Use of residual redundancy in the design of joint source/channel coders

-The need to transmit large amounts of data over a band-limited channel has led to the development of various data compression schemes. Many of these schemes function by attempting to remove redundancy from the data stream. An unwanted side-effect of this approach is to make the information transfer process more vulnerable to channel noise. Efforts at protecting against errors involve the reinsertion of redundancy and an increase in bandwidth requirements. We present a technique for providing error protection without the additional overhead required for channel coding. We start from the premise that, during source coder design, for the sake of simplicity or due to imperfect knowledge, assumptions have to be made about the source which are often incorrect. This results in residual redundancy at the output of the source coder. The residual redundancy can then be used to provide error protection in much the same way as the insertion of redundancy in convolutional coding provides error protection. In this paper we develop an approach for utilizing this redundancy. To show the validity of this approach, we apply it to image coding using DPCM, and obtain substantial performance gains, both in terms of objective as well as subjective measures.