Rate-adaptive transmission of H.263 video for multicode DS/CDMA cellular systems in multipath fading

The variable bit rate nature of compressed video remains a challenge to the transmission of real-time video over mobile CDMA cellular networks. Indeed, H.263 and MPEG-4 video bitstreams are characterized. by high peak rates and frequent rate variations, which are difficult to support in 2.5G and 3G mobile networks. In this paper, we propose a simple scheme which minimizes the peak transmission rate and its variance, which leads to a lower average bit-error rate (BER) and thus a higher received video quality. By introducing a small delay in the decoding process, the video output stream can be buffered at the video decoder end. We propose an algorithm which uses this buffering capability to perform real-time smoothing of the video stream. The transmitter then varies the number of codes assigned to the stream in order to support the remaining smaller rate variations. We simulate an end-to-end video communication system for the IS-95B uplink. It consists of an H.263 codec, an H.223 multiplexer and the physical layer components of the IS-95B standard. The transmitted signal is subject to multipath fading and multiple-access interference, obtained by simulating all the other users in the cell. Our joint smoothing/rate adaptation algorithm leads to a significant gain in the video quality scheme, as compared to previous approaches.