Extremely High Frequency Band Research Articles

High-Capacity, Weather-Resilient MIMO Feeder Links in Multibeam Satellite Systems

Next-generation satellite systems targeting multi-Terabit-per-second throughput require surmounting layers of design challenges. For feeder links, extremely high frequency (EHF) band is desired to overcome spectrum limitations and reduce equipment size. Multiple gateways are utilized to aggregate their bandwidths and serve as site diversity, mitigating the increased susceptibility of the EHF band to atmospheric attenuation. Toward this, multiple-input multiple-output (MIMO) technology is well suited for feeder links that share the same time, frequency, and polarization resources. This paper provides novel extension of MIMO-enabled feeder links when clustering more than two gateways and mounting more than two antennas onboard geostationary multibeam satellite, exploiting line-of-sight MIMO on uplinks and downlinks. Arsenal of countermeasures against inter-antenna interference and weather impairments is designed to maximize gains in signal-to-noise ratio, spatial multiplexing, and spatial diversity. Comparisons between offered sum rates and theoretical MIMO capacity are provided when gateway clusters form linear versus circular patterns. Methodology for gateway diversity is developed and analyzed when deploying redundant MIMO feeder links that handle rerouted traffic. Algorithms for ground-based channel state information (CSI) acquisition are designed and implemented in receiver architecture that tackles strong practical impairments. Numerical studies reveal that MIMO-enabled feeder links offer greatly enhanced overall network availability compared with state-of-the-art single-input single-output (SISO) solutions.

On the Computation and Approximation of Outage Probability in Satellite Networks With Smart Gateway Diversity

The utilization of extremely high frequency (EHF) bands can achieve very high throughput in satellite networks (SatNets). Nevertheless, the severe rain attenuation at EHF bands imposes strict limitations on the system availability. Smart gateway diversity (SGD) is considered indispensable in order to guarantee the required availability with reasonable cost. In this context, we examine a load-sharing SGD (LS-SGD) architecture, which has been recently proposed in the literature. For this diversity scheme, we define the system outage probability (SOP) using a rigorous probabilistic analysis based on the Poisson binomial distribution (PBD), and taking into consideration the traffic demand as well as the gateway (GW) capacity. Furthermore, we provide several methods for the exact and approximate calculation of SOP. As concerns the exact computation of SOP, a closed-form expression and an efficient algorithm based on a recursive formula are given, both with quadratic worst-case complexity in the number of GWs. Finally, the proposed approximation methods include well-known probability distributions (binomial, Poisson, normal) and a Chernoff bound. According to the numerical results, binomial and Poisson distributions are by far the most accurate approximation methods.

Graphene Epoxy-Based Composites as Efficient Electromagnetic Absorbers in the Extremely High-Frequency Band.

We report on the synthesis of the epoxy-based composites with graphene fillers and test their electromagnetic shielding efficiency by the quasi-optic free-space method in the extremely high-frequency (EHF) band (220-325 GHz). The curing adhesive composites were produced by a scalable technique with a mixture of single-layer and few-layer graphene layers of few-micrometer lateral dimensions. It was found that the electromagnetic transmission, T, is low even at small concentrations of graphene fillers: T<1% at a frequency of 300 GHz for a composite with only ϕ = 1 wt% graphene. The main shielding mechanism in composites with the low graphene loading is absorption. The composites of 1 mm in thickness and a graphene loading of 8 wt% provide an excellent electromagnetic shielding of 70 dB in the sub-terahertz EHF frequency band with negligible energy reflection to the environment. The developed lightweight adhesive composites with graphene fillers can be used as electromagnetic absorbers in the high-frequency microwave radio relays, microwave remote sensors, millimeter wave scanners, and wireless local area networks.

Nanoelectromagnetic of the N-doped single wall carbon nanotube in the extremely high frequency band.

Materials offering excellent mechanical flexibility, high electrical conductivity and electromagnetic interference (EMI) attenuation with minimal thickness are in high demand, particularly if they can be easily processed into films. Carbon nanotube films deposited on a PDMS substrate combine these requirements. In this work, the potential of single wall carbon nanotubes (SWCNT) deposited on flexible polydimethylsiloxane (PDMS) polymer substrates for EMI attenuation is demonstrated. A 6-micrometer-thick SWCNT film exhibits EMI shielding effectiveness of 24.5 decibels in the extreme high frequency band (EHF), reaching 40 decibels when the SWCNTs are N-doped, which is one of the highest specific EMI attenuation performances optimized with film thickness realized to date. This performance stems from the good electrical conductivity of N-SWCNT films (150 Siemens per centimeter) and possible internal multireflections within the SWCNTs network. The excellent mechanical flexibility and easy coating processing enable them to sheathe complex shaped surfaces while providing high electromagnetic interference attenuation efficiency.

Estimation of the Propagation Impairments of Satellite Systems Design in the SHF and EHF Bands in Subtropical Region

Super high frequency (SHF) to extremely high frequency (EHF) bands offer many advantages such as scalability, high asymmetrical traffics and the ability to permit highspeed digital communications due to larger bandwidths among others. However, frequencies greater than 10 GHz leadto signal fading due to physical phenomena related to the propagation of radio waves through the atmosphere. In order to ensure the necessary Quality of Service (QoS) against various transmissions and other impairments at these coverages, not only rain attenuation, which is recognized to be the most significant impairment must be considered. Extra fading due to tropospheric constituents, like snow, water vapour, clouds, gaseous and scintillations caused by air turbulence must also be considered. In this paper, the effects of rain attenuation A (dB) in a heavy rainfall sub-tropical regions for SHF and EHF bands at a given carrier frequency in an average year has been estimated by the synthetic storm technique (SST) and an associated formula that links A to frequency for fixed probabilities. Additional fading due to water vapor, clouds, oxygen and scintillations is estimated by applying the ITU-R formulae. The total attenuation (rain attenuation plus other propagation impairments) obtained is applied to Quadrature Phase Shift Keying (QPSK) modulation scheme en route Earth-satellite-Earth link, with regenerative transponders, in order to obtain a specify maximum bit error rate (BER) tolerated by the end users.

Performance Analysis of Cooperative Wireless Backhaul Networks Operating at Extremely High Frequencies

Extremely high frequency (EHF) bands above 50 GHz have been proposed to be used as backhaul links of modern cellular mobile networks. They provide interconnectivity between the base stations and the core network. In this paper, we propose the employment of cooperative techniques in backhaul networks. More specifically, the outage performance analysis of a simple cooperative diversity system operating at EHF bands is presented. The destination node combines the direct link with the signal received through a regenerative relay using selection combining. A combined statiform and convective model of rainfall rate for the rain attenuation prediction is considered. The correlation properties and the joint statistics among the microwave paths are also calculated. Numerical results present the impact of the geometrical parameters and the climatic conditions on the outage performance.

Study of Ultrawide-Band Transmission in the Extremely High Frequency (EHF) Band

The growing demand for broad-band wireless communication links and the lack of wide frequency bands within the conventional spectrum, causes us to seek bandwidth in the higher microwave and millimeter-wave spectrum at extremely high frequencies (EHF) above 30 GHz. One of the principal challenges in realizing modern wireless communication links in the EHF band are phenomena occuring during electromagnetic wave propagation through the atmosphere. A space-frequency approach for analyzing wireless communication channels operating in the EHF band is presented. Propagation of the electromagnetic radiation is studied in the frequency domain, enabling consideration of ultrawide-band modulated signals. The theory is employed for the analysis of a communication channel operating at EHF which utilizes pulse amplitude modulated signals. The atmospheric absorptive and dispersive effects on pulse propagation delay, pulse width and distortion are discussed. The theory and model are demonstrated in a study of ultrashort-pulse transmission at 60 GHz.