In recent years, a combined utilization of ad-hoc communication and cellular mobile radio systems has been considered for vehicular networking in future Intelligent Transportation Systems (ITSs). The development of hybrid system protocols, algorithms and architectures require comprehensive performance investigations typically carried out by means of simulations. The main contribution of this article is to introduce a top-down design methodology for building realistic simulation scenarios tailored to the requirements in vehicular communication and suitable for multiple levels of abstraction in simulations. Within this paper the focus is set on the example city of Doha, Qatar: Building upon a macroscopic layer including static environmental data and a realistic cellular network, it is shown how to embed microscopic sub-scenarios with detailed modelling of individual user mobility into the macroscopic world. Exemplary sub-scenarios are derived with respect to applications considered for ITS. As a proof of concept, in the first part of the article, the design process is demonstrated for an LTE network in conjunction with IEEE 802.11p based vehicular communication. In the second part of the article, exemplary individual simulation results at the link-level are presented for both considered radio technologies.

Reliable vehicular communication is considered an important precondition for future intelligent transportation systems (ITSs). Recently, a combination of ad-hoc direct communication and infrastructure based cellular networks are considered to enable seamless connectivity and sufficient Quality of Service (QoS) for all types of vehicular applications. Within this paper a novel algorithm to enable data traffic steering between ad-hoc IEEE 802.11p based dedicated short range communication and LTE for Vehicle-to-X (V2X) communication is presented. Based on the system-level evaluation of cell loads and radio channel congestion the network based performance of the proposed algorithm is analyzed and compared to the conservative approach of using exclusively IEEE 802.11p for message dissemination. First simulation results in a realistic urban intersection scenario show significant improvement of the quality of service.

As an important scatterer in vehicle-to-X (V2X) communication scenarios, traffic signs frequently appear along roads and can affect the propagation channel appreciably. Although traffic signs can be considered as an important part in such scattering scenarios, knowledge of their bistatic radar cross section (RCS) is still absent. This paper presents an integration of the analytical models, full-wave simulation, measurement, and validation of the bistatic RCS of three types of representative traffic signs for V2X communication. First, the total RCS of the traffic signs is calculated by summing up the field contributions of the individual parts with their own phase relationships. Furthermore, simulations using full-wave analysis are performed to validate the analytical models for RCSs in the far field under plane-wave illumination. Since the high-frequency calculation techniques used here are applicable only under plane-wave excitation, the traffic-sign parts are divided into small elements, where this precondition is locally valid. Measurements are conducted in an open-area test site at the National Metrology Institute of Germany to validate the model in the near field (spherical wave from a point source). Corresponding comparisons show that the method of decomposing the traffic sign into small parts supports an effective way to embed the analytical models into ray-tracing tools, thus improving propagation modeling in V2X communication.

Small cells and device-to-device (D2D) communications will play a vital role in the realization of the next generation of wireless mobile communication systems (IMT-2020 or 5G). Both of them involve transmitters and receivers less than 10 m high inducing a more complex urban environment. This paper presents a framework of integrating composite urban furniture, e.g., traffic signs, traffic lights, etc., into ray-tracing tools. The framework starts with the theoretical modeling for radar cross section of furniture components and validation of full-wave analysis simulation in the far field. Then, in order to locally fulfill the far field condition in the small cells or D2D scenarios, the furniture is divided into small segments so that the models in the far field are still applicable. Finally, the decomposed furniture is implemented in a ray-tracing tool and validated by measurements in real scenarios. Under this framework, researchers can improve the ray-tracing tools with more essential elements of urban environment. Last but not least, this paper provides a case study to demonstrate the implementation of the framework, and the results show that the traffic signs indeed influence the vehicle-to-vehicle communications, which is one of the most frequently occurring applications of outdoor D2D systems.

This paper presents an evaluation of the Long Term Evolution (LTE) link level performance for vehicular communication. For this, doubly-selective stochastic channel models originally derived for IEEE 802.11p networks are adapted according to the LTE system characteristics. These modified channel models are implemented into a LTE link level simulator. By comparing the simulation results with results obtained using classical cellular channel models it is shown that a more detailed modeling of the channel dynamics typical for vehicular communications is of great importance. Moreover, the comparison with the physical layer performance of an IEEE 802.11p system shows good potential to utilize LTE for vehicular applications or as part of a hybrid communication system.

In this paper, a top-down approach to create a realistic simulation scenario for joint IEEE 802.11p and Long Term Evolution (LTE) performance evaluations is presented. Applying this approach, a scenario suited for both link and system level simulations based on the city of Doha, Qatar is developed. The scenario allows the investigation of different use-cases considered for future intelligent transportation systems (ITSs). Preliminary simulation results for IEEE 802.11p and LTE are presented for one particular area.

In this paper, a physical (PHY) layer performance comparison for 3GPP Long Term Evolution (LTE) and IEEE 802.11p in a realistic urban street intersection scenario is presented. For this approach standard compliant link level simulation tools in combination with ray-optical channel modeling are utilized. Results are analyzed with respect to an intersection collision warning application where a suitable performance metric is derived to analyze the individual performances with respect to the packet error ratio in the downlink. In the absence of a line of sight (LOS) path for a Vehicle-to-Vehicle (V2V) link, the results show promising potential of LTE to outperform a dedicated IEEE 802.11p based communication link even when considering full buffer intercell-interference condition.