SoftCast

Abstract

Abstract-Video broadcast and mobile video challenge the conventional wireless design. In broadcast and mobile scenarios the bit rate supported by the channel differs across receivers and varies quickly over time. The conventional design however forces the source to pick a single bit rate and degrades sharply when the channel cannot not support the chosen bit rate. This paper presents SoftCast, a clean-slate design for wireless video where the source transmits one video stream that each receiver decodes to a video quality commensurate with its specific instantaneous channel quality. To do so, SoftCast ensures the samples of the digital video signal transmitted on the channel are linearly related to the pixels' luminance. Thus, when channel noise perturbs the transmitted signal samples, the perturbation naturally translates into approximation in the original video pixels. Hence, a receiver with a good channel (low noise) obtains a high fidelity video, and a receiver with a bad channel (high noise) obtains a low fidelity video.We implement SoftCast using the GNURadio software and the USRP platform. Results from a 20-node testbed show that SoftCast improves the average video quality (i.e., PSNR) across broadcast receivers in our testbed by up to 5.5 dB. Even for a single receiver, it eliminates video glitches caused by mobility and increases robustness to packet loss by an order of magnitude.

Subsampling of 3D Pixel Blocks as a Video Compression Method for Analog Transmission

“…In particular, the schemes are designed to achieve graceful quality degradation for wireless channels whose conditions may vary unpredictably and drastically. Some of the schemes such as SoftCast [6], ParCast [7], LineCast [8], OmniCast [9], and FeatureCast [10] provide signals which can be transmitted in an analog form with a small amount of digital metadata. The metadata are used to scale power in visual data chunks according to their impact on quality.…”