After a decade of research and technology development, road cooperative systems based on vehicle-to-vehicle and vehicle-to-roadside infrastructure communication are currently in a trial phase. Major field operational tests (FOTs) are carried out to verify the operation of cooperative systems in real environments and assess the impact of applications on road safety, traffic efficiency as well as driver behavior and user satisfaction. Standards to achieve interoperability are developed and a potential introduction of a cooperative system is prepared. An FOT is exposed to various requirements from research, standards and deployment that are -- at least partially -- adverse to each other. We study the dependencies for the case of the DRIVE~C2X project, a pan-European FOT for cooperative system. The paper puts the technologies used in the FoT, particularly focusing on communication, into the context of research activities for cooperative systems. We show that the FOT is based on technologies for a minimal cooperative system that is ready to be introduced and sustainably deployed. Further, we identify research concepts and technologies that did not find their way into the basic cooperative system yet and discuss potential directions for future enhancement of the minimal system.
The detection of potential collisions between vehicles is one of the main functionalities of Vehicular Ad-Hoc Networks (VANETs). Vehicles periodically exchange beacon messages by using wireless communication. From the obtained information the receiver calculates the collision probability by predicting the potential movement of every neighbor. Due to the highly dynamic movement of vehicles the accuracy of a prediction is mainly related to the detailed knowledge about the sender. However, as wireless communication suffers from interference due to a saturated communication channel, the context information within a beacon has to be limited. To accomplish this issue while achieving highly accurate predictions, we propose a scalable sender-centric prediction approach based on the available sender's context information.
Wireless vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication holds great promise for significantly reducing the human and financial costs of vehicle collisions. A common characteristic of this communication is the broadcast of a device's core state information at regular intervals (e.g. a vehicle's speed and location, or a traffic signal's state and timing). The aggregate of these uncoordinated broadcasts will lead to channel congestion under dense traffic scenarios, with a resulting reduction in the effectiveness of the collision avoidance applications making use of the transmitted information. Active congestion control using distributed techniques is a topic of great interest for establishing the scalability of this technology for deployment. This paper defines a new congestion control algorithm that can be applied to the message rate of devices in this vehicular environment. While other published approaches rely on binary control, the LInear MEssage Rate Integrated Control (LIMERIC) algorithm takes advantage of full precision control inputs that are available on the wireless channel. The result is provable convergence to fair and efficient channel utilization in the deterministic environment, under simple criteria for setting adaptive parameters. This "perfect" convergence avoids the limit cycle behavior inherent to binary control. We also discuss several practical aspects associated with implementing LIMERIC, including: guidelines for the choice of system parameters to obtain desired utilization outcomes, a gain saturation technique that maintains robust stability under all conditions, convergence with asynchronous updates, and the implications of measurement noise for statistical properties of convergence. The paper illustrates key analytical results using MATLAB numerical results, and employs standard NS-2 simulations to demonstrate the performance of LIMERIC in several high density scenarios.
Collision-free transmission is important to achieving reliable and delay-bounded wireless communication, which is mandated by many safety-related applications in vehicular ad-hoc networks (VANETs). Contention-based MAC protocols, e.g., 802.11p, are prone to transmission collisions due to the absence of node coordination, while traditional TDMA-based protocols have difficulty coping with fast-changing network topology. We propose Reservation Protocol (RP) - a near collision-free MAC protocol that is specifically designed for VANETs. By disseminating position beacons, nodes in RP predict the trajectories of their neighbors and anticipate possible transmission collisions. Reservation messages are exchanged among rival nodes in order to avoid potential conflicts. Simulation-based evaluation shows that at the cost of longer average medium access delay, the collision probability in RP protocol is considerably lower than 802.11p in various load scenarios.
Visible Light Communication (VLC) is a fast-growing technology to provide data communication using low-cost and omni-present LEDs and photodiodes. In this paper, we examine the key proper-ties in enabling vehicular VLC (V2LC) networks as follows. We first develop a custom V2LC research platform on which we expe-rimentally evaluate the feasibility of a V2LC system under working conditions in relation to link resilience to visible light noise and interference. Our experiments show that a receiver's narrow field-of-view angle makes V2LC resilient to visible light noise from sunlight and legacy lighting sources as well as to interference from active VLC transmitters. Then, by leveraging our experimental characterization as the basis of modifications to our simulator, we examine V2LC's performance in providing network services for vehicular applications. Our key findings include: (i) in dense vehicular traffic conditions (e.g., urban highway during peak hours), V2LC takes advantage of multiple available paths to reach vehicles and overcomes the effects of packet collisions; (ii) in the presence of a visible light blockage in traffic, V2LC can still have a significant number of successful transmissions by opportunistically using dynamic inter-vehicle gaps.
Wireless vehicular networks have highly complex and dynamic channel state leading to a challenging environment to maintain connectivity and/or achieve high levels of throughput while also satisfying latency requirements of diverse vehicular applications. Adaptation over a large parameter space such as multiple frequency bands, novel modulation and coding schemes, and routing protocols is important in achieving good performance in this challenging setting. Vehicles now include a plethora of sensors which can be used to establish a clearer notion of the environmental context. However, while it is well understood that wireless performance greatly depends on this contextual information, protocols that leverage this information to improve wireless performance have yet to be fully developed. In this work, we will lay a foundation for developing context-aware intelligence to interface with existing adaptation protocols at multiple layers of the network stack. The core of this system consists of a context-aware collection, decision, and distribution (C2D2) engine. We give a brief overview of the architecture, design, and operation of the C2D2 engine.
Safety applications are among the key drivers in VANET research. Their study is complex as it encompasses different disciplines, from wireless networking to car dynamics, to drivers' behavior, not to mention the economic and legal aspects. This work presents a simulative study of emergency braking applications tackled by embedding a mobility, cars' dynamic, and driver's behavior model into a detailed networking simulator (ns-3). The results, derived both at the network and at the application level, capture correctly the interactions of the communications and protocols with the car's adaptive cruise control system and the driver's behavior for cars that are not equipped with communication devices. The paper presents in detail the improvements we contribute in simulation techniques and model completeness. It introduces a novel and easy message aggregation technique to empower message re-propagation while controlling the network load during the peak due to the emergency braking. Finally it discusses the effectiveness of such applications as a function of the market penetration rate, showing that even cars that are not equipped with communication devices benefit from the smoother and earlier reaction of those cars that can communicate and whose adaptive cruise control implements a correct deceleration strategy.
Communication performance in VANETs under high channel load is significantly degraded due to packet collisions and messages drops, also referred to as local channel congestion. So far, research was focused on the control of transmit power and the limitation of the messages rate to mitigate the effects of high load. Few attention has been paid to the carrier sensing setup, i.e controlling WHEN the channel is indicated as clear. In previous work, we identified that the Clear Channel Assessment (CCA) as part of the carrier sensing is a very efficient way of controlling the spatial reuse under high load. The CCA threshold determines at which received power level the channel is sensed busy. In this paper, we propose a stepwise CCA Threshold Adjustment (CTA) depending on how long the packet has been waiting already for medium access. This basic and robust approach mitigates significantly the problem of local message queue drops and hence local congestion. The simulation study confirms the reduction of the average and maximum medium access delay as well as the prevention of message queue drops. Even under inaccurate CCA thresholds among the vehicles, fairness in medium access can be maintained by using CTA. In all cases, the awareness of each vehicle is dramatically improved within the safety-critical area of each vehicle.
Broadcasting is the primary way of exchanging time-sensitive information in VANETs. However, contiguous loss of broadcasts among vehicles may lead to situations where a vehicle has not heard from a neighbor for extensive periods of time. The goal of this work is to provide an analysis of this invisible neighbor problem and the impact the selected transmission range and packet generation rate of a vehicle have on the occurrences of this problem. Specifically, this work studies this problem in the context of application-specific safety requirements, i.e., the goal is to minimize the number of invisible neighbors within a certain region of interest (ROI), whose size depends on the type of safety application. Extensive simulation results indicate that the combination of relatively large transmission ranges and small packet generation rates (e.g., 2-4 packets/s) lead to the lowest number of invisible neighbors.
We propose a design methodology to determine the optimal transmission parameters for delay-critical safety applications in vehicular ad hoc networks. We develop a model to characterize the delay requirements needed to prevent rear-end collisions. By adopting a stochastic geometry framework to simultaneously address multi-user interference, path loss, and fading, we then analytically derive the transmission rate, range, and channel access probability of the nodes that satisfy the delay requirement at a target success probability.
Recently, there has been much interest in using radiometric identification (also known as wireless fingerprinting) for the purposes of authentication. Previous work has shown that using radiometric identification can discriminate among devices with a high degree of accuracy when simultaneously using multiple radiometric characteristics. Additionally, researchers have noted the potential for wireless fingerprinting to be used for more devious purposes, specifically that of privacy invasion or compromise. In fact, any such radiometric characteristic that is useful for authentication is useful for privacy compromise. To date, there has not been any proposal of how to mitigate such privacy loss for many of these radiometric characteristics, and specifically no such proposal for how to mitigate such privacy loss in a low-cost manner. In this paper, we investigate some limits of an attacker's ability to compromise privacy, specifically an attacker that uses a transmitter's carrier frequency. We propose low-cost mechanisms for mitigating privacy loss for various radiometric characteristics. In our development and evaluation, we specifically consider a vehicular network (VANET) environment. We consider this environment in particular because VANETs will have the potential to leak significant, long-term information that could be used to compromise drivers' personal information such as home address, work address, and the locations of any businesses the driver frequents. While tracking a vehicle using visually observable information (e.g., license plates) to obtain personal information is possible, such means require line-of-sight, whereas radiometric identification would not. Finally, we evaluate one of our proposed mechanisms via simulation. Specifically, we evaluate our carrier frequency switching mechanism, comparing it to the theory we develop, and we show the precision with which vehicles will need to switch their physical layer identities given our parameterization for VANETs.
This paper presents a set of experiments, performed using an IEEE 802.11p physical layer implementation based on the open-source ath5k driver, in both line of sight (LOS) and non-line of sight (NLOS) conditions. The results are compared against theoretical models and simulation of the same scenarios with proper propagation and channel models. The communication range in LOS can reach values larger than 1Km, while in NLOS scenarios, this communication range is decreased to the order of hundreds of meters.
Inter-vehicle communication with the objective to increase safety and efficiency of our transportation network has been studied extensively in the last few years. However, we are still struggling in answering the fundamental question of to which extent can inter-vehicle communication improve our wide-area transportation network that consists of more than several cities?. In this position paper we discuss from a methodological point of view and by analyzing recent trends how the VANET community could move forward with respect to evaluation methodologies. Based on our observations, we argue that the vehicular networking community might need to extend its perspective -- from bits and packets towards information-centric models -- when assessing efficiency gains in large scale scenarios, thereby providing a multi-scale approach as it is done in various disciplines. We further believe that the community should join forces to convert existing results as well as current and upcoming measurements to provide information-centric models of inter-vehicular communication. We finally propose a modeling approach that could serve as a foundation for future joint efforts and which might take us one step closer to the answer of the fundamental question stated above.
In this paper we present the Distributed Construct Underlying Topology (D-CUT) algorithm, a self-organized algorithm aim to provide efficient, and reliable hierarchical topology by minimizing the interference between network participants. The D-CUT algorithm produces a geographically optimized clustering of the network, by grouping dense and consecutive nodes into clusters which are separated by maximally possible gaps. This type of clustering allows strong connections between cluster members and reduces the inter cluster interference. In addition, the awareness of each vehicle to the composition of its own cluster, and the location of its members enables a very intuitive and straightforward scheme for organizing and coordinating the vehicular network to achieve congestion control and efficient medium access performance. We show theoretically provable bounds for the algorithm performance as well as simulation study that supports our results.
Environment preservation has become a prominent issue around the world. As traditional internal combustion engine (ICE) vehicles have been major contributors of air pollution, electric vehicles (EVs) are gaining popularity. However, due to the limited electricity supply of battery pack, EVs need to be charged frequently and each charge takes long time. This may degrade travel efficiency and driver comfort. To address this issue, this paper aims to minimize charging waiting time through intelligently scheduling charging activities spatially and temporally. A theoretical study has been conducted to formulate the waiting time minimized charging scheduling problem and derive a performance upper bound (i.e., the theoretical lower bound of charging waiting time). Based on the insights discovered from the theoretical analysis, a practical distributed scheme has been proposed. Extensive simulation results verify that the proposed design can achieve a waiting time near the theoretical lower bound.
The periodic transmission of status updates by all vehicles in a vehicular network represents a service primitive that forms the basis for a lot of envisioned applications, in particular safety related ones. Due to the limited resources that a wireless communication system like IEEE 802.11p is capable to provide, the question raises how much data each node may provide to the system such that the information can still be delivered with the quality of service required by the applications. In this work, local broadcasts capacity is introduced together with straight-forward upper and lower bounds, and estimated by extensive detailed simulations. We show that the ratio of simulation-based capacity estimates and the upper bound is similar for a wide range of system configurations and that the communication system may only be used up to 22% of its upper capacity bound such that service requirements can still be fulfilled.
A large portion of vehicular safety applications require reliable broadcasting. IEEE 802.11p has been shown to have doubtful performance in this aspect [2]. In [1] we have proposed a Dynamic Channel Reservation (DCR) protocol to provide low packet loss probability for vehicular communication by exploiting the unique structure of vehicular networks (VANET), and employing a dynamic TDMA mechanism. In this work, we address the situation when there is asymmetric traffic demands from vehicles on the two sides of a roadway, under which condition the throughput performance of unmodified DCR would be significantly degraded, due to its static partition and allocation of TDMA channels to each side of the road. We therefore augment DCR by designing a protocol to dynamically allocate channels to the two sides of the road according to their time-varying traffic demands. Our design replaces the need for vehicles on the two sides to contend for each TDMA channel with a mechanism for them to contend for the boundary between the contiguous sets of channels allocated to the two sides. Preliminary ns-2 simulations show that our design enhances DCR and delivers low packet loss rate and higher throughput regardless of the level of asymmetry of the traffic demand
Path loss and delay profile models for ITS applications based on the measured data at 700MHz band are presented.
