[57] A method for data exchange between first and second communication systems, the method comprising:
(i) receiving a signal representative of a digital data stream generated in the first communication system, and processing said data stream to translate it into a predetermined sequence of frequencies;
(ii) concurrently operating an array of acoustic transmitters to generate an acoustic signal in the form of a superposition of frequency components generated by the acoustic transmitters, respectively, and allowing transmission of said acoustic signal to the second communication system;
(iii) receiving a multi-frequency acoustic signal and processing it in accordance with data indicative of the predetermined sequence of frequencies to thereby reconstruct a data stream received from the second communication system.
