Vector-quantised cordless videophone transceivers

Abstract

A variety of adaptively re-configurable wireless videophone transceivers are proposed and their video quality, bit rate, robustness and complexity issues are analysed. A suite of fixed but arbitrarily programmable low-rate, perceptually weighted vector quantised (VQ) codecs with and without run-length compression (RLC) are contrived for quarter common intermediate format (QCIF) videophone sequences. The 11.36 kbps codec 1 is BCH(127,71,9) coded to a rate of 20.32 kbps and this arrangement is comparatively studied along with the 8 kbps codec 2 and BCH(127,50,13) scheme, which has the same 20.32 kbps overall rate. The source-sensitivity matched systems 1-6 characterised in a table were contrived to comparatively study the range of system design options. For example, using codec 1 in system 1 and coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSAQAM), an overall signalling rate of 9 kBd was yielded. Over lower quality channels the 4QAM mode of operation had to be invoked, which required twice as many time slots to accommodate the resulting 18 kBd stream. The robustness of systems 2, 3, 4 and 6 was increased using automatic repeat requests (ARQ), inevitably reducing the number of users supported, which was between 6 and 16. In a bandwidth of 200 kHz, similarly to the Pan-European GSM mobile radio system's speech channel, using systems 1, 3, 4 or 5 for example, 16 and 8 videophone users can be supported in the 16 QAM and 4 QAM modes, respectively. The basic system characteristics are highlighted.