The Study And Implement Of Compression Algorithm For Lossless Base Logging Data

With the logging data can only be transmitted through the cables from the position under kilometers of the well for the special logging environment. The massive data bring severe challenge to the transmission of seismic data. In addition, the massive data and limited bandwidth are responsible for the network disconnection, retransmission and often causing wrong code, which make the unreliable data reach to the surface equipment. Therefore, it becomes inevitable to make compression of logging data.LZW is a dictionary-based lossless compression algorithm, with the high compression ratio and convenient implementation in software and hardware, but the traditional LZW compression algorithm has low efficiency and dictionary overflow problems. This paper proposes an improved logging data of LZW algorithm, increasing the count bits in a dictionary entry and using a Hash Function data structure to query dictionary. Experimental results show that the proposed compression algorithm achieved good compression. Logging data was compressed in the hole and then was transmitted to the ground, and next, the original data reduction can be achieved on the ground. It relieves the problem of logging data transmission and improves the transmission rate of logging data effectively.In the part of hardware, the paper describes a design scheme of system, adopting improved LZW algorithm, basing FPGA platform, which presents real-time lossless compression for the data. The paper adopts the Smart Fusion2 based on Flash structure of Microsemi on the hardware platform, with high security and reliability and low power consumption. It describes the whole compression system using modular design, including the front buffer, the operation of hash function, the dictionary, the state machine and the conversion of data, and verifies the function of the system.Finally, the whole hardware compression system are analyzed and validated comprehensively and systematically.The test result show that,after the data compressed by compression system designed in this paper,decompression data transmited to the upper computer is consistent with the original data,which illustrate this system is a reliable design with practical values.