Advanced Symbol-level Precoding Schemes for Interference Exploitation in Multi-antenna Multi-user Wireless Communications

The utilization of multi-antenna transmitters relying on full frequency reuse has proven to be an effective strategy towards fulfilling the constantly increasing throughput requirements of wireless communication systems. As a consequence, in the last two decades precoding has been a prolific research area, due to its ability to handle the interference arising among simultaneous transmissions addressed to different co-channel users. The conventional precoding strategies aim at mitigating the multi-user interference (MUI) by exploiting the knowledge of the channel state information (CSI). More recently, novel approaches have been proposed where the aim is not to eliminate the interference, but rather to control it so as to achieve a constructive interference effect at each receiver. In these schemes, referred to as symbol-level precoding (SLP), the data information (data symbols) is used together with the CSI in the precoding design, which can be addressed following several optimization strategies. In the context of SLP, the work carried out in this thesis is mainly focused on developing more advanced optimization strategies suitable to non-linear systems, where the per-antenna high-power amplifiers introduce an amplitude and phase distortion on the transmitted signals. More specifically, the main objective is to exploit the potential of SLP not only to achieve the constructive interference at the receivers, but also to control the per-antenna instantaneous transmit power, improving the power dynamics of the transmitted waveforms. In fact, a reduction of the power variation of the signals, both in the spatial dimension (across the different antennas) and in the temporal dimension, is particularly important for mitigating the non-linear effects. After a detailed review of the state of the art of SLP, the first part of the thesis is focused on improving the power dynamics of the transmitted signals in the spatial dimension, by reducing the instantaneous power imbalances across the different antennas. First, a SLP per-antenna power minimization scheme is presented, followed by a related max-min fair formulation with per-antenna power constraints. These approaches allow to reduce the power peaks of the signals across the antennas. Next, more advanced SLP schemes are formulated and solved, with the objective of further improving the spatial dynamics of the signals. Specifically, a first approach performs a peak power minimization under a lower bound constraint on the per-antenna transmit power, while a second strategy minimizes the spatial peak-to-average power ratio. The second part of this thesis is devoted to developing a novel SLP method, referred to as spatio-temporal SLP, where the temporal variation of the transmit power is also considered in the SLP optimization. This new model allows to minimize the peak-to-average power ratio of the transmitted waveforms both in the spatial and in the temporal dimensions, thus further improving the robustness of the signals to non-linear effects. Then, this thesis takes one step further, by exploiting the developed spatio-temporal SLP model in a different context. In particular, a spatio-temporal SLP scheme is proposed which enables faster-than-Nyquist (FTN) signaling over multi-user systems, by constructively handling at the transmitter side not only the MUI but also the inter-symbol interference (ISI). This strategy allows to benefit from the increased throughput provided by FTN signaling without imposing additional complexity at the user terminals. Extensive numerical results are presented throughout the thesis, in order to assess the performance of the proposed schemes with respect to the state of the art in SLP. The thesis concludes summarizing the main research findings and identifying the open problems, which will constitute the basis for the future work

Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications

The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well

Adaptive waveform design for SAR in a crowded spectrum

This thesis concerns the development of an adaptive waveform design scheme for synthetic aperture radar (SAR) to support its operation in the increasingly crowded radio frequency (RF) spectrum, focusing on mitigating the effects of external RF interference. The RF spectrum is a finite resource and the rapid expansion of the telecommunications industry has seen radar users face a significant restriction in the range of available operational frequencies. This crowded spectrum scenario leads to increased likelihood of RF interference either due to energy leakage from neighbouring spectral users or from unlicensed transmitters. SAR is a wide bandwidth radar imaging mode which exploits the motion of the radar platform to form an image using multiple one dimensional profiles of the scene of interest known as the range profile. Due to its wideband nature, SAR is particularly vulnerable to RF interference which causes image impairments and overall reduction in quality. Altering the approach for radar energy transmission across the RF spectrum is now imperative to continue effective operation. Adaptive waveforms have recently become feasible for implementation and offer the much needed flexibility in the choice and control over radar transmission. However, there is a critically small processing time frame between waveform reception and transmission, which necessitates the use of computationally efficient processing algorithms to use adaptivity effectively. This simulation-based study provides a first look at adaptive waveform design for SAR to mitigate the detrimental effects of RF interference on a pulse-to-pulse basis. Standard SAR systems rely on a fixed waveform processing format on reception which restricts its potential to reap the benefits of adaptive waveform design. Firstly, to support waveform design for SAR, system identification techniques are applied to construct an alternative receive processing method which allows flexibility in waveform type. This leads to the main contribution of the thesis which is the formation of an adaptive spectral waveform design scheme. A computationally efficient closed-form expression for the waveform spectrum that minimizes the error in the estimate of the SAR range profile on a pulse to pulse basis is derived. The range profile and the spectrum of the interference are estimated at each pulse. The interference estimate is then used to redesign the proceeding waveform for estimation of the range profile at the next radar platform position. The solution necessitates that the energy is spread across the spectrum such that it competes with the interferer. The scenario where the waveform admits gaps in the spectrum in order to mitigate the effects of the interference is also detailed and is the secondary major thesis contribution. A series of test SAR images demonstrate the efficacy of these techniques and yield reduced interference effects compared to the standard SAR waveform

Advanced receivers and waveforms for UAV/Aircraft aeronautical communications

Nowadays, several studies are launched for the design of reliable and safe communications systems that introduce Unmanned Aerial Vehicle (UAV), this paves the way for UAV communication systems to play an important role in a lot of applications for non-segregated military and civil airspaces. Until today, rules for integrating commercial UAVs in airspace still need to be defined, the design of secure, highly reliable and cost effective communications systems still a challenging task. This thesis is part of this communication context. Motivated by the rapid growth of UAV quantities and by the new generations of UAVs controlled by satellite, the thesis aims to study the various possible UAV links which connect UAV/aircraft to other communication system components (satellite, terrestrial networks, etc.). Three main links are considered: the Forward link, the Return link and the Mission link. Due to spectrum scarcity and higher concentration in aircraft density, spectral efficiency becomes a crucial parameter for largescale deployment of UAVs. In order to set up a spectrally efficient UAV communication system, a good understanding of transmission channel for each link is indispensable, as well as a judicious choice of the waveform. This thesis begins to study propagation channels for each link: a mutipath channels through radio Line-of-Sight (LOS) links, in a context of using Meduim Altitude Long drones Endurance (MALE) UAVs. The objective of this thesis is to maximize the solutions and the algorithms used for signal reception such as channel estimation and channel equalization. These algorithms will be used to estimate and to equalize the existing muti-path propagation channels. Furthermore, the proposed methods depend on the choosen waveform. Because of the presence of satellite link, in this thesis, we consider two low-papr linear waveforms: classical Single-Carrier (SC) waveform and Extented Weighted Single-Carrier Orthogonal Frequency-Division Multiplexing (EW-SC-OFDM) waveform. channel estimation and channel equalization are performed in the time-domain (SC) or in the frequency-domain (EW-SC-OFDM). UAV architecture envisages the implantation of two antennas placed at wings. These two antennas can be used to increase diversity gain (channel matrix gain). In order to reduce channel equalization complexity, the EWSC- OFDM waveform is proposed and studied in a muti-antennas context, also for the purpose of enhancing UAV endurance and also increasing spectral efficiency, a new modulation technique is considered: Spatial Modulation (SM). In SM, transmit antennas are activated in an alternating manner. The use of EW-SC-OFDM waveform combined to SM technique allows us to propose new modified structures which exploit exces bandwidth to improve antenna bit protection and thus enhancing system performances

Searches for Neutrinos from Supernovae Using Cherenkov In-Ice Detectors

Supernovae mark the violent death of massive stars. They are among the most energetic processes known to exist in the Universe. Neutrinos play crucial roles in supernova processes. Besides the low-energy neutrinos emitted during the core-collapse process of the supernova, there may be neutrinos of much higher energies that are generated after the core-collapse. In this work, a new detector embedded in Antarctic glacier ice is studied, with sensitivity to extra-galactic supernova low-energy neutrino bursts. It is demonstrated that the development of optical sensors with large effective area and low noise rate is a requirement. For the proposed detector, several extra-galactic supernova neutrino detections per year are feasible. In addition, a multi-messenger data analysis program is carried out, which registers high-energy neutrino bursts with the IceCube detector and triggers follow-up observations with optical telescopes. No significant excess of neutrino bursts is found. Therefore, upper limits on the jet supernova model are derived. For model values of the jet Lorentz factor Γjet = 10 and the jet kinetic energy Ejet = 3 × 1051 erg, only about 8% of all core-collapse supernovae hosting a jet are consistent with the data.Suche nach Supernova-Neutrinos mit Cherenkov-Detektoren in Eis Supernovae sind gewaltige Explosionen am Lebensende massereicher Sterne. Sie gehören zu den energiereichsten bekannten Prozessen im Universum. Neutrinos spielen entscheidende Rollen während und nach Supernova-Explosionen. Neben den niederenergetischen Neutrinos, die während des Kernkollapsprozesses der Supernova emittiert werden, könnten Neutrinos von sehr viel höherer Energie nach dem Kernkollaps enstehen. In dieser Arbeit wird ein neues Detektorkonzept untersucht, mit Sensitivität für extragalaktische niederenergetische Supernova-Neutrino-Blitze. Die Notwendigkeit der Entwicklung optischer Sensoren mit großer effektiver Fläche und niedriger Rauschrate wird aufgezeigt. Der untersuchte Detektor könnte mehrere extra-galaktische Supernova-Neutrino-Detektionen pro Jahr liefern. Weiter wird ein multi-messenger Datenanalyseprogramm durchgeführt, welches hochenergetische Neutrinoblitze mit dem IceCube-Detektor registriert und automatisch Nachfolgebeobachtungen mit optischen Teleskopen auslöst. Kein signifikanter Exzess von Neutrino-Blitzen wird gefunden. Entsprechend werden obere Grenzen auf das Jet-Supernova-Modell berechnet. Für die Modellparameter Lorentzfaktor Γjet = 10 und kinetische Energie des Jets Ejet = 3 × 1051 erg sind höchstens etwa 8% aller Kernkollaps-Supernovae als Träger eines solchen Jets mit den Daten verträglich

Engineering planetary lasers for interstellar communication

Transmitting large amounts of data efficiently among neighboring stars will vitally support any eventual contact with extrasolar intelligence, whether alien or human. Laser carriers are particularly suitable for high-quality, targeted links. Space laser transmitter systems designed by this work, based on both demonstrated and imminent advanced space technology, could achieve reliable data transfer rates as high as 1 kb/s to matched receivers as far away as 25 pc, a distance including over 700 approximately solar-type stars. The centerpiece of this demonstration study is a fleet of automated spacecraft incorporating adaptive neural-net optical processing active structures, nuclear electric power plants, annular momentum control devices, and ion propulsion. Together the craft sustain, condition, modulate, and direct to stellar targets an infrared laser beam extracted from the natural mesospheric, solar-pumped, stimulated CO2 emission recently discovered at Venus. For a culture already supported by mature interplanetary industry, the cost of building planetary or high-power space laser systems for interstellar communication would be marginal, making such projects relevant for the next human century. Links using high-power lasers might support data transfer rates as high as optical frequencies could ever allow. A nanotechnological society such as we might become would inevitably use 10 to the 20th power b/yr transmission to promote its own evolutionary expansion out of the galaxy

Research on the propagation efficiency of ultrasonic guided waves in the rail

Ultrasonic guided waves (UGW) technique has the advantages of low detection frequency, long detection distance, strong anti-electromagnetic interference ability, and large coverage. Hence it has potential advantages in real-time detection of breakages in the rail. Based on the research background of UGW-based broken rail detection, this paper focuses on the characteristics optimization of piezoelectric ultrasonic transducers (PUTs) to improve the propagation efficiency of UGW in the rail. Due to the influence of energy attenuation, multimodal, dispersion, and on-site noise when the UGW propagates in the rail, the amplitude of the received UGW signal is low and the signal-to-noise ratio is poor. Therefore, this thesis mainly systematically studies the characteristics optimization of PUTs from the aspects of impedance matching, driving circuit optimization, and excitation signal optimization. The main work is as follows: 1. To deeply study of the electromechanical characteristics of longitudinal vibration sandwich piezoelectric ultrasonic transducer (referred to as PUTs), the PSpice equivalent circuit models of a piezoelectric ultrasonic transducer and the PSpice equivalent circuit model of a pitch-catch setup are established based on one-dimensional wave and transmission line theory. The PSpice model of the PUT and the PSpice model of the pitch-catch setup are analyzed from the time and frequency domains, respectively, and the accuracy of the built PSpice models is verified through some experiments. It is shown that the PSpice model of a PUT established above is highly scalable and can be combined with amplifiers, driving circuits, diodes. 2. With the aim of solving the problem of impedance mismatch between the piezoelectric ultrasonic transducer and the driving circuit and the rail surface, the effect of the impedance matching on the electromechanical properties of the piezoelectric ultrasonic transducer was studied from the electrical and acoustic ends, respectively. From the electrical side, the effects of different electrical impedance matching networks on the electromechanical characteristics of PUTs are studied in both time and frequency domains. It is shown that in the two LC impedance matching networks, the matching network formed by the series inductance and parallel capacitance is better. From the acoustic side, an experimental method is used to study the effect of acoustic impedance matching on the transient characteristics of PUTs. It is concluded that when the epoxy resin is doped with 10% tungsten powder and the coating thickness is 8 mm, the acoustic impedance matching effect is better. 3. To overcome the problems of the existing driving circuits that the excitation voltage is not high enough, the extra high voltage DC voltage is required and the impedance matching is not considered, this thesis proposed a high voltage pulse driving circuit based on the full-bridge topology. The driving circuit takes into account the suppression of overshoot and oscillation when the power MOSFET is turned off, and at the same time conducts the impedance matching and tailing absorption of the excitation signal for PUTs. The suppression of overshoot and oscillation adopts the RC snubber circuit, and the tailing absorption is accomplished by a bleeder resistor and a bidirectional thyristor. The correctness and effectiveness of the proposed high-voltage pulse driving circuit are verified through experiments. It was also found that the combined use of electrical impedance matching and absorption circuits can effectively improve the energy conversion efficiency of PUTs. 4. To obtain the optimal performance of PUTs, the excitation signal of PUTs is optimized in terms of excitation signal frequency and excitation coding. First of all, to solve the problem of PUTs with having a resonance frequency shift after loading, this thesis proposes an optimal excitation frequency tracking method based on a digital band-pass tracking filtering. Then its correctness and stability are verified through some field experiments. Secondly, to improve the signal-to-noise ratio of the UGW signal, it is proposed to apply the Barker code excitation method to the broken rail detection, and use the pulse compression technique at the receiving end to realize the rapid recognition of the signal characteristics. Finally, for the case where the pulse-compressed signal produces undesirable peak sidelobes due to the effects of bandwidth, multipath, and noise, an adaptive peak detection algorithm based on the Hilbert transform combined with a digital bandpass tracking filter and a triangle filter. The accuracy and effectiveness of the above-mentioned Barker code excitation method and the adaptive peak detection algorithm are verified through experiments. The study in this thesis presents a feasible solution for improving the propagation efficiency of UGW in the rails and at the same time provides theoretical guidance for the large-scale application of the real-time broken rail detection system based on UGW

Optimization of Operation Sequencing in CAPP Using Hybrid Genetic Algorithm and Simulated Annealing Approach

In any CAPP system, one of the most important process planning functions is selection of the operations and corresponding machines in order to generate the optimal operation sequence. In this paper, the hybrid GA-SA algorithm is used to solve this combinatorial optimization NP (Non-deterministic Polynomial) problem. The network representation is adopted to describe operation and sequencing flexibility in process planning and the mathematical model for process planning is described with the objective of minimizing the production time. Experimental results show effectiveness of the hybrid algorithm that, in comparison with the GA and SA standalone algorithms, gives optimal operation sequence with lesser computational time and lesser number of iterations

Optimization of Operation Sequencing in CAPP Using Hybrid Genetic Algorithm and Simulated Annealing Approach

In any CAPP system, one of the most important process planning functions is selection of the operations and corresponding machines in order to generate the optimal operation sequence. In this paper, the hybrid GA-SA algorithm is used to solve this combinatorial optimization NP (Non-deterministic Polynomial) problem. The network representation is adopted to describe operation and sequencing flexibility in process planning and the mathematical model for process planning is described with the objective of minimizing the production time. Experimental results show effectiveness of the hybrid algorithm that, in comparison with the GA and SA standalone algorithms, gives optimal operation sequence with lesser computational time and lesser number of iterations

Autonomous Navigation of Automated Guided Vehicle Using Monocular Camera

This paper presents a hybrid control algorithm for Automated Guided Vehicle (AGV) consisting of two independent control loops: Position Based Control (PBC) for global navigation within manufacturing environment and Image Based Visual Servoing (IBVS) for fine motions needed for accurate steering towards loading/unloading point. The proposed hybrid control separates the initial transportation task into global navigation towards the goal point, and fine motion from the goal point to the loading/unloading point. In this manner, the need for artificial landmarks or accurate map of the environment is bypassed. Initial experimental results show the usefulness of the proposed approach.COBISS.SR-ID 27383808