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This paper presents a downlink multi-user network model based on sparse code multiple access (SCMA), where two phases cooperative transmission strategy is introduced to reduce the average outage probability. Motivated by the fact that the reliability is an important indicator in the next generation mobile communication system. Two strategies are considered: in the direct transmission strategy, the communication between the base station and the users is completed in one phase, where the relay is inexistent. In the two phases cooperative transmission strategy, any number of relays at fixed positions are placed to improve the performance of the system. To verify the performance of cooperative transmission and direct transmission, we derive the exact expressions of average outage probabilities for these two strategies. The simulation and analytical results are presented to estimate the performances of the …