基于旋转阀控制脉冲重构的钻井液QPSK信号解码及误码率分析

钻井液压力正交相移键控(QPSK)调制具有高密度携带及传输井下信息特点,其信号的解调与解码关系到所携带信息的正确恢复。通过建立信号的相位解调及旋转阀转速控制脉冲重构的数学模型,研究解调系统固有干扰及信号噪声对脉冲重构的影响;根据重构脉冲的幅度判别研究信号解码的可行性;通过建立重构脉冲的信噪比数学模型,对误码率进行理论分析。结果表明,解调系统固有干扰与信号噪声均对脉冲重构产生影响,且固有干扰影响较大;脉冲重构时,相邻码元编码产生的脉冲电平差值较小,使得误码阈值降低,上述影响更易引起误码。误码率的理论计算结果与仿真分析结果基本一致,可以将误码率分析模型用于钻井液压力QPSK信号传输效果的可靠性评估。

Decoding of drilling pressure QPSK signals based on control pulses reconstruction of rotary valve and bit error rate analysis

Modulation of drilling fluid pressure quadrature phase shift keying (QPSK) is capable of carrying and transmitting high density downhole measured information. Demodulation and decoding of the signal concern correct recovery of the downhole information carried in the signals. The impact of signal noise and inherent interference from demodulating system on pulses reconstruction were studied by establishing mathematical models of signals phase demodulation and reconstruction of the rotary valve control pulses. The feasibility of signals decoding is studied by amplitude recognition of the reconstructed pulses, and the bit error rate (BER) is analyzed theoretically by establishing SNR (signal to noise ratio) mathematical model of the reconstructed pulses. Results show while both the inherent interference of the demodulating system and the noise level have impacts on pulse reconstruction, the interference contributes significantly more. In reconstructing the pulses, the bit error occurs more easily due to the lower bit error threshold caused by smaller pulse level differences in the adjacent coded symbols. The BER in the theoretical computation is basically identical to that of simulation results, suggesting thatthe BER analysis model can be used for evaluating the reliability of the signals transmission.