钻柱声传输信号多载波调制激励分析

在随钻声遥测技术中，周期性钻柱结构产生的多重回波极易造成严重的码间干扰和较高误码率，为此，根据钻柱信道的多径传输特性，基于短钻杆条件下多载波传输的实验分析，建立了多节钻杆与管箍的周期性信道有限差分模型。考虑地面噪声和信道内多径回波干扰，利用最小均方自适应均衡，基于“4钻杆—3管箍”信道结构进行了多载波调制性能仿真分析。仿真结果表明，与单载波PSK（Phase-Shift-Keying）调制相比，OFDM（Orthogonal Frequency Division Multiplexing）多载波调制可使误码率平均降低约50%；在非周期性结构下其传输性能受信道变化敏感，但相同条件下仍优于PSK调制，且通过子载波相位补偿可有效改善误码率、提高传输性能。

Analysis of Multi-carrier Modulation Excitation for Acoustic Transmission Signal in Drillstring

The multiple echoes caused by periodic structure of drillstring in acoustic telemetry while drilling tend to result in the serious intersymbol interference and high bit error rate. According to the multipath transmission characteristics of drillstring, based on the analysis of multi-carrier acoustic transmission experiment along a short drill pipe, a finite difference model for a periodic channel composed of multiple drill pipes and tool joints is established. Considering the surface noises and multipath echo interferences in channel, a Least Mean Square adaptive equalization method is introduced. Then the multi-carrier modulation performance is simulated by using a drillstring structure comprising four drill pipes and three tool joints. The simulation results show that the orthogonal frequency division multiplexing (OFDM)-based multi-carrier modulation can obtain the bit error rate (BER) of 50 % less than phase-shift-keying (PSK) modulation. Although it is more sensitive to non-periodic channel structure, the BER is more superior to PSK modulation and can be effectively improved by use of phase sub-carrier phase compensation.