Coding with dynamic rate control for low-delay image transmission over CDMA fading channels

In the context of low-delay reliable image transmission over CDMA slowly Rayleigh fading channels, this paper addresses the proposal of a coding control technique that dynamically adapts the source coder rate to the channel condition, in order to transmit coded image data with low delay. In previous work, we proposed tools for error-resilient coding in order to improve the quality of transmitted images over the aforementioned channel. However, in case of degrading channel conditions, an increase in the transmission delay may result due to the use of an equal ARQ error control for all coded image data. Therefore, we propose to decrease the volume of coded data when the channel is in poor condition to decrease the amount of data to be transmitted with ARQ, and hence reduce the image transmission delay. The approach proposed to dynamically control the coder rate to the channel condition is based on an estimate of the channel status. The scheme proposed is shown to offer acceptable delay and high resistance to transmission errors.