A Novel SCMA Codebook Construction Based on Extended Factor Graph Design

Sparse code multiple access (SCMA) is a representative code domain non-orthogonal multiple-access (NOMA) technique, which is widely considered as a promising candidate to support massive connectivity for 5G wireless networks. In this paper, we solve the problem of designing powerful SCMA codes with iterative decoding for the block fading channel. We propose a novel SCMA codebook construction based on extended factor graph (EFG) design. The proposed novel SCMA codebook construction can obtain full block diversity gain under block fading channel by extending the codewords to multiple resources blocks (RBs). According to the transmission characteristics of SCMA in the block fading channel, we establish the full diversity EFG construct criterions and a general full block diversity EFG construct algorithm is proposed. The pairwise error probability (PEP) analysis and average symbol error rate (SER) formula are presented. The PEP analysis allows us to clearly illustrate the full block diversity obtained by extending the codewords to multiple RBs. Using simple bounds on the probability of error, we show that the SCMA construction presented in this letter achieves full diversity order. The diversity gain of the propose codebook construction is also verified via the Monte-Carlo simulation.