Virtual time reversal mirror chirp rate keying for multi-users underwater acoustic communication

To solve the problem of multi-user communication in severe frequency-selective fading channel, a multi-user communication algorithm based on VTRM (Virtual Time Reverse Mirror) Chirp-rate keying is proposed. The proposed algorithm selects up-chirp and down-chirp signal as the carriers. And receiver uses the relationship between fractional Fourier transform domain and central frequency of Chirp signal to demodulate the received signals. The VTRM technology can reduce the multipath effect on the system. And diversity of Chirp-rate is used as the multiple access to distinguish different users. The proposed scheme can support four users to communication with the 10 kHz bandwidth, 425 bps data rate per user of the proposed communication scheme is realized. Water pool and sea experiment verified that the data could be transmitted effectively using the proposed scheme and bit error rate was 10^-3 order of magnitude.