Bernhard Kloiber

Performance of CAM based safety applications using ITS-G5A MAC in high dense scenarios

ETSI ITS-G5 is the current vehicle-to-vehicle communication technology in Europe, which will be standardized by ETSI TC ITS1. It is based on IEEE 802.11p and therefore uses a CSMA/CA scheme for Media Access Control (MAC). In this paper we analyze the performance of Cooperative Awareness Message (CAM) based safety applications using the ETSI ITS-G5 MAC technology in a challenging scenario with respect to MAC issues: A suitable freeway segment with 6 lanes in each direction. The freeway scenario is thoroughly modeled and implemented in the well known ns-3 simulation environment. Based on this model, the paper shows the performance of CAM based safety applications under MAC challenging conditions. We provide a set of simulation results resting upon a particular performance metric which incorporates the key requirements of safety applications. Finally we analyze two concrete example scenarios to determine how reliable CAM based safety applications are in high dense traffic scenarios with respect to MAC issues.

Dice the TX power — Improving Awareness Quality in VANETs by random transmit power selection

Future safety-related vehicular applications require reliable information exchange provided by cooperative Vehicular Ad-hoc NETworks (VANETs). Although the vehicular WLAN standard IEEE 802.11p has been adapted to the challenging vehicular environment, it has not been adapted to the stringent communication requirements imposed by vehicular applications. In particular, broadcast transmissions are mostly periodic and initiated at common TX powers. This makes potential interferences recurring instead of spurious and lowers the performance of medium access for vehicular applications. In this paper, we propose to leverage recurring interferences by randomly selecting each TX power following a given probability distribution. Such randomization reduces the chances of recurring interferences, and the probability distribution provides control to the applications regarding the required Awareness Quality, in particular by providing a higher Awareness Quality at close range. This concept also reduces congestions by transmitting less at high distances. It is transparent to the applications, and manages to improve the Awareness Quality in a dense highway by a factor 2 to 20, yet at a factor 2 to 3 lower channel load.

Information-centric opportunistic data dissemination in Vehicular Ad Hoc Networks

This paper addresses the problem of efficient data dissemination in Vehicular Ad Hoc Networks (VANETs), which particularly suffer from changing densities in the network topology due to congested and sparse traffic on the roads. We present a new network layer protocol in the family of geographic network protocols, which makes use of distance and time information following a dissemination strategy to efficiently distribute messages adapting to the varying densities in VANETs. We have evaluated the protocol in different road density scenarios and its performance has been proved in comparison to two other recent protocols of the art.

Bayesian cooperative relative vehicle positioning using pseudorange differences

Forward collision warning systems, lane change assistants or cooperative adaptive cruise control are examples of safety relevant applications that rely on accurate relative positioning between vehicles. Current solutions estimate the position of surrounding vehicles by measuring the distance with a RADAR sensor or a camera system. The perception range of these sensors can be extended by the exchange of GNSS information between the vehicles using an inter-vehicle communication link. In this paper we analyze two competing strategies against each other: the subtraction of the absolute positions estimated in each vehicle and the differentiation of GNSS pseudoranges. The aim of the later approach is to cancel out correlated errors in both receivers and, thus, achieve a better relative position estimate. The theoretical analysis is backed with Monte-Carlo simulations and empirical measurements in real world scenarios. Further on, two Bayesian approaches that make use of pseudorange differences are proposed. In a Kalman Filter pseudorange and Doppler measurements are used to estimate the baseline between two vehicles. This is extended in a second filter using on-board inertial and speed sensors following a multisensor fusion approach. The performance is evaluated in both, a highway and an urban scenario. The multisensor fusion approach proves to be able to stabilize the baseline estimate in GNSS challenging environments, like urban canyons and tunnels.

Random Transmit Power Control for DSRC and its Application to Cooperative Safety

Cooperative safety applications require dedicated short-range communications (DSRC) to provide position-awareness of neighboring vehicles at a specific level of reliability, i.e., awareness-quality, up to a given distance, i.e., awareness-range. However, heavy communication loads negatively impact such awareness requirements due to communication impairments, ranging from strict capacity limitations of DSRC channels to correlated packet collisions due to periodic communication patterns. Transmission control strategies may adapt power or rate to control such impairments but risk missing the requirements of cooperative safety applications. In this paper, we design a new awareness control strategy by implementing a spatial awareness framework. Specifically, we adapt the distribution of the awareness-quality as a function of the awareness-range. Therefore, we first propose random transmit power control (RTPC), which manages to provide different levels of awareness-quality at different ranges, while mitigating correlated packet collisions by randomizing them in space. As RTPC is able to reduce the channel load, we secondly propose to combine RTPC with transmit rate control (TRC) and to benefit from the gained channel resources by subsequently increasing the update-rate and by implication, the quality of position-awareness. The spatial awareness control capability of RTPC+TRC has been evaluated through simulations. We discuss the influence of RTPC+TRC on cooperative safety applications exemplarily for the forward collision warning (FCW) application.

Slipstream cooperative adaptive cruise control — A conceptual ITS application for electric vehicles

The Electric Vehicle is seen to be one of the most important enablers for a more environmentally friendly mobility of people. Unfortunately, state of the art electric vehicles suffer from a series of problems, with facing a very limited traveling distance compared to gasoline vehicles being one of the most relevant ones. In this paper we present an approach how to reduce the energy consumption while traveling over longer distances by using the slipstream effect behind a vehicle ahead. We show how this can be implemented as a specialized form of cooperative adaptive cruise control, one of the innovative Intelligent Transportation System applications. The paper elaborates in detail on the reliability of the application from the perspective of the current ITS communication technology, by means of two example scenarios, and outlines also on other aspects of implementing Slipstream Cooperative Adaptive Cruise Control for electric vehicles.

Random transmit jitter against correlated packet collisions in vehicular safety communications

In Vehicular Safety Communication (VSC) vehicles periodically broadcast so called Cooperative Awareness Messages (CAM) to make neighboring vehicles being aware of their current status like position, speed and heading. Such periodic transmissions on top of the Dedicated Short Range Communication (DSRC) technology can cause temporal correlated (recurring) collisions, which increase the delay between consecutive awareness updates from a certain vehicle. In this paper we propose to add a controlled random jitter to the nominal CAM broadcast interval at the application/facilities layer. Thus, we aim for making temporal correlated packet collisions more uncorrelated in time and by implication significantly decrease the delay between consecutive CAM updates (update delay or inter-reception time). The benefit of our approach has been demonstrated by simulating a multi-lane highway scenario at different traffic/data load conditions. By adding a random transmit jitter we were able to reduce the amount of correlated collisions by more than factor 10, and by consequence to improve the update delay performance by up to two orders of magnitude.

Interoperability testing suite for C2X communication components

This paper presents a collection procedures to perform interoperability tests of C2X communication equipment. Following a cross layer approach, interoperability test purposes on radiocommunication equipment, networking layer algorithms, C2X applications and use cases are analyzed. Along with this analysis the main conclusions gathered from the execution of the proposed test cases on a concrete C2X prototype system will be presented.

Bigger is better — Combining contention window adaptation with geo-based backoff generation in DSRC networks

The vision of safer transportation is strongly driven by the introduction of Vehicular Safety Communications (VSC) to enable new cooperative safety applications. In highly dense traffic scenarios, however, the current Dedicated Short Range Communications (DSRC) technology is expected to face serious performance problems due to simultaneous transmissions making packets to collide with each other. In this paper, we first analyze the sources of packet collisions. The analysis reveals a significant amount of simultaneous transmissions as vehicles have chosen the same backoff counter, especially in the close vicinity, which is the most critical area with respect to safety. Based on these observations, we then introduce a new concept for DSRC backoff generation called geo-backoff. It implements two countermeasures: First, we increase the Contention Window (CW) to reduce the probability of simultaneous transmissions in general. Second, we exploit geographical information for generating the current backoff counter to further reduce the probability of packet collisions at short (critical) ranges. We analyze our concept from a traditional TX-RX perspective (latency) as well as an RX-centric perspective (update delay). The simulation results indeed have shown that geo-backoff is able to improve the communication performance, but the improvement is mainly dominated by just increasing the CW.