Estimating millimeter wave channels using out-of-band measurements

Channel estimation and beam training can be a source of significant overhead in establishing millimeter wave (mmWave) communication links, especially in high mobility applications like connected vehicles. In this paper, we highlight the opportunities and challenges associated with leveraging channel state information acquired at a lower frequency as a form of side information on a higher frequency channel. We focus on the relationship between spatial correlation matrices of sub-6 GHz and mmWave channels. We provide a transform that can be used to relate the spatial correlation matrix derived at one frequency to another much different frequency. We derive an expression for the excess mean squared error and use it to evaluate the performance experienced by using the transformed correlation in mmWave channel estimation.