# Error Resilient Coding Techniques for Video Delivery over Vehicular Networks
## 2 Related Work
They use three tablets: one of them acts as an access point and the other two act as the video sender/receiver. They use erasure codes, based in eXclusive OR (XOR) operations, in order to protect the video traffic from losses. Their work lacks in accuracy because they use the 802.11b/g/n protocols instead of the 802.11p protocol, which is the protocol specifically developed for vehicular networks. In [11], the authors present the Multichannel Error Recovery Video Streaming (MERVS) scheme, a streaming protocol in which the most relevant video frames are transmitted using the Transmission Control Protocol (TCP) protocol, and the least relevant video frames are transmitted using the User Datagram Protocol (UDP) protocol. TCP is in charge of retransmitting lost frames, so the protection is guaranteed by this protocol. The main restriction is that TCP mechanisms insert a great delay in the transmission and to overcome this drawback the authors use a mechanism called Quick-Start which alleviates the delay to some extent. There is no information about the bit rate of the compressed video sequence used, nor its frame rate. In addition, no information is presented about if any amount of background traffic has been injected into the scenario in order to reproduce realistic conditions. So it is difficult to evaluate if this TCP scheme is valid when several TCP flows compete. In [12,13], the authors propose two mechanisms called Shield and AntArmour, to protect video streaming in vehicular networks, and they make comparisons between them. Shield uses the network and video statistics to make a self-adaptive mechanism in order to provide different protection levels to network packets. They use the combination of the general network criteria and the video details criteria in a Hierarchical Fuzzy System (HFS) which has been previously trained in order to make real-time decisions. This proposal is based in the H.264/AVC standard and so it cannot benefit from the HEVC features. AntArmour uses a scheme which is based in ant colonies to dynamically allocate the precise amount of redundancy to protect the video stream. In a similar way as Shield works, there is a first off-line step to gather information and feed a fuzzy logic system, and then, the real-time values are computed and passed to the system to obtain the appropriate level of redundancy. These statistics are computed on a car-to-car video streaming basis, so the generalization for other type of video delivery as video broadcasting seems not an easy step. In [14] an error recovery protocol called Hybrid Error Recovery Protocol(HERP) is presented. It is the combination of two strategies mixing redundancy with retransmission of missing data to make the video stream robust against data loss. HERP uses unequal error protection of data packets, regarding the frame type, which may lead to an optimization of the final reconstructed video quality. One of the objections to the experiments driven in that work is the low resolution of exchanged videos. The results may be different when using higher resolution videos, as the number of packets per frame would considerably increase. In a previous work ([15]), we evaluated RaptorQ codes performance in the protection of video streaming in vehicular networks. In the present work, new techniques have been proposed. The most significant one is the introduction of a new coding element which is the combination of a slice with a tile (that we call tileslice). To the author's knowledge, no previous works have used this specific combination of these two HEVC features. In this work, a comparative analysis of the compression efficiency of slices and tiles has also been carried out. As well, seven new encoding modes introducing different levels of intra refresh have been designed and have been evaluated, together with the two simple encoding modes tested in [15].