Large-Scale Grant-Free Sparse Chaos Code Multiple Access Scheme for 5G IoT

In the fifth-generation mobile communications system (5G), wireless connections among numerous Internet of things (IoT) devices will be accommodated in the massive machine-type communications (mMTC) scenario. To realize such massive connectivity, non-orthogonal multiple access (NOMA) technologies have been proposed for 5G. As one of the NOMA schemes, we have proposed a grant-free sparse chaos code multiple access (GF-SCCMA) scheme exploiting the principle of chaos communications for mMTC. It realizes both physical layer security and large-capacity transmission. However, in conventional studies, a message-passing algorithm (MPA) was used in the receiver, which required relatively high calculation complexity, and the maximum number of users in GF-SCCMA was limited to approximately 10. Therefore, we propose an application of the Gaussian belief propagation (GaBP) algorithm for user signal detection to realize a large-scale transmission of more than 50 users with low calculation complexity. The improved transmission performances are shown through numerical simulations, by comparison with a conventional grant-free low-density signature scheme.