Patent ID: 7835228

Claim:
A method for transmitting data between modems through a medium that transmits acoustic waves comprising the following steps: emitting from a first modem, acoustic waves in to the medium, comprising packets of at least two types, pure data, and acknowledgment of receipt messages, wherein each packet is formed of three components: a—an acquisition preamble formed of a set of pulses of finite duration, for presence detection and a joint determination of initial values of a time shift and of a frequency shift, b—data proper, c—a set of unmodulated fixed carriers suitable for permanently estimating the frequency shift, receiving with a second modem, the acoustic waves emitted by the first modem; demodulating the data proper with the second modem based on the acquisition preamble and the set of unmodulated fixed carriers, wherein non-linear frequency ramps, rising or falling “hyperbolic chirps” with characteristics fixed by duration and extreme frequencies used (minimum and maximum), are used for the pulses of the acquisition preamble.