Research On Co-channel Interference Avoidance Technologies In GEO/LEO Double-layer Satellite Communication Networks

With the rapid development of communication systems,people's requirements for high data rate communication are gradually significant.Due to the limitations of the ground network in remote coverage areas,satellite network system as a supplement together with the ground network system provides people with efficient and convenient communication services.LEO satellite communication system has the advantages of short communication distance and low path loss,which makes up for the shortcomings of GEO satellite and get more applications.Due to the limitation of spectrum resources,LEO satellite and GEO Satellite need to share the same spectrum,so the double-layer satellite communication network needs to solve the problem of spectrum scarcity through spectrum sharing,expand satellite broadband services,and ultimately improve the spectrum utilization.In this paper,the same frequency interference analysis and interference avoidance technologies for the downlink of GEO / LEO double-layer satellite communication network are studied.First of all,the development of double-layer satellite communication network and the research status of the same frequency interference avoidance at home and abroad are reviewed.In view of the current utilization of spectrum resources and the international standards and suggestions for spectrum sharing of double-layer satellite communication network,the research of shared frequency band is determined in Ka frequency band.Then,several interference avoidance techniques are analyzed and compared,which provide a theoretical basis for the later study of power control algorithm and cognitive beam hopping algorithm.Then,the influence factors of the same frequency interference in the double-layer satellite communication network are studied in detail.The co-existence of communication nodes is analyzed from the three-dimensional model of time,space and frequency,and then under the condition of the same frequency interference,the interference analysis is carried out by using the time change to represent the space coordinate of LEO satellite during the operation process.According to the interference characteristics,the beam power control technology is proposed to avoid the same frequency interference.However,due to the non-convex nature of the beam power control algorithm model,only the local optimal solution can be obtained.Therefore,according to the characteristics of beam power control model,an optimal power control algorithm is proposed,which optimizes the problem of multiple ratio sum by fractional programming,and improves the performance of LEO communication network while avoiding the interference to GEO network.Finally,due to the limitation of power control technologies in improving the performance of LEO system,inspired by the flexible allocation of more available resources,cognitive beam hopping algorithm is proposed to avoid interference.Firstly,a cognitive beam hopping algorithm based on dynamic frequency multiplexing is proposed.The algorithm allocates the frequency hopping sequence of LEO beam hopping reasonably,and carries out dynamic frequency multiplexing on the beam hopping sequence,so as to avoid the interference to GEO system,reducing the interference between multiple beams of LEO satellite.Although the cognitive beam hopping algorithm based on dynamic frequency multiplexing can reduce the interference to the GEO satellite system,it is still not flexible in the reasonable allocation of beam capacity for LEO users' requests.Then a cognitive beam hopping algorithm based on the distance threshold is proposed.The beam hopping sequence is designed based on the distance threshold,which can avoid the interference to the GEO network and improve the flexibility of beam capacity allocation of LEO system.