Sparse chaos code multiple access scheme achieving larger capacity and physical layer security

Massive machine-type communications (mMTC) scenarios that can accommodate Internet of things (IoT) device communications are currently being considered for implementation in fifth generation mobile communication systems. To support the dynamic traffic present in mMTC systems, grant-free non-orthogonal multiple access schemes have been proposed. In these schemes, both system capacity enhancement and transmit protocol simplification are achieved, and an overloaded transmission of more than one hundred percent of the capacity of the number of transmit samples is conducted. However, demand still exists for more capacity to accommodate massive devices. On the other hand, a simple method for ensuring the security of mMTC systems is required to suppress the energy consumption of IoT devices and reduce the amount of signal processing required at the central receive stations. In this paper, to satisfy these requirements, we propose a novel grant-free sparse chaos code multiple access (GF-SCCMA) scheme for mMTC systems in which sparse code multiple access is supplied based on chaos signals and physical layer security is ensured. GF-SCCMA is a non-orthogonal multiple access scheme in which only pairs sharing common keys can decode data by utilizing a chaotic codebook of transmission sequences. Furthermore, the distribution of the output log likelihood ratio is improved by using chaos-based quasi-Gaussian modulation, and enhancement of the capacity is achieved for conventional schemes when the outer channel code is concatenated. The improved performances in terms of capacity and security are shown through numerical simulations.