  In this paper, a sparse Kronecker-product (SKP) coding scheme is proposed for
unsourced multiple access. Specifically, the data of each active user is
encoded as the Kronecker product of two component codewords with one being
sparse and the other being forward-error-correction (FEC) coded. At the
receiver, an iterative decoding algorithm is developed, consisting of matrix
factorization for the decomposition of the Kronecker product and soft-in
soft-out decoding for the component sparse code and the FEC code. The cyclic
redundancy check (CRC) aided interference cancelation technique is further
incorporated for performance improvement. Numerical results show that the
proposed scheme outperforms the state-of-the-art counterparts, and approaches
the random coding bound within a gap of only 0.1 dB at the code length of 30000
when the number of active users is less than 75, and the error rate can be made
much lower than the existing schemes, especially when the number of active
users is relatively large.
