Guest editorial: 6G new multiple access technology

As a basic technology at physical layer of mobile communications, non-orthogonal multiple access has been attracting wide attention across the academia and the industry. During the standardization of the fifth-generation (5G) of mobile communications, 3GPP conducted preliminary study on non-orthogonal multiple access without reaching the consensus to standardize the technology. Since 2017, there have been a number of breakthroughs in the area of massive access by academic researchers. With the consideration of finite codeword length, several information-theoretic capacity bounds were derived for non-orthogonal unsourced transmission, showing the enormous performance advantage over orthogonal multiple access. Meanwhile, channel coding for multi-user systems has become a hot topic in academia, and is being combined with the compressed sensing technology for active user detection and the estimation of wireless channels in massive access. Extensive papers on scheduling-based superposition transmissions are also seen in academia, for instance, rate-splitting multiple access (RSMA), etc. In early 2022, an emerging technology initiative (ETI) was formed in IEEE—Next-Generation Multiple Access (NGMA) with the purpose of encouraging research on multiple access in academia and industry, and their collaboration. In May 2022, new multiple access (NMA) task force group was created in IMT-2030 Promotion Group of China, with the hope to accelerate the study on transmission schemes, channel coding and modulation, receiver algorithms, system performance analysis, etc. The NMA group would facilitate the early harmonization of technical solutions, prepare for the input to ITU-R Technical Trends of IMT-2030 and provide design guidance of multiple access in 6G air interface standards to be started in 2025.