  Efficient signal detectors are rather important yet challenging to achieve
satisfactory performance for large-scale communication systems. This paper
considers a non-orthogonal sparse code multiple access (SCMA) configuration for
multiple-input multiple-output (MIMO) systems with recently proposed orthogonal
time frequency space (OTFS) modulation. We develop a novel low-complexity yet
effective customized Memory approximate message passing (AMP) algorithm for
channel equalization and multi-user detection. Specifically, the proposed
Memory AMP detector enjoys the sparsity of the channel matrix and only applies
matrix-vector multiplications in each iteration for low-complexity. To
alleviate the performance degradation caused by positive reinforcement problem
in the iterative process, all the preceding messages are utilized to guarantee
the orthogonality principle in Memory AMP detector. Simulation results are
finally provided to illustrate the superiority of our Memory AMP detector over
the existing solutions.
