This thesis considers the video encoder rate for transmission of encoded QCIF video signals with resolution (176x144 pixel) over wireless channels. Because the bandwidth available for third generation mobile phone allowing multimedia to transmit data at bit rate up to 2 Mbit/s, the encoder rate should be changed properly due to the time-varying channel in order to maintain the signal quality. Considering the nature of wireless channel, the quality of the signal depends on many conditions; for example, the distance between user and base station and the velocity of the user related to the base stations. We consider the impact of bursty fading effect on signal quality. Since the error occurs periodically, the transmission system requires careful control of the error without increasing the overhead for error protection significantly. This thesis introduced the multiple code rate system whose rate can be adjusted due to the capacity of the transmission channel. The level of buffer can indicate the information of the channel in Hybrid ARQ (Automatic Repeat reQuest) system, an error control system that employs both FEC (Forward Error Correction) and Retransmission Request. The video-encoding standard used in this thesis is ITU-T H.263 according to the wireless transmission system used in the thesis. The system, which can encode steps of bit rate, may switch the encoded rate by three major parameters, quantization parameter, frame skip, and encoded mode with the I-frame refreshing technique. Changing parameters of encoder, based on the ITU-T standard, H.263 can vary both the encoded rate and the quality of the moving pictures. Simulation results show that the system does not only lead to the smoothness of changing picture quality which is maintained to 80-90% measured by PSNR and frame density but also reduces the load of the data buffer either in short or long fading period and increases the transmission rate to 80-90% compared with those of high bit rate video.
