Signal and receiver design for low-power acoustic communications using m-ary orthogonal code keying

Low-power, low received signal-to-noise-ratio (SNR) signals have potential for reducing the impact on marine life from acoustic communications. Here we explore the use of bandlimited pseudo-noise m-ary orthogonal code keying (MOCK) scheme using m-sequences. Analysis and simulation of receiver structure for synchronisation and data demodulation performance is carried out. Performance of M-OCK is compared with m-ary quadrature amplitude modulation with direct-sequence spread-spectrum (M-QAM DSSS). Real-world channel experiments are carried out with transmission power for the MOCK sequences limited to less than 1 W acoustic power (170.8 dB re 1 μPa at 1 m) and transmission range varied from 100 m to 10 km in the North Sea. Synchronisation at 10 km is achieved with effective received signal-to-noise-ratio of less than -9.96 dB, and data demodulation of 140.7 bit/s raw throughput with pre-coding bit-error-rate (BER) 0.5 × 10-1 (symbol-error-rate (SER) 0.1) and 46.9 bit/s raw throughput with pre-coding BER 0.9 × 10-3 (SER 1.95 × 10-3). Error-free synchronisation and data demodulation is achieved at ranges up to 2 km, demonstrating data rates in excess of 140 bit/s.