| Satellite-ground-link high-rate high-efficiency data transmission technique is one of the key supports for the development of high-resolution low-Earth-orbit Earth observation satellite systems.Following the high-sensitivity,high-precision,multi-task and multi-function trend of space-based Earth observation techniques,there will be a big boost of the on-board storage and down-link transmission data volume.Traditional satellite-ground-link data transmission technologies can hardly meet the needs of future payload data transmission.Under this background,considering the low-Earth-orbit satellite-ground links,the dissertation works on new transmission scheme,system architecture and corresponding key techniques for improving the satellite-ground data transmission efficiency from two aspects: rational arrangement of link resources and improvement of bandwidth utilization.The proposed scheme targets at Gbps high-rate transmission,transmitting high volume of data down-link to the ground station within limited time and using the limited power and bandwidth resources.The main research work is as follows:1.According to the the demand for high-precision payload data transmission,a high-efficiency high-rate satellite-ground data transmission scheme is studied,focusing on "improving the synthetical efficiency of the transmission system".The ―three-layer satellite-ground data transmission‖ scheme is proposed based on the core techniques of variable coding modulation,orthogonal multi-carrier transmission as well as high-order digital modulation and multi-rate channel coding.Based on the proposed scheme,the architecture and module composition of the transmission system are designed.2.The ―three-layer satellite-ground data transmission‖ scheme applies variable coding modulation as the high-layer core idea.A VCM schedule designing algorithm is illustrated for optimizing the average data efficiency within the data transmission period,in order to fit the link budget curve and fully utilize the link power resource.Corresponding automatic design algorithm is also proposed.3.The ―three-layer satellite-ground data transmission‖ scheme applies multi-carrier transmission as middle-layer core technique.Filtered quasi-orthogonal frequency division multiplexing waveform is proposed and the waveform design as well as modulation/demodulation techniques are discussed in detail.The proposed waveform has the advantages of high-spectrum efficiency,low computational complexity and low transmission overhead,which is suitable for satellite-ground data transmission scenarios and can meet the high-rate high-efficiency data transmission needs.Oriented to the application scenario,waveform parameters are optimal designed.The data structure of multi-carrier symbols as well as the physical layer transmission frame are discussed.4.Receiver synchronization algorithms are studied serving to the ―three-layer satellite-ground data transmission‖ scheme.Based on received signal model,frame detection and symbol synchronization integrated algorithm,carrier coarse synchronization algorithm,sampling offset compensation algorithm and phase tracking method are proposed with their principle analysis,performance evaluation and hardware implementation.It provides fast tracking and compensation for satellite-ground-link time-varying Doppler effects.The system-level evaluation of transmission performance as well as the comparison with existing schemes prove that the research works of the dissertation enhance transmission efficiency with the new scheme,helping to better utilize the well-built X-band ground station and providing data transmission technical supports to the future complex Earth observation missions with high-precision and multi-task payloads. |
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