Diversity Embedded Space–Time Codes

2010 48th Annual Allerton Conference on Communication, Control, and Computing (Allerton)

2010

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.

Section: Methodsmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

SoftCast: Clean-slate scalable wireless video

2010 48th Annual Allerton Conference on Communication, Control, and Computing (Allerton)

2010

“…During the video broadcast, all nodes other than the sender act as receivers. 7 For each receiver, we compute the average SNR of its channel and the PSNR of its received video. To plot the video PSNR as a function of channel SNR, we divide the SNR range into bins of 0.5 dB each, and take the average PSNR across all receivers whose channel SNR falls in the same bin.…”

Section: Methodmentioning

confidence: 99%

“…However, the problem is that in scenarios with multiple or mobile receivers, the wireless PHY cannot present an error-free lossless channel to all receivers and at all times without reducing everyone to a conservative choice of modulation and FEC and hence a low bit rate and a corresponding low video quality. 7 We decode the received video packets offline because the GNUradio Viterbi decoder can not keep up with packet reception rate. Multicast to three receivers.…”

Section: Methodmentioning

confidence: 99%

SoftCast

SIGCOMM Comput. Commun. Rev.

2010

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.

“…Some proposals put more FEC coding on the base layer than the enhancement layers [6]. Others employ embedded diversity coding [7,10], where a high-rate code allows the enhancement layer to harness good channel realizations, while the embedded high-diversity code provides guarantees that at least the base layer is received reliably. Hierarchical modulation and super-position coding are examples of this approach [5,15,26].…”

Section: Related Workmentioning

confidence: 99%

A cross-layer design for scalable mobile video

Proceedings of the 17th Annual International Conference on Mobile Computing and Networking

2011

205

130

Today's mobile video suffers from two limitations: 1) it cannot reduce bandwidth consumption by leveraging wireless broadcast to multicast popular content to interested receivers, and 2) it lacks robustness to wireless interference and errors. This paper presents SoftCast, a cross-layer design for mobile video that addresses both limitations. To do so, SoftCast changes the network stack to act like a linear transform. As a result, the transmitted video signal becomes linearly related to the pixels' luminance. Thus, when noise perturbs the transmitted signal samples, the perturbation naturally translates into approximation in the original video pixels. This enables a video source to multicast a single stream that each receiver decodes to a video quality commensurate with its channel quality. It also increases robustness to interference and errors which now reduce the sharpness of the received pixels but do not cause the video to glitch or stall. We have implemented SoftCast and evaluated it in a testbed of software radios. Our results show that it improves the average video quality for multicast users by 5.5 dB, eliminates video glitches caused by mobility, and increases robustness to packet loss by an order of magnitude.