| dc.description.abstract | Vehicle-to-X (V2X) communication systems are expected to provide tremendous
benefits associated with the safety and traffic efficiency on roads. The successful
deployment of emerging technologies like V2X requires channel models accurately
representing fading statistics in environments where those technologies are used. The
accuracy is, of course, a major concern when adapting or developing a suitable channel
model for test and evaluation purposes. However, it is also important to take into
account the simplicity of a channel model, which is crucial for efficient numerical
computations and computer simulations. Reconciling simplicity and accuracy is a
rather complex task to accomplish, which requires sophisticated parameter computation
methods. To the best of our knowledge, only a limited number of investigations
address the channel modelling and parametrization problems for vehicular propagation
scenarios in the literature. In order to fill this gap, we concentrate on the
development of new sophisticated channel modelling approaches and efficient parameter
computation methods for the design of V2X communication systems in this
dissertation.
In general, there are two main applications of channel models: (1) for the design
and test of wireless communication systems and (2) for the optimization of existing
communication systems. For the design and test purposes, more general statistical
models such as Rice and Rayleigh channel models are preferred. Those channel
models provide a fundamental insight into propagation phenomena and at the same
time they greatly simplify the theoretical and numerical computations to assess the
performance of wireless communication systems. For the optimization purposes,
however, measurement-based channel models are commonly used. The main advantage
of such channel models is that they always accurately reflect the physical reality.
In this dissertation, we will focus on the channel models designed for both of those
application purposes.
A significant part of this dissertation will be devoted to the thorough analysis and
design of Rayleigh and Rice fading channel models. We investigate the correlation
properties of those channels assuming asymmetrical shapes of Doppler power spectral
densities (PSDs). In fact, this is what we often observe in real-world propagation
scenarios. In this regard, we will present an analytical expression for the autocorrelation
function (ACF) of Rice processes that captures such realistic scenarios. Another
important contribution to this topic is the novel iterative nonlinear least square approximation
method for the design of Rice and Rayleigh channel simulators based on sum-of-sinusoids (SOS), as well as sum-of-cisoids (SOC) approaches. The idea
behind the proposed method is very simple. The parameters of the simulation model
are extracted from the reference model, such as the stochastic Rice and Rayleigh
channel models, by fitting the statistical properties of interest, e.g. the ACF and the
probability density function (PDF). We show that the proposed method outperforms
several other methods in designing channel simulators with desired distribution and
correlation properties. We also show that the proposed method provides a subtle balance
between channel model’s simplicity and accuracy in designing Rayleigh and
Rice channel simulators.
The parametrization is a process of determining the key parameters specifying
the channel model. This process has a great influence on the reliability of the developed
channel model. It is therefore highly desirable if those parameters are extracted
from measurements. In fact, this idea constitutes the fundamental concept behind
measurement-based channel modelling approach. The measurement-based models
are important in the sense that they can be used for the optimizations of the wireless
communication system. Hence, the problem of computing the channel model parameters
from the measurements is of special interest. In this regard, we propose iterative
nonlinear least square approximation method for the design of measurementbased
channel simulators. Through detailed investigations and comparative studies,
we demonstrate that the proposed method is highly flexible and outperforms several
other conventional methods in terms of reproducing the correlation characteristics
obtained from several measurements. In addition, we introduce a new approach
for the design of channel models for V2X communications in tunnel environments,
where the number of scatterers contributing to the total received power is relatively
small. | nb_NO |
