## 4 Performance Evaluation
### Bit Error Rate Performance  
The figures from Figures 6-8 present the Bit Error Rate (BER) performances of the proposed and referenced network and channel coding methods, as illustrated in Figure 3. In each figure, subfigures (a) and (b) depict the BER performances for the color video and depth map streams, respectively. The X-axis represents the hierarchical value (\(\alpha\)), the Y-axis represents the relay location (\(\lambda\)), and the Z-axis represents the BER. For the theoretical analysis of LLR and the exact BER calculation used in this paper, please refer to the appendix of [11] and [17], respectively.  
In the case of the proposed method shown in Figure 6, the BER performance for the color video stream improves as \(\alpha\) increases, while the BER for the depth map stream deteriorates. This trend is consistent across different relay locations, except when \(\alpha\) is between 0.1 and 0.4. Additionally, the target BER is set to \(10^{-6}\) for the more important stream (color video) and \(10^{-5}\) for the less important stream (depth map). As a result, the color stream meets the target BER when \(\alpha\) is greater than 0.6, while the depth stream meets the target BER only when \(\alpha\) is exactly 0.6.  
For the first referenced method shown in Figure 7, the BER performance of the color video stream improves with increasing \(\alpha\), whereas the BER for the depth map stream worsens. However, this method shows suboptimal performance unless the relay node is positioned near the center. Consequently, the BERs for both color and depth streams meet their respective target BERs when \(\alpha\) is greater than 0.4 and 0.3, respectively, but only if the relay is located near the center (i.e., \(\lambda\) is between 0.4 and 0.6).  
Finally, for the second referenced method shown in Figure 8, the BER performance exhibits a similar pattern to the proposed method in Figure 6, but it can be observed that the second referenced method has a lower BER performance than the proposed method. Based on these BER performances, the following conclusions can be intuitively drawn.  
* The qualities of left and right views may be improved as the hierarchical value \(\alpha\) increases because the increased \(\alpha\) makes the 2D color streams stronger. However, the quality improvement becomes saturated at any moment.
* Relay positioning significantly affected the performance, with central locations providing balanced protection to both streams due to equal path gains, while asymmetric placements favored the nearer stream.
* Increasing the \(\alpha\) does not necessarily improve the quality of the virtual center view. This is because the virtual view is typically generated by synthesizing the color views and the related depth maps. In other words, since the quality of the depth maps, which are degraded due to the increased \(\alpha\), also affects the quality of the virtual center view, increasing the \(\alpha\) may not always be good for the quality.  
Figure 5: The example of view synthesis using MPEG VSRS.  
* It can be found that the higher modulation level (e.g., 16 QAM) is more sensitive to the effect of path loss. Therefore, the proposed and the second referenced methods may show improved qualities of left and right views compared to that of the first reference method, regardless of the relay location.
* However, in the case of the virtual center view, perhaps only certain \(\alpha\) values in the proposed method are expected to show improved quality. This is because only a certain \(\alpha\) value of the proposed method reaches the target BERs of the 2D color and depth streams, respectively, regardless of the relay location (e.g., \(\alpha=0.6\) in Figure 6).  
Figure 6: BER performances of the proposed network and channel coding method: as \(\alpha\) increases, the BER for the color video stream improves, while the BER for the depth stream deteriorates, highlighting the trade-off in protection levels between streams.