Joint Source-Channel Coding for Deep-Space Image Transmission using Rateless Codes

TL;DR

This paper introduces a novel joint source-channel coding scheme using rateless linear codes for deep-space image transmission, eliminating the need for entropy coding and optimizing for channel capacity matching.

Contribution

The paper proposes a new fixed-to-fixed length linear index coding scheme with systematic Raptor codes over GF(4), tailored for deep-space image transmission, improving robustness and rate adaptation.

Findings

Achieves a continuum of coding rates matching channel capacity.

Avoids fragile entropy coding stages, enhancing error resilience.

Outperforms traditional schemes used in Mars Rover missions.

Abstract

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 successive refinement scalar quantization. Unlike conventional schemes, in the proposed system the quantized transform coefficients are linearly mapped into channel symbols using systematic linear encoders. 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 fragile to channel post-decoding residual errors. We use linear codes over GF(4), which are particularly suited for this application, since they are matched to the dead-zone quantizer symbol alphabet and to the QPSK modulation used on the deep-space communication channel. We optimize the proposed system where the linear codes are systematic Raptor codes over GF(4). The rateless property of Raptor encoders allows to achieve a "continuum" of coding rates, in order to accurately match the channel coding rate to the transmission channel capacity and to the quantized source entropy rate for each transform subband and refinement level. 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.