Grant-Free Rateless Multiple Access: A Novel Massive Access Scheme for Internet of Things

Rateless multiple access (RMA) is a novel non-orthogonal multiple access framework that is promising for massive access in Internet of Things due to its high efficiency and low complexity. In the framework, after certain registration, each active user, respectively, transmits to the access point randomly based on an assigned random access control function until receiving an acknowledgement. In this letter, by exploiting the intrinsic access pattern of each user, we propose a grant-free RMA scheme, which no longer needs the registration process as in the original RMA, thus greatly reduces the signaling overhead and system latency. Furthermore, we propose a low-complexity joint iterative detection and decoding algorithm in which the channel estimation, the active user detection, and the information decoding are done simultaneously. Finally, we propose a method based on density evolution to evaluate the system performance.