Dual-mode vector-quantized low-rate cordless videophone systems forindoors and outdoors applications

摘要

Dual-mode reconfigurable wireless videophone transceivers arenproposed for noise-, rather than interference-limited indoors andnoutdoors applications and their video quality, bit rate, robustness, andncomplexity issues are analyzed. A suite of fixed, but arbitrarilynprogrammable low-rate, perceptually weighted vector quantized (VQ)ncodecs with and without run-length compression (RLC) are contrived fornquarter common intermediate format (QCIF) videophone sequences. Then11.36-kb/s Codec 1 is Bose-Chaudhuri-Hochquenghem (BCH) (127,71,9) codednto a rate of 20.32 kb/s and this arrangement is comparatively studiednalong with the 8-kb/s Codec 2 and BCH (127,50,13) scheme, which has thensame 20.32-kb/s overall rate. The source-sensitivity matched Systems 1-6ncharacterized in a table were contrived to comparatively study the rangenof system design options. For example, using Codec 1 in System 1 andncoherent pilot symbol assisted 16-level quadrature amplitude modulationn(16-PSAQAM), an overall signaling rate of 9 kBd was yielded, if thennoise-limited channel had a signal-to-noise ratio (SNR) in excess ofnabout 22 dB in the vicinity of the basestation or in indoors scenarios.nIn contrast, over lower quality outdoors channels near the fringes ofnthe cell, the more robust 4-QAM mode of operation had to be invoked,nwhich required twice as many time slots to accommodate the resultingn18-kBd stream and hence, reduced the total number of users supported.nThe robustness of Systems 2-4, and 6 was increased using automaticnrepeat requests (ARQ), again, inevitably reducing the number of usersnsupported, which was between 6 and 16. In a bandwidth of 200 kHz,nsimilarly to the Pan-European GSM mobile radio system's speech channel,nusing Systems 1, 3, 4, or 5, for example, 16 and eight videophone usersncan be supported in the 16- and 4-QAM modes, respectively, while inndual-mode cells the number of users is between eight and 16. The basicnsystem characteristics are highlighted