Analysis of Multi-carrier Modulation Excitation for Acoustic Transmission Signal in Drillstring
LI Cheng;;LIU Zhao;DING Tian-huai;FAN Shang-chun;
Journal of Vibration and Shock ›› 2014, Vol. 33 ›› Issue (3) : 1-4.
Analysis of Multi-carrier Modulation Excitation for Acoustic Transmission Signal in Drillstring
LI Cheng1,2 , LIU Zhao1,2, DING Tian-huai3, FAN Shang-chun1,2
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.
drillstring / acoustic transmission signal / multipath channel / multi-carrier modulation excitation / noise suppression {{custom_keyword}} /
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