# Covert Surveillance Video Transmission with QAM Constellations Modulation
## 4 Experiments and Analysis  
In this section, we present simulation results based on test conditions, showcasing the transmission rates of surveillance videos under different transmission powers and the covertness performance metrics corresponding to these power levels. Throughout all subsequent tests, the 16\(-\)QAM modulation scheme, as employed in the H.264/AVC protocol, is utilized. Additionally, we conduct comparisons of transmission rates and covertness metric values based on various channel coefficients and receiver noise levels. To assess the effectiveness and superiority of the proposed optimal probability theory, we compare optimization results obtained using the backtracking line method from [40]. To enhance the effectiveness and authenticity of the experimental results, we set the experimental parameters as follows: the covert signal detection channel coefficient \(g_{w}\) is set to 0.4 and 0.8 and the covert communication detection channel noise variance \(\sigma_{w}\) is set to 1.5 and 1, respectively; the covert signal receiver channel coefficient \(g_{b}\) is set to 0.4 and 0.8 and the covert signal receiver channel noise variance \(\sigma_{w}\) is set to 1.5 and 1, respectively. Additionally, we set the code block length \(n\) to \(1\times 10^{6}\) and the number of symbols in a single-axis constellation set \(N\) to 4. Figure 4a provides a visual comparison of the outcomes obtained using our novel Taylor expansion method and the exact values. The covertness metric \(\epsilon\), spanning from 0 to 1, serves as an indicator of covertness performance, with smaller values denoting enhanced concealment. As depicted in the visual representation, there is a noticeable decline in transmission rate as the covertness metric diminishes. Remarkably, our proposed Taylor expansion approximation method exhibits a remarkable concordance with the computationally derived exact values. This alignment underscores the high degree of accuracy achieved by our approximation approach. Such close correspondence not only validates the precision of our proposed method but also underscores the efficacy of the theoretical framework derived from this approximation. Figure 4b illustrates the relationship between absolute error and the covertness metric \(\epsilon\). As the covertness metric decreases, the fitting accuracy exhibits exponential improvement. In the considered scenarios (\(\epsilon\leq 0.01\)), the fitting accuracy reaches \(10^{-5}\), fully satisfying the precision requirements for our experimental objectives. This validation further solidifies the practical applicability and robustness of our proposed approach within the context of covert communication systems. Figure 4(a) provides a comprehensive depiction of the intricate trade-off between the covertness metric and transmission power across varying detection channel coefficients. To benchmark the efficacy of our proposed theoretical framework, we systematically contrast its outcomes to optimization results derived using the backtracking line method. Specifically, we investigate covert transmission scenarios for surveillance videos by setting the detection channel coefficient \(g_{w}\) to the values of 0.4 and 0.8. At \(g_{w}\) = 0.4, our proposed methodology reveals a discernible decline in covertness performance with increasing transmission power. Notably, at lower power levels, our approach consistently outshines the comparative backtracking line method, as evidenced by lower covertness metric values. This observation underscores the superiority of our method in achieving enhanced covertness, particularly when confronted with constraints on power levels. Conversely, at higher transmission power levels, both methodologies converge to approximately equal covertness metric values. This convergence suggests that relying solely on the design of QAM constellation probabilities may not be sufficient to ensure the covert transmission of surveillance videos at elevated power levels.