Joint source-channel coding for deep space image transmission using rateless codes

A new coding scheme for image transmission over noisy channel is proposed. Similar to standard image compression, the scheme includes a linear transform followed by embedded scalar quantization. Joint source-channel coding is implemented by optimizing the rate allocation across the source subbands, treated as the components of a parallel source model. The quantized transform coefficients are linearly mapped into channel symbols, using systematic linear encoders of appropriate rate. This fixed-to-fixed length “linear index coding” approach avoids the use of an explicit entropy coding stage (e.g., arithmetic or Huffman coding), which is typically non-robust to postdecoding residual errors. Linear codes over GF(4) codes are particularly suited for this application, since they are matched to the alphabet of the quantization indices of the dead-zone embedded quantizers used in the scheme, and to the QPSK modulation used on the deep-space communication channel. Therefore, we optimize a family of systematic Raptor codes over GF (4) that are particularly suited for this application since they allow for a continuum of coding rates, in order to adapt to the quantized source entropy rate (which may differ from image to image) and to channel capacity. Comparisons are provided with respect to the concatenation of state-of-the-art image coding and channel coding schemes used by Jet Propulsion Laboratories (JPL) for the Mars Exploration Rover (MER) Mission.