The Design of Protograph LDPC Codes as Source Codes in a JSCC System

Although joint source-channel coding (JSCC) based on double protograph low-density parity-check (LDPC) codes has been shown to be an excellent solution for wireless communication, the protograph LDPC code for source coding needs to be optimized to improve the error-floor performance. In this letter, first, it is found that optimized protograph LDPC codes for channel coding are not optimal for source compression, which indicates that the source codes in the JSCC systems need to be designed specifically. Second, a rate-1/2 source code is designed by using the source decoding threshold as evaluation criteria. Finally, low rate source codes are designed by code lengthening. The protograph extrinsic information transfer analysis and the bit error rate simulation have shown that the proposed source codes obtain higher source decoding thresholds than conventional codes, which extend the range of compressible source entropies and improve the error-floor performance in the JSCC system.