sDMCM—A Semantic Digital Modulation Constellation Mapping Scheme for Semantic Communication

The current state of semantic communication research is primarily based on analog modulation, whereas digital communication is more prevalent in practical applications. However, traditional digital modulation constellation mapping designs are not suitable for semantic communication, as they are primarily focused on minimizing the bit error rate of the transmitted data rather than the change in the numerical value of the semantic information. To address this issue, a semantic digital modulation constellation mapping (sDMCM) scheme based on pulse amplitude modulation (PAM)/quadrature amplitude modulation (QAM) is proposed, that considers the internal correlation of the semantic information. In addition, this article proposes using the mean-squared error (MSE) of the semantic information between the transmitter and receiver as a performance metric for semantic communication. This article also provides the theoretical MSE performance of the proposed sDMCM through formula derivation. Finally, the simulation results match the theoretical results, demonstrating the rationality of the theoretical derivation. Comparing the proposed sDMCM scheme with traditional mapping schemes, such as Gray, Pseudo-Gray (Pe-Gray), and structural quadrant (SQ) constellations in an image semantic communication system under the additive white Gaussian noise (AWGN) channel, the restored image can tolerate an SNR drop of about 3 dB while maintaining the same multiscale structure similarity (MS-SSIM) performance. In addition, sDMCM is applied in an industrial Internet of Things semantic communication system to validate its role in IoT applications.