Academic literature on the topic 'Communications and networks technologies'

Internal communication is considered to be fundamental process for organization. The information and communication technology (ICT) has been a strong trigger of organizational change in every aspect, as well as in internal communication. This paper investigates ICT tools usage effects on internal communication. Three research hypothesis were set up: (i) employees’ perceived importance of internal communication has a relationship with their ICT usage, (ii) employees’ perceived quality of internal communication has a relationship with their ICT usage, and (iii) ICT tools usage contributes to the perceived impact of IT on informing, motivation, productivity, loyalty, organizational development understanding, reducing rumors within organization of employees, willingness to change and overall satisfaction of employees. In order to test hypothesis, data were collected via an online survey conducted among Croatian public relations experts. Data mining was applied in data analysis: including both, descriptive (distributions) and predictive models (Bayesian networks). Sensitivity analysis of Bayesian networks identified significant factors of successful internal communication. Results showed that Skype usage mostly contributed to the quality of internal communication, whereas social network usage mostly contributed to the perceived importance of internal communication. Bayesian network model identified e-mail usage as a predictor of employees informing and chat usage as predictor for productivity of employees. Organizations’ management should embrace opportunities that new technologies have brought to the field of internal communications and use it as a tool for improvement.

The traffic of the distribution automation communication network under different size and applications is analyzed based on the communications models. From the network availability and the resource utilization, the distribution automation adaptability is compared with the different communication networks combined with the current main power terminal communication network technologies. The results provide an important theoretical basis for the planning of the distribution automation communication network.

Emergency situations such as wildfires, water floods, or even terrorist attacks require continuous communication between the coordination centres, the several on-the-field teams, and their respective devices to properly address the adverse circumstances. From a technological point of view, this can be best seen as a live Ubiquitous Sensor Network—composed of human beings (e.g., first responders, victims) and devices (e.g., drones, environmental sensors, radios)—with stringent and special communication requirements in terms of flexibility, mobility, reliability, bandwidth, heterogeneity, and speed of deployment. However, for this specific use case, most of the already deployed and well-known communication technologies (e.g., satellite, 4G/5G) might become unusable and hard to repair due to the associated effects of the disaster itself. The purpose of this paper is (1) to review the emergency communications challenges, (2) to analyse the existing surveys on technologies for emergency situations, (3) to conduct a more updated, extensive, and systematic review of the emergency communications’ technologies, and (4) to propose a heterogeneous communication architecture able to communicate between moving agents in harsh conditions. The proposed approach is conceived to link the relocating agents that constitute a Ubiquitous Sensor Network spanning a large-scale area (i.e., hundreds of square kilometres) by combining Near Vertical Incidence Skywave technologies with Drone-Based Wireless Mesh Networks. The conclusions derived from this research aim to set up the fundamentals of a rapidly deployable Emergency Communications System inspired by the Ubiquitous Sensor Network paradigm.

The contemporary wireless transmitter in addition to information symbols transmits also training symbols in order to help the receivers in the estimation of the information symbols by estimating the channel state information (CSI). In this paper, we look at existing wireless communication technologies in light of environment-aware wireless communications, which is a new concept of wireless communications that queries the time-invariant CSI from the local or global database, using information about the transmitter and receiver location. Thus, this study is the first critical review of the potential of today’s terrestrial wireless communication systems including wireless cellular technologies (GSM, UMTS, LTE, NR), wireless local area networks (WLANs), and wireless sensor networks (WSNs), for estimating CSI, the ratio between training and information symbols and the rate of channel variation, and the potential use of time invariable CSI in environment aware wireless communications. The research reveals, that early communication systems provide means for narrowband channel estimation and the CSI is only available as channel attenuation based on signal level measurements. By increasing the frequency bandwidth of communications, the CSI is estimated in some form of channel impulse response (CIR) in almost all currently used radio technologies, but this information is generally not available outside the communication systems. Also, the CSI is estimated only for the channel with active communications. The new radio technology (NR) offers the possibility of estimating the CIR for non-active channels as well, and thus the possibility of initiating environmentally aware wireless communications.

The need for high-quality communications networks is urgent in data-based farming. A particular challenge is how to achieve reliable, cost-efficient, secure, and broadband last-mile data transfer to enable agricultural machine control. The trialed ad hoc private communications networks built and interconnected with different alternative wireless technologies, including 4G, 5G, satellite and tactical networks, provide interesting practical solutions for connectivity. A remotely controlled tractor is exemplified as a use case of machine control in the demonstrated private communication network. This paper describes the results of a comparative technology analysis and a field trial in a realistic environment. The study includes the practical implementation of video monitoring and the optimization of the control channel for remote-controlled unmanned agricultural tractors. The findings from this study verify and consolidate the requirements for network technologies and for cybersecurity enablers. They highlight insights into the suitability of different wireless technologies for smart farming and tractor scenarios and identify potential paths for future research.

Scientific and theoretical approaches to the implementation of a heterogeneous mobile communication network based on SDN/NFV and SDR technologies are described. The architecture of the future heterogeneous network is proposed, taking into account the evolution of emerging standards and key technologies. An algorithm for dynamic bandwidth allocation and reservation between several logical channels at a certain moment of time to provide QoS for information flows in future networks is created. A simulation model of network traffic service with parameters corresponding to real networks has been made. The study of femtocell SDR load, as the main convergent device at the level of heterogeneous network access by users of different generation mobile communication technologies has been conducted.

Maritime wireless mesh networks (MWMNs) are conceived to provide network connectivity for maritime users and enable them to communicate with correspondent users connected to terrestrial communication networks. The high cost and low data-rate of satellite and other legacy maritime communication technologies and systems deployed in MWMNs pose major limitation to establish reliable and affordable maritime communications. In addition, the design of routing protocols in MWMNs remains a significant challenge due to the lack of reliable communication infrastructure and complexity of maritime environment. This paper explains the existing maritime communication technologies and routing protocols which could be deployed in implementing reliable MWMNs. Comprehensive guidelines are outlined to easily understand and critically assess the different deployed maritime communication networks and systems with routing protocols, and identify the milestones in the process of developing and implementing broadband MWMNs.

As an enhancement of cellular networks, the future-generation 5G network can be considered an ultra-high-speed technology. The proposed 5G network might include all types of advanced dominant technologies to provide remarkable services. Consequently, new architectures and service management schemes for different applications of the emerging technologies need to be recommended to solve issues related to data traffic capacity, high data rate, and reliability for ensuring QoS. Cloud computing, Internet of things (IoT), and software-defined networking (SDN) have become some of the core technologies for the 5G network. Cloud-based services provide flexible and efficient solutions for information and communications technology by reducing the cost of investing in and managing information technology infrastructure. In terms of functionality, SDN is a promising architecture that decouples control planes and data planes to support programmability, adaptability, and flexibility in ever-changing network architectures. However, IoT combines cloud computing and SDN to achieve greater productivity for evolving technologies in 5G by facilitating interaction between the physical and human world. The major objective of this study provides a lawless vision on comprehensive works related to enabling technologies for the next generation of mobile systems and networks, mainly focusing on 5G mobile communications.

The past few years have seen a major change in cellular networks, as explosive growth in data demands requires more and more network capacity and backhaul capability. New wireless technologies have been proposed to tackle these challenges. One of the emerging technologies is device-to-device (D2D) communications. It enables two cellular user equipment (UEs) in proximity to communicate with each other directly reusing cellular radio resources. In this case, D2D is able to offload data traffic from central base stations (BSs) and significantly improve the spectrum efficiency of a cellular network, and thus is one of the key technologies for the next generation cellular systems. Radio resource management (RRM) for D2D communications and how to effectively exploit the potential benefits of D2D are two paramount challenges to D2D communications underlaying cellular networks. In this thesis, we focus on four problems related to these two challenges. In Chapter 2, we utilise the mixed integer non-linear programming (MINLP) to model and solve the RRM optimisation problems for D2D communications. Firstly we consider the RRM optimisation problem for D2D communications underlaying the single carrier frequency division multiple access (SC-FDMA) system and devise a heuristic sub-optimal solution to it. Then we propose an optimised RRM mechanism for multi-hop D2D communications with network coding (NC). NC has been proven as an efficient technique to improve the throughput of ad-hoc networks and thus we apply it to multi-hop D2D communications. We devise an optimal solution to the RRM optimisation problem for multi-hop D2D communications with NC. In Chapter 3, we investigate how the location of the D2D transmitter in a cell may affect the RRM mechanism and the performance of D2D communications. We propose two optimised location-based RRM mechanisms for D2D, which maximise the throughput and the energy efficiency of D2D, respectively. We show that, by considering the location information of the D2D transmitter, the MINLP problem of RRM for D2D communications can be transformed into a convex optimisation problem, which can be efficiently solved by the method of Lagrangian multipliers. In Chapter 4, we propose a D2D-based P2P le sharing system, which is called Iunius. The Iunius system features: 1) a wireless P2P protocol based on Bittorrent protocol in the application layer; 2) a simple centralised routing mechanism for multi-hop D2D communications; 3) an interference cancellation technique for conventional cellular (CC) uplink communications; and 4) a radio resource management scheme to mitigate the interference between CC and D2D communications that share the cellular uplink radio resources while maximising the throughput of D2D communications. We show that with the properly designed application layer protocol and the optimised RRM for D2D communications, Iunius can significantly improve the quality of experience (QoE) of users and offload local traffic from the base station. In Chapter 5, we combine LTE-unlicensed with D2D communications. We utilise LTE-unlicensed to enable the operation of D2D in unlicensed bands. We show that not only can this improve the throughput of D2D communications, but also allow D2D to work in the cell central area, which normally regarded as a “forbidden area” for D2D in existing works. We achieve these results mainly through numerical optimisation and simulations. We utilise a wide range of numerical optimisation theories in our works. Instead of utilising the general numerical optimisation algorithms to solve the optimisation problems, we modify them to be suitable for the specific problems, thereby reducing the computational complexity. Finally, we evaluate our proposed algorithms and systems through sophisticated numerical simulations. We have developed a complete system-level simulation framework for D2D communications and we open-source it in Github: https://github.com/mathwuyue/py- wireless-sys-sim.

Optical packet switching (OPS) is the most prominent candidate transport solution that can seamlessly integrate electrical and optical layers by transferring certain switching functionality from electronics to optics, thus alleviating unnecessarily slow and expensive optical-electrical-optical conversions and signal processing at the switching node. Optical Label Switching (OLS) is an important aspect of the optical packet switched network that enables very low-latency forwarding of ultra-high bit-rate, protocol-independent packets entirely in the optical domain. The objective of the proposed research is to develop novel, efficient techniques to realize several key enabling technologies such as optical label generation and encoding, optical label swapping, all-optical buffering, and spectral efficient transmission system for optical label switched based OPS networks. A novel scheme of generating optical label at the ingress node using optical carrier suppression and separation (OCSS) technique is proposed. This scheme does not suffer from any unavoidable interference, limited extinction ratio or strict synchronization requirements between payload and label as observed by the currently available other label generation methods. One of the primary challenges to realize optical label swapping at the core node of scalable OLS network is the insertion of new optical labels without any wavelength conversion for same wavelength packet routing. A novel mechanism to realize same wavelength packet switching without using any conventional wavelength converter in the OLS network carrying differential phase-shift keying (DPSK) modulated payload and on-off keying (OOK) modulated optical label is demonstrated. Also a new dense wavelength division multiplexing (DWDM) optical buffer architecture using optical fiber delay lines that can provide wavelength selective reconfigurable variable delays is proposed. Optical packet switching provides automated, reconfigurable, and faster provision of both wavelength and bandwidth with finer granularity in the optical layer. However, a newer, cost-effective, and spectrally efficient optical transmission technology is essential to support the explosive bandwidth demand expected by the future optical packet switched networks. To meet this challenge, a spectrally efficient solution for transporting 40 Gbps per channel data over 50 GHz spaced DWDM system is developed by exploiting optical carrier suppression and separation technique and optical duobinary modulation.

Wireless network virtualization (WNV) and millimeter wave (mmW) communications are emerging as two key technologies for cellular networks. Virtualization in cellular networks enables wireless services to be decoupled from network resources (e.g., infrastructure and spectrum) so that multiple virtual networks can be built using a shared pool of network resources. At the same time, utilization of the large bandwidth available in mmW frequency band would help to overcome ongoing spectrum scarcity issues. In this context, this dissertation presents efficient frameworks for building virtual networks in sub-6 GHz and mmW bands. Towards developing the frameworks, first, we derive a closed-form expression for the downlink rate coverage probability of a typical sub-6 GHz cellular network with known base station (BS) locations and stochastic user equipment (UE) locations and channel conditions. Then, using the closed-form expression, we develop a sub-6 GHz virtual resource allocation framework that aggregates, slices, and allocates the sub-6 Ghz network resources to the virtual networks in such a way that the virtual networks' sub-6 GHz downlink coverage and rate demands are probabilistically satisfied while resource over-provisioning is minimized in the presence of uncertainty in UE locations and channel conditions. Furthermore, considering the possibility of lack of sufficient sub-6 GHz resources to satisfy the rate coverage demands of all virtual networks, we design a prioritized sub-6 GHz virtual resource allocation scheme where virtual networks are built sequentially based on their given priorities. To this end, we develop static frameworks that allocate sub-6 GHz resources in the presence of uncertainty in UE locations and channel conditions, i.e., before the UE locations and channel conditions are revealed. As a result, when a slice of a BS serves its associated UEs, it can be over-satisfied (i.e., resources left after satisfying the rate demands of all UEs) or under-satisfied (i.e., lack of resources to satisfy the rate demands of all UEs). On the other hand, it is extremely challenging to execute the entire virtual resource allocation process in real time due to the small transmission time intervals (TTIs) of cellular technologies. Taking this into consideration, we develop an efficient scheme that performs the virtual resource allocation in two phases, i.e., virtual network deployment phase (static) and statistical multiplexing phase (adaptive). In the virtual network deployment phase, sub-6 GHz resources are aggregated, sliced, and allocated to the virtual networks considering the presence of uncertainty in UE locations and channel conditions, without knowing which realization of UE locations and channel conditions will occur. Once the virtual networks are deployed, each of the aggregated BSs performs statistical multiplexing, i.e., allocates excess resources from the over-satisfied slices to the under-satisfied slices, according to the realized channel conditions of associated UEs. In this way, we further improve the sub-6 GHz resource utilization. Next, we steer our focus on the mmW virtual resource allocation process. MmW systems typically use beamforming techniques to compensate for the high pathloss. The directional communication in the presence of uncertainty in UE locations and channel conditions, make maintaining connectivity and performing initial access and cell discovery challenging. To address these challenges, we develop an efficient framework for mmW virtual network deployment and UE assignment. The deployment decisions (i.e., the required set of mmW BSs and their optimal beam directions) are taken in the presence of uncertainty in UE locations and channel conditions, i.e., before the UE locations and channel conditions are revealed. Once the virtual networks are deployed, an optimal mmW link (or a fallback sub-6 GHz link) is assigned to each UE according to the realized UE locations and channel conditions. Our numerical results demonstrate the gains brought by our proposed scheme in terms of minimizing resource over-provisioning while probabilistically satisfying virtual networks' sub-6 GHz and mmW demands in the presence of uncertainty in UE locations and channel conditions.
Doctor of Philosophy
In cellular networks, mobile network operators (MNOs) have been sharing resources (e.g., infrastructure and spectrum) as a solution to extend coverage, increase capacity, and decrease expenditures. Recently, due to the advent of 5G wireless services with enormous coverage and capacity demands and potential revenue losses due to over-provisioning to serve peak demands, the motivation for sharing and virtualization has significantly increased in cellular networks. Through wireless network virtualization (WNV), wireless services can be decoupled from the network resources so that various services can efficiently share the resources. At the same time, utilization of the large bandwidth available in millimeter wave (mmW) frequency band would help to overcome ongoing spectrum scarcity issues. However, due to the inherent features of cellular networks, i.e., the uncertainty in user equipment (UE) locations and channel conditions, enabling WNV and mmW communications in cellular networks is a challenging task. Specifically, we need to build the virtual networks in such a way that UE demands are satisfied, isolation among the virtual networks are maintained, and resource over-provisioning is minimized in the presence of uncertainty in UE locations and channel conditions. In addition, the mmW channels experience higher attenuation and blockage due to their small wavelengths compared to conventional sub-6 GHz channels. To compensate for the high pathloss, mmW systems typically use beamforming techniques. The directional communication in the presence of uncertainty in UE locations and channel conditions, make maintaining connectivity and performing initial access and cell discovery challenging. Our goal is to address these challenges and develop optimization frameworks to efficiently enable virtualization and mmW technologies in cellular networks.

Mestrado em Engenharia Eletrónica e Telecomunicações
Low-Power Wide Area Networks (LPWANs) are one set of technologies that are growing in the eld of the Internet of Things (IoT). Due to the long range capabilities and low energy consumption, Low-Power Wide Area Networks (LPWANs) are the ideal technologies to send small data occasionally. With their unique characteristics, LPWANs can be used in many applications and in di erent environments such as urban, rural and even indoor. The work developed in this dissertation presents a study on the LPWAN LoRa technology, by testing and evaluate its range, signal quality properties and its performance in delivering data. For this, three distinct scenarios are proposed and tested. The inclusion of LoRa in a multi-technology data gathering platform is the key objective of this dissertation. For this it is proposed: (1) an organization based in clusters of sensor nodes; (2) a Media Access Control (MAC) protocol to provide e cient communications through the LoRa technology; and nally, (3) a Connection Manager that is capable of managing the di erent available technologies in the sensor nodes and that is able to adapt its actions according to the acquired data type is proposed. The performed tests aim to perceive which type of parameters can in uence the performance of the overall proposed solution, as well as the advantages of a multi-technology approach in a data gathering platform.
Low-Power Wide Area Networks (LPWANs) são um conjunto de tecnologias em crescimento na área da Internet of Things (IoT). Devido ás suas capacidades de comunicar a longo alcance e de baixo consumo energético, as LPWANs apresentam-se como a tecnologia ideal para o envio ocasional de pequenas porções de dados. Ao possuírem características únicas, as LPWANs podem ser usadas em diversas aplicações e em diferentes ambientes, sejam eles urbanos, rurais ou interiores. O trabalho desenvolvido nesta dissertação apresenta um estudo acerca da tecnologia Long Range (LoRa), uma LPWAN, testando e avaliando o seu alcance, a qualidade do sinal e o desempenho na entrega de dados. Para isso, três cenários distintos são propostos e testados. A inclusão de LoRa numa plataforma de aquisição de dados com múltiplas tecnologias e um dos objectivos chave desta dissertação. Para isso, são propostas: (1) uma organização baseada em clusters de sensores; (2) um protocolo de controlo de acesso ao meio (MAC) para permitir que as comunicações através de LoRa sejam eficientes; e finalmente, (3) um gestor de conectividade com capacidade de gerir as diferentes tecnologias disponíveis nos sensores e que seja capaz de agir consoante o tipo de dados adquiridos. Os testes efectuados tem como objectivo perceber que tipo de parâmetros podem influenciar o desempenho global da soluçao proposta, bem como as vantagens de usar uma abordagem baseada em múltiplas tecnologias numa plataforma de aquisição de dados.

Over the past decade, wireless data communication has experienced a phenomenal growth, which is driven by the popularity of wireless devices and the growing number of bandwidth hungry applications. During the same period, various advanced communication technologies have emerged to improve network throughput. Some examples include multi-input multi-output (MIMO), full duplex, cognitive radio, mmWave, among others. An important research direction is to understand the impacts of these new technologies on network throughput performance. Such investigation is critical not only for theoretical understanding, but also can be used as a guideline to design algorithms and network protocols in the field. The goal of this dissertation is to understand the impact of some advanced technologies on network throughput performance. More specifically, we investigate the following three technologies: MIMO, full duplex, and mmWave communication. For each technology, we explore the performance envelope of wireless networks by studying a throughput maximization problem.
Ph. D.

L’étude réalisée dans ce mémoire porte sur la communication et la transmission des données dans le contexte des réseaux de capteurs. Pour améliorer la fiabilité de transmission, des relais sont insérés entre les capteurs et la destination afin de pouvoir corriger les erreurs de transmissions en utilisant des codes LDPC. L’architecture est donc optimisée grâce aux codes en blocs mais aussi à l’aide des protocoles de détection d’erreurs et aussi à l’aide de la combinaison de la correction et de la détection d’erreurs. Les systèmes d’antennes multiples forment également une option très intéressante pour l’amélioration des performances. L’efficacité énergétique est étudiée dans les différents protocoles et solutions proposés. Une optimisation conjointe du codage de canal et du codage de réseau physique est également effectuée
The work done in this study focuses on communication and data transmission in the context of sensor networks. To improve the reliability of transmission, relays are inserted between the sensors and the destination in order to correct errors in transmissions using LDPC codes. The architecture is optimized thanks to the block codes but also to the error detection protocols and the use of a combination of the error correction and detection. Another interesting way to improve performances is to use multiple antenna systems. Energy efficiency is evaluated in the protocols studied and the solutions proposed. Besides, a joint optimization of channel coding and physical network coding is proposed in this paper

The unlicensed wireless spectrum offers exciting opportunities for developing innovative wireless applications. This has been true ever since the 2.4 GHz band and parts of the 5 GHz bands were first opened for unlicensed access worldwide. In recent years, the 5 GHz unlicensed bands have been one of the most coveted for launching new wireless services and applications due to their relatively superior propagation characteristics and the abundance of spectrum therein. However, the appetite for unlicensed spectrum seems to remain unsatiated; the demand for additional unlicensed bands has been never-ending. To meet this demand, regulators in the US and Europe have been considering unlicensed operations in the 5.9 GHz bands and in large parts of the 6 GHz bands. In the last two years alone, the Federal Communications Commission in the US has added more than 1.2 GHz of spectrum in the pool of unlicensed bands. Wi-Fi networks are likely to be the biggest beneficiaries of this spectrum. Such abundance of spectrum would allow massive improvements in the peak throughput and potentially allow a considerable reduction of latency, thereby enabling support for emerging wireless applications such as augmented and virtual reality, and mobile gaming using Wi-Fi over unlicensed bands. However, access to these bands comes with its challenges. Across the globe, a wide range of incumbent wireless technologies operate in the 5 GHz and 6 GHz bands. This includes weather and military radars, and vehicular communication systems in the 5 GHz bands, and fixed-service systems, satellite systems, and television pick-up stations in the 6 GHz bands. Furthermore, due to the development of several cellular-based unlicensed technologies (such as Licensed Assisted Access and New Radio Unlicensed, NR-U), the competition for channel access among unlicensed devices has also been increasing. Thus, coexistence across wireless technologies in the 5 GHz and 6 GHz bands has emerged as an extremely challenging and interesting research problem. In this dissertation, we first take a comprehensive look at the various coexistence scenarios that emerge in the 5 GHz and 6 GHz bands as a consequence of new regulatory decisions. These scenarios include coexistence between Wi-Fi and incumbent users (both in the 5 GHz and 6 GHz bands), coexistence of Wi-Fi and vehicular communication systems, coexistence across different vehicular communication technologies, and coexistence across different unlicensed systems. Since a vast majority of these technologies are fundamentally different from each other and serve diverse use-cases each coexistence problem is unique. Insights derived from an in-depth study of one coexistence problem do not help much when the coexisting technologies change. Thus, we study each scenario separately and in detail. In this process, we highlight the need for the design of novel coexistence mechanisms in several cases and outline potential research directions. Next, we shift our attention to coexistence between Wi-Fi and vehicular communication technologies designed to operate in the 5.9 GHz intelligent transportation systems (ITS) bands. Until the development of Cellular V2X (C-V2X), dedicated short range communications (DSRC) was the only major wireless technology that was designed for communication in high-speed and potentially dense vehicular settings. Since DSRC uses the IEEE 802.11p standard for its physical (PHY) and medium access control (MAC) layers, the manner in which DSRC and Wi-Fi devices try to gain access to the channel is fundamentally similar. Consequently, we show that spectrum sharing between these two technologies in the 5.9 GHz bands can be easily achieved by simple modifications to the Wi-Fi MAC layer. Since the design of C-V2X in 2017, however, the vehicular communication landscape has been fast evolving. Because DSRC systems were not widely deployed, automakers and regulators had an opportunity to look at the two technologies, consider their benefits and drawbacks and take a fresh look at the spectrum sharing scenario. Since Wi-Fi can now potentially share the spectrum with C-V2X at least in certain regions, we take an in-depth look at various Wi-Fi and C-V2X configurations and study whether C-V2X and Wi-Fi can harmoniously coexist with each other. We determine that because C-V2X is built atop cellular LTE, Wi-Fi and C-V2X systems are fundamentally incompatible with each other. If C-V2X and Wi-Fi devices are to share the spectrum, considerable modifications to the Wi-Fi MAC protocol would be required. Another equally interesting scenario arises in the 6 GHz bands, where 5G NR-U and Wi-Fi devices are likely to operate on a secondary shared basis. Since the 6 GHz bands were only recently considered for unlicensed access, these bands are free from Wi-Fi and NR-U devices. As a result, the greenfield 6 GHz bands provide a unique and rare opportunity to freshly evaluate the coexistence between Wi-Fi and cellular-based unlicensed wireless technologies. We study this coexistence problem by developing a stochastic geometry-based analytical model. We see that by disabling the listen before talk based legacy contention mechanism---which has been used by Wi-Fi devices ever since their conception---the performance of both Wi-Fi and NR-U systems can improve. This has important implications in the 6 GHz bands, where such legacy transmissions can indeed be disabled because Wi-Fi devices, for the first time since the design of IEEE 802.11a, can operate in the 6 GHz bands without any backward compatibility issues. In the course of studying the aforementioned coexistence problems, we identified several gaps in the literature on the performance analysis of C-V2X and IEEE 802.11ax---the upcoming Wi-Fi standard. We address three such gaps in this dissertation. First, we study the performance of C-V2X sidelink mode 4, which is the communication mode in C-V2X that allows direct vehicular communications (i.e., without assistance from the cellular infrastructure). Using our in-house standards-compliant network simulator-3 (ns-3) simulator, we perform simulations to evaluate the performance of C-V2X sidelink mode 4 in highway environments. In doing so, we identify that packet re-transmissions, which is a feature introduced in C-V2X to provide frequency and time diversity, thereby improving the system performance, can have the opposite effect if the vehicular density increases. In fact, packet re-transmissions are beneficial for C-V2X system performance only at low vehicular densities. Thus, if vehicles are statically configured to always use/disable re-transmissions, the maximum potential of this feature is not realized. Therefore, we propose a simple and effective, distributed re-transmission control mechanism named Channel Congestion Based Re-transmission Control (C2RC), which leverages the locally available channel sensing results to allow vehicles to autonomously decide when to switch on re-transmissions and when to switch them off. Second, we present a detailed analysis of the performance of Multi User Orthogonal Frequency Division Multiple Access (MU OFDMA)---a feature newly introduced in IEEE 802.11ax---in a wide range of deployment scenarios. We consider the performance of 802.11ax networks when the network comprises of only 802.11ax as well as a combination of 802.11ax and legacy stations. The latter is a practical scenario, especially during the initial phases of 802.11ax deployments. Simulation results, obtained from our ns-3 based simulator, give encouraging signs for 802.11ax performance in many real-world scenarios. That being said, there are some scenarios where naive usage of MU OFDMA by an 802.11ax-capable Wi-Fi AP can be detrimental to the overall system performance. Our results indicate that careful consideration of network dynamics is critical in exploiting the best performance, especially in a heterogeneous Wi-Fi network. Finally, we perform a comprehensive simulation study to characterize the performance of Multi Link Aggregation (MLA) in IEEE 802.11be. MLA is a novel feature that is likely to be introduced in next-generation Wi-Fi (i.e., Wi-Fi 7) devices and is aimed at reducing the worst-case latency experienced by Wi-Fi devices in dense traffic environments. We study the impact of different traffic densities on the 90 percentile latency of Wi-Fi packets and identify that the addition of a single link is sufficient to substantially bring down the 90 percentile latency in many practical scenarios. Furthermore, we show that while the addition of subsequent links is beneficial, the largest latency gain in most scenarios is experienced when the second link (i.e., one additional) link is added. Finally, we show that even in extremely dense traffic conditions, if a sufficient number of links are available at the MLA-capable transmitter and receiver, MLA can help Wi-Fi devices to meet the latency requirements of most real-time applications.
Doctor of Philosophy
Wireless networks have become ubiquitous in our lives today. Whether it is cellular connectivity on our mobile phones or access to Wi-Fi hotspots on laptops, tablets, and smartphones, never before has wireless communication been as integral to our lives as it is today. In many wireless communication systems, wireless devices operate by sending signals to and receiving signals from a central entity that connects to the wired Internet infrastructure. In the case of cellular networks, this entity is the cell tower deployed by the operators (such as ATandT, Verizon, etc. in the US), while the Wi-Fi router deployed in homes and offices plays this role in Wi-Fi networks. There is also another class of wireless systems, where wireless devices communicate with each other without requiring to communicate with any central entity. An example of such a distributed communication system---which is fast gaining popularity---is vehicular communication networks. End-user devices (e.g. cellphone, laptop, tablet, or a vehicle) can communicate with each other or the central entity only if they are both tuned to the same frequency channel. This channel can lie anywhere within the radio frequency spectrum, but some frequency channels (the collection of channels is referred to as frequency bands) are more favorable—--in terms of how far the signal sent over these channels can reach—--than others. Another dimension to these frequency bands is the licensing mechanism. Not all frequency bands are free to use. In fact, most frequency bands in the US and other parts of the world are licensed by the regional regulatory agencies. The most well-known example of this licensing framework is the cellular network. Cellular operators spend large amounts of money (to the tune of billions of dollars) to gain the privileges of exclusively operating in a given frequency band. No other operator or wireless device is then allowed to operate in this band. Without any external interfering wireless device, cellular operators can guarantee a certain quality of service that is provided to its customers. Thus, the benefits of using licensed frequency bands are obvious but these bands and their associated benefits come at a high price. An alternative to licensed frequency bands are the unlicensed ones. As the name suggests, unlicensed frequency bands are those where any two or more wireless devices can communicate with each other (subject to certain rules) without having to pay any licensing fees. Unsurprisingly, because there is no limit to who or how many devices can communicate over these bands, wireless devices in these bands frequently experience external interference, which manifests to the end-user in terms of interruption of service. The best example of a wireless technology that uses unlicensed bands is Wi-Fi. One of the greatest advantages of Wi-Fi networks is that anyone can purchase a Wi-Fi router and deploy it within their homes or offices—--flexibility not afforded by licensed bands. However, this very flexibility and ease-of-use can sometimes contribute negatively to Wi-Fi performance. Arguably, we have all faced scenarios where the performance of Wi-Fi is poor. This is most likely to happen in scenarios where there are hundreds (or even thousands) of neighboring Wi-Fi devices, such as at stadiums, railway stations, concerts, etc. Based on our discussions above, it is clear as to why Wi-Fi performance suffers in such scenarios. Thus, although unlicensed bands are lucrative in terms of low-cost, and ease of use, there is no guarantee on how good a voice/video call or a video streaming session conducted over Wi-Fi will be. The above problem is well-known and well-researched. Regulators, researchers, and service providers actively seek solutions to offer better performance over unlicensed bands. An obvious solution is to make more unlicensed bands available; if all neighboring Wi-Fi users communicate with their respective routers on different channels, everyone could communicate interference-free. The problem, however, is that frequency bands are limited. Even more limited are those bands that support wireless communications over larger distances. Another solution is to improve the wireless technology—if a Wi-Fi device can more efficiently utilize the channel, its performance is likely to improve. This fact has driven the constant evolution of all wireless technologies. However, there are fundamental limits to how much a frequency channel can be exploited. Therefore, in recent years, stakeholders have turned to spectrum sharing. Even though a wireless network may possess an exclusive license to operate on a given frequency band, its users do not use the band everywhere and at all times. Then why not allow unlicensed wireless devices to operate in this band at such places and times? This is precisely the premise of spectrum sharing. In this dissertation, we look at the problem of coexistence between wireless technologies in the 5 GHz and 6 GHz bands. These two bands are extremely lucrative in terms of their relatively favorable propagation characteristics (i.e., their communication range) and the abundance of spectrum therein. Consequently, these bands have garnered considerable attention in recent years with the objective of opening these bands up for unlicensed services. However, the 5 GHz and 6 GHz bands are home to several licensed systems, and the performance of these systems cannot be compromised if unlicensed operations are allowed. Significant activity has taken place since 2013 concerning new technologies being developed, new spectrum sharing scenarios being proposed, and new rules being adopted in these two bands. We begin the dissertation by taking a comprehensive look at these issues, describing the various coexistence scenarios, surveying the existing literature, describing the major challenges, and providing directions for potential research. Next, we look at three coexistence problems in detail: (i) coexistence of dedicated short range communications (DSRC) and Wi-Fi, (ii) coexistence of cellular V2X (C-V2X) and Wi-Fi, and (iii) coexistence of 5G New Radio Unlicensed (5G NR-U) and Wi-Fi. The former two scenarios involve the coexistence of Wi-Fi with a vehicular communication technology (DSRC or C-V2X). These scenarios arose due to considerations in the US and Europe to allow Wi-Fi operations (on an unlicensed secondary basis) in the spectrum that was originally reserved for vehicular communications. Our work shows that because DSRC and Wi-Fi are built on top of fundamentally similar protocols, they are, to an extent, compatible with each other, and coexistence between these two technologies can be achieved by relatively simple modifications to the Wi-Fi protocol. However, C-V2X, owing to its inheritance from the cellular LTE, is not compatible with Wi-Fi. Consequently, significant research is required if the two technologies are to share the spectrum. On the other hand, in the coexistence of 5G NR-U and Wi-Fi, we focus on the operations of these two technologies in the 6 GHz bands. NR-U is a technology that is built atop the 5G cellular system, but is designed to operate in the unlicensed bands (in contrast to traditional cellular systems which only operate in licensed bands). Although these two technologies can coexist in the 5 GHz and 6 GHz bands, we restrict our attention in this dissertation to the 6 GHz bands. This is because the 6 GHz bands are unique in that the entire range of the 6 GHz bands were opened up for unlicensed access all at once recently, and no Wi-Fi or NR-U devices currently operate in these bands. As a result, we can learn from the mistakes made in the 5 GHz bands, where a vast majority of today's Wi-Fi networks operate. Our work shows that, indeed, we can take decisive steps---such as disabling certain Wi-Fi functions---in the 6 GHz bands, which can facilitate better coexistence in the 6 GHz bands. Finally, in the course of identifying and tackling the various coexistence scenarios in the 5 GHz and 6 GHz bands, we identify some open issues in the performance of new wireless technologies designed to operate in these bands. Specifically, we highlight the need to better understand and characterize the performance of Multi User Orthogonal Frequency Division Multiple Access (MU OFDMA), a feature common in cellular networks but newly introduced to Wi-Fi, in the upcoming Wi-Fi 6 generation of devices. We propose and evaluate an analytical model for the same. We also characterize the performance of Multi Link Aggregation---which a novel feature likely to be introduced in future Wi-Fi 7 devices---that is aimed at reducing the worst-case delay experienced by Wi-Fi devices in dense traffic conditions. Additionally, we identify an issue in the performance of the distributed operational mode of C-V2X. We show that packet re-transmissions, which is a feature aimed at improving the performance of C-V2X, can have a counter-productive effect and degrade the C-V2X performance in certain environments. We address this issue by proposing a simple, yet effective, re-transmission control mechanism.

Dynamic spectrum access (DSA) wireless networks focus on using RF spectrum more efficiently and dynamically. Significant progress has been made during the past few years. For example, many measurements of current spectrum utilization are available. Theoretical analyses and computational simulations of DSA networks also abound. In sharp contrast, few network systems, particularly those with a decentralized structure, have been built even at a small scale to investigate the performance, behavior, and dynamics of DSA networks under different scenarios. This dissertation provides the theory, design, and implementation of a software radio-based decentralized DSA network prototype, and its enabling technologies: software radio, signal detection and classification, and distributed cooperative spectrum sensing. By moving physical layer functions into the software domain, software radio offers an unprecedented level of flexibility in radio development and operation, which can facilitate research and development of cognitive radio (CR) and DSA networks. However, state-of-the-art software radio systems still have serious performance limitations. Therefore, a performance study of software radio is needed before applying it in any development. This dissertation investigates three practical issues governing software radio performance that are critical in DSA network development: RF front end nonlinearity, dynamic computing resource allocation, and execution latency. It provides detailed explanations and quantitative results on SDR performance. Signal detection is the most popular method used in DSA networks to guarantee non-interference to primary users. Quickly and accurately detecting signals under all possible conditions is challenging. The cyclostationary feature detection method is attractive for detecting primary users because of its ability to distinguish between modulated signals, interference, and noise at a low signal-to-noise ratio (SNR). However, a key issue of cyclostationary signal analysis is the high computational cost. To tackle this challenge, parallel computing is applied to develop a cyclostationary feature based signal detection method. This dissertation presents the methodâ s performance on multiple signal types in noisy and multi-path fading environments. Distributed cooperative spectrum sensing is widely endorsed to monitor the radio environment so as to guarantee non-interference to incumbent users even at a low SNR and under hostile conditions like shadowing, fading, interference, and multi-path. However, such networks impose strict performance requirements on data latency and reliability. Delayed or faulty data may cause secondary users to interfere with incumbent users because secondary users could not be informed quickly or reliably. To support such network performance, this dissertation presents a set of data process and management schemes in both sensors and data fusion nodes. Further, a distributed cooperative sensor network is built from multiple sensors; together, the network compiles a coherent semantic radio environment map for DSA networks to exploit available frequencies opportunistically. Finally, this dissertation presents the complete design of a decentralized and asynchronous DSA network across the PHY layer, MAC layer, network layer, and application layer. A ten-node prototype is built based on software radio technologies, signal detection and classification methods, distributed cooperative spectrum sensing systems, dynamic wireless protocols, and a multi-channel allocation algorithm. Systematic experiments are carried out to identify several performance determining factors for decentralized DSA networks.
Ph. D.

Doutoramento em Engenharia Eletrotécnica - Telecomunicações
The work presented herein, studies Next Generation Optical Access Networks (NG-OAN) economically (e.g. energy consumption) and technologically (e.g. rate, reach and dedicated/shared bandwidth). The work is divided into four main topics: energy efficiency in optical access architectures, novel spectrally efficient Long-Reach Passive Optical Networks (LR-PON), crosstalk impacts in heterogeneous and homogenous access networks and hybrid optical wireless transmissions. We investigate the impact of user profiles, optical distribution network topologies and equipment characteristics on resource sharing and power consumption in LR-PON. To have a clear vision on the energy consumption evolution of each part of NG-OAN, a model is proposed to evaluate the energy efficiency of optical access technologies. A spectrally efficient bidirectional Ultra-Dense Wavelength Division Multiplexing (UDWDM) PON architecture is developed using Nyquist shaped 16-ary quadrature amplitude modulation, offering up to 10 Gb/s service capabilities per user or wavelength. Performance of this system in terms of receiver sensitivity and nonlinear tolerance under different network transmission capacity conditions are experimentally optimized. In bi-directional transmis-sion, using frequency up/down-shifting of Nyquist pulse shaped signal from optical carrier, a full bandwidth allocation and easy maintenance of UDWDM networks as well as reduction of Rayleigh back-scattering are achieved. Moreover, self-homodyne detection is used to relax the laser linewidth requirement and digital signal processing complexity at the optical network unit. Simplified numerical model to estimate the impact of Raman crosstalk of multi-system next generation PONs in video overlay is proposed. Coexistence of considered G.98X ITU-T series and coherent multi-wavelength systems is considered and assessed. Additionally, the performances of bidirectional hybrid optical wireless coherent PONs over different optical distribution network power budgets and hybrid splitting ratios are evaluated.
O trabalho aqui apresentado estuda redes óticas de acesso de próxima geração (NG-OAN) nas vertentes económica (consumo de energia) e tecnológica (taxa, alcance e largura de banda dedicada/partilhada). O trabalho está dividido em quatro grandes temas de investigação: a eficiência energética em arquiteturas de acesso ótico, as redes óticas passivas de longo alcance (LR-PON) com nova eficiência espetral, o impacto da diafonia em redes de acesso heterogéneas e homogéneas e as transmissões ópticas híbridas com tecnologias sem fio. Investiga-se o impacto dos perfis dos utilizadores, as tipologias da rede de distribuição ótica, as características do equipamento de partilha de recursos e o consumo de energia em LR-PON. Para se ter uma visão clara sobre o consumo de energia de cada parte das NG-OAN, é proposto um modelo para avaliar a eficiência energética das tecnologias de acesso óticas. Desenvolve-se uma arquitetura PON bi-direcional com elevada eficiência espetral, recorrendo a multiplexagem por divisão de comprimento de onda ultra-densa (UDWDM), modulação de amplitude em quadratura com formato de impulso de Nyquist, oferecendo até 10 Gb/s por utilizador/comprimento de onda. O desempenho deste sistema em termos de sensibilidade do recetor e da tolerância à resposta não linear do canal de comunicação, sob diferentes condições de transmissão, é avaliado experimentalm-ente. Em transmissão bi-direcional, utilizando desvio de frequência (cima/baixo) do impulso com formato de Nyquist relativo à portadora ótica conseguiu-se uma alocação de largura de banda completa e uma manutenção mais simplificada de redes UDWDM, bem como a redução do espalhamento de Rayleigh. Além disso, a deteção auto-homodina é usada para relaxar o requisito de largura de linha do laser e a complexidade do processamento digital de sinal nas unidades da rede ótica. Propõe-se um modelo numérico simplificado para estimar o impacto da diafonia de Raman em sistemas PON de próxima geração, com sobreposição do sinal de vídeo. É analisada a coexistência da série G.98X ITU-T e são considerados e avaliados sistemas coerentes multi-comprimento de onda. Adicionalmente avaliam-se os desempenhos de PONs bi-direcionais híbridas, considerando tecnologia coerente e propagação por espaço livre, para diferentes balanços de potência e taxas de repartição na rede ótica de distribuição.

This study leveraged existing data infrastructure and relationships from the Feed the Future Senegal Naatal Mbay (“flourishing agriculture”) project, funded by the US Agency for International Development (USAID) and implemented by RTI International from 2015 to 2019. The research informed and empowered farmer organizations to track and respond to rural households in 2020 as they faced the COVID-19 pandemic. Farmer organizations, with support from RTI and local ICT firm STATINFO, administered a survey to a sample of 800 agricultural households that are members of four former Naatal Mbay–supported farmer organizations in two rounds in August and October 2020. Focus group discussions were conducted with network leadership pre- and post–data collection to contextualize the experience of the COVID-19 shock and to validate findings. The results showed that farmers were already reacting to the effects of low rainfall during the 2019 growing season and that COVID-19 compounded the shock through disrupted communications and interregional travel bans, creating food shortages and pressure to divert seed stocks for food. Food insecurity effects, measured through the Household Food Insecurity Access Scale and cereals stocks, were found to be greater for households in the Casamance region than in the Kaolack and Kaffrine regions. The findings also indicate that farmer networks deployed a coordinated response comprising food aid and access to personal protective equipment, distribution of short-cycle legumes and grains (e.g., cowpea, maize) and vegetable seeds, protection measures for cereals seeds, and financial innovations with banks. However, food stocks were expected to recover as harvesting began in October 2020, and the networks were planning to accelerate seed multiplication, diversify crops beyond cereals, improve communication across the network. and mainstream access to financial instruments in the 2021 growing season. The research indicated that the previous USAID-funded project had likely contributed to the networks’ COVID-19 resilience capacities by building social capital and fostering the new use of tools and technologies over the years it operated.

Peculiar features of digital environment include: integration of ICTs; use of local and global networks and resources; support and development of qualitatively new technologies of information processing; active use of modern means, methods and forms of teaching in the educational process. The organization of activities in terms of digital learning environment provides appropriate changes in the interaction between subjects of the educational process. Today, means and technologies of the information and communication networks (ICNs), in particular the Internet, which custom and operational-procedural properties were changed at the initial stage from closed local to open ones at present, become widespread. The development of ICNs (from closed local to open ones) changes the typology of learning environments. The following models of learning environments, which widely use ICT and ICN tools (with basic features that characterize them) are distinguished: using the local communication network for presentation of educational information; using the local communication network and open network resources; using open network resources; for independent use of open network resources directly in the classroom by a student; for use of open network resources by a student in the process of independent learning activity; for use by a student educational resources, specially created by a teacher, as well as resources of an open networks in his independent learning activity.

The publication explores the features of the digital technologies’ usage to organize the work of the Young Scientists’ Councils and describes the best practices. The digital transformation of society and the quarantine restrictions caused by the COVID-19 pandemic have forced the use of various digital technologies for scientific communication, the organization of work for youth associations, and the training of students and Ph.D. students. An important role in increasing the prestige of scientific activity and encouraging talented young people to participate in scientific projects belongs to the Young Scientists’ Councils, which are created at scientific institutions and higher education institutions. It is determined that the peculiarities of the work of Young Scientists’ Councils are in providing conditions for further staff development of the institution in which they operate; contribution to the social, psychological and material support of young scientists and Ph.D. students; creating an environment for teamwork and collaborative partnership; development of leadership and organizational qualities; contribution to the development of digital competence. The advantages of using electronic social networks in higher education and research institutions are analyzed, namely: general popularity and free of charge; prompt exchange of messages and multimedia data; user-friendly interface; availability of event planning functions, sending invitations, setting reminders; support of synchronous and asynchronous communication between network participants; possibility of access from various devices; a powerful tool for organizing the learning process; possibility of organization and work of closed and open groups; advertising of various events, etc. Peculiarities of managing the activity of the Young Scientists’ Council with the use of digital technologies are determined. The Young Scientists’ Council is a social system, and therefore the management of this system refers to social management. The effectiveness of the digital technologies’ usage to manage the activities of the Young Scientists’ Council depends on the intensity and need for their use to implement organizational, presentation functions and to ensure constant communication. The areas to apply digital technologies for the work managing of Young Scientists’ Councils are sorted as the presentation of activity; distribution of various information for young scientists; conducting questionnaires, surveys; organization and holding of scientific mass events; managing of thematic workgroups, holding of work meetings. It is generalized and described the experience of electronic social networks usage for organizing and conducting of scientific mass events.

Swift changes in society, related to sciences technicians’ development, technologies, by the increase of general volume of information, pull out new requirements for maintenance, structure, and quality of education. It requires teachers to diversify a tool in the direction of the increase in possibilities of the use of mobile technologies and computer systems. Lately in the world, more attention spared to the use of mobile learning, which in obedience to «Recommendations of UNESCO on the questions of a policy in the area of mobile learning» foresees the use of mobile technology, both separate and together with other by informational computer technologies. [1]. Mobile learning allows using the open informational systems, global educational networks, unique digital resources which belong to different educational establishments and co-operate with each other. The use of existent educational resources and creation of own, based on the academic resources from informative space, allows to promote the interest of students to the study of physics, to take into account the individual features, and also features of region and framework of society of the country. During the last years in Ukraine competency-based approach to the organization of studies certainly one of basic. The new Education Act addresses the key competencies that every modern person needs for a successful life, including mathematical competence; competence in natural sciences, engineering, and technology; innovation; information and communication competence [2]. This further emphasizes the importance of providing students with quality physical education and the problems associated with it. Using mobile technology in professional teaching work, the teacher has the opportunity to implement the basic principles of the competence approach in teaching physics. An analysis of the data provided in the official reports of the Ukrainian Center for Educational Quality Assessment showed that the number of students making an external independent assessment in physics and choosing a future profession related to physics has decreased significantly. This is due to the loss of students' interest in physics and the complexity of the content of the subject, as well as the increase in the amount of information that students need to absorb. In this article, we explore the possibilities of mobile technology as a means of teaching physics students and give our own experience of using mobile technology in the process of teaching physics (for example, the optics section in primary school).