Multi-Carrier Rateless Multiple Access: A Novel Protocol for Dynamic Massive Access

In the future Internet of Things (IoT), a multitude of objects are to be provided with always-on-line connections and dynamic access to the network services, which brings new challenges to multiple access protocol design. In this paper, a novel multiple access protocol, termed as ``multi-carrier rateless multiple access (MC-RMA)'', is proposed to overcome such challenges. Instead of assigning the available resource elements (REs) to the users in a fixed and centralized manner, the base station (BS) simply assigns a specific distribution profile to each user, with which each user randomly chooses a certain number of coded symbols, linearly combines them, and then transmits the resultant signal to BS until receiving an acknowledgement (ACK) from BS. The transmission process of each user, as well as those of all the users as a whole, resembles a special form of linear superposition rateless coding and the user information can be decoded using the low-complexity belief propagation (BP) algorithm. Due to the inherent rate adaptation property of rateless codes, the proposed RMA protocol is quite suitable for dynamic massive access in future IoT.