis evaluates Long-Term Evolution (LTE) and Dedicated Short Range Communications (DSRC) in terms of service quality and latency, and provides guidelines for design of cooperative LTE-DSRC systems for V2X communications. An extensive simulation analysis shows that (1) the number of users in need of warning has an effect on latency, and more so for LTE than for DSRC, (2) the DSRC priority parameter has an impact on the latency, and (3) wider system bandwidths and smaller cell sizes reduce latency for LTE. The end-to-end latency of LTE can be as high as 1.3 s, whereas the DSRC latency is below 15 ms for up to 250 users. Also, improving performance of systems is as much as important as studying about latency. One method to improving performance is using a better suitable antenna for physical communication. The mobility of vehicles results in a highly variable propagation channel that complicates communication. Use of a smart, steerable antenna can be one solution. The most commonly used antennas for vehicular communication are omnidirectional. Such antennas have consistent performance over all angles in the horizontal plane; however, rapidly steerable directional antennas should perform better in a dynamic propagation environment. A linear array antenna can perform dynamical appropriate azimuth pattern by having different weights of each element. The later section includes (1) identifying beam pattern parameters based on locations of a vehicular transmitter and fixed receivers and (2) an approach to find weights of each element of linear array antenna. Through the simulations with our approach and realistic scenarios, the desired array pattern can be achieved and array element weights can be calculated for the desired beam pattern. Based on the simulation results, DSRC is preferred to use in the scenario which contains large number of users with setup of higher priority, and LTE is preferred to use with wider bandwidth and smaller cell size. Also, the approach to find the controllable array antenna can be developed to the actual implementation of hardware with USRP. / Master of Science

The aim of this work is to show the effectiveness of techniques that allow a user to maintain its privacy and anonymity while participating in real word scenario. Users need to communicate with each other in many situations in order to share information. This creates the danger of the user’s privacy being breached and it can discourage users from taking active participation in any information sharing task. There are many real scenarios or application where users want to remain anonymous while having their communication secured. This is so in vehicular communication systems. Group signatures are versatile cryptographic tools that are suitable when we need security and privacy protection. A group signature scheme allows members of a group to sign messages on behalf of the group. Any receiver can verify the message validity but cannot discover the identity of the sender from the signed message or link two or more messages from the same signer. However, the identity of the signer can be discovered by an authority using a signed message. For this reason, Group Signature schemes were proposed in the context of vehicular communication systems. In this context, communication and computation overheads are critical. Thus, the focus of this thesis is to implement and compare different group signature schemes in terms of overhead introduced due to processing cost, and analytically evaluate their suitability for vehicular communication scenarios.