In-Band Ambient FSK Backscatter Communications Leveraging LTE Cell-Specific Reference Signals

A long term evolution (LTE) signal is ubiquitously present, which make it an attractive signal source for ambient backscatter communications (AmBC). In this paper, we propose a system that uses LTE cell-specific reference signals (CRSs) transmitted by a base station as an ambient source and channel estimator at the user equipment (UE) as an AmBC receiver. One of the challenges in AmBC is direct path interference (DPI): The direct signal from the transmitter to the receiver is several orders of magnitude stronger than the scattered path. We propose a solution that operates withing the original LTE band. In order to mitigate the DPI, the backscatter device (BD) performs a frequency shift keying (FSK) modulation that introduces an artificial Doppler shift to the channel which is larger than the natural Doppler but still small enough such that it can be tracked by the channel estimator at the UE. We demonstrate the feasibility of the proposed system by Proof-of-Concept implementation and compare its performance against the simulation results. Measurement results show that we could achieve bit error probabilities less than
$10^{-2}$
with ambient LTE signal having SNR of 5 dB operating on 486 MHz band having 7.68 MHz bandwidth.