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arXiv · 2005.03755

On Phase Offsets of 802.11ac Commodity WiFi

Anatolij Zubow·Piotr Gawlowicz·Falko Dressler
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Abstract

We analyze the phase offsets between RF chains of modern IEEE 802.11ac chips. We investigate both the 2.4 and 5GHz bands on a per OFDM subcarrier level. Results reveal that the phase offset between receive antennas is due to random phase rotations semi-time-invariant with up to four possible values. Moreover, it is frequency-dependent. We propose a simple algorithm, which allows us to correct the phase offset on the fly without any calibration. As proof-of-concept, we implemented Angle of Arrival (AoA) using MUSIC algorithm. To achieve higher accuracy we stitched the thirteen overlapping 20MHz channels available in 2.4GHz band together to effectively have a single 80MHz channel. Results show very good AoA precision although only two receive antennas were used.

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Anatolij Zubow, Piotr Gawlowicz, Falko Dressler. 2020-05-07. On Phase Offsets of 802.11ac Commodity WiFi. https://doi.org/10.23919/wons51326.2021.9415548

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