Visual Media Coding and Transmission

9.3 Link Adaptation for Video Services

(Portion reprinted, with permission, from H. Kodikara, S.T. Worrall, A.M. Kondoz, A.H. Sadka, “Combined adaptive spreading gain control and unequal error protection for real-time video communications over WCDMA System”, 5th Int. Workshop on Image Analysis for Multimedia Interactive Services (WIAMIS'2004), Lisbon, Portugal, 21–23 April 2004. ©2004 IEEE.)

The previous sections investigated the performance of video in error-prone environments. The time-varying channel conditions resulting from the mobility of the terminal and the surroundings were not considered. The effects of time-varying channel conditions (slow-fading) on video performance and the techniques that can be used to mitigate these effects are investigated in this section. A performance enhancement method for real-time video communications employing link adaptation is discussed. A novel link-adaptation algorithm, which is based on feedback channel information including BLER, received signal strength (RSS), and the first-order statistic of the RSS is proposed and analyzed. Two approaches for link adaptation are investigated. First, the effects of a link-adaptation scheme at the video frame level, which aims to optimize video quality by varying the channel-coding scheme and video source rate for a fixed channel allocation, is studied. Second, a link-adaptation algorithm with a goal of maximizing the overall access network throughput is developed at the radio block level. Another ...