Error-propagation prevention technique for real-time video transmission over ATM networks

Abstract

Video sequences compressed by the current videocompression standards-such as MPEG-1/2 and H.261/H.263, which include motion compensation and variable-length coding-are very sensitive to channel disturbances. There exist many error-concealment techniques that can improve the video quality substantially. However, they generally do not prevent or terminate the error propagation. The forced intraupdate technique was proposed for H.245 recently. In this paper, we present an efficient temporal error-propagation prevention method that implements the forced intraupdate concept implicitly. Once an error is detected at the decoder, the starting address of the erroneous macroblocks is sent back to the encoder. The encoder marks the possible damaged area, and the encoding process continues as normal except that the motion estimation will probably not refer to the erroneous part. Thus, the impact of the cell loss is limited to the erroneous slice only, and the damage from the error propagation is greatly reduced. Simulation results of MPEG-2 coding over asynchronous transfer mode (ATM) networks show that the error concealment with feedback can effectively isolate the error and reduce the damage to give satisfactory performance even when the cell-loss rate is higher than 1%. With the delay analysis of ATM networks, we also show that in most cases, the encoder has adequate time to get the feedback information before processing the next I-or P-frames. Index Terms-Asynchronous transfer mode (ATM), error concealment, error prevention, error propagation, quality of service, video coding. I. INTRODUCTION T HE MOST commonly used video-compression techniques are based on MPEG-1/2 [1]-[3] or H.26x-i.e., H.261 or H.263 [4], [5]-where motion compensation, discrete cosine transform (DCT)-based coding, variable-length coding (VLC), and adaptive quantization are performed. These coding techniques are very sensitive to channel disturbances. A single error may cause error propagation in both spatial and temporal domains. Both MPEG and H.26x streams are constructed by layered structures. In MPEG, a groupof-pictures (GOP) layer generally includes one intrapicture (I-frame), several predicted pictures (P-frames), and several bidirectional predictive pictures (B-frames). The H.26x coding streams may consist of one I-frame and many P-frames or PB-frames. Each picture is further divided into a number of slices, or group of blocks (GOB) in H.26x, of contiguous macroblocks (MB's). A slice is the minimum element that Manuscript