Threshold Evaluation in Link Adaptation Schemes for Progressive Images Transmission

Link adaptation (LA) has been demonstrated to be a very effective technique to improve transmission reliability in wireless communication systems subject to fading channel fluctuations. Due to the diffusion in commercial systems, LA techniques should take into account realistic channel models, low complexity algorithms, and application requirements. In this work, after analyzing the adaptive modulation and coding (AMC) performance for progressive images transmission, we propose a modified AMC technique that jointly takes into account both the channel variations and the progressive nature of the encoded bitstream. Since different priorities are assigned to the bits by the source encoder, an unequal error protection AMC method, that enhances transmission reliability for high priority bits, is necessary. Rather than increasing the complexity of the channel coding and modulation techniques, we adopt classical AMC methods optimizing the thresholds for the selection of opportunist modulation and coding schemes. The results show that the proposed technique is robust even with non-ideal channel state information.