Toward a digital acoustic underwater phone

The paper deals with the design of a digital acoustic underwater phone prototype. Digital techniques allow to achieve a synthesized speech with a quality close to the telephonic one. The input speech signal is compressed down to 5.45 kbit/s using a CELP coder. The bit rate is 6 kbit/s before channel coding and expected to be about 8 kbits/s after channel coding. A QPSK modulation with differential encoding was chosen to transmit the useful signal. For the receiver the authors use a scheme where synchronization and equalization (FSE+DFE) were jointly optimized. The whole system (unidirectional link) has been implemented on single DSPs (Motorola 56001) and tested successfully in a very difficult environment (IFREMER pool).<
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