Design of coded digital telemetry system for acoustic downhole channel with drilling noise

Logging-while-drilling (LWD) and measurement-while-drilling (MWD) applications have prompted the development of acoustic telemetry for retrieving downhole data. In this paper, a multilevel frequency shift keying (ML-FSK) modulation transceiver with pseudo-coherent differential energy detection is proposed and optimized for such acoustic telemetry applications. The motivation of employing the proposed multilevel FSK transceiver is its ability to cancel the effect of large drilling noise (drill bit noise and surface noise) with a low-complexity transceiver architecture, and its relative ease of dealing with oscillator or clock drifts caused by the harsh operating environment. To achieve better bit error rate (BER) over non-coherent demodulation while retaining the drilling noise cancellation capability, the receiver is modified to a pseudo-coherent demodulator. To further improve robustness, forward error correction (FEC) coding is applied and several coding options are evaluated over realistic acoustic drill string channel in the presence of drilling noise. The drill string channel investigated is made up of 110 segments, spans 1.011 km in length, has a characteristic comb-filter channel structure, with four pass bands (2^nd, 3^rd, 4^th and 5^th) used for telemetry.