  Rateless Multiple Access (RMA) is a novel non-orthogonal multiple access
framework that is promising for massive access in Internet of Things (IoT) due
to its high efficiency and low complexity. In the framework, after certain
\emph{registration}, each active user respectively transmits to the access
point (AP) randomly based on an assigned random access control function (RACf)
until receiving an acknowledgement (ACK). In this work, 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 signalling overhead and system latency. Furthermore, we
propose a low-complexity joint iterative detection and decoding algorithm in
which the channel estimation, active user detection, and information decoding
are done simultaneously. Finally, we propose a method based on density
evolution (DE) to evaluate the system performance.
