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A wideband high-gain circularly polarized (CP) shaped dielectric horn-lens antenna (SDHLA) operating in the frequency band between 6.7 and 18.2 GHz [fractional impedance bandwidth (FIBW) of 92.4%] with a 3-dB axial-ratio in the frequency range from 8.1 to 16.3 GHz [fractional axial-ratio bandwidth (FARBW) of 67.2%], is presented. The antenna, composed of a suitably shaped dielectric horn, integrated with a super-ellipsoidal-axicon dielectric lens made out of stacked thin dielectric disks, is mounted on a printed circuit board (PCB) where a microstrip line terminated with a wideband radial stub is used to excite a S-shaped slot through which the circular polarization is achieved. Parameterized 3D Lamé curves, describing the horn and lens profile, are used to optimize the antenna design. The antenna features a peak realized gain exceeding 13.1 dBi that is beneficial in a variety of applications, such as digital video broadcasting (DVB), remote sensing, weather monitoring, satellite communications, and air traffic control. The full-wave electromagnetic solver CST Studio Suite™, based on a locally conformal finite integration technique (FIT), was employed to design and characterize the antenna whose performances were found to be in good agreement with the experimental measurements.

This article investigates the limits of focal-plane array (FPA) technology by studying a double-reflector antenna system with wide-Angle scan capabilities. The proposed reflector configurations are analyzed in terms of effective isotropic radiated power (EIRP) maximization, minimization of the required total number of array elements for a wide-scan range, and the highest number of simultaneously active array elements of the phased-Array feed. Presented configurations have capabilities to operate in the scan range up to ± 30° in azimuth (±35 beamwidths scan) and ± 3° in elevation. It has been demonstrated how different optimizations could allow to build systems with varying performance in terms of the key operation parameters, such as array size, EIRP, and the number of active array elements. A detailed analysis is provided that demonstrates the potential applicability of this concept in future millimeter-wave (mm-wave) applications.

The active and dynamic control of the TeraHertz (THz) waves is highly demanded due to the rapid development of wireless communication systems. Recently, reconfigurable intelligent surface (RIS) has gained significant attention due to their tremendous potential in controlling the electromagnetic waves. Particularly, RIS-based wireless communications are promising for improving the system���s performance by properly designing the reflection coefficient of the unit cell. In this work, we investigate a graphene-based RIS for active and dynamic control of THz waves. The RIS design consists of rectangular graphene meta-atoms periodic array placed over a metallic grounded silicon substrate. An equivalent circuit modeling of the RIS design and its solution is provided. The RIS performance is numerically analyzed. The graphene-based RIS achieves nearly 100% reflection in the operational frequency ranging from 0.1 to 4 THz. The perfect reflection is insensitive to the polarization and the incident angles. Moreover, 100% absorption in the graphene-based RIS is achieved by electrically reconfiguring the metaatom response via the chemical potential of the graphene. The graphene RIS also achieves the anomalous reflection performance by controlling the number of unit cells and phase gradient of RIS. In view of the effective THz wireless communication environment, this paper finally presents a simple RIS-aided communication model to study the impact of the proposed graphene-based RIS on the signal-to-noise ratio. The results reveal that the proposed THz RIS with graphene meta-atoms is promising for efficient and intelligent THz wireless communications., �� 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Machine learning (ML) has shown its success in many areas such as computer vision, natural language processing, robot control, and gaming. ML also draws significant attention in the wireless communication society. However, applying ML schemes to wireless communication networks is not straightforward, there are several challenges need to addressed: 1). Training data in communication networks, especially in physical and MAC layer, are extremely limited; 2). The high-dynamic wireless environment and fast changing transmission schemes in communication networks make offline training impractical; 3). ML tools are treated as black boxes, which lack of explainability. This dissertation tries to address those challenges by selecting training-efficient neural networks, devising online training frameworks for wireless communication scenarios, and incorporating communication domain knowledge into the algorithm design. Training-efficient ML algorithms are customized for three communication applications: 1). Symbol detection, where real-time online learning-based symbol detection algorithms are designed for MIMO-OFDM and massive MIMO-OFDM systems by utilizing reservoir computing, extreme learning machine, multi-mode reservoir computing, and StructNet; 2) Channel estimation, where residual learning-based offline method is introduced for WiFi-OFDM systems, and a StructNet-based online method is devised for MIMO-OFDM systems; 3) Radio resource management, where reinforcement learning-based schemes are designed for dynamic spectrum access, as well as ORAN intelligent network slicing management. All algorithms introduced in this dissertation have demonstrated outstanding performance in their application scenarios, which paves the path for adopting ML-based solutions in practical wireless networks. Doctor of Philosophy Machine learning (ML), which is a branch of computer science that trains machine how to learn a solution from data, has shown its success in many areas such as computer vision, natural language processing, robot control, and gaming. ML also draws significant attention in the wireless communication society. However, applying ML schemes to wireless communication networks is not straightforward, there are several challenges need to addressed: 1). Training issue: unlike areas such as computer vision where large amount of training data are available, the training data in communication systems are limited; 2). Uncertainty in generalization: ML usually requires offline training, where the ML models are trained by artificially generated offline data, with the assumption that offline training data have the same statistical property as the online testing one. However, when they are statistically different, the testing performance can not be guaranteed; 3). Lack of explainability, usually ML tools are treated as black boxes, whose behaviors can hardly be explained in an analytical way. When designed for wireless networks, it is desirable for ML to have similar levels of explainability as conventional methods. This dissertation tries to address those challenges by selecting training-efficient neural networks, devising online training frameworks for wireless communication scenarios, and incorporating communication domain knowledge into the algorithm design. Training-efficient ML algorithms are customized for three communication applications: 1). Symbol detection, which is a critical step of wireless communication receiver processing, it aims to recover the transmitted signals from the corruption of undesired wireless channel effects and hardware impairments; 2) Channel estimation, where transmitter transmits a special type of symbol called pilot whose value and position are known for the receiver, receiver estimates the underlying wireless channel by comparing the received symbols with the known pilots information; 3) Radio resource management, which allocates wireless resources such bandwidth and time slots to different users. All algorithms introduced in this dissertation have demonstrated outstanding performance in their application scenarios, which paves the path for adopting ML-based solutions in practical wireless networks.

In this paper, a compact tuned reconfigurable microstrip antenna for fifth generation (5G) mobile communications is designed to operate at 28 GHz or 38 GHz or both frequencies. The proposed antenna can be reconfigured by using a group of PIN diodes switches across a slit in the upper traditional patch antenna or through the ground plane side. The tuning between the 28 GHz and 38GHz frequency bands can be achieved through ON/OFF states of the PIN diodes switches. The tuned reconfigurable antenna is simulated using CST software package and then fabricated and measured. The simulated and measured results show good agreement with a little deviation. The proposed tuned antenna is small in size with 18×11.25 mm2 overall area.

This paper proposes a method to realize ideal lithium niobate (LiNbO3) A1 resonators. By introducing subwavelength through-holes between the interdigital transducer (IDT) electrodes on the LiNbO3 surface, all unfavorable spurious modes of the resonators can be suppressed completely. It is convenient and valid for various IDT electrode parameters and different LiNbO3 thicknesses. Also, this method does not require additional device fabrication steps. At the same time, these through-holes can greatly reduce the suspended area of the LiNbO3 thin film, thus significantly improving the design flexibility, compactness, mechanical stability, temperature stability, and power tolerance of the resonators (and subsequent filters). It is expected to become an important means to promote the practical application of LiNbO3 A1 filters and even all Lamb waves filters.

The exponential growth of the Internet of Things (IoT) is being witnessed nowadays in different sectors. This makes IoT data communications more complex and harder to manage. Addressing such a challenge using a centralized model is an ineffective approach and would result in security and privacy difficulties. Technologies such as blockchain provide a potential solution to enable secure and effective management of IoT data communication in a distributed and trustless manner. In this paper, a novel lightweight blockchain-centric IoT architecture is proposed to address effective IoT data communication management. It is based on an event-driven smart contract that enables manageable and trustless IoT data exchange using a simple publish/subscribe model. To maintain system complexity and overhead at a minimum, the design of the proposed system relies on a single smart contract. All the system operations that enable effective IoT data communication among the different parties of the system are defined in the smart contract. There is no direct blockchain–IoT-device interaction, making the system more useable in wide IoT deployments incorporating IoT devices with limited computing and energy resources. A practical Ethereum-based implementation of the system was developed with the ability to simulate different IoT setups. The evaluation results demonstrated the feasibility and effectiveness of the proposed architecture. Considering varying-scale and varying-density experimental setups, reliable and secure data communications were achieved with little latency and resource consumption.

Reconfigurable intelligent surface (RIS) has been shown as a promising technique to increase the channel randomness for secret key generation (SKG) in low-entropy channels (e.g., static or line-of-sight (LoS)), without small-scale fading. In this letter, we show that even with the aid of RIS, collaborative eavesdroppers (Eves) can still estimate the legitimate Alice-Bob channel and erode their secret key rates (SKRs), since the RIS induced randomness is also reflected in the Eves’ observations. Conditioned on Eves’ observations, if the entropy of RIS-combined legitimate channel is zero, Eves are able to estimate it and its secret key. Leveraging this, we design a multi-Eve scheme against the RIS-secured LoS dominated scenarios, by using the multiple Eves’ observations to reconstruct the RIS-combined legitimate channel. We further deduce a closed-form secret key leakage rate under our designed multi-Eve scheme, and demonstrate the results via simulations. Engineering and Physical Sciences Research Council (EPSRC): EP/V026763/1

In this paper, a compact dual-wideband fractal antenna is created for Bluetooth, WiMAX, WLAN, C, and X band applications. The proposed antenna consists of a circularly shaped resonator that contains square slots and a ground plane where a gap line is incorporated to increase the gain and bandwidth with a small volume of 40 × 34 × 1.6 mm3. The patch was supported by the FR4 dielectric, which had a permittivity of 4.4 and tan δ = 0.02. A 50 Ω microstrip line fed this antenna. The antenna was designed by the HFSS program, and after that, the simulated results were validated using the measured results. The measurement results confirm that the suggested antenna achieves dual-band frequencies ranging from 2.30 to 4.10 GHz, and from 6.10 GHz to 10.0 GHz, resonating at 2.8, 3.51, 6.53, and 9.37 GHz, respectively, for various applications including commercial, scholarly, and medical applications. Moreover, the antenna’s ability to operate within the frequency range of 3.1–10.6 GHz is in accordance with the FCC guidelines for the use of UWB antennas in breast cancer detection. Over the operational bands, the gain varied between 2 and 9 dB, and an efficiency of 92% was attained. A good agreement between the simulation and the measured results was found.

THz frequencies offer enormous amounts of bandwidth, which could solve the current speed bottleneck for next-generation wireless communications. Recent reports show sub-THz links offering capacities of hundreds of Gbit/s, finally approaching those of state-of-the-art optical transmission channels. Non-etheless, generation, transport, detection and processing of signals in the THz range is far from being a trivial task. Even though the recent evolution of integrated technology is starting to indicate that chip-scale THz technology could gradually close the so-called “THz gap,” much work still needs to be done to enable functional systems, in particular in terms of efficiency. Photonics can be of help, thanks to its extremely low loss and broad bandwidth. Yet, a particularly critical aspect hindering the deployment of THz technology is that state-of-the-art photonics devices generally do not offer sufficient electro-optical bandwidth to process THz signals. Plasmonics, by focusing electromagnetic surface waves at sub-wavelength scales, can play a key role in this quest, as it finally enables the realization of electro-optical devices such as modulators and detectors displaying sufficient compactness and speeds to reach the THz range. This paper overviews recent achievements on plasmonic-based modulators displaying characteristics of speed, efficiency and linearity that enable high-performance access to this much desired frequency range.

[ES] Las ciudades modernas están al límite de su capacidad en el plano horizontal. Muchas de ellas tienen un problema de tráfico muy complejo de paliar o resolver. La movilidad aérea urbana promete ser la revolución que puede resolver la saturación del tráfico en los futuros escenarios urbanos. Se espera que el crecimiento del mercado de la movilidad aérea urbana muestre una tendencia positiva constante, pero la tecnología asociada necesita aumentar su madurez. La gestión de múltiples vehículos aéreos, que dependen de tecnologías en auge como la inteligencia artificial y las estaciones de control en tierra automatizadas, requerirá una conexión tierra-aire-tierra sólida e ininterrumpida para completar sus trayectorias. La exigencia de una conexión ininterrumpida está naturalmente relacionada con una comprensión completa de los fenómenos que afectan al canal aire-tierra. La primera contribución es proponer un modelo de canal que pueda capturar las consecuencias de dichos fenómenos. Normalmente, un modelo de este tipo puede emitir el estado del canal en un punto determinado, prediciendo el estado del canal a lo largo de la trayectoria de la aeronave. Un modelo muy detallado exige herramientas y datos que proporcionen la información necesaria. La descripción y enumeración de cada pieza de información necesaria para una simulación de canal satisfactoria componen la segunda contribución. Una vez conocido el estado del canal, se pueden optimizar los puntos recorridos por la aeronave para cubrir aquellos con mejor rendimiento del canal. La tercera y última contribución es la propuesta de un conjunto de algoritmos de optimización para encontrar la ruta más adecuada. El algoritmo de optimización constituye el planificador de trayectorias, del que se espera que explore eficazmente el espacio de búsqueda y proponga una trayectoria que cumpla con los objetivos predefinidos: máxima calidad aire-tierra, disponibilidad y tiempo de vuelo. Cada método propuesto se pone a prueba en varios escenarios. Estos escenarios incluyen diversas situaciones que pueden estresar a los métodos y favorecer la elección de uno de ellos. Las situaciones incluidas son diferentes condiciones del terreno y zonas de exclusión aérea., [CA] Les ciutats modernes estan al límit de la seua capacitat al pla horitzontal. Moltes tenen un problema de trànsit molt complex de pal·liar o resoldre. La mobilitat aèria urbana promet ser la revolució que pot resoldre la saturació del trànsit als futurs escenaris urbans. S'espera que el creixement del mercat de la mobilitat aèria urbana mostre una tendència positiva constant, però la tecnologia associada necessita augmentar-ne la maduresa. La gestió de múltiples vehicles aeris, que depenen de tecnologies en auge com la intel·ligència artificial i les estacions de control a terra automatitzades, requerirà una connexió terra-aire-terra sòlida i ininterrompuda per completar les seues trajectòries. L'exigència d'una connexió ininterrompuda està relacionada naturalment amb una comprensió completa dels fenòmens que afecten el canal aire-terra. La primera contribució és proposar un model de canal que puga capturar les conseqüències dels fenòmens esmentats. Normalment, un model d'aquest tipus pot emetre l'estat del canal en un punt determinat, predient l'estat del canal al llarg de la trajectòria de l'aeronau. Un model molt detallat exigeix eines i dades que proporcionen la informació necessària. La descripció i l'enumeració de cada peça d'informació necessària per a una simulació de canal satisfactòria componen la segona contribució. Una vegada conegut l'estat del canal, es poden optimitzar els punts recorreguts per l'aeronau per tal de cobrir aquells amb el millor rendiment del canal. La tercera i última contribució és la proposta d'un conjunt d'algorismes d'optimització per trobar la ruta més adequada. L'algorisme d'optimització constitueix el planificador de trajectòries, del qual s'espera que explore eficaçment l'espai de cerca i propose una trajectòria que complisca els objectius predefinits: màxima qualitat aire-terra, disponibilitat i temps de vol. Cada mètode proposat es posa a prova a diversos escenaris. Aquests escenaris inclouen diverses situacions que poden estressar els mètodes i afavorir-ne l'elecció. Les situacions incloses són diferents condicions del terreny i les zones d'exclusió aèria., [EN] Modern cities are at the limit of their capacity in the horizontal plane. Many of them have a traffic problem that is highly complex to alleviate or solve. Urban air mobility promises to be the revolution that can solve traffic saturation in future urban scenarios. The growth of the urban air mobility market is expected to show a constant positive tendency, but the associated technology needs to raise its readiness levels. Managing aerial vehicle fleets, dependent on rising technologies such as artificial intelligence and automated ground control stations, will require a solid and uninterrupted connection to complete their trajectories. The requirement for an uninterrupted connection is naturally connected to a complete understanding of phenomena affecting the air-to-ground channel. The first contribution to the field is to propose a channel model that can capture the consequences of said phenomena. Typically, such a model can output the channel state at a given point, predicting the channel state throughout the aircraft's trajectory. A highly detailed model demands tools and data to deliver the necessary information. The description and enumeration of each piece of information required for a successful channel simulation compose the second contribution to the field. Once the channel state is known, the travelled points by the aircraft can be optimised to cover those with better channel performance. The third and last contribution to the field is proposing a set of optimisation algorithms to find the most suitable route. The optimisation algorithm forms the path planner, expected to efficiently explore the search space and propose a trajectory compliant with predefined objectives: maximum air-to-ground quality, availability, and flight time. Each proposed method is tested in various scenarios. These scenarios include various situations that can stress the methods and favour the choice of one. Included situations are different terrain conditions and no-fly zones.

—In this paper, a de-noising approach in conjunction with channel estimation (CE) algorithm for OFDM systems using singular spectrum analysis (SSA) is presented. In the proposed algorithm, the initial CE is computed with the aid of traditional linear minimum mean square error (LMMSE) algorithm, and then further channel is evaluated by considering the low rank eigenvalue approximation of channel correlation matrix related to channel using SSA. Simulation results on bit error rate (BER) revealed that the method attains an improvement of 7 dB, 5 dB and 3 dB compared to common LSE, MMSE and SVD based methods respectively. With the help of statistical correlation coefficient (C) and kurtosis (k), the SSA method utilized to de-noise the received OFDM signal in addition to CE. In the process of denoising, the received OFDM signal will be decomposed into different empirical orthogonal functions (EOFs) based on the singular values. It was established that the correlation coefficients worked well in identifying useful EOFs only up to moderate SNR  12dB. For low SNR

The ever-increasing demand for applications with stringent constraints in device density, latency, user mobility, or peak data rate has led to the appearance of the last generation of mobile networks (i.e., 5G). However, there is still room for improvement in the network spectral efficiency, not only at the waveform level but also at the Radio Resource Management (RRM). Up to now, solutions based on multicast transmissions have presented considerable efficiency increments by successfully implementing subgrouping strategies. These techniques enable more efficient exploitation of channel time and frequency resources by splitting users into subgroups and applying independent and adaptive modulation and coding schemes. However, at the RRM, traditional multiplexing techniques pose a hard limit in exploiting the available resources, especially when users' QoS requests are unbalanced. Under these circumstances, this paper proposes jointly applying the subgrouping and Non-Orthogonal Multiple Access (NOMA) techniques in 5G to increase the network data rate. This study shows that NOMA is highly spectrum-efficient and could improve the system throughput performance in certain conditions. In the first part of this paper, an in-depth analysis of the implications of introducing NOMA techniques in 5G subgrouping at RRM is carried out. Afterward, the validation is accomplished by applying the proposed approach to different 5G use cases based on vehicular communications. After a comprehensive analysis of the results, a theoretical approach combining NOMA and time division is presented, which improves considerably the data rate offered in each use case. This work was supported in part by the Italian Ministry of University and Research (MIUR), within the Smart Cities framework, Project Cagliari2020 ID: PON04a2_00381; in part by the Basque Government under Grant IT1234-19; and in part by the Spanish Government [Project PHANTOM under Grant RTI2018-099162-B-I00 (MCIU/AEI/FEDER, UE)].

The high bandwidth and data rate demands of future wireless communications such as 6G and beyond can no longer be met with existing technologies that are mainly based on naturally occurring three-dimensional materials. The terahertz (THz) band refers to the electromagnetic frequency range lying between the millimetre-wave band and the infrared band, and it has become an increasingly promising frequency band that has the potential to be exploited for high-speed wireless communication networks of the future. Lately, the realisation of THz devices has been expedited through the emergence of two-dimensional materials (2DMs), such as graphene, perovskites, and transition metal dichalcogenides that can potentially unlock some long-standing problems related to the development of efficient control of transmission and detection of THz waves. In this paper, we cover several essential electrical features of 2DM, namely graphene, MOs2, and perovskite enabled THz devices that are being used to design efficient systems for future wireless communication systems.

Sustainable urban mobility refers to the sustainable transportation mode in terms of social, environmental, and climate impacts. Cycling has emerged as one of the most sustainable means of urban travel due to its flexibility, low costs, reduced carbon emissions, improved traffic, and mobility in cities. Vehicle-to-vehicle (V2V) communication is becoming a reality standard. Non-motorized vehicles, such as bikes, are expected to participate in V2V and Vehicle-To-Everything (V2X) networking alongside cars and trucks, although they have gotten significantly less attention. In this paper, we analyze and experimentally evaluate Bike-to-Bike (Bi2Bi) wireless communication in different urban scenarios, considering full topo-morphological characteristics of urban environments by means of deterministic 3D Ray Launching hybrid simulations. Communication and data exchange between bikes relies on the IEEE 802.15.4 standard, and specifically, on ZigBee. We analyze Bi2Bi communication and cooperation towards sustainable smart mobility, following a holistic approach providing a tool based on the city platform to monitor and understand the impact of mobility at both city and citizen level and to provide accurate information on carbon footprint reduction, for multiple city/system stakeholders.

Peer reviewed: True, Active modification of the polarization state is a key feature for the next-generation of wireless communications, sensing, and imaging in the THz band. The polarization modulation performance of an integrated metamaterial/graphene device is investigated via a modified THz time domain spectroscopic system. Graphene’s Fermi level is modified through electrostatic gating, thus modifying the device’s overall optical response. Active tuning of ellipticity by >0.3 is reported at the resonant frequency of 0.80 THz. The optical activity of transmitted THz radiations is continuously modified by >21.5o at 0.71 THz. By carefully selecting the transmitted frequency with the relative angle between the incoming linear polarization and the device’s symmetry axis, active circular dichroism and optical activity are almost independently exploited. Finally, this all-electronically tuneable versatile polarization device can be used in all applications requiring an ultrafast modulation such as polarization spectroscopy, imaging, and THz wireless generation.

The arrival of new wireless technologies have allowed us to push the requirements of wireless communications systems to stricter levels in terms of data rate, bit error rate, energy efficiency or spectral efficiency. Some of these technologies are receive spatial modulation (RSM) or transmit beamforming (TxBF) in millimeter-wave (mmWave) bands. However, they require a large amount of energy consumption (radiofrequency (RF) chains and analog-to-digital converters (ADC) at each antenna) and may suffer a performance degradation due to the lack of channel scattering, shadowing situations and higher path losses. The use of a reconfigurable intelligent surface (RIS) is a viable technology that mitigates these problem with low-cost passive elements, at virtually no additional energy consumption. This study proposes the use of RIS in a single user (SU) multiple-input multiple-output (MIMO) communication with RSM and TxBF to improve a downlink (DL) transmission in fifth-generation (5G) mmWave. It shows that having RIS assisting the communication is more than good option for mmWave communications where there is no multipath as it can improve the transmission rate in TxBF in shadowed areas. However, it is the transmissions with RSM that get the most benefit from the use of RIS in terms of bit error rate. La llegada de las nuevas tecnologías inalámbricas nos ha permitido llevar los requisitos de los sistemas de comunicaciones inalámbricas a niveles más estrictos en términos de tasa de datos, tasa de error de bits, eficiencia energética o eficiencia espectral. Algunas de estas tecnologías son RSM o TxBF en bandas milimétricas (mmWave). Sin embargo, requieren una gran cantidad de consumo de energía (cadenas de radiofrecuencia (RF) y convertidores analógico a digital (ADC) en cada antena) y pueden sufrir una degradación del rendimiento debido a la falta de dispersión de canales, situaciones de shadowing y mayores pérdidas de propagación. El uso de una superficie reconfigurable inteligente (RIS) es una tecnología viable que mitiga estos problemas con elementos pasivos de bajo costo, prácticamente sin consumo de energía adicional. Este estudio propone el uso de RIS en una comunicación SU-MIMO con RSM y TxBF para mejorar una transmisión DL en 5G mmWave. Demuestra que tener RIS asistiendo a la comunicación es más que una buena opción para las comunicaciones mmWave donde no hay propagación multicamino, ya que puede mejorar la tasa de transmisión en TxBF en áreas con shadowing. Sin embargo, son las transmisiones con RSM las que obtienen mayor beneficio del uso de RIS en términos de tasa de error de bit. L'arribada de les noves tecnologies sense fil ens ha permès portar els requisits dels sistemes de comunicacions sense fil a nivells més estrictes en termes de taxa de dades, taxa d'error de bits, eficiència energètica o eficiència espectral. Algunes d'aquestes tecnologies són RSM o TxBF en bandes mil·limètriques (mmWave). No obstant això, requereixen una gran quantitat de consum d'energia (cadenes de radiofreqüència (RF) i convertidors de senyal analògica a digital (ADC) a cada antena) i poden patir una degradació del rendiment a causa de la manca de dispersió de canals, situacions de shadowing i majors pèrdues de propagació. L'ús d'una superfície reconfigurable intel·ligent (RIS) és una tecnologia viable que mitiga aquests problemes amb elements passius de baix cost, pràcticament sense consum d'energia addicional. Aquest estudi proposa l'ús de RIS en una comunicació SU-MIMO amb RSM i TxBF per millorar una transmissió DL a 5G mmWave. Demostra que tenir RIS assistint a la comunicació és més que una bona opció per a les comunicacions mmWave on no hi ha propagació multicamí, ja que pot millorar la taxa de transmissió a TxBF en àrees amb shadowing. Tot i això, són les transmissions amb RSM les que obtenen major benefici de l'ús de RIS en termes de taxa d'error de bit.

Unmanned aerial vehicles (UAVs) and reconfigurable intelligent surfaces (RIS) are the promising emerging technologies proposed for the 6th-Generation (6G) network to improve the capacity, reliability, and coverage of wireless communications. By integrating the UAV with RIS (RIS-UAV), the three-dimensional (3D) mobility of the UAV can be leveraged to establish strong line-of-sight links with the ground nodes, while the RIS intelligently reflect the signals toward the desired directions. However, the existing literature on RIS-UAV systems mainly assumes the use of passive elements, which suffers from the double path-loss problem. The use of active elements in RIS, which could improve the reflected link performance at the cost of increased energy consumption, has not been considered for the RIS-UAV system. Further, the energy efficiency of a RIS-UAV with active elements remains as an open direction because there is a need to investigate the feasibility of either an active or hybrid RIS-UAV implementation. This paper proposes active and hybrid RIS-UAVs and investigates the energy efficiencies of active and hybrid RIS-UAVs in comparison with existing passive RIS-UAVs and conventional UAV relays. The numerical results reveal that the proposed hybrid and active RIS-UAV relaying schemes can provide up to 14 times and 26 times improvement as compared to the passive RIS-UAV, respectively. As opposed to the active RIS-UAV that requires a larger power budget, half-duplex UAV relays that have a lower spectral efficiency, and full-duplex UAV relays that suffer from self-interference, the hybrid RIS-UAV emerges as a promising option to assist the ground communication system.

Age of Information (AoI) is a performance metric that can be used to measure the freshness of information. Since its inception, it has captured the attention of the research community and is now an area of active research. By its definition, AoI measures the elapsed time period between the present time and the generation time of the information. AoI is fundamentally different from traditional metrics such as delay or latency as the latter only considers the transit time for a packet to traverse the network. Among the state-of-the-art in the literature, we identify two limitations that deserve further investigation. First, many existing efforts on AoI have been limited to information-theoretic exploration by considering extremely simple models and unrealistic assumptions, which are far from real-world communication systems. Second, among most existing work on scheduling algorithms to optimize AoI, there is a lack of research on guaranteeing AoI deadlines. The goal of this dissertation is to address these two limitations in the state-of-the-art. First, we design schedulers to minimize AoI under more practical settings, including varying sampling periods, varying sample sizes, cellular transmission models, dynamic channel conditions, etc. Second, we design schedulers to guarantee hard or soft AoI deadlines for each information source. More important, inspired by our results from guaranteeing AoI deadlines, we develop a general design framework that can be applied to construct high-performance schedulers for AoI-related problems. This dissertation is organized into three parts. In the first part, we study two problems on AoI minimization under general settings. (i) We consider general and heterogeneous sampling behaviors among source nodes, varying sample size, and a cellular-based transmission model. We develop a near-optimal low-complexity scheduler---code-named Juventas---to minimize AoI. (ii) We study the AoI minimization problem under a 5G network with dynamic channels. To meet the stringent real-time requirement for 5G, we develop a GPU-based near-optimal algorithm---code-named Kronos---and implement it on commercial off-the-shelf (COTS) GPUs. In the second part, we investigate three problems on guaranteeing AoI deadlines. (i) We study the problem to guarantee a hard AoI deadline for information from each source. We present a novel low-complexity procedure, called Fictitious Polynomial Mapping (FPM), and prove that FPM can find a feasible scheduler for any hard deadline vector when the system load is under ln 2. (ii) For soft AoI deadlines, i.e., occasional violations can be tolerated, we present a novel procedure called Unstable Tolerant Scheduler (UTS). UTS hinges upon the notions of Almost Uniform Schedulers (AUSs) and step-down rate vectors. We show that UTS has strong performance guarantees under different settings. (iii) We investigate a 5G scheduling problem to minimize the proportion of time when the AoI exceeds a soft deadline. We derive a property called uniform fairness and use it as a guideline to develop a 5G scheduler---Aequitas. To meet the real-time requirement in 5G, we implement Aequitas on a COTS GPU. In the third part, we present Eywa---a general design framework that can be applied to construct high-performance schedulers for AoI-related optimization and decision problems. The design of Eywa is inspired by the notions of AUS schedulers and step-down rate vectors when we develop UTS in the second part. To validate the efficacy of the proposed Eywa framework, we apply it to solve a number of problems, such as minimizing the sum of AoIs, minimizing bandwidth requirement under AoI constraints, and determining the existence of feasible schedulers to satisfy AoI constraints. We find that for each problem, Eywa can either offer a stronger performance guarantee than the state-of-the-art algorithms, or provide new/general results that are not available in the literature. Doctor of Philosophy Age of Information (AoI) is a performance metric that can be used to measure the freshness of information. It measures the elapsed time period between the present time and the generation time of the information. Through a literature review, we have identified two limitations: (i) many existing efforts on AoI have employed extremely simple models and unrealistic assumptions, and (ii) most existing work focuses on optimizing AoI, while overlooking AoI deadline requirements in some applications. The goal of this dissertation is to address these two limitations. For the first limitation, we study the problem to minimize the average AoI in general and practical settings, such as dynamic channels and 5G NR networks. For the second limitation, we design schedulers to guarantee hard or soft AoI deadlines for information from each source. Finally, we develop a general design framework that can be applied to construct high-performance schedulers for AoI-related problems.

R1C2Random geometric graphs can be used in constructing topology formations for wireless ad-hoc networks (WANETs), including wireless sensor networks, flying ad-hoc networks, and others. They are useful for energy-saving schemes where a randomly alternating subset of deployed nodes is turned off temporarily (without compromising the network connectivity). This also improves network security by periodically re-routing the data flow, which makes it harder for third parties to run a traffic analysis. In the area and target coverage scenarios, a WANET deployment is desired to have maximal area coverage efficiency, which implies covering the largest possible area using the fewest number of nodes by maintaining the connectivity as well. Although deterministic topology formations offering optimal area coverage are known, a random node deployment method that grants connectivity and area coverage maximality has not been presented, to the best of our knowledge. This study introduces a novel topology formation method, called CoRMAC, that consistently yields tree-formed random geometric graphs that are guaranteed to be connected and offer maximal area coverage for any given area size and node cardinality. The area coverage maximality of CoRMAC is formally proven. Extensive theoretical and computational analyses have been provided to demonstrate its graph-theoretic, Euclidean, and networking features. Moreover, comparisons were made with other approaches to show the effectiveness of the proposed method. IEEE

The continue evolution in wireless communication systems aims to provide adequate parameters in terms of higher transmission bit rates, capacity and increased spectral efficiency. All these deriving from the context of IoT, IIoT and the 5G applications such as Enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (uRLLC) and Massive Machine-Type Communications (mMTC). Physical layer functionalities such as MIMO can increase throughput and provide higher coverage/capacity relations. However, its performance is directly affected by radio channel characteristics defined in the radio channel matrix and other conditions such as employed antenna spacing, human scattering influence or phase evolution effect. In this research work, three particular and useful study cases have been performed. Firstly, the performance of a MIMO system operating within a 5G NR FR1 capable band is analyzed, by considering volumetric channel analysis in frequency/power as well as in time domain and the impact of variable antenna spacing. The results show a clear benefit in received power level as antenna spacing is increased from 1λ to 3λ in the case of a complex indoor scenario. Secondly, we analyzed the influence of human scattering in a complex indoor environment consisting in a conference room in a plenary layout. For this study, 5G NR FR1 frequency band was also considered. Results show that 0% of human occupancy has 3 dB enhancement over 100% occupancy when analyzing BER values. Besides, it was also observed an important decrease in total power levels received: there is a loss of around 10 dBm when 50% occupancy, another 6 dBm loss when premise is complete compering with 50% and a total of 16 dBm of loss between 100% occupancy over empty place. In the context of IoT and IIoT, aiming to enable context aware environments, distributed transceiver systems capable of providing low cost, low latency capabilities are required. Single Input Multiple Output systems provide an adequate solution by enabling non-coherent energy-based detection. Phase distributions play a key role in transceiver location and hence overall system operation. Finally, in this thesis, SIMO operation based on volumetric phase analysis is performed on indoor scenarios, employing deterministic 3D Ray Launching channel estimation. The proposed methodology enables the estimation of system performance as a function of distributed transceiver location, aiding in network planning and deployment tasks. Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011) Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

Herein thin films of PbSe are coated onto amorphous glass, amorphous silicon (a−Si) and crystalline n−type Si (n−Si) wafers by the thermal evaporation technique under a vacuum pressure of 10− 5 mbar. The films are structurally, morphologically, compositionally, optically and electrically characterized. Strong effect of the nature (amorphous or crystalline) and type (Si or glass) of the substrate on the physical properties of lead selenide films is detected. Of these properties the crystallite sizes decreased and the microstrain, the stacking faults and defect density increased and the energy band gap is blue shifted when (a, n)-Si substrates replaces glass. In addition, the use of crystalline n−Si substrates instead of a−Si removed the free carrier absorption from a−Si/ p−PbSe improving the quantum efficiency of the devices. Opto-electronically, n−Si/p−PbSe films showed photosensor characteristics that suit both visible light and infrared technology applications. The photosensors displayed high current responsivity, external quantum efficiency percentages and response times reaching respective values of 1.4 A/W, 172% and 60 μs. In addition, the n−Si/p−PbSe photosensors which were used as detectors to receive wireless light signals generated from light pulses of 10 kHz frequencies showed smart features nominating them as promising devices for laser sensing and visible light communication technology. WOS:001007916200001 Q3

This undergraduate textbook is intended for one semester courses in wireless communications, both in undergraduate programs of engineering and informatics schools, as well as for postgraduate programs of schools that want to integrate a course on wireless communications in their curriculum. The aim of the textbook is to provide the reader with the theoretical background of the basic concepts of wireless communications, emphasizing the technological developments of today and tomorrow. Initially, in chapter 1, a valuation of the various wireless technologies and models is made, emphasizing those that dominate today and will concern us in the future. Subsequently, in chapter 2, the antenna operating principles and characteristics are analyzed, and the operation of microstip and linear antennas is explained in detail. Chapter 3 gives the theoretical background of the statistical description of the wireless medium. Chapters 4 and 5 present signal modulation and demodulation schemes, and chapter 6 describes channel coding and decoding techniques, emphasizing those used in 4G and 5 G. Chapter 7 analyzes channel equalization techniques. Chapters 8, 9 and 10 present the basic techniques and parameters of multiple-access systems. More specifically, chapter 8 describes the TDMA, FDMA and Packet Radio methods, in chapter 9 spread spectrum systems are analyzed, with CDMA as the main representative, and chapter 10 presents the basic principles of the OFDM implementation. Finally, chapters 11 and 12 introduce the reader to the Multi-Input Multi-Output systems (ΜΙΜΟ) that dominate 4G and 5G. More precisely, chapter 11 analyzes the Single-User Multi-Input Multi-Output systems (SU-MIMO) and chapter 12 analyzes Multiple-User MIMO systems (MU-MIMO), as well as massive MIMO and mmWave massive MIMO that have been introduced in 5G NR., Το παρόν προπτυχιακό σύγγραμμα προορίζεται για εξαμηνιαία μαθήματα σε ασύρματες τηλεπικοινωνίες, τόσο σε προπτυχιακά προγράμματα σχολών Μηχανικών και Πληροφορικής, όσο και για μεταπτυχιακά προγράμματα σχολών που θέλουν να εντάξουν το μάθημα των ασύρματων τηλεπικοινωνιών στο πρόγραμμα τους. Στόχος του συγγράμματος είναι να αποκτήσει ο αναγνώστης το θεωρητικό υπόβαθρο των βασικών εννοιών των ασύρματων τηλεπικοινωνιών δίνοντας έμφαση στις τεχνολογικές εξελίξεις του σήμερα και του αύριο. Αρχικά, στο κεφάλαιο 1, γίνεται αποτίμηση των διαφόρων τεχνολογιών και προτύπων ασυρμάτων συστημάτων, δίνοντας έμφαση σε αυτές που κυριαρχούν σήμερα και θα μας απασχολήσουν στο εγγύς μέλλον. Στη συνέχεια, στο κεφάλαιο 2, αναλύονται οι αρχές λειτουργίας και τα χαρακτηριστικά των κεραιών, και επεξηγείται λεπτομερώς η λειτουργία των τυπωμένων κεραιών και των στοιχειοκεραιών. Στο κεφάλαιο 3 δίνεται το θεωρητικό υπόβαθρο της στατιστικής περιγραφής του ασύρματου μέσου. Στα κεφάλαια 4 και 5 παρουσιάζονται οι μέθοδοι διαμόρφωσης και αποδιαμόρφωσης σήματος, και στο κεφάλαιο 6 γίνεται περιγραφή των μεθόδων κωδικοποίησης και αποκωδικοποίησης καναλιού, δίνοντας βαρύτητα σε αυτές που χρησιμοποιούνται στο 4G και 5G. Στο κεφάλαιο 7 αναλύονται οι τεχνικές ισοστάθμισης καναλιού. Τα κεφάλαια 8, 9 και 10 παρουσιάζουν τις βασικές τεχνικές και παραμέτρους συστημάτων πολλαπλής πρόσβασης στο ασύρματο μέσο. Πιο συγκεκριμένα; στο κεφάλαιο 8 περιγράφονται οι μέθοδοι TDMA, FDMA και Packet Radio, στο κεφάλαιο 9 αναλύονται τα συστήματα μετάδοσης διασποράς φάσματος, με κυριότερο εκπρόσωπο το CDMA, και στο κεφάλαιο 10 παρουσιάζονται οι βασικές αρχές υλοποίησης του OFDM. Τέλος, τα κεφάλαια 11 και 12 εισάγουν τον αναγνώστη στα συστήματα πολλαπλών εισόδων-πολλαπλών εξόδων (ΜΙΜΟ) που κυριαρχούν στα 4G και 5G. Πιο συγκεκριμένα στο κεφάλαιο 11 αναλύονται τα συστήματα πολλαπλών εισόδων-πολλαπλών εξόδων ενός χρήστη (SU-MIMO) και στο κεφάλαιο 12 γίνεται ανάλυση των συστημάτων πολλαπλών χρηστών ΜΙΜΟ (MU-MIMO), massive MIMO και mmWave massive MIMO που έχουν εισαχθεί στο 5G NR.

This paper presents a novel algorithm to emulate the Rician K-factor of a wireless communication environment using a reverberation chamber. In particular, it was focused on the frequency bands used by 5G technology for data transmission. Unlike the current state of the art, the increase of the Rician K-factor is not achieved by inserting lossy material in the chamber, but through the proposed algorithm, which selects a subset of electromagnetic field realizations inside the chamber. The algorithm was first applied to the results of a simulation obtained by using an analytical model that predicts the main physical quantities inside a rectangular cavity where a multiple monopole source stirring action is implemented. Subsequently, the robustness of the algorithm and its applicability was tested on a set of data retrieved from experimental measurements. In all of the considered scenarios, the validity of the proposed method was demonstrated.

Nowadays, Wireless Power Transmission (WPT) is being studied as a possible solution to some of the energy problems globally. Regarding this technology there are still advances to be completed. This dissertation focuses on WPT radiative and not only addresses a theoretical study about the implementation of a satellite to supply a lunar station, but also the development of an important module for a complete system aimed to charge mobile devices. In the first part of this dissertation a simulator is implemented with the objective of evaluating a lunar satellite orbit and obtaining information regarding the minimum distance for transmission and the available energy to operate the on-board transmitters. The simulator allows to change the characteristics of the satellite, the different parameters of the transmitter system and to perform an evaluation for different orbits. As an example, it is demonstrated how it is possible a Energy Budget evaluation, in which the amount of energy reaching the lunar station is estimated by assuming the necessary specifications. The other part of the dissertation contributes to the development of a module designated as Feedback Channel for use in WPT systems on Earth. Integrated into such system, it measures the power in the receiver and communicates that information to the transmitter, so the transmitter adjusts the focus direction to the direction with the highest power value. The approach used in the Feedback Channel is intended not to use complex methods, but to be easily modified for systems requiring other characteristics and to be the target of study for the tarting point of similar modules for the satellite analyzed in the first part. Hoje em dia, a Transmissão de Energia Sem Fios é estudada como possível solução para alguns dos problemas energéticos globais. Relativamente a essa tecnologia, ainda existem avanços a completar. Esta dissertação foca-se na Transmissão de Energia Sem Fios radiativa e, não só aborda um estudo teórico acerca da implementação de um satélite para fornecer energia a uma estação lunar, como também o desenvolvimento de um módulo importante para um sistema completo direcionado ao carregamento de dispositivos móveis. Na primeira metade desta dissertação é implementado um simulador com o objetivo de avaliar órbitas de satélites ao redor da Lua e obter informação relativamente à distância mínima que pode ocorrer a transmissão e que energia está disponível para operar os transmissores a bordo. O simulador permite alterar as características do satélite, os diferentes parâmetros do sistema transmissor e fazer uma avaliação para diferentes órbitas. Como exemplo, é demonstrado de que maneira pode ser feito o Planeamento Energético, onde se estima o valor de energia que chega à estação lunar ao assumir as necessárias especificações. A outra metade da dissertação contribui para o desenvolvimento de um módulo designado de Canal de Feedback utilizado em sistemas de Transmissão de Energia Sem Fios na Terra. Integrado num sistema destes permite medir a potência no recetor e comunicar essa informação ao transmissor por forma a este ajustar a direção do foco para a direção com o maior valor de potência. A abordagem utilizada no Canal de Feedback tem como objetivo não recorrer a métodos complexos, mas ser facilmente alterada para sistemas que requerem outras características e ser alvo de estudo para o ponto de partida de módulos semelhantes ao satélite abordado na primeira parte. Mestrado em Engenharia Eletrónica e Telecomunicações

This paper presents a novel physical-layer security approach to protect the information exchanged in a wireless communication system based on OFDM. In this method, QAM symbols that are fed into the IFFT block are split into two subsets. The first subset of symbols is placed on non-scrambled (indexing) subcarriers, whereas the remaining symbols are transmitted on scrambled (data) subcarriers. Based on the bits placed on the indexing subcarriers, a permutation matrix that defines the (data-based) scrambling sequence of the data subcarriers is determined using an algorithm that is known a priori between the transmitter and receiver. The mapping between indexing bits and scrambling sequences is designed to minimize error propagation when there are erroneous received indexing bits (i.e. Gray-mapped sequences). Closed form formulas that approximate the Bit Error Probability (BEP) of the baseline (non-scrambled) and proposed (scrambled) OFDM transmissions are determined for different link configurations. The impact of the proposed physical-layer security scheme on the BEP is minimal, while increasing notably the number of combinations that an eavesdropper must check in order to execute a brute-force search attack., This work received funding from the Spanish ministry of science and innovation under project IRENE PID2020-115323RB-C31 (AEI/FEDER,UE) and from the Deanship of Scientific Research at Jordan University of Science and Technology, Irbid, Jordan

Advanced technologies are required in future mobile wireless networks to support services with highly diverse requirements in terms of high data rate and reliability, low latency, and massive access. Deep Learning (DL), one of the most exciting developments in machine learning and big data, has recently shown great potential in the study of wireless communications. In this article, we provide a literature review on the applications of DL in the physical layer. First, we analyze the limitations of existing signal processing techniques in terms of model accuracy, global optimality, and computational scalability. Next, we provide a brief review of classical DL frameworks. Subsequently, we discuss recent DL-based physical layer technologies, including both DL-based signal processing modules and end-to-end systems. Deep neural networks are used to replace a single or several conventional functional modules, whereas the objective of the latter is to replace the entire transceiver structure. Lastly, we discuss the open issues and research directions of the DL-based physical layer in terms of model complexity, data quality, data representation, and algorithm reliability.

The Internet of Vehicles (IoV) paradigm aims to improve road safety and provide a comfortable driving experience for Internet-connected vehicles, by transmitting early warning and infotainment signals to Internet-connected vehicles in the network. The unique characteristics of the IoV, such as their mobility and pervasive Internet connectivity, expose such networks to many cyberattacks. In particular, jamming attacks represent a considerable risk to their performance, as they can significantly affect vehicles’ functionality, possibly leading to collisions in dense networks. This paper presents a new scheme enabling the detection and localization of jamming attacks carried out within an IoV network. We consider several scenarios, e.g., where the Internet-connected vehicles and the jammer are statically positioned, as when parked on a street, moving in the same direction and with variable speeds, and moving in opposite directions. We leverage the physical-layer characteristics of the received signals, particularly the Received Signal Strength (RSS), and devise a solution minimizing the jammer localization error based on a set of antennas deployed on the vehicle. Specifically, we compute the power emitted by the jammer and received by the arrays of omnidirectional antennas and we use such values to estimate the location of the jammer in the previous-cited scenarios. Through an extensive simulation campaign, we provide a thorough study of our algorithm, evaluating the effect of several system and channel parameters on the measurement error. The results obtained for all scenarios show a significant localization accuracy, i.e., ranging from 0.23 meters to 13 meters, depending on the channel conditions. This publication was supported by Qatar University Graduate Assistantship.

Unmanned aerial vehicle (UAV)-empowered communications have gained significant attention in recent years due to the promise of agile coverage provision for a large number of various mobile nodes on the ground and in three-dimensional (3D) space. Consequently, there is a need for efficient spectrum utilization in these dense aerial networks, which is characterized through radio environment maps (REMs), the construction of which is an important research area. Nevertheless, due to the difficult collection of radio frequency (RF) data, there are limited works that are based on real-world measurement campaigns. This paper presents a novel experimental setup that includes a constellation of three UAVs, the communication signals of which are measured by a software-defined radio (SDR) mounted on a separate UAV. It follows a trajectory that defines the REM’s two-dimensional (2D) area on a plane, executed at four altitudes, to extend the REM to 3D. The measurements are then processed and their features (received mean power level, average difference of the mean power, percentage of meaningful correlations) are analyzed in the temporal, spatial, and frequency domains to determine the utilization of a 20 MHz band in the 2.4 GHz spectrum, as well as their variation with altitude. This analysis provides a base for research in reducing the amount of measurements (by identifying the regions of low and of high interest) and spectrum occupancy prediction for UAV-based communication coexistence.

Smart health presents an ever-expanding attack surface due to the continuous adoption of a broad variety of Internet of Medical Things (IoMT) devices and applications. IoMT is a common approach to smart city solutions that deliver long-term benefits to critical infrastructures, such as smart healthcare. Many of the IoMT devices in smart cities use Bluetooth technology for short-range communication due to its flexibility, low resource consumption, and flexibility. As smart healthcare applications rely on distributed control optimization, artificial intelligence (AI) and deep learning (DL) offer effective approaches to mitigate cyber-attacks. This paper presents a decentralized, predictive, DL-based process to autonomously detect and block malicious traffic and provide an end-to-end defense against network attacks in IoMT devices. Furthermore, we provide the BlueTack dataset for Bluetooth-based attacks against IoMT networks. To the best of our knowledge, this is the first intrusion detection dataset for Bluetooth classic and Bluetooth low energy (BLE). Using the BlueTack dataset, we devised a multi-layer intrusion detection method that uses deep-learning techniques. We propose a decentralized architecture for deploying this intrusion detection system on the edge nodes of a smart healthcare system that may be deployed in a smart city. The presented multi-layer intrusion detection models achieve performances in the range of 97-99.5% based on the F1 scores. 2022 by the authors. This publication was made possible by an NPRP grant, NPRP 10-0125-170250 from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors. Scopus

Network optimization plays an important role in 5G/next-G networks, which requires knowledge of network parameters (e.g., channel state information). The majority of existing works assume that all network parameters are either given a prior or can be accurately estimated. However, in many practical scenarios, some parameters are uncertain at the time of allocating resources and can only be modeled by random variables. Further, we only have limited knowledge of those uncertain parameters. For instance, channel gains are not exactly known due to channel estimation errors, network delay, limited feedback, and a lack of cooperation (between networks). Therefore, a practical solution to network optimization must address such uncertainty inside wireless networks. There are three approaches to address such a network uncertainty: stochastic programming, worst-case optimization, and chance-constrained programming (CCP). Among the three, CCP has some unique benefits compared to the other two approaches. Stochastic programming explicitly requires full distribution knowledge, which is usually unavailable in practice. In comparison, CCP can work with various settings of available knowledge such as first and second order statistics, symmetric properties, or limited data samples. Therefore, CCP is more flexible to handle different network settings, which is important to address problems in 5G/next-G networks. Further, worst-case optimization assumes upper or lower bounds (i.e., worst cases) for the uncertain parameters and it is known to be conservative due to its focus on extreme cases. In contrast, CCP allows occasional and controllable violations for some constraints and thus offers much better performance in resource utilization compared to worst-case optimization. The only drawback of CCP is that it may lead to intractability due to its probabilistic formulation and limited knowledge of the underlying random variables. To date, CCP has not been well utilized in the wireless communication and networking community. The goal of this dissertation is to extend the state-of-the-art of CCP techniques and address a number of challenging network optimization problems. This dissertation is correspondingly organized into two parts. In the first part, we assume the uncertain parameters are only known by their mean and covariance (without distribution knowledge). We assume these statistics are rather stationary (i.e., time-invariant for a sufficiently long time) and thus can be accurately estimated. In this setting, we introduce a novel reformulation technique based on the mean and covariance to derive a solution. In the second part, we assume these statistics are time-varying and thus cannot be accurately estimated.In this setting, we employ limited data samples that are collected in a small time window and use them to derive a solution. For the first part, we investigate four research problems based on the mean and covariance of the uncertain parameters: - In the first problem, we study how to maximize spectrum efficiency in underlay coexistence.The interference from all secondary users to each primary user must be kept below a given threshold. However, there is much uncertainty about the channel gains between the primary users and the second users due to a lack of cooperation between them. We formulate probabilistic interference constraints using CCP for the primary users. For tractability, we introduce a novel and powerful reformulation technique called Exact Conic Reformulation (ECR). With limited knowledge of mean and covariance, ECR offers an equivalent reformulation for the intractable chance constraints with tractable deterministic constraints without relaxation errors. After reformulation, we employ linearization techniques to the mixed-integer non-linear problem to reduce the computation complexity. We show that our proposed approach can achieve near-optimal performance and stands as a performance benchmark for the underlay coexistence problem. - To find a solution for the same underlay coexistence problem that can be used in the real world, we need to find a solution in "real-time". The real-time requirement here refers to finding a solution in 125 us (the minimum time slot for small cells in 5G). Our proposed solution has three steps. First, it employs ECR to reformulate the original CCP into a deterministic optimization problem. Then it decomposes the problem and narrows down the search space into a smaller but promising one. By random sampling inside the promising search space and through local search, our proposed solution can meet the 125 us requirement in 5G while achieving 90% optimality on average. - We further apply CCP, predicated on the reformulation technique ECR, to two other problems. * We study the problem of power control in concurrent transmissions. Our objective is to maximize energy efficiency for all transmitter-receiver pairs with capacity requirements. This problem is challenging due to mutual interference among different transmitter-receiver pairs and the uncertain channel gain between any transmitter and receiver. We formulate a CCP and reformulate it into a deterministic problem using ECR. Then we employ Geometric Programming (GP) with a tight approximation to derive a near-optimal solution. * We study task offloading in Mobile Edge Computing (MEC) where the number of processing cycles of a task is unknown until completion. The goal is to minimize the energy consumption of the users while meeting probabilistic deadlines for the tasks. We formulate the probabilistic deadlines into chance constraints and then use ECR to reformulate them into deterministic constraints. We propose a solution that consists of periodic scheduling and schedule updates to choose the offloaded tasks and task-to-processor assignments at the base station. In the second part, we investigate two research problems based on limited data samples of the uncertain parameters: - We study MU-MIMO beamforming based on Channel State Information (CSI). The goal is to derive a beamforming solution---minimizing power consumption at the BS while meeting the probabilistic data rate requirements of the users---by using very limited CSI data samples. For our CCP formulation, we explore the idea of Wasserstein ambiguity set to quantify the distance between the true (but unknown) distribution and the empirical distribution based on the limited data samples. Our proposed solution---Data-Driven Beamforming (D^2BF)---reformulates the CCP into a non-convex deterministic optimization problem based on the properties of Wasserstein ambiguity set. Then D^2BF employs a novel convex approximation to the non-convex deterministic problem, which can be directly solved by commercial solvers. - For a solution to the MU-MIMO beamforming to be useful in the real world, it must meet the "real-time" requirement. Here, the real-time requirement refers to 1 ms, which is one transmission time interval (TTI) under 5G numerology 0. We present ReDBeam---a Real-time Data-driven Beamforming solution for the MU-MIMO beamforming problem (minimizing power consumption while offering probabilistic data rate guarantees to the users) with limited CSI data samples. RedBeam is a parallel algorithm and is purposefully designed to take advantage of the vast parallel processing capability offered by GPU. ReDBeam generates a large number of initial solutions from a promising search space and then refines each solution by a local search. We show that ReDBeam meets the 1 ms real-time requirement on a commercial GPU and is orders of magnitude faster than other state-of-the-art algorithms for the same problem. Doctor of Philosophy Network optimization plays an important role in 5G/next-G networks. In a wireless network optimization problem, we typically want to maximize or minimize an objective function under a set of performance or resource constraints. Knowledge of network parameters is typically required in these problems. The majority of existing works assume that all network parameters are either given a prior or can be accurately estimated. However, in many practical scenarios, some parameters are uncertain in nature and cannot be accurately estimated beforehand. This dissertation addresses uncertainty in wireless network optimizations using chance-constrained programming (CCP). CCP can work with limited knowledge of uncertain parameters such as statistics or data samples, instead of full distribution information. In a CCP formulation, violations of certain target performance or requirement thresholds are expressed as probabilistic constraints and the frequency of such violations is bounded through a risk parameter. By changing this risk level, CCP offers a unique trade-off between the guaranteed threshold violation probabilities and the achieved objective value. The only drawback of CCP is that it may lead to intractability due to its probabilistic formulation and limited knowledge of the underlying random variables. The goal of this dissertation is to extend the state-of-the-art of CCP techniques to address a number of challenging network optimization problems. This dissertation is organized into two parts. In the first part, the mean and covariance of the uncertain parameters are assumed to be stationary and thus can be accurately estimated. Our main contribution is a novel reformulation technique for CCP called Exact Conic Reformulation (ECR). Based on knowledge of mean and covariance, ECR is able to offer an equivalent reformulation for the intractable chance constraints with tractable deterministic constraints without relaxation errors. We apply CCP, predicated on ECR, to address three problems: (i) scheduling and power control in underlay coexistence; (ii) power control in concurrent transmissions, and (iii) task offloading in Mobile Edge Computing (MEC). For the first problem, we further address the "real-time" requirement in a solution and propose a solution that can meet the stringent timing requirement. In the second part, when the uncertain parameters are non-stationary and their statistics cannot be accurately estimated, we propose to employ limited data samples that are collected over a small window and use them to develop a solution. To demonstrate the efficacy of this approach, we investigate the MU-MIMO beamforming problem that minimizes the power consumption of the base station while providing probabilistic guarantees to users' data rates. We further address the timing requirement for such a solution in practice, and present a real-time data-driven beamforming solution for MU-MIMO.

This paper presents an illustration of how knowledge from the field of special functions, orthogonal polynomials and numerical series can be applied to solve a very important problem in the field of modern wireless communications. We present the formulas for the probability density function (PDF) and cumulative distribution function (CDF) of the composite signal envelope over an mm-Wave channel. The formulas for the PDF and CDF are expressed in the convergent infinity series form. The main contribution of the paper is in estimating the upper bounds for absolute truncation error in evaluating PDF and CDF of the signal envelope. We also derive the formulas for the required number of terms in the summation under the condition of achieving a given accuracy for typical values of channel parameters. In deriving these formulas, we use the alternating series estimation theorem, as well as some properties of orthogonal polynomials in order to derive upper bounds for hypergeometric functions. Based on the newly derived formulas, numerical results are presented and commented upon. The analytical results are verified by Monte Carlo simulations. The results are essential in the designing and performance estimating of the fifth-generation (5G) and beyond wireless networks.

International audience; In spectrum sensing issues, like in any other classification problem, the performance of the classification task is significantly impacted by the feature selection. This paper proposes a new hybrid optimization algorithm to optimize feature selection for a Deep Neural Network (DNN) classifier. To surpass the premature convergence problem and improve the exploitation ability of the original Black Widow Optimization Algorithm (BWO), we mix a modified version of BWO and Particle Swarm Optimization (PSO), called MBWPSO. The aim is to enhance the performance of a blind spectrum sensing approach in the context of cognitive radio (CR) for wireless communications. Computer simulations show that the MBWPSO algorithm outperforms the original one and a set of state-of-the-art algorithms (i.e., HS, BBO, PSO, and SA) algorithms. The MBWPSO also exhibits the best performance once applied for feature selection in the above context

A study of the behavior of NB-IoT wireless communication in an industrial indoor environment was conducted in this paper. With Wireless Insite software, a scenario in the industrial sector was simulated and modeled. Our research examined how this scenario or environment affected the communication parameters of NB-IoT’s physical layer. In this context, throughput levels among terminals as well as between terminals and transceiver towers, the power received at signal destination points, signal-to-noise ratios (SNRs) in the environment, and distances between terminals and transceivers are considered. These simulated results are also compared with the calculated or theoretical values of these parameters. The results show the effect of the industrial setting on wireless communication. The differences between the theoretical and simulated values are also established.

[ES] La quinta generación de comunicaciones móviles cambia el paradigma de la arquitectura de red hacia el uso de funciones virtualizadas, no sólo a nivel de transporte (núcleo de red o core network), sino también a nivel de la red de acceso radio RAN (Radio Access Network), permitiendo el empleo de distintos softwares sobre un hardware genérico para facilitar las actualizaciones y la introducción de nuevas funcionalidades de manera ágil. Así mismo, existen nuevas corrientes que proponen la transcripción del concepto de código abierto a las interfaces y arquitecturas RAN, permitiendo el desarrollo de componentes a terceros y facilitando la interoperabilidad para ganar flexibilidad y eficiencia en los despliegues radio 5G. La apertura de los protocolos e interfaces de la RAN ha resultado en el concepto de una nueva arquitectura de red denominada Open RAN (O-RAN), que además busca introducir técnicas de IA/ML para el análisis de datos y la toma de decisiones a través de nuevos componentes como el RIC (Radio Intelligent Controller), ejecutándose on-premise, en el edge o en el cloud según las necesidades de latencia y requisitos del caso de uso concreto. En este trabajo se busca desplegar la RAN de una red 5G basada en el estándar O-RAN, empleando la implementación software de código abierto de OpenAirInterface (OAI) y dispositivos de radio definida por software USRPs, haciendo hincapié en el uso y analizando las posibilidades del novedoso controlador radio RIC introducido en la arquitectura O-RAN., [EN] The fifth generation of mobile communications changes the paradigm of network architecture towards the use of virtualized functions, not only at the transport level (core network), but also at the radio access network (RAN) level, allowing the use of multiple software over a generic hardware, to facilitate upgrades and the introduction of new functionalities in an agile manner. There are also new trends that propose the transcription of the open source concept to RAN interfaces and architectures, allowing the development of third-party components and facilitating interoperability to gain flexibility and efficiency in 5G radio deployments. The opening of RAN protocols and interfaces has resulted in the concept of a new network architecture called Open RAN (O-RAN), which also seeks to introduce AI/ML techniques for data analysis and decision making through new components such as the RIC (Radio Intelligent Controller), running on-premise, on the edge or in the cloud depending on latency needs and use case requirements. In this work we seek to deploy the RAN of a 5G network based on the O-RAN standard, employing the OpenAirInterface (OAI) open source software implementation and USRPs software defined radio devices, emphasizing the use and analyzing the possibilities of the novel RIC radio controller introduced in the O-RAN architecture.

U posljednjih se dvadeset godina naglo razvija bežično elektroničko komuniciranje mobilnih korisnika, a posebno nakon uvođenja satelitskih veza . Mobilne bežične telekomunikacije postaju temelj u suvremenoj pomorskoj djelatnosti čime se skromno utvrđuje i daljinsko upravljanje brodom. Pomorske komunikacije se znatno unaprijeđuju uvođenjem najnovijih tehnologija poput interneta, satelita i dr. Dvojnost razvoja kako terestričkih tako i satelitskih radioveza donosi nove mogućnosti, ali i alternative. Unatoč prednostima ovih novih tehnologija koje pridonose znatno većem stupnju automatizacije sigurno je da ljudski faktor i dalje ostaje presudan. Bežične mreže mogu osigurati mrežni pristup telefonima, računalima, aplikacijama, bazama podataka u krajnjem Internetu i to na brodovima koji su na udaljenim lokacijama pružajući pri tome korisnicima mogućnost da pribavljaju, kopiraju i upravljaju podacima virtualno s bilo koje lokacije. Uz kvalitetno rukovanje operatora sigurnosti plovidbe trebala bi znatno porasti, a kvalitetna razmjena će razmijeniti informacija će unaprijediti pomorsko gospodarsko u cjelini. U prvom dijelu autor opisuje osnovne pomorske telekomunikacije i kako one utječu na sigurnost plovidbe i članove brodske plovidbe tijekom pojedinog pomorskog pothvata. Drugi dio završnog rada opisuje moguću širu primjenu u pomorstvu te razmatranje mogućih inovacija., In the last twenty years, wireless electronic communication of mobile users has developed rapidly, especially after the introduction of satellite connections. Mobile wireless telecommunication is becoming the basis of modern maritime activity, which modestly determines the remote control of the ship. Maritime communications are significantly improved by the introduction of the latest technologies such as the Internet, satellites, etc. The duality of the development of both terrestrial and satellite radio links brings new possibilities, but also alternatives. Despite the advantages of these new technologies, which contribute to a significantly higher degree of automation, it is certain that the human factor still remains crucial. Wireless networks can provide network access to phones, computers, applications, databases in the final Internet and on ships that are in remote locations, giving users the opportunity to acquire, copy and manage data virtually from any location. With the quality handling of operators, navigation safety should increase significantly, and a quality exchange of information will improve the maritime economy as a whole. In the first part, the author describes basic maritime telecommunications and how they affect the safety of navigation and members of the ship's navigation during a particular maritime venture. The second part of the final paper describes the possible wider application in the maritime sector and the consideration of possible innovations.

Sustainability and sustainable development are topics that are increasingly addressed in the ICT sector including wireless networks. Yet, their interpretations vary a great deal depending on the person without a commonly agreed approach. This paper presents an overview of sustainability and sustainable development in the context of ICTs and wireless networks highlighting the urgency of introducing sustainability principles at all levels and stages of ICT technology development. The paper presents a way forward to adopt sustainability principles into future technology design considering the triple bottom line of economic, social and environmental sustainability perspectives. A change in mindset is urgently needed and all stakeholders need to act in their own capacity as well as collaboratively to make the wireless networks and their use truly sustainable without green-washing. New metrics need to be defined and measured to respond to growing concerns as today’s metrics, such as total consumed mobile data are far from sustainable. Time to act is now as the design criteria for the future sustainable 6G are defined in the next years.

Cataloged from PDF version of article. Thesis (Master's): Bilkent University, Department of Electrical and Electronics Engineering, İhsan Doğramacı Bilkent University, 2022. Includes bibliographical references (leaves 73-78). Future wireless communications is expected to bring significant changes along with a number of emerging technologies such as 5G, virtual reality, edge computing, and IoT. These developments pose unprecedented demands in terms of capacity, coverage, latency, efficiency, flexibility, compatibility, and quality of experience on wireless communication systems. Machine Learning (ML) techniques are considered as a promising tool to tackle this challenge due to their ability to manage big data, powerful nonlinear mapping, and distributed computing capabilities. There have been many research results addressing different aspects of ML algorithms and their connections to wireless communications; however, there are still various challenges that need to be addressed. In particular, their use for communication systems with memory, is not fully investigated. With this motivation, this thesis considers an application of ML, in particular, deep learning (DL), techniques for communications over intersymbol interference (ISI) channels. In this thesis, we propose DL-based channel equalization algorithms for channels with ISI. We introduce three different DL-based ISI detectors, namely sliding bidirectional long short term memory (Sli-BiLSTM), sliding multi layer perceptron (Sli-MLP), and sliding iterative (Sli-Iterative), and demonstrate that they are computationally efficient and capable of performing equalization under a variety of channel conditions with the knowledge of the channel state information. We also employ sliding bidirectional gated recurrent unit (Sli-BiGRU) and Sli- MLP, which are more suitable for use with fixed ISI channels. As an extension, we also examine DL-based equalization techniques for multiple-input multipleoutput (MIMO) ISI channels. Numerical results show that proposed models are well suited for equalization of ISI channels with perfect as well as noisy CSI for a broad range of signal-to-noise ratio (SNR) levels as long as the ISI length is very close to the optimal solution, namely, the maximum likelihood sequence estimation, implemented through the Viterbi Algorithm while having considerably less complexity, and they have superior performance compared to MMSE-based channel equalization. by Berke Eren M.S.

The huge spreading of COVID-19 viral outbreak to several countries motivates many of the research institutions everywhere in numerous disciplines to try decreasing the spread rate of this pandemic. Among these researches are the robotics with different payloads and sensory devices with wireless communications to remotely track patients’ diagnosis and their treatment. That is, it reduces direct contact between the patients and the medical team members. Thus, this paper is devoted to design and implement a prototype of wireless medical robot (MR) that can communicate between patients and medical consultants. The prototype includes the modelling of a four-wheeled MR using systems' identification methodology, from which the model is utilized in control design and analysis. The required controller is designed using the proportional-integral-derivative (PID) and Fuzzy logic (FLC) techniques. The MR is equipped onboard with some medical sensors and a camera to acquire vital signs and physical parameters of patients. The MR model is obtained via an experimental test with input/output signals in open-loop configuration as single–input–single–output from which the estimation and validation results demonstrate that the identified model possess about 89% of the output variation/dynamics. This model is used for controllers' design with PID and FLC, the response of which is good for heading angle tracking. Concerning the medical measurements, more than two thousand real recorded Photo-plethysmography (PPG) signals and Blood Pressure (BP) are used to find the appropriate BP estimation model. Towards this objective, some experiments are designed and conducted to measure the PPG signal. Finally, the BP is estimated with mean absolute error of about 4.7 mmHg in systolic and 4.8 mmHg in diastolic using Artificial Neural Network.

In order to realize the automation of transport equipment, according to the automatic guided vehicle (AGV) kinematics model, the trajectory tracking control of AGV with front wheel steering and rear wheel drive is studied. Lyapunov function is used to ensure the global stability of the system. Time-varying state feedback method based on integral backstepping is adopted, introducing virtual feedback, a trajectory tracking controller for AGV with nonholonomic constraints is proposed. In order to ensure the smooth motion of AGV, the speed and acceleration limited strategy of AGV is introduced into the controller. Simulation results show that the algorithm is fast, accurate and globally stable for different paths.

International audience; Due to highly variant traffic in downlink (DL) and uplink (UL) in heterogeneous networks (HetNets), dynamic time-division duplexing (TDD) is proposed to dynamically allocate UL and DL resources. Under the same circumstances, downlink and uplink decoupled access (DUDA) is introduced to balance between UL and DL transmissions and to further improve the system performance. Rather than belonging to a specific cell, a mobile user can receive the downlink traffic from one base station (BS) and send uplink traffic through another BS. In this article, we analytically investigate a joint TDD and DUDA statistical model with multiple small cells deployment. This model is based on a geometric probability approach. Taking all possible TDD subframes combinations between the macro and small cells, coupled and decoupled cell associations strategies are investigated in details. We derive analytical expressions for the capacity and the interference, considering a network of one macro cell and multiple small cells. We build on the derived capacity expressions to measure the decoupling gain and thus, identify the location of the interferer small cell where the decoupled mode maintains a higher gain in both DL and UL. Monte-Carlo simulations results are presented to validate the accuracy of the statistical model.

the frequency bands below 6 GHz, which have traditionally been used for the transmission of wireless communications systems, are saturated. Therefore, the search for new frequency bands has been focused on higher frequencies. In this scenario, characterizing the propagation in bands above 6 GHz for various propagation environments is necessary. In this article, an empirical propagation model is presented to predict indoor propagation losses from 10 to 20 GHz. The model was obtained from measurements carried out inside an anechoic chamber, which was designed and built with an internal cover of polyurethane foam as absorbent material and metallic external cover. Measurements were performed in distance and frequency steps of 10 cm and 50 MHz, respectively. In addition, the atmospheric conditions of temperature, humidity and oxygen level inside the chamber were modified, through the insertion of oxygen and water vapor. In order to emulate the weather conditions of mountainous and coastal places. It was determined that the variation of the oxygen and humidity concentration improves the propagation conditions by 7 dB and 15 dB, respectively., Actualmente, las bandas de frecuencia inferiores a 6 GHz, las cuales, clásicamente han sido utilizadas para la transmisión de sistemas de comunicaciones inalámbricas, se encuentran saturadas. Por lo que, la búsqueda de nuevas bandas de frecuencia es necesaria y ha sido enfocada a frecuencias superiores. En este escenario, caracterizar la propagación en bandas superiores a 6 GHz para diversos entornos de propagación es necesario. En el presente artículo se presenta un modelo de propagación empírico para predecir las pérdidas de propagación en interiores de 10 a 20 GHz. El modelo fue obtenido a partir de medidas realizadas dentro de una cámara anecoica, la cual fue diseñada y construida con cubierta interna de espuma de poliuretano como material absorbente y cobertura externa metálica. Las medidas se realizaron en saltos de distancia y frecuencia de 10 cm y 50 MHz, respectivamente. Además, se modificaron las condiciones atmosféricas de temperatura, humedad y nivel de oxígeno en el interior de la cámara, a través de la inserción de oxígeno y vapor de agua. Con el fin de emular las condiciones climatológicas de lugares montañosos y costeros. Se determinó que la variación de la concentración de oxígeno y humedad mejora las condiciones de propagación en 7 dB y 15 dB, respectivamente.

In recent years, the Smart City concept has grown in popularity, and a significant number of cities around the world have adopted smart city strategies. Smart and sustainable cities are an emerging urban development approach due to their immense potential to improve environmental sustainability. The Smart City concept is based on collecting, analyzing, and displaying a large amount of data and information concerning urban systems and subsystems. As time goes by, the capacity of smart cities for generating digital information has grown exponentially. However, this digital information is heterogeneous, massive, collected from different sources, generated in different formats, and in most cases not structured, which exacerbates the situation of extracting valuable knowledge from data. Therefore, it is fundamental to handle the significant volumes of heterogeneous sensed data and to integrate such data along with information and analysis tools into a comprehensive platform. This can ensure the security, efficiency, and performance of the different Smart City tasks. A comprehensive software platform could provide services such as facilities for application development, integration of heterogeneous data sources, deployment, and management to ease the construction of sophisticated Smart Cities’ applications. In this context, the work begins with a concise description of the concept of smart city and the technologies involved in it. It addresses the development of an urban data platform along with how to obtain and integrate information from sensors and other data sources, in order to provide aggregated and intelligent views of raw data to support various domains within the city; in our case, smart mobility. The platform architecture is implemented following a five-layer model that considers elements from perception, sensing to data management, processing, and visualization. With the aim of evaluating the efficiency of the developed platform, three different use cases are described and analyzed, which have been implemented in the city of Pamplona, Spain, as vertical services linked to the platform: intelligent urban mobility-bike handling, bike-2-bike communication, and restricted vehicle access zone control system. Ultimately, this work provides an experiment to assess different long-range wireless communication technologies to enable their implementation within an urban environment. This work was partially supported by the European Union’s Horizon 2020 Research and Innovation Programme (STARDUST-Holistic and Integrated Urban Model for Smart Cities) under Grant 774094, by the Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (Agencia Estatal de Investigación, Fondo Europeo de Desarrollo Regional-FEDER, European Union) under Grant RTI2018-095499-B-C31 IoTrain, and by Gobierno de Navarra under Grant PC183-184 (Securing information and applications in V2G environments, SECV2G). Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011) Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

In some scenarios, the log-logistic (LL) distribution is shown to provide the best fit to field measurements in the context of wireless channel modeling. However, a fading channel model based on the LL distribution has not been formulated yet. In this work, we introduce the L-distribution as a reformulation of the LL distribution for channel modeling purposes. We provide closed-form expressions for its PDF, CDF, and moments. Performance analysis of wireless communication systems operating under L-fading channels is exemplified, providing exact and asymptotic expressions for relevant metrics such as the outage probability and the average capacity. Finally, important practical aspects related to the use of the L-distribution for channel fitting purposes are discussed in two contexts: (i) millimeter-wave links with misaligned gain, and (ii) air–ground channels in unmanned aerial vehicle communications., European Social and Regional Funds, Junta de Andalucia P18-RT-3175 UMA20-FEDERJA-002, Universidad de Malaga, Universidad de Granada

The 3rd Generation Partnership Project (3GPP) narrowband Internet of Things (NB-IoT) over non-terrestrial networks (NTN) is the most promising candidate technology supporting 5G massive machine-type communication. Compared to geostationary earth orbit, low earth orbit (LEO) satellite communication has the advantage of low propagation loss, but suffers from high Doppler shift. The 3GPP proposes Doppler shift pre-compensation for each beam region of the satellite. However, user equipment farther from the beam center has significant residual Doppler shifts even after pre-compensation, which degrades link performance. This study proposes residual Doppler shift compensation by adding demodulation reference signal symbols and reducing satellite beam coverage. The block error rate (BLER) data are obtained using link-level simulation with the proposed technique. Since the communication time provided by a single LEO satellite moving fast is short, many LEO satellites are necessary for seamless 24-h communication. Therefore, with the BLER data, we analyze the link budget for actual three-dimensional orbits with a maximum of 162 LEO satellites. We finally investigate the effect of the proposed technique on performance metrics such as the per-day total service time and maximum persistent service time, considering the number of satellites and the satellite spacing. The results show that a more prolonged and continuous communication service is possible with significantly fewer satellites using the proposed technique.