Research On Adaptive Coding And Modulation Technology Of Satellite Communication Based On LDPC Code

Satellite communication can provide a seamless transmission and play animportant role in earthquake relief. But satellite communication exists severe rain fadingat Ka-band, which leads to a serious decline and time-varying channel. Adaptive Codingand Modulation (ACM) is an effective technology to overcome rain attenuation and thetime-variation of channel. ACM can effectively improve throughput and spectrumefficiency comparing to the traditional fixed transmission, which can also make full useof the frequency resources. The specific research contents of this dissertation areintroduced as follows.The first part introduces the background and significance of the research anddecomposes the article into several modules based on the implementation framework ofACM. What’s more, this part gives the overall framework and the distribution ofcontents.There are three aspects about LDPC code in this part. Firstly, the basic theory ofLDPC code is elaborated from various aspects such as basic knowledge about LDPC,the configuration of parity check matrix, LDPC encoding and decoding and so on. Adetailed description of LDPC codes based on IEEE802.16e standard is stated. Secondly,this part introduces rate-compatible methods about LDPC code, and proposes a simplepuncturing algorithm based on LDPC with quasi-dual-diagonal structure. Thesimulation results prove the effectiveness and practicality of the algorithm. The last partresearches on the application of Low-Density Parity-Check Codes under high-ordermodulation, which combines the coding and modulation. A detailed analysis is given fortwo methods of the initialization information calculation under high-order modulation.This part lays the foundation of Adaptive Coding and Modulation.This part studies adaptive modulation and coding based on LDPC codes.According to the framework of ACM system, the first part gives a research and analysison the key technologies of the ACM, which includes SNR estimation, transmissionmode, MCS selection algorithm and so on. From the simulation results, it is confirmedthat the system with ACM can adaptively adjusted transmission mode following the channel variation, and get a better performance of throughput,availability, interrupttime, and annual spectrum efficiency relatively compared to the fixed transmissionmode in the ideal case.The last part researches on the impaction of SNR feedback error, delay and channeltime-varying on ACM, and proposes relevant solutions. This part mainly studies SNRforecasting technique to resist the influence of delay, and proposes a SNR predictionmethod combined signal-to-noise ratio estimation with LMS algorithm. From thesimulation results, it can be found that the predicted SNR value through the algorithm iscloser to the true value. It reduces the impact of delay comparing to the method whichuses the instantaneous SNR to select the transmission mode of the next moment. Finally,Threshold adjustment algorithm is elaborated to weaken the influence of channelcondition variation. Simulation results show that ITA algorithm can weaken the damageto throughput due to the change of channel condition.