A Holistic Investigation on Terahertz Propagation and Channel Modeling Toward Vertical Heterogeneous Networks

User-centric and low latency communications can be enabled not only by small cells but also through ubiquitous connectivity. Recently, the vertical heterogeneous network (V-HetNet) architecture is proposed to backhaul/fronthaul a large number of small cells. Like an orchestra, the V-HetNet is a polyphony of different communication ensembles, including geostationary orbit (GEO), and low-earth orbit (LEO) satellites (e.g., CubeSats), and networked flying platforms (NFPs) along with terrestrial communication links. In this study, we propose the Terahertz (THz) communications to enable the elements of V-HetNets to function in harmony. As THz links offer a large bandwidth, leading to ultra-high data rates, it is suitable for backhauling and fronthauling small cells. Furthermore, THz communications can support numerous applications from inter-satellite links to in-vivo nanonetworks. However, to savor this harmony, we need accurate channel models. In this paper, the insights obtained through our measurement campaigns are highlighted, to reveal the true potential of THz communications in V-HetNets.Comment: It has been accepted for the publication in IEEE Communications Magazin

A Prospective Look: Key Enabling Technologies, Applications and Open Research Topics in 6G Networks

The fifth generation (5G) mobile networks are envisaged to enable a plethora of breakthrough advancements in wireless technologies, providing support of a diverse set of services over a single platform. While the deployment of 5G systems is scaling up globally, it is time to look ahead for beyond 5G systems. This is driven by the emerging societal trends, calling for fully automated systems and intelligent services supported by extended reality and haptics communications. To accommodate the stringent requirements of their prospective applications, which are data-driven and defined by extremely low-latency, ultra-reliable, fast and seamless wireless connectivity, research initiatives are currently focusing on a progressive roadmap towards the sixth generation (6G) networks. In this article, we shed light on some of the major enabling technologies for 6G, which are expected to revolutionize the fundamental architectures of cellular networks and provide multiple homogeneous artificial intelligence-empowered services, including distributed communications, control, computing, sensing, and energy, from its core to its end nodes. Particularly, this paper aims to answer several 6G framework related questions: What are the driving forces for the development of 6G? How will the enabling technologies of 6G differ from those in 5G? What kind of applications and interactions will they support which would not be supported by 5G? We address these questions by presenting a profound study of the 6G vision and outlining five of its disruptive technologies, i.e., terahertz communications, programmable metasurfaces, drone-based communications, backscatter communications and tactile internet, as well as their potential applications. Then, by leveraging the state-of-the-art literature surveyed for each technology, we discuss their requirements, key challenges, and open research problems

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial

A prospective look: key enabling technologies, applications and open research topics in 6G networks

The fifth generation (5G) mobile networks are envisaged to enable a plethora of breakthrough advancements in wireless technologies, providing support of a diverse set of services over a single platform. While the deployment of 5G systems is scaling up globally, it is time to look ahead for beyond 5G systems. This is mainly driven by the emerging societal trends, calling for fully automated systems and intelligent services supported by extended reality and haptics communications. To accommodate the stringent requirements of their prospective applications, which are data-driven and defined by extremely low-latency, ultra-reliable, fast and seamless wireless connectivity, research initiatives are currently focusing on a progressive roadmap towards the sixth generation (6G) networks, which are expected to bring transformative changes to this premise. In this article, we shed light on some of the major enabling technologies for 6G, which are expected to revolutionize the fundamental architectures of cellular networks and provide multiple homogeneous artificial intelligence-empowered services, including distributed communications, control, computing, sensing, and energy, from its core to its end nodes. In particular, the present paper aims to answer several 6G framework related questions: What are the driving forces for the development of 6G? How will the enabling technologies of 6G differ from those in 5G? What kind of applications and interactions will they support which would not be supported by 5G? We address these questions by presenting a comprehensive study of the 6G vision and outlining seven of its disruptive technologies, i.e., mmWave communications, terahertz communications, optical wireless communications, programmable metasurfaces, drone-based communications, backscatter communications and tactile internet, as well as their potential applications. Then, by leveraging the state-of-the-art literature surveyed for each technology, we discuss the associated requirements, key challenges, and open research problems. These discussions are thereafter used to open up the horizon for future research directions

Terahertz Wireless Channels: A Holistic Survey on Measurement, Modeling, and Analysis

Terahertz (0.1-10 THz) communications are envisioned as a key technology for sixth generation (6G) wireless systems. The study of underlying THz wireless propagation channels provides the foundations for the development of reliable THz communication systems and their applications. This article provides a comprehensive overview of the study of THz wireless channels. First, the three most popular THz channel measurement methodologies, namely, frequency-domain channel measurement based on a vector network analyzer (VNA), time-domain channel measurement based on sliding correlation, and time-domain channel measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are introduced and compared. Current channel measurement systems and measurement campaigns are reviewed. Then, existing channel modeling methodologies are categorized into deterministic, stochastic, and hybrid approaches. State-of-the-art THz channel models are analyzed, and the channel simulators that are based on them are introduced. Next, an in-depth review of channel characteristics in the THz band is presented. Finally, open problems and future research directions for research studies on THz wireless channels for 6G are elaborated.Comment: to appear in IEEE Communications Surveys and Tutorial

Optimization of Spectrum Management in Massive Array Antenna Systems with MIMO

Fifth generation (5G), is being considered as a revolutionary technology in the telecommunication domain whose the challenges are mainly to achieve signal quality and great ability to work with free spectrum in the millimetre waves. Besides, other important innovations are the introduction of a more current architecture and the use of multiple antennas in transmission and reception. Digital communication using multiple input and multiple output (MIMO) wireless links has recently emerged as one of the most significant technical advances in modern communications. MIMO technology is able to offer a large increase in the capacity of these systems, without requiring a considerable increase in bandwidth or power required for transmission. This dissertation presents an overview of theoretical concepts of MIMO systems. With such a system a spatial diversity gain can be obtained by using space-time codes, which simultaneously exploit the spatial domain and the time domain. SISO, SIMO and MISO systems are differentiated by their channel capacity and their configuration in relation to the number of antennas in the transmitter/receiver. To verify the effectiveness of the MIMO systems a comparison between the capacity of SISO and MIMO systems has been performed using the Shannon’s principles. In the MIMO system some variations in the number of antennas arrays have been considered, and the superiority of transmission gains of the MIMO systems have been demonstrated. Combined with millimetre waves (mmWaves) technology, massive MIMO systems, where the number of antennas in the base station and the number of users are large, is a promising solution. SDR implementations have been performed considering a platform with Matlab code applied to MIMO 2x2 Radio and Universal Software Peripheral Radio (USRP). A detailed study was initially conducted to analyze the architecture of the USRP. Complex structures of MIMO systems can be simplified by using mathematical methods implemented in Matlab for the synchronization of the USRP in the receiver side. SISO transmission and reception techniques have been considered to refine the synchronization (with 16-QAM), thus facilitating the future implementation of the MIMO system. OpenAirInterface has been considered for 4G and 5G implementations of actual mobile radio communication systems. Together with the practical MIMO, this type of solution is the starting point for future hardware building blocks involving massive MIMO systems.A quinta geração (5G) está sendo considerada uma tecnologia revolucionária no setor de telecomunicações, cujos desafios são principalmente a obtenção de qualidade de sinal e grande capacidade de trabalhar com espectro livre nas ondas milimétricas. Além disso, outras inovações importantes são a introdução de uma arquitetura mais atual e o uso de múltiplas antenas em transmissão e recepção. A comunicação digital usando ligaçõe sem fio de múltiplas entradas e múltiplas saídas (MIMO) emergiu recentemente como um dos avanços técnicos mais significativos nas comunicações modernas. A tecnologia MIMO é capaz de oferecer um elevado aumento na capacidade, sem exigir um aumento considerável na largura de banda ou potência transmitida. Esta dissertação apresenta uma visão geral dos conceitos teóricos dos sistemas MIMO. Com esses sistemas, um ganho de diversidade espacial pode ser obtido utilizando códigos espaço-tempo reais. Os sistemas SISO, SIMO e MISO são diferenciados pela capacidade de seus canais e a sua configuração em relação ao número de antenas no emissor/receptor. Para verificar a eficiência dos sistemas MIMO, realizou-se uma comparação entre a capacidade dos sistemas SISO e MIMO utilizado os princípios de Shannon. Nos sistemas MIMO condecideraram-se algumas variações no número de agregados de antenas, e a superioridade dos ganhos de transmissão dos sistemas MIMO foi demonstrada. Combinado com a tecnologia de ondas milimétricas (mmWaves), os sistemas massivos MIMO, onde o número de antenas na estação base e o número de usuários são grandes, são uma solução promissora. As implementações do SDR foram realizadas considerando uma plataforma com código Matlab aplicado aos rádios MIMO 2x2 e Universal Software Peripheral Radio (USRP). Um estudo detalhado foi inicialmente conduzido para analisar a arquitetura da USRP. Estruturas complexas de sistemas MIMO podem ser simplificadas usando métodos matemáticos implementados no Matlab para a sincronização do USRP no lado do receptor. Consideraram-se técnicas de transmissão e recepção SISO para refinar a sincronização (com 16-QAM), facilitando assim a implementação futura do sistema MIMO . Considerou-se o OpenAirInterface para implementações 4G e 5G de sistemas reais de comunicações móveis. Juntamente com o MIMO na pratica, este tipo de solução é o ponto de partida para futuros blocos de construção de hardware envolvendo sistemas MIMO massivos