Underwater acoustic communication system of AUV

The underwater acoustic communication system (UACS) is an important part of an AUV. We developed an underwater acoustic communication system for a AUV: IASS-1, which is based on both MFSK and MPSK. Generally a AUV sends a large amount of data to the host vessel, and MPSK modulation is adopted. The receiver on the host vessel adopts space diversity (SD), a decision feedback equalizer (DFE), and fast self-optimized LMS phase estimator (FOLMSPE) techniques jointly. The fast self-optimized LMS (FOLMS) algorithm is implemented in the DFE. A short vertical hydrophone array is suspended or towed on the host vessel for signal reception. The separation between each hydrophone is far larger than the wavelength. The MFSK modulation and convolution code are adopted when the host vessel sends a message to the AUV. The receiver on AUV adopts the Viterbi algorithm. This well-known mechanism, using MFSK and convolution code, performs well when the transmission rate is low. Compared with MPSK modulation, it has the advantage of being very resistant to the most difficult multipath propagation, and is less sensitive to the vessel scattered wave. IAAS-1 was tested in a lake and was successfully operated at ranges over 100-4000 m (constrained by the test area). The symbol rate for QPSK is 2.5 ks/s and 5.0 ks/s. The bit error rate (BER) is between 10^-4 and 10^-5