An unequal coding scheme for space image transmission within the framework of CCSDS recommendations

In this paper, we propose a new coding scheme for space image transmission, which combines the unequal error protection (UEP) by partial superposition transmission (referred to as UEP-by-PST) with coded modulation standards recommended by the Consultative Committee for Space Data Systems (CCSDS). The raw image is first processed by the recommended image compressor, and then encoded by the UEP-by-PST system. In the UEP-by-PST system, the compressed image sequence is distinguished as two parts, the more important data (MID) and the less important data (LID). Both of the MID and LID are encoded by the CCSDS recommended low-density parity-check (LDPC) code. The codeword corresponding to the LID is superimposed with the codeword (in its interleaved version) corresponding to the MID. Finally, the encoded sequences are modulated by the Gaussian minimum shift keying (GMSK) and transmitted. Numerical results show that, over additive white Gaussian noise (AWGN) channels, the proposed UEP coding scheme outperforms the traditional equal error protection (EEP) coding scheme up to 30 dB in terms of the peak signal to noise ratio (PSNR).