## 5 Simulation and Analysis
### Position Detection of Light Spot under Beacon Spread-Spectrum Modulation  
To verify the effective detection of the light-spot position under beacon spread-spectrum modulation, the range and linear region of light-spot detection were tested and compared with direct detection. When the power of the beacon light received by the QD was \(-\)36 dBm, the light-spot positions were recorded for two different incident light-spot radii under both methods; these were 0.7 mm and 1 mm, respectively. When employing spread-spectrum technology, the depth of the modulation PRN was set to 127. For comparison purposes, under the same conditions regarding the light-spot radius and QD output SNR, direct detection was utilized to detect the light-spot position. As this paper investigates integrated measurement and communication technology, the direct method directly modulates the laser using beacon data. At the receiving end, the position was calculated using the absolute value of the signal. The position data were recorded  
Figure 6: The auto-correlation values of the Punctual code under the phase acquisition and tracking states of the digital phase-locked loop.  
along the \(x\)-axis as the light spot moved, with measurements taken every 10 \(\upmu\)m. The true light-spot position was calculated based on the collected voltages and compared with the method proposed in this paper. In Figure 7, \(\upomega\) represents the light-spot radius. The red solid line and green dashed line represent the x-coordinate curves obtained via direct detection with a modulation PRN depth of 127 and without spread-spectrum technology (\(G_{p}=1\)), respectively.  
As shown in Figure 7, the beacon spread-spectrum modulation method effectively detects the receiving position of the light spot. Its detection range and linear region are similar to those of direct detection, with the x-coordinate curves maintaining good linearity within the interval (\(-\)0.2, 0.2). At the same time, as the spot radius increases, the linear areas of the two increase when the radius is 1 mm. Figure 7 demonstrates that spread-spectrum technology can effectively detect the position of the light spot without affecting the detection range or radius of the light spot. Both detection methods are affected by the relationship between the true position and the relative position. Therefore, employing the optimized light-spot linear region method proposed in references [9, 11, 12, 13] can further enhance the relationship between the relative position and the true position of QD light-spot detection using spread-spectrum technology. This optimization aims to maintain the linearity of QD detection within a broader range. Moreover, it can be inferred from Figure 7 that, under beacon spread-spectrum modulation, the jitter of the detected light-spot position is reduced compared to direct detection, thereby enhancing the ability of the QD to perform light-spot position detection. As discussed in Section 3, the modulation of spreading sequences with different depths can achieve varying gain effects. Therefore, this study further compares the variation in the precision of QD position detection under different SNRs by modulating PRN sequences of different depths.