Coded Tandem Spreading for Grant-free Random Access System with Massive Connections

With the thriving of internet of things (IoT) industry, the importance of massive machine type communication (mMTC) is increasingly significant. Due to massive connections in mMTC, grant-free random access is preferred for the sake of saving the control signaling overheads. Currently, various techniques has been proposed to address the challenges in the grant-free random access system. Among them, tandem spreading is a novel spreading mechanism to solve the collision problem. In this paper, a generalized version of tandem spreading is introduced as the coded tandem spreading multiple access (CTSMA). Compared to the previous work, CTSMA enables multiple redundancy segments to support more simultaneous transmissions. Moreover, a flexible tandem spreading codebook design is introduced. Simulation results show the advantage of CTSMA on other related schemes and indicate the factors to influence the CTSMA performance under different conditions.