Robust Angle Estimation for Hybrid mmWave Systems

In this paper, we consider robust channel estimation for a millimeter wave (mmWave) massive MIMO system that is equipped with uniform linear arrays (ULA). Most current angle estimation methods for mmWave systems are developed for time-varying or time-invariant channels. We propose a robust method that is applicable to both types of channels. This is done by employing time-varying precoders and combiners that are submatrices of banded Toeplitz matrices (SBT). With time-varying SBT precoding we can fabricate a time-varying channel and the channel can be estimated as if it is a time-varying channel whether the actual channel is time-varying or not. Furthermore, SBT precoding and combining preserve the shift invariance property of the received data matrix. Due to the preservation of shift invariance property, we can employ any existing method developed for two-dimensional (2D) angle estimation. Simulation results are given to show that the proposed time-varying SBT precoding provides robust and accurate channel estimates with a low complexity.