1、PDF外文：http:/ 2008 届毕业设计说明书 第 1 页 共 15 页 英文原文 Mixed DSP /FPGA implementation of an error-resilient image transmission system based on JPEG2000 Marco Grangetto,Enrico Magli, Maurizio Martina, Fabrizio Vacca Abstract This paper describes a demonstrator of an er
2、ror-resilient image communication system over wireless packet networks, based on the novel JPEG2000 standard. In particular, the decoder implementation is addressed, which is the most critical task in terms of complexity and power consumption, in view of use on a wireless portable terminal for cellu
3、lar applications. The system implementation is based on a mixed DSP/FPGA architecture, which allows to parallelize some computational tasks, thus leading to efficient system operation. 1 Introduction Nowadays, there is a growing interest in the end-to-end transmission of images, es
4、pecially motivated by the short-term deployment of next generation mobile communication services (UMTS-IMT2000). However, transmission in a networked, tetherless environment provides both opportunities and challenges. The wireless context implies that the data may undergo bit errors and packet losse
5、s, making it necessary to foresee error recovery modalities. It is thereby necessary that image communication techniques are provided with the ability to recover, or at least conceal, the effect of such losses. The forthcoming JPEG2000 image com-pression standard has been designed to match these req
6、uirements, and embeds some error detection and concealment tools. This paper addresses the development of a demonstrator of an error-resilient JPEG2000 decoder implementation for image communication over a lossy packet network. The robustness to packet erasures is achieved by combining the fle
7、xibility of the JPEG2000 framework with the powerfulness of source-channel adaptive, optimized Reed-Solomon codes. The decoder implementation is particularly significant in the context of wireless 中北大学 2008 届毕业设计说明书 第 2 页 共 15 页 portable terminals for next-generation ce
8、llular systems, where the limited power budget and available dimensions impose severe constraints on the design of a multimedia processing sys-tem. 2 System overview In the following we provide a brief description of the functional units of the implemented system. 2.1
9、 JPEG2000 image compression JPEG2000 is the novel ISO standard for still image coding, and is intended to provide innovative solutions according to the new trends in multimedia technologies. At the time of this writing, the standard is in advanced publication stage； the Final Commi
10、ttee Draft is the most recent JPEG2000 description publicly available, which our implementation conforms to. JPEG2000 not only yields superior performance with respect to existing standards in terms of compression capability and subjective quality, but also numerous additional functionalities, such
11、as loss less and lossy compression, progressive transmission, and error resilience. The architecture of the JPEG2000 is based on the transform coding approach. An image may be divided into several sub-images (tiles), to reduce memory and computing requirements. A biorthogonal discrete wavelet transf
12、orm (DWT) is first applied to each tile, whose output is a series of versions of the tile at different resolution levels (subbands)； then, the transform coefficients are quantized, independently for each subband, with an embedded dead-zone quantizer. Each subband of the wavelet decomposition is divi
13、ded into rectangular blocks (code-blocks), which are in- dependently encoded with EBCOT (Embedded Block Coding with Optimized Truncation) ； this latter is based on a bit-plane approach (i.e. the most significant bits of the subband coefficients are transmitted first), context modeling and arithmetic
14、 coding. The bit stream output by EBCOT is organized by the rate allocator into a sequence of layers, each layer containing contributions from each code-block； the truncation points associated with each layer are optimized in the rate distortion sense. The final JPEG2000 bit stream consists of a mai
15、n header, followed by one or more sec-tions corresponding to individual tiles. Each tile comprises a tile header and a layered 中北大学 2008 届毕业设计说明书 第 3 页 共 15 页 representation of the included code-blocks, organized into packets. In order to form a progressive bitstream, i
16、.e. one that can be only partially decoded with minimal penalty, the layers are formed and ordered in such a way that the most important information is placed at the beginning of the bitstream. The JPEG2000 decoder performs exactly the same steps (except for rate allocation), in reverse order: synta
17、x parsing, codeblock decoding by EBCOT, inverse quantization, inverse DWT, and tile mosaicking； this is sketched in the right-hand-side box of Fig. 1. 2.2 Adaptive Reed-Solomon packet protection Although JPEG2000 embodies advanced error concealment techniques to mitigate the effect
18、 of errors, it does neither contain, nor specify any error correction method, in order to recover lost packets. On the other hand, packet losses are likely to occur in a network potentially subject to congestion, as is often the case in practice. In order to overcome this problem, a technique has be
19、en recently proposed, called Unequal Loss Protection (ULP), and based on the joint use of RS codes and packet interleaving, as shown in the left-hand-side of Fig. 1. Let us consider a maximum rate allocated to the image transmission, e.g. N packets of size L； the source bitstream is rowwise inserted
20、 in the interleaving matrix, followed by a proper amount of parity symbols, say Ti for the i-th row. The packets are read on the columns of the interleaver. The allocation problem consists in finding the optimal partitioning between source and code symbols for each row of the interleaver, so as to m
21、aximize the quality of service at the receiver； see for implementation details. At the decoder, due to the error correction capability of RS codes, the i-th row can be exactly recovered provided that the number of packet erasures has been less than Ti. Figure 1 System architecture 2.3 Proposed system In this paper we present a demonstrator of a complete decoder for image
