| Logging-While-Drilling(LWD) is a modern drilling technology of real-time measurement of downhole information and upload technology in drilling process. LWD can directly observed downhole engineering paramenters, and gain understanding of the earth formations in real time. This knowledge is not only useful for formation evaluation and correlation,it is also important in geosteering and reservoir characterization. The best data transfer method is still the core of LWD.Acoustic data transmission has the advantage of higher rate of data transmission,low cost of development and simple structure. This technique will be applied brodly. There are many other problems encountered in drilling channel, such as larger ambient noise, much-limited bandwidth, much-extended propagation latency, seriously inter-symbol interference which lower severely the reliabilities and validity of the downhole information transmission. Orthogonal Frequency Division Multiplexing(OFDM) is counter multipath, fully use of the frequency band and good anti-interference performance.This paper based on one-dimension acoustic spread model, studies the properties of the drillstring system of acoustic transmission, and presents the frequency-scattering equation, in this paper, we analyse the relation of passband, stopband and drillstring parameters, and make the numerical value simulation on the momentary state of the drillstring system with ANSYS;Then adjust the key link (codec,modulation and demodulation) for matlab simulation;Application numerical simulation methods to certification the modulation and demodulation.The results indicate that the 1/3 coding efficiency and QPSK technology can improve the reliability of the data communications,lower the bit error rate of the LWD acoustic tranmission system.Establish the basis to further studies for LWD acoustic transmission technology.
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