Modern vehicles are equipped with wireless communication technologies, allowing them to communicate with each other and forming large self-organized ad hoc networks (or vehicular ad hoc networks (VANETs)). VANETs, while promising new approaches for improving road safety, require privacy of vehicles (or drivers) to be protected from a variety of threats. Although pseudonym schemes have provided a promising solution at the upper layers, privacy attacks could still be carried out from medium access control (MAC) layer. In this paper, we first introduce a new MAC layer context linking attack, which could link the old and new pseudonyms of a vehicle by analyzing its transmission characteristics. To deal with the attack, we propose a time division multiple access based MAC-layer-Attack-Resistant Pseudonym (MARP) scheme. Unlike traditional approaches that design the MAC protocols and pseudonym schemes separately, MARP allows vehicles to change their transmission slots and pseudonyms collaboratively. Thus, the unlinkability is guaranteed. Taking the pseudonym age, anonymity set size and time-to-confusion as the location privacy metrics, we derive an analytical model to quantify location privacy achieved in MARP. The analytical model is general to be applied for other pseudonym schemes. Extensive simulation results have validated the analytical model, showed that MARP can resist the MAC context linking attack and guarantee location privacy and efficient transmission for vehicles in VANETs.

Pseudonyms have been adopted to preserve identity privacy of nodes in distributed networks. Frequent and unlinkable changes of pseudonyms need to be enabled by having at least k nodes change together to confuse potential eavesdroppers. Existing approaches either depend on the coordination from central controllers, or involve interactive signaling between the nodes. This can potentially compromise privacy. This paper proposes a fully uncoordinated approach to change pseudonyms in distributed networks, where each node uses a pseudonym until its expiration and then changes after a random delay. We develop a new model to analyse the time-varying population of changing pseudonyms. Critical conditions are analytically established, under which individual nodes can independently change their pseudonyms while their identity privacy is preserved. The conditions are validated by illustrative examples. Corroborated by simulations, the accuracy of the analytical model improves, as the number of nodes increases. The analysis confirms that, the k-anonymity can be achieved at a negligible throughput loss in the case of large networks.

In vehicular ad hoc networks (VANETs), safety messages must be protected for location privacy. Pseudonym schemes have provided a promising solution. However, attacks could still be carried out from the medium access control (MAC) layer. In this paper, we present a new MAC semantic linking attack that links the new and old pseudonyms by analyzing the vehicles' transmission patterns in the MAC layer, even if they change pseudonyms simultaneously. To deal with the attack, a MAC layer aware pseudonym (MAP) scheme is proposed. The MAP scheme is compatible with the standard and coordinates each vehicle to access the wireless medium in a time- slotted manner. In MAP scheme, vehicles change pseudonyms and slot utilization pattern consistently. The interactive influence between the pseudonym changing and safety message transmission is evaluated. Taking the pseudonym age, anonymity set size, time-toconfusion and packet delivery ratio as the performance metrics, extensive simulation results have verified that the MAP scheme can improve the location privacy and enhance transmission efficiency in VANETs.

Communication security is one of the most significant issues to draw people's attention in vehicular ad-hoc networks (VANETs). To prevent from malicious nodes and ensure the confidence and integrity of the messages, vehicles have to authenticate each other and support message signature and encryption. As the most prospective approaches, though the generally accepted wireless access for vehicular environment (WAVE) specifications have standardized the security algorithms to exchange the confidential data between vehicles, few of systems consider two technical aspects of signature and encryption together and implement on the real on-board unit (OBU). In this paper, a WAVE based secured vehicular communication system has been developed and WAVE security algorithms ECDSA and ECIES have been implemented to enhance communication security. The certificate authority (CA) has been introduced to the algorithms for authentication and preventing from the malicious nodes. The alternative security levels have been designed according to the different types of messages. Considering the execution time and communication cost of the constituent steps, real-world test has been conducted in our proposed application scenarios to manifest how security procedures affect the communication performance. The results have attested that the system in different security levels can achieve a secure data transmission with no effect on communication.

Many broadcast protocols have been proposed in Vehicular ad-hoc Network (VANET) for safety applications and traffic efficiency. GeoBroadcast, which the sender sends information to the geographical area, has been standardized by the ETSI Technical Committee ITS. The routing protocol is a key technology satisfying communication requests of high reliability, low delay and universality for GeoBroadcast. However, there are few implementation and field test of routing protocol. This paper proposes a Received Signal Strength Indicator (RSSI) based Omni-Directional Routing (ROR) Algorithm. This protocol based on the combination of two protocols: the Greedy Forwarding (GF) that is a sender-based protocol, and the Contention-Based Forwarding (CBF) that is a receiver-based protocol. Furthermore, ROR takes RSSI, driving direction and dynamic scene into account. Meanwhile we conduct extensive field tests with more than twenty vehicles to evaluate the performance of vehicle communication in terms of Packet Loss Rate (PLR), Node Coverage Ratio (NCR) and Average End-to-End Delay (E2ED). By comparing the performance of CBF and Advanced Forwarding protocol with the ROR, ROR in real vehicle's environment has higher NCR and lower E2ED, in particular when the topology of the vehicles changes frequently in the target area.

In this paper, we propose a hierarchical architecture based on software defined networking (SDN) to manage the physical resources in vehicular ad-hoc networks (VANETs), namely sdnMAC. First of all, a novel roadside unit (denoted by ROFS) is designed, which is an OpenFlow switch equipped with a wireless interface. Then, a hierarchical architecture is proposed for sdnMAC, consisting of two tiers, one is the management of the ROFSs by the Controller, the other is management of vehicles by ROFSs. Due to the cooperative share of slots information, sdnMAC can provide pre-warning of collisions and agility to topology change and varying densities of vehicles.

Advertising among vehicles has become popular with the proliferation of vehicular ad-hoc networks (VANETs). Since the price of the advertisements broadcast in such networks decay over time, distributing advertisements with a high price value to more private vehicles can generate more revenues to the sellers. In this paper, we consider a bus-based priced advertising scenario in a VANET, in which the buses act as the sources of advertisements and broadcast advertisements to private vehicles running within their communication range. Meanwhile, in the area where no bus exists, private vehicles share their advertising segments. The manner in which the buses and the private vehicles distribute and share advertisements in the network so as to draw the largest benefit is addressed in our formulated problem. To solve this problem, a bus-based priced advertisement dissemination scheme dubbed Bus-Ads is proposed by using coalition formation game. First, a bus-broadcast method is presented to enable each bus to distribute the priced advertising segments with the largest potential benefit to surrounding private vehicles. Second, we apply coalition formation game to guide private vehicles to construct broadcast coalitions for efficient advertisement sharing. Simulation results demonstrate that our proposed Bus-Ads method can achieve about twice the total benefits compared with that of the non-coalition-based approach.

Compared with the CSMA based MAC protocols, the slotted reservation solutions could be more adaptable for VANETs. However, the high mobility and mobile hidden terminal (MHT) issues in vehicular environments cause a challenge of efficient and scalable slotted scheduling for TDMA MAC protocols. This paper proposes a novel near collision free reservation (CFR) MAC which is based on a recent VeMAC protocol to provide near collision free scheduling and address the mobile hidden terminal issue in VANETs. In former distributed TDMA MAC proposals like VeMAC, on the control channel of DSRC communication system, each vehicle randomly reserves dedicated time slots. However, the slot reservation of CFR MAC is more structural, based on the driving status and traffic flow of each vehicle. The performance of CFR MAC is verified via simulations and comparisons with IEEE 802.11p and VeMAC to demonstrate that superiority of CFR MAC.