## 4 Experimental Simulation
### Performance Analysis of OFDM Signal Demodulation  
#### 4.2.1 Simulation of Demodulation Process of OFDM Signals by FUBSR and SUUBSR Systems  
To further verify the demodulation effect of OFDM signals in the FUBSR and SUUBSR systems, as well as the integration of these two systems with the OFDM signal demodulation process, constellation diagrams at the receiver end of different stochastic resonance systems are plotted under the condition of an SNR of 2 dB. The demodulation performance of the system for OFDM signals is analyzed by examining the deviation of each point in the constellation diagram from the central position. The simulation parameters are set as follows: the number of subcarriers is 64, the number of OFDM signal symbols is 20, and the modulation method is 16 QAM. Under the condition of an SNR of 2 dB, using the quantum particle swarm optimization algorithm, the optimal parameter sets \(a=4.71,v=3.3493,r=1.6614;a=1.1,v=0.4161,r=1.6,\gamma=0.511\), for the two systems are obtained by optimizing the system parameters based on the OFDM signal SNR as the evaluation metric. The constellation diagrams before and after the demodulation of the OFDM signal processed by the FUBSR system under 16 QAM modulation are shown in Figures 10 and 11.  
Figure 10 shows the constellation diagram of the OFDM signal after passing through a Gaussian channel. As can be seen from Figure 10, due to the influence of Gaussian noise, the constellation diagram of the OFDM signal becomes very chaotic. Figure 11 depicts the constellation diagram of the OFDM signal demodulated by the FUBSR system. Compared to Figure 10, the points in Figure 11 are more concentrated around the 16 initial central points, indicating that the FUBSR system can be combined with the demodulation process of OFDM signals. However, there are still many points deviating, indicating that the demodulation effect is not ideal.  
Figure 12 shows the constellation diagram of the OFDM signal demodulated by the SUUBSR system proposed in this paper. Most of the points in Figure 12 are clustered around the 16 initial central points, with only a small number of points deviating. This  
Figure 11: Constellation diagram of the demodulated OFDM signal processed by the FUBSR system.  
Figure 10: Constellation diagram of an OFDM signal passing through a Gaussian channel.  
indicates that the demodulation performance of the SUUBSR system for OFDM signals is better than that of the FUBSR system.  
To further verify the demodulation performance of the proposed system in this paper for OFDM signals under different subcarrier modulation schemes, the simulation parameters are kept consistent with those for 16 QAM subcarrier modulation. The FUBSR system and the SUUBSR system are used to demodulate and simulate OFDM signals with QPSK and 64 QAM modulation schemes. The constellation diagrams of the OFDM signals processed by the FUBSR system and the SUUBSR system after demodulation, under QPSK and 64 QAM subcarrier modulation schemes, are shown in Figure 13. From Figure 13, it can be observed that under both QPSK and 64 QAM subcarrier modulation schemes, the constellation diagrams of the OFDM signals processed by the SUUBSR system exhibit better clustering than those processed by the FUBSR system.  
Figure 12: Constellation diagram of the demodulated OFDM signal processed by the SUUBSR system.  
Figure 13: Simulation of the demodulation effects of OFDM signals under different modulation methods for the two systems. (**a**) Simulation of the demodulation effects of OFDM signals with QPSK modulation for the FUBSR system. (**b**) Simulation of the demodulation effects of OFDM signals with QPSK modulation for the FUBSR system. (**c**) Simulation of the demodulation effects of OFDM signals with 64 QAM modulation for the FUBSR system. (**d**) Simulation of the demodulation effects of OFDM signals with 64 QAM modulation for the FUBSR system.