Enhancing mmWave DOA Estimation by Cumulative Power Gradient At Low SNR

We propose a novel direction-of-arrival (DOA) estimation method for hybrid millimeter-wave massive MIMO systems at low SNR. Unlike the existing hierarchical-search-based methods that directly estimate the DOA from the angular power, we investigate the angular power gradient based on beamforming with incremental gains. Then, we leverage the difference of beamforming gain among codebook levels and adopt a cumulative positive angular power gradient for estimation. Specifically, codewords for analog precoders are selected from different levels of a codebook that cover the same direction during every spatial sweep. Moreover, the power difference is proved to be a weak detector of source existence according to its sign, enabling the angular distribution estimation of the signal strength. Finally, the DOAs are estimated from peaks of the cumulative product of the previously measured signal strength. Simulation results show considerably enhancements of DOA performance at low SNR.