Design Of Logging While Drilling Data Compression System Based On FPGA

Logging while drilling technology is developing rapidly,so logging instruments are also developing in the direction of multi-parameter and high-precision.Data transmission technology is the core technology of logging while drilling.Accuracy and real-time data transmission is very important for logging while drilling.At present,mud pulse technology is the most common and longest application because of its simple method and low cost.However,the low transmission rate and poor anti-interference ability of the mud pulse transmission method make it difficult to carry out real-time transmission of the collected mass formation information.To solve this problem,a data compression system while drilling can be designed to compress the collected parameters,increase the data transmission amount and improve the transmission efficiency.Compared with the traditional method of data compression based on software platform,hardware compression has significant advantages in resource utilization,task execution efficiency and system power consumption.Therefore,this paper proposes and designs a data compression system based on FPGA while drilling.The main research contents and results can be summarized as follows:1.After the investigation and analysis of lossless compression algorithms,the Huffman algorithm was selected as the basic algorithm of compression while drilling system by comprehensively considering the factors of algorithm compression rate,real-time performance and hardware implementation complexity.Then the principle of traditional Hufman coding and adaptive Huffman coding is described in detail.2.After analyzing the characteristics of logging while drilling data,it is found that there is no redundancy between adjacent bytes.The data between adjacent frames have strong correlation and redundancy.The interframe residual prediction method can eliminate the redundancy and improve the compression ratio.At the same time,in order to avoid the phenomenon that the data dependence is too strong and the channel error code makes all the data decompression wrong,the method of grouping according to the frames and inter-frame prediction within the group is proposed.Compared with the pure interframe prediction method,the compression ratio of the intra-group interframe prediction algorithm is reduced,but the error resistance ability is improved,and it is more suitable for the engineering environment.3.The fixed probability Huffman coding is applied to the residual values to effectively implement the Huffman algorithm for grouping interframe prediction of data compression while drilling.According to the algorithm principle,the structure based on block interframe prediction Huffman algorithm is built on the FPGA hardware platform with the modular idea.The design and implementation of the algorithm are completed by preprocessing,inter-frame operation,Huffman coding,bit splicing logic and other modules.Finally,simulation test and hardware test are carried out to verify the accuracy and effectiveness of the hardware algorithm design.4.In order to further improve the compression ratio of the data compression system while drilling,the Huffman algorithm based on the grouping inter-frame prediction is proposed.The residuals of adjacent gamma values in each frame are predicted,and other physical quantities are still predicted between frames.The residual values of interframe prediction and intra-frame prediction were coded with fixed probability Huffman to further reduce the entropy and improve the compression ratio.According to the principle of the algorithm,the preprocessing and Huffman coding modules are optimized on FPGA,and the inter-frame prediction and check bit additional modules are added to complete the design and implementation of the algorithm on FPGA.Finally,simulation test and hardware test are carried out to verify the accuracy and effectiveness of the hardware algorithm.5.The performance of two data compression systems based on block interframe prediction algorithm and block interframe prediction Huffman algorithm is compared.The average compression ratio of the inter-frame prediction Huffman algorithm is 1.52,and the average compression ratio of the intra-frame prediction Huffman algorithm is1.59.The Huffman algorithm based on inter-frame prediction is superior to the inter-frame prediction algorithm in terms of compression ratio and real-time performance.The compression system of data while drilling based on FPGA is designed with the Huffman algorithm of grouping inter-frame prediction.The design of the algorithm can meet the demand of real-time transmission of data while drilling in mud pulse channel.The system compresses the logging data accurately and effectively with good compression performance,which is of great significance to the improvement of data transmission efficiency and technical progress of logging while drilling.