Multiple Antenna Techniques for Terahertz Nano-Bio Communication

Using higher frequency bands becomes an essential demand resulting from the explosive wireless traffic needs and the spectrum shortage of the currently used bands. This paper presents an overview on the terahertz technology and its application in the area of multi-input multi-output antenna system and in-vivo nano-communication. In addition, it presents a preliminary study on applying multiple input-single output (MISO) antenna technique to investigate the signal propagation and antenna diversity techniques inside the human skin tissues, which is represented by three layers: stratum corneum (SC), epidermis, and dermis layers, in the terahertz (THz) frequency range (0.8-1.2) THz. The spatial antenna diversity is investigated in this study to understand MISO system performance for two different in-vivo channels resulting from the signal propagation between two transmitting antennas, located at the dermis layer, and one receiving antenna, located at epidermis layer. Three techniques are investigated: selection combining (SC), equal-gain combing (EGC), and maximum-ratio combining (MRC). The initial study indicates that using multiple antenna technique with THz might be not useful for in-vivo nano-communication

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

Channel Measurement and Characterization with Modified SAGE Algorithm in an Indoor Corridor at 300 GHz

The much higher frequencies in the Terahertz (THz) band prevent the effective utilization of channel models dedicated for microwave or millimeter-wave frequency bands. In this paper, a measurement campaign is conducted in an indoor corridor scenario at 306-321 GHz with a frequency-domain Vector Network Analyzer (VNA)-based sounder. To realize high-resolution multipath component (MPC) extraction for the direction-scan measurement campaigns in the THz band, a novel modified space-alternating generalized expectation-maximization (SAGE) algorithm is further proposed. Moreover, critical channel characteristics, including the path loss, shadow fading, K-factor, delay spread, angular spreads, cluster parameters, and cross correlations are calculated and analyzed in the LoS case. Besides, two contrasted measurement campaigns in the NLoS case are conducted, with and without additional reflective foils on walls to serve as effective scatterers. Comparison results indicate that the reflective foils are useful to improve the channel conditions in the NLoS case by nearly 6 dB, which is potential to be utilized as alternative of intelligent reflecting surfaces (IRS) to enhance the coverage ability of THz communications.Comment: 12 pages, 8 figure

CHANNEL MODELING FOR FIFTH GENERATION CELLULAR NETWORKS AND WIRELESS SENSOR NETWORKS

In view of exponential growth in data traffic demand, the wireless communications industry has aimed to increase the capacity of existing networks by 1000 times over the next 20 years. A combination of extreme cell densification, more bandwidth, and higher spectral efficiency is needed to support the data traffic requirements for fifth generation (5G) cellular communications. In this research, the potential improvements achieved by using three major 5G enabling technologies (i.e., small cells, millimeter-wave spectrum, and massive MIMO) in rural and urban environments are investigated. This work develops SPM and KA-based ray models to investigate the impact of geometrical parameters on terrain-based multiuser MIMO channel characteristic. Moreover, a new directional 3D channel model is developed for urban millimeter-wave (mmW) small cells. Path-loss, spatial correlation, coverage distance, and coherence length are studied in urban areas. Exploiting physical optics (PO) and geometric optics (GO) solutions, closed form expressions are derived for spatial correlation. Achievable spatial diversity is evaluated using horizontal and vertical linear arrays as well as planar 2D arrays. In another study, a versatile near-ground field prediction model is proposed to facilitate accurate wireless sensor network (WSN) simulations. Monte Carlo simulations are used to investigate the effects of antenna height, frequency of operation, polarization, and terrain dielectric and roughness properties on WSNs performance

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

Reconfigurable Intelligent Surfaces based system design for future 6G wireless networks

Future sixth generation (6G) wireless networks perceive the THz band as essential to support the high volume of wireless traffic data being generated in the network, thus enabling ultra high transmission rates. However, the behaviour of the THz frequency spectrum affects the propagation occurring in the wireless communication system due to high attenuation, leading to severe propagation losses. Reconfigurable intelligent surfaces (RIS) are a promising technology to overcome the limitations present in the THz waveband by reshaping the wave direction, thus enabling the signal to propagate towards its intended target. RIS have many applications in wireless systems, specifically in the optimization of the communication network performance when combined with ultra-massive multiple-input multiple-output antennas (UM-MIMO). UMMIMO systems are critical for implementing THz frequencies as the large number of antennas provides high directivity pencil like beams, thereby enabling easy data spread from the transmitter towards the receiver. To achieve low complexity whilst deploying UM-MIMO systems, hybrid precoders must be implemented. This dissertation aims to design and evaluate a RIS-assisted communication model for ultra-massive MIMO systems to extend coverage range and to improve the energy and spectral efficiency of 6G communications. To maximize the achievable rate of the structure, an algorithm will be developed to calculate the phase shifts of the individual RIS elements, and the implementation of various hybrid precoding structures. Several numerical results will be obtained through various simulations and analysed to give insight into which design is best suited for RIS-assisted THz communication system through the achievable rates obtained.As futuras redes sem fios da sexta geração (6G) consideram a frequência Terahertz fundamental para suportar o elevado número de tráfego gerado na rede, permitindo assim elevadas taxas de transmissão de dados. Todavia, o comportamento do espectro de frequências THz condiciona a propagação que ocorre no sistema de comunicação pela sua elevada atenuação, originando graves perdas de propagação. Superfícies inteligentes reconfiguráveis (RIS) são uma tecnologia promissora para ultrapassar as limitações existentes na faixa dos THz ao moldarem a direção da onda, permitindo que o sinal se propague para o destinatário. Os RIS dispõem de inúmeras aplicações nos sistemas sem fios, especificamente na otimização do desempenho da rede de comunicações ao utilizarem antenas ultra massivas de múltipla entradas e saídas. Os sistemas UM-MIMO são fundamentais para implementar frequências THz pelo elevado número de antenas, facilitando a propagação de dados desde o emissor e recetor. A fim de alcançar uma complexidade reduzida nos sistemas UM-MIMO, é necessário implementar pré-codificadores híbridos. Esta dissertação pretende conceber um sistema de comunicação para redes sem fios ultra massivo MIMO assistido por RIS para melhorar a eficiência energética das comunicações 6G e do espectro e o alcance da cobertura. De modo a maximizar a taxa alcançável do modelo, será desenvolvido um algoritmo para calcular a quantização das mudanças de fase dos elementos RIS sendo implementado várias estruturas híbridas de pré-codificação. Os resultados numéricos serão analisados a fim de revelar qual a configuração ideal para o sistema de comunicação THz assistido por RIS mediante as taxas alcançáveis obtidas