Channel estimation techniques for next generation mobile communication systems

Mención Internacional en el título de doctorWe are witnessing a revolution in wireless technology, where the society is demanding new services, such as smart cities, autonomous vehicles, augmented reality, etc. These challenging services not only are demanding an enormous increase of data rates in the range of 1000 times higher, but also they are real-time applications with an important delay constraint. Furthermore, an unprecedented number of different machine-type devices will be also connected to the network, known as Internet of Things (IoT), where they will be transmitting real-time measurements from different sensors. In this context, the Third Generation Partnership Project (3GPP) has already developed the new Fifth Generation (5G) of mobile communication systems, which should be capable of satisfying all the requirements. Hence, 5G will provide three key aspects, such as: enhanced mobile broad-band (eMBB) services, massive machine type communications (mMTC) and ultra reliable low latency communications (URLLC). In order to accomplish all the mentioned requirements, it is important to develop new key radio technologies capable of exploiting the wireless environment with a higher efficiency. Orthogonal frequency division multiplexing (OFDM) is the most widely used waveform by the industry, however, it also exhibits high side lobes reducing considerably the spectral efficiency. Therefore, filter-bank multi-carrier combined with offset quadrature amplitude modulation (FBMC-OQAM) is a waveform candidate to replace OFDM due to the fact that it provides extremely low out-ofband emissions (OBE). The traditional spectrum frequencies range is close to saturation, thus, there is a need to exploit higher bands, such as millimeter waves (mm-Wave), making possible the deployment of ultra broad-band services. However, the high path loss in these bands increases the blockage probability of the radio-link, forcing us to use massive multiple-input multiple-output (MIMO) systems in order to increase either the diversity or capacity of the overall link. All these emergent radio technologies can make 5G a reality. However, all their benefits can be only exploited under the knowledge and availability of the channel state information (CSI) in order to compensate the effects produced by the channel. The channel estimation process is a well known procedure in the area of signal processing for communications, where it is a challenging task due to the fact that we have to obtain a good estimator, maintaining at the same time the efficiency and reduced complexity of the system and obtaining the results as fast as possible. In FBMC-OQAM, there are several proposed channel estimation techniques, however, all of them required a high number of operations in order to deal with the self-interference produced by the prototype filter, hence, increasing the complexity. The existing channel estimation and equalization techniques for massive MIMO are in general too complex due to the large number of antennas, where we must estimate the channel response of each antenna of the array and perform some prohibitive matrix inversions to obtain the equalizers. Besides, for the particular case of mm-Wave, the existing techniques either do not adapt well to the dynamic ranges of signal-to-noise ratio (SNR) scenarios or they assume some approximations which reduce the quality of the estimator. In this thesis, we focus on the channel estimation for different emerging techniques that are capable of obtaining a better performance with a lower number of operations, suitable for low complexity devices and for URLLC. Firstly, we proposed new pilot sequences for FBMC-OQAM enabling the use of a simple averaging process in order to obtain the CSI. We show that our technique outperforms the existing ones in terms of complexity and performance. Secondly, we propose an alternative low-complexity way of computing the precoding/postcoding equalizer under the scenario of massive MIMO, keeping the quality of the estimator. Finally, we propose a new channel estimation technique for massive MIMO for mm-Wave, capable of adapting to very variable scenarios in terms of SNR and outperforming the existing techniques. We provide some analysis of the mean squared error (MSE) and complexity of each proposed technique. Furthermore, some numerical results are given in order to provide a better understanding of the problem and solutions.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Antonia María Tulino.- Secretario: Máximo Morales Céspedes.- Vocal: Octavia A. Dobr

Study on the Influence Mechanism of Inner Oil to the Impact Resistance of the Fixed-roof Storage Tank against the Explosion Blast Wave

PresentationThe explosion blast wave in the chemical park will cause the domino effect and serious damage to the surrounding tanks. In order to study the influence mechanism of the inner oil on the impact resistance of the large-scale fixed-roof storage tank against the explosion blast wave, the finite element software LS-DYNA is used to establish finite element model of 5,000 m3 fixed-roof storage tank with inner oil height of 0m, 5 m, 10 m and 15 m, when the vertical height of the explosion point center to the ground is 0.4m, 5m, 10m, 15m, respectively. The failure process, the maximum displacement of tank wall, the total energy, kinetic energy and internal energy transformed from explosion are obtained by simulation and analysis. The results show: the failure process of the tank is mainly concave deformation and buckling deformation, no matter how the oil height changes. Stress concentration commonly occurs at the maximum displacement of the concave deformation and the plastic hinge lines produced by the buckling deformation; the maximum displacement of the tank wall is mainly affected by the relative vertical height between explosion point and oil; when the explosion point mass and the horizontal distance from the point to the nearby tank wall are constant, the total energy of the tank transformed from explosion is mainly affected by the oil height, and it is almost not affected by the change of the vertical height of the explosion point. And the maximum displacement of the tank wall is irrelevant with the total energy of the tank

SINR analysis of OFDM and f-OFDM for machine type communications

Proceeding of: 2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), Valencia, 4-8 septiembre, 2016.Machine type communications (MTC) have been growing significantly in recent years and this tendency is foreseen to be kept in the near future playing an increasingly important role in the industry. The signals used for MTC will coexist with the current and next generation cellular systems. Therefore it is of interest to study how they can perform jointly and the viability of coexistence of signals from both systems. We focus in one of the new waveforms being discussed for 5G, namely on filtered-OFDM (f-OFDM), along with traditional OFDM. The interference is analysed for both types of signals and the expression of the SINR is found allowing us to compare the behavior of OFDM and f-OFDM in these circumstances. Some simulations are shown to validate the theoretical analysis and explore some foreseen MTC scenarios.This work has been partly funded by projects MACHINE (TSI-100102-2015-17) and ELISA (TEC2014-59255-C3-3-R)

Spurious detection of phase synchronization in coupled nonlinear oscillators

Coupled nonlinear systems under certain conditions exhibit phase synchronization, which may change for different frequency bands or with presence of additive system noise. In both cases, Fourier filtering is traditionally used to preprocess data. We investigate to what extent the phase synchronization of two coupled R\"{o}ssler oscillators depends on (1) the broadness of their power spectrum, (2) the width of the band-pass filter, and (3) the level of added noise. We find that for identical coupling strengths, oscillators with broader power spectra exhibit weaker synchronization. Further, we find that within a broad band width range, band-pass filtering reduces the effect of noise but can lead to a spurious increase in the degree of synchronization with narrowing band width, even when the coupling between the two oscillators remains the same.Comment: 4 pages,6 figure

Non-Coherent Multiuser Massive MIMO-OFDM with Differential Modulation

Proceedings of: ICC 2019 - 2019 IEEE International Conference on Communications (ICC), 20-24 may, 2019, Shanghai.Massive multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) are wireless technologies adopted by the Fifth Generation (5G) of mobile communications. The channel estimation and pre/postequalization processes in coherent detection schemes for massive MIMO-OFDM are a challenging task, where several issues are faced, such as pilot contamination, channel calibration, matrix inversions, among others. Moreover, they increase the energy consumption and latency of the system. A non-coherent technique relying on DPSK constellation has been proposed for a singlecarrier scheme, assuming flat-fading. In our paper, we extend this technique to be combined with OFDM, where the channel is doubly dispersive (time and frequency). We will show that the differential modulation can be performed either in the time or frequency domain, where the latter suffers from an additional phase rotation, which should be estimated and compensated. We provide the analytical expression of the signal-to-interferenceand-noise ratio (SINR) for both cases, and we show numerical results in order to verify our analysis.This work has been funded by project TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE)

Low-complexity zero-forcing equalization for massive MIMO-OFDM

This poster has been accepted for presentation at the IEEE Communication Theory Workshop (IEEE CTW 2018 ), 15-16 May, 2018, Miramar Beach, Florida.Massive MIMO combined with OFDM are key techniques in the evolution of mobile communications. In this context, to the best of our knowledge, the channel estimation and the equalizers have never been jointly considered. We propose an alternative low-complexity method to compute the ZF equalizers, which consists of exchanging the order of the interpolation and computation of the equalizer. For massive MIMO, this strategy provides the same performance and considerably lower number of operations, compared to the traditional scheme.This work has been partly funded by projects MACHINE (TSI-100102-2015-17), ELISA (TEC2014-59255-C3-3-R) and TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE)