New UEP mapping strategy in LDPC-coded modulation systems

A new modulation strategy for low-density parity-check (LDPC) coded modulation system was proposed, which was suitable for unequal error protection (UEP). In one codeword, the more important bits were given stronger protection than less important bits through different mapping strategies, which could be applied to both regular LDPC codes and irregular LDPC codes. The new modulation strategy can make a good trade-off between conventional 4QAM and 16QAM. Compared with 8PSK, when coding rate is 0.5, the new strategy can provide a better BER performance meanwhile the same spectral efficiency. And the new modulation strategy also performs better than the bit-reliability based mapping strategy in reference existed. Extrinsic information transfer (EXIT) charts were used to explain this im-provement for regular and irregular LDPC codes respectively.