1,720,965 research outputs found
Valutazione e Miglioramenti di Modelli, Protocolli e Sistemi per Wi-Fi in banda mmWave
Full text linkLa prossima generazione di reti di comunicationi, conosciuta come 5G, promette di avere velocità e coperture nettamente superiori alle reti 4G. Per ottenere queste prestazioni è stato proposto di utilizzare sia nuove tecnologie che evoluzioni di tecniche già conosciute e studiate in passato. La novità più acclamata è l'uso di frequenze superiori al passato che vanno dai 6~ai 100~GHz, anche chiamate onde millimetriche, o MilliMeter Wave (mmW) in inglese. Molti studi degli anni passati si sono focalizzati su questo intervallo di frequenze, cercando di renderle utilizzabili e superando alcune loro peculiarità, tra cui (i) la poca copertura dovuta a perdite di potenza maggiori sulle lunghe distanze rispetto a frequenze più basse, (ii) la loro estrema facilità ad essere bloccate da persone ed oggetti, e (iii) una forte tendenza a concentrare la potenza in poche direzioni circoscritte.
In questa tesi analizziamo e proponiamo modelli che consentono studi più approfonditi sulle reti di nuova generazione a diversi livelli. Con l'obiettivo di migliorare gli standard Wi-Fi di prossima generazione, noti anche come Wireless Gigabit (WiGig), ci siamo concentrati principalmente su simulazioni di rete full-stack, dato il maggior grado di realismo rispetto ai modelli matematici da una parte, e il minor costo unito a una maggiore flessibilità rispetto a soluzioni hardware. Siamo stati in grado di migliorare e creare modelli che spaziano su quasi tutti i livelli dello stack di comunicazione, dal livello fisico (PHY) fino al livello applicazione (APP). Questo ci ha permesso di ottenere una visione completa della rete mmW, rendendoci in grado di progettare e caratterizzare modelli migliori.
Partendo dal canale mmW stesso, descriveremo le nostre proposte per modificare modelli di canale noti per migliorare le prestazioni di simulazione ed estendere l'analisi di rete a scenari mai esplorati prima, a causa della mancanza di strumenti disponibili. Sono stati studiati modelli di antenne e, con l'ausilio di tecniche di machine learning, sono state ottenute configurazioni ottimali specifiche per la banda mmW. Focalizzandosi sugli standard WiGig, sono stati fatti lavori sull'ottimizzazione degli algoritmi di scheduling a livello MAC, pensati appositamente per applicazioni con carattere quasi periodico. Infine, abbiamo analizzato, caratterizzato e modellato il traffico di realtà aumentata e virtuale (conosciuto anche come realtà estesa (XR), una delle applicazioni quasi-periodiche più importanti che dovrebbero essere ampiamente utilizzate nelle reti 5G.The 5th Generation (5G) of communication networks is currently being deployed, promising better than ever capacity, responsiveness, and coverage. Many new technologies, as well as evolutions of old technologies, have been harvested to improve over the previous generation, such as the usage of high frequencies commonly known as the MilliMeter Wave (mmW) band. These new bands, typically ranging between 6~and 100~GHz, have long been studied, trying to overcome many of their peculiarities such as (i) low range due to high free-space propagation loss, (ii) high susceptibility to blockage, and (iii) sparse directionality, among others.
In this thesis, we analyze and propose models that allow more in-depth studies on next-generation networks on different levels. Aiming to improve the next-generation IEEE~802. 11 standards, also known as Wireless Gigabit (WiGig), we focused mainly on full-stack network simulations, given the higher degree of realism with respect to mathematical models, and the much lower cost and flexibility with respect to hardware testbeds. We were able to improve and create models ranging across almost all levels of the communication stack, from the Physical (PHY) up to the Application (APP) layers. This allowed us to obtain a holistic view of the mmW-based network, making us able to design and characterize better models.
Starting from the mmW channel itself, we will describe our proposals to modify well-known channel models to improve simulation performance and extend network analysis to scenarios that were never explored before, due to a lack of available tools. Antenna models were studied, and, with the help of machine learning techniques, optimal configurations specific for the mmW band were obtained. Moving towards the WiGig protocol stack, works have been done on the optimization of Medium Access Control (MAC)-layer scheduling algorithms, specifically tailored for quasi-periodic applications. Finally, we analyzed, characterized, and modeled eXtended Reality (XR) traffic, one of the most prominent types of quasi-periodic applications that are forseen to be largely used in 5G networks
Accuracy vs. Complexity for mmWave Ray-Tracing: A Full Stack Perspective
No full textThe millimeter wave (mmWave) band will provide multi-gigabits-per-second connectivity in the radio access of future wireless systems. The high propagation loss in this portion of the spectrum calls for the deployment of large antenna arrays to compensate for the loss through high directional gain, thus introducing the need for a spatial dimension in the channel model to accurately represent the performance of a mmWave network. In this perspective, ray tracing can characterize the channel in terms of Multi Path Components (MPCs) to provide a highly accurate model, at the price of extreme computational complexity (e.g., for processing detailed environment information about the propagation), which may limit the scalability of the simulations. In this paper, we present possible simplifications to improve the trade-off between accuracy and complexity in ray-tracing simulations at mmWaves by reducing the total number of MPCs. The effect of such simplifications is evaluated from a full-stack perspective through end-to-end simulations, testing different configuration parameters, propagation scenarios, and higher-layer protocol implementations. We then provide guidelines on the optimal degree of simplification, for which it is possible to reduce the complexity of simulations with a minimal reduction in accuracy for different deployment scenarios
Scalable and Accurate Modeling of the Millimeter Wave Channel
No full textCommunication at millimeter wave (mmWave) frequencies is one of the main novelties introduced in the 5th generation (5G) of cellular networks. The opportunities and challenges associated with such high frequencies have stimulated a number of studies that rely on simulation for the evaluation of the proposed solutions. The accuracy of simulations largely depends on that of the channel model, but popular channel models for mmWaves, such as the Spatial Channel Models (SCMs), have high computational complexity and limit the scalability of the scenarios. This paper profiles the implementation of a widely-used SCM model for mmWave frequencies, and proposes a simplified version of the 3GPP SCM that reduces the computation time by up to 12.5 times while providing essentially the same distributions of several metrics, such as the Signal-to-Interference-plus-Noise Ratio (SINR) in large scale scenarios. We also give insights on the use cases in which using a simplified model can still yield valid results
An Open Framework to Model Diffraction by Dynamic Blockers in Millimeter Wave Simulations
Full text linkThe millimeter wave (mmWave) band will be exploited to address the growing demand for high data rates and low latency. The higher frequencies, however, are prone to limitations on the propagation of the signal in the environment. Thus, highly directional beamforming is needed to increase the antenna gain. Another crucial problem of the mmWave frequencies is their vulnerability to blockage by physical obstacles. To this aim, we studied the problem of modeling the impact of second-order effects on mmWave channels, specifically the susceptibility of the mmWave signals to physical blockers. With respect to existing works on this topic, our project focuses on scenarios where mmWaves interact with multiple, dynamic blockers. Our open source software includes diffraction-based blockage models and interfaces directly with an open source Radio Frequency (RF) ray-tracing software.9 pages, 7 figures, 1 tables. This paper has been accepted for presentation at the 20th Mediterranean Communication and Computer Networking Conference. Copyright IEEE 202
Simulation of next-generation cellular networks with ns-3: Open challenges and new directions
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The challenges of Scheduling and Resource Allocation in IEEE 802.11ad/ay
No full textThe IEEE 802.11ad Wi-Fi amendment enables short-range multi-gigabit communications in the unlicensed 60 GHz spectrum, unlocking new interesting applications such as wireless Augmented and Virtual Reality. The characteristics of the Millimeter Wave (mmW) band and directional communications allow increasing the system throughput by scheduling pairs of nodes with low cross-interfering channels in the same time-frequency slot. On the other hand, this requires significantly more signaling overhead. Furthermore, IEEE 802.11ad introduces a hybrid MAC characterized by two different channel access mechanisms: contention-based and contention-free access periods. The coexistence of both access period types and the directionality typical of mmW increase the channel access and scheduling complexity in IEEE 802.11ad compared to previous Wi-Fi versions. Hence, to provide the Quality of Service performance required by demanding applications, a proper resource scheduling mechanism that takes into account both directional communications and the newly added features of this Wi-Fi amendment is needed. In this paper, we present a brief but comprehensive review of the open problems and challenges associated with channel access in IEEE 802.11ad and propose a workflow to tackle them via both heuristic and learning-based methods
Contention-free Scheduling of Periodic Traffic Sources in WiGig: Simulation Framework and Performance Analysis
No full textThe latest IEEE 802.11 amendments provide support to directional communications in the Millimeter Wave spectrum, thus making it possible to wirelessly approach several emerging use cases, such as eXtended Reality (XR), telepresence, and remote control of industrial facilities. However, these applications require stringent Quality of Service (QoS), that only contention-free scheduling algorithms can guarantee. In this paper, we propose a framework for the joint admission control and scheduling of periodic traffic streams over mmWave Wireless Local Area Networks based on Network Simulator 3 (ns-3), a popular full-stack open-source network simulator. Moreover, we design a baseline algorithm to handle scheduling requests, and evaluate its performance with a full-stack perspective. The algorithm is tested in three scenarios, where we investigated different configurations and features to highlight the trade-offs between contention-based and contention-free access strategies
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
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