Hardware implementation of underwater acoustic localization system for bridge scour monitoring

This paper reports the first round of design and hardware implementation experience for localization of acoustic transmitter in a river. The application of the acoustic localization is bridge scour monitoring where smart rocks are equipped with acoustic communication systems to communicate with nodes at river banks. The time difference of arrival (TDOA) is measured by transmitting maximum-length pseudo-noise (PN) sequences and payload periodically using On-Off Keying (OOK) modulation at carrier frequency of 125 kHz. The receiver nodes at river banks use simple non-coherent detection to find the peak of PN correlation. The detected peak indexes are then used to estimate the TDOA for localizing the transmitter. The hardware transceiver is implemented on a Texas Instruments (TI) digital signal processor (DSP) platform. The major challenges encountered in the implementation and field tests included timing errors at separate transceivers, transceiver front end for high carrier frequency, environmental harshness, electro-magnetic interference, and acoustic multi-paths. Remedies are reported, including using GPS receivers at riverbank nodes, bandpass sampling and interface of ADC/DAC to DSP, and first-arrival peak detection algorithm.