## 3 Available Techniques to Reduce the Bandwidth of the 360-Degree Video
### Tiling
#### 3.2.8 OpCASH
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Source** & \multicolumn{2}{c}{**Technique**} & \multicolumn{2}{c}{**Result**} & \multicolumn{1}{p{113.8 pt}}{**Limitation**} \\ \hline
[34] & \(\bullet\) & Dynamic adaptive HTTP streaming (DASH). & \(\bullet\) & Saved 76\% bandwidth in comparison to the non-tiling scheme. Saved 52\% downloaded volume in comparison to fixed tiling schemes. & A fixed tiling scheme requires tile selection algorithms. \\ \hline
[12] & \(\bullet\) & Dynamic adaptive HTTP streaming (DASH). & \(\bullet\) & Enable High-quality service with high interactivity with HMD with low management required from VR providers. & Improved adaption algorithms are required to predict head movement, as well as a new video encoding approach to do quality-differentiated encoding for high-resolution videos. \\ \hline
[38] & \(\bullet\) & Dynamic adaptive HTTP streaming (DASH). & \(\bullet\) & Increased video bitrates (\(\leq\)46\%) for video tiles in users’ viewports. & Require a better tile weighting approach with data-driven probabilistic as well as an improved rate adaption algorithm. \\ \hline
[37] & \(\bullet\) & MPEG-DASH SRD. & \(\bullet\) & Improve performance with an adaptive rate allocation method for tile streaming based on available bandwidth. \\ \hline
[35] & \(\bullet\) & Variable-sized tiling scheme. & \(\bullet\) & The same PSPNR was obtained with 41-46 percent reduced bandwidth consumption than [34]. & The 360 JND model is based on the results of a survey in which the values of 360\({}^{\circ}\) video-specific characteristics were varied individually. \\ \hline
[36] & \(\bullet\) & Higher sphere-to-2D projection efficiency. The ffmpeg360 program transcodes 360-degree videos and assesses the quality of 360-degree videos based on user head movement patterns. & & The 360 JND model is based on the results of a survey in which the values of 360\({}^{\circ}\) video-specific characteristics were varied individually. \\ \hline
[39] & \(\bullet\) & Created collection of views with the rectilinear projection referred to as “minview”, which have smaller FOVs than cube faces, hence able to save encoded 360-degree videos’ storage size while maintaining the quality. & Saved up to 16\% encoded video size without much quality loss. & Fixed tiles, each minview might well be encoded into segments individually, and the streaming client could request these segments as needed. \\ \hline
[39] & \(\bullet\) & Adapt sidelink. Weighted tile allocation. Two-stage optimization technique. & [PERSON], [PERSON] [39] formulated optimization problems based on the interaction between tile quality level selection, sidelink sender selection, and bandwidth allocation to optimize the overall utility of all users. & When the number of groups is increased from 10 to 50, the tile quality degrades because less bandwidth can be provided to each group as the number of groups \\ \hline
[40] & \(\bullet\) & Variable-sized tiling scheme. Adap MEC cache usage. ILP-based technique for determining the best cache tile configuration on the MEC server. & OpCASH obtained more than 95 percent VP coverage from cache after only 24 views of the video. When compared to a baseline that illustrates standard tile-based caching, OpCASH reduces data fetched from content servers by 85\% and overall content delivery time by 74\%. & Improve real-time tile encoding features on content servers by including tile quality selection in the ILP formulation and increasing the variable quality level tiles streaming in. Next, in a lab scenario, interact with many edge nodes using real-world user testing to achieve the biggest benefit at the edge layer. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of existing tiling approaches.