摘要：In Time-Division Duplex (TDD) massive Multiple- Input Multiple-Output (MIMO) systems, pilot contamination becomes the performance bottleneck when the number of terminals is larger than that of available pilot sequences. In this paper, we first deduce the general formulas for uplink Signal-to- Interference Ratio (SIR) and channel capacity in single-cell massive MIMO circumstances with insufficient pilot sequences. Then, in order to enhance the Quality of Service (QoS) for the terminals who suffer from severe pilot contamination, an optimization problem is formulated to maximize the minimum uplink capacity of all terminals. Next, because the complexity of finding the optimal pilot assignment is too high, a suboptimal two-step assignment approach with low complexity is proposed to solve the optimization problem. Compared with the random pilot assignment scheme in single-cell massive MIMO systems, simulation results prove the effectiveness of this two-step scheme in obtaining better minimum uplink SIR and minimum channel capacity when the number of BS antennas is great but finite. Meanwhile, the average capacity of all terminals can also be improved.
