Hermes is a Single-Input Single-Output (SISO) underwater acoustic modem that\r\nachieves very high-bit rate digital communications in ports and shallow waters. Here, the\r\nauthors study the capability of Hermes to support Multiple-Input-Multiple-Output (MIMO)\r\ntechnology. A least-square channel estimation algorithm is used to evaluate multiple\r\nMIMO channel impulse responses at the receiver end. A deconvolution routine is used to\r\nseparate the messages coming from different sources. This paper covers the performance of\r\nboth the channel estimation and the MIMO deconvolution processes using either simulated\r\ndata or field data. The MIMO equalization performance is measured by comparing three\r\nrelative root mean-squared errors (RMSE), obtained by calculations between the source\r\nsignal (a pseudo-noise sequence) and the corresponding received MIMO signal at various\r\nstages of the deconvolution process; prior to any interference removal, at the output of the\r\nLinear Equalization (LE) process and at the output of an interference cancellation process\r\nwith complete a priori knowledge of the transmitted signal. Using the simulated data, the\r\nRMSE using LE is -20.5 dB (where 0 dB corresponds to 100% of relative error) while the lower bound value is -33.4 dB. Using experimental data, the LE performance is -3.3 dB\r\nand the lower bound RMSE value is -27 dB.
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