Angle of Arrival Estimation within One OFDM Symbol Leveraging Agile Beamforming

This paper introduces a method for estimating the angle of arrival (AoA) of a wireless signal using phased array antennas. Our method leverages the spatio-temporal degrees of freedom provided by the use of a configurable phased array to rapidly create a succession of beam-patterns within the duration of a single OFDM symbol. The received signal, modulated by the successive beam-pattern gains, is then processed to estimate the AoA and to reconstruct the pre-modulated signal. We implement this concept using 5G-compliant waveforms and a custom 5G testbed equipped with mmWave phased array antennas, precise beamforming control, and 5G signal processing. The testbed provides predictable beam shapes and calibration-free beamforming with 1 ° resolution. Beams can be switched as fast as every 240 ns. The testbed is operated at 92.16MSPS sampling rate with 120 kHz OFDM sub-carrier spacing (~ 8.33 μ<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S$</tex> symbol period). The AoA estimation method is evaluated across: (a) SNRs ranging from 0 to 24 dB; (b) AoA within an angular range of up to 80° in the azimuthal plane; and (c) switching among different number of beams (3 to 16 beams) within every OFDM symbol. As an example, when 8 beams are switched within one OFDM symbol, the AoA is estimated with an RMS error of below 1.2° across an 80° azimuthal range when the SNR is greater than 12 dB. Our experimental results demonstrate precise AoA estimation with only 1 digitized I/Q data stream by leveraging fast beam switching capabilities.