An Accurate DOA Estimation Method for mmWave Large-Scale Antenna Arrays

High-precision direction of arrival (DOA) estimation is of great significance for multi-user high-speed communication using millimeter-wave large-scale arrays. To deal with the issues of degraded received signal quality due to wideband effects, reduced signal dimension caused by hybrid structures, and high computational complexity required in multi-user angle estimation, this paper proposes a high-precision DOA estimation method based on wideband signal phase measurement. Firstly, this paper establishes a system model and wideband received signal model for millimeter-wave large-scale arrays with a hybrid structure, and demonstrates the impact of wideband effects. Secondly, this paper derives the Cra⁃ mer-Rao lower bound (CRLB) for DOA estimation and proposes an optimal training sequence design method that satisfies constant modulus constraints by minimizing CRLB. Subsequently, for single-user scenarios, this paper proposes a gridless high-precision DOA estimation method based on phase measurement reaching CRLB progressively. For multi-user scenari⁃ os, an iterative DOA estimation algorithm using the expectation maximization (EM) method is proposed on the basis of sin⁃ gle-user DOA estimation to avoid dimension disaster caused by joint estimation and reduce computational complexity. Sim⁃ ulation results verify the effectiveness of the proposed algorithm. When the signal-to-noise ratio (SNR) exceeds 5 dB, the single-user and multi-user estimation algorithms proposed in this paper can progressively achieve CRLB, and the DOA esti⁃ mation performance surpasses traditional estimation methods, avoiding the impact of wideband effects and signal dimension reduction.