Research On Application Of ACM Technology In Mobile Satellite Communication

In order to ensure the effective transmission of information in different environments,the adaptive coding and modulation(ACM)technique can be used to compensate for the fading of signal in satellite communication,which caused by many factors,such as weather fading,shadow fading,multipath effect and so on.Existing work on ACM assumes the availability of accurate channel state information at the satellite transmitter.However,due to the time-varying of the channel and the huge round-trip delay,the application of this adaptation is greatly limited in the mobile satellite environment.In order to take effective measures to avoid the influence of delay,overcome the limitations of existing adaptive methods,and improve the transmission performance of adaptive systems by optimization algorithm,it is of great significance and value to solve the problem that the ACM is affected by transmission delay in mobile satellite communication.Firstly,this paper introduces the classical model of the mobile satellite communication link,including the basic principles,system structure,statistical relations and the elaboration of other aspects.At the same time,combining with the conversion relationship between Loo's model and shadow Rice model,the single-state and multi-state link model suitable for mobile satellite communication environment is constructed.The channel sequence is further realized through simulation.Finally,the correlation of time-varying channel is studied.The relationship between the correlation of time-varying channel and link feedback delay is analyzed,which lays a foundation for analyzing the effect of link delay on adaptive systems.Secondly,the basic theory of ACM technology is introduced in detail,including the basic principle,workflow and performance in the ideal state.According to the source of acquiring channel information,the ACM is divided into open-loop and closed-loop adaptive technologies.The optimal adaptive method is given in the ideal state.At the same time,with the ideal adaptive environment,the optimal threshold selection algorithm and performance optimization algorithm for adaptive coded modulation are analyzed.The spectral efficiency performance of the system satisfying different constraints is given.Through the comparison of simulation experiments,the influence of the change of transmission power and bit error rate constraints on the spectralefficiency of ACM system is verified.Finally,based on the characteristics of mobile satellite channel,an adaptive coding and modulation method using partial channel information is proposed to solve the problem of feedback delay in satellite adaptive process.According to the line-of-sight information of the downlink and the statistic information of the feedback multipath channel,the transmitter realizes the adaptive process of the uplink in the mobile satellite communication.Meanwhile,this paper presents an optimized ACM strategy and power allocation method with the constraint of the average transmit power and average bit error rate,which overcome the limitations of existing adaptation.The simulation results also show the effectiveness of the proposed method.