Atmospheric Attenuation Research Articles

Identifying some regularities of radio frequency propagation of a radar system by analyzing different environmental effects

Free space path loss is a function of frequency and propagation distance and the RF signal propagates at light speed in all directions in free space. The performance evaluation of wireless and radar communication technologies is related to understanding the propagation environments. This work presents the modeling of several RF propagation properties that include atmospheric attenuation due to rain, free space path loss, gas, and fog, as well as multipath propagations caused by ground bounces. The methodology discusses the developed model according to the series of (ITU) International Telecommunication Union references to radio wave propagation. This work discusses the Free Space Path Losses (FSPL), and Propagation Losses (PL) due to the atmosphere, precipitation, snow, rain, clouds, fog, atmospheric lensing and absorption, and polarization mismatch. The work also discusses the vertical coverage diagram and radar propagation factor. The obtained results demonstrate that the PL increases with frequency and range, at a 90-degree roll angle, the attenuation approaches infinity, and as the altitude rises, the amount of attenuation caused by lensing decreases. The analysis of attenuation at 1 km vs. frequency variations, at roughly 60 GHz, indicated a high absorption owing to air gas. Lensing attenuations are also offered as secondary outputs for convenience, the wideband channels present higher performance crossways and a wide range of target height as expected. When the target height increases, the influence of multi-path fading approximately vanishes entirely due to the variation increasing in the spreading delay between the bounce and direct pathway signals. This will reduce the coherence sum between these two samples on receiving by the target

A Cooperative Routing Scheme Using Inter-Satellite Links to Assist Data Downloading for LEO Satellite Networks.

Low earth orbit (LEO) satellite networks can provide Internet service to users in areas where cellular networks are difficult to deploy. One critical function of satellites is to transfer data from satellite networks to ground core network through earth stations (ESs). The Ka-band multiple-input multiple-output (MIMO) can be used to establish feeder links with larger bandwidth between satellites and ESs. However, propagation at the Ka band is subjected to rain attenuation and various atmospheric fading mechanisms, which severely reduce the maximum link capacity. As a result, the insufficient capacity of feed link becomes the throughput bottleneck of satellite networks. In order to increase network throughput, it is important to fully use feeder link resources. In this paper, we propose a cooperation scheme to route packets to ESs through a well-resourced feeder link, such that the bandwidth of the feeder links can be fully utilized and the throughput of data downloading at the ESs is maximized. Firstly, we model the satellite network system and the feeder link based on MIMO technology. Then, a Maximum-Flow-Minimum-Cost (MCMF) routing algorithm consisting of two Linear Programs (LPs) is presented to compute maximum-flow routings for data download. Eventually, a variety of simulations are conducted to assess the proposed scheme, which shows that the cooperative routing scheme outperforms the existing SiRRS method in terms of throughput and delay.

Analysis of QAM Based Wavelength Division Multiplexing – Free Space Optical Communication Systems

Free-space optical communication (FSO) is a technology that entails the transmission of information through the atmosphere from one point to the other. Optical signal traversing the atmospheric channel suffers attenuation due to scattering and absorption of the signal by aerosols, fog, atmospheric gases. This work is focused on improving the performance of the system by increasing the capacity using WDM optical networks in free space using QAM modulation technique. The system is evaluated by using eight independent information sources and analyzing the BER and eye diagrams.

Simulation of solar neutron flux in the Earth's atmosphere for three selected flares

We performed simulations of the solar neutron (ns) flux in the Earth's atmosphere associated with three significant flares (X17 of September 07, 2005, X1.3 of September 07, 2017 and M2.9 of September 08, 2017). The input of the simulations was calculated on the basis of ns signals detected at ground level by the Solar Neutron Telescope of Sierra Negra (SNT-SN), in Mexico, and by the FIB scintillator of the Space Environment Data Acquisition-Attached Payload on board of the International Space Station. Since ns can produce Extensive Air Showers (EAS) in the Earth's atmosphere, we used the CORSIKA code and FLUKA subroutines to simulate the particle fluxes associated with the X17, X1.3 and M2.9 flares. We studied the average longitudinal variations of particle flux and energy loss through the atmosphere to estimate the ns flux impinging on the SNT-SN. The results of the simulated interactions and multiplicities of the particles, as a function of their energy, showed that 11–13% of the ns, released by the X17 flare, could overcome the atmospheric attenuation and propagate from the top of the atmosphere to the SNT-SN (4580 m a.s.l.) without producing EAS. On the other hand, ns associated with the X1.3 and M2.9 flares were lost due to atmospheric attenuation and the production of new particles; therefore, they were not detected at ground level by the SNT- SN. The characterization of these events allowed to develop an automatic tool for the analysis of ns emissions associated with solar flares.

Range and Capacity Considerations for Terahertz-Systems for 6G Mobile and Wireless Communication

Discussions on research directions towards systems beyond 5G/6G have started. One of the potential elements of future mobile and wireless systems are new radio systems in the (sub)-Terahertz domain above 100 GHz for communication and sensing purposes. This paper is investigating potentially available frequency bands based on the ITU Radio Regulation, basic propagation conditions above 100 GHz including the different additional path loss contributions on top of distance dependent path loss such as atmospheric and rain attenuation, foliage and wall penetration loss. The impact on system performance like range and channel capacity is considered under idealized conditions at Shannon limit and demonstrated by indoor and outdoor, uplink and downlink scenarios. Radiation limits based on internationally accepted regulations are taken into account in scenarios, where humans are directly involved in the communication. In other scenarios less stringent requirements apply. The main purpose of this paper is to get an understanding from a system perspective of the relation between achievable data throughput versus range and system bandwidth for different propagation conditions and carrier frequency ranges and to investigate basic physical limits. This understanding helps in the identification of use cases, applications and economic considerations on system deployment.

Investigation of engineering models for sound propagation in a near-shore environment

This work presents an engineering approach to model the acoustic response of a sandy beach and its contribution to atmospheric sound attenuation of a near-shore acoustic source. Predictions of the sound pressure level at different ranges along the acoustic path are obtained with a parabolic equation solver that accounts for refraction and surface impedance variation along the propagation path. In this case study, sound propagates over flat water (126 m) and flat, smooth, sand (40 m). Experimental data are collected using a technique that uses chirp diversity to synchronize acoustic data with meteorological data. Sound pressure levels measured at the water’s edge and two range locations beyond the shoreline were compared to numerical results. Three models for acoustic behavior of sand were used to predict the sound pressure level at the beach. In particular, one of the models shows that transport properties of sand can be approximated by assuming sand grains are spherical particles. Generally strong agreement was found between predicted and measured sound pressure levels at the water’s edge. At 20 meters beyond the shoreline, modeling the beach with a reflective surface demonstrates an accuracy within 2 dB. When modeling the beach as a homogeneous absorber, none of the models proposed provided accurate results. However, when the sound absorption heterogeneity of the beach is accounted for using direct measurements of the effective flow resistivity, a better agreement (± 2 dB) was found at both 20 and 40 m beyond the shoreline. This work shows that good agreement between predictions and data can be also achieved by displacing the water–sand transition. Moving the transition to the location where the water saturation of the sand is below 10% and modeling the remaining beach with a semi-infinite layer of dry sand also produces agreement within 2 dB.

Comprehensive performance analysis of hybrid FSO/RF space–air–ground integrated network

Free space optics (FSO) communication due to its large optical carrier bandwidth offers better data rates close to gigabits per second (GBPS) compared to radio frequency (RF) communication and can support seamless ubiquitous high-speed broadband connectivity, which is a significant requirement for sixth-generation (6G) communication. It is also envisioned that the data transmission in 6G communication will be over space–air–ground integrated network (SAGIN) to provide broadband global mobile connectivity. Thus, our main aim in this paper is to investigate the performance of a dual-hop (DH) system model utilizing high-altitude platform station (HAPS) as a relay station with FSO communication for SAGIN scenario, which is expected to be featured in 6G communication. Despite various advantages, HAPS-based FSO satellite communication (SATCOM) is undermined by several factors such as atmospheric turbulence, pointing errors, and atmospheric attenuation. To improve the system performance in terms of capacity and reliability, hybrid FSO/RF communication with RF link as a backup is utilized between ground station (GS) and HAPS. Further, comprehensive end-to-end system performance is investigated by deriving unified closed-form expressions for outage probability and average symbol error rate (SER). We also obtain approximate upper bound expressions for ergodic capacity and outage capacity. The asymptotic expressions are also derived to obtain the diversity order. Here, FSO and RF links are modelled using generalized Malaga distribution with non-zero boresight pointing errors and shadowed κ−μ distribution, respectively. Further, the closed-form expressions for optimum switching threshold signal-to-noise ratio (SNR) are derived and the obtained optimal SNR values are verified using a numerical optimization technique. Finally, the results show that the proposed DH SAGIN-based hybrid FSO/RF SATCOM system is more reliable as well as achieves higher capacity compared to the FSO-based SATCOM systems.

Analysis of echo signal modulation characteristic parameters on aerial and space targets

Based on the scattering characteristic, the comparison of RCS (radar cross-section) at different positions of a target in the same direction of incidence can be obtained first by extruding or deleting part of the entity. A simulation method of aerial&space targets echo characteristics (A&STEC) is proposed that is universal to aerial and space targets. We utilize a fixed-wing UAV (unmanned aerial vehicle) and typical missiles in simulation. The echo signal modulation characteristic parameters are calculated theoretically by the atmospheric attenuation model, the finite element method and a MUMPS solver. The verification simulations show that this method can analyze the influence of the target shape, incident direction, detection position and detection frequency on echo waveform, intensity and energy distribution. The results show that the profile of echo waveform can invert the general shape of the target. The relationship between time and intensity can determine whether the target is moving towards or away from the detector in addition. These conclusions can provide a reference for the ballistic missile target tracking and the defense against UVA intrusion in theory.

Nested Bee Hive: A Conceptual Multilayer Architecture for 6G in Futuristic Sustainable Smart Cities.

Several smart city ideas are introduced to manage various problems caused by overpopulation, but the futuristic smart city is a concept based on dense and artificial-intelligence-centric cities. Thus, massive device connectivity with huge data traffic is expected in the future where communication networks are expected to provide ubiquity, high quality of service, and on-demand content for a large number of interconnected devices. The sixth-generation (6G) network is considered the problem-solving network of futuristic cities, with huge bandwidth and low latency. The expected 6G of the radio access network is based on terahertz (THz) waves with the capability of carrying up to one terabit per second (Tbps). THz waves have the capability of carrying a large amount of data but these waves have several drawbacks, such as short-range and atmospheric attenuation. Hence, these problems can introduce complications and hamper the performance of the 6G network. This study envisions futuristic smart cities using 6G and proposes a conceptual terrestrial network (TN) architecture for 6G. The nested Bee Hive is a scalable multilayer architecture designed to meet the needs of futuristic smart cities. Moreover, we designed the multilayer network infrastructure while considering the expectations from a network of futuristic smart cities and the complications of THz waves. Extensive simulations are performed using different pathfinding algorithms in the 3D multilayer domain to evaluate the performance of the proposed architecture and set the dynamics of futuristic communication of 6G.

Performance Analysis of a Vertical FSO Link with Energy Harvesting Strategy.

In this paper we investigate the application of free space optical (FSO) communications, energy harvesting, and unmanned aerial vehicles (UAVs) as key technology enablers of a cost-efficient backhaul/fronthaul framework for 5G and beyond (5G+) networks. This novel approach is motivated by several facts. First, the UAVs, acting as relay nodes, represent an easy-to-deploy and adaptive network that can provide line-of-sight between the base stations and the gateways connected to the core network. Second, FSO communications offer high data rates between the UAVs and the network nodes, while avoiding any potential interference with the 5G radio access networks. Third, energy harvesting in the optical domain has the potential to extend the UAVs’ battery life. Nevertheless, the presence of atmospheric turbulence, atmospheric attenuation, and pointing errors in the FSO links severely degrades their performance. For this reason an accurate yet tractable modelling framework is required to fully understand whether an UAV-FSO backhaul/fronthaul network with energy harvesting can be applied. To this end, we consider a composite channel attenuation model that includes the effect of turbulence fading, pointing errors, and atmospheric attenuation. Using this model, we derive analytical closed-form expressions of the average harvested energy as a function of the FSO link parameters. These expressions can be used to improve energy harvesting efficiency in FSO link design. We have applied our proposed expressions to evaluate the energy harvested in vertical FSO links for a variety of real scenarios under a modified on-off keying (OOK) scheme optimized for energy harvesting. From the simulations carried out in this paper, we demonstrate that significant values of harvested energy can be obtained. Such performance enhancement can complement the existing deployment charging stations.

Spectral Light Curve Simulation for Parameter Estimation from Space Debris

Characterisation of space debris has become a fundamental task to facilitate sustainable space operations. Ground-based surveillance provides the means to extract key attributes from spacecraft. However, signal inversion attempts are generally under-constrained, which is why an increase in measurement channels through multispectral observations is expected to benefit parameter estimation. The current approach to simulating space debris observation at the Institute of Technical Physics of the German Aerospace Centre (DLR) in Stuttgart relies on monochromatic images taken from the POV-Ray render engine to form light curve signals. Rendered scenes are generated based on the location of an observer by propagating a target’s orbit and rotation. This paper describes the simulation of spectral light curves through the extension of DLR’s Raxus Prime simulation environment. Light reflections are computed using the Mitsuba2 spectral render engine, while atmospheric attenuation is accounted for by the radiative transfer library libRadTran. A validation of the simulator was achieved using multispectral measurements, carried out at the Uhlandshöhe research observatory in Stuttgart. Measured and synthetic data were found to be in agreement based on an RMS error <1% of the total measured signal count. Further, simulated spectral products were used to determine a target’s surface material composition and rotation state and examine aspects of laser ranging to non-cooperative targets.

A Transmission Efficiency Evaluation Method of Adaptive Coding Modulation for Ka-Band Data-Transmission of LEO EO Satellites.

Nowadays low Earth orbit (LEO) Earth observation (EO) satellites commonly use constant coding modulation (CCM) or variable coding modulation (VCM) schemes for data transmission to ground stations (G/S). Compared with CCM and VCM, the adaptive coding modulation (ACM) could further improve the data throughput of the link by making full use of link resource and the time-varying characteristics of atmospheric attenuation. In order to comprehensively study the data transmission performance, one new index which could be utilized as a quantitative index for the satellite-to-ground data transmission scheme selection, the transmission efficiency factor (TEF) of LEO satellites is proposed and defined as “the product of the link availability and the average useful data rate”. Then, the transmission efficiency of CCM, VCM and ACM at typical G/S with different weather characteristics at Ka-band is compared and analyzed. The results show that ACM is more suitable for the G/S with moderate and abundant rainfall. Compared with the CCM of MCS 28, for Beijing G/S and Sanya G/S, ACM not only improves the transmission efficiency with the TEF increased by 3.62% and 24.51%, respectively, but also improves the link availability with the outage period reduced by 82.47% and 75.18%, respectively.

Measuring the Influence of Environmental Conditions on Automotive Lidar Sensors.

Safety validation of automated driving functions is a major challenge that is partly tackled by means of simulation-based testing. The virtual validation approach always entails the modeling of automotive perception sensors and their environment. In the real world, these sensors are exposed to adverse influences by environmental conditions such as rain, fog, snow, etc. Therefore, such influences need to be reflected in the simulation models. In this publication, a novel data set is introduced and analyzed. This data set contains lidar data with synchronized reference measurements of weather conditions from a stationary long-term experiment. Recorded weather conditions comprise fog, rain, snow, and direct sunlight. The data are analyzed by pairing lidar values, such as the number of detections in the atmosphere, with weather parameters such as rain rate in mm/h. This results in expectation values, which can directly be utilized for stochastic modeling or model calibration and validation. The results show vast differences in the number of atmospheric detections, range distribution, and attenuation between the different sensors of the data set.

Narrow bandgap Al0.15In0.85As0.77Sb0.23 for mid-infrared photodetectors.

Mid-IR is a useful wavelength range for both science and military applications due to its low atmospheric attenuation and ability to be used for passive detection. However, many solutions for detecting light in this spectral region need to be operated at cryogenic temperatures as their required narrow bandgaps suffer from carrier recombination and band-to-band tunneling at room temperature leading to high dark currents. These problems can be alleviated by using a separate absorption, charge, and multiplication avalanche photodiode. We have recently demonstrated such a device with a 3-µm cutoff using Al0.15In0.85As0.77Sb0.23, as the absorber, grown on GaSb. Here we investigate Al0.15In0.85As0.77Sb0.23 as a simple PIN homojunction and provide metrics to aid in future designs using this material. PL spectrum measurements indicate a bandgap of 2.94 µm at 300 K. External quantum efficiencies of 39% and 33% are achieved at 1.55 µm and 2 µm respectively. Between 180 K and 280 K the activation energy is ∼0.22 eV, roughly half the bandgap of Al0.15In0.85As0.77Sb0.23, indicating thermal generation is dominant.

Light fidelity performance via hybrid free space optic/fiber optic communication under atmospheric disturbance

Light f idelity (Li-Fi) considers technology in optical wireless communication (OWC) that utilize visible light for transmission in free space, visible light communication (VLC) technology was chosen to overcome the interference issues of radio frequency (RF) communication and it also has higher bandwidth and is more secure. This paper aims to analyse the influence of atmospheric attenuation on the end-users of VLC system that consisted of five light-emitting diodes (LEDs) distributed in a room, which in t urn linked with the hybrid optical system includes a multi-channel of free space optic (FSO) connected with a fiber-optic channel (FOC). The hybrid system to the end-user was estimated in terms of bit error rate, quality factor, and signal power under dust-rain weather conditions. In the dust scenario, the suggested system achieved acceptable bit-error-rate (BER) to a distance of 1, 100 m. In rainy conditions, the performance accomplished acceptable BER to a distance of 3000 m. The VLC system's end-user also was evaluated under the effectiveness of the variation of irradiance and incident angles. Despite the harsh environmental conditions imposed on the communication network, VLC has proven its ability to maintain acceptable performance in end-user.

Secure Communication Channels Using Atmosphere-Limited Line-of-Sight Terahertz Links

Terahertz wireless links offer great promise for realizing physical-layer security due to the high directionality and the high path loss. In this work, we investigate the resilience against eavesdropping attacks in a directional terahertz link which exploits the attenuation due to the water vapor absorption resonances for enhanced security. The magnitude of the atmospheric attenuation can be controlled by tuning the carrier frequency relative to the peak of a water vapor absorption line. This idea can be used to thwart an eavesdropper by restricting the broadcast range of the signal. We develop a channel model for an eavesdropping scenario in which an attacker is located along a line-of-sight link. We explore through both experiments and calculations the performance of the terahertz channel, as well as the tradeoff between performance and security. Our results demonstrate the feasibility of limiting the broadcast range by making use of atmospheric conditions, paving the way for a simple yet powerful physical-layer security protocol for the terahertz range.

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.

Compensation method for atmospheric attenuation of laser radiation in active electro-optical systems with dynamic spectral processing of optical signals

This paper describes the compensation method for atmospheric attenuation of laser radiation, which can be implemented in active electro-optical systems with pre-detector dynamic spectral processing of optical signals. In these electro-optical systems, the spectral flux of sensing radiation is formed using multispectral laser signals based on a priori information about the spectral reflectance of the target and background. The sensing signal formed in this way ensures maximum suppression of the background signal at the output of system with minimal attenuation of the target signal. The influence of atmospheric radiation attenuation on operation of an active electro-optical system with dynamic spectral processing has been analyzed. It has been shown that the laser radiation attenuation in the atmosphere significantly affects the efficiency of dynamic spectral processing of optical signals (leads to a decrease in the target image contrast). The developed compensation method for atmospheric attenuation of radiation in active electro-optical systems with dynamic spectral processing is based on the fact that the spectral intensity of the sensing radiation is formed not only on the basis of a priori data on spectral characteristics of the target and background, but also takes into account the spectral transmittance of the optical radiation propagation medium.

Tropical Terrestrial Free Space Optical Link Performance Analysis

Free Space Optical (FSO) has a very good potential alternative solution to Radio Frequency (RF) to provide high terrestrial wireless communication. In tropical region, the only drawback of FSO is atmospheric attenuation due to mainly haze and rain. This study investigates the performance of FSO system over link distances that ranges between 9 km to 12 km as the average visibility in Kuala Lumpur, Malaysia is 10 km. Two models used to predict the atmospheric attenuation, namely Kruse model and modified Kruse model. These models are valid to predict the haze attenuation for visibilities that range between 9 to 12 km. The modified/corrected Kruse model shows some limitations in the prediction of haze attenuation over longer wavelength. However, the study indicates that attenuation due to haze is low, while air quality in Kuala Lumpur, Malaysia is acceptable. As the size of haze particles varies from 0.01 to 1 µm, the longer wavelength is preferable as 1550 nm to enhance FSO performance compared to 850 nm and 600 nm wavelengths. Thus, the longer wavelength is the optimal choice to enhance the FSO performance as it caused low scattering.

Estimation and performance analysis of multiple incident beam misalignment in spatial diversity based FSO transmissions

A novel approximated misalignment model of an alignment error with multiple incident beams in the position detection of the pointing, acquisition, and tracking (PAT) system is developed for spatial diversity based free-space optical (FSO) communication system. A centroid algorithm used in position detection of the incident beam to align transceivers for the PAT system can make additional pointing errors when multiple beams are incident on the position detector. The centroid algorithm measures the alignment errors through the ratio of the segmented received powers from the position detector. Therefore, the distant arrangement of transmitters and the atmospheric fading affect the alignment error, and the pointing loss of FSO communication increases. We propose a statistical misalignment model with multiple incident beams and analyze the transmission performance using this model to achieve power-efficient FSO communication. The optimum beam width with the misalignment model can reduce the transmit power required to satisfy system demands and outage probability with redundant power for reliable FSO communication.