LOW BIT-RATE VIDEO TRANSMISSION OVER FADING CHANNELS FOR WIRELESS MICROCELLULAR SYSTEMS

We consider the transmission of QCIF resolution (176 x 144 pixels) vid eo signals over wireless channels at transmission rates of 64 kb/s and below. The bursty nature of the errors on the wireless channel requir es careful control of transmission performance without unduly increasi ng the overhead for error protection. A dual-rate source coder is pres ented that adaptively selects a coding rate according to the current c hannel conditions, An Automatic Repeat reQuest (ARQ) error control tec hnique is employed to retransmit erroneous data-frames. The source cod ing rate is selected based on the occupancy level of the ARQ transmiss ion buffer. Error detection followed by retransmission results in less overhead than forward error correction for the same quality. Simulati on results are provided for the statistics of the frame-error bursts o f the proposed system over code division multiple access error rates o i 10(-3) to 10(-4).