Optimal Erasure Protection Assignment for Scalable Compressed Data with Small Channel Packets and Short Channel Codeword
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Optimal Erasure Protection Assignment for Scalable Compressed Data with Small Channel Packets and Short Channel Codewords Johnson Thie School of Electrical Engineering & Telecommunications, The University of New South Wales, Sydney, NSW 2052, Australia Email: [email protected]
David Taubman School of Electrical Engineering & Telecommunications, The University of New South Wales, Sydney, NSW 2052, Australia Email: [email protected] Received 24 December 2002; Revised 7 July 2003 We are concerned with the efficient transmission of scalable compressed data over lossy communication channels. Recent works have proposed several strategies for assigning optimal code redundancies to elements in a scalable data stream under the assumption that all elements are encoded onto a common group of network packets. When the size of the data to be encoded becomes large in comparison to the size of the network packets, such schemes require very long channel codes with high computational complexity. In networks with high loss, small packets are generally more desirable than long packets. This paper proposes a robust strategy for optimally assigning elements of the scalable data to clusters of packets, subject to constraints on packet size and code complexity. Given a packet cluster arrangement, the scheme then assigns optimal code redundancies to the source elements subject to a constraint on transmission length. Experimental results show that the proposed strategy can outperform previously proposed code redundancy assignment policies subject to the above-mentioned constraints, particularly at high channel loss rates. Keywords and phrases: unequal error protection, scalable compression, priority encoding transmission, image transmission.
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INTRODUCTION
In this paper, we are concerned with reliable transmission of scalable data over lossy communication channels. For the last decade, scalable compression techniques have been widely explored. These include image compression schemes, such as the embedded zerotree wavelet (EZW) [1] and set partitioning in hierarchical trees (SPIHT) [2] algorithms and, most recently, the JPEG2000 [3] image compression standard. Scalable video compression has also been an active area of research, which has recently led to MPEG-4 fine granularity scalability (FGS) [4]. An important property of a scalable data stream is that a portion of the data stream can be discarded or corrupted by a lossy communication channel without compromising the usefulness of the more important portions. A scalable data stream is generally made up of several elements with various dependencies such that the loss of a single element might render some or all of the subsequent elements useless but not the preceding elements. For the present work, we focus our attention on “erasure” channels. An erasure channel is one whose data, prior to transmission, is partitioned into a sequence of symbols,
each of which either arrives at the destination without error, or is entirely lost. The erasure channel is a good model for modern packe
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