In this paper, we concern the uplink of an industrial Internet of Things (IIoT) communication system, in which multiple single-antenna users timely upload data to a receiver having a large number of antennas over Rayleigh fading channels. To satisfy the stringent requirement of latency in the channel estimation phase of this system, we first use a phase-shift keying (PSK) modulation division scheme for each pair of users. Specifically, the absolutely additively uniquely decomposable constellation pair (AAUDCP) is allocated for two random users. With the same pilot sequence, it proves the modulated PSK symbols can be uniquely identified when the number of receiver antennas goes to infinity in a noise-free case. In a noise case, to improve the reliability of this system, we propose a smart user pairing algorithm with low complexity by maximizing the minimum signal to interference plus noise ratio at the receiver for all pairs of users. Finally, the computer simulations show that the proposed scheme can improve the system's error performance effectively.