| Airborne real-time transmission of remote sensing data is a key factor in remote sensing applications, especially in emergency issues such as, disaster monitoring, military surveillance etc. It is very important and of great valuable to research and develop high performance, reliable, flexible and easy to use airborne real-time transmission system of remote sensing data.Constructions of different mode of airborne real-time transmission system such as air-ground, air-satellite-ground, air-air-ground and their applications have been analyzed in this thesis. Design requirements have been deduced according to their characteristics of transmitting channel.For small air-platform based air-satellite-ground mode real-time transmission system, high sensitive receiver plays an important role in system designing. As demodulator threshold of receiver decreasing, performances of traditional SNR (signal to noise ratio) estimation and carrier lock detection deteriorate greatly. A novel iterative SNR estimation method based on statistical parameter has been proposed in this thesis, which provides good estimation even at SNR below 0 dB, and its amount of calculation is greatly reduced compared with other iterative methods with similar performance. A carrier lock detection function was deduced, which almost has the best performance when SNR is below 3dB. Effects of digital filter quantization errors on performance of receiver have been analyzed thoroughly, which provide the criterion to determine the word length and order of FIR.In addition, designing, simulation and implementation of communication subsystem of airborne data remote sensing real-time transmission system and digital immediate frequency receiver based on FPGA have been discussed in details.
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