Abstract:
Data transmission system of logging while drilling achieves real-time communication between ground and under well accurately and effectively by acoustic wave transmitting along the drillstring. A drillstring channel is periodically constructed by pipes and joints. By theoretical analysis and modeling simulation, the spectrum of drillstring channel is a comb-filtering-like transfer function composed of alternating passed bands and stop bands. A finite impulse response (FIR) filter is used to approximate the spectrum and to build a simulation platform of the channel. Vector orthogonal frequency division multiplexing technology (V-OFDM) can convert the multipath fading channel into a number of vector sub-channels. The number of error bits which are leaded by channel spectral nulls can be reduced and the robustness can be increased by diversity gain when eliminating symbol interference by adding right amount of cyclic prefix. Simulation and test results show that this technology can reduce data redundancy and increase transmission efficiency extremely when meeting the need of low bit error rate.