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By utilizing chirp-BOK (binary orthogonal keying) modulation into a troposphere scattering communication system, a lower demodulation threshold can be achieved with excellent linear frequency modulation properties in a strong noise and weak signal environment. Firstly, the bit error rate (BER) formula of chirp-BOK modulation over a Rayleigh fading channel was derived theoretically. Then, the BER performance with different chirp-BOK parameters were numerically calculated. In order to investigate the performance of chirp-BOK over deeping fading troposphere scattering link, a seven-path equal-delay Rayleigh fading model was employed. Finally, the system BER performance was simulated under different tap delay and time–bandwidth product parameters. The results demonstrate that when BER reaches 10 − 4 , the optimal configuration of the system achieves a gains approximately from 1.7 dB to 10 dB compared to non-optimized configuration under different Path-Gain-Vector with varying tap delays. [ABSTRACT FROM AUTHOR]

Clear-air echo studies are usually based on isotropic turbulence theory. But the theory has been considered incomplete by modern turbulence theory. The intermittence of turbulence can reveal obvious shortcomings in the existing studies of clear-air echoes. The mechanism of clear-air echo scattering needs to be supplemented. This paper introduces the troposcatter theory, normally used in over-the-horizon communication, to fill the gap left by Bragg scattering. By treating radar as a self-transmitted and self-received device, the equivalent transmission loss of weather radar is established and compared with the recommendations of the Radiocommunication Sector of the International Telecommunication Union (ITU-R). The results show that the S-band radar transmission loss aligns with ITU-R recommendations. There is also a linear regression relationship between the radar transmission loss and height, which conforms to the troposcatter theory. This means that the theory of troposcatter scattering is a supplement to the theory of Bragg scattering. Tropospheric scattering can be thought of as general Bragg scattering. Meanwhile, based on ITU-R recommendations, this study also provides a new way for the recognition of biological echoes. [ABSTRACT FROM AUTHOR]

In this article, a broadband 1-D high-gain beam steering solution to steer sum and difference patterns for tracking the optimum common scatter volume of troposcatter links at ${X}$ -band is presented. The novel steering arrangement consists of a $D = 70$ cm offset parabolic cylindrical (OPC) reflector fed by a triple-mode circular waveguide (TM-CW) horn antenna integrated with a two-element dielectric wedge-based Risley prism and a parabolic phase correcting dielectric lens (PCDL). The proposed hybrid beam steering reflector-feed obviates the need for complex 3-axes based gimbals to mechanically steer the conventional reflector-feed assembly. In the proposed hybrid reflector-feed arrangement, steering is achieved using a simple axial rotation of smaller Risley prism components at the feed. The broadband high-gain attribute required for an efficient troposcatter link is achieved by the proposed hybrid reflector-feed with much smaller and compact moving parts compared to traditional axial rotation-based mechanical steering arrangements. The simulated gain of the proposed antenna operating in TE11 mode at broadside is 25.7 dBi. A prototype of the proposed beam steering solution is built and tested in an anechoic chamber. The OPC reflector prototype is made of lightweight composite carbon fiber/fiber glass material thus reducing the overall antenna assembly weight. Experimental results show close agreement with the simulated ones. All three modes of TM-CW horn are steered by ±19° with TE11 mode patterns showing scan losses lower than 1 dB. The measured null depths for TM01 and TE21 modes are lower than −23 dB at 10 GHz. The peak of the sum and the nulls of the difference patterns are separated by a minimum difference of 25 dB at 10 GHz.

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Signal scattering in the troposphere is a phenomenon referred to as “troposcatter”, and it is promising method for wireless communication beyond the line of sight (b-LOS). For a troposcatter communication system, it is important to develop a channel model for the tropospheric scatter. Recently, b-LOS communication using troposcatter received much attention for its application to military communication. Thus, a comprehensive review and analysis of conventional ITU-R troposcatter propagation models and recent results would be a timely study. Accordingly, in this study, we analyze and simulate the tropospheric scatter propagation model proposed by the ITU-R. Troposcatter propagation models in ITU-R recommendations consist of three parts: basic transmission loss, gaseous absorption, and a precipitation fading model. The ITU-R P.2001 simulation model shows basic transmission losses of 210 dB and 240 dB at 0.2 GHz and 2 GHz in 300 km distances, respectively. The ITU-R P.452 model results in 20 dB less loss, but this is dependent on measurement conditions. Gaseous absorption and precipitation fading have less than 1 dB loss for frequencies less than 2 GHz, but can increase to be over 10 dB in loss for frequencies of 2 GHz and above. We also review recent studies on tropospheric scatter channel models and communication systems. In addition to these reviews, we examine recent studies on ray tracing methods for tropospheric scatter channel models.

Two clear-air over-the-horizon propagation mechanisms affecting the Automatic Identification System (AIS) detection range are considered. Comparison results are presented between the path loss due to tropospheric ducting and path loss due to tropospheric scattering (troposcatter) for the AIS frequencies. The calculations are based on the well-known parabolic equation approximation to the wave equation, in which a simple troposcatter formula is incorporated. In most studied cases, the ducting ensures a significantly greater reduction in path loss than troposcatter even when the AIS frequencies are not well trapped in the duct. Emphasis is placed on the elevated trapping layers, and some features that may make ducting propagation less favorable in terms of increasing the AIS detection range are discussed. [ABSTRACT FROM AUTHOR]

Troposcatter propagation delay is one of the most significant sources of errors in troposcatter time comparison. The existing methods of calculating troposcatter propagation delay face problems in terms of effectively reflecting the influence of the meteorological environment on troposcatter propagation delay, due to the insufficient spatial and temporal resolution of the meteorological data. This article proposes a high-precision calculation method for troposcatter propagation delay based on atmospheric reanalysis data. The troposcatter propagation path and the refractive index along the troposcatter data were obtained by combining 3D ray tracing with the European Centre for Medium-Range Weather Forecasts' Reanalysis 5 (ERA5), with high spatial and temporal resolution. This found the hour-level time delay in troposcatter. The geometric delay, path delay, and total propagation delay of the troposcatter were calculated and analyzed via 12 scattering links in 6 typical geographical regions. It was found that the path delay was the main cause of the propagation delay of troposcatter, and that the proportion of geometric delay in the total propagation delay increased along with an increase in link distance. The propagation delay changed noticeably in different seasons. The path delay was higher in summer and lower in winter, the geometric delay was lower in summer and higher in winter, and the total propagation delay was mainly high in summer and low in winter. There were differences in delay date, seasonal fluctuation amplitude, and in hourly fluctuation standard deviation among different geographic areas. [ABSTRACT FROM AUTHOR]

Two clear-air over-the-horizon propagation mechanisms affecting the Automatic Identification System (AIS) detection range are considered. Comparison results are presented between the path loss due to tropospheric ducting and path loss due to tropospheric scattering (troposcatter) for the AIS frequencies. The calculations are based on the well-known parabolic equation approximation to the wave equation, in which a simple troposcatter formula is incorporated. In most studied cases, the ducting ensures a significantly greater reduction in path loss than troposcatter even when the AIS frequencies are not well trapped in the duct. Emphasis is placed on the elevated trapping layers, and some features that may make ducting propagation less favorable in terms of increasing the AIS detection range are discussed.

At present, 5G base stations are densely distributed in major cities based on improving user concentrations and the large demand for services in urban hotspot areas. Moreover, 5G communication requires more accurate communication propagation loss (PL) monitoring. Low-build areas, such as suburbs and rural areas, are prone to forming relatively stable tropospheric ducts, which can bend the signal to the surface in the duct-trapping layer for multiple reflections. Due to the random flow of the atmospheric air mass, each reflection of the communication signal is re-scattered in the troposphere through the top of the duct layer, thereby expanding the propagation range of the signal and changing the expected effect of radio wave propagation. If ducting and troposcatter effects happen in the 5G base station antenna layer, co-channel interference (CCI) could occur, affecting the quality of electromagnetic propagation. Urban links in the plain area have no major terrain obstacles, but ground fluctuations and land cover scattering have a greater impact on the signal scattering at the bottom of the duct. On the basis of the forward-propagation theory, this paper adds factors, such as ducting the forecast value using real weather parameters, terrain, and land cover-type distributions to evaluate the CCIs of over-the-horizon communications on the intercity link. Based on 1300 sets of randomly generated terrains and landforms, two deep learning (DL) models were used to predict the PL of over-the-horizon communications between cities in a land-based ducting environment. The accuracy of LSTM prediction could reach 98.4%. The verification of PL prediction using DL in this paper allows for quick and efficient prediction of PL in the land-based ducting of intercity links using land cover characteristics. [ABSTRACT FROM AUTHOR]

The atmospheric environment is one of the critical factors affecting troposcatter transmission loss and propagation delay. This article proposes a new estimation model that can accurately calculate troposcatter transmission loss and propagation delay with a numerical weather model (NWM). The ERA5 reanalysis data as the NWM are applied to construct the new model. The 3-D ray-tracing and beam splitting are used to calculate propagation paths and delays. Compared with the existing methods, the new model thoroughly considered the bending and delaying effects of the atmospheric environment on electromagnetic waves, resulting in more accurate estimates. The transmission loss calculation capability of the new model is compared with the International Telecommunication Union (ITU) model and the terrestrial trans-horizon propagation loss data banks. The propagation delay calculation capability is compared with the Bello model. These comparison results show that the new model sufficiently reflects the meteorological environment’s influence on transmission loss and propagation delay. Finally, the daily variation characteristics of losses and delays are analyzed using the new model and further validate the model performance. [ABSTRACT FROM AUTHOR]

As information technology advances, the need for distributed communications on the battlefield continues to grow. Moreover, NATO activities are multi-nation engagements, and necessitate communications between member countries and from the theater of operations back to command centers. The NATO Information Systems Technology (IST) 172 research task group has investigated non-satellite and non-high frequency (HF) technologies for beyond line-of-sight (BLOS) communications, creating links between disparate battlefield nodes. The study examines existing and emerging capabilities within the NATO member nations, and considering their applicability to six representative communications scenarios. The representative scenarios and the technologies which support BLOS are presented herein. An operational vignette is also presented which applies the solutions outlined in the report as an example. [ABSTRACT FROM AUTHOR]