钻柱信道内双声接收器的回波抑制方法分析

Analysis of echo cancellation method using two acoustic receivers in a drill string channel

在随钻测井中地面噪声与周期性信道结构形成的下行回波导致传输性能降低,为此,结合钻柱信道的噪声分析,利用上、下行信道的瞬态脉冲响应,构建回波噪声抑制模型,提出了双声接收器的检测方式。在钻柱激励端分别施加单位正弦脉冲信号和PSK调制数据,在接收端耦合下行的高斯噪声,应用钻柱内一维低频纵波传输的有限差分算法,在单接收器和双接收器模式下时域和频域仿真分析了钻柱内声信号的传输特性,验证了双声接收器检测方式的有效性。该方法可实现井下回波噪声的抑制,从而改善信噪比,提高传输速率,为钻柱声遥测系统优化设计提供方法基础。

Aiming at transmission performance reduction caused by downlink echoes resulting from ground surface noise and periodic structure of a drill string channel in logging while drilling, an acoustic signal detection method using dual acoustic receivers was presented here. Based on analysis of noises existing in a drill string channel, with the proposed method a theoretical suppression model of echo noises was built by using the transient pulse responses in uplink and downlink channels. Then a unit sinusoidal pulse signal and phase shift keying modulated data were respectively imposed on the drill string at its excitation end, an additive white Gaussian noise was applied at its receiving end. By applying a finite-differential algorithm for one-dimensional propagation of longitudinal waves with lower frequency along the drill string, the transmission characteristics of acoustic signals in the periodic pipe structure transmission channel were analyzed in one-receiver mode and dual-receiver mode with time and frequency domain simulations. The simulation results proved the validity of the signal detection method using two acoustic receivers to extract original data information from acoustic waves propagating along the drill string. This method could realize echo cancellation and downhole noise reduction, improve signal-to-noise ratio and raise transmission rate. The proposed method provided methodological foundation for optimal design of acoustic telemetry systems.