ADAPTIVE LOW-RATE WIRELESS VIDEOPHONE SCHEMES

The design and performance of a range of wireless videophone transceiv ers are presented. Highly bandwidth efficient, fixed but arbitrarily p rogrammable rate, perceptually weighted Discrete Cosine Transform (DCT ) based video codecs are proposed for quarter common intermediate form at (QCIF) videophone sequences. Perceptually weighted cost/gain contro lled motion compensation and quad-class DCT-based compression is appli ed with and without run-length coding. Specifically, we propose video codecs having transmission rates in the range of 5-11.36 kbps and pres elected the 11.36 kbps Codec 1, the 8.52 kbps Codec 2 and the 8 kbps C odec 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 C odec 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) techniqu e was invoked in order to keep transmitter and receiver aligned amongs t hostile channel conditions. When using Codec 1 in System 1 and coher ent 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 r equired twice as many time slots to accommodate the resulting 18 kBd s tream. The system's robustness was increased using Automatic Repeat Re quest (ARQ), inevitably reducing the number of users supported, which was between 6 and 19 for the various systems. In a bandwidth of 200 kH z, similarly to the Pan-European GSM mobile radio system's speech chan nel, using System 1 for example 16 and 8 videophone users can be suppo rted in the 16QAM and 4QAM modes, respectively. All system features ar e summarized in Table III.