## 3 Simulation Results  
The MIMO underwater channel model in [27] was adopted, which exhibited a carrier central frequency of 11.5 kHz, an underwater channel bandwidth of 4 kHz, and a transmission distance of 1 km. Figure 2 illustrates the BER performances of the \(2\times 2\) DM-based MIMO-FBMC UAMCA with channel estimation errors (CEEs) of 0% (perfect channel estimation), 5%, 10%, and 20%. In Figures 2-5, the symbols 'o', and '\(\Delta\)' denote the BPSK and 4-OQAM modulation technology, respectively. In Figures 2-5, the colors 'black','red', 'blue', and 'fuchsia' denote the proposed UAMCA with CEEs of 0%, 5%, 10%, and 20%, respectively. The BER performances of the proposed UAMCA with CEEs of 0%, 5%, 10%, and 20%, using BPSK modulation technology, and for a signal-to-noise ratio (SNR) of 12.59 dB, are \(2\times 10^{-6}\), \(2.67\times 10^{-6}\), \(4.67\times 10^{-6}\), and \(2.13\times 10^{-5}\), respectively. The BER performances of the proposed UAMCA using 4-OQAM modulation with all other conditions retained from the BPSK system, are \(2.93\times 10^{-5}\), \(5.73\times 10^{-5}\), 0.00011, and 0.00041, respectively. The simulation results demonstrate that the BER performances of the proposed UAMCA with BPSK modulation technology are better than those of the system with 4-OQAM modulation technology. Furthermore, the BER performances of the proposed UAMCA degraded as the CEEs increased. The transmission BERs requirements for underwater voice, image, and data signals are \(10^{-3}\), \(10^{-4}\), and \(10^{-5}\), respectively. Consequently, low transmission power can be achieved for underwater voice, image, and data multimedia communication. The power-saving (PS) ratio of the DM-based MIMO-FBMC UAMCA is defined as follows:  
\[PS=(1-r_{n,p})\times 100\% \tag{6}\]  
Figures 3-5, depict the PS ratios of the DM-based MIMO-FBMC UAMCA with BERs of \(10^{-3}\), \(10^{-4}\), and \(10^{-5}\), respectively, for CEEs of 5%, 10%, and 20%. Figure 3 depicts that the \(N_{o}\) values for the proposed UAMCA using BPSK modulation technology, with the BER of \(10^{-3}\) and a PS ratio of 27%, are 0.1238, 0.1105, and 0.0869, respectively. \(N_{o}\) is the power spectral density of additive white Gaussian noise (AWGN). Figure 2: The BER performances of the \(2\times 2\) DM-based MIMO-FBMC UAMCA with CEEs of 0%, 5%, 10%, and 20%. Figure 4: The PS ratio of the \(2\times 2\) DM-based MIMO-FBMC UAMCA with the BER of \(10^{-4}\), for CEEs of 5%, 10%, and 20%. Figure 3: The PS ratio of the \(2\times 2\) DM-based MIMO-FBMC UAMCA with the BER of \(10^{-3}\), for CEEs of 5%, 10%, and 20%. The \(N_{o}\) values for the proposed UAMCA using 4-OQAM modulation technology, with the BER of \(10^{-3}\) and a PS ratio of 27%, are 0.0791, 0.0695, and 0.0581, respectively. Figure 4 depicts that the \(N_{o}\) values for the proposed UAMCA using BPSK modulation technology, with the BER of \(10^{-4}\) and a PS ratio of 27%, are 0.0606, 0.0574, and 0.0422, respectively. The \(N_{o}\) values for the proposed UAMCA using 4-OQAM modulation technology, with the BER of \(10^{-4}\) and a PS ratio of 27%, are 0.0352, 0.0304, and 0.0246, respectively. Figure 5 depicts that the \(N_{o}\) values for the proposed UAMCA using BPSK modulation technology, with the BER of \(10^{-5}\) and a PS ratio of 27%, are 0.0358, 0.0337, and 0.0254, respectively. Finally, The \(N_{o}\) values for the proposed UAMCA using 4-OQAM modulation technology, with the BER of \(10^{-5}\) and a PS ratio of 27%, are 0.0223, 0.0199, and 0.0167, respectively. With increasing transmission BER requirements for underwater voice, image, and data signals, \(N_{o}\) decreases, with the same PS ratio. As the CEEs increase, \(N_{o}\) decreases, with the same PS ratio. The \(N_{o}\) of 4-OQAM is less than that of BPSK, with the same PS ratio. Consequently, the PS ratios of BPSK are greater than those of 4-OQAM under BERs of \(10^{-3}\), \(10^{-4}\), and \(10^{-5}\). As the CEEs decrease, the PS ratio increases.