| With the increasing demand for communication,low-earth orbit(LEO)satellite communication systems have become a hot topic,and countries and commercial companies have joined the trend of building LEO satellite constellations.However,the increase in the number of satellites has made frequency and orbit resources very crowded.Reasonable and efficient use of spectrum resources can help promote the sustainable development of LEO satellite systems.To achieve efficient utilization of spectrum and orbit resources,it is necessary to study the interference mechanisms between large-scale LEO satellite constellation systems and other radio systems and formulate corresponding interference avoidance strategies based on the interference characteristics between systems.Broadband LEO communication satellites widely use Ku,Ka,and Q/V bands.These frequency bands are also applied for other communication services,such as terrestrial communication services,geostationary orbit(GSO)satellite fixed services,and satellite broadcasting services.In order not to interfere with existing communication systems,broadband LEO communication satellites need to adopt mitigation methods.In addition to considering the compatibility between systems using the same frequency,non-geostationary satellite orbit(NGSO)satellite systems also need to consider spectrum coexistence with adjacent frequency systems.For example,the frequencies of radio astronomy services(RAS)include 10.6-10.7 GHz in the Ku band and 42.5-43.5 GHz in the Q/V band,which are adjacent to the frequency bands of NGSO satellite fixed services.Since radio astronomy systems have extremely strict constraints on harmful interference,LEO communication satellite system design needs to consider spectrum coexistence with RAS.To solve the challenge of spectrum compatibility in LEO satellite communication systems,this article explores the compatibility between LEO satellite communication systems and GSO satellite systems,between LEO satellite systems,and between LEO satellite systems and radio astronomy systems.The compatibility challenge between LEO satellite communication systems and GSO satellite systems lies in the design of interference avoidance strategies.The ITU RS.1503 recommendation has provided an assessment method of the interference from LEO satellite systems to GSO satellite systems,and satellite operators can use the GIBC interference simulation module provided by ITU to verify whether LEO satellite systems produce harmful interference to GSO satellites.Common strategies to avoid interference from LEO satellite systems to GSO satellite systems include spatial separation,power control,and beamforming methods.Progressive pitch is a spatial separation-based interference avoidance technology proposed by One Web,which aims to ensure a certain angle separation between LEO satellites and GSO satellites to avoid harmful interference.In addition to avoiding interference,seamless coverage of the LEO satellite constellation system is an especially important indicator.The design of the progressive pitch aims to minimize the impact on the LEO satellite communication capacity while meeting the constraints of spatial separation and seamless coverage.Based on the study of interference characteristics,the worst-case interference event occurs when the LEO satellite,GSO satellite,and GSO earth station are in a line.To meet the requirements of inline interference and seamless coverage,we establish an optimization problem that maximizes system capacity with constraints.By discretizing the optimization problem,we propose a solution that combines brutal force search and genetic algorithm.According to the simulation results,this solution can maximize the communication capacity of the satellite system under the constraints.The challenges of spectrum compatibility between LEO satellite systems include assessing harmful interference and studying interference avoidance strategies.Currently,there is no recognized interference assessment criteria and tool for LEO satellite systems.This article conducts in-depth research on interference related to LEO satellite communication systems.One of the main characteristics of interference between LEO satellite systems is their time-varying nature.Interference is most intense and of short duration when the interfering satellite,the interfered satellite,and the related earth station are in a line.In order to assess interference between LEO satellite systems,we extracted interference scenarios and proposed corresponding interference analysis models.Firstly,we classify interference and theoretically analyze the signalto-noise ratio of the victim satellite system using stochastic geometry.In addition,NGSO satellites may adopt complex methods of satellite selection,which makes theoretical analysis of interference very difficult.Therefore,we have established a simulation model for interference between LEO satellite systems,which supports the inputs of interference avoidance strategies,beam scheduling strategies,and interference scenarios.Finally,in order to evaluate harmful interference,our interference assessment indicators include availability,communication quality degradation,and degradation of spectrum efficiency.The challenges of spectrum compatibility between LEO satellite systems and RAS include interference assessment and interference avoidance strategy design.To evaluate interference between LEO satellite systems and radio astronomy operations,we have developed an interference analysis and simulation framework according to ITU regulations and recommendations.This framework can simulate the interference of a single NGSO satellite constellation on a radio telescope,as well as analyze the aggregate interference generated by multiple NGSO satellite systems.By inputting satellite system parameters,including constellation configuration,user distribution,and beam scheduling strategy,the framework can predict the distribution of interference received by radio telescopes in different latitudes and observation directions.The simulation results can provide a reference for satellite operators to analyze interference and guide the development of interference avoidance strategies.This article mainly focuses on the study of spectrum compatibility of LEO satellite systems and provides input for the design of LEO satellite constellation systems.To achieve efficient utilization of frequency and orbit resources,spectrum utilization needs to be constrained to ensure spectrum coexistence between different communication systems.According to frequency allocation,systems that may interfere with LEO satellite communication systems include GSO satellite systems,terrestrial communication systems,and radio astronomy systems.Studying interference related to LEO satellite systems is crucial for achieving sustainable use of spectrum resources. |
