Search

The increasing number of vehicles on the road places high demands for autonomous driving in future intelligent transportation systems (ITSs). To realize automated services in ITSs, high-accuracy positioning is increasingly important, while positioning simultaneity for high-mobility vehicles should be guaranteed. Existing positioning systems have many constraints in locating vehicles in urban environments, making it difficult to meet the performance requirements. With the development of 6G, massive numbers of high-frequency base stations (BSs) are expected to be deployed to ensure connectivity and benefit positioning performance. However, high-frequency signals have severe distance attenuations and strong sensitivity to the non-line-of-sight (NLoS) environment that is prevalent in cities. Intelligent reflecting surface (IRS), with its ability to control signal reflections and create beyond-LoS communications, is a promising technology to improve positioning performance in urban vehicular networks. In this article, we discuss the existing positioning systems and explain the potentials of IRS for future BS-enabled positioning systems. We also provide an example to illustrate how to optimize the performance of IRS-aided vehicle positioning systems. Furthermore, we highlight important issues and give future directions. [ABSTRACT FROM AUTHOR]

Recently, megaconstellations with a massive number of low Earth orbit (LEO) satellites are being considered as a possible solution for providing global coverage due to relatively low latency and high throughput compared to geosynchronous orbit (GEO) satellites. However, as the number of satellites and operators participating in the LEO constellation increases, inter-satellite interference will become more severe, which may yield marginal improvement or even decrement in network throughput. In this article, we introduce the concept of satellite clusters that can enhance network performance through satellites’ cooperative transmissions. The characteristics, formation types, and transmission schemes for the satellite clusters are highlighted. Simulation results evaluate the impact of clustering from coverage and capacity perspectives, showing that when the number of satellites is large, the performance of clustered networks outperforms the unclustered ones. The viable network architectures of the satellite cluster are proposed based on the 3rd Generation Partnership Project (3GPP) standard. Finally, the future applications of clustered satellite networks are discussed. [ABSTRACT FROM AUTHOR]

Reducing carbon dioxide (CO2) emissions has been a global concern for urban development. In recent years, while the Suomi-National Polar-Orbiting Partnership Satellite–Visible Infrared Imaging Radiometer Suite (Suomi-NPP VIIRS) nighttime light (NTL) data have been widely used to estimate CO2 emissions, the Luojia 1–01 NTL data with finer spatial resolution have rarely been used for this purpose. Therefore, this letter estimated four types of sectoral CO2 emissions (i.e., urban residential, services, industrial, and transport) in Chinese cities by merging two sets of NTL data with functional urban zoning information. The results show that Luojia 1–01 data outperformed Suomi-NPP VIIRS data in estimating total CO2 emissions. Regarding the disaggregated estimation of CO2 emissions in the service, industrial, and urban residential sectors, Luojia 1–01 data surpassed Suomi-NPP VIIRS data. However, Suomi-NPP VIIRS data were better suitable for estimating the transport CO2 emissions than Luojia 1–01 data. We found linear regression more appropriate for estimating CO2 emissions in the service, transport, and urban residential sectors, but the power function regression was more suitable for estimating CO2 emissions in the industrial sector. Our results will help provide a scientific reference for selecting optimal NTL data as well as regression models to be used in estimating sectoral CO2 emissions, which are also essential for achieving China’s carbon emissions targets. [ABSTRACT FROM AUTHOR]

Futuristic 6G technologies will integrate emerging low-Earth orbit (LEO) megaconstellations into terrestrial networks, promising to provide ubiquitous, low-latency and high-throughput network services on-demand. However, several unique characteristics of satellites (e.g., high dynamics and error-prone operational environments) make it very challenging to unleash the potential of megaconstellations and accomplish these aforementioned promises. [ABSTRACT FROM AUTHOR]

Cirrus cloud contributes significantly to earth's radiation budget and the greenhouse effect. The Advanced Himawari Imager (AHI) onboard the Himawari-8 satellite lacks a 1.37 μm band, sensitive to monitoring cirrus clouds. This article proposed a conditional generative adversarial network-based data-to-data translation (D2D) model to generate a hypothetical AHI 1.37 μm band. For training and testing the D2D model, the Geo-Kompsat-2A Advanced Meteorological Imager (AMI) 1.37 μm bands and other highly correlated bands to cirrus from July 24, 2019 to July 31, 2020, were used. The D2D model exhibited a high level of agreement (mean of statistics: correlation coefficient (CC) = 0.9827, bias = 0.0004, and root-mean-square error (RMSE) = 0.0086 in albedo units) between the observed and D2D-generated AMI 1.37 μm bands from validation datasets. The application of the D2D model to the AHI sensor showed that the D2D-generated AHI 1.37 μm band was qualitatively analogous to the observed AMI 1.37 μm band (average of statistics: bias = 0.0026, RMSE = 0.0191 in albedo units, and CC = 0.9158) on the 1st, 15th, and 28th of each month of 2020 in the common observing regions between Korea and Japan. The validation results with the CALIPSO data also showed that the D2D-generated AHI 1.37 μm band performed similarly to the observed AMI 1.37 µm band. Consequently, this article can significantly contribute to cirrus detection and its application to climatology. [ABSTRACT FROM AUTHOR]

In this paper, we investigate security and energy efficiency of multicast communication in cognitive satellite terrestrial networks. To achieve high spectrum efficiency and low interference power transmissions in the cognitive terrestrial network, the rate splitting multiple access scheme (RSMA) is employed to prompt the massive access of the secondary users. In particular, we derive analytical and asymptotic closed-form expressions for secrecy outage probability of the satellite terrestrial network with eavesdropping, interfering, and imperfect channel state information. Hence, a beamforming (BF) scheme based on RSMA for secondary network is proposed to suppress eavesdropping, mitigate interference, and enhance energy efficiency of the proposed system model. Then, we transform non-convex optimization constraints into resoluble problems utilizing Taylor series expansion and successive convex approximation. Finally, simulation results corroborate the above theoretical analysis and highlight the superiority of the designed BF scheme on security and energy efficiency. [ABSTRACT FROM AUTHOR]

Predicting the safety of urban roads for navigation via global navigation satellite systems (GNSS) signals is considered. To ensure the safe driving of automated vehicles, a vehicle must plan its trajectory to avoid navigating on unsafe roads (e.g., icy conditions, construction zones, narrow streets, and so on). Such information can be derived from roads’ physical properties, the vehicle’s capabilities, and weather conditions. From a GNSS-based navigation perspective, the reliability of GNSS signals in different locales, which is heavily dependent on the road layout within the surrounding environment, is crucial to ensure safe automated driving. An urban road environment surrounded by tall objects can significantly degrade the accuracy and availability of GNSS signals. This article proposes an approach to predict the reliability of GNSS-based navigation to ensure safe urban navigation. Satellite navigation reliability at a given location and time on a road is determined based on the probabilistic position error bound of the vehicle-mounted GNSS receiver. A metric for GNSS reliability for ground vehicles is suggested, and a method to predict the conservative probabilistic error bound of the GNSS navigation solution is proposed. A satellite navigation reliability map is generated for various navigation applications. As a case study, the reliability map is used in a proposed optimization problem formulation for automated ground vehicle safety-constrained path planning. [ABSTRACT FROM AUTHOR]

New scenarios and use cases are raising following the birth of the fifth generation of mobile communications. The Internet of Things (IoT) is one of the main use cases which are growing, leading to a massive amount of data that need to be exchanged throughout the Internet. Satellite communication networks are essential in remote and isolated environments and can support fully connected environments by offloading the terrestrial infrastructure concerning delay–tolerant traffic flows. However, satellite network resources are limited and expensive, so they need to be carefully used in order to avoid waste and satisfy the required user performance. The multi-access edge computing (MEC) concept can be exploited in this context to allow data preprocessing at the edge, i.e., close to the users, so reducing the amount of data that has to traverse the backhaul satellite link and, in some cases, reducing data delivery times. This article analyses the performance of a satellite architecture in the IoT framework highlighting the advantages brought by MEC, also including data aggregation and compression techniques. [ABSTRACT FROM AUTHOR]

In recent years, satellite-integrated content centric networking (SCCN) has become an important solution for the future network with excellent bandwidth savings and file distribution capability in a wide range by the intrinsic caching function. At present, however, the high-speed changes of satellite network topology and coverage make it difficult to predict the file popularity of SCCN network, resulting in a low timeliness. This will lead to low node cache efficiency and bad data distribution performance. To address this issue, in this article, we have proposed a deep learning-enabled file popularity-aware caching replacement mechanism to achieve efficient file distribution in SCCN. In the proposed mechanism, we have developed a virtual location division scheme to keep the return path of content data invariable by remapping the time-varying topology of network into a static topology with virtual nodes. Furthermore, we have put forward a minimum delay file-caching set algorithm to predict the popularity of files in the proposed SCCN via a well-designed deep learning framework, which can find those high-popularity files most worthy of caching. The simulation results verified the proposed method can obviously degrade the access delay of all users and the cache hit ratio of satellite nodes, compared with current strategies, i.e., cache everything everywhere with least recently used, probCache, content-aware placement and discovery, and replacement (APDR), respectively. [ABSTRACT FROM AUTHOR]

For data communications over long distances, optical wireless satellite networks (OWSNs) can offer lower latency than optical fiber terrestrial networks (OFTNs). However, when is it beneficial to switch or crossover from an OFTN to an OWSN for lower latency data communications? In this article, we introduce a crossover function that enables to find the crossover distance, i.e., a distance between two points on the surface of the Earth beyond which switching or crossing over from an OFTN to an OWSN for data communications between these points is useful in terms of latency. Numerical results reveal that a higher refractive index of optical fiber (or $i$) in an OFTN and a lower altitude of satellites (or $h$) in an OWSN result in a shorter crossover distance. To account for the variation in the end-to-end propagation distance that occurs over the OWSN, we examine the crossover function in four different scenarios. Numerical results indicate that the crossover distance varies with the end-to-end propagation distance over an OWSN and is different for different scenarios. We calculate the average crossover distance over all scenarios for different $h$ and $i$ and use it to evaluate the simulation results. Furthermore, for a comparative analysis of OFTNs and OWSNs in terms of latency, we study three different OFTNs having different refractive indexes and three different OWSNs having different satellite altitudes in three different scenarios for long-distance intercontinental data communications, including connections between New York and Dublin, Sao Paulo and London, and Toronto and Sydney. All three OWSNs offer better latency than OFTN2 (with $i_{2}$ = 1.3) and OFTN3 (with $i_{3}$ = 1.4675) in all scenarios. For example, for Toronto–Sydney connection, OWSN1 (with $h_{1}$ = 300 km), OWSN2 (with $h_{2}$ = 550 km), and OWSN3 (with $h_{3}$ = 1100 km) perform better than OFTN2 by 18.11%, 16.08%, and 10.30%, respectively, while they provide an improvement in latency of 27.46%, 25.67%, and 20.54%, respectively, compared to OFTN3. OWSN1 performs better than OFTN1 (with $i_{1}$ = 1.1) for Sao Paulo–London and Toronto–Sydney connections by 2.23% and 3.22%, respectively, while OWSN2 outperforms OFTN1 for Toronto–Sydney connection by 0.82%. For New York–Dublin connection, all OWSNs while for Sao Paulo–London connection, OWSN2 and OWSN3 exhibit higher latency than OFTN1 as the corresponding average crossover distances are greater than the shortest terrestrial distances between cities in these scenarios. Multiple satellites (or laser intersatellite links) on its shortest paths drive up the propagation distance to the extent that OWSN3 ends up with a higher latency than OFTN1 for the Toronto–Sydney intercontinental connection scenario although the related average crossover distance is less than the shortest terrestrial distance between Toronto and Sydney. The challenges related to OWSNs and OFTNs that may arise from this work in future are also highlighted. [ABSTRACT FROM AUTHOR]

A low Earth orbit (LEO) satellite system has a range of missions delivering economic, environmental, and social benefits utilized by everyone almost every day. However, there exists a challenge for operational management of satellites in LEO because they are not accessible from a given point of earth at all times. In that case, a problem evolves that should be solved is to find a valid broadcasting pattern between satellites and ground stations. Nevertheless, being defined as the satellite broadcast scheduling (SBS) problem almost three decades ago, the few numbers of published studies on the problem used a restricted variety of solution approaches. The recent advances in information technology and tremendous undergoing change in the industrial automation entails handling the SBS problem more comprehensively and propose innovative solution approaches. This article proposes and evaluates three metaheuristic approaches for the SBS problem. A relaxation and decomposition approach is also proposed for generating tighter upper bounds to make justified performance evaluations. Besides the benchmark problems reported in the literature, new benchmark instances are generated and used in computational experiments. Results are evaluated to be promising and highlight the effectiveness and robustness of the proposed approaches. [ABSTRACT FROM AUTHOR]

The space-air-ground-sea integrated network (SAGSIN) plays an important role in offering global coverage. To improve the efficient utilization of spectral and hardware resources in the SAGSIN, integrated sensing and communications (ISAC) has drawn extensive attention. Most existing ISAC works focus on terrestrial networks and cannot be straightforwardly applied in satellite systems due to the significantly different electromagnetic wave propagation properties. In this work, we investigate the application of ISAC in massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite systems. We first characterize the statistical wave propagation properties by considering beam squint effects. Based on this analysis, we propose a beam squint-aware ISAC technique for hybrid analog/digital massive MIMO LEO satellite systems exploiting statistical channel state information. Simulation results demonstrate that the proposed scheme can operate both the wireless communications and the target sensing simultaneously with satisfactory performance, and the beam-squint effects can be efficiently mitigated with the proposed method in typical LEO satellite systems. [ABSTRACT FROM AUTHOR]

This paper considers the joint channel estimation and device activity detection in the grant-free random access systems, where a large number of Internet-of-Things devices intend to communicate with a low-earth orbit satellite in a sporadic way. In addition, the massive multiple-input multiple-output (MIMO) with orthogonal time-frequency space (OTFS) modulation is adopted to combat the dynamics of the terrestrial-satellite link. We first analyze the input-output relationship of the single-input single-output OTFS when the large delay and Doppler shift both exist, and then extend it to the grant-free random access with massive MIMO-OTFS. Next, by exploring the sparsity of channel in the delay-Doppler-angle domain, a two-dimensional pattern coupled hierarchical prior with the sparse Bayesian learning and covariance-free method (TDSBL-FM) is developed for the channel estimation. Then, the active devices are detected by computing the energy of the estimated channel. Finally, the generalized approximate message passing algorithm combined with the sparse Bayesian learning and two-dimensional convolution (ConvSBL-GAMP) is proposed to decrease the computations of the TDSBL-FM algorithm. Simulation results demonstrate that the proposed algorithms outperform conventional methods. [ABSTRACT FROM AUTHOR]

Ground-based Augmentation System (GBAS) augments Global Navigation Satellite Systems (GNSS) to support the precision approach and landing of aircraft. To guarantee integrity, existing single-frequency GBAS utilizes position-domain geometry screening to eliminate potentially unsafe satellite geometries by inflating one or more broadcast GBAS parameters. However, GBAS availability can be drastically impacted in low-latitude regions where severe ionospheric conditions have been observed. Thus, we developed a novel geometry-screening algorithm in this study to improve GBAS availability in low-latitude regions. Simulations demonstrate that the proposed method can provide 5–8 percentage point availability enhancement of GBAS at Galeão airport near Rio de Janeiro, Brazil, compared to existing methods. [ABSTRACT FROM AUTHOR]

The transmission of huge amounts of data generated from various sensors is the basis and prerequisite for the analysis and prediction of the marine ecosystem. The special geographical conditions of the ocean determine that its data transmission is different from the common terrestrial data transmission. In this study, a marine environmental monitoring network architecture is proposed to collect environmental data from marine ecosystems using a heterogeneous network constructed by a multi-hop network and a satellite network. Considering the characteristics of satellite networks, such as high bandwidth delay product (BDP), long latency and high bit error rate, this work proposes a transmission scheme that improves the transmission performance of Transmission Control Protocol/Internet Protocol (TCP/IP)-based Internet networks over satellite networks. The improved scheme increases the monitoring data transmission rate, distinguishes between random data loss and congested data loss, rationalizes the threshold in fast recovery, and improves the overall transmission performance of the marine environmental monitoring network. The experimental results show that the proposed scheme can greatly improve the transmission performance of the monitoring network compared with traditional transmission protocols. The network model proposed in this study makes full use of current advanced network technologies, including multi-hop networks, wireless sensor networks, and satellite networks to expand the monitoring area at sea. This study provides a useful reference for the network model and data transmission for ocean monitoring. [ABSTRACT FROM AUTHOR]

Next-generation satellite systems require more flexibility in resource management such that available radio resources can be dynamically allocated to meet time-varying and non-uniform traffic demands. Considering potential benefits of beam hopping (BH) and non-orthogonal multiple access (NOMA), we exploit the time-domain flexibility in multi-beam satellite systems by optimizing BH design, and enhance the power-domain flexibility via NOMA. In this paper, we investigate the synergy and mutual influence of beam hopping and NOMA. We jointly optimize power allocation, beam scheduling, and terminal-timeslot assignment to minimize the gap between requested traffic demand and offered capacity. In the solution development, we formally prove the NP-hardness of the optimization problem. Next, we develop a bounding scheme to tightly gauge the global optimum and propose a suboptimal algorithm to enable efficient resource assignment. Numerical results demonstrate the benefits of combining NOMA and BH, and validate the superiority of the proposed BH-NOMA schemes over benchmarks. [ABSTRACT FROM AUTHOR]

Integrated terrestrial-satellite networks (ITSNs) are the promising trends of future networks. However, there exist great challenges when performing video multicast in ITSNs due to the strong heterogeneity of users in comprehensive satellite coverage and the inter-system complex co-channel interference. To overcome these, we make the first attempt to propose an efficient cooperative robust video multicast (CRVM-ITSN) framework in ITSNs. The basic idea is to leverage the non-orthogonal multiple access technique in the cooperative transmission of ITSNs to achieve high-efficiency robust video multicast. The desired robust multicast performance realizes that the recovered video quality can adapt to diverse channel conditions of users. In CRVM-ITSN, to achieve the optimal cooperative transmission performance, power allocation and chunk scheduling of video data are jointly formulated as a distortion minimization problem, which is a non-convex mixed integer non-linear programming problem. To solve it, we design a provably convergent optimal algorithm by converting it to be convex. Besides, based on the theorem on optimal chunks selection of satellite cooperative transmission, a low-complexity chunk grouping algorithm is proposed to accelerate the optimal algorithm. Simulation results have demonstrated the superiority of proposed CRVM-ITSN against existing reference schemes, achieving about 4.1dB more gains in the recovered video quality. [ABSTRACT FROM AUTHOR]

Earth observation systems play important roles in many critical applications. The rapid increase of the number of satellites and their sensing capability, however, makes it challenging to send the massive amount of observed data back to the Earth. One promising direction to enhance the earth observation throughput is to use inter-satellite communication. Towards this, we identify two key design factors: 1) the capability to support on-demand scheduling of inter-satellite communication; and 2) the capability to co-optimize the scheduling of observation and transmission missions. For both, rigorous study is needed to determine whether they provide sufficient throughput gain to justify their additional complexity. Our work formulates a generic earth observation and transmission problem to study the maximum network throughput under different settings. By succinctly modeling the different constraints using a generalized time-varying graph representation, we can efficiently find the optimal scheduling solutions. We conduct an extensive study, which shows that using 40 relay satellites from the “starlink” constellation can increase the throughput of 10 sensing satellites from the “Gaofen” constellation by more than 400%. In particular, on-demand scheduling under heavy load and co-optimization of observation/transmission under light but time-critical load can improve the throughput by more than 180% and 100%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effect of the strong time-varying transmission distance on the performance of the low-earth orbit (LEO) satellite-terrestrial transmission (STT) system. We propose a new analytical framework using finite-state Markov channel (FSMC) model and time discretization method. Moreover, to demonstrate the applications of the proposed framework, the performances of two adaptive transmissions, rate-adaptive transmission (RAT) and power-adaptive transmission (PAT) schemes, are evaluated for the cases when the transmit power or the transmission rate at the LEO satellite is fixed. Closed-form expressions for the throughput, energy efficiency (EE), and delay outage rate (DOR) of the considered systems are derived and verified, which are capable of addressing the capacity, energy efficiency, and outage rate performance of the considered LEO STT scenarios with the proposed analytical framework. [ABSTRACT FROM AUTHOR]

Nonterrestrial communications have emerged as a key enabler for seamless connectivity in the upcoming generation networks. This kind of network can support high data rate communications among aerial platforms (i.e., unmanned aerial vehicles (UAVs), high-altitude platforms (HAPs), and satellites) and cellular networks, achieving anywhere and anytime connections. However, there are many practical implementation limitations, especially overload power consumption, high probability of blockage, and dynamic propagation environment. Fortunately, the recent technology reconfigurable intelligent surface (RIS) is expected to be one of the most cost-efficient solutions to address such issues. RIS with low-cost elements can bypass blockages and create multiple line-of-sight (LoS) links and provide controllable communication channels. In this article, we present a comprehensive literature review on the RIS-assisted nonterrestrial networks (RANTNs). First, the framework of the RANTNs is introduced with detailed discussion about distinct properties of RIS in NTNs and the two deployment types of RIS, that is, terrestrial RISs (TRISs), and aerial RISs (ARISs), and the classification of RANTNs, including RIS-assisted air-to-ground (A2G)/ground-to-air (G2A), ARIS-assisted ground-to-ground (G2G), and RIS-assisted air-to-air (A2A) communications. In combination with next-generation communication technologies, the advanced technologies in RANTNs are discussed. Then, we overview the literature related to RANTNs from the perspectives of performance analysis and optimization, followed by the widely used methodologies. Finally, open challenges and future research direction in the context of the RANTNs are highlighted. [ABSTRACT FROM AUTHOR]

In this article, one-to-many suboptimal assignments, for various capacity allocation metrics, in high-throughput multibeam satellite systems, under the smart gateway diversity concept, are studied. Furthermore, in the analysis both the offered and requested capacities in the satellite network and the dynamic variations of the atmospheric satellite channels are considered. The objectives, from the literature, of maximization of both minimum and total system’s satisfaction ratios are investigated. Moreover, the dissatisfaction ratio, defined as the multiplicative inverse of satisfaction ratio, is examined as a new proposed metric under the objectives of minimization of both maximum and total system’s dissatisfaction ratios. In order to approach the optimal values of aforementioned binary optimization problems a two-step heuristic approach is described where first a continuous pairing solution is given based on fractional programming theory for the satisfaction problems and the difference of convex programming theory for the dissatisfaction problems. Then, a continuous to discrete feasible matching solution is provided for all cases. The proposed two-step schemes have very low complexity based on simulations and the latter show small relative error compared with the optimal performance of the exhaustive algorithms that have exponential time complexity. [ABSTRACT FROM AUTHOR]

With the advent of the space industry, hybrid satellite-terrestrial cooperative systems (HSTCSs) have drawn significant attention due to their prominent advantages. Besides, a novel modulation technique called spatial modulation (SM), which uses transmit antenna indices as additional information conveying source, is another technology envisioned to be used for next-generation communication systems. In this article, we propose to use SM in an HSTCS scheme consisting of a satellite, multiple terrestrial relays with multiple-input and multiple-output configuration, and a destination node equipped with multiple antennas on the ground. We derive a union bound for the symbol error probability in a fairly exact form and diversity order to shed light on the significant system parameters on the performance. Our theoretical results are validated through Monte Carlo simulations, and it is shown that using the SM technique provides a better error performance in the considered HSTCS system when compared to vertical Bell Laboratories layered space-time and space-time Alamouti codes. [ABSTRACT FROM AUTHOR]

The development of reusable rockets makes it possible to launch a massive number of low earth orbit satellites for Internet access. These satellites are expected to be connected by inter-satellite links (ISLs) to provide global Internet service to end-users on the surface of the earth. From the infrastructure’s perspective, the ISLs can be implemented with lasers, forming the optical satellite networks. The design of terrestrial optical networks is usually traffic-driven, meaning more links/bandwidth are deployed to the traffic-intensive areas. But, the orbiting nature of satellites determines that laser ISLs are also moving at high velocities, making the presence of corresponding bandwidth loosed coupled with a specific area. As a result, the traffic-driven network design methodology will be inapplicable to the optical satellite networks. In this work, we model the optical satellite networks and define the laser ISL planning problem, Accordingly, we propose an ISL removal algorithm to remove parts of the ISLs from the grid-mesh topology to improve the average bandwidth utilization ratio (i.e., bandwidth efficiency) while maintaining networks’ reliability and availability. We conduct a simulation study based on the Starlink constellation to evaluate the grid-mesh topology and to investigate the proposed algorithm’s impact on the network performance. Results show that the bandwidth resource in the grid-mesh topology can hardly be used efficiently and removing certain ISLs properly can improve the bandwidth efficiency of optical satellite networks significantly. We also gain another interesting insight that maintaining too many ISLs will not improve, but degrade the network availability. [ABSTRACT FROM AUTHOR]

Recent years have seen a reemergence of interest and investment in low Earth orbit (LEO) satellite constellations. First proposed in the 1990s, the construction of such constellations was once the hopeful plan of companies, such as Iridium, Globalstar, Odyssey, and Teledesic [1]. Unfortunately, most of these plans never fully came to fruition as the upfront construction costs were unfeasible, and a new competing network implementing fiber optic cables was introduced. These fiber optic cable networks promised users high data rates at a fraction of the construction costs of a satellite network. Today, as worldwide data throughput and coverage requirements increase beyond the capacity of fiber optic cable networks, companies, such as SpaceX, Amazon, ViaSat, OneWeb, and Telesat, are resurrecting the idea of LEO constellations [2]. In order to avoid the fate of their predecessors, these companies must build robust constellations with reliable satellites as launching satellites comes at high costs. One of the most critical systems aboard these satellites is the communication terminal that allows each satellite to communicate with other satellites in the constellation. [ABSTRACT FROM AUTHOR]

5G systems are becoming a reality and the evolution toward beyond 5G and 6G systems is already being defined, also to cope with the ever increasing capacity demanded by on-ground users. This will pose challenging requirements on the feeder link of future satellite systems, which risks to become a bottleneck for the overall system performance. In this article, we propose a novel architecture of linear precoding for the feeder link of a broadcast satellite system operating with full frequency reuse to significantly enhance the achievable capacity. The architecture has been simulated and tested in a challenging multifrequency scenario, where Ku, Ka, Q/V, and W bands have been considered for transmission. The numerical performance analysis and the open issues related to the practical realization of the proposed architecture are also thoroughly discussed. [ABSTRACT FROM AUTHOR]

Polarized scanning atmospheric corrector (PSAC) onboard the HuanjingJianzai-2 (HJ-2) A/B satellites is a cross-track scanning polarimetric remote sensor that measures the intensity and direction of light reflected by the Earth and its atmosphere by nine full polarized spectral bands from near-ultraviolet (near-UV) to shortwave infrared (SWIR). In particular, geolocation accuracy is an important factor for polarization observations. An automatic coastline inflection method (CIM) is implemented for PSAC geolocation error estimation. Over five months of globally middle or low latitude coastline area measurements are used to obtain statistical result. The results of the comparison with the Global Self-Consistent, Hierarchical, High-Resolution Geography (GSHHG) Database show that the PSAC geolocation error is smaller than 0.38 ground sample distance (GSD) or 3.25 km in 95% confidence level. In cross-track direction, the geolocation error estimation is affected by the instrument sampling characteristics, such as spatial response function (SRF). Thus, the correction method is proposed by establishing relationship between measurement radiance in CIM and offset proportion of PSAC GSD. The biases are obviously reduced after correction. [ABSTRACT FROM AUTHOR]

In this paper, we study the physical-layer security of a hybrid satellite-terrestrial network composed of a satellite, multiple terrestrial decode-and-forward (DF) relays and users in the presence of a terrestrial eavesdropper who attempts to tap legitimate information from both satellite and relays. We consider two different scenarios: I) the channel state information (CSI) of wiretap links is known, and II) the CSI of wiretap links is unknown. Accordingly, optimal and suboptimal relay-user pairing schemes are proposed for the aforementioned two scenarios, respectively. Specifically, a relay-user pair maximizing the secrecy rate is chosen as the optimal one to participate in the transmission, where all links’ CSI is used to perform relay-user pairing. However, suboptimal relay-user pairing scheme is designed only relying on the main links’ CSI without requiring wiretap links’ CSI, where a relay-user pair with the maximal transmission rate of main link is selected. Also, closed-form expressions of secrecy outage probability with both integer and rational fading severity parameter are derived in the case of satellite links undergo Shadowed-Rician fading and terrestrial links subject to Rayleigh fading. Furthermore, asymptotic secrecy outage probability analysis is conducted in the high signal-to-noise ratio region. Numerical results reveal that relay-user pairing is beneficial to further improve physical-layer security of the hybrid satellite-terrestrial network. [ABSTRACT FROM AUTHOR]

The Chinese Ocean Color and Temperature Scanner (COCTS) onboard Haiyang-1 (HY-1) series satellites has two thermal infrared channels with the spectrum range of 10.30–11.40 and 11.40– $12.50 \ \mu \text{m}$ for sea surface temperature (SST) observations. To reprocess the Haiyang-1B (HY-1B) COCTS SST, the Bayesian cloud detection and optimal estimation (OE) SST retrieval were applied to COCTS data in this study. The Bayesian cloud detection algorithm that has been developed is based on Bayes’ theorem and uses a simulation of COCTS observations. The MODerate resolution atmospheric TRANsmission (MODTRAN) model was used for the simulation of COCTS brightness temperatures. SSTs were retrieved from COCTS by OE from 2009 to 2011 in the northwest Pacific. A comparison of COCTS OE SST with in situ SST showed that the COCTS SSTs are cooler than buoy measurements by −0.23 °C on average, and the standard deviation (SD) of differences was 0.51 °C. A large component of the mean difference is attributable to the cool skin effect at the ocean surface (typically −0.15 °C to −0.2 °C), with the remainder being attributable to simulation and calibration biases. The mean difference of COCTS OE SST with matched skin temperatures from the advanced along-track scanning radiometer (AATSR) is closer to zero, being −0.09 °C, with an SD of 0.49 °C. These validation results of COCTS OE SST demonstrate that Bayesian cloud detection and OE SST retrieval algorithm work well for improving COCTS SST accuracy and show the potential of these methods to help develop SST products for operational HY-1 satellites: HY-1C and HY-1D. [ABSTRACT FROM AUTHOR]

Over the years, a fixed window for smoothing radiometer cold-space and warm-load counts and processing brightness temperature in calibration has been used for all microwave sounders at European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) and NOAA. Although this practice is based on ground tests and legacy satellites, it remains unclear if this empirical parameter is optimal for in-orbit radiometers, as the space environment is different from the ground and radiometers may drift. We found that the fixed window is not optimal and leads to large noise. We have developed an adaptive window that accommodates channel differences and temporal changes in hardware. Our method has reduced noise by as much as 50% for 183 GHz channels of MetOp-C microwave humidity sounder (MHS). We observed temporal jumps and shifts in counts, gain, and noise of 89 and 190 GHz, and accordingly, the adaptive window can adjust to reduce such an impact. Further analyses reveal that $1/f$ noise plays an important role for determining the adaptive window. $1/f$ noise is nonstationary and gives rise to the fluctuation of counts and gain. As a result, for channels with large $1/f$ noise a short window should be used to mitigate the fluctuation. Our study suggests that an adaptive method has advantages over the fixed method for considering channel differences and time-varying noise. [ABSTRACT FROM AUTHOR]

In this simulation study, the operational GNSS satellites of global positioning system (GPS), Galileo, global navigation satellite system (GLONASS), and BeiDou navigation satellite system (BDS), which are currently in service, are used to transmit signals for global navigation satellite system reflectometry (GNSS-R) measurement. low Earth orbit (LEO) constellations composed of 8, 16, and 24 satellites and with two different patterns, the 2-D-lattice flower constellation (2-D-LFC) and the 3-D-lattice flower constellation (3-D-LFC), are designed considering the tradeoff among three objectives, namely the visited coverage (VC), the revisited coverage (RC) and the total cost of the constellation. Two multiobjective evolutionary algorithms (MOEAs), the nondominated sorting genetic algorithm II (NSGA-II) and the multiobjective evolutionary algorithm based on decomposition (MOEA/D), are applied to solve this multiobjective optimization problem (MOP). The optimal constellations meeting the best tradeoff for the three objectives are picked out, and the distributions of the reflected points observed by them are presented and compared. It is found that NSGA-II generally performs better with respect to the convergence and the diversity of the Pareto solutions. The optimal tradeoff constellations are generally with inclinations of around 67° to 77° and orbital altitudes of nearly 1000 km. For certain number of satellites, the latitudinal and longitudinal distributions of the number of the reflected points observed by the optimal 2-D-LFC and 3-D-LFC are highly similar to each other. Moreover, with the resolution of $0.25^{\circ }\,\,\times \,\,0.25^{\circ }$ , the VCs of the optimal 8-satellite and 16-satellite 3-D-LFCs reach 58.30% and 79.59%, respectively, and the optimal 24-satellite 2-D-LFC and 3-D-LFC can achieve an average revisit time of about 11.0 and 10.2 h, respectively. [ABSTRACT FROM AUTHOR]

The integration between the satellite network and the terrestrial network will play a key role in the upcoming sixth-generation (6G) of mobile cellular networks thanks to the wide coverage and bandwidth offered by satellite networks. To leverage this integration, we propose a proactive traffic offloading scheme in an integrated multi-satellite terrestrial network (IMSTN) that considers the future networks’ heterogeneity and predicts their variability. Our proposed offloading scheme hinges on traffic prediction to answer the stringent requirements of data-rate, latency and reliability imposed by heterogeneous and coexisting services and traffic namely enhanced mobile broadband (eMBB), massive machine-type communications (mMTC) and ultra-reliable low latency communication (URLLC). However, the fulfilment of these requirements during offloading in dynamic IMSTN comes at the expense of significant energy consumption and introduces inherently supplementary latency. Therefore, our offloading scheme aims to balance the fundamental trade-offs first between energy consumption and the achievable data-rate and second between energy consumption and latency while meeting the respective needs of the present traffic. Our findings prove the importance of the cooperation between the multi-satellite network and the terrestrial network conditioned by traffic prediction to enhance the performance of IMTSN in terms of latency and energy consumption. [ABSTRACT FROM AUTHOR]

Due to the considerable fading arising from the long-distance transmission between satellites and terrestrial terminals as well as the complex geographic environments on the earth, aerial relays have been designed to facilitate the information delivery between the satellites and terrestrial terminals when reliable direct data transmissions cannot be achieved. In this paper, a cooperative satellite-aerial-terrestrial network (CSATN) system including a satellite (S), an aerial relay (R), and a terrestrial receiver (D) is considered, while decode-and-forward relay scheme is adopted. Specifically, inspired by the beam shape of the transmission signal from S, we model the operation space of R as a circular truncated cone to accurately reflect the practical large-scale transmission scenarios, the height of which is decided by the upper and lower limitations of the operation height of R. Thus, considering the randomness of R and D and employing geometric probability theory, the exact and asymptotic outage probability (OP) of S-R, S-D, and R-D links is studied, and then the end-to-end outage performance of CSATN is investigated accordingly by using approximation method. Finally, numerical results are presented to validate our proposed analysis. [ABSTRACT FROM AUTHOR]

Satellite-aerial communication (SAC) is the most necessary and reliable way to bridge the aerial terminals with their remote command and control center when terrestrial relay infrastructure is unavailable. However, as an inescapable obstacle, adjacent space interference from neighboring satellites unavoidably leads to the loss of the performance of SACs. To uncover the impacts of space interference, in this paper, a SAC system including a satellite (S), an aerial platform (D), and a space interference (I) is considered. Specifically, S operates in a circular orbit and I, which is randomly distributed in the neighboring space around S, produces a jamming signal to interfere with the information delivery between S and D. Considering the randomness of S and I and employing geometric probability theory, an approximate and asymptotic outage probabilities of the considered SAC system are studied. Moreover, the multi-interference scenario is investigated accordingly. Finally, numerical results are presented to validate our proposed analysis and some insightful conclusions are achieved to reveal the effects of spatially random space interference on SAC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article proposes a novel atmospheric data-driven Q-band satellite channel model using two artificial neural networks, i.e., multilayer perceptron and long short-term memory (LSTM), to estimate real-time channel attenuation at Q-band via a set of atmospheric parameters. Seven atmospheric parameters for modeling satellite channel attenuation are selected by the least absolute shrinkage and selection operator (LASSO) algorithm from 14 commonly used atmospheric parameters. Simulation results demonstrate that the multilayer perceptron-based atmospheric data-driven Q-band satellite channel model via those seven atmospheric parameters is more accurate and less complex than that via the 14 atmospheric parameters. Meanwhile, the accuracy performance of multilayer perceptron- and LSTM-based atmospheric data-driven Q-band satellite channel models, such as absolute errors and mean-squared errors (MSEs), is discussed and analyzed. The complexity of multilayer perceptron and LSTM in this model, such as training time, loading time, and estimation time, is also investigated. It can be seen that the estimated channel attenuation can well align with the measured channel attenuation. [ABSTRACT FROM AUTHOR]

Optical Intersatellite Links (OISLs) are being considered for future Global Navigation Satellite System (GNSS) constellations. Thanks to OISLs, the constellation incorporates improved clock synchronization and precise ranging among the satellites, which are essential features to achieve accurate time and orbit determination. High data rate communications within the space segment also reduce ground segment dependency, by means of decentralized access to information. However, the dual optimization of data and navigation performance metrics requires a careful assignment of OISLs to the available laser communication terminals on-board. To this end, we present a contact plan design scheme based on a degree constrained minimum spanning tree heuristic applied to such OISL-enabled GNSS (O-GNSS) constellations. Results on the Kepler system, a novel GNSS proposal, show that a fair distribution of connectivity among the constellation can be ensured while optimizing its range-based position estimation capabilities (PDOP). A PDOP improvement of 85 % is reached on average by the optimized contact plan with respect to a generic scheduler that disregards the geometrical distribution of the chosen links. [ABSTRACT FROM AUTHOR]

As the advanced satellite network can provide extremely diverse data to various types of users, it is of vital importance to achieve data security using encryption over satellite channels. However, since the avalanche effect makes encryption techniques vulnerable to bit errors in the wireless channel, a more powerful encryption technique is required for data confidentiality. In addition, an efficient method for exchanging encryption keys between receivers and transmitters should be capable of managing a large scale of satellites in the network. In this article, we propose a novel superencryption method of joint encryption and channel coding, cipher feedback-advanced encryption standard (CFB-AES)-TURBO, which combines AES in the upper layer and turbo coding as bulk encryption in the physical layer. Because we introduce turbo coding in the CFB mode with AES for each block, our scheme can accomplish dual goals of data protection and bit error correction. We select an encryption block size to maximize throughput based on channel conditions and the security level required for a user, and present a key exchanging solution. We derive processing time gains and analyze computational complexity of the CFB-AES-TURBO. The bit error rate performance improvement with about 12-dB coding gain is achieved. We also enhance the security performance by $10^{15 000}$ times and provide indistinguishability. Finally, we analyze the total expected latency, suggest the minimum key refresh time of geostationary Earth orbit satellites. [ABSTRACT FROM AUTHOR]

In civil or military applications, a transmitter on Earth may utilize different means of communications. A typical example is the naval craft, which often radiates very high frequency signals received by a satellite system and high frequency signals received by land-based observers. This article concentrates on the combination of land-based and satellite-based over-the-horizon (OTH) geolocations. A quadratic constrained weighted least-squares optimization model for the combined geolocation is established and a differentiable exact penalty solution is developed to locate the OTH transmitter in an iterative manner, which is shown to have robust convergence performance. Theoretical analysis is presented, which involves the Cramér–Rao bound for combined geolocation under the constraint of ellipsoidal Earth model and the closed-form expression of mean square error for the proposed method. Numerical examples are provided to validate our theoretical analysis and illustrate that the proposed method outperforms other geolocation methods in a wide range of scenarios. [ABSTRACT FROM AUTHOR]

With the rapid development of nongeostationary orbit (NGSO) constellation networks, the co-frequency interference between geostationary orbit (GSO) and NGSO systems is becoming increasingly inevitable. Due to the characteristics of complex multimission planning and the large spatial and temporal scale of NGSO constellations, it is difficult to maximize the system performance under the constraints of GSO networks' interference protections. In this article, based on an iterative greedy algorithm, a modified Q-learning approach in reinforcement learning (RL) is proposed to upgrade the system performance of NGSO network. Compared with the traditional RL algorithms, this modified approach has the advantages of improving the system performance and meeting the aggregate interference protections of GSO networks, by redefining the actions, rewards, and Q-tables. Simulation results show that by adopting the proposed algorithm, all NGSO links timely select and flexibly adapt their actions, including access objects, transmission powers, communication rates, as well as modulation and coding schemes, to achieve more global rewards with co-frequency interference constraints. [ABSTRACT FROM AUTHOR]

Enabling global Internet access is challenging for cellular-based Internet of Things (IoT) due to the limited range of terrestrial network services. One viable solution is to deploy IoT over satellite systems for coverage extension. However, operating a hybrid satellite–terrestrial network might incur high satellite bandwidth consumption and excessive service latency. Aiming to reduce the content delivery latency from the Internet-connected gateway to the users, this article proposes a two-tier cache-enabled model with full-duplex transmissions where content caches are deployed at the satellite and ground station. A closed-form solution for the successful delivery probability (SDP) of the files is derived considering the requested content distributions and channel statistics. Then, the SDP performance under common caching policies can be evaluated. The results are also used to optimize cache placement under caching capacity constraints. Numerical results demonstrate the performance improvements of the proposed system over those of single-tier cache-aided and half-duplex transmission systems. [ABSTRACT FROM AUTHOR]

Fixed Satellite Services (FSS) used to be alone at the C-Band spectrum in most countries. Since the deployment of 5G in many countries (i.e., 3.3–3.6 GHz), FSS is not the exclusive system in the C-Band anymore. In order to minimize the detrimental interference for the FSS to allowable levels, regional exclusion zones of maximum radiated power in 5G base stations (BS) are proposed and evaluated. In this paper, a measurement campaign has been carried out, and an analysis of the interference has been studied. A filtering model, namely Filter to Remove Broadband Interference 5G (FIREBRING), is proposed and analyzed concerning the carrier-to-noise ratio (C/N). Moreover, this paper focuses on the evaluation of the 5G interference into the FSS. The proposed solution deployed an Low-Noise Block (LNB) with a band frequency of 3.7 to 4.2 GHz to test the satellite down-conversion signal at the receiver. The paper offered a complete analysis of the 5G signal, taking into account the implications of out-of-band emissions, potentially LNB saturation into FSS receiver, and the repercussions of the deployment of the 5G BS active antenna systems. With the LNB and down-converter in place, it can be found that the signal interference between 1.450 GHz and 1.550 GHz, is nearly 18 dB. [ABSTRACT FROM AUTHOR]

In this paper, we consider an imperfect hardware hybrid satellite-terrestrial network, where the satellite communication with a ground user equipment (UE) is aided by the multiple amplify-and-forward 3-D mobile unmanned aerial vehicle (UAV) relays. Herein, we consider that all transceiver nodes are corrupted by the radio frequency hardware impairments (RFHI). Furthermore, a stochastic mixed mobility model is employed to characterize the instantaneous location of 3-D mobile UAV relays in a cylindrical cell with UE lying at its center on the ground plane. Taking into account the aggregate RFHI model for satellite and UAV relay transceivers and the random 3-D distance-based path loss for UAV relay–UE links, we investigate the outage probability and corresponding asymptotic outage behavior of the system under an opportunistic relay selection scheme in a unified form for shadowed-Rician satellite links’ channels and Nakagami-m as well as Rician terrestrial links’ channels. We corroborate theoretical analysis by simulations. [ABSTRACT FROM AUTHOR]

In this paper, we study a joint user pairing and power allocation problem in the 5th generation (5G) satellite random access (RA) networks, where some user equipments (UEs) are assisted by relay satellite UEs to establish satellite access. We aim to maximize the total sum rate of the RA system by jointly optimizing user pairing and power allocation. The above joint optimization problem is a non-convex mixed-integer problem, which is challenging to solve. To solve this problem, we decompose it into two subproblems. Firstly, a problem for optimal user pairing is formulated to find the optimal user pairing relationship. To solve this subproblem efficiently, a Q-learning based distributed user pairing algorithm (QL-DUPA) is proposed, which converts the user pairing problem to a Q-learning process. The Q-learning process can achieve a near-optimal solution and is practically feasible. Then, a problem for optimal power allocation is formulated to find the optimal power allocation coefficients in each user pair. The subproblem is convex and the optimal solution is obtained using convex optimization. Next, a satellite RA scheme with collision resolution is proposed based on the joint optimization of user pairing and power allocation, and we analyze its total sum rate. Simulation results show that the proposed satellite RA scheme with collision resolution greatly outperforms the existing schemes in terms of total sum rate. [ABSTRACT FROM AUTHOR]

This paper considers a dual-hop cooperative satellite-unmanned aerial vehicle (UAV) communication system including a satellite (S) and a group of cluster headers (CHs) which are respectively with a group of uniformly distributed UAVs. Specifically, the CHs serve as aerial decode-and-forward relays to forward the information transmitted by the S to the UAVs. Moreover, free-space optical (FSO) and radio frequency (RF) technologies are respectively adopted over S-CH and CH-UAV links to exploit the high directivity of FSO over long-distance transmission and the omnidirectional coverage ability of RF. The positions of the CHs in the three-dimensional space follow the Matérn hard-core point processes type-II, in which each CH cannot be closer to another by less than a predefined distance. Three different cases over CH-UAV links are considered during the performance modeling: interference-free, interference-dominated, and interference-and-noise. Then, the coverage performance of the S-CH link and the CH-UAV link in the aforementioned three cases is studied and the closed-form analytical expressions of the coverage probability (CP) over both two links are derived. Additionally, the asymptotic expressions for the CP over S-CH link and CH-UAV link in the interference-free case are derived. Finally, numerical results are provided to validate our proposed analytical models and thus some meaningful conclusions are achieved. [ABSTRACT FROM AUTHOR]

Integrated satellite-terrestrial networks (ISTNs) are one of the new research directions for future 5G networks. Satellite coverage enables 5G communication throughout most of the world. However, the security concerns associated with the inherent broadcast nature of satellites are rarely considered. As an emerging security paradigm in 5G terrestrial communication, physical layer security (PLS) could have potential applications in an ISTN. This article describes the challenges of applying PLS to an ISTN, including correlated channels, co-channel interference, multiuserand multi-eavesdropper scenarios, and reliability concerns. The impacts of these challenges on the security performance of an ISTN and the corresponding solutions are analyzed for further comparison. Finally, we conclude the article by predicting future trends of PLS in an ISTN. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the secure vehicle communications in cybertwin-enabled integrated satellite-terrestrial networks, where the digital twins (DTs) in the cybertwin space reflects the physical entities (i.e., satellite, terrestrial base station (BS), and vehicles). Particularly, considering the channel similarity between different satellite links versus the randomness difference in terrestrial links, it is challenging to reach the secure transmission in satellite and terrestrial links independently with limited resources. Considering the information exchange in the cybertwin space can support an information sharing between such physical entities, the secure transmission design by using the heterogeneous satellite-terrestrial resources can be conducted from a global perspective. With the channel feedback information of vehicles gathered at the cybertwin, the co-channel interference caused by the spectrum sharing is leveraged to assist the implementation of secure transmissions in the integrated satellite-terrestrial vehicle network. Specifically, the problems of maximizing the secrecy rate of satellite-to-vehicle link and the terrestrial BS-to-vehicle link are formulated, respectively. To solve such two problems, we propose two corresponding beamforming optimization approaches, where semi-definite relaxation (SDR) and semi-definite programming (SDP) are adopted due to the non-convexity. In addition, the tightness of SDR is proved and the complexity of proposed approaches is also analyzed. Finally, extensive numerical simulations are carried out and results show the effectiveness of our proposed approach. [ABSTRACT FROM AUTHOR]

Internet-of-Things (IoT) is being widely embraced with the number of connected devices growing rapidly. Moreover, IoT applications are emerging in diverse verticals such as connected cars, connected factories, and smart agriculture. For new business models, in order to meet key network performance indicators, connectivity must be flexible and agile. An integrated satellite-aerial-terrestrial network (I-SAT) has recently stimulated interest in providing wireless communication due to its high maneuverability, versatile deployment, and pervasive connectivity. The resource planning, task distribution, and action management of an I-SAT can be accomplished through effective acquisition, coordination, transmission, and aggregation of diverse information. This paper considers an I-SAT network, in which multiple unmanned aerial vehicles (UAVs) with aerial stations and a terrestrial base station (BS), in a cognitive setting, in the presence of satellite-receiver communication, are deployed to support smart vehicles on the ground. By taking into account different limitations and Quality of Service (QoS) constraints, the goal is to maximize the average throughput among users by jointly optimizing user association, BS/UAV transmission power, and UAV trajectory. The formulated problem is a non-convex optimization problem with a complicated expression that is hard to solve. To tackle this problem, an alternating iterative algorithm based on the block descent method is proposed. Precisely, the problem is subdivided into three subproblems, transmitter-vehicle association optimization, BS/UAV power allocation optimization, and UAV trajectory control. Then, in an iterative process, these subproblems are solved sequentially. The proposed solution uses a segment-by-segment technique, which breaks the complete UAV flight trajectory into smaller time segments to reduce computation time when the network service period is considerable. As a result, each time segment’s optimization can be solved more quickly. Furthermore, the paper presents the results of network simulations carried out to assess the efficiency of the proposed solution. The findings show that the presented scheme outperforms different benchmark schemes in terms of the average user throughput when observing multiple different scenarios. [ABSTRACT FROM AUTHOR]

The integrated satellite-terrestrial network is promising to provide global broadband communication service. However, the long propagation delay of satellite-terrestrial links will lead to high communication delay when users access the Internet via satellites. In this paper, we investigate the cooperative multilayer edge caching in the integrated satellite-terrestrial network to reduce the communication delay, in which the base station cache, the satellite cache, and the gateway cache cooperatively provide content service for ground users. We first propose the three-layer cooperative caching model of the network, based on which we analyze the content retrieving process and derive the cache hit probability for different caching locations. Considering limited cache sizes, we formulate the content placement problem to minimize the average content retrieving delay of users. Then, two caching strategies, the non-cooperative caching strategy and the cooperative caching strategy, are proposed with exhaustive theoretical analysis. By introducing the concept of delay reduction gains, the optimal caching strategies are obtained based on the proposed iterative algorithms. Finally, numerical results are presented to demonstrate the performance of the proposed cooperative caching architecture and the caching strategies. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the outage performance of an uplink (UL) non-orthogonal multiple access (NOMA)-based hybrid satellite-terrestrial relay network (HSTRN), in which two users communicate with the satellite through a decode-and-forward (DF) relay due to the lack of direct link. To provide a comprehensive yet hitherto unexplored outage analysis framework, we consider a more generalized channel model, i.e., the terrestrial and satellite links, respectively, undergo $\alpha -\mu $ and $\kappa -\mu $ shadowed fadings. Under fixed power allocation (FPA) for both multiple access phase and relaying phase, we firstly study three successive interference cancellation (SIC) decoding schemes, of which the first two are refined from existing schemes, while the third one, named as extended SIC (ESIC), is proposed in this paper to satisfy the quality of service (QoS) decoding criterion, which is shown to offer better performances for both users as compared to the former two SIC schemes. We also propose a novel dynamic power allocation (DPA) scheme for the multiple access phase, termed as enhanced DPA (EDPA), to overcome both users’ error floor (EF) issue yet provide better user fairness than the conventional DPA in the literature. We then analyze the exact and asymptotic outage performance for three SIC and the EDPA schemes under the generalized channel setting. It is shown that both the proposed ESIC and EDPA can circumvent the EF issue and moreover, each has its own advantage in terms of the diversity order (DO). Our results also reveal that there exists a trade-off between ESIC and EDPA, since the former requires a premise on users’ targets rates to overcome the EF and once this premise is satisfied, no DO degradation will occur, while the latter does not entail such a premise but may face potential DO degradation. Finally, we present numerical results to verify the theoretical analysis, manifest the impacts of key parameters on the system performance, and demonstrate the advantages of our proposed network over other benchmarks. [ABSTRACT FROM AUTHOR]

In this paper, we consider downlink low Earth orbit (LEO) satellite communication systems where multiple LEO satellites are uniformly distributed over a sphere at a certain altitude according to a homogeneous binomial point process (BPP). Based on the characteristics of the BPP, we analyze the distance distributions and the distribution cases for the serving satellite. We analytically derive the exact outage probability, and its approximated expression is obtained using the Poisson limit theorem. With these derived expressions, the system throughput maximization problem is formulated under the satellite-visibility and outage constraints. To solve this problem, we reformulate it with bounded feasible sets and propose an iterative algorithm to obtain near-optimal solutions. Simulation results perfectly match the derived exact expressions for the outage probability and system throughput. The analytical results of the approximated expressions are fairly close to those of the exact ones. It is also shown that the proposed algorithm for the throughput maximization is very close to the optimal performance obtained by a two-dimensional exhaustive search. [ABSTRACT FROM AUTHOR]