Adaptive low-rate wireless videophone schemes

Abstract

The design and performance of a range of wireless videophone transceivers are presented. Highly bandwidth efficient, fixed but with arbitrarily programmable rate, perceptually weighted discrete cosine transform (DCT) based video codecs are proposed for quarter common intermediate format (QCIF) videophone sequences. Perceptually weighted cost/gain controlled motion compensation and quad-class DCT-based compression is applied with and without run-length coding. Specifically, we propose video codecs having transmission rates in the range of 5-11.36 kbps and preselected the 11.36 kbps codec 1, the 8.52 kbps codec 2 and the 8 kbps codec 2a, for which we designed the intelligent reconfigurable systems 1-5. After sensitivity-matched binary Bose-Chaudhuri-Hocquenghem (BCH) forward error correction (FEC) coding the data rate associated with codec 1 and codec 2a became 20.32 kbps, while that of codec 2 was 15.24 kbps. Throughout these systems a partial forced update (PFU) technique was invoked in order to keep transmitter and receiver aligned amongst hostile channel conditions. When 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 system's robustness was increased using automatic repeat requests (ARQ), inevitably reducing the number of users supported, which was between 6 and 19 for the various systems. In a bandwidth of 200 kHz, similarly to the Pan-European GSM mobile radio system's speech channel, using system 1 for example, 16 and 8 videophone users can be supported in the 16QAM and 4QAM modes, respectively. >