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Rateless Unsourced Random Access

Massive Machine-Type Communication (mMTC) is expected to support massive connectivity for a large number of machine-type devices (MTDs). In many practical applications, the base station (BS) only needs to recover the list of received messages instead of the identities of active users, which is called unsourced random access (URA). In this paper, we propose a rateless URA scheme, which builds a bridge between rateless code and URA. Specifically, every active user divides the message into several sub-blocks, selects certain sub-blocks and linearly combines them in each time slot according to the transmission pattern, which is randomly chosen from a common pattern matrix by the user before transmission. Then the index of the transmission pattern and the coded sub-block are stitched together, mapped into a codeword in a common codebook and transmitted. At the receiver, the decoder creates decoding trees to group the coded sub-blocks by transmission patterns and recover the original messages. Simulation results verify the remarkable performance of the proposed URA scheme.