  In this paper, we consider a constant envelope (CE) pilot-based
low-complexity technique for frequency synchronization in multi-user massive
MIMO systems. Study of the complexity-performance trade-off shows that this
CE-pilot-based technique provides better MSE performance when compared to
existing low-complexity high-PAPR pilot-based CFO (carrier frequency offset)
estimator. Numerical study of the information rate performance of the TR-MRC
receiver in imperfect CSI scenario with this CE-pilot based CFO estimator shows
that it is more energy-and-spectrally efficient than existing low-complexity
CFO estimator in massive MIMO systems. It is also observed that with this
CE-pilot based CFO estimation, an $\mathcal{O}(\sqrt{M})$ array gain is
achievable.
