Multiple Access Design for Joint Semantic and Classical Communications

This chapter investigates the multiple access design for joint semantic and classic bit-oriented communications. For the resulting heterogeneous semantic and bit multiuser network, we discuss both orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA), with an emphasis on investigating the attractive interplay between semantic communications and NOMA, namely NOMA-enabled semantic communications and semantic communications-enhanced NOMA. (i) For NOMA-enabled semantic communications, we propose a semi-NOMA scheme for efficiently facilitating the heterogeneous semantic and bit multiuser communication, which unifies conventional NOMA and OMA schemes. The fundamental performance limit, namely semantic-versus-bit rate region, is characterized, which shows the superiority of the proposed semi-NOMA. (ii) For semantic communications-enhanced NOMA, we propose an opportunistic semantic and bit communication approach to alleviate the early-late rate disparity issue in NOMA. Numerical case studies demonstrate that significant performance gain can be achieved for NOMA by employing semantic communications than bit communications.