An Acoustic OFDM System with Symbol-by-Symbol Doppler Compensation for Underwater Communication

Abstract

We propose an acoustic OFDM system for underwater communication, specifically for vertical link communications such as between a robot in the sea bottom and a mother ship in the surface. The main contributions are (1) estimation of time varying Doppler shift using continual pilots in conjunction with monitoring the drift of Power Delay Profile and (2) symbol-by-symbol Doppler compensation in frequency domain by an ICI matrix representing nonuniform Doppler. In addition, we compare our proposal against a resampling method. Simulation and experimental results confirm that our system outperforms the resampling method when the velocity changes roughly over OFDM symbols. Overall, experimental results taken in Shizuoka, Japan, show our system using 16QAM, and 64QAM achieved a data throughput of 7.5 Kbit/sec with a transmitter moving at maximum 2 m/s, in a complicated trajectory, over 30 m vertically.

Design and implementation of low power encoder incorporating adaptive modulation for multi user OFDM system

“…Space diversity is adopted in OFDM system to improve the diversity properties to reduce bit error rate. The power consumption of the conventional OFDM system [9] is high which is not suitable for adavnced 4G/5G wireless communication systems. The error rate is also high due to the time varying channels.…”