Terrestrial Links Research Articles

Characterization of Rain Attenuation in 80–200 GHz From Experimental Drop Size Distributions

The use of frequencies well into the EHF band (30-300 GHz) is a key element in 5G and beyond technologies. Rain attenuation is the major impairment affecting terrestrial radio links in this band. In the absence of enough experimental measurements, rain attenuation can be estimated by using physical models of radiowave scattering in rain drops combined with information about the rain Drop Size Distributions (DSD). In this work, the characterization of rain attenuation in the 80-200 GHz frequency range is carried out from a large database of twelve years of experimental DSD gathered in Madrid, Spain. Rain attenuation is estimated for each collected minute of rain using two approaches: a first one based on the assumption of raindrops as spherical and the application of the Mie theory, and a second one that uses a non-spherical raindrop model and electromagnetic simulations and is consequently more realistic. The main results show that the currently used ITU-R model generally underestimates rain specific attenuation; the influence of polarization becomes smaller and negligible as frequency approaches 200 GHz; and rain specific attenuation significantly varies due to the spread of the DSD. Moreover, a model for this variability of rain attenuation is also proposed.

The Refractive Effect of k-Factor on Radio Propagation over Lokoja, Nigeria

The effective earth radius factor (k-factor) has a refractive propagation effect on transmitted radio signals thus making its study necessary for the proper planning of terrestrial radio links and power budget. This study was carried out over the city of Lokoja, Nigeria, using ten years (2011 to 2020) atmospheric data of temperature, pressure and humidity both at the surface (12 m) and at 100 m AGL. The data were retrieved from European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5. The k-factor yearly variation follows the same trend with minimum and maximum values obtained during dry and wet season months respectively. In addition, the highest mean value of 1.00042 was recorded in the month of August while the lowest value of 1.00040 was recorded in the month of January with an overall mean value of 1.0003. This value is less than the recommended standard of 1.33 by ITU-R. The propagation effect corresponding to k < 1.33 is sub-refractive. The implication of this on radio wave propagation, especially terrestrial communications is that transmitted wireless signal is prone to losses. This can be mitigated through an effective power budget: Choice of transmitting antenna’s height and gain, so as to improve the Quality of Service over the study area.

Polar-Coded Transmission over 7.8-km Terrestrial Free-Space Optical Links

Free-space optical (FSO) communications can offer high-capacity transmission owing to the properties of the laser beams. However, performance degradation caused by atmospheric turbulence is an urgent issue. Recently, the application of polar codes, which can provide capacity-achieving error-correcting performance with low computational cost for decoding, to FSO communications has been studied. However, long-distance and real-field experiments have not been conducted in these studies. To the best of our knowledge, this study is the first to present the experimental results of polar-coded transmission over 7.8-km FSO links. Using experimental data, we investigated the performance of polar codes over atmospheric channels, including their superiority to regular low-density parity-check codes. We expect that our results will offer a path toward the application of polar codes in high-speed optical communication networks including satellites.

Evaluation of Refractivity Gradient and k-factor within the Lower Troposphere of Maiduguri and Enugu under Two Climatic Zones in Nigeria

Estimation of radio refractivity is important in the planning and design of terrestrial radio communication links for the availability and accessibility of strong networks and signals. This paper investigates the refractivity gradient, effective earth radius factor (k), and the geo-climatic factor K in the first 1km of the troposphere of two selected stations (Maiduguri and Enugu) under different climatic zones in Nigeria. The indirect method of measuring radio refractivity was employed in this study to take measurements over the two selected stations. Vertical profile values of pressure (hPa), Temperature (°C), and Relative humidity (%) within the first 1 km were extracted from MERRA MAIMCPASM V5.20 database profile obtained from a satellite sounding instrument by NASA in the United States. MatLab programming language was used to evaluate the refractivity gradient, k-factor, and geo-climatic factor using the equations recommended by ITU. The results showed that Enugu was predominantly sub-refractive due to the tropical savannah climate while Maiduguri encountered both sub-refractive and normal refractive conditions due to the hot semi-arid climate, and unstable and extreme weather conditions in the region.

Teletraffic analysis and simulation on FSO systems: the traffic generators approach

Free Space Optical Communications (FSO) has become an interesting topic to researchers in recent years since the amount of data generated by devices is growing, and it is necessary to use data links that support high bandwidth to transmit them from one device to another. This technology is used to establish not only terrestrial links but also space links.A CubeSat satellite is generally deployed in the Low Earth Orbit (LEO) region. To maintain the altitude, the satellite must have a high orbital speed. For that reason, the time to transmit data between a particular ground station and the CubeSat satellite is limited. On the other hand, the volume, mass, and energy storage capacity are restricted in a CubeSat. The greater the bandwidth capacity of radio frequency links, the greater the demand for volume, mass, and energy they require. For that reason, to transmit a significant amount of data, traditional radio frequency links are not suitable and are becoming replaced by FSO as technology improves.Despite research in physical layer technologies on FSO (modulation schemes, error mitigation techniques, pointing and tracking systems), there is very little research in the literature about data link layer protocols for FSO. Secondly, there is little research to measure the data traffic demand on CubeSat satellites so that a certain data link layer protocol can be selected or adapted to be implemented in an FSO system.This paper presents research to address the issue of teletraffic through the use of traffic generators. The result is the design and development of a traffic generator for a discrete event simulator that will later be used to observe the behavior and to measure the performance of the Selective Repeat ARQ protocol in a simulated satellite FSO link, in order to propose improvements to adapt the protocol to this scenario.

A Link Planning and DDoS Attack Detection in SDN Based Integrated Space-Terrestrial Networks

It is expected that 5G networks would require both great dependability and stability as fundamental requirements. The introduction of a satellite component into LTE (long term evolution) networks has emerged as an attractive solution for meeting these requirements. This will enable the provision of backup interoperability to essential base stations and the routing of traffic away from crowded locations. During peak hours, the demand for their terrestrial links must be increased or even adopted in the case of anticipated breakdown or repair. Integrated spaceterrestrial networks have shown to be an advantageous design due to its broad coverage and high precision. Designing a network routing plan is not a straightforward process when the complex relative motion of low-earth-orbit (LEO) satellites and unmanned aircraft systems (UAS) is considered (UAS). To be more explicit, the major difficulty is discovering how to locate acceptable connections in timevarying network settings to offer reliable and effective UAS data transmission. This study begins with a motion analysis of satellites and UASs to discover which access satellites are most suited for usage with UASs. This is done in order to resolve the aforementioned problem. In order to provide an effective and reliable intersatellite link (ISL) deployment between access satellites, double exponential smoothing (DES) is afterwards proposed as an alternative to traditional routing. This is required to guarantee the timely delivery of UAS data. The simulation results demonstrate that the proposed DES approach is both feasible and effective. A time series-based method known as DES is used to compute the port information in an adjustable manner, and an algorithm known as SVM (Support Vector Machine) is utilized to determine if a Distributed Denial of Service (DDoS) attack has really occurred. Experiments that are typical demonstrate that the UAS may greatly reduce the controller's workload while maintaining dependable detection accuracy.

Space-Terrestrial Cooperation Over Spatially Correlated Channels Relying on Imperfect Channel Estimates: Uplink Performance Analysis and Optimization

A whole suite of innovative technologies and architectures have emerged in response to the rapid growth of wireless traffic. This paper studies an integrated network design that boosts system capacity through cooperation between wireless access points (APs) and a satellite for enhancing the network’s spectral efficiency. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">As for our analytical contributions</i> , upon coherently combing the signals received by the central processing unit (CPU) from the users through the space and terrestrial links, we first mathematically derive an achievable throughput expression for the uplink (UL) data transmission over spatially correlated Rician channels. Our generic achievable throughput expression is applicable for arbitrary received signal detection techniques employed at the APs and the satellite under realistic imperfect channel estimates. A closed-form expression is then obtained for the ergodic UL data throughput, when maximum ratio combining is utilized for detecting the desired signals. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">As for our resource allocation contributions</i> , we formulate the max-min fairness and total transmit power optimization problems relying on the channel statistics for performing power allocation. The solution of each optimization problem is derived in form of a low-complexity iterative design, in which each data power variable is updated relying on a closed-form expression. Our integrated hybrid network concept allows users to be served that may not otherwise be accommodated due to the excessive data demands. The algorithms proposed allow us to address the congestion issues appearing when at least one user is served at a rate below his/her target. The mathematical analysis is also illustrated with the aid of our numerical results that show the added benefits of considering the space links in terms of improving the ergodic data throughput. Furthermore, the proposed algorithms smoothly circumvent any potential congestion, especially in face of high rate requirements and weak channel conditions.

Impact of Scintillation Effect on Clear Weather and Fog Conditions using MDM-WDM Modulation Technique

The 5th generation optical wireless communication technologies have unique features of higher data rate, scalability in bandwidth, license free spectrum, cost effectiveness, easy deplorability and secured transmission. The role of free space optical (FSO) communication becomes important as the applications of next generation technologies are evolving in almost every sector. In this work, the performance of the terrestrial FSO MDM-WDM link has been investigated through a DP-QPSK modulation scheme at a data rate of 1000 Gbps. The link attenuation has been analysed with the help of Gamma- Gamma and Lognormal scintillation models considering clear weather and varying fog conditions. The link performance has been evaluated through SNR and received optical power for a varying distance of up-to 20 Km.

English

The spatial diversity techniques are broken down and explained systematically along with its combination which includes Maximum Ratio Combining (MRC), Equal Gain Combining (EGC) and Simple Selection Combining (SC) under the influence of atmospheric-induced turbulence fading in Free Space Optical (FSO) communication. Diversity is a technique used to prevent or reduce multipath. Multipath is a phenomenon describing propagation that results in the signals reaching the antenna by two or more paths. There is an extreme difficulty for a transmitted signal to be detected by a receiver in a case of increased turbulence. This research provides a forum for the receiver with some forms of diversity. The validation of the recommended simulation is through Additive White Gaussian Channel without combiner of the same process. The results display that Maximum Ratio Combining (MRC) has the greatest mitigation level of fading in comparison with others. Consequently, where fading is more dominant like on a terrestrial FSO link, Maximum Ratio Combining (MRC) can be used. Overall, the findings suggest the capability of the model in mitigating atmospheric turbulence especially for the 5G wireless networks in the terrestrial link. Key words: Free Space Optical Communication (FSO), Atmospheric Turbulence, Additive White Gaussian Channel (AWGC), Maximum Ratio Combining (MRC), Equal Gain Combining (EGC), Selection Combining (SC) and Additive White Gaussian Noise (AWGN).

An Optimized Planning Tool for Microwave Terrestrial and Satellite Link Design

Today, the internet is fundamental to social inclusion. There are many people that live in remote areas, and the only way to supply internet services is through the use of microwave terrestrial and satellite systems. Thus, it is important to have efficient tools to design and optimize these systems. In this paper, a tool with the objective to shorten the time spent in the design process of microwave terrestrial and satellite point-to-point links is presented. This tool can be applied in academia by engineering students, providing an extended analysis of many sections of a link project design, as well as in professional practice by telecommunication engineering departments, presenting a concise step-by-step interactive design process. This tool uses three-dimensional world visualization, with the Cesium Application Programming Interface (API), to display and analyze site-specific characteristics that can disrupt the link’s quality of service (QoS). Using this visualization, two ray-tracing algorithms were developed to analyze signal diffraction and reflection mainly throughout terrestrial links. Using this new algorithm, an innovative process for signal diffraction and reflection calculations was created. Using updated standards provided by the International Telecommunication Union Radiocommunication Sector (ITU-R), the characteristics of the defined simulated links could be predicted, thus providing the user with the metrics of signal quality and system link budget.

Investigation of Point Refractivity Gradient and Geoclimatic Factor at 70 m Altitude in Yenagoa, Nigeria

The quality of services provided via Inter-Terrestrial radio communication links such as GSM networks, Wide Area Network (WAN), Radio and TV broadcasts is largely influenced by some meteorological parameters such as temperature, pressure and humidity. Proper knowledge of these parameters, specifically at microwave antenna heights (about 70m) is important in order to maintain an effective line-of-sight (LOS) link even during the worst weather conditions. The geoclimatic factor is an important quantity that must be considered in the design of terrestrial links for effective wireless communication. This work utilized satellite data from the European Center for Medium-Range Weather Forecasts (ECMWF) to compute the point refractivity gradient and geoclimatic factor for Yenagoa and its environs. The research was necessitated by the paucity of research on this subject matter for Yenegoa. The results of the research show that point refractivity gradient and geoclimatic factor in the study area vary with season. The average point refractivity gradient and geoclimatic factor at 70 m above the ground level are:136.433 N-unit/Km and 6.638633E-05 respectively. This implies that radiowaves propagating in this region at the said altitude is most likely to be super refractive in both rain and clear air atmospheric conditions. Rain or worst condition refers to the period when atmospheric components such as hydrometeor, lithometeor, aerosol have significant effects on propagated radio signals. Clear-air conditions means when maximum possible signal is received such that the most threatening atmospheric components (rain drops) have negligible effects on propagated signal. The results will be useful for radio engineers in the design and configuration of inter-terrestrial microwave links in Yenagoa and Its environs for optimum quality of service.

Outage performance for full-duplex relaying satellite-terrestrial multi-antenna NOMA systems with imperfect SIC

Due to the masking effect, a reliable line-of-sight transmission between a satellite and terrestrial nodes is not always guaranteed, and a half-duplex (HD) relaying is commonly performed in literature to assist such transmission. However, the system efficiency could be seriously degraded with the HD relaying as a two-time slot is required for a dual-hop information transmission. Therefore, in this paper, a full-duplex (FD) relaying, which can enable signal receiving and transmitting simultaneously, is considered for a satellite-terrestrial non-orthogonal multiple access (NOMA) system consisting of a multi-antenna satellite source, a FD relay, and two multi-antenna destination nodes. Specifically, the satellite source adopts a maximum ratio transmission scheme to transmit a NOMA signal to the relay, and the relay deploys a decode-and-forward protocol to forward the information to two destination nodes simultaneously, which employ the maximal ratio combining strategy to process the received signals. Assuming the satellite link experiences Shadowed-Rician fading and the terrestrial links undergo Nakagami-m fading distribution, both analytical and asymptotic expressions of outage probability (OP) for two destination nodes are presented in the presence of residual self-interference and imperfect successive interference cancellation. In addition, an adaptive power allocation (APA) scheme is performed, and the system throughput under the delay-limited transmission mode is also analyzed. Finally, Monte-Carlo simulations are adopted to verify the accuracy of those derived analytical expressions. Numerical results show that the OP performance with the FD mode outperforms that with the HD one, and adopting the APA scheme can result in the best OP performance.

Performance Analysis of NOMA-Based Hybrid Satellite-Terrestrial Relay System Using mmWave Technology

This paper investigates the performance of NOMA-based hybrid Satellite-Terrestrial relays system (HSTR) using the millimeter wave (mmWave) technology. Furthermore, the relays are equipped with multiple antennas and utilize the amplify and forward (AF) protocol to forward the satellite’s superimposed information to multiple destinations. Then, the rain coefficient is considered as the fading factor of the mmWave band to choose the best relay. We considered the shadowed-Rician fading and Nakagami-m fading for satellite links and terrestrial links respectively, and in addition, we evaluated the shadowing effect for satellite links with two modes of: frequent heavy shadowing (FHS) and average shadowing (AS). With these suggestions, the closed-form outage probability (OP) and approximate ergodic capacity (EC) are derived to evaluate the efficiency of the proposed system. Next contribution of the research is an asymptotic analysis for the OP, which is derived in order to gain additional insight into important system parameters. Finally, the theoretical derivation is validated through simulation results and analyzed the impact of significant parameters. These results demonstrate NOMA’s superiority to the traditional orthogonal multiple access (OMA) method in the proposed system.

Digital transformation of technological IP portfolio analysis for complex domain of satellite communication innovations

The latest mobile network protocols, currently adopted by most of global telecom-services, are at the level of fifth generation (5G) technological standards. However, 5G speed and bandwidth will not be likely to catch up with the advanced AI- and IoT-based applications, which require very low latency with wide coverage. Thus, industry is looking ahead beyond 5G (B5G) communication enabling technologies. Further, in order to provide global communications without disconnections due to geographical barriers (e.g., oceans and high mountains lacking base stations), low earth orbit (LEO) satellites become the ideal solution for connecting entire global network with terrestrial and non-terrestrial links. In this research, the integration of LDA topic modeling, clustering algorithm, technology-function matrix, and s-curve modeling is proposed to analyze complex IP portfolio for B5G satellite technologies. The domain ontology, which describes the transdisciplinary features of the B5G satellite technology taxonomy, is derived and refined in a hierarchical schema after thorough literature review and 2357 domain patents being collected and analyzed. This research aims to discover the main trends and the potentials of satellite communication technologies through novel tech-mining techniques in both macro- and micro-levels. During macro-analyses, trends of global inventions, the leading assignees, and the distribution of technology categories are depicted. We identify the leading patent assignees with their domain patents (published from 2012 to 2021) and distributions under sub-technical categories. Further, the micro-analyses discover the innovations of major technological themes, showing key R&D hot-spots, cold-spots and lifecycle maturities of sub-technical categories. Finally, the research strategies for technical-savvy countries (e.g., Taiwan, with advances in its semiconductor and ICT industries) are presented highlighting its strategic innovations related to the complex communication domain.

Physical Layer Security in Interference Limited Land Mobile Satellite Communication Systems: Safeguarding Data Transmission

This paper focuses on evaluating the secrecy performance of a downlink land mobile satellite (LMS) system. The system faces the challenge of providing secure communication between a satellite and a legitimate user while an eavesdropper is present on the ground. Additionally, co-channel interference signals at the user's destination are considered. To address these issues, the study proposes a novel approach that utilizes Shadowed-Rician fading channels for satellite links and Nakagami-m fading for interfering terrestrial links. The main objective is to enhance the physical layer security of Interference-Limited Land Mobile Satellite Communication Systems. The approach incorporates advanced signal processing, beamforming, and artificial noise techniques to effectively manage interference. Encryption, authentication mechanisms, and intelligent power control strategies are implemented to protect transmitted data and optimize signal strength while reducing the risk of interception by potential eavesdroppers. Through comprehensive simulations, the proposed approach is thoroughly evaluated, demonstrating its effectiveness in achieving improved secrecy performance and increased resilience against security threats. The findings highlight the potential for its application in secure satellite communication systems operating in interference-constrained environments.

Artificial Intelligent For Rainfall Estimation In Tropical Region : A Survey

Rainfall monitoring in real-time is a mandatory in tropical areas such as Indonesia. As a country with various topographical conditions ranging from low-lying urban areas, highlands, to mountainous valleys, Indonesia is prone to hydrometeorological disasters in the form of flash floods and landslides. The strategic geographical position at the equator, between the Pacific and Indian oceans, and surrounded by vast oceans, combined with various natural phenomena related to the dynamics of the atmosphere and the ocean, makes high-density rainfall observations indispensable for both disaster mitigation and climate monitoring. As a vast tropical and archipelagic country, Indonesia currently has around 1000 automatic rainfall sensors and still requires more sensors to increase the spatial resolution of the observation network. Increasing the density of the observation network using both rain gauges and weather radar poses a problem of high operational costs. Therefore, several alternative rainfall observation systems are required. In the last decade, there have been several studies related to rainfall measurements using artificial intelligence from various meteorological variables, including the exploitation of microwave signals from radio telecommunications links, both terrestrial and satellite using high frequency bands. In this survey paper, we review and discuss research articles related to rainfall estimation using state-of-the-art methods in artificial intelligence using meteorological observation data, remote sensing, terrestrial and satellite microwave communication links. In conclusion, we present several future research challenges that can be applied to increase the density of rainfall observation networks.

Green Interference Based Symbiotic Security in Integrated Satellite-Terrestrial Communications

In this paper, we investigate secure transmissions in integrated satellite-terrestrial communications and the green interference based symbiotic security scheme is proposed. Particularly, the co-channel interference induced by the spectrum sharing between satellite and terrestrial networks and the inter-beam interference due to frequency reuse among satellite multi-beam serve as the green interference to assist the symbiotic secure transmission, where the secure transmissions of both satellite and terrestrial links are guaranteed simultaneously. Specifically, to realize the symbiotic security, we formulate a problem to maximize the sum secrecy rate of satellite users by cooperatively beamforming optimizing and a constraint of secrecy rate of each terrestrial user is guaranteed. Since the formulated problem is non-convex and intractable, the Taylor expansion and semi-definite relaxation (SDR) are adopted to further reformulate this problem, and the successive convex approximation (SCA) algorithm is designed to solve it. Finally, the tightness of the relaxation is proved. In addition, numerical results verify the efficiency of our proposed approach.

In Living Color: Pigment-Based Microbial Ecology At the Mineral-Air Interface.

Pigment-based color is one of the most important phenotypic traits of biofilms at the mineral-air interface (subaerial biofilms, SABs), because it reflects the physiology of the microbial community. Because color is the hallmark of all SABs, we argue that pigment-based color could convey the mechanisms that drive microbial adaptation and coexistence across different terrestrial environments and link phenotypic traits to community fitness and ecological dynamics. Within this framework, we present the most relevant microbial pigments at the mineral-air interface and discuss some of the evolutionary landscapes that necessitate pigments as adaptive strategies for resource allocation and survivability. We report several pigment features that reflect SAB communities' structure and function, as well as pigment ecology in the context of microbial life-history strategies and coexistence theory. Finally, we conclude the study of pigment-based ecology by presenting its potential application and some of the key challenges in the research.

Outage performance for wireless-Powered relaying satellite-Terrestrial NOMA systems

This study investigates the outage performance for a wireless-powered relaying satellite-terrestrial system, which consists of a satellite source, a relay, a power beacon, and two users. In particular, the satellite source transmits its information to the relay, which uses up all the harvested energy from the power beacon with a nonlinear energy harvesting mode to forward a superimposed signal of the source and its own information under a non-orthogonal multiple access protocol. Assuming the satellite link experiences Shadowed-Rician fading and the terrestrial links undergo Nakagami-m fading distribution, the analytical expressions of outage probability for both users are presented in the presence of imperfect successive interference cancellation. In addition, the optimal power allocation factor, which can result in the best outage performance, is also obtained. Finally, Monte-Carlo simulations are used to verify the accuracy of the analytical expressions.

Performance of Spectrum Sharing in Hybrid Satellite Terrestrial Network with Opportunistic Relay Selection

In this paper, we consider the uplink of a hybrid satellite-terrestrial spectrum sharing system, in which satellite terminal communicates with satellite through terrestrial relay-assisted transmission. To accommodate expanding networks within limited spectrum, spectrum sharing is considered a promising candidate. For the system in which satellite terminals and terrestrial terminals share spectrum, we propose opportunistic relay selected spectrum sharing method based on decoding and forwarding protocol. Selecting the optimal relay station is aimed at minimizing the outage probability of the satellite terminal and maximizing the throughput of the system. Due to spectrum sharing policy and imperfections in the RF front end, we also consider the effects of cochannel interference (CCI) and hardware impairments (HIs). The satellite link is modeled as Shadowed-Rician fading, and the terrestrial link uses Nakagami-m fading. In addition, we deduce the closed-form analytical expressions of the satellite terminal outage probability, deduce the asymptotic expressions under the condition of high signal-to-noise ratio, and analyze their achievable diversity orders. Numerical and simulation results validate the performance gain of opportunistic relay selection compared to partial relay selection. Monte Carlo simulations confirm the correctness of the theoretical analysis and illustrate the effects of CCI and HIs on the system.