Fairness-based pilot allocation in multi-cell massive MIMO systems

This paper addresses the fairness-based pilot allocation (PA) problem in multi-cell time-division duplex (TDD) massive MIMO systems. In such systems, the pilot contamination constitutes a major bottleneck, making the signal-to-interference ratio (SIR) saturated. In this work, we first derive the relation between asymptotic uplink SIR and PA. Based on the derived SIR, a fairness-based PA problem is formulated as a 0-1 integer programming problem to guarantee the fairness among users. Since the formulated problem is NP-hard, a centralized PA solution is proposed through reformulating the fairness-based PA problem as a mixed integer linear programming problem (MILP). In addition, to further decrease the computational complexity, a greedy PA solution is proposed based on the criterion that the user suffering the severest interference has the highest priority in PA. Simulation results show that the proposed two PA schemes are approximately optimal with much lower computational complexity than existing PA schemes.