Modeling and characterization of urban radio channels for mobile communications

Results of this thesis contribute in modeling and characterization of radio channels for future mobile communications. The results are presented mainly in three parts: a) modeling of propagation mechanisms, b) methodology of developing a propagation model, c) characterization of urban radio channel. One of the main propagation physical phenomena that have an important role in diverting signals to non line of sight scenarios is the diffraction process. This thesis proposes diffraction coefficients that have better agreement with finite difference time domain solution and rigorous diffraction theory than the coefficient commonly used in propagation predictions for mobile communications. The importance of diffuse scattering has also been investigated and showed that this physical process may have a key role in urban propagation, with a particular impact on the delay spread and angular spread of the signal at the receiver. This thesis proposes wideband propagation models for main and perpendicular streets of urban street grids. The propagation models are ray-based and are given in explicit mathematical expressions. Each ray is characterized in terms of its amplitude, delay, and angle of arrival, angle of departure for vertical and horizontal polarizations. Each of these characteristics is given in a closed mathematical form. Having wideband propagation model in explicit expression makes its implementation easy and computation fast. Secondary source modeling approach for perpendicular streets has also been introduced in this thesis. The last part of the thesis deals with characterization of urban radio channels for extracting parameters that help in successful design of mobile communication systems. Knowledge of channel characteristics enables reaching optimum trade off between system performance and complexity. This thesis analyzes measurement results at 2 GHz to extract channel parameters in terms of Rake finger characteristics in order to get information that helps to optimize Rake receiver design for enhanced-IMT2000 systems. Finger life distance has also been investigated for both micro- and small cell scenarios. This part of the thesis also presents orthogonality factor of radio channel for W-CDMA downlink at different bandwidths. Characterization of dispersion metrics in delay and angular domains for microcellular channels is also presented at different base station antenna heights. A measure of (dis-) similarity between multipath components in terms of separation distance in delay and angular domains is introduced by the concept of distance function, which is a step toward in development of algorithm extraction and analysis multipath clustering. In summary, the significant contributions of the thesis are in three parts. 1) Development of new diffraction coefficients and corrections of limitations of existing one for accurate propagation predictions for mobile communications. 2) Development of wideband propagation models for urban street grid. The novelty of the model is the development in explicit mathematical expressions. The developed models can be used to study propagation problem in microcellular urban street grids. 3) Presenting channel parameters that will help in the design of future mobile communication systems (enhanced-IMT2000), like number of active fingers, finger life distance, and orthogonality factors for different bandwidths. In addition, a technique based on multipath separation distance is proposed as a step toward in development of algorithms for extraction and analysis of multipath clusters.reviewe

28 GHz and 73 GHz Millimeter-Wave Indoor Propagation Measurements and Path Loss Models

This paper presents 28 GHz and 73 GHz millimeter- wave propagation measurements performed in a typical office environment using a 400 Megachip-per-second broadband sliding correlator channel sounder and highly directional steerable 15 dBi (30 degrees beamwidth) and 20 dBi (15 degrees beamwidth) horn antennas. Power delay profiles were acquired for 48 transmitter-receiver location combinations over distances ranging from 3.9 m to 45.9 m with maximum transmit powers of 24 dBm and 12.3 dBm at 28 GHz and 73 GHz, respectively. Directional and omnidirectional path loss models and RMS delay spread statistics are presented for line-of-sight and non-line-of-sight environments for both co- and cross-polarized antenna configurations. The LOS omnidirectional path loss exponents were 1.1 and 1.3 at 28 GHz and 73 GHz, and 2.7 and 3.2 in NLOS at 28 GHz and 73 GHz, respectively, for vertically-polarized antennas. The mean directional RMS delay spreads were 18.4 ns and 13.3 ns, with maximum values of 193 ns and 288 ns at 28 GHz and 73 GHz, respectively.Comment: 7 pages, 9 figures, 2015 IEEE International Conference on Communications (ICC), ICC Workshop

Multipath propagation characterization for terrestrial mobile and fixed microwave communications

Multipath propagation is a key issue studied throughout this thesis, and it causes dispersions in delay, frequency and spatial domains. These are dominant phenomena in both terrestrial mobile and fixed wideband communications. In this thesis, multipath propagation mechanisms including diffraction, refraction, reflection and scattering are studied when radio waves interact with dielectric and metallic objects, or an atmospheric duct. Measurements were also performed for empirical modelling and validation of the theoretical work carried out in this thesis. By using physical optics (PO) method, the attenuation by double knife edges with ground reflections is solved for the first time under a general formula of the attenuation by multiple knife edges with ground reflections derived in this thesis, and some important and interesting conclusions are obtained. The attenuations by curvilinear-topped obstacles and by multiple flat-topped obstacles are also presented in closed forms. The results are the simplest and easiest ones available now, and they can be applied for field strength predictions both in mobile and fixed microwave communications. Based on three-ray (direct, reflected and super-refracted) and two-ray (direct and super-refracted) multipath models for plane and spherical earth, respectively, frequency selective fading (FSF) and depolarization due to clear air are studied by simulations and experiments for terrestrial line-of-sight (LOS) microwave links and dual-polarized communication systems. Novel simulation methods have been introduced and applied based on the fact that the amplitudes and excess delays of the rays are functions of the (modified) refractive index gradients which are random variables with exponential and normal distributions inside and outside the duct in lower atmosphere, respectively. Some important empirical or semi-empirical models and parameters are presented at 5 GHz based on large amount of measured data in indoor and outdoor environments. The results include path loss models, excess delay and rms delay spread, spatial and frequency correlations, window (sector) length of averaging fast fading components, path number distribution, and tapped-delay-line (TDL) channel models. These empirical or semi-empirical parameters and models are the latest results achieved at 5 GHz, and they are of great importance in designing of future wireless local area networks (WLAN), especially the TDL models are developed for the first time in this frequency band. Using a general autocorrelation function derived in this thesis for three-dimensional (3-D) scattering environments, a novel theoretical modelling method is developed to study the propagation mechanisms of different types of Doppler spectra observed in measurements. The 3-D autocorrelation function is connected to the probability density functions (PDF) of the angles of arrival (AoAs) of the scattered waves and the antenna radiation patterns in the azimuth and elevation planes. This is a new work which tries to define and explain the physical reasons of 3-D Doppler spectra from propagation point of view. A new computer simulation method for wideband 3-D received signal level in an urban environment is developed under the general assumptions of the distributions for path number, amplitude, excess delay etc. This simulation method can provide detailed fading characteristics for wideband mobile communications in a specific urban environment.reviewe

Experimental analysis of multidimensional radio channels

In this thesis new systems for radio channel measurements including space and polarization dimensions are developed for studying the radio propagation in wideband mobile communication systems. Multidimensional channel characterization is required for building channel models for new systems capable of exploiting the spatial nature of the channel. It also gives insight into the dominant propagation mechanisms in complex radio environments, where their prediction is difficult, such as urban and indoor environments. The measurement systems are based on the HUT/IDC wideband radio channel sounder, which was extended to enable real-time multiple output channel measurements at practical mobile speeds at frequencies up to 18 GHz. Two dual-polarized antenna arrays were constructed for 2 GHz, having suitable properties for characterizing the 3-D spatial radio channel at both ends of a mobile communication link. These implementations and their performance analysis are presented. The usefulness of the developed measurement systems is demonstrated by performing channel measurements at 2 GHz and analyzing the experimental data. Spatial channels of both the mobile and base stations are analyzed, as well as the double-directional channel that fully characterizes the propagation between two antennas. It is shown through sample results that spatial domain channel measurements can be used to gain knowledge on the dominant propagation mechanisms or verify the current assumptions. Also new statistical information about scatterer distribution at the mobile station in urban environment is presented based on extensive real-time measurements. The developed techniques and collected experimental data form a good basis for further comparison with existing deterministic propagation models and development of new spatial channel models.reviewe

Map-based channel model parameterization and comparison of three different deterministic channel modelling methods

Abstract. The interest in studying the channel characteristics is exponentially increasing with the growth of the communication systems. Various channel modelling approaches have been discussed in the past decades. The ray-tracing based channel models are distinguished from the other channel models as they consider the environmental information and thus are expected to reflect the real propagation phenomena that exist in that specific environment. The goal of this thesis is to study the propagation channel characteristics of the three different channel models. The two deterministic channel models are the simplified map-based ray tracing channel model implemented in the METIS project and the full ray tracing-based channel model implemented by the Beijing Jiaotong University. The third channel model is the hybrid model based on METIS map-based channel. It uses the deterministic part of the METIS map-based channel model. Full ray-tracing based models require detailed description of the propagation environment or map and they target on site-specific channel modelling. Such site-specific models are not typically required in performance testing of devices, where the target is to ensure device performance in a typical propagation environment and possibly to cover some extreme cases. The simplifying map-based approach contradicts with the full ray tracing method in the way that the information of the map is reduced by approximating the building shapes and introducing artificial tiles to make scattering in the walls and ground reflections. Map-based channel modelling provides additional realism in channel models compared to traditional stochastic models applied in performance testing. The urban street canyon scenario was chosen to be modelled. The comparison was carried out at 3.5 GHz by means of performance metrics such as total path loss, LOS and NLOS propagation conditions at UE positions, K-factor, RMS delay spread, statistics of angles, angle spreads, and cross polarization ratios. The results have showed similarities in the LOS UE positions and dissimilarities in the NLOS UE positions. The reasons are identified and explained in the discussion section. It is decided to investigate the radio channel characteristics of the METIS map-based channel model and hybrid channel model for the future study purpose

Radio frequency channel characterization for energy harvesting in factory environments

This thesis presents ambient energy data obtained from a measurement campaign carried out at an automobile plant. At the automobile plant, ambient light, ambient temperature and ambient radio frequency were measured during the day time over two days. The measurement results showed that ambient light generated the highest DC power. For plant and operation managers at the automobile plant, the measurement data can be used in system design considerations for future energy harvesting wireless sensor nodes at the plant. In addition, wideband measurements obtained from a machine workshop are presented in this thesis. The power delay profile of the wireless channel was obtained by using a frequency domain channel sounding technique. The measurements were compared with an equivalent ray tracing model in order to validate the suitability of the commercial propagation software used in this work. Furthermore, a novel technique for mathematically recreating the time dispersion created by factory inventory in a radio frequency channel is discussed. As a wireless receiver design parameter, delay spread characterizes the amplitude and phase response of the radio channel. In wireless sensor devices, this becomes paramount, as it determines the complexity of the receiver. In reality, it is sometimes difficult to obtain full detail floor plans of factories for deterministic modelling or carry out spot measurements during building construction. As a result, radio provision may be suboptimal. The method presented in this thesis is based on 3-D fractal geometry. By employing the fractal overlaying algorithm presented, metallic objects can be placed on a floor plan so as to obtain similar radio frequency channel effects. The environment created using the fractal approach was used to estimate the amount of energy a harvesting device can accumulate in a University machine workshop space