Video coding for transport over wireless channels

Many wireless multimedia applications require video coding schemes and underlying transport that can provide acceptable quality of service to the end users. Due to the burst errors nature of wireless channels and the error propagation property of compressed video, suitable source and channel coding schemes are required to handle such conditions.; In this dissertation, we investigate the effects of retransmissions and packet-errors on video quality by considering the scenario of using an Automatic Repeat Request (ARQ) scheme for two-way video communications over wireless Rayleigh-fading channels. We first show that during the retransmissions of error packets, due to the reduced channel throughput and the video encoder buffer fill-up, the video rate-control algorithm significantly reduces the number of bits allocated to each video frame. This results in video quality degradation and many skipped frames. To minimize the number of frames skipped, we propose improved rate-control schemes that take into consideration the effects of the video buffer fill-up, an a priori channel model, and the channel feedback information. We investigate the effect of using a hybrid ARQ/Forward Error Correction (FEC) scheme to improve the Peak-Signal-to-Noise-Ratio (PSNR). We also show that a Discrete Cosine Transform (DCT) coefficient soft-thresholding scheme can be applied to further improve video quality. As a result, our proposed rate-control schemes encode the video sequences with less frame skipping and with higher PSNR compared to the commonly used rate-control algorithm Test Model Near Term 8 (TMN8).; We also consider the case where a low-delay constraint requires that a corrupted retransmitted packet not be retransmitted again. This results in packet-errors and significant PSNR drops. To reduce the number of packet-errors, we propose a low-delay interleaving scheme which combines the video encoder buffer with the interleaving memory so that the interleaving does not increase the delay and the memory in the video encoder. In addition to the interleaving, the retransmission strategy itself could be improved. We propose a conditional retransmission scheme to reduce the number of retransmissions to improve the effective channel throughput by utilizing the concealment error and the channel condition information. Simulation results show significant PSNR improvements compared to TMN8.