Abstract
The performance of Sparse Code Multiple Access (SCMA) communication system with Logarithmic Message Passing
Algorithm (log-MPA) decoder is introduced. To boost the performance, a Low-Density Parity-Check Code LDPC is used
together with Belief Propagation (BP) decoder. LDPC is chosen due to its sparsity property that complements the sparsity
nature of SCMA for maximum efficiency and minimum complexity. Three distinct SCMA configurations are used. These
are: A (4 x 4 x 6), B (4 x 16 x 6), and C (5 x 4 x 10) where the (K x M x V) are numbers of resources, codewords and
users respectively. The performance of these configuration is shown in various channel conditions, various LDPC code
rates and various numbers of SCMA iterations (NSCMA), to find the local minimum value of log-MPA. Simulation results
showed that the LDPC greatly boosted the performance in mentioned configurations: In A configuration, a gain of 13
dB was observed. Configuration B experienced a substantial improvement of 23.5 dB, while C achieved a gain of 20.5
dB. Notably, configuration B stood out with the highest gain, attributed to LDPC’s exceptional performance with high
data rates, as the data transmitted in B was double that of A.