FIXED-RATE VIDEO CODECS FOR MOBILE RADIO SYSTEMS

A comparative study of arbitrarily programmable, but fixed-rate videop hone codecs using quarter common intermediate format (QCIF) video sequ ences scanned at 10 frames/s is offered. In contrast to existing and f orthcoming standard schemes, such as the H.261, H.263 and MPEG2, MPEG4 codecs, which rely on bandwidth-efficient but error-sensitive variabl e-length coding techniques combined with a complex self-descriptive bi tstream structure, the proposed codecs exhibit a more robust, regular bitstream and a constant bitrate. Clearly, their philosophy is differe nt from the above error-sensitive and variable-rare standard schemes, since these constant-rate codecs were designed to allow direct replace ment of mobile radio voice codecs in second generation wireless system s, 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, respe ctively. This philosophy can, however, be adopted to higher-rate syste ms, such as the Digital European Cordless Telecommunications (DECT) an d the Universal Mobile Telecommunications System (UMTS). The Type 1 co decs proposed benefit from invoking sophisticated compression techniqu es in order to achieve best video quality at a given bitrate. In contr ast, the Type 2 schemes introduced maximise the codecs' error resilien ce at the cost of slightly reduced video quality under error-free cond itions. Gain-cost quantised, fixed but arbitrarily programmable rate d iscrete cosine transformed (DCT) video codecs, vector-quantised (VQ) a nd quad-tree (QT) coded algorithms are proposed and their video qualit y, complexity, compression ratio and error resilience trade-offs are c omparatively analysed under identical conditions. Finally, our candida te codecs are compared to the standard H261, H.263 and MPEG2 benchmark codecs.