Theses - Department of Electrical and Electronics Engineering
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Item Open Access 2-18 GHZ MMIC distributed amplifiers(Bilkent University, 1994) Ergun, SanlıUsing GaAs Monolithic Microwave Integrated Circuit (MMIC) technology three distributed amplifiers are realized. Two of these amplifiers employ single gate FETs and operate in the 2-18 GHz frequency range. They have 4.5 and 6.5 dB gain, respectively. The third amplifier utilizes cascode connected FETs. This amplifier operates in the 2-20 GHz range and has a gain of ~10 dB. All the three amplifiers have input and output return losses better than 10 dB. The isolation of the amplifiers with single gate FETs is better than 20 dB, whereas the cascode connection improves the isolation over 30 dB. The amplifiers are designed for a 50O-svstem. The simulations are made linearly, and the results match the theoretical work. In the design of these amplifiers a more detailed method is used in which the artificial transmission lines are investigated and optimized in their frequency behaviour. Besides, to realize these amplifiers, a new parametrized cell library for GEC-Marconi’s F20 foundry process is created and utilized.Item Open Access 3-dimensional median-based algorithms in image sequence processing(Bilkent University, 1990) Alp, Münire BilgeThis thesis introduces new 3-dimensional median-based algorithms to be used in two of the main research areas in image sequence proc(',ssi,ng; image sequence enhancement and image sequence coding. Two new nonlinear filters are developed in the field of image sequence enhancement. The motion performances and the output statistics of these filters are evaluated. The simulations show that the filters improve the image quality to a large extent compared to other examples from the literature. The second field addressed is image sequence coding. A new 3-dimensional median-based coding and decoding method is developed for stationary images with the aim of good slow motion performance. All the algorithms developed are simulated on real image sequences using a video sequencer.Item Open Access 3D dynamic modeling of spherical wheeled self-balancing mobile robot(Bilkent University, 2012) İnal, Ali NailIn recent years, dynamically stable platforms that move on spherical wheels, also known as BallBots, gained popularity in the robotics literature as an alternative locomotion method to statically stable wheeled mobile robots. In contrast to wheeled platforms which do not have to explicitly be concerned about their balance, BallBot platforms must be informed about their dynamics and actively try to maintain balance. Up until now, such platforms have been approximated by simple planar models, with extensions to three dimensions through the combination of decoupled models in orthogonal sagittal planes. However, even though capturing certain aspects of the robot’s motion is possible with such decoupled models, they cannot represent inherently spatial aspects of motion such as yaw rotation or coupled inertial effects due to the motion of the rigid body. In this thesis, we introduce a novel, fully-coupled 3D model for such spherical wheeled balancing platforms. We show that our novel model captures important spatial aspects of motion that have previously not been captured by planar models. Moreover, our new model provides a better basis for controllers that are informed by more expressive system dynamics. In order to establish the expressivity and accuracy of this new model, we present simulation studies in dynamically rich situations. We use circular paths to reveal the advantages of the new model for fast maneuvers. Additionally, we introduce new inverse-dynamics controllers for a better attitude control and investigate within simulations the capability of sustaining dynamic behaviors. We study the relation between circular motions in attitude angles and associated motions in positional variables for BallBot locomotion.Item Open Access 3D electron density estimation in the ionosphere by using IRI-Plas model and GPS measurements(Bilkent University, 2016-05) Tuna, HakanThree dimensional imaging of the electron density distribution in the ionosphere is a crucial task for investigating the ionospheric effects. Dual-frequency Global Positioning System (GPS) satellite signals can be used to estimate the Slant Total Electron Content (STEC) along the propagation path between a GPS satellite and ground based receiver station. However, the estimated GPS-STEC are very sparse and highly non-uniformly distributed for obtaining reliable 3D electron density distributions derived from the measurements alone. Standard tomographic re- construction techniques are not accurate or reliable enough to represent the full complexity of variable ionosphere. On the other hand, model based electron density distributions are produced according to the general trends of the iono- sphere, and these distributions do not agree with measurements, especially for geomagnetically active hours. In this thesis, a novel regional 3D electron density distribution reconstruction technique, namely IONOLAB-CIT, is proposed to as- similate GPS-STEC into physical ionospheric models. The IONOLAB-CIT is based on an iterative optimization framework that tracks the deviations from the ionospheric model in terms of F2 layer critical frequency and maximum ionization height resulting from the comparison of International Reference Ionosphere ex- tended to Plasmasphere (IRI-Plas) model generated STEC and GPS-STEC. The IONOLAB-CIT is applied successfully for the reconstruction of electron den- sity distributions over Turkey, during calm and disturbed hours of ionosphere using Turkish National Permanent GPS Network (TNPGN-Active). Reconstruc- tions are also validated by predicting the STEC measurements that are left out in the reconstruction phase. The IONOLAB-CIT is compared with the real ionosonde measurements over Greece, and it is shown that the IONOLAB-CIT results are in good compliance with the ionosonde measurements. The results of the IONOLAB-CIT technique are also tracked and smoothed in time by using Kalman filtering methods for increasing the robustness of the results.Item Open Access 3D model compression using image compression based methods(Bilkent University, 2007) Köse, KıvançA Connectivity-Guided AdaptiveWavelet Transform (CGAWT) based mesh compres- sion algorithm is proposed. On the contrary to previous work, the proposed method uses 2D image processing tools for compressing the mesh models. The 3D models are ¯rst transformed to 2D images on a regular grid structure by performing orthogonal projections onto the image plane. This operation is computationally simpler than pa- rameterization. The neighborhood concept in projection images is di®erent from 2D images because two connected vertex can be projected to isolated pixels. Connectiv- ity data of the 3D model de¯nes the interpixel correlations in the projection image. Thus the wavelet transforms used in image processing do not give good results on this representation. CGAWT is de¯ned to take advantage of interpixel correlations in the image-like representation. Using the proposed transform the pixels in the detail subbands are predicted from their connected neighbors in the low-pass subbands of the wavelet transform. The resulting wavelet data is encoded using either \Set Parti- tioning In Hierarchical Trees" (SPIHT) or JPEG2000. SPIHT approach is progressive because di®erent resolutions of the mesh can be reconstructed from di®erent partitions of SPIHT bitstream. On the other hand, JPEG2000 approach is a single rate coder. The quantization of the wavelet coe±cients determines the quality of the reconstructed model in JPEG2000 approach. Simulations using di®erent basis functions show that lazy wavelet basis gives better results. The results are improved using the CGAWT with lazy wavelet ¯lterbanks. SPIHT based algorithm is observed to be superior to JPEG2000 based mesh coder and MPEG-3DGC in rate-distortion.Item Open Access 3D reconstruction of point clouds using multi-view orthographic projections(Bilkent University, 2006) Topçu, OsmanA method to reconstruct 3D point clouds using multi-view orthographic projections is examined. Point clouds are generated by means of a stochastic process. This stochastic process is designed to generate point clouds that mimic microcalcification formation in breast tissue. Point clouds are generated using a Gibbs sampler algorithm. Orthographic projections of point clouds from any desired orientation are generated. Volumetric intersection method is employed to perform the reconstruction from these orthographic projections. The reconstruction may yield erroneous reconstructed points. The types of these erroneous points are analyzed along with their causes and a performance measure based on linear combination is devised. Experiments have been designed to investigate the effect of the number of projections and the number of points to the performance of reconstruction. Increasing the number of projections and decreasing the number of points resulted in better reconstructions that are more similar to the original point clouds. However, it is observed that reconstructions do not improve considerably upon increasing the number of projections after some number. This method of reconstruction serves well to find locations of original points.Item Open Access 5G PDSCH: performance analysis of DMRS and PTRS designs for channel and phase noise estimation in MM-WAVE(Bilkent University, 2021-08) Pekcan, Doğan KutayThe mm-Wave is one of the main enablers for the performance requirements of 5G. Although it provides communication systems with huge bandwidth and data rates, it also has some disadvantages as the carrier frequencies can significantly exceed 6 GHz and go up to 300 GHz. For example, there are significant challenges such as propagation loss and severe phase noise (PN). The PN can be observed in two parts: common phase error (CPE) and inter-carrier interference (ICI). In the literature, there are algorithms for the estimation and compensation of PN for OFDM-based systems. We apply both CPE and ICI compensation algorithms for 5G PDSCH at the carrier frequency of 70 GHz. Detailed performance analysis is performed for demodulation reference signal (DMRS) based channel estimation and phase-tracking reference signal (PTRS) based PN estimation. We observe the effects of different reference signal parameters in 5G for each PN compensation algorithm. For this purpose, we use up-to-date power spectral density (PSD) models for PN modeling and show uncoded bit error rate (BER) graphs obtained via extensive simulations for MATLAB's tapped delay line (TDL) channels. We also analyze the system performance under very high Doppler, where PTRS based channel estimation is compared with DMRS based channel estimation.Item Open Access A 600W on-coil Class-E RF power amplifier array with dynamic phase control for 3T MRI(Bilkent University, 2022-09) Arslan, Abdullah ErkamDue to their size and cooling constraints, conventional Magnetic Resonance Imaging (MRI) places radio frequency (RF) amplifiers away from the scanner. These RF amplifiers have relatively low efficiency due to the matching of 50Ω output impedance for means of transmission with cables. Switching Class-E amplifiers on the other hand, by default need a bare RLC network as their load and thus can be directly integrated with the bare unmatched coils and reduce the cost and power losses significantly. This thesis aims to build up on the previous theses’ line of work including [1, 2, 3, 4, 5]. Instead of mitigating the symptoms, chronic problems of artifacts have been fixed by focusing on their root causes in the FPGA side of the updated design.The driver has been updated, timing problems have been resolved. FPGA design is also extended to support multichannel phase control. A dual channel imaging configuration of on-coil Class-E amplifiers with on-the-fly digital fine phase control is presented for 3T MRI. The system can control the phase with less than 2° granularity (this setting can be fine-tuned down to 0.15°). Without any mechanical intervention with the coil setup, using merely phase control, illuminated slice depth is modulated to three times its base-size during scantime. B1 field maps are also extracted for another setup. Periodically linear switching (PLS) circuit model of the Class-E amplifier is derived and computed, yielding a simulator with fast and customizable optimization capability. The PLS model is also verified by SPICE and theoretical analysis.Item Open Access A 94-GHz phase inverter-variable gain amplifier in SiGe BiCMOS(Bilkent University, 2017-07) Aydoğan, YiğitPhased array radar systems are capable of steering the beam of radio waves electronically by adjusting the gain and phase of each antenna element as desired. In order to achieve that, each element has to have gain/phase control and these parameters have to be controlled separately. In W-Band designs, constant gain- 360 phase control is di cult to achieve due to parasitic e ects of high frequencies which may quickly di er across di erent settings. Dividing the phase control task into di erent blocks in system eases the design di culties. A well developed WBand technology SiGe BiCMOS is also crucial to achieve high frequencies and system control. In this thesis, a 94-GHz SiGe BiCMOS phase inverter with variable gain ampli- er is developed. Single bit-180 phase inversion enables to use multiple bit-180 phase shifter which is easier to design in W-Band. In addition to that, variable gain ampli er allows to use this circuit in phased array systems for amplitude tapering to achieve desired beam forming.Item Open Access A comprehensive analysis of GaN HEMTs: electro-mechanical behavior, defect generation, and drain LAG reduction with HfO2 layers(Bilkent University, 2023-07) Güneş, BurakGallium Nitride High Electron Mobility Transistors (GaN HEMTs) have rapidly emerged as a transformative technology, owing to the unique properties of the substrate material. They are poised to become a revolutionary advancement in RF amplifier applications, primarily due to their capability to operate at high frequencies and power levels with superior efficiency compared to conventional devices. Despite the rapid progressions, a noticeable gap persists in the literature regarding the relation-ship between mechanical stresses, defect generation, and their subsequent impact on the electrical characteristics of AlGaN/GaN HEMTs. Moreover, current dispersion effects, which are trapping induced reductions in output power, continues to remain a pressing issue. To address these limitations, this study first adopts a multifaceted approach and integrates mechanical simulations and Raman spectroscopy, in order to resolve fine details of stress distributions that a diffraction-limited Raman probe cannot resolve. This enables an extensive modeling of stresses in a typical HEMT structure and helps elucidate the underlying dynamics of defect generation, with the ultimate goal of informing and guiding the development of advanced fabrication techniques. In a second study, an ultrathin blanket dielectric deposition approach was devised to alleviate surface trapping, and consequently, mitigate current dispersion. The proposed streamlined fabrication process yielded a substantial improvement in device performance without compromising the transistor transfer characteristics.Item Open Access A preclinical arbitrary waveform magnetic particle imaging scanner for multi-frequency imaging(Bilkent University, 2023-08) Yılmaz, Beril AlyüzMagnetic Particle Imaging (MPI) is a tracer based tomographic imaging modal-ity that images the spatial distribution of the magnetic nanoparticles (MNPs) using their nonlinear magnetization response. MPI is a rapidly growing and safe imaging modality with high temporal and spatial resolution, together with high sensitivity. In MPI, different types of MNPs and the properties of their local environment such as viscosity and temperature can be identified via the relax-ation behavior of the MNPs. The optimal drive field (DF) frequency depends on the application of interest. In addition, the sensitivity of quantitative mapping can benefit from imaging at multiple DF frequencies. However conventional MPI systems utilize an impedance matching circuitry tuned to a specific DF frequency to mitigate the reactive power, which in turn restricts the operation of the MPI systems to that frequency. In this thesis, a preclinical arbitrary waveform (AW) MPI scanner is proposed to enable flexible functionality in a wide range of oper-ating frequencies. The AW MPI scanner features three specialized components:(1) an AW drive coil with a reduced inductance achieved by utilizing Rutherford cable windings to enable wideband imaging in a preclinical-size MPI scanner, (2) a gradiometric receive coil designed to have zero mutual inductance with the AW drive coil to alleviate the effect of the direct feedthrough signal while sensitively receiving the MNP signal, and (3) additional capacitor banks to block DC cur-rent while avoiding distortions in the DF waveform. This thesis also proposes a technique for multi-frequency imaging in a single scan using the developed AW MPI scanner. Experimental imaging results demonstrate that MPI images and relaxation maps can be successfully achieved at multiple DF frequencies using the developed AW MPI scanner and the proposed multi-frequency imaging technique.Item Open Access Ablation cooled material removal with bursts of ultrafast pulses(Bilkent University, 2016-01) Kerse, M. CanMaterial processing with femto-second pulses allows precise and non-thermal material removal and being widely used in scientific, medical and industrial applications. However, due to low ablation speed at which material can be removed and the complexity of the associated laser technology, where the complexity arises from the need to overcome the high laser induced optical breakdown threshold for e cient ablation, its potential is limited. Physics of the interaction regime hinders a straightforward scaling up of the removal rate by using more powerful lasers due to e ects such as plasma shielding, saturation or collateral damage due to heat accumulation. In analogy to a technique routinely used for atmospheric re-entry of space shuttles since 1950s, ablation cooling, is exploited here to circumvent this limitation, where rapid successions of pulses repeated at ultrahigh repetition rates were applied from custom developed lasers to ablate the target material before the residual heat deposited by previous pulses di use away from the interaction region. This constitutes a new, physically unrecognized and even unexplored regime of laser- material interactions, where heat removal due to ablation is comparable to heat conduction. Proof-of-principle experiments were conducted on a broad range of targets including copper, silicon, thermoelectric couplers, PZT ceramic, agar gel, soft tissue and hard tissue, where they demonstrate reduction of required pulse energies by three orders of magnitude, while simultaneously increasing the ablation e ciency by an order of magnitude and thermal- damage-free removal of brain tissue at 2 mm3/min and tooth at 3 mm3/min, an order-of-magnitude faster than previous results.Item Open Access Accurate and efficient solutions of electromagnetic problems with the multilevel fast multipole algorithm(Bilkent University, 2009) Ergül, Özgür SalihThe multilevel fast multipole algorithm (MLFMA) is a powerful method for the fast and efficient solution of electromagnetics problems discretized with large numbers of unknowns. This method reduces the complexity of matrix-vector multiplications required by iterative solvers and enables the solution of largescale problems that cannot be investigated by using traditional methods. On the other hand, efficiency and accuracy of solutions via MLFMA depend on many parameters, such as the integral-equation formulation, discretization, iterative solver, preconditioning, computing platform, parallelization, and many other details of the numerical implementation. This dissertation is based on our efforts to develop sophisticated implementations of MLFMA for the solution of real-life scattering and radiation problems involving three-dimensional complicated objects with arbitrary geometries.Item Open Access Activity management algorithm for improving energy efficiency of small cell base stations in 5G heterogeneous networks(Bilkent University, 2014) Aykın, IrmakHeterogeneous networks (HetNets) are proposed in order to meet the increasing demand for next generation cellular wireless networks, but they also increase the energy consumption of the base stations. In this thesis, an activity management algorithm for improving the energy efficiency of HetNets is proposed. A smart sleep strategy is employed for the operator deployed pico base stations to enter sleep and active modes. According to that strategy, when the number of users exceeds the turn on threshold, the pico node becomes active and when the number of users drop below the turn off threshold, it goes into sleep mode. Mobile users dynamically enter and leave the cells, triggering the activation and deactivation of pico base stations. The performance of the system is examined for three different cellular network architectures: cell on edge (COE), uniformly distributed cells (UDC) and macro cell only network (MoNet). Two different user distributions are considered: uniform and hotspot. The effects of number of hotspot users and sleep energies of pico nodes on the energy efficiency are also investigated. The proposed activity management algorithm increases the energy efficiency, measured in bits/J, by 20%. The average bit rates achieved by HetNet users increase by 29% compared with the MoNet architecture. Thus, the proposed activity control algorithm increases the spectral efficiency of the network while consuming the energy more efficiently.Item Open Access Activity recognition invariant to position and orientation of wearable motion sensor units(Bilkent University, 2019-04) Yurtman, ArasWe propose techniques that achieve invariance to the placement of wearable motion sensor units in the context of human activity recognition. First, we focus on invariance to sensor unit orientation and develop three alternative transformations to remove from the raw sensor data the effect of the orientation at which the sensor unit is placed. The first two orientation-invariant transformations rely on the geometry of the measurements, whereas the third is based on estimating the orientations of the sensor units with respect to the Earth frame by exploiting the physical properties of the sensory data. We test them with multiple state-of-the-art machine-learning classifiers using five publicly available datasets (when applicable) containing various types of activities acquired by different sensor configurations. We show that the proposed methods achieve a similar accuracy with the reference system where the units are correctly oriented, whereas the standard system cannot handle incorrectly oriented sensors. We also propose a novel non-iterative technique for estimating the orientations of the sensor units based on the physical and geometrical properties of the sensor data to improve the accuracy of the third orientation-invariant transformation. All of the three transformations can be integrated into the pre-processing stage of existing wearable systems without much effort since we do not make any assumptions about the sensor configuration, the body movements, and the classification methodology. Secondly, we develop techniques that achieve invariance to the positioning of the sensor units in three ways: (1) We propose transformations that are applied on the sensory data to allow each unit to be placed at any position within a pre-determined body part. (2) We propose a transformation technique to allow the units to be interchanged so that the user does not need to distinguish between them before positioning. (3) We employ three different techniques to classify the activities based on a single sensor unit, whereas the training set may contain data acquired by multiple units placed at different positions. We combine (1) with (2) and also with (3) to achieve further robustness to sensor unit positioning. We evaluate our techniques on a publicly available dataset using seven state-of-the-art classifiers and show that the reduction in the accuracy is acceptable, considering the exibility, convenience, and unobtrusiveness in the positioning of the units. Finally, we combine the position- and orientation-invariant techniques to simultaneously achieve both. The accuracy values are much higher than those of random decision making although some of them are significantly lower than the reference system with correctly placed units. The trade-off between the exibility in sensor unit placement and the classification accuracy indicates that different approaches may be suitable for different applications.Item Open Access Adaptive ambulance redeployment via multi-armed bandits(Bilkent University, 2019-09) Şahin, ÜmitcanEmergency Medical Services (EMS) provide the necessary resources when there is a need for immediate medical attention and play a signi cant role in saving lives in the case of a life-threatening event. Therefore, it is necessary to design an EMS system where the arrival times to calls are as short as possible. This task includes the ambulance redeployment problem that consists of the methods of deploying ambulances to certain locations in order to minimize the arrival time and increase the coverage of the demand points. As opposed to many conventional redeployment methods where the optimization is primary concern, we propose a learning-based approach in which ambulances are redeployed without any a priori knowledge on the call distributions and the travel times, and these uncertainties are learned on the way. We cast the ambulance redeployment problem as a multi-armed bandit (MAB) problem, and propose various context-free and contextual MAB algorithms that learn to optimize redeployment locations via exploration and exploitation. We investigate the concept of risk aversion in ambulance redeployment and propose a risk-averse MAB algorithm. We construct a data-driven simulator that consists of a graph-based redeployment network and Markov tra c model and compare the performances of the algorithms on this simulator. Furthermore, we also conduct more realistic simulations by modeling the city of Ankara, Turkey and running the algorithms in this new model. Our results show that given the same conditions the presented MAB algorithms perform favorably against a method based on dynamic redeployment and similarly to a static allocation method which knows the true dynamics of the simulation setup beforehand.Item Open Access Adaptive control of a one-legged hopping robot through dynamically embedded spring-loaded inverted pendulum template(Bilkent University, 2011) Uyanık, İsmailPractical realization of model-based dynamic legged behaviors is substantially more challenging than statically stable behaviors due to their heavy dependence on second-order system dynamics. This problem is further aggravated by the dif- ficulty of accurately measuring or estimating dynamic parameters such as spring and damping constants for associated models and the fact that such parameters are prone to change in time due to heavy use and associated material fatigue. In the first part of this thesis, we present an on-line, model-based adaptive control method for running with a planar spring-mass hopper based on a once-per-step parameter correction scheme. Our method can be used both as a system identifi- cation tool to determine possibly time-varying spring and damping constants of a miscalibrated system, or as an adaptive controller that can eliminate steady-state tracking errors through appropriate adjustments on dynamic system parameters. We use Spring-Loaded Inverted Pendulum (SLIP) model, which is the mostly used, effective and accurate descriptive tool for running animals of different sizes and morphologies, to evaluate our algorithm. We present systematic simulation studies to show that our method can successfully accomplish both accurate tracking and system identification tasks on this model. Additionally, we extend our simulations to Torque-Actuated Dissipative Spring-Loaded Inverted Pendulum (TD-SLIP) model towards its implementation on an actual robot platform. In the second part of the thesis, we present the design and construction of a onelegged hopping robot we built to test the practical applicability of our adaptive control algorithm. We summarize the mechanical, electronics and software design of our robot as well as the performed system identification studies to calibrate the unknown system parameters. Finally, we investigate the robot’s motion achieved by a simple torque-actuated open loop controller.Item Open Access Adaptive digital predistortion for linearization of power amplifier(Bilkent University, 2009) Şekerlisoy, BurakIn most communication systems, power amplifiers are used to obtain high output power. The nonlinear characteristics of the power amplifier leads to the distortion of the output signal. This distortion affects the efficiency of the power amplifier. The way to reduce this effect is to linearize the power amplifier near the saturation region where it is nonlinear. The widely used technique for the linearization of power amplifiers is predistortion. The proposed technique for predistortion uses a LUT(look-up-table), a complex multiplier, an address calculator, delay elements and an adaptation logic. A new adaptation logic to update the LUT coefficients, is used. The predistorter is simulated in Matlab software using a baseband model for the power amplifier. 16-QAM baseband modulation is used to simulate the predistorter. In order to see the performance of the proposed predistorter, hardware logic is implemented in FPGA and experimental setup with RF circuits and RF power amplifier is used. For different LUT sizes, the algorithm is tested and for the LUT size of 64, nearly 15 dB improvement in power spectrum is observed. The LUT size of 64 is observed to be the optimal LUT size in the experiments.Item Open Access Adaptive digital predistortion for power amplifier linearization(Bilkent University, 2008) Aslan, Makbule PehlivanHigh power amplification of linear modulation schemes which exhibit fluctuating envelopes, invariably leads to the generation of distortion and intermodulation products. In order to avoid these effects, maintaining both power and spectral efficiency, it is necessary to use linearization techniques. By using linearization techniques, the amplifier can be operated near the saturation with good efficiency and linearity. The technique proposed here is predistortion based on a look-up table (LUT) method using input and output signal envelopes. The predistortion is implemented using a LUT and an address generation block that selects the appropriate coefficient from the LUT, given the magnitude of the input signal. The testing of the predistorter is done by using a baseband system model which consists of a 16-QAM modulator, an upsampler, a raised cosine filter, the predistorter and a baseband behavioural amplifier model. The performance of the predistorter with a new LUT update method is evaluated in terms of power efficiency and spectrum efficiency. MATLAB simulations show that to obtain up to 25-30 dB improvement in power spectrum is possible and sufficiently large LUT size is needed to reduce the background noise level. Furthermore, the performance of the predistorter in the case of an amplifier with memory is also investigated. The algorithms have been implemented on an FPGA chip. The performance of the system is as predicted in MATLAB simulations.Item Open Access Adaptive energy management for solar energy harvesting wireless sensor nodes(Bilkent University, 2018-09) Aydin, Abdul KerimWireless Sensor Networks (WSN) will have a key role in the upcoming era of the Internet of Things (IoT) as they will be forming the basis of communication infrastructure. Energy harvesting has been a widely used instrument for prolonging the battery life and enhancing the quality of service (QoS) of sensor nodes (SN). In this study, we investigate adaptive transmission policies for a solar-powered wireless sensor node which is tasked with sending status updates to a gateway as frequently as possible with energy-neutral operation constraints. On the basis of empirical data, we model the daily variations of the solar energy harvesting process with a Discrete Time Markov Chain (DTMC). When the number of states of the DTMC is increased, the harvesting process is modeled more accurately. Using the DTMC model, we formulate the energy management problem of the WSN node as a Markov Decision Process (MDP); and based on this model, we use the policy iteration algorithm to obtain optimal energy management policies so as to minimize the average Age of Information (AoI) of the corresponding status update system. We validate the effectiveness of the proposed approach using datasets belonging to two different locations with 20 years of solar radiance data.