Source and channel coding for mobile multimedia communications

Abstract

The transmission of coded video signals is perceptually favoured to provide, to the receiving end, a constant quality with respect to time. In the block type of video coders, like ITU H.263, maintaining a constant quality necessitates a certain amount of consistency in the quantisation process. The step-size quantisation parameter Qp remains unaltered all over the coding process time in order to offer a fixed rate of distortion to the decoded sequence, the fact that is visually perceived as a constant-quality scene. Due to the spatial and temporal tedundancies of raw video signals, maintaining a fixed quantisation parameter leads to the bit rate variability of an encoded video stream. However, the bit rate variability characteristic of an encoded video signal can be considered as an impediment for bit-error detection and correction when a video stream is transmitted over error-prone environments such as mobile radio links, and high interference terrestrial links. This paper incorporates the discussion and implementation of some algorithms applied to ITU H.263 video coding algorithm to enhance its resilience to channel degradation and maintain its performance when its bit stream is transmitted over error-prone media. The resilience techniques are analysed and evaluated through objective and subjective measurements. Moreover, a high quality in-house vocoder for low bit rate applications is described and its error resilience issues are addressed.