Coherent Chirp Generation by Narrowband Transceiver Chips for ToF Indoor Localization.

We present an approach for indoor localization of radio nodes using commercial off-the-shelf (COTS), low-cost, low-power, transceiver chips, found in many internet of things (IoT) applications. As such chips are typically narrowband by design, suitable localization schemes are narrowband as well, e.g., based on received signal strength indication (RSSI) or angle of arrival (AoA) measurements. Naturally, these techniques are prone to multipath fading in indoor scenarios. To circumvent this, we show that for a typical transceiver chip it is possible to generate reproducible frequency-chirped wideband signals with deterministic behavior, suitable for time of flight (ToF) localization. Despite the simplicity of the deployed radio, it is possible to predict the phase of this waveform in order to use a signal model for filtering at the receiver side. In an exemplary implementation based on a Texas Instruments CC2510 chip, we achieve an overall signal bandwidth of up to 80 MHz, centered at 2.44 GHz. With a synchronized receiver infrastructure in a simple scenario, an absolute localization error below 1 m in 90% of the cases can be reached even with a fast, sub-optimal time difference of arrival (TDoA) multilateration algorithm.