A flexible feedback framework for 5G massive MIMO systems

Massive MIMO systems are a key technology for next generation cellular networks. Albeit their numerous advantages, they present a dimensionality challenge when the number of users and the number of antenna ports increases, especially when the number of antennas grows increasingly large. In this paper, we propose a novel flexible codebook design framework that leverages the approximation of the covariance matrix with a Kronecker product model of three domain components: azimuth, vertical and uncorrelated dimensions. We derive the component matrices of the Kronecker product model, and we present simulation results to corroborate this approximation. The analysis in this paper lays the theoretical foundation for usage of a product codebook to reduce the complexity and the dimensionality of feedback in massive MIMO systems.