  Being an effective non-orthogonal multiple access (NOMA) technique, sparse
code multiple access (SCMA) is promising for future wireless communication.
Compared with orthogonal techniques, SCMA enjoys higher overloading tolerance
and lower complexity because of its sparsity. In this paper, based on
deterministic message passing algorithm (DMPA), algorithmic simplifications
such as domain changing and probability approximation are applied for SCMA
decoding. Early termination, adaptive decoding, and initial noise reduction are
also employed for faster convergence and better performance. Numerical results
show that the proposed optimizations benefit both decoding complexity and
speed. Furthermore, efficient hardware architectures based on folding and
retiming are proposed. VLSI implementation is also given in this paper.
Comparison with the state-of-the-art have shown the proposed decoder's
advantages in both latency and throughput (multi-Gbps).
