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Future IoT applications provoke the connectivity and reliability requirements of machine-type communications, which yield mMTC and URLLC, respectively. In mMTC, grant-free NOMA is adopted to serve massive machine-type devices with low signaling overhead. The challenge of grantfree NOMA for mMTC is the collision induced by non-orthogonal resource allocation. Various grantfree NOMA techniques have been proposed to address this challenge, aiming at high connectivity. In this article, we introduce a novel grant-free NOMA approach, namely coded tandem spreading multiple access (CTSMA). The basic idea is that the data packet of each user is divided into segments, and redundancy segments are generated by coding through the data segments, and multiple orthogonal spreading codes are utilized to tandemly spread the data symbols of different segments from one user. Thereby, collision only occurs …