  Massive multiple-input multiple-output (MIMO) are expected to significantly
enhance the spectrum efficiency (SE) and energy efficiency (EE) of future
cellular systems. Since the performance gain of massive MIMO is fundamentally
limited by pilot contamination, pilot reuse design is crucial to achieve
reasonable cell throughput and user rate. In this paper, we leverage stochastic
geometry to model pilot reuse in massive MIMO systems by introducing a guard
region model to match realistic pilot allocation strategies. The uplink
signal-to-interference-plus-noise ratio (SINR) distribution is analytically
derived, based on which the benefits of pilot reuse on cell-throughput and
user-rate are investigated. The optimal pilot reuse factor for uplink
transmission is obtained. We also find through simulations that increasing the
pilot reuse factor beyond a certain value would not improve user-rate, and
could even lead to a significant loss of the cell throughput.
