Hadamard codewords as orthogonal spreading sequences in synchronous DS CDMA systems for mobile radio channels

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

2011

202

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.

Section: Resilience To Packet Lossmentioning

confidence: 99%

A cross-layer design for scalable mobile video

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

2011

202

130

“…Each SoftCast slice is a linear combination of all chunks. SoftCast produces these slices by multiplying the chunks with the Hadamard matrix, which is typically used in communication systems to redistribute energy [2,35]. The Hadamard matrix is an orthogonal transform composed entirely of +1s and -1s.…”

Section: Resilience To Packet Lossmentioning

confidence: 99%

SoftCast: Clean-slate scalable wireless video

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.

“…Each SoftCast slice is a linear combination of all chunks. SoftCast produces these slices by multiplying the chunks with the Hadamard matrix, which is typically used in communication systems to redistribute energy [2,25]. The Hadamard matrix is an orthogonal transform composed entirely of +1s and -1s.…”

Section: Resilience To Packet Lossmentioning

confidence: 99%

“…• For multicast receivers of SNRs in the range [5,25] dB, SoftCast improves the average video quality by 5.5 dB over the best performer of the two baselines.…”

Section: Introductionmentioning

confidence: 97%

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.