Analysis And Implementation Of The Key Technologies Of Adaptive Transmission For Proximity-1 Space Based On FPGA

With the development of deep space exploration activities, the requiments for deep space communication system are becoming higher. Proximity-1 space link attracted much attention with its moderate signals, short time delays, and short, independent sessions. Due to the complexity of deep space communication environment, the communication efficiency of the whole system is greatly restricted by the same transmission parameters. Adaptive transmission technology can adjust the parameters adaptively according to different channel conditions, and it can improve the system spectrum utilization efficiency while meeting the system error performance. In this paper, the key technologies of adaptive rate transmission system are analyzed in detail base on the studies of conventional communication system and CCSDS proximity-1 protocol.Firstly, according to the proximity-1 protocol and proximity-1 space link environment, we analyze the adaptive algorithm and design the whole implementation scheme of the adaptive transmission system. Furthermore, we also determine the system implementation platform based on the analysis on the basic theory of conventional transmission system.Secondly, to guarantee the receiving performance, we carry out the modules of signal detection and adaptive digital AGC. The signal detection is to control the working status of the receiver including three modules: blind estimation of SNR, adaptive dual threshold design and cyclic spectrum detection. The digital AGC is to maintain the amplitude of the received signal and ensure that the performance of the receiver is not affected by the large degree of signal.Thirdly, we analyze the modules of rate switching, synchronization algorithm, SNR estimation algorithm and rate switching criterion in the adaptive transmission system. We use the method of changing the number of sampling points in a symbol to complete the rate switching. The variable filter bandwidth and the adjustable drow ratio of the programmable CIC filter can help complete the process of multi-rate synchronization with Costas loop. It adopts the method of Gardner loop and detecting the head of ASM to finish symbol and frame synchronization. The rate switching criterion is based the system error and can acquire the different rate under different system performance.Finally, we simulate the adaptive transmission system with Modelsim and successfully implement the hardware circuit in the signal processing platform with FPGA and DSP. The results of simulation verify the integrity and reliability of the designed system.