A Rate-Control Scheme for Video Transport over Wireless Channe

We investigate the scenario of using the Automatic Repeat reQuest (ARQ) retransmission scheme for two-way video communications over wireless Rayleigh fading channels. Video quality is the major concern of these applications. We show that during the retransmissions of error packets, due to the reduced channel throughput, the video encoder buffer may fill-up quickly and cause the TMN8 rate-control algorithm to significantly reduce the bits allocated to each video frame. This results in PSNR (Peak Signal-to-Noise Ratio) 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 also show that a DCT (Discrete Cosine Transform) 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 TMN8. 4 List of Symbols: J 0 (2πf D ∆t) : the subscript under J is " zero " , π is " pi " , and ∆ is " Delta " in Section II.B. S 0 : the subscript under S is " zero " S 1 : the subscript under S is " one " P 00 : the subscript under P is " zero " and " zero " P 01 : the subscript under P is " zero " and " one " P 10 : the subscript under P is " one " and " zero " P 11 : the subscript under P is " one " and " one " ∈ : " belong to " in Section III. 63 2 1 c c c L = C : the mark above the symbols c and C is " ^ " (a cap). } , , , { 63 2 1 c c c ′ ′ ′ = ′ L C : the mark at the upper right side of the symbols c and C is a prime. β is " beta " , σ is " sigma " , α is " alpha " in equation (14)-(16). λ is " lambda " in equation (22) and (23). Q : the mark at the upper right side of the symbol Q is a star. δ : " delta " in Section IV.C.