large-scale antenna array to serve multiple UEs, has been widely envisaged as one of the major candidate technologies for the fifth generation (5G) cellular networks owing to its favorable features, such as huge spectral efficiency and energy efficiency gains[@yang_performance_2013; @rusek_scaling_2013; @zhang_capacity_2013; @gaohui_2014; @hu_esprit-based_2014]. Like in the conventional small-scale MU-MIMO systems, user selection is also important in massive MU-MIMO systems[@bjornson_optimal_2014; @nam_joint_2014; @lee_asympt_2014; @xu_user_2014], though it faces new challenges. More specifically, in the user selection for conventional MU-MIMO systems, it is usually assumed that the number of candidate-UEs, $N$, is much larger than that of the BS antennas, $M$. Therefore, upon employing instantaneous channel state information (CSI)-aided user selection methods (e.g. SUS), multiuser diversity gains can be harvested to boost the overall system performance. By contrast, in massive MIMO systems, it is impractical to have $N\gg M$, since $M$ is already very large. Moreover, the computational complexity of the conventional user selection methods might be too high for the massive MIMO systems. For example, the computational complexity of SUS is roughly $\mathcal{O}(M^3N)$[@yoo_optimality_2006], which will cause huge consumption of power and computational resources if $M$ becomes large.

Recently, a range of user selection schemes have been proposed for massive MIMO systems. The time-division 