FM Rider: Two-FSK Modulation-Based Ambient FM Backscatter Over 100 m Distance

Backscatter communication (BackCom) technology represents a low-cost and battery-free technology for Internet-of-Things (IoT) applications. One variant of BackCom, termed as ambient BackCom, which uses ambient signals to eliminate the need for a dedicated carrier source is more advantageous due to reduced system complexity and cost. Previous studies on ambient BackCom have primarily relied on amplitude modulation-based systems like on–off-keying (OOK) modulation, which achieved a maximum tag-to-receiver (Rx) distance of less than five meters. Alternatively, frequency-shift-keying (FSK)-based ambient BackCom systems have demonstrated improved distance, but with limitations. This work introduces an ambient broadcast frequency-modulation (FM) BackCom system utilizing in-band 2FSK-based modulation, designed to be compatible with both mono and stereo radio systems and extend communication distance. In order to successfully detect the backscatter 2FSK symbols, two pivotal technologies are employed: first, a quadrature demod-based in-phase/quadrature (
$I$
/
$Q$
) sample processing method enhances the signal-to-interference-plus-noise ratio (SINR). This enhancement has been substantiated through theoretical analysis, simulations, and cable-connected experiments. Second, a moving window-based 2FSK demodulation strategy is implemented, exhibiting resilience to tag frequency instability. The proposed system significantly enhances the tag-to-Rx communication distance, achieving an impressive range of over 100 m, a considerable improvement over the current state-of-the-art. The performance of the proposed system is evaluated in both cable-connected and outdoor environments, achieving a maximum bit rate of 333 bits per second (bps) at a distance of 58 m and a maximum communication distance of 107 m at a bit rate of 200 bps.