## 2 System Models
\begin{table}
\begin{tabular}{c c} \hline \hline
**Technology** & **Technology Characteristics** \\ \hline FBMC modulation & PHYDAS FBMC technology [25] \\ FFT size & 64-points \\ Channel coding & (2000, 1000) LDPC code encoder with a code rate of 1/2, \\  & a column weight of 3, a row weight of 6 \\ MIMO & \(2\times 2\) DM \\ Power levels & 0.09, 0.18, 0.27,..., 1 \\ BER limits for voice transmission & \(10^{-3}\) \\ BER limits for image transmission & \(10^{-4}\) \\ BER limits for data transmission & \(10^{-5}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The parameters of the proposed \(2\times 2\) DM-based MIMO-FBMC UAMCA. As a result, the adaptive 2 \(\times\) 2 DM-based MIMO-FBMC signal with the power assignment method can be represented as follows:  
\[\mu_{n,p,k,b}(t)=\sum_{b=1}^{MK}\sum_{k=1}^{K-1}r_{n,p}A_{n,p,k,b}\phi_{p,k,b}(t) \tag{4}\]  
where \(r_{n,p}\) is the transmission power weighting of the \(nth\) user, transmitted on the \(p\)th underwater microphones. The signal received on the \(qth\) hydrophone, for the \(nth\) user, is expressed as follows:  
\[y_{n,q,k,b}(t)=\sum_{p=1}^{p}\mu_{n,p,k,b}(t)*h_{p,q}(t)+w_{p,q}(t) \tag{5}\]  
where \(h_{p,q}(t)\) is the underwater multipath tapped-delay line channel impulse response of the \(p\)th transmission underwater microphone and the \(qth\) receiver hydrophone, for the \(nth\) user. \(p\) is 1 or 2, and \(q\) is 1 or 2. The SNRs (signal-to-noise) of the \(n\)-th user, for received voice, image, and data multimedia packets, can be detected using the double window detection algorithm [26] and are denoted with the symbols '\(SNR_{n,toxic}\)', '\(SNR_{n,image}\)', and '\(SNR_{n,data}\)', respectively. The proposed underwater multimedia transmission power assignment algorithm (UMTPAA) for the 2 \(\times\) 2 DM-based MIMO-FBMC UAMCA technology is summarized as follows:  
1. With the output information obtained from the OCPN mechanism, assign the transmission packet rates for underwater voice, image, and data signals
2. Adopt the appropriate modulation scheme to meet the quality of services requirements for underwater voice, image, and data multimedia communication. 3. Set up the initial underwater transmission power level of \(r_{n,p}\) as 0.54 for voice, image, and data multimedia signals. 4. Measure the received \(SNR_{n,toxic}\), \(SNR_{n,image}\), and \(SNR_{n,data}\) of the \(n\)-th user, for received underwater voice, image, and data multimedia packets, respectively. 5. If the measured \(SNR_{n,toxic}\), \(SNR_{n,image}\), and \(SNR_{n,data}\) of the received underwater voice, image, and data multimedia packets, respectively, exceed the underwater multimedia threshold SNRs at the required multimedia BERs of \(10^{-3}\), \(10^{-4}\), and \(10^{-5}\), respectively, for voice; and the image or data packets are achieved, then update \(r_{n,p}\) as \(r_{n,p}=r_{n,p}-\Delta\), where \(\Delta\) is equal to 0.09. If \(r_{n,p}\geq 0.09\), go to Step 4; otherwise, go to Step 7. 6. If the measured \(SNR_{n,toxic}\), \(SNR_{n,image}\), and \(SNR_{n,data}\) of the received underwater voice, image, and data multimedia packets, respectively, is less than the underwater multimedia threshold SNRs at the required multimedia BERs of \(10^{-3}\), \(10^{-4}\), and \(10^{-5}\), respectively, for voice; and the image or data packets is achieved, then update \(r_{n,p}\) as \(r_{n,p}=r_{n,p}+\Delta\), where \(\Delta\) is equal to 0.09. If \(r_{n,p}\leq 1\), go to Step 4; otherwise, go to Step 7. 7. Downgrade the modulation scheme. If the modulation scheme is not 4-OQAM, then go to Step 4. 8. Upgrade the modulation scheme. If the modulation scheme is not BPSK, go to Step 4. The receiver structure has the inverse function of the transmitter structure. The 2 \(\times\) 2 DM-based MIMO-FBMC received multimedia packets were demodulated using a 2 \(\times\) 2 DM-based MIMO-FBMC demodulator, and the 2 \(\times\) 2 DM-based MIMO-FBMC multimedia demodulation packets were extracted as output.