Multi-user Scheduling Schemes And Performance Evaluation For Satellite Communication Systems

With the commercialization of the 5th-Generation(5G)mobile communication systems,international communication organizations and industry insiders have begun to look forward to 6th-Generation(6G)mobile communication systems.Due to its advantages such as wide coverage,unrestricted geographical conditions,and high communication quality,the satellite communication system can solve the “information island” problem caused by insufficient coverage of terrestrial wireless systems in remote areas.Thus,it is considered to be an important part of 6G communication systems.As an important part of the satellite communication system research,performance analysis has aroused widespread concern of scholars at home and abroad,and there have been many literatures.But the existing works are mainly aimed at the downlink of satellite communications,and usually only focus on the single user scenario.However,in the practical applications,the satellite communication network needs to provide services for multiple terrestrial users for its wide coverage characteristic.Therefore,this dissertation mainly studies the multi-user scheduling strategy in the satellite communication system and evaluates its performance,which provides useful guidelines for the engineers to implement satellite system design.The main contributions of this dissertation are outlined as follows:1.Considering the multi-source multi-destination satellite system based on the decode-and-forward(DF)protocol,where both uplink and downlink experience shadowed-Rician(SR)fading,two scheduling schemes,namely,opportunistic scheduling(OS)/selection combining(SC)and OS/maximum ratio combining(MRC)schemes,are proposed and the outage performances of these two schemes are studied.Considering the effects of antenna pattern and path loss,a practical satellite channel model is first established and the end-to-end signal-to-noise ratio(SNR)expression is also obtained for the considered system,where the uplink employs the OS scheme while the downlink adopts the SC or MRC approaches.Then,the closed-form outage probability(OP)expressions for the considered system with OS/SC and OS/MRC schemes are derived,respectively.Furthermore,the asymptotic OP formulas at high SNR are also developed.Finally,numerical results not only confirm the validity of the theoretical formulas,but also show that the diversity order of the both schemes depends on the number of source nodes and destination nodes.However,the difference in coding gain leads to the difference in system performance.2.Considering the multi-antenna multi-source single-destination satellite system based on the selective decode-and-forward(SDF)protocol,a scheme of maximum ratio transmission(MRT)at the source and MRC at the destination is proposed,and the system outage performance is investigated.By taking the effects of antenna pattern and path loss into account,the equivalent output SNR expression of the considered system is first obtained.Then,the closed-form system outage probability(SOP)expression for the considered system is derived,where both uplink and downlink obey SR distribution.The main advantage of our theoretical formula is that it can be uniformly used in the case of integer and rational Nakagami fading parameters in SR channel parameters.Furthermore,the asymptotic SOP formula at high SNR is also presented.Finally,simulation results verify the rationality of the exact and asymptotic SOP expressions,and prove that the diversity order of the system depends on the number of source nodes and the number of antennas configured by the source and destination nodes,however,the pitch angle of the link between the satellite and the terrestrial user only affects the system coding gain.In the practical system design,when it is inconvenient or difficult to increase the transmission power or transmission bandwidth,the advantages of a multi-antenna system can bring greater diversity order,thereby improving the communication quality of the system.3.Considering the multi-source single-destination satellite system based on the SDF protocol,where both uplink and downlink experience SR fading,the system secrecy outage performance is studied.By taking the effects of antenna pattern and path loss into account,the end-to-end SNR expression is obtained for the considered system with the SDF protocol.Then,based on the output SNR expression,the exact and asymptotic system secrecy outage probability(SSOP)expressions are derived.Finally,the numerical simulation results validate the effectiveness of the secrecy performance evaluation,and show that the shadowing severity of the downlink does not influence the achievable secrecy diversity order of the system,but affects the security performance of the system by changing the secrecy outage SNR gain.In addition,the aggressiveness of eavesdroppers can have a fatal effect on the performance of the system.