This article describes the implementation of a multiple-input multiple-output acoustic communication link in shallow water conditions to enable a software-defined acoustic modem with a maximum transmission rate of 20 kbps in a 5-kHz bandwidth. The reliability improvement of a low-complexity Alamouti space–time block code is evaluated to improve the diversity in a high-rate transmission mode using single carrier modulation, as well as in a low-rate transmission mode relying on continuous-phase frequency-shift keying. Using measurements in realistic subsea conditions, the effect of the spatial channel correlation is demonstrated. It is found that for the space–time block code/continuous-phase frequency-shift keying, the spatial diversity is significantly degraded due to the high spatial correlation. In contrast, for the high-mode transmission rate, space–time block code with single carrier modulation offers a bit error rate improvement by a factor over hundred, in comparison to a single transmit element, demonstrating that the multiple-input multiple-output optimal code depends on the software-defined acoustic modem transmission mode.

本文介绍了在浅水条件下实现多输入多输出声学通信链路的方法，以使软件定义的声学调制解调器在5 kHz带宽内的最大传输速率为20 kbps。评估了低复杂度Alamouti空时分组码的可靠性，以改善使用单载波调制的高速率传输模式以及依赖连续相位频移的低速率传输模式的分集键控。通过在现实的海底条件下进行测量，证明了空间通道相关性的影响。发现对于空时分组码/连续相频移键控，由于高空间相关性，空间分集显着降低。相反，对于高模式传输速率，