Systems with Massive Number of Antennas: Distributed Approaches

As 5G is entering maturity, the research interest has shifted towards 6G, and specially the new use cases that the future telecommunication infrastructure needs to support. These new use cases encompass much higher requirements, specifically: higher communication data-rates, larger number of users, higher accuracy in localization, possibility to wirelessly charge devices, among others.The radio access network (RAN) has already gone through an evolution on the path towards 5G. One of the main changes was a large increment of the number of antennas in the base-station. Some of them may even reach 100 elements, in what is commonly referred as Massive MIMO. New proposals for 6G RAN point in the direction of continuing this path of increasing the number of antennas, and locate them throughout a certain area of service. Different technologies have been proposed in this direction, such as: cell-free Massive MIMO, distributed MIMO, and large intelligent surface (LIS). In this thesis we focus on LIS, whose conducted theoretical studies promise the fulfillment of the aforementioned requirements.While the theoretical capabilities of LIS have been conveniently analyzed, little has been done in terms of implementing this type of systems. When the number of antennas grow to hundreds or thousands, there are numerous challenges that need to be solved for a successful implementation. The most critical challenges are the interconnection data-rate and the computational complexity.In the present thesis we introduce the implementation challenges, and show that centralized processing architectures are no longer adequate for this type of systems. We also present different distributed processing architectures and show the benefits of this type of schemes. This work aims at giving a system-design guideline that helps the system designer to make the right decisions when designing these type of systems. For that, we provide algorithms, performance analysis and comparisons, including first order evaluation of the interconnection data-rate, processing latency, memory and energy consumption. These numbers are based on models and available data in the literature. Exact values depend on the selected technology, and will be accurately determined after building and testing these type of systems.The thesis concentrates mostly on the topic of communication, with additional exploration of other areas, such as localization. In case of localization, we benefit from the high spatial resolution of a very-large array that provides very rich channel state information (CSI). A CSI-based fingerprinting via neural network technique is selected for this case with promising results. As the communication and localization services are based on the acquisition of CSI, we foresee a common system architecture capable of supporting both cases. Further work in this direction is recommended, with the possibility of including other applications such as sensing.The obtained results indicate that the implementation of these very-large array systems is feasible, but the challenges are numerous. The proposed solutions provide encouraging results that need to be verified with hardware implementations and real measurements

Model predictive current control of switched reluctance motor with inductance auto-calibration

The thesis is composed of three papers, which investigate the application of Model Predictive Controller (MPC) for current control of Switched Reluctance Motor (SRM). Since the conventional hysteresis current control method is not suitable for high power SRM drive system with low inductance and limited switching frequency, MPC is a promising alternative approach for this application. The proposed MPC can cope with the measurement noise as well as uncertainties within the machine inductance profile. In the first paper, a MPC current control method for Double-Stator Switched Reluctance Motor (DSSRM) drives is presented. A direct adaptive estimator is incorporated to follow the inductance variations in a DSSRM. In the second paper, the Linear Quadratic (LQ) form and dynamic programming recursion for MPC are analyzed, afterwards the unconstrained MPC solution for stochastic SRM model is derived. The Kalman filter is employed to reduce the variance of measurement noises. Based on Recursive Linear-Square (RLS) estimation, the inductance profile is calibrated dynamically. In the third paper, a simplified recursive MPC current control algorithm for SRM is applied for embedded implementation. A novel auto-calibration method for inductance surface estimation is developed to improve current control performance of SRM drive in statistic terms. --Abstract, page iv

Re-Sonification of Objects, Events, and Environments

abstract: Digital sound synthesis allows the creation of a great variety of sounds. Focusing on interesting or ecologically valid sounds for music, simulation, aesthetics, or other purposes limits the otherwise vast digital audio palette. Tools for creating such sounds vary from arbitrary methods of altering recordings to precise simulations of vibrating objects. In this work, methods of sound synthesis by re-sonification are considered. Re-sonification, herein, refers to the general process of analyzing, possibly transforming, and resynthesizing or reusing recorded sounds in meaningful ways, to convey information. Applied to soundscapes, re-sonification is presented as a means of conveying activity within an environment. Applied to the sounds of objects, this work examines modeling the perception of objects as well as their physical properties and the ability to simulate interactive events with such objects. To create soundscapes to re-sonify geographic environments, a method of automated soundscape design is presented. Using recorded sounds that are classified based on acoustic, social, semantic, and geographic information, this method produces stochastically generated soundscapes to re-sonify selected geographic areas. Drawing on prior knowledge, local sounds and those deemed similar comprise a locale's soundscape. In the context of re-sonifying events, this work examines processes for modeling and estimating the excitations of sounding objects. These include plucking, striking, rubbing, and any interaction that imparts energy into a system, affecting the resultant sound. A method of estimating a linear system's input, constrained to a signal-subspace, is presented and applied toward improving the estimation of percussive excitations for re-sonification. To work toward robust recording-based modeling and re-sonification of objects, new implementations of banded waveguide (BWG) models are proposed for object modeling and sound synthesis. Previous implementations of BWGs use arbitrary model parameters and may produce a range of simulations that do not match digital waveguide or modal models of the same design. Subject to linear excitations, some models proposed here behave identically to other equivalently designed physical models. Under nonlinear interactions, such as bowing, many of the proposed implementations exhibit improvements in the attack characteristics of synthesized sounds.Dissertation/ThesisPh.D. Electrical Engineering 201

Automatic design of analogue circuits

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Evolvable Hardware (EHW) is a promising area in electronics today. Evolutionary Algorithms (EA), together with a circuit simulation tool or real hardware, automatically designs a circuit for a given problem. The circuits evolved may have unconventional designs and be less dependent on the personal knowledge of a designer. Nowadays, EA are represented by Genetic Algorithms (GA), Genetic Programming (GP) and Evolutionary Strategy (ES). While GA is definitely the most popular tool, GP has rapidly developed in recent years and is notable by its outstanding results. However, to date the use of ES for analogue circuit synthesis has been limited to a few applications. This work is devoted to exploring the potential of ES to create novel analogue designs. The narrative of the thesis starts with a framework of an ES-based system generating simple circuits, such as low pass filters. Then it continues with a step-by-step progression to increasingly sophisticated designs that require additional strength from the system. Finally, it describes the modernization of the system using novel techniques that enable the synthesis of complex multi-pin circuits that are newly evolved. It has been discovered that ES has strong power to synthesize analogue circuits. The circuits evolved in the first part of the thesis exceed similar results made previously using other techniques in a component economy, in the better functioning of the evolved circuits and in the computing power spent to reach the results. The target circuits for evolution in the second half are chosen by the author to challenge the capability of the developed system. By functioning, they do not belong to the conventional analogue domain but to applications that are usually adopted by digital circuits. To solve the design tasks, the system has been gradually developed to support the ability of evolving increasingly complex circuits. As a final result, a state-of-the-art ES-based system has been developed that possesses a novel mutation paradigm, with an ability to create, store and reuse substructures, to adapt the mutation, selection parameters and population size, utilize automatic incremental evolution and use the power of parallel computing. It has been discovered that with the ability to synthesis the most up-to-date multi-pin complex analogue circuits that have ever been automatically synthesized before, the system is capable of synthesizing circuits that are problematic for conventional design with application domains that lay beyond the conventional application domain for analogue circuits

Algorithms and architectures for the multirate additive synthesis of musical tones

In classical Additive Synthesis (AS), the output signal is the sum of a large number of independently controllable sinusoidal partials. The advantages of AS for music synthesis are well known as is the high computational cost. This thesis is concerned with the computational optimisation of AS by multirate DSP techniques. In note-based music synthesis, the expected bounds of the frequency trajectory of each partial in a finite lifecycle tone determine critical time-invariant partial-specific sample rates which are lower than the conventional rate (in excess of 40kHz) resulting in computational savings. Scheduling and interpolation (to suppress quantisation noise) for many sample rates is required, leading to the concept of Multirate Additive Synthesis (MAS) where these overheads are minimised by synthesis filterbanks which quantise the set of available sample rates. Alternative AS optimisations are also appraised. It is shown that a hierarchical interpretation of the QMF filterbank preserves AS generality and permits efficient context-specific adaptation of computation to required note dynamics. Practical QMF implementation and the modifications necessary for MAS are discussed. QMF transition widths can be logically excluded from the MAS paradigm, at a cost. Therefore a novel filterbank is evaluated where transition widths are physically excluded. Benchmarking of a hypothetical orchestral synthesis application provides a tentative quantitative analysis of the performance improvement of MAS over AS. The mapping of MAS into VLSI is opened by a review of sine computation techniques. Then the functional specification and high-level design of a conceptual MAS Coprocessor (MASC) is developed which functions with high autonomy in a loosely-coupled master- slave configuration with a Host CPU which executes filterbanks in software. Standard hardware optimisation techniques are used, such as pipelining, based upon the principle of an application-specific memory hierarchy which maximises MASC throughput

Practical implementation of long-horizon direct model predictive control

Thesis (MEng)--Stellenbosch University, 2018.ENGLISH ABSTRACT: The use of model predictive control in power electronics has increased significantly in recent years. More specifically, the so-called direct model predictive control methods are primarily considered for power electronic converters due to their switching nature. In direct control methods the output of the controller directly manipulates the converter inputs, which are restricted to integers, without the use of a modulator. However, predominantly, only a short horizon of one prediction step is considered. This can be attributed to two reasons. Firstly, it has been previously regarded that longer horizons do not provide any performance benefits in power electronics. Secondly, the computational burden associated with prediction horizon increases exponentially, discouraging practical consideration. Recently it was shown that the stigma that longer horizons do not provide performance benefits is false, and that long horizons do indeed increase the harmonic performance of a converter. In fact, if the prediction horizon is long enough, model predictive control can compete with the highly regarded optimised pulse patterns in terms of harmonic distortion. Furthermore, it was shown that the optimization problem of direct model predictive control with long horizons can be reformulated as an integer least-squares. A branch-and-bound method, known as sphere decoding, can solve the reformulated optimization problem in a time-efficient manner, enabling practical considerations. The primary contribution of this thesis is the practical implementation of long-horizon direct model predictive control. A detailed description of the implementation of the controller within a field programmable gate-array is given. It is shown that, for almost 90% of the cases, only 8:4 μs are required to calculate the optimal inputs for a three-phase neutral-point-clamped inverter when using a prediction horizon of 5 with a sampling interval of 25 μs. Continuing on the practical implementation of long-horizon direct model predictive control, experimental results are captured and analysed for prediction horizons one to five. The claim that longer horizons do provide a performance increase is validated through experimental results. A decrease of roughly 8:5% in total total harmonic distortion at a switching frequency of 250 Hz is achieved when adopting a prediction horizon of five instead of one. The secondary contribution of this thesis is the proposal of a method to selectively suppress selected harmonics. The formulation of the method is explained, and simulations are used to verify the suppression of harmonics.AFRIKAANSE OPSOMMING: Die toepassing van modelvoorspellendebeheer vir drywsingselektronika het aansienlik toegeneem in die afgelope paar jaar. Die sogenaamde direkte voorspellende beheer tegnieke is veral van toepassing tot die veld van drywingselektronika as gevolg van die skakelnatuur van die toerusting. ’n Modulator is afwesig wanneer direkte beheer metodes gebruik word, omdat die beheersein direk aan die intree van die omsetter gekoppel word. Die beheersein is daarom beperk tot heelgetalle. Oor die algemeen word ’n kort voorspellings horison van een gebruik. Daar is hoofsaaklik twee redes hiervoor. Eerstens, in die verlede was daar verneem dat langer horison geen voordelige bydra tot die optrede van ’n drywsingelektroniese toestel in hou nie. Tweedens, berekeninge wat verband hou met die voorspellings horison verhoog eksponensieel en ontmoedig daarom die gebruik daarvan. Dit was redelik onlangs bewys dat langer horisonne wel ’n beduidende positiewe bydrae tot die werking van drywingselektroniese toestelle maak. Indien die horison lank genoeg is, kan voorspellende beheer redelik goed kompeteer met die hoog aangeskrewe optimalepulspatrone. Verder was dit bewys dat die direkte-voorspellendebeheer optimeringsprobleem herformuleer kan word as ’n heelgetal-kwadratiese optimeringsprobleem. ’n Metode wat bekend staan as sfeerdekodering kan gebruik word om die herformuleerde optimeringsprobleem effektief op te los, wat die praktiese gebruik daarvan bemoedig. Die primêre bydrae van die tesis is die praktiese implementering van direkte modelvoorspellendebeheer met lang horisonne. ’n Gedetailleerde beskrywing om die beheerder binne ’n veldprogrammeerbare hekskikking te implementeer word aangebied. Dit word bewys dat in byna 90% van die gevalle slegs 8:4 μs benodig word om die optimale intree te bereken vir ’n driefase neutralepuntgeklampte omsetter, wanneer ’n voorspellings horison van vyf gebruik word met ’n monsterperiode van 25 μs. Verder word praktiese resultate aangebied vir voorspellendehorisonne vanaf een tot vyf. Dit word bewys dat langer horisonne verbetering rakende die harmoniese gedrag van drywingselektroniese toestelle teweeg bring. ’n Afname van 8:5% in stroomharmoniesedistorsie teen ’n skakelfrekwensie van 250 Hz word waargeneem, wanneer ’n voorspellendehorison van vyf in plaas van een gebruik word. Die sekondêre bydrae van die tesis is die bekendstelling van ’n metode om harmonieke selektief te onderdruk. Die formulering van die metode word verduidelik en simulasies word uitgevoer om te bevestig dat harmoieke wel onderdruk word

Linear-Phase FIR Digital Filter ‎Design with Reduced Hardware Complexity using Discrete Differential Evolution

Optimal design of xed coe cient nite word length linear phase FIR digital lters for custom ICs has been the focus of research in the past decade. With the ever increasing demands for high throughput and low power circuits, the need to design lters with reduced hardware complexity has become more crucial. Multiplierless lters provide substantial saving in hardware by using a shift add network to generate the lter coe cients. In this thesis, the multiplierless lter design problem is modeled as combinatorial optimization problem and is solved using a discrete Di erential Evolution algorithm. The Di erential Evolution algorithm\u27s population representation adapted for the nite word length lter design problem is developed and the mutation operator is rede ned for discrete valued parameters. Experiments show that the method is able to design lters up to a length of 300 taps with reduced hardware and shorter design times