Pilot hopping in massive MIMO systems: Spectral efficiency analysis and achievable rates

In this paper, we analyze the performance of multi-cell least-square (LS) channel estimation using pilot sequence hopping and pilot reuse strategy for pilot decontamination. We obtain achievable rates in uplink synchronous system in L-cell system using LS channel estimation and zero forcing (ZF) detection. Polynomial expansion approximation is performed to obtain a closed form bound of the asymptotic sum-rate. We show that pilot hopping can achieve significant spectral efficiency gain compared to the conventional non-hopping schemes. Moreover, the number of antennas can be also greatly reduced when using the pilot hopping. However, the achieved gains depend on the pilot reuse factor β. It is shown that this gain is not monotonic function of β in some cases and therefore brings to attention that a careful cell planning is required when applying pilot hopping.