What is MPA (Message passing calculation)?

Message Passing Algorithm (MPA) can iteratively identify the multiplexed SCMA codewords. The current multi-user detection scheme for sparse code multiple access (SCMA) is an iterative message passing algorithm (MPA) in which the message update technique is in an equal way. Another technique is utilized to diminish the decoding complexity of the MPA computation, by setting dynamic thresholds based on the signal-to-noise ratio (SNR) to lessen pointless calculation.