Jörg Nuckelt

Vehicle-to-Vehicle IEEE 802.11p performance measurements at urban intersections

During the last few years, vehicle-to-vehicle (V2V) wireless communication has become a key objective for enabling future cooperative safety applications, such as intersection collision warning. In this paper, we present the results of a 5.9 GHz V2V performance measurement campaign at four different urban intersections under NLOS conditions using commercial off-the-shelf wireless interface cards which meet the 802.11p and ITS-G5 specifications. Particularly, we quantify the packet delivery ratio (PDR) and received signal strength indication (RSSI) levels associated with different scenario conditions with respect to vehicle positioning, intersection geometry and traffic density. We determine reliable communication ranges which constitute an important metric for V2V collision avoidance applications.

Simulation and Measurement-Based Vehicle-to-Vehicle Channel Characterization: Accuracy and Constraint Analysis

In this paper, a deterministic channel model for vehicle-to-vehicle (V2V) communication is compared against channel measurement results collected during a V2V channel measurement campaign using a channel sounder. Channel metrics such as channel gain, delay and Doppler spreads, eigenvalue (EV) distribution, and antenna correlations are derived from the ray-tracing (RT) simulations as well as from the measurement data obtained from two different measurements in an urban four-way intersection. The channel metrics are compared separately for line-of-sight (LOS) and non-LOS (NLOS) situations. Most power contributions arise from the LOS component (if present) as well as from multipaths with single bounce reflections. Measurement and simulation results of the received power show a very good agreement in the presence of LOS, as most of the received power is carried by the LOS component. In NLOS, the difference is large because the ray-tracer is unable to capture some of the channel characteristics due to the underlying limitations of our ray-based propagation model. Despite the limitations, the model is suitable to characterize some, but not all, of the channel properties in a sufficient manner. We find that the diffuse scattering and multibounced nonspecular reflections must be considered for an accurate prediction of the channel in such a rich scattering environment.

Comparison of Ray Tracing and Channel-Sounder Measurements for Vehicular Communications

This paper presents the results of an accuracy assessment of a deterministic channel model for vehicle-to-vehicle (V2V) communications. Channel simulations obtained from the ray-tracing model developed by TU Braunschweig are compared to data gathered during the DRIVEWAY V2V channel measurement campaign at 5.6 GHz in the city of Lund in summer 2009. The analysis focuses on PDP and channel gains in an urban four-way intersection scenario. Despite some implementation-based limitations of the ray-tracing model, a very good agreement between simulation and measurement results is achieved. Most relevant power contributions arising from multiple-bounce specular reflections as well as from single-bounce non-specular reflections are captured by the deterministic model. We also discuss the question to what extent roadside obstacles like traffic signs, parked cars or lamp posts have to be considered when characterizing the V2V channel.

Performance Evaluation of Wiener Filter Designs for Channel Estimation in Vehicular Environments

Future communication systems for car-to-x (C2X) applications have to meet stringent requirements regarding reliability issues. Channel estimation (CE) - as one of the key tasks that affect the system performance - has to be able to cope with the rapidly changing channel conditions. Applying a Wiener filter (WF) is one very efficient method to reduce the estimation error of any channel estimation approach. This paper deals with design aspects of Wiener filter coefficients and their impact on the system performance. Parameters like noise variance, maximum excess delay of the channel impulse response as well as the assumed shape of the power delay profile (PDP) are considered. The resulting performance benefit of different filter designs is evaluated by means of IEEE 802.11p physical (PHY) layer simulations.

Physical Layer Performance Comparison of LTE and IEEE 802.11p for Vehicular Communication in an Urban NLOS Scenario

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.

Linear Diversity Combining Techniques Employed in Car-to-X Communication Systems

This paper presents performance evaluation results of different linear diversity combining techniques that have been applied to IEEE 802.11p based Car-to-X (C2X) communication systems. More precisely, we employed the Selection Combining (SC), the Equal Gain Combining (EGC) and the Maximum Ratio Combining (MRC) algorithms to systems with multiple receiver antennas and compared the resulting performance to that of single-receive antenna systems. Concerning the great challenges of typical C2X propagation channels that go along with a strong time variance and long multipath delays, the use of multiple receive antennas in combination with adequate signal combining algorithms can clearly improve the reliability of the communication system even under poor Signal-to-Noise Ratio (SNR) conditions. Based on physical (PHY) layer simulations, the achieved performance of different diversity combining techniques has been evaluated using stochastic models of double-selective fading channels.

Investigation of MPC Correlation and Angular Characteristics in the Vehicular Urban Intersection Channel Using Channel Sounding and Ray Tracing

This paper examines the multiple-input multiple-output (MIMO) characteristics of the vehicular MIMO channel at 5.9 GHz by analyzing the correlation of multipath components (MPCs) in the case of high antenna separation and the angular characteristics of the same scenario. The scenario is selected as crossing traffic on urban intersections. The 2 × 2 channel measurements with a wideband channel sounder are employed for the correlation analysis, and in parallel, the same scenario is simulated with a ray-tracing tool for the analysis of the angular domain. We introduce measures and tools to describe the relevant characteristics and the performance; the limitations of the ray-tracing simulation are also subdued to critical evaluation. The focus of this paper is set on the evaluation of the presented method on one selected experiment (combination of measurement and ray-tracing simulation) rather than on an exhaustive statistical analysis of many scenarios. The combination lies in the higher level of analyzing the MIMO characteristics of the channel using two different methods. The results provide that the MIMO channels show a similar power level in terms of mean MPC power, but the linear correlation stays relatively low. Specifically, discrete MPCs tend to be more highly correlated than diffuse MPCs. Furthermore, the angular spread is highly dynamic but small and substantially increases when both vehicles are near the center of the intersection. Significant power contributions caused by buildings along the roadside are identified.