MPEG-4 image transmission using MAP source-controlled channeldecoding

摘要

In this paper, we develop an error resilient variant of the MPEG-4nembedded zerotree wavelet coder, suitable for mobile fading channels.nThe residual redundancy in the compressed bit stream provides implicitnerror protection through the use of source-controlled channel decoding;nno explicit channel coding is used. We propose two slight modificationsnto the MPEG-4 coder. The first removes the arithmetic coding in thenlowest frequency subband so that hidden Markov model-based MAPnestimation of both the source index and the channel state can be easilynapplied. The change in bit rate is negligible, while performance duringnsevere channel fading conditions can be greatly increased. The secondnmodification adds variable length packetization to the compressed bitnstream created from the higher frequency subbands. The individualnpackets are independently decodable. An optional rearrangement of thenbits in each packet allows MAP estimation to be applied to thesensubbands as well. Simulation results show a significant performancenimprovement for the overall system