A Raptor Code Based Unsourced Random Access with Coordinated Tree-Raptor Decoding Algorithm

The widespread applications of the Internet of Things (IoT) have brought about explosive growth in the number of IoT devices. A new grant-free random access paradigm called unsourced random access (URA) provides a new direction for massive Machine Type Communication (mMTC), especially when users do not need to identify themselves. This paper presents a Raptor code based URA over additive white Gaussian noise (AWGN) channels. In this scheme, the messages of each active user are encoded with fixed-rate standardized RaptorQ code to generate a block of coded symbols, followed by tree code and sparse regression code (SPARCs). Furthermore, at receiver, a coordinated tree-Raptor decoding algorithm is designed to realize the coded fragments stitching and to further enhance the transmission reliability. Simulation results show that the new scheme performs well, especially when the number of active users is large, compared with the related URA schemes.