A Study on Sparse Spreading Multiple Access for Massive Internet of Things (IoT) Communications

Abstract

This paper addresses a problem of massive connectivity with millions of Internet of Things (IoT) devices. Massive connectivity is one of the most important requirements for the next generation of networks. In this paper, we propose sparse spreading multiple access which overloads a large number of users on limited sizes of resources as a solution for massive connectivity. o do this, first, a single low density signature (LDS) codebook is used for accessing the medium to transmit data and a pilot signal. The number and length of the signature is designed to maximize the access rate. Second, a compressed sensing method is utilized for estimating user activity and channel impulse response vector from overloaded pilot signals. To maximize successive detection rates, we organize a particular spreading signature by concatenating multiple codewords from the LDS codebook and utilize the active user information and estimated channel information jointly. Third, an adaptive message passing algorithm (MPA) is applied to minimize inter-code interference between users who use the same sparse code casually.