Dual-mode Vector-quantised Low-rate Cordless Videophone Systems for Indoors and Outdoors Applications

J. Streit, L. Hanzo

Department of Electronics and Computer Science,
Univerity of Southampton, SO17 1BJ, UK.
Tel: +44 703 593125, Fax: +44 703 593045
Email: lh@ecs.soton.ac.uk

This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version will be superseded.

Accepted by the IEEE for publication in the IEEE Tr. on Vehicular Technology


Dual-mode re-configurable wireless videophone transceivers are proposed for noise-, rather than interference-limited indoors and outdoors applications 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 Table 1 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, if the noise-limited channel had a signal-to-noise ratio (SNR) in excess of about 22 dB in the vicinity of the base station or in indoors scenarios. In contrast, over lower quality outdoors channels near the fringes of the cell the more robust 4QAM mode of operation had to be invoked, which required twice as many time slots to accommodate the resulting 18 kBd stream and hence reduced the total number of users supported. The robustness of Systems 2, 3, 4 and 6 was increased using Automatic Repeat Requests (ARQ), again, 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 16QAM and 4QAM modes, respectively, while in dual-mode cells the number of users is between 8 and 16. The basic system characteristics are highlighted in Table 1.

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