A Simple DFT-aided Spatial Basis Expansion Model and Channel Estimation Strategy for Massive MIMO Systems

This paper proposes a new transmission strategy for the multiuser massive multiple-input multiple-output (MIMO) systems, including uplink/downlink channel estimation and user scheduling for data transmission. A discrete Fourier transform (DFT) aided spatial basis expansion model (SBEM) is first introduced to represent the uplink/downlink channels with much few parameter dimensions by exploiting angle reciprocity and the physical characteristics of the uniform linear array (ULA). With SBEM, both uplink and downlink channel estimation of multiuser can be carried out with very few amount of training resources, which significantly reduces the training overhead and feedback cost. Meanwhile, the pilot contamination problem in the uplink raining is immediately relieved by exploiting the spatial information of users. To enhance the spectral efficiency and to fully utilize the spatial resources, we also design a greedy user scheduling scheme during the data transmission period. Compared to existing low-rank models, the newly proposed SBEM offers an alternative for channel acquisition without need of channel statistics for both TDD and FDD systems based on the angle reciprocity. Moreover, the proposed method can be efficiently deployed by the fast Fourier transform (FFT). Various numerical results are provided to corroborate the proposed studies.