Longan: Ultra-Low-Power, Long-Range LoRa Receiver for LPWANs

Low-Power Wide-Area Networks (LPWANs) are essential for IoT connectivity, but they face a longstanding fundamental challenge: achieving both continuous receiver availability and long-term battery operation without compromising network performance. In low-duty-cycle modes like LoRaWAN’s Class A or B, data timeliness and network throughput are limited, and devices are deaf to peer transmissions, restricting topologies to a single hop, hindering scalability in practical applications. While Class C enables always-on operation for real-time communication and multi-hop networking, commercial LoRa transceivers consume up to 42.4 mW in this mode, rendering sustained battery-powered deployments infeasible. Recent low-power designs cut consumption to sub-milliwatt levels but limit communication ranges to mere hundreds of meters, undermining LPWAN’s “wide-area’’ vision. This paper introduces Longan, the first LoRa receiver to overcome this power-range tradeoff boundary, enabling kilometer-scale links with a power of about 1 mW only. Longan achieves this via two breakthroughs: (1) We design a novel LoRa receiver analog radio frequency (RF) front-end that exploits negative differential resistors for high-efficiency signal amplification while simultaneously reducing power consumption by 2–3 orders of magnitude; (2) Building on this, we further introduce an architectural decoupling of detection and demodulation, and design a lightweight analog dechirping circuit using our front-end. This circuit enables always-on preamble detection at just one-tenth the power of digital counterparts, triggering COTS demodulation only on demand. Evaluation shows that Longan sustains continuous detection at 1.16 mW, a 36 × reduction from COTS LoRa, while preserving sensitivity within 3–13 dB of commercial devices and enabling long-range communication.