Delay and Doppler Spreads of Nonstationary Vehicular Channels for Safety-Relevant Scenarios

Abstract

Vehicular communication channels are characterized by a non-stationary time-and frequencyselective fading process due to fast changes in the environment. We characterize the distribution of the envelope of the first delay bin in vehicle-to-vehicle channels by means of its Rician K-factor. We analyze the time-frequency variability of this channel parameter using vehicular channel measurements at 5.6 GHz with a bandwidth of 240 MHz for safety-relevant scenarios in intelligent transportation systems (ITS). This data enables a frequency-variability analysis from an IEEE 802.11p system point of view, which uses 10 MHz channels. We show that the small-scale fading of the envelope of the first delay bin is Rician distributed with a varying K-factor. The later delay bins are Rayleigh distributed.Manuscript received yyyyyyy.2014. L. Bernadó and T. Zemen (corresponding author) are with Forschungszentrum Telekommunikation Wien (FTW), 2 We demonstrate that the K-factor cannot be assumed to be constant in time and frequency. The causes of these variations are the frequency-varying antenna radiation patterns as well as the time-varying number of active scatterers, and the effects of vegetation. We also present a simple but accurate bimodal Gaussian mixture model, that allows to capture the K-factor variability in time for safety-relevant ITS scenarios. I. INTRODUCTIONIntelligent transportation systems (ITS) have gained much interest in the last years. They have the potential to strongly reduce the rate of accidents and environmental pollution with the help of reliable wireless vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. New receiver algorithms for vehicular communications are first evaluated using numeric link level simulations which rely on accurate channel models. Key factors influencing the wave propagation in vehicular channels are the low position of the antenna on the rooftop of the vehicle, the larger number of metallic objects close to the communication link, and the high mobility of the transmitter (TX) and the receiver (RX). The combination of all these aspects, as in vehicular communications, give rise to a non-stationary fading process. Therefore, it is necessary to study and characterize the small-scale fading statistics in vehicular channels, see e.g. [1]-[9], since non-stationary vehicular channel properties have a large impact on the performance of a communication system [10], [11].In this paper we particularly focus on the characteristic of the Rician K-factor of non-stationary vehicular channels. The K-factor K = 10log 10 (r 2 /2σ 2 ) [dB] (1)is defined as the ratio of the energy of the specular part r 2 and the diffuse part 2σ 2 of the received signal [12], [13]. Often, the specular part consists only of the line of sight (LOS) component, but specular components can also stem from flat good reflecting surfaces (e.g. traffic signs) where the impinging wave is reflected into a single direction.

Time-varying K factor of the mm-Wave vehicular channel: Velocity, vibrations and the road quality influence

“…[19], [20]) narrowband method of moments [21]. We rely on the traditional method for estimation of the K factor from measured power versus time where the LOS component is determined by a peakfinder.…”

In-vehicle channel sounding in the 5.8-GHz band

“…The following papers, namely [10][11][12], describe measurement-based narrowband channel models for different situations: on highways, in cities, and on country roads. Different aspects of non-stationary vehicular channel measurements in the frequency band of our interest are addressed in [13,14]. Reports from some intervehicular measurement campaigns in the 5.9-GHz band are also made available in [15] and [16].…”

Generic stochastic modeling of vehicle-to-vehicle wireless channels

“…(5)]. The Rayleigh PDF is appropriate when multipath propagation occurs in dense scattering environments such as V-V channels under heavy traffic with obstructed LOS path [56]. The existence of one specular component, i.e., 1 s L  , with deterministic amplitude, 1 b , together with the diffuse part of equation (10) leads to a Rice PDF [49, Ch.…”

“…(5)]. The Rice PDF is suitable for V-V channels when the LOS path is unobstructed [56]. Apart from the Rayleigh and Rice, the literature contains several other PDFs based on the general model of equation (10).…”