561 research outputs found
SpaceRIS: LEO Satellite Coverage Maximization in 6G Sub-THz Networks by MAPPO DRL and Whale Optimization
Satellite systems face a significant challenge in effectively utilizing
limited communication resources to meet the demands of ground network traffic,
characterized by asymmetrical spatial distribution and time-varying
characteristics. Moreover, the coverage range and signal transmission distance
of low Earth orbit (LEO) satellites are restricted by notable propagation
attenuation, molecular absorption, and space losses in sub-terahertz (THz)
frequencies. This paper introduces a novel approach to maximize LEO satellite
coverage by leveraging reconfigurable intelligent surfaces (RISs) within 6G
sub-THz networks. The optimization objectives encompass enhancing the
end-to-end data rate, optimizing satellite-remote user equipment (RUE)
associations, data packet routing within satellite constellations, RIS phase
shift, and ground base station (GBS) transmit power (i.e., active beamforming).
The formulated joint optimization problem poses significant challenges owing to
its time-varying environment, non-convex characteristics, and NP-hard
complexity. To address these challenges, we propose a block coordinate descent
(BCD) algorithm that integrates balanced K-means clustering, multi-agent
proximal policy optimization (MAPPO) deep reinforcement learning (DRL), and
whale optimization (WOA) techniques. The performance of the proposed approach
is demonstrated through comprehensive simulation results, exhibiting its
superiority over existing baseline methods in the literature
Serviços pós-4G em redes de satélite LEO com recepção multi-pacote e com handover
Dissertação para obtenção do Grau de Mestre em
Engenharia Electrotécnica e de ComputadoresUm pacote com erros, quer seja devido à existência de colisões ou ruído no canal, é normalmente descartado e necessita de ser retransmitido, levando a perdas de desempenho.
A junção do protocolo H-ARQ (Hybrid Automatic Retransmission reQuest) com técnicas de recepção multi-pacote e com diversidade temporal como o NDMA (Network Diversity Multiple Access), melhoram o desempenho, visto terem a capacidade de pedir
transmissões extra e combinar todos os sinais recebidos no mesmo período. Contudo, o
atraso provocado pelo tempo de ida e volta na comunicação com uma rede de satélites,
limita o número de retransmissões que possam ser pedidas pelos terminais para garantir
qualidade de serviço.
Esta tese considera o desenho de um protocolo híbrido que combina H-ARQ com NDMA
para redes satélites com tráfego atribuído a pedido. O protocolo S-NDMA (Satellite
NDMA) é apresentado, juntamente com modelos analíticos para o seu desempenho. É
analisada a sua eficiência energética, tendo em conta requisitos de qualidade de serviço
(QoS). O sistema é feito para satélites de órbita baixa (LEO) e com SC-FDE (Single-Carrier with Frequency Domain Equalization). É feita também uma comparação de desempenhos
deste esquema com H-NDMA (Hybrid-NDMA), mostrando que é eficiente em termos
energéticos e que cumpre requisitos de QoS para serviços exigentes como videochamadas.
São necessários vários satélites para cobrir uma vasta área do planeta. Como os satélites
estão em constante movimento, a zona de cobertura associada a cada satélite também se
desloca. Isto leva a uma necessidade do terminal móvel trocar constantemente de ligação para um novo satélite. Nesta dissertação são propostos dois esquemas para S-NDMA: o tradicional com interrupção temporária de ligação, e um novo com continuidade de ligação baseado em SIMO distribuído. São estudadas a viabilidade e desempenho dos dois esquemas, analisando-se a eficiência energética, o efeito de Doppler, o ponto óptimo de troca e o atraso no tempo na comunicação entre terminais móveis e satélites
Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges
With the rapid development of marine activities, there has been an increasing
number of maritime mobile terminals, as well as a growing demand for high-speed
and ultra-reliable maritime communications to keep them connected.
Traditionally, the maritime Internet of Things (IoT) is enabled by maritime
satellites. However, satellites are seriously restricted by their high latency
and relatively low data rate. As an alternative, shore & island-based base
stations (BSs) can be built to extend the coverage of terrestrial networks
using fourth-generation (4G), fifth-generation (5G), and beyond 5G services.
Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs.
Despite of all these approaches, there are still open issues for an efficient
maritime communication network (MCN). For example, due to the complicated
electromagnetic propagation environment, the limited geometrically available BS
sites, and rigorous service demands from mission-critical applications,
conventional communication and networking theories and methods should be
tailored for maritime scenarios. Towards this end, we provide a survey on the
demand for maritime communications, the state-of-the-art MCNs, and key
technologies for enhancing transmission efficiency, extending network coverage,
and provisioning maritime-specific services. Future challenges in developing an
environment-aware, service-driven, and integrated satellite-air-ground MCN to
be smart enough to utilize external auxiliary information, e.g., sea state and
atmosphere conditions, are also discussed
Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications
Full-Duplex Wireless for 6G: Progress Brings New Opportunities and Challenges
The use of in-band full-duplex (FD) enables nodes to simultaneously transmit
and receive on the same frequency band, which challenges the traditional
assumption in wireless network design. The full-duplex capability enhances
spectral efficiency and decreases latency, which are two key drivers pushing
the performance expectations of next-generation mobile networks. In less than
ten years, in-band FD has advanced from being demonstrated in research labs to
being implemented in standards and products, presenting new opportunities to
utilize its foundational concepts. Some of the most significant opportunities
include using FD to enable wireless networks to sense the physical environment,
integrate sensing and communication applications, develop integrated access and
backhaul solutions, and work with smart signal propagation environments powered
by reconfigurable intelligent surfaces. However, these new opportunities also
come with new challenges for large-scale commercial deployment of FD
technology, such as managing self-interference, combating cross-link
interference in multi-cell networks, and coexistence of dynamic time division
duplex, subband FD and FD networks.Comment: 21 pages, 15 figures, accepted to an IEEE Journa
Evolution of Non-Terrestrial Networks From 5G to 6G: A Survey
Non-terrestrial networks (NTNs) traditionally have certain limited applications. However, the recent technological advancements and manufacturing cost reduction opened up myriad applications of NTNs for 5G and beyond networks, especially when integrated into terrestrial networks (TNs). This article comprehensively surveys the evolution of NTNs highlighting their relevance to 5G networks and essentially, how it will play a pivotal role in the development of 6G ecosystem. We discuss important features of NTNs integration into TNs and the synergies by delving into the new range of services and use cases, various architectures, technological enablers, and higher layer aspects
pertinent to NTNs integration. Moreover, we review the corresponding challenges arising from the technical peculiarities and the new approaches being adopted to develop efficient integrated
ground-air-space (GAS) networks. Our survey further includes the major progress and outcomes from academic research as well as industrial efforts representing the main industrial trends, field
trials, and prototyping towards the 6G networks
Proceedings of the Fifth International Mobile Satellite Conference 1997
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments
Evolution of Non-Terrestrial Networks From 5G to 6G: A Survey
Non-terrestrial networks (NTNs) traditionally have certain limited applications. However, the recent technological advancements and manufacturing cost reduction opened up myriad applications of NTNs for 5G and beyond networks, especially when integrated into terrestrial networks (TNs). This article comprehensively surveys the evolution of NTNs highlighting their relevance to 5G networks and essentially, how it will play a pivotal role in the development of 6G ecosystem. We discuss important features of NTNs integration into TNs and the synergies by delving into the new range of services and use cases, various architectures, technological enablers, and higher layer aspects
pertinent to NTNs integration. Moreover, we review the corresponding challenges arising from the technical peculiarities and the new approaches being adopted to develop efficient integrated
ground-air-space (GAS) networks. Our survey further includes the major progress and outcomes from academic research as well as industrial efforts representing the main industrial trends, field
trials, and prototyping towards the 6G networks
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