High-rate acoustic communications for ocean observatories-performance testing over a 3000 m vertical path

The viability of acoustically-linked, long-term ocean sensing is dependent on the power efficiency of the communications system. Energy storage in the deep ocean remains costly despite advances in battery technology, and thus, maximizing data throughput at constant power is an important goal. In preparation for future deep-water applications, a test was previously conducted in 3000 m water to measure the performance of a communications system using a number of different signaling techniques. The signals included BPSK, QPSK and 8-PSK modulation with data rates up to 15000 bits per second. Several receivers were used, including directional transducers, both baffled and un-baffled, as well as a small omnidirectional array. Reliable communication at up to 15000 bps using 7.5 W at the transmitter was achieved. The baffled directional receiver offered the best performance, while the omni-directional array provided approximately 50% less throughput. Source-receiver motion was found to impact system performance and results using an improved Doppler tracking and compensation method are described. Details of the results using various modulation methods and receiver combinations are discussed and their performance extrapolated to full-ocean depth as an aid to the design of future ocean observatory links.