599 research outputs found
A geometry-based stochastic MIMO model for vehicle-to-vehicle communications
Vehicle-to-vehicle (VTV) wireless communications have many envisioned applications in traffic safety and congestion avoidance, but the development of suitable communications systems and standards requires accurate models for the VTV propagation channel. In this paper, we present a new wideband multiple-input-multiple-output (MIMO) model for VTV channels based on extensive MIMO channel measurements performed at 5.2 GHz in highway and rural environments in Lund, Sweden. The measured channel characteristics, in particular the non-stationarity of the channel statistics, motivate the use of a geometry-based stochastic channel model (GSCM) instead of the classical tapped-delay line model. We introduce generalizations of the generic GSCM approach and techniques for parameterizing it from measurements and find it suitable to distinguish between diffuse and discrete scattering contributions. The time-variant contribution from discrete scatterers is tracked over time and delay using a high resolution algorithm, and our observations motivate their power being modeled as a combination of a (deterministic) distance decay and a slowly varying stochastic process. The paper gives a full parameterization of the channel model and supplies an implementation recipe for simulations. The model is verified by comparison of MIMO antenna correlations derived from the channel model to those obtained directly from the measurements
Realistic geometry-based stochastic channel models for advanced wireless MIMO systems
The employment of multiple antennas at both the Transmitter (Tx) and Receiver (Rx)
enables the so-called Multiple-Input Multiple-Output (MIMO) technologies to greatly
improve the link reliability and increase the overall system capacity. MIMO has been
recommended to be employed in various advanced wireless communication systems,
e.g., the Fourth Generation (4G) wireless systems and beyond. For the successful
design, performance test, and simulation of MIMO wireless communication systems, a
thorough understanding of the underlying MIMO channels and corresponding models
are indispensable. The approach of geometry-based stochastic modelling has widely
been used due to its advantages, such as convenience for theoretical analysis and
mathematical tractability.
In addition, wireless Vehicle-to-Vehicle (V2V) communications play an important role
in mobile relay-based cellular networks, vehicular ad hoc networks, and intelligent
transportation systems. In V2V communication systems, both the Tx and Rx are
in motion and equipped with low elevation antennas. This is di erent from conventional
Fixed-to-Mobile (F2M) cellular systems, where only one terminal moves. This
PhD project is therefore devoted to the modelling and simulation of wireless MIMO
channels for both V2V and F2M communication systems.
In this thesis, we rst propose a novel narrowband Three Dimensional (3D) theoretical
Regular-Shape Geometry Based Stochastic Model (RS-GBSM) and the corresponding
Sum-of-Sinusoids (SoS) simulation model for non-isotropic MIMO V2V Ricean fading
channels. The proposed RS-GBSM has the ability to study the impact of the Vehicular
Tra c Density (VTD) on channel statistics and jointly considers the azimuth
and elevation angles by using the von Mises-Fisher (VMF) distribution. Moreover, a
novel parameter computation method is proposed for jointly calculating the azimuth
and elevation angles in the SoS channel simulator. Based on the proposed 3D theoretical
RS-GBSM and its SoS simulation model, statistical properties are derived
and thoroughly investigated. The impact of the elevation angle in the 3D model on
key statistical properties is investigated by comparing with those of the corresponding
Two Dimensional (2D) model. It is demonstrated that the 3D model is more practical
to characterise real V2V channels, in particular for pico-cell scenarios.
Secondly, actual V2V channel measurements have shown that the modelling assumption
of Wide Sense Stationary (WSS) is valid only for very short time intervals. This fact inspires the requirement of non-WSS V2V channel models. Therefore, we propose
a novel 3D theoretical wideband MIMO non-WSS V2V RS-GBSM and corresponding
SoS simulation model. Due to the dynamic movement of both the Tx and Rx,
the Angle of Departure (AoD) and Angle of Arrival (AoA) are time-variant, which
makes our model non-stationary. The proposed RS-GBSMs are su ciently generic
and adaptable to mimic various V2V scenarios. Furthermore, important local channel
statistical properties are derived and thoroughly investigated. The impact of
non-stationarity on these channel statistical properties is investigated by comparing
with those of the corresponding WSS model. The proposed non-WSS RS-GBSMs are
validated by measurements in terms of the channel stationary time.
Thirdly, realistic MIMO channel models with a proper trade-o between accuracy
and complexity are indispensable for the practical application. By comparing the
accuracy and complexity of two latest F2M standardised channel models (i.e., LTE-A
and IMT-A channel models), we employ some channel statistical properties as the
accuracy metrics and the number of Real Operations (ROs) as the complexity metric.
It is shown that the LTE-A MIMO channel model is simple but has signi cant
aws
in terms of the accuracy. The IMT-A channel model is complicated but has better
accuracy. Therefore, we focus on investigating various complexity reduction methods
to simplify the IMT-A channel model. The results have shown that the proposed
methods do not degrade much the accuracy of the IMT-A channel model, whereas
they can signi cantly reduce the complexity in terms of the number of ROs and
channel coe cients computing time.
Finally, to investigate the non-stationarity of the IMT-A MIMO channel model, we
further propose a non-WSS channel model with time-varying AoDs and AoAs. The
proposed time-varying functions can be applied to various scenarios according to moving
features of Moving Clusters (MCs) and a Mobile Station (MS). Moreover, the impacts
of time-varying AoDs and AoAs on local statistical properties are investigated
thoroughly. Simulation results prove that statistical properties are varied with time
due to the non-stationarity of the proposed channel model.
In summary, the proposed reference models and channel simulators are useful for
the design, testing, and performance evaluation of advanced wireless V2V and F2M
MIMO communication systems
Stationarity analysis of V2I radio channel in a suburban environment
Due to rapid changes in the environment, vehicular communication channels no longer satisfy the assumption of wide-sense stationary uncorrelated scattering. The non-stationary fading process can be characterized by assuming local stationarity regionswith finite extent in time and frequency. The local scattering function (LSF) and channel correlation function (CCF) provide a framework to characterize the mean power and correlation of the non-stationary channel scatterers, respectively. In this paper, we estimate the LSF and CCF from measurements collected in a vehicle-to-infrastructure radio channel sounding campaign in a suburban environment in Lille, France. Based on the CCF, the stationarity region is evaluated in time as 567 ms and used to capture the non-stationary fading parameters. We obtain the time-varying delay and Doppler power profiles fromthe LSF, and we analyze the corresponding root-mean-square delay and Doppler spreads. We show that the distribution of these parameters follows a lognormal model. Finally, application relevance in terms of channel capacity and diversity techniques is discussed. Results show that the assumption of ergodic capacity and the performance of various diversity techniques depend on the stationarity and coherence parameters of the channel. The evaluation and statistical modeling of such parameters can provide away of tracking channel variation, hence, increasing the performance of adaptive schemes
Measurement Based Channel Characterization and Modeling for Vehicle-to-Vehicle Communications
Vehicle-to-Vehicle (V2V) communication is a challenging but fast growing technology that has potential to enhance traffic safety and efficiency. It can also provide environmental benefits in terms of reduced fuel consumption. The effectiveness and reliability of these applications highly depends on the quality of the V2V communication link, which rely upon the properties of the propagation channel. Therefore, understanding the properties of the propagation channel becomes extremely important. This thesis aims to fill some gaps of knowledge in V2V channel research by addressing four different topics. The first topic is channel characterization of some important safety critical scenarios (papers I and II). Second, is the accuracy or validation study of existing channel models for these safety critical scenarios (papers III and IV). Third, is about channel modeling (paper V) and, the fourth topic is the impact of antenna placement on vehicles and the possible diversity gains. This thesis consists of an introduction and six papers: Paper I presents a double directional analysis of vehicular channels based on channel measurement data. Using SAGE, a high-resolution algorithm for parameter estimation, we estimate channel parameters to identify underlying propagation mechanisms. It is found that, single-bounce reflections from static objects are dominating propagation mechanisms in the absence of line-of-sight (LOS). Directional spread is observed to be high, which encourages the use of diversity-based methods. Paper II presents results for V2V channel characterization based on channel measurements conducted for merging lanes on highway, and four-way street intersection scenarios. It is found that the merging lane scenario has the worst propagation condition due to lack of scatterers. Signal reception is possible only with the present LOS component given that the antenna has a good gain in the direction of LOS. Thus designing an antenna that has an omni-directional gain, or using multiple antennas that radiate towards different directions become more important for such safety critical scenarios. Paper III presents the results of an accuracy study of a deterministic ray tracing channel model for vehicle-to-vehicle (V2V) communication, that is compared against channel measurement data. It is found that the results from measurement and simulation show a good agreement especially in LOS situations where as in NLOS situations the simulations are accurate as far as existing physical phenomena of wave propagation are captured by the implemented algorithm. Paper IV presents the results of a validation study of a stochastic NLOS pathloss and fading model named VirtualSource11p for V2V communication in urban street intersections. The reference model is validated with the help of independent channel measurement data. It is found that the model is flexible and fits well to most of the measurements with a few exceptions, and we propose minor modifications to the model for increased accuracy. Paper V presents a shadow fading model targeting system simulations based on channel measurements. The model parameters are extracted from measurement data, which is separated into three categories; line-of-sight (LOS), LOS obstructed by vehicles (OLOS), and LOS blocked by buildings (NLOS), with the help of video information recorded during the measurements. It is found that vehicles obstructing the LOS induce an additional attenuation in the received signal power. The results from system level vehicular ad hoc network (VANET) simulations are also presented, showing that the LOS obstruction affects the packet reception probability and this can not be ignored. Paper VI investigates the impact of antenna placement based on channel measurements performed with four omni-directional antennas mounted on the roof, bumper, windscreen and left-side mirror of the transmitter and receiver cars. We use diversity combining methods to evaluate the performance differences for all possible single-input single-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) link combinations. This investigation suggests that a pair of antennas with complementary properties, e.g., a roof mounted antenna together with a bumper antenna is a good solution for obtaining the best reception performance, in most of the propagation environments. In summary, this thesis describes the channel behavior for safety-critical scenarios by statistical means and models it so that the system performance can be assessed in a realistic manner. In addition to that the influence of different antenna arrangements has also been studied to exploit the spatial diversity and to mitigate the shadowing effects. The presented work can thus enable more efficient design of future V2V communication systems
Massive MIMO channel modelling for 5G wireless communication systems
Massive Multiple-Input Multiple-Output (MIMO) wireless communication systems,
equipped with tens or even hundreds of antennas, emerge as a promising technology
for the Fifth Generation (5G) wireless communication networks. To design and evaluate
the performance of massive MIMO wireless communication systems, it is essential
to develop accurate, flexible, and efficient channel models which fully reflect the characteristics
of massive MIMO channels. In this thesis, four massive MIMO channel
models have been proposed.
First, a novel non-stationary wideband multi-confocal ellipse Two-Dimensional (2-D)
Geometry Based Stochastic Model (GBSM) for massive MIMO channels is proposed.
Spherical wavefront is assumed in the proposed channel model, instead of the plane
wavefront assumption used in conventional MIMO channel models. In addition, the
Birth-Death (BD) process is incorporated into the proposed model to capture the
dynamic properties of clusters on both the array and time axes.
Second, we propose a novel theoretical non-stationary Three-Dimensional (3-D) wideband
twin-cluster channel model for massive MIMO communication systems with
carrier frequencies in the order of gigahertz (GHz). As the dimension of antenna arrays
cannot be ignored for massive MIMO, nearfield effects instead of farfield effects
are considered in the proposed model. These include the spherical wavefront assumption
and a BD process to model non-stationary properties of clusters such as cluster
appearance and disappearance on both the array and time axes.
Third, a novel Kronecker Based Stochastic Model (KBSM) for massive MIMO channels
is proposed. The proposed KBSM can not only capture antenna correlations but
also the evolution of scatterer sets on the array axis. In addition, upper and lower
bounds of KBSM channel capacities in both the high and low Signal-to-Noise Ratio
(SNR) regimes are derived when the numbers of transmit and receive antennas are
increasing unboundedly with a constant ratio.
Finally, a novel unified framework of GBSMs for 5G wireless channels is proposed.
The proposed 5G channel model framework aims at capturing key channel characteristics
of certain 5G communication scenarios, such as massive MIMO systems, High
Speed Train (HST) communications, Machine-to-Machine (M2M) communications,
and Milli-meter Wave (mmWave) communications
Propagation channel characterisation and modelling for high-speed train communication systems
High-mobility scenarios, e.g., High-Speed Train (HST) scenarios, are expected to be
typical scenarios for the Fifth Generation (5G) communication systems. With the
rapid development of HSTs, an increasing volume of wireless communication data
is required to be transferred to train passengers. HST users demand high network
capacity and reliable communication services regardless of their locations or speeds,
which are beyond the capability of current HST communication systems. The features
of HST channels are significantly different from those of low-mobility cellular
communication systems. For a proper design and evaluation of future HST wireless
communication systems, we need accurate channel models that can mimic the
underlying channel characteristics, especially the non-stationarity for different HST
scenarios. Inspired by the lack of such accurate HST channel models in the literature,
this PhD project is devoted to the modelling and simulation of non-stationary
Multiple-Input Multiple-Output (MIMO) channels for HST communication systems.
In this thesis, we first give a comprehensive review of the measurement campaigns
conducted in different HST scenarios and address the recent advances in HST channel
models. We also highlight the key challenges of HST channel measurements and
models. Then, we study the characterisation of non-stationary channels and propose
a theoretical framework for deriving the statistical properties of these channels.
HST wireless communication systems encounter different channel conditions due to the
difference of surrounding geographical environments or scenarios. HST channel models
in the literature have either considered large-scale parameters only and/or neglected
the non-stationarity of HST channels and/or only consider one of the HST scenarios.
Therefore, we propose a novel generic non-stationary Geometry-Based Stochastic
Model (GBSM) for wideband MIMO HST channels in different HST scenarios, i.e.,
open space, viaduct, and cutting. The corresponding simulation model is then developed
with angular parameters calculated by the Modified Method of Equal Area
(MMEA). The system functions and statistical properties of the proposed channel
models are thoroughly studied. The proposed generic non-stationary HST channel
models are verified by measurements in terms of stationary time for the open space
scenario and the Autocorrelation Function (ACF), Level Crossing Rate (LCR), and
stationary distance for the viaduct and cutting scenarios. Transmission techniques which are capable of utilising Three-Dimensional (3D) spatial
dimensions are significant for the development of future communication systems.
Consequently, 3D MIMO channel models are critical for the development and evaluation
of these techniques. Therefore, we propose a novel 3D generic non-stationary
GBSM for wideband MIMO HST channels in the most common HST scenarios. The
corresponding simulation model is then developed with angular parameters calculated
by the Method of Equal Volume (MEV). The proposed models considers several timevarying
channel parameters, such as the angular parameters, the number of taps, the
Ricean K-factor, and the actual distance between the Transmitter (Tx) and Receiver
(Rx). Based on the proposed generic models, we investigate the impact of the elevation
angle on some of the channel statistical properties. The proposed 3D generic
models are verified using relevant measurement data.
Most standard channel models in the literature, like Universal Mobile Telecommunications
System (UMTS), COST 2100, and IMT-2000 failed to introduce any of the HST
scenarios. Even for the standard channel models which introduced a HST scenario,
like IMT-Advanced (IMT-A) and WINNER II channel models, they offer stationary
intervals that are noticeably longer than those in measured HST channels. This has
inspired us to propose a non-stationary IMT-A channel model with time-varying parameters
including the number of clusters, powers, delays of the clusters, and angular
parameters. Based on the proposed non-stationary IMT-A channel model, important
statistical properties, i.e., the time-variant spatial Cross-correlation Function (CCF)
and time-variant ACF, are derived and analysed. Simulation results demonstrate
that the stationary interval of the developed non-stationary IMT-A channel model
can match that of relevant HST measurement data.
In summary, the proposed theoretical and simulation models are indispensable for the
design, testing, and performance evaluation of 5G high-mobility wireless communication
systems in general and HST ones in specific
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