Navegando por Assunto "Escalabilidade"

Agora exibindo 1 - 2 de 2

Acesso aberto (Open Access)
Cross-layer optimizations for multimedia distribution over Wireless Multimedia Sensor Networks and Flying Ad-Hoc Networks with quality of experience support
(Universidade Federal do Pará, 2014-07-16) ROSÁRIO, Denis Lima do; BRAUN, Torsten Ingo; http://lattes.cnpq.br/5439824326239585; CERQUEIRA, Eduardo Coelho; http://lattes.cnpq.br/1028151705135221
The proliferation of multimedia content and the demand for new audio or video services have fostered the development of a new era based on multimedia information, which allowed the evolution of Wireless Multimedia Sensor Networks (WMSNs) and also Flying Ad-Hoc Networks (FANETs). In this way, live multimedia services require realtime video transmissions with a low frame loss rate, tolerable end-to-end delay, and jitter to support video dissemination with Quality of Experience (QoE) support. Hence, a key principle in a QoE-aware approach is the transmission of high priority frames (protect them) with a minimum packet loss ratio, as well as network overhead. Moreover, multimedia content must be transmitted from a given source to the destination via intermediate nodes with high reliability in a large scale scenario. The routing service must cope with dynamic topologies caused by node failure or mobility, as well as wireless channel changes, in order to continue to operate despite dynamic topologies during multimedia transmission. Finally, understanding user satisfaction on watching a video sequence is becoming a key requirement for delivery of multimedia content with QoE support. With this goal in mind, solutions involving multimedia transmissions must take into account the video characteristics to improve video quality delivery. The main research contributions of this thesis are driven by the research question how to provide multimedia distribution with high energy-efficiency, reliability, robustness, scalability, and QoE support over wireless ad hoc networks. The thesis addresses several problem domains with contributions on different layers of the communication stack. At the application layer, we introduce a QoE-aware packet redundancy mechanism to reduce the impact of the unreliable and lossy nature of wireless environment to disseminate live multimedia content. At the network layer, we introduce two routing protocols, namely video-aware Multi-hop and multi-path hierarchical routing protocol for Efficient VIdeo transmission for static WMSN scenarios (MEVI), and cross-layer link quality and geographical-aware beaconless OR protocol for multimedia FANET scenarios (XLinGO). Both protocols enable multimedia dissemination with energy-efficiency, reliability and QoE support. This is achieved by combining multiple cross-layer metrics for routing decision in order to establish reliable routes.
Acesso aberto (Open Access)
Scalable AP selection strategies for user-centric cell-free massive MIMO networks
(Universidade Federal do Pará, 2024-06-06) FREITAS, Marx Miguel Miranda de; COSTA, Daniel Benevides da; http://lattes.cnpq.br/0644241968356756; https://orcid.org/0000-0002-5439-7475; VALCARENGHI, Luca; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434
User-centric (UC) cell-free (CF) massive multiple-input multiple-output (MIMO) systems are promising technologies for beyond 5G (B5G) networks. In these systems, the user equipment (UE) is associated with a subset of access points (APs) distributed into the coverage area, leading to improvements in macro-diversity and spectral efficiency (SE) compared to conventional cell-based systems. Despite the benefits, challenges such as scalable AP selection strategies, computational complexity (CC), and inter-central processing unit (CPU) coordination may still exist in these systems. In this regard, this thesis proposes a novel and general AP selection framework that affords scalability for UC systems, enabling more efficient use of the network resources, such as transmission power and reduced processing demands. The solution is based on a matched-decision among the most suitable connections for APs and UEs. Moreover, three strategies to fine-tune the AP clusters of UEs are proposed, aiming to reduce the number of APs connected to each UE without compromising the SE. Simulation results reveal that the matched-decision framework improves up to 163% the SE of the 95% likely UEs compared with baseline schemes. A heuristic approach that reduces the effects of inter-CPU coordination is also proposed. It decreases the number of inter-coordinated UEs (i.e., UEs connected to multiple CPUs) on each CPU to reduce signaling demands on backhaul links. Numerical results indicate that the proposed method mitigates inter-CPU coordination while yielding slight degradation in SE and improving energy efficiency (EE). Finally, this thesis investigates the performance of UC systems with limited processing capacity. Specifically, it is assumed that the CC of performing channel estimation and precoding signals does not increase with the number of APs. Thus, the UE can only be associated with a finite number of APs. Furthermore, a method is proposed for adjusting the AP clusters according to the network implementation, i.e., centralized or distributed. The results show that UC systems can keep the SE under minor degradation even if the CC up to 96%. Besides, the proposed method for adjusting the AP cluster leads to further reductions in CC.