Low Power Wide-Area Network (LPWAN) has shown its long-distance and low-power features for aboveground Internet-of-Things (IoT) communication, presenting a potential to extend to underground cross-soil communication over a wide area, which has not been investigated before. The variation of soil conditions brings significant signal polarization misalignment, degrading communication reliability. We propose Demeter, a low-cost, low-power programmable antenna design to keep reliable cross-soil communication automatically. First, we propose a hardware architecture to enable polarization adjustment on commercial-off-the-shelf (COTS) single-RF-chain LoRa radio. Moreover, we develop a low-power programmable circuit to adjust polarization. We further design an energy-efficient heuristic calibration algorithm to keep signal polarization alignment automatically. We demonstrate Demeter in indoor environments. The antenna is buried in a plastic container filled with gardening soil to simulate the node underground. Meanwhile, we use the COTS LoRa gateway as a receiver to show the RSSI and SNR variations.

Demeter-Demo: Demonstrating Cross-soil LPWAN with Low-cost Signal Polarization Alignment