Abstract: This paper studies a massive single-input multiple-output uplink system, in which a single-antenna transmitter needs to transmit data to the receiver with a large-scale antenna array in a timely and reliable manner. In this system, the channel coefficients are assumed to remain constant during two consecutive symbol periods and change independently during the next two time symbol periods. For such a system model, we propose a mapping scheme for massive uniquely factorable constellation (MUFC), with an emphasis on avoiding the instantaneous channel state information acquisition as well as improving the system’s reliability. Specifically, we first perform constellation segmentation for the MUFC based on a Riemannian distance (RD) criterion. Then, using the trellis coding method, a specific mapping scheme for the MUFC constellation is provided. The theoretical simulation results show that the mapping scheme can increase the minimum RD between the modulated output signal sequences and improve the RD detector's error performance at the receiving end. Finally, the simulation results verify the effectiveness of our proposed scheme.