Manifold Optimization Based Beamforming for DoA and DoD Estimation with a Single Multi-Mode Antenna

Both direction-of-arrival (DoA) and direction-of-departure (DoD) of a radio signal contain valuable information for localization. Their estimation with antenna arrays is well known. More recently, multi-mode antennas (MMAs), building on the theory of characteristic modes, have been investigated for DoA estimation. This paper introduces joint DoA and DoD estimation with a single MMA on transmitter and receiver side. In general, the polarization of a signal transmitted by an MMA varies with the direction, which makes an appropriate signal model necessary. For best performance, optimized transmit beamforming should be performed. We derive the Cramér-Rao bound (CRB) for DoA and DoD estimation with MMAs, propose an optimized beamformer (OBF), which minimizes the CRB, and evaluate its performance.