Jonathan Ledy

A survey of V2V channel modeling for VANET simulations

Most Vehicle to Vehicle (V2V) network protocols are evaluated by simulation. However in most network simulators, the physical layer suffers from a lack of realism. Therefore, realistic V2V channel modeling has become a crucial issue in Intelligent Transportation Systems (ITS) networks. V2V channels are known to exhibit specific features which imply the design of new simulation models. In this survey paper, we first recall the main physical features of such wireless time and frequency dispersive channels. Next, three “simulation-ready” V2V channel models found in the literature are reviewed. Finally, two complete VANET simulation frameworks are presented. They illustrate the importance of a realistic channel and physical layer modeling in vehicular networking.

An enhanced AODV protocol for VANETs with realistic radio propagation model validation

In this paper we evaluate V-AODV a version of AODV (Ad-hoc On-demand Distance Vector) especially created for Vehicular Ad-hoc NETworks (VANETs). V-AODV is designed to run with a complex cross layered metric based on both delay from node to node and Bit Error Rate (BER) coming from the physical layer. We conducted simulations with the NS2 simulator taking in account a realistic environment tool called Communication Ray Tracer (CRT). Our results show that the basic propagation models usually in use with NS2 are not suitable for VANETs simulations. We also show that when using a routing metric based on delay and BER, the first parameter is more relevant in terms of QoS than the second one.

A Semi-Deterministic Channel Model for VANETs Simulations

Todays advanced simulators facilitate thorough studies on Vehicular Ad hoc NETworks (VANETs). However the choice of the physical layer model in such simulators is a crucial issue that impacts the results. A solution to this challenge might be found with a hybrid model. In this paper, we propose a semi-deterministic channel propagation model for VANETs called UM-CRT. It is based on CRT (Communication Ray Tracer) and SCME—UM (Spatial Channel Model Extended—Urban Micro) which are, respectively, a deterministic channel simulator and a statistical channel model. It uses a process which adjusts the statistical model using relevant parameters obtained from the deterministic simulator. To evaluate realistic VANET transmissions, we have integrated our hybrid model in fully compliant 802.11 p and 802.11 n physical layers. This framework is then used with the NS-2 network simulator. Our simulation results show that UM-CRT is adapted for VANETs simulations in urban areas as it gives a good approximation of realistic channel propagation mechanisms while improving significantly simulation time.

AODV enhancements in a realistic VANET context

Ad hoc On demand Distance Vector (AODV) is a commonly used routing protocol for Vehicular Ad hoc NETworks (VANET). This paper presents and analyzes several AODV enhancements propositions dedicated to the VANET context. Communication protocol tuning can yield significant gains in energy efficiency, resource requirement, and overall network performance, all of which is of particular importance in VANETs. Alternatively, multipath routing allows the establishment of multiple paths between a pair of source and destination nodes in mobile ad hoc networks. It has recently received more and more attention and is typically proposed to increase the reliability of data transmission. This paper shows how AODV tuning and multipath routing behave under realistic VANET simulations.

A novel predictive link state indicator for ad-hoc networks

Mobile Ad-hoc Networks (MANET) and more specifically their vehicular variant (VANET) have to deal with fast changing channel conditions, specifically in urban areas. Routing protocols that have to build end to end paths over such volatile links typically react to link failure. In this paper we present a novel PHY layer based link state indicator which aims to predict such failure. The proposed link state indicator is related to the IEEE 802.11 standard and relies on the OFDM decoding process. PhySimWifi is a detailed and accurate implementation of the OFDM-based IEEE 802.11 standard that provide access to all the steps of a packet reception and incorporates realistic channel models. When using it in the ns-3 simulator, the received packets decoding errors / success gives us the material to compute our predictive estimator. This new link state indicator is entirely based on the PHY level. The efficiency of the proposed indicator is validated by reference to PHY and NET packet reception ratio of the monitored link. The efficiency of the proposed new indicator is validated by comparing it with an Signal to Noise Ratio based predictive link state estimator.

Impact of Realistic Simulation on the Evaluation of Mobile Ad Hoc Routing Protocols

Todays advanced simulators facilitate thorough studies on vehicular ad hoc networks (VANETs). However, the choice of the physical layer and the mobility models in such simulators is a crucial issue that greatly impacts the results. Realistic simulation of routing protocols in VANETs is still an open question. Indeed, only a few works address routing protocols comparison performed under realistic conditions. This paper compares common reactive, proactive, hybrid, and geographic routing protocols using a simulation platform integrating a realistic physical layer and mobility models. It also presents and analyzes several reactive protocol enhancement propositions dedicated to the VANETs context, such as multipath routing, but also protocols tuning, which allows it to adapt faster. They all have lot of attention and are typically proposed to increase the reliability of data transmission. This paper studies the behavior of each protocol in different situations and analyzed their advantages and drawbacks. Results presented in this paper give an important explanation on the contradictory results found in similar works. Finally, our realistic simulations show that reactive protocols are the best suited for VANETs, and more especially the dynamic Mobile Adhoc NETwork on-demand protocol.

Performance comparison of BER-based routing protocols under realistic conditions

To face QoS constraints of multimedia applications, many researches focus on improving the standard MANET routing protocols. Nevertheless, only few works relating to the comparison of enhanced heuristics are available. In those literature, the comparison parameters are measured through simulations performed mainly under unrealistic conditions. In this paper, we compare BER-based enhancements of AODV and OLSR when they have to deal with mobility and multi-communication. We point out that link quality, influenced by obstacles in the propagation field, should be taken into account in MANET routing protocols enhancement simulations.

Road vehicle relative motion estimation using gyro-free IMUs and system independent observers

Abstract Control applications in the domain of autonomous vehicles need robust, accurate and fast motion estimators. Estimation techniques generally fuse absolute and relative positions. This paper presents another approach which computes the system relative motion thanks to linear accelerometers and without rate gyroscopes. This method, known as Gyroscope-Free (GF), allows relative motion to be computed using only data from multiple accelerometers spread all around the object. A major aspect of this contribution is to get rid of any dynamic system model in the estimator such that the method proposed can be applied to any real application. A GF-Inertial Measurement Unit (IMU) relative motion estimator using an Extended Kalman filter (EKF) without system model is introduced and implemented on a real world test bench. Results show the suitability of the proposed estimator.

Data Fusion for a Forecasting Link State Indicator in VANETs

Due to their lack of assessment mechanisms of link quality in VANET environments, routing protocols do not deal efficiently with highly volatile links. One way to fill this gap would be to anticipate links breakages with new route computation. Currently available link quality indicators are not sufficiently responsive to consider forecasting. In this paper we present a novel predictive link quality indicator that is based on the OFDM decoding steps into the PHY layer. The events generated by these steps are threated by a data fusion algorithms. The resulting link quality indicator presents interesting forecasting characteristics and is suitable for a cross-layer usage in routing protocols.