Toward Robust ISAC Beam Tracking: Experimental OFDM-Enhanced Monopulse AoA Estimation with Reduced Tracking Variability

Abstract

In this paper, we propose an experimental Orthogonal Frequency Division Multiplexing (OFDM)-assisted extension of the monopulse methodology that reduces estimation fluctuations in Angle of Arrival (AoA) estimation by exploiting multiple subcarrier-derived monopulse ratios within a single transmission frame. The proposed methodology effectively enhances the angular stability based on frequency-domain averaging. A low-cost Software-Defined Radio (SDR) platform is used in experiments that obtain real-life over-the-air measurements to prove that it can be adopted by a wide range of Commercial Off-The-Shelf (COTS) embedded systems. The results highlight substantial performance improvements compared to the conventional single-ratio monopulse estimation, achieving up to 30% reduction in Root Mean Square Error (RMSE) and Standard Deviation (STD) and 43% reduction in Mean Absolute Error (MAE). The suggested approach maintains the low complexity of classical monopulse tracking while significantly enhancing robustness, making it suitable for real-time AoA estimation in future 6G positioning and Integrated Sensing and Communication (ISAC) systems leveraging a wide range of COTS devices.