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

Attenuation by a Human Body and Trees as well as Material Penetration Loss in 26 and 39 GHz Millimeter Wave Bands

This paper investigates the attenuation by a human body and trees as well as material penetration loss at 26 and 39 GHz by measurements and theoretical modeling work. The measurements were carried out at a large restaurant and a university campus by using a time domain channel sounder. Meanwhile, the knife-edge (KE) model and one-cylinder and two-cylinder models based on uniform theory of diffraction (UTD) are applied to model the shape of a human body and predict its attenuation in theory. The ITU (International Telecommunication Union) and its modified models are used to predict the attenuation by trees. The results show that the upper bound of the KE model is better to predict the attenuation by a human body compared with UTD one-cylinder and two-cylinder models at both 26 and 39 GHz. ITU model overestimates the attenuation by willow trees, and a modified attenuation model by trees is proposed based on our measurements at 26 GHz. Penetration loss for materials such as wood and glass with different types and thicknesses is measured as well. The measurement and modeling results in this paper are significant and necessary for simulation and planning of fifth-generation (5G) mm-wave radio systems in ITU recommended frequency bands at 26 and 39 GHz

L-4, a Well-Tolerated and Orally Active Inhibitor of Hedgehog Pathway, Exhibited Potent Anti-tumor Effects Against Medulloblastoma in vitro and in vivo

Inhibition of aberrant Hedgehog (Hh) pathway had been proved to be a promising therapeutic intervention in cancers like basal cell carcinoma (BCC), medulloblastoma (MB), and so on. Two drugs (Vismodegib, Sonidegib) were approved to treat BCC and more inhibitors are in clinical investigation. However, the adverse effects and drug resistance restricted the use of Hh inhibitors. In the present study, 61 synthesized compounds containing central backbone of phthalazine or dimethylpyridazine were screened as candidates of new Hh signaling inhibitors by performing dual luciferase reporter assay. Among the compounds, L-4 exhibited an IC50 value of 2.33 nM in the Shh-Light II assay. L-4 strongly inhibited the Hh pathway in vitro and blocked the Hh pathway by antagonizing the smoothened receptor (Smo). Remarkably, L-4 could significantly suppress the Hh pathway activity provoked by Smo mutant (D473H) which showed strong resistant properties to existing drugs such as Vismodegib. Orally administered L-4 exhibited prominent dose-dependent anti-tumor efficacy in vivo in Ptch+/-; p53-/- MB allograft model. Furthermore, L-4 showed good tolerance in acute toxicity test using ICR mice. These evidences indicated that L-4 was a potent, well-tolerated, orally active inhibitor of Hedgehog pathway, and might be a promising candidate in development of Hh-targeted anti-cancer drugs

Learning-Based Context-Aware Resource Allocation for Edge Computing-Empowered Industrial IoT

Edge computing provides a promising paradigm to support the implementation of industrial Internet of Things (IIoT) by offloading computational-intensive tasks from resource-limited machine-type devices (MTDs) to powerful edge servers. However, the performance gain of edge computing may be severely compromised due to limited spectrum resources, capacity-constrained batteries, and context unawareness. In this paper, we consider the optimization of channel selection which is critical for efficient and reliable task delivery. We aim at maximizing the long-term throughput subject to long-term constraints of energy budget and service reliability. We propose a learning-based channel selection framework with service reliability awareness, energy awareness, backlog awareness, and conflict awareness, by leveraging the combined power of machine learning, Lyapunov optimization, and matching theory. We provide rigorous theoretical analysis, and prove that the proposed framework can achieve guaranteed performance with a bounded deviation from the optimal performance with global state information (GSI) based on only local and causal information. Finally, simulations are conducted under both single-MTD and multi-MTD scenarios to verify the effectiveness and reliability of the proposed framework

Codebooks design and performance evaluation based on antenna array response and signal to noise ratio for mmWave communication

Codebook design is a key point in beam-forming which is necessary for millimetre Wave (mmWave) communication to compensate its huge free space path loss. In beam-forming codebook, the transmitter and the receiver co-operate to select the optimum pre-designed code vectors to satisfy robust, efficient, and reliable transmission link between two pairs. In our study, we propose a new codebook structure based on unique phase states. Based on the Array Factor (AF) and Signal-to-Noise Ratio (SNR), the proposed codebook is compared and evaluated with the uniform weighting codebook, circular array codebook, and IEEE 802.15.3c standard codebook. The results show that the proposed codebook achieves comparable SNR and array directivity with the IEEE 802.15.3c, but higher peak and wide dynamic range of SNR and better array directivity compared with the uniform weighting and circular antenna codebooks. Thus, the proposed codebook is expected to improve signal quality and increase user throughput significantly

Distributed Rate-Control and Delay-Guaranteed Scheduling in MR-MC Wireless Mesh Networks

Wireless mesh networks (WMNs) can provide flexible wireless connections in smart city, Internet of Things (IoT), and device-to-device (D2D) communications. The performance of WMNs can be greatly enhanced by adopting the multi-radio multi-channel (MR-MC) technique, which enables a node to communicate with more nodes simultaneously. However, increasing the number of data flows will result in network congestion and longer end-to-end delays. In this paper, a distributed rate-control and delay-aware (DRDA) scheduling algorithm is proposed based on a multidimensional conflict graph. To satisfy the arrival rate and delay constraints of a flow, two virtual queues are constructed. All the actual and virtual queues are stabilized by the Lyapunov drift optimization method. The scheduling policy of each flow is optimized only based on the local information. The simulation results show that our proposed algorithm can maintain the stability of all the queues and strictly satisfy the arrival rate and delay constraint of each flow in the network as well