Design of permutation-based sparse code multiple access system

We consider the problem of designing a sparse code multiple access (SCMA) codebook that is based on permutation. Conventional SCMA is a multidimensional codebook-based non-orthogonal spreading technique, in which each layer of incoming bits are directly mapped to multidimensional codewords which have nonzero entries on the same resources. In this paper, unlike the traditional SCMA scheme, the data bits to be transmitted determine the nonzero entry locations based on the permutation. The proposed SCMA codebooks are converted to a multiuser code-division multiple-access (CDMA) detection system before applying an iterative decoder. The complexity of the proposed iterative decoder is lower in comparison to exponential message passing algorithm (MPA) and outperforms in terms of bit-error-rate (BER).