Development of an ultra-low-power bidirectional LoRa backscatter tag

The increasing demand for Internet of Things (IoT) applications calls for more low-power wireless sensor systems and networks. In order to relay the sensor’s data while adhering to low-power constraints, a low-power transmission method is required. In this contribution, we introduce a bidirectional Long Range (LoRa) backscatter tag that enables long-range transmissions. Only Commercial off-the-shelf (COTS) components are utilized to assemble the tag, including the microcontroller itself. Unlike many existing solutions, our system is compatible with commodity LoRa transmitters and receivers, eliminating the need for an Software Defined Radio (SDR) to function.We realize the transmission from the tag to the receiver by frequency shifting LoRa symbols within the LoRa bandwidth such that the receiver interprets them as a different symbol. The receiver will decode bits as logical ones if they deviate from a predefined bit sequence due to symbol shifting, while unchanged symbols are interpreted as zeros. For downlink communication to the tag and wake-up functionality, a switch between the transmitter and antenna window-modulates the continuous carrier signal to generate the ON-OFF Keying (OOK) wake-up sequence.In our experiments, we achieved a downlink range of 60m with a transmission power of 10dBm. Due to limited line-of-sight space at our test site, we restricted backscatter transmission power to 6dBm, to test the limit of our tag, achieving a backscatter range of 500m with the tag consuming only 670µW of power.