This paper derives a vehicle-to-vehicle (V2V) channel model assuming a typical propagation scenario in which the local scatterers move with random velocities in random directions. The complex channel gain of the proposed V2V channel model is provided. Subsequently, for different scatterer velocity distributions, the corresponding autocorrelation function (ACF), power spectral density (PSD), and the Doppler spread of the channel are derived, shown, and confirmed by the available measurement data. It is shown that the Gaussian mixture (GM) and the exponential distribution can accurately describe the velocity distribution of relatively fast and slow moving scatterers, respectively. Since the proposed V2V channel model flexibly covers several communication scenarios as special cases, including fixed-to-vehicle (F2V) and fixed-to-fixed (F2F) scenarios in the presence of both fixed and moving scatterers, it is obvious that the presented results are important for the performance analysis of cutting-edge vehicular communication systems.

This paper proposes a novel probability density function (PDF) for the distribution of local scatterers inside a disk centered on the mobile station (MS). The new scattering model is introduced as the unified disk scattering model (UDSM), as it unifies a variety of typical circularly symmetric scattering models into one simple model. By adjusting a designated shape factor controlling the distribution of the scatterers, both the uniform circular and uniform ring scattering models can be obtained as special cases. Furthermore, the original Gaussian and uniform hollow-disk scattering models can be approximated with a high level of accuracy. In addition to these established scattering models, any continuous concentrations of local scatterers from a high density near the MS to a high density close to the outer edge of the disk can also be achieved. Under the assumption of single-bounce scattering, the joint PDF of the angle-of-departure and angle-of-arrival (AoA) and the joint PDF of the time-of-arrival and AoA are derived. Subsequently, the corresponding marginal PDFs are provided in closed form. Finally, the UDSM is validated by several measured channels, showing that the UDSM outperforms several other geometric models proposed in the literature. The proposed model is useful for the designers of cutting-edge vehicular communication technologies to study the system performance under different scattering conditions.

This paper introduces a new approach to developing stochastic nonstationary channel models, the randomness of which originates from a random trajectory of the mobile station (MS) rather than from the scattering area. The new approach is employed by utilizing a random trajectory model based on the primitives of Brownian fields (BFs), whereas the position of scatterers can be generated from an arbitrarily 2-D distribution function. The employed trajectory model generates random paths along which the MS travels from a given starting point to a fixed predefined destination point. To capture the path loss, the gain of each multipath component is modeled by a negative power law applied to the traveling distance of the corresponding plane wave, whereas the randomness of the path traveled results in large-scale fading. It is shown that the local received power is well approximated by a Gaussian process in logarithmic scale, even for a very limited number of scatterers. It is also shown that the envelope of the complex channel gain follows closely a Suzuki process, indicating that the proposed channel model superimposes small-scale fading and large-scale fading. The local power delay profile (PDP) and the local Doppler power spectral density (PSD) of the channel model are also derived and analyzed.

The emerging non-wearable fall detection systems rely on processing radio waves reflected off the body of the home user who has no active interaction with the system, increasing the user privacy and acceptability. This paper proposes a nonstationary channel model that is important for the development of such systems. A three-dimensional stochastic trajectory model is designed to capture targeted mobility patterns of the home user. The model is featured with a forward fall mechanism, which is actuated at a random point along the path. A transmitter emits radio waves throughout an indoor propagation environment, while a receiver collects fingerprints of the scattering objects on the emitted waves. The corresponding radio channel is modelled by a process capturing the time-variant Doppler effect caused by the home occupant. The time-frequency behaviour of the non-stationary channel is studied by computing the Doppler power spectral density and by performing spectrogram analysis. The instantaneous mean Doppler shift and Doppler spread are derived and simulated. The model is confirmed with experimental results performed at 5.9 GHz. The results are insightful for developing reliable fall detection algorithms, while the model is useful for studying the impact of different walking/falling patterns on the overall fall detection system performance.

In this paper, we derive a vehicle-to-vehicle (V2V) channel model assuming a typical propagation scenario in which the local scatterers move with random velocities in random directions. The complex channel gain of the proposed V2V channel model is provided. Subsequently, for different scatterer velocity distributions, the corresponding autocorrelation functions (ACFs) are derived, illustrated, and compared with the classical ACF derived under the assumption of fixed scatterers. Furthermore, under specific conditions, highly accurate approximations for the ACFs are provided in closed form. Since the proposed V2V channel model covers several communication scenarios as special cases, including fixed-to-vehicle (F2V) and fixed-to-fixed (F2F) scenarios in the presence of both fixed and moving scatterers, it is obvious that the presented results are important for the designers of cutting-edge vehicular communication systems.

A standard assumption in mobile fading channel modelling is that the mobile station (MS) moves along a straight line with constant speed. In practice, this assumption is violated in most propagation scenarios. For the development of more realistic channel models, it is therefore important to relax this restriction by allowing the MS to change its velocity. In this paper, we study the effect of velocity changes on the statistical properties of multipath fading channels. Expressions will be derived for the local autocorrelation function (ACF), the Wigner-Ville spectrum, the average Doppler shift, and the Doppler spread. Our findings show that a variation of the speed and/or the direction of the MS results in a non-stationary channel model. The Wigner-Ville spectrum cannot be interpreted physically as a generalized Jakes (Clarke) power spectral density (PSD); although it includes the latter one for the special case that the MS moves with constant velocity.