Frequency Synchronization for OFDM-Based Massive MIMO Systems

Abstract

Massive multiple input multiple output (MIMO) is a key technology in the fifth-generation wireless networks. However, its performance heavily relies on accurate synchronization. Additionally, synchronization can impose an enormous amount of computational complexity to the system. To deal with this issue, in this paper, we propose a low-complexity frequency synchronization technique with a high accuracy for the uplink of multiuser orthogonal-frequency-division multiplexing-based massive MIMO systems. First, we propose a carrier frequency offset (CFO) estimation whose computational complexity increases only linearly with respect to the number of base station (BS) antennas. Second, we propose a CFO compensation method that is performed after combining the received signals at the BS antennas, and as a result, its computational complexity is independent of the number of BS antennas. As a third contribution, the effect of the CFO estimation error is studied, and it is proven that by applying our proposed CFO compensation technique, the CFO estimation error causes only a constant phase shift. We then propose an algorithm to efficiently calculate and remove the estimation error. Our simulation results testify the efficacy of our proposed synchronization technique. As it is demonstrated, our proposed synchronization technique leads to a bit error rate performance that is very close to the one for a fully synchronous system.