Fixed-Rate Video Codecs for Mobile Radio Systems

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Description/Abstract

A comparative study of arbitrarily programmable, but fixed-rate videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s is offered. In contrast to existing and forthcoming standard schemes, such as the H.261, H.263 and MPEG2. MPEG4 codecs, which rely on bandwidth-efficient but error-sensitive variable-length coding techniques combined with a complex self-descriptive bitstream structure, the proposed codecs exhibit a more robust, regular bitstream and a constant bitrate. Clearly, their philosophy is different from the above error-sensitive and variable-rate standard schemes, since these constant-rate codecs were designed to allow direct replacement of mobile radio voice codecs in second generation wireless systems, such as the Pan-European GSM, the American IS-54 and IS-95 as well as the Japanese systems, operating at 13, 8, 9.6 and 6.7 kbit/s, respectively. This philosophy can, however, be adopted lo higher rate systems, such as the Digital European Cordless Telecommunications (DECT) and the Universal Mobile Telecommunication system (UMTS). The Type I codecs proposed benefit from invoking sophisticated compression techniques in order to achieve best video quality at a given bitrate. In contrast, the Type 2 schemes introduced maximize the codecs' error- resilience at the cost of slightly reduced video quality under error-Cree conditions. Gain-cost quantized, fixed but arbitrarily programmable rate discrete cosine transformed (DCT) video codecs, vector-quantised (VQI and quad-tree (QT) coded algorithms arc proposed and their video quality. complexity. compression ratio and error resilience trade-offs are comparatively analysed under identical conditions. Finally, our candidate codecs are compared to the standard H26 I . H.263 and MPEG2 benchmark codecs.