Dieter Smely

Performance evaluation of IEEE 802.11p infrastructure-to-vehicle tunnel measurements

In this contribution, we discuss and analyze results from real-world performance measurements for IEEE 802.11p during September 2010 along the highway S1 near Vienna, Austria. More specifically, we evaluate the frame success ratio and goodput of the IEEE 802.11p physical (PHY) layer for a infrastructure-to-vehicle (I2V) scenario in a tunnel. We report and discuss the observed frame success ratios and goodputs for various PHY parameter settings and investigate the impact of the propagation environment and the traffic situation inside the tunnel.

On roadside unit antenna measurements for vehicle-to-infrastructure communications

In this paper, we discuss and analyze results from real-world vehicle-to-infrastructure measurements in an IEEE 802.11p-based vehicular ad hoc network. For our experiments we have used six roadside units (RSUs) mounted on highway gantries equipped with five different antenna types. We compare the performance of directional and omnidirectional antennas and analyze performance improvements in terms of coverage range and throughput, achievable by using directional antennas. Our results show that the use of directional antennas yields substantial performance improvements in IEEE 802.11p-based networks. However, for high-gain antennas even more careful RSU antenna positioning with respect to the lane geometry is required.

Relaying for IEEE 802.11p at road intersection using a vehicular non-stationary channel model

Traffic s afety at road intersections can be improved by establishing reliable communications between vehicles. For vehicle-to-vehicle communications, this requires information exchange in non line-of-sight (NLOS) conditions due to the obstruction by buildings. In order to overcome the low receive signal-to-noise ratio (SNR) due to NLOS, we consider to place a relay at road intersections to enhance the reliability of communication links. In this paper, we implement a vehicular non-stationary geometry based stochastic channel model for road intersections, which is an extension of an existing highway channel model. The model is verified by comparison with vehicular channel measurements. Using the proposed channel model, we present link level simulation results for IEEE 802.11p relaying at varying transmitter/receiver locations using different channel estimation techniques. The results show that a relay at the intersection is able to greatly extend the reliable communications region. Besides, in the high SNR regime with moderate or high mobility transmitter and receiver, the block type least square channel estimator is the bottleneck that limits the relaying performance. An advanced iterative channel estimator is also simulated, which exhibits robustness against increased vehicle velocities.

Performance analysis of vehicle-to-vehicle tunnel measurements at 5.9 GHz

In this contribution, we discuss and analyze results from real-world performance measurements for IEEE 802.11p along motorway A22 near Vienna, Austria. More specifically, we evaluate the frame success ratio and goodput of the IEEE 802.11p physical layer for a vehicle-to-vehicle scenario in a tunnel. We report and discuss the observed frame success ratios and goodputs for radio channels between the transmit and the receive antenna with and without a line-of-sight component, and investigate the impact of the propagation environment and the traffic situation inside the tunnel.

Throughput of Self-Organizing Time Division Multiple Access MAC Layer for Vehicular Networks Based on Measured SNR Time-Series

IEEE802.11p is an approved amendment to the IEEE802.11 standard providing wireless access in vehicular environments (WAVE). It defines enhancements to the Physical layer (PHY) and Medium Access Control (MAC) for the support of Intelligent Transport Systems (ITS). This includes communication links between vehicles as well as between vehicles and a roadside infrastructure. The current MAC method uses randomized backoff in the case of access collisions which induces upredictable communication delays. It is known that such unpredictable delays severely limit the value of safety-related services. The most effective way forward is to design a protocol that suits vehicular traffic and safety- related service constraints and can coexist with the current IEEE802.11p MAC method. Self-Organizing Time Division Multiple Access (STDMA) is a suitable alternative, due to its structured channel access, predictable delay and periodic character. This contribution presents the time-evolution of throughput based on measured signal-to-noise ratio time-series of four vehicles driving on the same road joining the channel. These time-series were acquired during a real-world experiment in the 5.9 GHz band during 2010. Our results show that a collision-free access featuring predictable communication delay is feasible.

Vehicular channel models: A system level performance analysis of tapped delay line models

Accurate predictions of vehicular communication conditions are vital for the development of intelligent transport systems and services, both on link level through channel models, as well as packet error models on system level. In this paper we investigate simple, yet flexible tapped delay line channel models that capture the essential aspects of vehicular communications through asymmetric power spectral densities and well chosen Doppler and delay spreads. We demonstrate how to generate such asymmetric fading traces, and use the implementation on a channel emulator to measure packet error probabilities using software defined radios. We then analyze the received packet traces with respect to mean packet loss and burstiness, and show the influence of the line of sight obstruction and Doppler frequencies on the packet burst behavior. We are thus able to demonstrate the link of fine-grained packet statistics and underlying physical channels.