Non-geostationary Orbit Satellite Research Articles

Connecting space missions through NGSO constellations: feasibility study

A satellite internet provider (e.g., Starlink, OneWeb, O3b mPOWR), despite possessing the capability to provide internet services to on-ground users in a global scale, can dramatically change the way space missions are designed and operated in the foreseeable future. Assuming a scenario where space mission satellites can access the internet via a space internet system, the satellite can be connected to the network permanently (24 × 7) and act as mere terminal independently from its location. The ability to communicate with the satellite on-demand has the potential to improve aspects such as real-time tasking, outage minimization, operation cost, and dependency on the ground. This paper performs a feasibility study on the concept of connecting space missions to the network through commercial mega-constellations. This study includes a review of existing and near-future space internet systems, identification of candidate space missions for the aforementioned concept, a necessary adaptation of existing Commercial off-the-shelf (COTS) terminals to be plugged into space mission satellites, assessment of communication performance, and investigation of the legal aspects of the radio frequency (RF) spectrum usage. The paper evidences that the concept is practically possible to implement in the near future. Among the studied space internet systems (i.e., Starlink, OneWeb, O3b mPOWER), O3b mPOWER stands out as the most suitable system allowing permanent coverage of low earth orbit (LEO) space missions with data rates that can reach up to 21 Mbps per satellite. Although the concept is very promising and can be implemented in the near future, our investigations show that some regulatory aspects regarding the RF usage should be solved for future exploitation of connecting space missions through NGSO (Non-Geostationary Satellite Orbit) constellations.

Interference analysis between NGSO systems based on the beam coverage and link angle

The existing interference assessment methods usually consider the special scenario of earth station coincidence. However, in practice, earth stations such as gate stations are sparsely distributed and often do not coincide. Aiming at the problem of how to efficiently calculate the co-frequency interference between Non-Geostationary Satellite Orbit (NGSO) systems with high complexity and a large amount of data, the influencing factors of interference scenes between NGSO systems with non-earth station coincidence are analyzed. The time-varying expression of the bit error rate (BER) of the interference evaluation index to measure the system performance is derived. An interference analysis method based on the beam coverage and link angle is proposed. In this method, four interference time-varying parameters are reduced to two. One of them is associated with the distance between earth stations, which is used to rapidly evaluate the probability of harmful interference between NGSO systems. It provides a reference for the construction of the spacing of earth stations.

Virtual Network Embedding for NGSO Systems: Algorithmic Solution and SDN-Testbed Validation

Non-Geostationary Orbit satellite (NGSO) is an essential element in 5G Non-Terrestrial Networks (NTNs), which can operate either independently or as complementary parts to terrestrial systems to boost the network capacity, coverage and resilience. Due to the highly dynamic topologies, one of the challenges in NGSO is how to harmonize the network virtualized resources to satisfy diverse quality of service requirements in an efficient manner. In this paper, we investigate Virtual Network Embedding (VNE) for integrated NGSO-terrestrial systems while considering dynamic topologies. We propose a Mixed Binary Linear Programming (MBLP) formulation for a Dynamic Topology-Aware VNE (DTA-VNE) algorithm. Given priori information about the network’s evolution over time, DTA-VNE plans the embedding for each Virtual Network Request (VNR) over its lifetime. In a highly dynamic environment, the VNE decision can be varying for different VNRs at the expense of a considerable cost of migrating traffic and reconfiguring resources. DTA-VNE aims at minimizing this migration cost to avoid unnecessary re-mappings. To tackle the exponential complexity of the MBLP, we propose an efficient algorithm based on relaxation approaches (DTA-R) to solve large-scale problems. In numerical results, the effectiveness of the proposed DTA-R is demonstrated with much lower migration cost than the conventional implementations. The trade-off between the computation time and migration cost of DTA-R is studied. Finally, we test DTA-R and the baselines in our developed MultI-layer awaRe SDN-based testbed for SAtellite-Terrestrial networks (MIRSAT) to precisely quantify the packet lost for each migration. DTA-R proved to reduce the packet lost by ~2.5-5% compared to baselines.

Interference Analysis of Coexisting 5G Networks and NGSO FSS Receivers in the 12-GHz Band

Despite the promising attributes of the 12 GHz band for expanding terrestrial 5G network’s capacity and coverage, interference between coexisting networks remains a major issue. This paper develops a simulation-based evaluation framework and investigates the harmful interference between the 5G radio links and incumbent fixed non-geostationary satellite orbit (NGSO) fixed satellite services (FSS) receivers of the 12 GHz band. A variety of features including actual deployment locations of 5G base stations (BSs) and fixed NGSO FSS receivers, industry-standardized beamforming at BSs, directional signal reception at FSS receivers, realistic propagation channels with obstruction from buildings, and channel scheduling at 5G BSs are incorporated in the interference study. Simulation results conducted in a realistic urban-micro deployment scenario confirm that the terrestrial 5G networks with directional BSs can coexist in the 12GHz band by suitably selecting exclusion zone’s radius around the FSS receiver. Simulation results also show that interference in the coexisting network can be notably reduced by appropriately activating BSs in the 12 GHz band based on their locations and surroundings.

Joint Optimization of Energy and Delay in NGSO Satellite Constellations: Cached Data Sharing Based on Spreading Dynamics

Edge caching has developed rapidly due to its ability to optimize both service delay and energy consumption significantly by reducing the traffic load in backhaul links. However, the mobility of edge devices will cause the reduction of the cached data available and the disappearance of the aforementioned advantages. This paper is intended for the cache strategy in the non-geostationary orbit (NGSO) satellite constellations and formulates an effective data sharing strategy between NGSO satellites for avoiding the invalidation of cached data. The density of cached data is a key indicator for the sharing strategy, because excessive sharing can increase the probability of cache hits at the expense of waste of resources and vice versa. Spreading dynamics is a physical model to describe the interaction of individuals in complex networks, which is helpful to predict the decisive threshold in the system. Therefore, this paper identifies the relationship between satellite speed, constellation structure, data size and hit probability, calculating a decisive threshold for the effective data density based on spreading dynamics. Meanwhile, the ideas of water-filling algorithm and reinforcement learning algorithm have been improved and applied to the data sharing strategy limited by the satellite cache space. Finally, the proposed strategy is compared with the traditional strategy in a variety of scenarios, and the results verify the effectiveness of the proposed optimization strategy in terms of energy consumption and service delay.

Adaptive Random Access and Data Transmission Scheme With Mixed Traffic in NGSO Satellite Networks

In non-geostationary orbit satellite networks, the resource is limited and the traffic under each satellite is in variation due to the motion of satellites and the non-uniform traffic on the ground. Generally, the uplink communication is guaranteed by successful random access (RA) and sufficient data transmission (DT) resources for various traffic types. Different traffic types usually have different requirements for resources, and joint resource management for mixed traffic tries to meet the needs of various traffic types at the same time and may improve uplink resource efficiency. However, existing strategies have not given integrative consideration to jointly allocate resources for RA and DT under dynamic mixed traffic demands, which leads to inefficient network resource utilization. Considering such a problem, we propose an adaptive random access and data transmission scheme for NGSO satellite networks in the mixed traffic scenario, considering two types of users, i.e., real-time users and best-effort users. Specifically, the utility functions of different types of users are introduced, and a utility-based access control and resource allocation algorithm is developed by solving the network utility maximization problem. Our scheme aims to achieve optimal uplink network utilization by adaptively controlling random access and allocating resources according to the dynamic demands of mixed traffic. Simulation results show that the proposed scheme outperforms other methods in terms of network utility, and exhibits near-optimal performance.

Satellite constellation design for 5G wireless networks of mobile communications

SummarySatellite constellation design plays an important role in satellite networks. Network constellation system design can affect the effectiveness of current improvements of the communications link and the management of the entire network. The power requirement of the mobile stations and ground stations is very high in a geostationary Earth orbit communication system, which means the terrestrial terminal is hard to be made handheld for fifth generation mobile communications. The emergence of nongeostationary orbit satellites such as low Earth orbit satellites greatly compensates for the disadvantage of geostationary Earth orbit satellites. Based on the classical constellation design method, the orthogonal circular orbit constellation is proposed. The design objectives considered here are the following: global Earth coverage by low Earth orbit satellites, the duration of continuously covering one mobile station by one satellite is more than 9.57 min, the access satellite link duration time of the mobile station is more than 4.79 min, and the number of satellites and orbits is to be minimum.

A Framework for Assessing the Interference from NGSO Satellite Systems to a Radio Astronomy System

As the number of non-geostationary orbit (NGSO) satellites continues to grow, interference with other communication systems, including radio astronomy systems (RASs), is becoming increasingly critical. In this study, an interference simulation framework was developed to analyse the potential impact of NGSO systems on RAS in accordance with the relevant International Telecommunication Union (ITU) regulations and recommendations. In addition to the simulation of interference generated by individual NGSO satellite systems, the framework also supports the analysis of aggregate interference from multiple NGSO satellite systems. By inputting satellite system parameters, including constellation configuration, user distribution and beam scheduling strategy, the framework is able to obtain interference probability distributions for a typical RAS ground station at different latitudes and observation directions. The simulation results provide a reference for the analysis of interference from NGSO satellite systems to RASs, and can also be used to guide the development of strategies to mitigate harmful interference to RASs.

NGSO Satellites Beam Hopping Strategy Based on Load Balancing and Interference Avoidance for Coexistence With GSO Systems

Non-geostationary orbit (NGSO) satellite communication system plays an important role in achieving seamless global coverage and addressing the digital divide. The uneven distribution of terrestrial users and the high mobility of NGSO satellites put forward higher requirements for resource management. In this letter, we propose a multi-satellite beam hopping scheme based on load balancing and interference avoidance, where the complicated multi-satellite joint beam hopping problem is decomposed into two sub-problems, namely the satellite-cell assignment problem and joint multi-satellite beam hopping pattern design problem. On the one hand, we rationally assign cells to different satellites for balancing the traffic load among satellites and reducing the interference to geostationary earth orbit (GSO) ground stations. On the other hand, an iterative multi-satellite beam hopping pattern design scheme based on minimizing co-channel interference criterion is adopted to achieve on-demand service. Simulation results indicate that the performance of load balancing and interference avoidance are improved compared to the maximum elevation angle access strategy. Besides, the proposed scheme outperforms other benchmarks in terms of the traffic satisfaction rate, and the optimality gap is only 0.1%.

Multi-Satellite Beam Hopping Based on Load Balancing and Interference Avoidance for NGSO Satellite Communication Systems

Due to the non-uniform distribution of the ground traffic demand and the high mobility of non-geostationary orbit (NGSO) satellites, how to make full use of the limited beam resources to serve users flexibly and efficiently is a brand-new challenge for NGSO communication systems. In order to achieve efficient spectrum utilization, the combination of full frequency multiplexing and beam hopping is a major trend in future satellite communication systems. However, conventional beam hopping methods are mainly based on geostationary satellites, which do not take into account the interference between satellites. This paper proposes a multi-satellite beam hopping algorithm based on load balancing and interference avoidance, which takes advantage of the multiple coverage features in the NGSO constellation and avoids intra-satellite interference and inter-satellite interference by designing beam-hopping patterns with spatial isolation characteristics. In particular, we decompose the multi-satellite beam hopping problem into three sub-problems, which are the multi-satellite load balancing problem, the single-satellite beam hopping pattern design problem, and the multi-satellite interference avoidance problem. Simulation results demonstrate that the proposed method reduces the load gap among satellites by about 72.5% and the average traffic satisfaction rate can reach 81.4%. Besides, our method has the lowest unmet capacity compared with other benchmarks, achieving better offered-requested data match.

System Dynamics and Tradeoffs in Radio Astronomical Data Transport of an Integrated Satellite Communication and Radio Astronomy System

This paper considers an integrated mega-constellation non-geostationary orbit satellite system which provides both communication and radio astronomical observation (RAO) services. We focus on RAO data transport from the RAO-conducting satellites (called source satellites) to the ground gateways where each gateway is directly connected to a certain number of satellites (called destination satellites). We introduce a generalized inter-satellite link (ISL) connection model which extends the existing approach of adjacent-only ISL connections to include non-adjacent ISL connections. This model is implemented with an upper limit on the ISL distance which can be adjusted for performance tradeoffs. Next, we develop analytical expressions to study two impacts of satellite dynamics on the RAO data transport. The first one concerns with the beam misalignment of individual ISL hops. The second one corresponds to whether destination satellites move outside the gateway coverage during the end-to-end delay interval of a data packet transport. Furthermore, we introduce delay, energy, and spectrum usage performance metrics and evaluate them to yield performance tradeoff guidelines. A simplified data transport path model is also presented to facilitate analytical performance evaluation and initial system design settings. Then, we present a new RAO data transport design which incorporates system dynamics and desired performance tradeoffs. Finally, analytical and simulation results and discussions are presented.

The Economic Benefits of Updating Regulations that Unnecessarily Limit Non-Geostationary Satellite Orbit Systems

The Economic Benefits of Updating Regulations that Unnecessarily Limit Non-Geostationary Satellite Orbit Systems

The Economic Benefits of Updating Regulations That Unnecessarily Limit Non-Geostationary Satellite Orbit Systems: Part II

The Economic Benefits of Updating Regulations That Unnecessarily Limit Non-Geostationary Satellite Orbit Systems: Part II

Adaptive Access Control and Resource Allocation for Random Access in NGSO Satellite Networks

In non-geostationary orbit (NGSO) satellite networks, users perform random access (RA) to establish connections. Due to the non-uniform traffic demands of RA in time and space, dynamic access control and resource allocation methods with low signaling overhead and high RA efficiency are required, where the RA efficiency is denoted as the number of successfully accessed users per resource block. Existing dynamic adjustment methods provide a feasible approach to improve RA efficiency with short update intervals, but the frequent updates of these methods result in high signaling overhead. Compared with the short-term update, update with a given longer interval could reduce update frequency, while it will lead to a reduction in RA efficiency for the accuracy of long-term prediction decreases. Hence, to improve RA efficiency and decrease signaling overhead at the same time, we propose a new adaptive access control and resource allocation scheme in this paper, where the length of update interval is adaptive to the changes in traffic. First, average random access efficiency (ARAE) is defined to evaluate the RA efficiency between each update. Then, to decrease signaling overhead while keeping high ARAE, adaptive access control and resource allocation scheme is proposed, where the adaptive traffic prediction step is introduced to forecast future traffic with adaptively selected update interval, and the access control and resource allocation step is designed to maximize ARAE based on forecasted traffic. Finally, the effectiveness of the proposed scheme is corroborated by simulations, which indicate our scheme is adaptive to varying demands and outperforms other methods with high ARAE and low signaling overhead.

Dynamic Routing Strategy for Directed Transmissions of High-Valued Contents in NGSO Satellite-Based Internet

Nongeostationary orbit (NGSO) satellite-based Internet is an important part of the future network. One single NGSO satellite has the characteristics of high-speed movement, small coverage area, and short connection time; therefore, the method of multisatellite collaboration is adopted in NGSO satellite-based Internet. Caching is an effective technique to reduce the transmission load and delay, especially for high-value content. However, the traditional caching cannot be applied to the NGSO satellite network directly due to the frequent switching of service satellites. As a result, some high-valued cached data need to be transmitted among satellites, such that an effective routing between the source and destination node needs to be established orderly in the satellite network. This paper proposes a dynamic routing strategy based on multilayer satellite architecture for unicast and multicast scenarios, respectively. For the unicast, a routing strategy based on Q -learning is proposed to optimize bandwidth and delay simultaneously, and the effectiveness is verified by the comparison against the traditional routing strategy. For the multicast, an advanced Q -learning multicast routing algorithm based on spatial directionality is proposed to optimize the overall transmission success rate and resource cost, and the superiority of the proposed routing strategy is verified by simulation results.

A Beam Search-Based Channel Allocation Method for Interference Mitigation of NGSO Satellites with Multi-Beam Antennas

In the past few years, non-geostationary orbit (NGSO) satellite communication constellations have regained popularity due to their conspicuous advantages. Nevertheless, with more NGSO satellites getting involved in communications, the spectrum resources should become much more scarce. Multi-beam high throughput satellite and spectrum sharing are two major techniques in communication design. The two techniques can significantly mitigate interference and highly augment the capacity of the communication system. Thus, they are commonly used in satellite communication systems nowadays. With a massive number of NGSO satellites comprising the communication system and moving in their orbits, interference scenarios are pretty complex. In this article, the relationship between the level of interference and the beam distance is deduced. Moreover, for beams with different tilting angles, the different off-axis angles may correspond to the same beam distance, which is directly related to the interference level. Through the interference analysis, we propose a channel allocation method that uses a beam search algorithm to optimize the channel allocation problem and achieves outstanding time efficiency. The performance of the proposed method is validated by a coexisting scenario of the geostationary orbit and NGSO satellite communication systems. The results show that the level of interference can be largely mitigated, and the capacity of communication systems is significantly augmented.

Beam Pointing Optimization Based Downlink Interference Mitigation Technique Between NGSO Satellite Systems

This letter proposes a novel interference mitigation technique for spectral coexistence between large-scale non-geostationary orbit (NGSO) satellite systems by optimizing satellite antenna beam pointing. Firstly, a dynamic exclusion zone of NGSO satellite antenna beam pointing is defined. Secondly, we transfer frequency compatibility problem between NGSO systems into a constrained nonlinear multivariate optimization problem considering the joint effect of link distances as well as angles between links and solve it using Genetic Algorithm (GA). Then we select actual working parameters of Starlink and OneWeb satellite systems to verify the effectiveness of proposed interference mitigation technique in the worldwide. The available time of the interfered system is up to 98.5% of total simulation run time after interference mitigation. The results show that the proposed interference mitigation technique can effectively mitigate the interference between NGSO satellite systems and guarantee signal to interference plus noise ratio (SINR) at the interfered earth station.

Interference analysis simulation method based on spatial position probability for NGSO communication constellation system

Aiming at the problem of co-frequency interference between non-geostationary orbit (NGSO) constellation system and geostationary orbit (GSO) satellite system, aggregated interference analysis model for NGSO multi-beam constellation system is established, and the dual step algorithm of spatial position probability is proposed for interference analysis simulation based on relevant ITU recommendations and reports. This method discretizes the spatial position of NGSO reference satellite by dividing the latitude and longitude grid. Then the probability density function of interference-to-noise ratio (I/N) can be obtained. Taking OneWeb and SINOSAT-5 system as the typical NGSO constellation system and GSO satellite system respectively, the interference analysis is performed by using the proposed method, and the results are verified with International common tool. The results illustrate that when the threshold of the number of NGSO satellites whose separation angle is not more than the included angle of the fine step size region is 20%, both the result accuracy and calculation efficiency can be balanced. The I/N distribution is related to the latitude of the ground station.

Low-Complexity Algorithm for Radio Astronomy Observation Data Transport in an Integrated NGSO Satellite Communication and Radio Astronomy System

An integrated non-geostationary orbit (NGSO) satellite communication and radio astronomy system (SCRAS), was recently proposed in [1] as a new coexistence paradigm. In SCRAS, the transportation of the radio astronomical observation (RAO) data from the space to the ground stations is an important problem, for which [1] proposed a linear programming optimization based algorithm. However, the computational complexity of this algorithm is quite high which is exacerbated by the need to re-compute the algorithm frequently due to the time-varying characteristics of the observing satellites, the Earth stations, and the RAO region. In this paper, to address this high complexity issue, we develop a low-complexity RAO data transport algorithm. In addition to the static resource constraint scenario considered in the existing work, we introduce a dynamic resource constraint scenario to exploit the knowledge of the satellite communication system (SCS) traffic statistics. We also present a modified version of the algorithm in [1] for the dynamic resource constraint scenario. In addition to the number of inter-satellite link (ISL) hops as the RAO data transport cost metric, we also evaluate the metric of the sum of the squared ISL hop distances which reflects the transmission energy cost. Furthermore, computational complexity analysis and data transport costs of the algorithms are presented. Our results show that the proposed algorithm yields several orders of computational complexity saving over the existing method while incurring a modest increase in the data transport cost. Our proposed dynamic resource constraint scenario provides plausible reduction of the RAO data transport cost.

Method to calculate the power-flux-density mask radiated by NGSO constellation system

The emerging fleet of non-geo stationary orbit (NGSO) constellation is composed of up to thousands of NGSO satellites, with highly dynamic multi-dimensional characteristics such as in the domains of space, time, frequency spectrum, and coding, etc. Therefore, the time-varying interference is inevitably caused to other radio systems (or services) in the sharing frequency. The problem of how to calculate the maximum emission from the NGSO constellation is solved in this paper. The beam gain patterns of the NGSO system, the beam configuration and coverage, and the minimum separation angles at terminals (data points) are introduced on the basis of the calculation framework of ITU-R S.1503-3. The general method of the power-flux-density(PFD) mask can also simplify the calculation process. An example of PFD mask is simulated in this paper. It can be known from the analysis that the more detailed operating parameters of the system, especially such as the handover strategy, the interference avoidance or mitigation strategy to be obtained, the more accurate results can be simulated, which is closer to the real value of the system working. The method can be used to calculate the PFD envelope in order to participate in the calculation of the downlink equivalent PFD.