The Research Of Error Control Technology Based On CCSDS AOS System

Both with the continuous development of space technology and with the increasing commercialization and internationalization of space activities, the demand for transmitting spatial data is higher and higher.For solving this problem, AOS system is proposed by the Consultative Committee for Space Data Systems (CCSDS), which can provide a more diverse, more flexible space-terra bidirectional data-transmission business.Compared with terrestrial link, space-terra link has a long transmission time and a high bit error rate. Because of these features,there are inevitabe mistakes and errors when transmitting image datas through the space-terra channel, which results in the visual quality descending. Therefore, an error control scheme based on the CCSDS AOS system is proposed in this topic, which aims at image transmission and enhancing its transmission performance.In the space-terra link of the image transmission, after the wavelet transforming, the low-frequency section contains nearly 90% information of the image while the high-frequency only contains some specific and edge information.Based on this,an error control scheme of the low-high frequency information transmission system is designed.For the low-frequency of the image,firstly ,it adoptes LDPC coding techniques, then if there is information which can not be encoded,it adopts go-back N retransmission to ensure the correctness of the image.For the high-frequency of the image, firstly ,it adopts LDPC coding techniques ,then if there is information which can not be encoded,it adopts retransmitted-time-limited Go-back N retransmission. Specific content includes:First of all, Go-back N retransmission scheme in CCSDS recommendition is used to transmit the low-frequency information of the image.Using the time and throughput calculateing model to simulate the scheme and analysis the relation between each parameter and throughput.Secondly,for the high-frequency information transmission,tranditional Go-back-N retransmission scheme is ameliorated in the topic,which called retransmitted-time-limited Go-back-N retransmission scheme.Based on this scheme,time,thoughput and success rate are firstly analysed and then simulated by data frame length,bit error rate,glide window size and retransmitted time limit parameters.Through the simulation, the results that the relations between each parameter and thoughput and the relations between each parameter and success rate are gained.Finally,LU encoding arithmetic and probability BP coding arithmetic of LDPC is studied.Correct-error coding model of image information is designed based on these theory.Then the relations between iterative time,coding efficiency and bit error rate are obtained by analysing the performance of the model.