## 4 Simulation and Analysis
### System Performance Analysis
This equivalence is primarily attributed to their effective utilization of the spatial resources provided by multiple antennas under similar channel conditions while maintaining signal independence and employing comparable signal processing strategies. Consequently, they achieve similar BER performance with reduced signal fading effects. Notably, in the \(1\times 1\) transceiver antenna configuration, the MIMO-FTN-OWC system without the interference cancellation algorithm achieves an approximate signal-to-noise ratio (SNR) of 31 dB compared to around 27 dB when utilizing the algorithm at a \(BER=10^{-3}\). Therefore, the proposed algorithm yields a coding gain of 4 dB. Figure 6: Magnitude–frequency characteristics. Figure 7: Comparison of signal sampling values (**a**) 4 PAM signals (**b**) FTN signals (**c**) signals after ISI cancellation. Figure 9 demonstrates the BER performance under medium turbulence conditions within the Gamma-Gamma channel for different numbers of transceiver antennas. It compares scenarios with and without the utilization of the proposed algorithm, at \(\tau=0.8\), \(ipce=0.5\), and \(\lambda=1550\) nm. Firstly, in the Single Input Single Output (SISO) system, employing the DL ISI cancellation algorithm improves system performance by 6 dB at \(BER=10^{-3}\) compared to its absence. In the MIMO system, with a fixed number of two transmitting antennas and varying receiving antennas set to two and four, respectively, utilizing the proposed algorithm improves system performance by 4.5 dB and 3 dB at \(BER=10^{-5}\) compared to its absence. Similarly, when four transmitting antennas are fixed while the receiving antennas are set to two and four, respectively, applying the proposed ISI cancellation algorithm improves system performance by 5.5 dB and 3 dB at \(BER=10^{-5}\) compared to its non-usage scenario. All aforementioned simulation results effectively demonstrate that our proposed MHSA-1D CNN-Bi-LSTM hybrid network successfully mitigates eliminates ISI introduced by FTN across various numbers of transceiver antennas, thereby significantly enhancing overall system performance. The optimal system performance is observed with a transceiver antenna configuration of \(4\times 2\), as shown in Figure 9. Therefore, this configuration is selected to investigate the algorithm's performance under varying turbulence intensities. Figure 10 presents a comparison of the BER performance with and without the proposed algorithm across weak, medium, and strong turbulence intensities, at \(\tau=0.8\), \(ipce=0.5\), and \(\lambda=1550\) nm. From the figure, it can be observed that utilizing the proposed ISI cancellation algorithm leads to an improvement in the system performance by 6.5 dB, 5.5 dB, and 7 dB, respectively, at  
Figure 8: Relationship between BER and SNR for our proposal and orthogonal system (OTS refers to Orthogonal Transmission System). Figure 9: Relationship between BER and SNR under different numbers of antennas. \(BER=10^{-5}\). This clearly demonstrates that the BER performance consistently surpasses that of the system without employing this algorithm. Under Gamma-Gamma medium turbulence conditions with an \(4\times 2\) antenna configuration, Figure 11 presents a comparison of the BER performance at different laser wavelengths with and without the proposed algorithm, when \(\tau=0.8\) and \(ipce=0.5\). At laser wavelengths of 1550 nm, 850 nm, 780 nm, and 635 nm, respectively, the system's performance is improved by 5.5 dB, 5 dB, 4.2 dB, and 3.4 dB at \(BER=10^{-5}\). The results indicate that as the laser wavelength increases, there is a decrease in BER along with an improved ability of the algorithm to eliminate interference.