A Size-Efficient DFT Codebook Approach for DoA Estimation with Hybrid Arrays

Most existing direction-of-arrival (DoA) estimation techniques are tailored for fully digital (FD) antenna arrays. However, as modern MIMO systems scale to hundreds or thousands of antennas, FD architectures become increasingly impractical due to the prohibitive number of analog-to-digital converters (ADCs) required. Hybrid Analog-Digital (HAD) ar-chitectures offer a more hardware-efficient alternative, but con-ventional DoA estimation methods designed for FD arrays are not directly applicable in this setting. To overcome this challenge, we propose a novel method to reconstruct the covariance matrix of an equivalent FD array using measurements from a HAD architecture. This enables the application of classical subspace-based DoA estimation techniques with minimal adaptation. This work proposes a DFT-based codebook design which exploits the structure of Cauchy-like matrices for fast DoA estimation, making it particularly attractive for applications such as satellite-based or rapidly reconfigurable systems.