| As a valuable mineral resource,oil is becoming more and more difficult to mine.The real-time well-logging information is of great significance for the efficient oil exploitation in oil fields.The well-logging data transmission system realizes the cable communication between the downhole well-logging instrument to the surface host computer.With the continuous development of multi-phase flow sensing technology,more and more types of sensing instruments and sensing arrays have placed higher demands on data transmission rates.In addition,the unique single-core cable channel and the high-temperature and high-pressure external environment make the well-logging data transmission system have higher requirements for frequency-band utilization and anti-jamming capability.Therefore,the performance of well-logging data transmission system restricts the development of well-logging information technology,and the development of high-speed and stable well-logging data transmission technology is of great significance.This thesis designs and implements the well-logging data transmission system.Through the analysis of system requirements and operating environment,the overall solution of well-logging data transmission system was designed,and the driver of each module was developed.Algorithms for coding and decoding,modulation and demodulation,cyclic prefix and other technologies in the physical layer of orthogonal frequency division multiplexing(OFDM),as well as channel estimation and synchronization techniques are implemented.This thesis also improves the tone reservation(TR)algorithm,which is one of the peak-to-average power ratio(PAPR)reduction algorithm widely studied in OFDM technology,and implements a low-complexity algorithm based on neural networks.Innovative research results of this thesis are as follows:1.A low-complexity PAPR reduction scheme is proposed.For the PAPR reduction problem existing in OFDM technology,the traditional TR algorithms have higher computational complexity.In this thesis,neural network technology is used to design a low-complexity TR algorithm using pre-generated peak-canceling signals.Simulation results show that the proposed algorithm achieves about 3.5d B PAPR reduction at complementary cumulative distribution function(CCDF)of 10-3.Compared with CC-TR,LSA-TR and CF-TR algorithms,the computational complexity of the proposed algorithm is reduced by more than 70%.2.OFDM technology is used to realize well-logging data transmission system,and channel estimation and synchronization technology are added.In this thesis,the constructed single-core cable channel model combined with Wiener filtering is used for channel estimation.Symbol timing synchronization is accomplished using dual energy windows,carrier frequency synchronization is accomplished according to the cyclic prefix,and sample frequency synchronization is accomplished based on the comb pilots.Experimental results show that the well-logging data transmission system achieves the transmission rate of 27.45Kbps under a low bandwidth of 50k Hz,and the bit error rate(BER)is 4.37×10-4.3.The development of well-logging data transmission system based on dual-core DSP is implemented by two processes,both at the transmitting end and the receiving end,which greatly improves the system performance.The analog front end portion of the system is developed using the AFE031 with greater integration and controllability.The correctness of each module in well-logging data transmission system is verified by tests. |
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