# Error Resilient Coding Techniques for Video Delivery over Vehicular Networks
## 6 Conclusions and Future Work  
Two complementary approaches for the protection of video streaming over vehicular networks have been proposed. The first one is based on source coding, by using and fine tuning some intrinsic features of the video encoder (HEVC). In this approach seven new encoding modes have been presented, which introduce intra refresh into the encoded bit stream in order to avoid the propagation of errors in the decoding step. Also, a new element called tileslice has been introduced, which offers the good encoding efficiency of tiles and the good error resilience features of slices. The second approach is based on a well-known FEC technique, RaptorQ codes. We have analyzed the RaptorQ performance with our video encoded streams, defining the configuration parameter set that introduces the lowest overhead with the highest level of protection. To the authors' knowledge, no other works in the literature have evaluated the proposed tools in a realistic VANET scenario as the one proposed here, including state-of-the-art video coding/decoding, packetization, channel coding/decoding with Raptor codes, and network delivery using realistic simulation tools that provide accurate network and traffic models. Even though it makes the video bit stream more robust against losses, the source coding approach, by itself, cannot guarantee the minimum level of visual quality in these networks, especially when moderate and high background traffic conditions are encountered. However, it can significantly improve the video quality (PSNR), if the appropriate combination of encoding mode and tiles/frame layout is selected, for a particular network conditions. From all the encoding modes proposed, the IPPP and LPI4 show the best performance in most of the situations. For isolated packet losses, the selected til/frm layout has a  
obtained. When packet losses are bursty in nature the layout has little influence because (a) the PLR is very similar for all the til/frm layouts and (b) the TLR value is in line with the PLR value because missing packets probably belong to the same tile(s). For moderate network load conditions the 4 and 6 til/frm layouts have in general a good performance, and for tight network conditions a high number of tiles per frame (8, 10) are needed to provide robustness to the video bit stream. Even though, FEC channel coding is necessary in video streaming over vehicular networks because the protection provided by source coding is not enough to guarantee video delivery. The combination of the two protection approaches (RaptorQ codes and source coding) offers good performance when RaptorQ codes are not able to recover all the missing packets and the source coding protection mitigates the propagation and multiplication effect of errors. In order to select a suitable setup for the delivering of video in urban vehicular networks, we recommend the use of an encoding mode which has both good compression efficiency while providing a certain level of robustness. To this extent, the LPI4 mode is the best positioned mode. When it comes to select a til/frm layout, the combination of low overhead, good error resilient features, and a low avalanche effect (when translating PLR into the resulting TLR), values from 4 to 6 til/frm are the best tradeoff. At last, if we are protecting video streams delivered under full coverage areas, a protection level of 10% (in combination with a good encoding mode and til/frm layout), may provide the required robustness against isolated losses, to guarantee an appropriate user experience.