Performance of channel coding and equalization for acoustic telemetry along drill strings

Real-time telemetry during drilling thousands of meters below the surface plays a key role in efficient utilization of oilfields. Current mud-pulse commercial systems are limited to only a few bits per second (bps). In this paper, we are interested in acoustic data transmission through the steel body of the drill string. We propose trellis coded modulation (TCM) coupled with multicarrier modulation. To cope with the intersymbol interference (ISI) and any synchronization issues at the receiver, joint carrier-phase synchronization and decision feedback equalization is used. In addition, weights based on the knowledge of the signal-to-noise-ratio (SNR) at different passbands are incorporated into the modified Viterbi decoder to improve the bit-error rate (BER). By using a realistic model of a 1-km-drill string channel, the BER performance of the acoustic system is demonstrated while achieving a signaling rate of 400 bps, about two orders of magnitude higher than current state-of-art mud-pulse telemetry systems. In addition, our results demonstrate that the decision feedback equalizer (DFE) is vastly less power-hungry than orthogonal frequency division multiplexing (OFDM).