Multi-rate transmission may lead to performance anomaly in an IEEE 802.11 network. It will decrease the throughputs of all the higher rate stations. This paper proposes an adaptive rate selection scheme for video service when performance anomaly occurs. Considering that video has the characteristic of tolerance to packet loss, we actively drop several packets so as to select the rates as high as possible for transmitting packets. Experiment shows our algorithm can decrease the delay and jitter of video, and improve the system throughput as well.
In this paper, the implementation of H.263 real-time encoding on DSP-TM13XX is described. This implementation method can be easily extended to other standards such as H.263+, MPEG-i, MPEG-2, MPEG-4 etc., because these standards are essentially very similar (i.e. Motion Compensate, Discrete Cosine Transform, Quantization and Entropy Coding). In addition, TM13XX series of DSPs utilize a very powerful, general purpose VLIW (Very Long Instruction Word) processor core which makes them ideal for the high performance embedded multimedia applications. The architecture and the characteristic of DSP that enable real-time multimedia processing are firstly represented. Second, We discussed the major problem of H.263 real-time encoding on the high performance DSP. In order to ensure the real-time video processing, the main coding time-consuming modules of the H.263 video standard and the idea of optimization are discussed in details. These optimal algorithms make fully use of the DSP architecture and play very important role for the realization of real-time video encoding on DSPs. Finally, We show the H.263 encoding experiment results based on the DSP for standalone application. For CIF format sequence image, the average encoding frame rate about 2Ofps is achieved, it is expected to be used in videophone, mobile video communication, remote monitor and so on.
A simple and effective error detection and error concealment based on the H.263 video decoder has been described in this paper. The H.263 syntax structure and semantics, VLC code word and continuity property of video signal at the video decoder are employed to process the error detection. The spatial and temporal correction is made full of use for error concealment. It has been found that this method can greatly improve the quality of the reconstruction images without decreasing the coding efficiency.