1,720,969 research outputs found
Effect of imperfect CSI on interference alignment in multiple-High Altitude Platforms based communication
Full text linkInterference Alignment (IA) offers maximum sum-rate in a wireless X channel. Though IA was proposed for maximizing sum-rate, its application for exploiting high data rate in air-to-ground communication has not been explored much. In this paper, the application of IA in a High Altitude Platform (HAP) to Ground Station (GS) communication is considered. Recent studies suggest that IA provides maximum sum-rate for a 2 × 2 transmitter–receiver system. However, independent channels are required to achieve IA conditions. The application of IA is proposed here for a generalized channel in an HAP-to-GS communication link that takes into account angle-of-departure and angle-of-arrival at the transmitter and at the receiver, respectively. We verify the minimum distance criteria in receiving nodes to achieve independent channels. Receivers are placed at optimal distance for best error performance. Furthermore, in view of an actual scenario, we investigate the effect of imperfect CSI, resulting from changes in imperfection in HAP's stabilization, in the performance of our model. The performance, in terms of Bit Error Rate (BER), is presented for IA and non-IA based communication. For this purpose, an analytical expression is developed for the probability of error. A perfect match is shown between the error rate measured with Monte Carlo simulations and the error probability found using the derived analytical expressions
Coverage, capacity and interference analysis for an aerial base station in different environments
Full text linkWith the advancing 5G technology of base stations mounted on aerial platforms, such as unmanned aerial vehicles, the issue of coverage area, capacity and inter-cell interference is assuming higher importance for the cellular networks. In this paper, we follow a deterministic approach to analyze these problems using the data obtained from a commercial software for wireless electromagnetic wave propagation. We analyze the above mentioned parameters by varying the threshold of the received power. Also, we find an optimal altitude and power consumption model for an aerial base station. Simulations were carried out in three generalized environments, Suburban, Urban and Urban High Rise, developed according to ITU-R parameters. To derive these results we used an air-to-ground channel model obtained from the analysis of simulation data
Fault Recovery in Time-Synchronized Mission Critical ZigBee-Based Wireless Sensor Networks
Full text linkA novel technique for ZigBee coordinator failure recovery and its impact on timing synchronization
No full textIn mission critical wireless sensor networks (WSNs) accurate timestamping of the occurrence of events measured by the sensor nodes is often required together with a high degree of reliability. While precise timestamping requires synchronization of the sensor nodes, reliability is obtained by adding redundancy in all potential single point of failure nodes. In this paper, we focus on a ZigBee-based WSN using two personal area network (PAN) coordinators with different PAN identifiers (IDs) and, for this configuration, we propose a solution where if the primary PAN coordinator goes down, connections are transferred to the other by changing the PAN ID of the nodes. Our proposed solution provides significant gains in terms of recovery speed and timing synchronization accuracy in comparison to a solution that is proposed in the literature
On-demand ultra-dense cloud drone networks: Opportunities, challenges and benefits
Full text linkThe paradigm of previous 4G cellular technology has led to an increase in requirements for high data rate demands of mobile users in 5G. In order to meet this demand, constant densification of communication networks was required. Ultra Dense Networks (UDNs) have been proposed as a promising 5G technology to fulfill these requirements by the efficient and dynamic distribution of the radio resources. However, for implementation of UDN, mobile operators have to face many challenges such as severe interference resulting in a limited capacity due to the dense deployment of small cells, site location and acquisition for the deployment of base stations, backhauling issues, energy consumption, etc. In this article, in order to alleviate these limitations, we propose a novel idea of Ultra Dense Cloud-Drone Network (UDCDN) architecture. This scheme is featured with "on-demand" quality and substantial flexibility in terms of deployment. This anchors the challenges of traditional UDN settings and offers numerous benefits. Through simulation results of cell coverage, we verify the genuineness of implementing the proposed scheme and offer a new paradigm shift for UDN
Coverage, interference and power consumption analysis of an aerial base station in case of drone assisted device-to-device communications
Full text linkLAUREA MAGISTRALEGli aeromobili a pilotaggio remoto (APR o UAV), comunemente conosciuti come droni, sono al giorno d'oggi largamente utilizzati come piattaforme aeree a bassa quota (LAPs) per gli scopi più svariati. Inizialmente, essi erano utilizzati esclusivamente per scopi militari come operazioni di sorveglianza o attività di ricognizione. Recentemente, hanno riscosso un enorme interesse anche in applicazioni civili, come operazioni di ricerca e salvataggio, rilevamenti meteo, monitoraggio della fauna selvatica, attività agricole, film making etc. Con l'imminente tecnologia 5G di base stations montate su piattaforme aeree, come UAVs, piccoli palloni aerostatici o droni, la copertura, la capacità, l'interferenza ed il consumo di potenza sono argomenti di rilevante importanza e considerazione per le reti cellulari. L'obiettivo della tesi è analizzare queste problematiche, gestendo i dati generati tramite un software di ray tracing chiamato “Wireless Insite” offerto da Remcom. Inizialmente, viene analizzata la variazione in copertura, come risultato dell'interferenza tra celle adiacenti rispetto al movimento dell'UAV e la sua variazione in altezza (da 100 a 2000 m), sulla base del traffico generato da utenti uniformemente distribuiti. Per fare questo, si considerano tre differenti scenari di propagazione: suburbano, urbano ed urbano in presenza di grattacieli. Inoltre, viene individuata l'altezza massima della base station aerea affinché la percentuale di copertura, nel caso in cui venga trasmessa una potenza pari a 18 dBm, sia massimizzata; particolare attenzione è riservata al consumo di potenza di una base station aerea. In conclusione, si considera il caso in cui si usi una stazione base aerea per una comunicazione Device-to-Device (D2D). Il caso ottimo e il caso pessimo sono analizzati e viene proposta una soluzione che permette di passare da una situazione di copertura parziale a una totale, con tutti i benefici del caso.Unmanned Aerial Vehicles (UAV), commonly known as drones, have been used as a low altitude platforms for many purposes. Initially they were used for military purposes, like surveillance or reconnaissance activities. Currently, they have received enormous interest in civil applications too, like search and rescue, weather detection, wildlife monitoring, farming, film making etc. With the upcoming 5G technology of base stations mounted on aerial platforms, such as UAVs, Helikite, Aerostats etc., the issues of coverage area, capacity, interference and power consumption are of massive importance in the context of cellular network. The aim of this thesis is to analyze and solve these problems, by processing data generated using a ray tracing and wireless electromagnetic propagation simulations tool called “Wireless Insite” by Remcom. Moreover, the variation in coverage area is analyzed, as a result of the inter-cell interference with respect to the movement of the UAV and its variation in height in the range between 100 m and 2000 m, on the basis of traffic intensity generated by uniformly distributed users on the ground. Three different propagation scenarios are considered: suburban, urban and urban high rise. Also, the optimal height of the aerial base station for a transmitted power of 18 dBm is identified to maximize the coverage percentage value. Then, an aerial base station power consumption analysis is done, to get the best transmitted power as a tradeoff between total consumed power and coverage percentage. Finally, the case of using an aerial base station in the case of drone-assisted Device-to-Device (D2D) communication is taken into account. A best and worst case is identified and a solution is proposed for the movement of the UAV to obtain the benefit of full coverage over partial coverage for a D2D user
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Increasing capacity of wireless networks through aerial base stations
No full textNell'ultima decade, a causa degli immensi requisiti della trasmissione ad alta velocità, le tecnologie cellulari si sono evolute fino a portare una vera e propria rivoluzione nell'industria delle telecomunicazioni. Attualmente, nell'IMT 2020, comunemente noto come quinta generazione della tecnologia cellulare, le applicazioni prese in considerazione sono state largamente etichettate come: enhanced mobile broadband (eMBB), massive machine type communication (mMTC), ultra-reliable and low latency communications (uRLLC), vehicle-to-vehicle (V2V) ed vehicle-to-infrastructure (V2X).
Per far fronte ai requisiti in costante aumento, in particolare durante eventi che causano flash mob quali conterti ed eventi sportivi, dove molte persone si concentrano in un'area ristretta usando servizi dati quali video streaming, condivisione foto etc, un aumento di densità della rete terrestre sta aquisendo enorme importanza sotto il nome di Ultra-Dense Networks (UDNs). Il traffico dati aumenta notevolmente grazie allo sviluppo di device ad alta risoluzione quali smart-phone, tablet e laptop con schermi 4k, con conseguente aumento della domanda di traffico dati.
Recentemente, Unmanned Aerial Vehicles (UAVs), comunemente noti come droni sono sotto studio per fornire servizi dati agli utenti nelle zone di periferia. Questi progetti furono iniziati da Google e Facebook con l'idea di sviluppare droni alimentati da pannelli fotovoltaici per fornire servizi internet. Successivamente, compagnie quali Qualcomm, China mobile e Nokia hanno iniziato ad investigare altri aspetti quali il controllo dei droni tramite stazioni base LTE, comunicazione cooperativa tra reti di droni etc. Qualcomm ha riportato l'effettuazione di handover in assenza totale di fallimenti del collegamento nel controllo autonomo di droni attraverso reti LTE. Simili progetti furono condotti da Ericsson e China Mobile con lo sviluppo di un prototipo per sperimentazione su campo. Inoltre, con tecniche quali ottimizzazione di flotta ed algoritmi anticollisione, le reti di droni potrebbero essere dispiegate in contesti urbani, come riportato da Nokia.
Con un simile itneresse da parte dell'industria e dell'accademia, la ricerca sugli UAV che agiscono da Aerial Base Station (ABS) ha ricevuto immediata attenzione. Per questo, questa tesi si focalizza su vari aspetti tecnologici riguardanti simili sistemi. Tuttavia, vi sono svariate direzioni nello sviluppo di reti ABS, in questa tesi ne discutiamo solo alcune. Il lavoro svolto in questa tesi inizia con la modellizzazione del canale Air-to-Ground (A2G). Vi sono molti modelli di canale A2G nella letteratura ma siccome il lavoro svolto in questa tesi è fornire la rete cellulare tramite UAV, si è preferito l'utilizzo di Low Altitude Aerial Platforms (LAPs), fino all'altitudine di 2000m. I modelli di canale esistenti di focalizzano su aerei commerciali o militari, che volano a velocità molto elevate, vicine alla barriera del suono o anche oltre. Simili velocità non sono adatte ad una rete ABS a causa dei frequenti handover. Inoltre, alcuni ricercatori hanno argomentato gli effetti del Doppler shift ad alte velocità che in ultimo impattano le prestazioni del sistema. Tuttavia, dalle analisi e simulazioni fornite in questa tesi, l'effetto del doppler non si è mostrato nel canale A2G con l'implementazione di forme d'onda 5G. A causa della non disponibilità dei parametri di canale per LAPs, delle misure sono state effettuate tramite simulazione usando un modello di propagazione per diversi ambienti: metropolitano, urbano e periferico. Questi ambienti sono generici e sviluppati usando parametri forniti dalle ITU-R. Per questo i risultati di queste simulazioni possono essere applicati ad ambienti reali con buona precisione. Inoltre, il lavoro sulla copertura cellulare, analisi di capacità ed interferenza, sono state condotte tramite simulazione ray tracing, la cui validità è confermata da un'analisi che ottiene espressioni in forma chiusa. I grafici ottenuti da queste espressioni vengono confrontati con quelli ottenuti dalle simulazioni. Successivamente, in questa tesi un nuovo sistema viene proposto per ottenere un ottimo rimpiazzo delle UDN a supporto dei flash mob. Questo sistema viene chiamato Ultra-Dense Cloud Drone Network (UDCDN). Questo sistema è vantaggioso perche fornisce una riduzione del Total Cost of Ownership (TCO) rispetto alle UDN. Inoltre UDCDN può essere dispeigato in base alla domanda, cioè solo quando richiesto in base al traffico ottenuto dal cloud. Inoltre, in questa tesi, è stato svolto del lavoro per implementare i parametri per le Ultra-Reliable Low Latency Communication (uRLLC) del 5G Physical Layer (PHY) sulle reti ABS per fornire una più affidabile rete agli utenti. Miglioramenti del Symbol Error Rate (SER) sono stati notati quando uRLLC fu implementato per il canale A2G con modulazione Generalized Frequency Division Multiplexing (GFDM). Inoltre, sono forniti risultati con l'introduzione di Carrier Frequency Offset (CFO) nel modello di sistema.
A seguito del lavoro sopra descritto, altri aspetti sono stati considerati in questa tesi. A disparte dalle reti ABS, una rete eterogenea (HetNet), che consiste in droni multi-tier e rete terrestre, viene vista come opzione più fattibile per le attuali reti cellulari. Per questo, questa tesi discute tre importanti aspetti che ottimizzano le reti ABS multi-tier: leggi per la sopravvivenza, copertura e mobilità per evitare problemi relativi all'interferenza intercellulare, frequenti handover etc. Successivamente, del lavoro è stato svolto sull'interference alignment (IA) per la massimizzazione del traffico. Tuttavia, IA richiede canali indipendenti per fornire migliore efficienza, ciò è inapplicabile per i LAPs. Per questo, questi studi servono meglio alle High Altitude Aerial Platform (HAP). Inoltre, un'ottima distanza di separazione tra ricevitori è stata definita.
Un'altro insieme di lavoro è stato svolto in questa tesi, che è stato parte di un progetto minore a parte del progetto maggiore che è stato riportato. Lo scopo di questo progetto era lo sviluppo di una piattaforma di Health and Usage Monitoring Systems (HUMS) basata su Internet of Things (IoT) per elicotteri. HUMs consiste in un sistema di registrazione integrato e monitoraggio che include sensori, acquisizione dati ed algoritmi software (sia a bordo che a terra) che sono forniti come unità con lo scopo di ridurre i costi di manutenzione e fornire migliore sicurezza e disponibilità. Per questo sistema lo scopo era dispiegare vbari sensori attraverso il veivolo e monitorare vari componenti avionici. Questi dati vengono raccolti in un gateway noto come Transmission Data Concentrator (TDC) per aggregazione e processing. I dati processati sono mandati al cloud usando la rete cellulare quando il veivolo è nel raggio di essa, altrimenti usando link satellitari.In the past decade, due to immense high speed data and wider connectivity requirements, the cellular technologies have been continuously evolving leading to a major revolution in telecommunication industry. Currently, under IMT 2020, commonly known as 5th Generation of Cellular Technology, the targeted applications have been broadly classified as: enhanced mobile broadband (eMBB), massive machine type communication (mMTC), ultra-reliable and low latency communications (uRLLC), vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2X).
In order to address the increasing data requirements, particularly, during flash crowds such as concerts, rallies, festivals, sport events etc, where many people gathered around in an area, use data services such as video streaming, photo sharing, video calls etc, higher densification of terrestrial network architecture is gaining immense importance in the name of Ultra-Dense Networks (UDNs). The data traffic increases manifold due to development of high resolution and big screen smart devices such as phones, tablets, laptops with 4K resolution, which eventually demands for higher data.
Recently, Unmanned Aerial Vehicles (UAVs), generally known as drones were started to be investigated to provide data service to the users in suburban areas. Such projects were initially started by Google and Facebook to develop solar powered drones providing internet services. Later, companies such as Qualcomm, China mobile and Nokia started to investigate on other aspects such as controlling the drones through LTE base stations, cooperative communication among the drone network etc. Successful handovers were reported by Qualcomm with zero link failure in autonomous drone control through LTE network. Similar project was conducted by Ericsson and China mobile with deployment of prototype in field trial. Also, with techniques such as swarm optimization and collision avoidance algorithms, the drone network could be deployed in the city environment as well, as reported by Nokia.
With such interest from industry and academia, research on UAVs acting as Aerial Base Stations (ABS) attained immediate attention. Therefore, this thesis mainly discusses about several technological aspects pertaining to such a system. Although, there are many research directions to the development of an ABS network, here we address certain directions. The work in this thesis, initially starts with the Air-to-Ground (A2G) Channel Modeling. There are many A2G channel models existing in the literature but since the work done here is to provide cellular network by UAVs, Low Altitude Aerial Platforms (LAPs) were preferred up to the altitude of 2000 m. The existing channel models mostly deal with commercial or military aircrafts, which fly at very high speeds near to subsonic or supersonic ranges. Such high speeds are not preferred for an ABS network to avoid frequent handovers. Also, some researchers have argued about the effect of Doppler shift at higher speeds which would finally lower the performance of the system. However, from the analysis and simulations provided in this thesis, effect of Doppler was not much observed with A2G channel and implementation of 5G waveforms. Due to unavailability of channel parameters for LAPs, measurements were performed using a radio propagation simulator for different environments: Suburban, Urban and Urban High Rise. These environments were generic since they were developed using ITU-R parameters for the simulator. Therefore, results from this simulator could be applied to practical environments with small degree of inaccuracy. Further, the work on cell coverage, capacity and interference analysis was conducted with simulation results obtained from the ray tracing simulator and verification of these results were done by performing analytical analysis and obtaining closed-form expressions. The graphs plotted using these expressions, matched with the graphs obtained from simulations with same simulation parameters. Later, in this thesis a new system was proposed as an optimal replacement to UDNs, to support the flash crowds. This system was termed as Ultra-Dense Cloud Drone Network (UDCDN). This system is advantageous as it offers reduction in Total Cost of Ownership (TCO) as compared to UDNs. Also, UDCDN is on-demand deployment system, i.e. it is deployed by the mobile operator only when required based on the data traffic information obtained from the cloud. Further, in the thesis, work has been done on implementing parameters for Ultra-Reliable Low Latency Communication (uRLLC) of 5G Physical Layer (PHY) on the ABS network to provide reliable and faster connectivity for ground users. Symbol Error Rate (SER) improvements were seen when uRLLC was implemented for A2G channel with Generalized Frequency Division Multiplexing (GFDM) modulation. Further, results were also provided by introducing Carrier Frequency Offset (CFO) in the system model.
Following the above work, other aspects were also considered in the thesis. Apart from primarily ABS network, a heterogeneous network (HetNet), consisting of multi-tier drone and terrestrial network, is seen as a more feasible options for the present cellular network. Therefore, further this thesis discusses about three major aspects which optimize the multi-tier ABS network: survivability, coverage and mobility laws to avoid issues related to inter-cell interference, frequent handovers, power deficiency etc. Later, work has also been done on interference alignment (IA) for maximizing the sum rate. However, IA demands for independent channels to provide better efficiency but at LAPs obtaining independent channels seems improbable. Therefore, such study serves better for a High Altitude Aerial Platform (HAP). An optimal receiver separation distance was also defined for the system.
Another set of work has been performed in this thesis, which formed as a minor project apart from the major one reported throughout. The aim of this project was to develop an Internet of Thing (IoT) based Health and Usage Monitoring Systems (HUMS) for a helicopter. HUMS is an integrated recording and monitoring system that includes sensors, data acquisition technology and software algorithms (both on-board and ground-based) that are provided as a unit with the goals of reducing maintenance costs and improving safety and availability. For this system, the goal was to deploy various sensors all throughout the aircraft for monitoring different avionics components health and lifecycle. This data was to be send to a common gateway, known as a Transmission Data Concentrator (TDC) for data aggregations and processing. This processed data was sent to the cloud using cellular network when the aircraft is in the range of terrestrial network, otherwise using the satellite network.DIPARTIMENTO DI ELETTRONICA, INFORMAZIONE E BIOINGEGNERIASystems and Control31MONTI-GUARNIERI, ANDREA VIRGILIOPERNICI, BARBAR
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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