Softlora – A LorA-based platform for accurate and secure timing

LoRa is an emerging low-power wide-area network technology. Existing studies have focused on LoRa’s communication performance. Differently, we study two physical properties of LoRa, i.e., its performance in timing the signal propagation and the transmitters’ frequency traits. Signal timing is a basis for implementing clock synchronization, ranging, and advanced physical (PHY) layer techniques such as concurrent decoding. However, LoRa end devices do not provide PHY-layer timestamping that is needed for accurate timing. We propose a SoftLoRa design that integrates a low-power software-defined radio receiver with a LoRa transceiver to provide PHY-layer access. Experiments show that SoftLoRa achieves microseconds timing accuracy over one kilometer and in a multistory building with strong signal attenuation. Signal propagation timing is in general susceptible to a frame delay attack. We implement this attack against LoRa by a combination of stealthy jamming and delayed replay. To address the attack, we investigate the inherent frequency biases of LoRa transmitters. With an efficient signal processing algorithm, our frequency bias estimation achieves a resolution of 0.14 parts-per-million (ppm) of the channel’s central frequency. This resolution is sufficient to detect the attack that introduces an additional frequency bias of one or more ppm. In summary, this work provides an accurate and secure LoRa-based timing approach based on the SoftLoRa design.