Abstract
Nowadays, more and more vehicles are equipped with communication capabilities, not only providing connectivity with onboard devices, but also with off-board communication infrastructures. From road safety (i.e., multimedia e-call) to infotainment (i.e., video on demand services), there are a lot of applications and services that may be deployed in vehicular networks, where video streaming is the key factor. As it is well known, these networks suffer from high interference levels and low available network resources, and it is a great challenge to deploy video delivery applications which provide good quality video services. We focus our work on supplying error resilience capabilities to video streams in order to fight against the high packet loss rates found in vehicular networks. So, we propose the combination of source coding and channel coding techniques. The former ones are applied in the video encoding process by means of intra-refresh coding modes and tile-based frame partitioning techniques. The latter one is based on the use of forward error correction mechanisms in order to recover as many lost packets as possible. We have carried out an extensive evaluation process to measure the error resilience capabilities of both approaches in both (a) a simple packet error probabilistic model, and (b) a realistic vehicular network simulation framework. Results show that forward error correction mechanisms are mandatory to guarantee video delivery with an acceptable quality level , and we highly recommend the use of the proposed mechanisms to increase even more the final video quality.
Highlights
Video delivery over vehicular networks is a challenging task
The other six modes have increasing Peak Signal-to-Noise Ratio (PSNR) values when the number of tiles per frame increases. This result is consistent throughout all the Packet Loss Ratio (PLR) tested, in all the experiments, we have observed that when a high number of tiles per frame is selected, the recovered video sequence obtains a better PSNR value
The overhead values for the rest of the layouts have not been included in these tables for the sake of concision and clarity, but they show monotonically increasing behavior: the higher the number of tiles per frame, the higher the overhead introduced by Forward Error Correction (FEC) protection
Summary
Video delivery over vehicular networks is a challenging task. On the one hand, video streaming requires high bandwidth and timely delivery, and, on the other hand, vehicular networks are error-prone environments with many challenges to deal with (changing topology, high relative speed of nodes, interferences, Doppler effect, etc.). The first one improves bit stream error resilience at source coding level, i.e., adapting and adjusting video encoding in such a way that the encoded bit stream may provide, up to certain data loss degree, good video quality to the user. For this task we have proposed (a) a new frame partition scheme (a mix of tiles and slices), and (b) seven intra-refresh encoding modes (ranging from low to high intra-refresh rates).
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