Research And Implementation Of Lossless Compression Technique For Space Telemetry Data

Because of the large amount of parameters and high sampling frequency, the total number of telemetry data is increasing gradually. The transmission time is prolonged in the case of fixed transmission speed and more spacecraft resources are occupied. Therefore, it is important to study the lossless compression technique of space telemetry data. On one hand, it can improve the transmission efficiency. On the other hand, it can reduce the spacecraft resources, especially transmitter power.In this paper, we mainly study the lossless compression technique of the space telemetry data, including three aspects: the combined interframe compression technique, the improved dictionary search mode of LZW and the FPGA implementation of the combined interframe compression technique.1) Up to now, the research of lossless compression technique of space telemetry data is about how to design the most efficient compression method to obtain the optimal compression ratio. Considering that the space telemetry data has local correlation and global correlation, we propose a combined compression algorithm based on the compression method in MPEG which can decrease the redundancy in the intraframe and interframe using LZW and RLE respectively. At the same time, we improve the output structure of the combined compression algorithm. Experimental results verify that the compression ratio of the interframe combined compression technique is lower than the traditional compression technique by 0.3. That is to say, it can get the better compression performance.2) Because LZW is such a compression technique that compress or decompress based on the dictionary, the search mode of dictionary has an effect on the latency of compression. At present, the primary search mode of LZW includes: sequential search, parallel search and hash table. But these three search modes all have their limitations. In this paper, we propose the multi-character parallel search mode on the basis of multiway tree, which can accelerate the search speed without affecting the compression ratio. Experimental results verify the compression time of the multi-character parallel search mode only occupies 40% of the serial search mode in condition of the same compression ratio.3) In order to apply the combined interframe compression technique to the Aerospace Engineering Project, a FPGA implementation of the combined interframe compression technique should be studied. The FPGA implementation is introduced in detail, which includes the whole structure and module division, the process flow, the implementation of RLE and LZW. Simulation results prove the feasibility and validity of the FPGA implementation.