Optimization of Hierarchical Modulation for Use of Scalable Media
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Research Article Optimization of Hierarchical Modulation for Use of Scalable Media Yongheng Liu1 and Conor Heneghan2 1 Department
of Electronic and Electrical Engineering, University College Dublin, Dublin, Ireland Digital Signal Processing Group, National University of Ireland, Dublin, Ireland
2 Communication
Correspondence should be addressed to Yongheng Liu, [email protected] Received 2 August 2009; Revised 3 January 2010; Accepted 13 January 2010 Academic Editor: Ling Shao Copyright © 2010 Y. Liu and C. Heneghan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper studies the Hierarchical Modulation, a transmission strategy of the approaching scalable multimedia over frequencyselective fading channel for improving the perceptible quality. An optimization strategy for Hierarchical Modulation and convolutional encoding, which can achieve the target bit error rates with minimum global signal-to-noise ratio in a single-user scenario, is suggested. This strategy allows applications to make a free choice of relationship between Higher Priority (HP) and Lower Priority (LP) stream delivery. The similar optimization can be used in multiuser scenario. An image transport task and a transport task of an H.264/MPEG4 AVC video embedding both QVGA and VGA resolutions are simulated as the implementation example of this optimization strategy, and demonstrate savings in SNR and improvement in Peak Signal-to-Noise Ratio (PSNR) for the particular examples shown.
1. Introduction Recent developments in media source coding have evolved from consideration not only of compression efficiency in terms of rate-distortion curves, but also on methods for providing easy-to-use scalability features. Scalability refers to the ability of the media delivery system to easily provide a range of spatial, temporal, and quality profiles in response to changing system conditions or user demands. For example, a person viewing a sports event on a mobile phone may be content to view a QCIF (176 × 144 pixels) resolution level at 25 fps, whereas a person with access to an HDTV may wish for a 50 fps, 720 p (1280 × 720 pixels) version of the same media. Such demands can be met using scalable video and audio coding, where lower resolution or lower quality signals can be reconstructed from partial bit streams. This allows simpler delivery of digital media, as networks and terminals can autonomously adapt to issues such as network heterogeneity and error-prone environments (e.g., wireless fading channels) [1]. Scalability allows the removal of parts of the bitstream, while achieving a rate-distortion
(R-D) performance with the remaining partial bitstream (at any supported spatial, temporal, or SNR resolution), that is, comparable to a “single-layer” approach [2], that is, nonscalable H.264/MPEG-4 AVC coding (at that particular resolution) [3]. However, in order to take maximum advan
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