Quantitative Characterization of LoRa Propagation: Model–Measurement Discrepancies in Ground-Based SAR Tracking Networks

Overview

Wilderness search-and-rescue (SAR) operations in U.S. national parks have remained consistently high over the past decade, placing sustained strain on emergency response systems. National Park Service data indicate rangers respond to approximately 4,000 to 4,500 rescues annually, totaling more than 40,000 missions between 2015 and 2025. In August 2024, Grand Canyon National Park conducted a coordinated multi-day search after a hiker was reported missing in the Desert View area, where steep canyon topography limited line-of-sight visibility and reduced the reliability of cellular or satellite based location sharing. Traditional tracking approaches, which rely heavily on cellular connectivity or user-activated emergency beacons, fail in complex terrain due to intermittent GPS reception and infrastructure dependence. The custom designed and manufactured Tracker, Ground Station, and PC Software presents a novel decentralized ground-based LoRaWAN grid tracking system designed to provide continuous, infrastructure independent situational awareness. Each backpack-mounted Tracker unit is built around the EFR32MG24 ARM Cortex-M33 microcontroller and integrates a u-blox SAM-M10Q GNSS receiver, a 6-axis inertial measurement unit for motion classification and fall detection, an analog MEMS microphone for acoustic distress recognition, and a MAX17048 fuel gauge for battery monitoring. Structured telemetry packets are transmitted at 5 Hz using an RFM95W 915 MHz LoRa transceiver across a sub-gigahertz grid network to a dedicated Ground Station and BLE-connected PC interface. Emergency conditions such as detected falls, prolonged inactivity, or abnormal acoustic signatures automatically generate SOS packets relayed through neighboring nodes. All telemetry is simultaneously logged to Winbond W25Q32JVSS SPI flash memory to preserve data during communication interruptions. Two radio propagation tests evaluated the wireless reliability of the Tracker and Ground Station: Test 1A, the Friis Log - Distance Path Loss Model, and Test 1B, the Signal Propagation Analysis. Test 1A evaluated three antenna types—Omnidirectional, 3 - Element Yagi, and Flat Whip—at 433 and 915 MHz to determine the best combination for long-range transmission. Based on the results, the Flat Whip antenna at 915 MHz was chosen to be evaluated in Test 1B, where RSSI and SNR were measured at distances of 50m, 100m, 500m, and 1000m under line-of-sight conditions. RSSI values decreased gradually, aligning with the Friis Log - Distance Path Loss Equation predictions: -86 dBm at 50m, -92 dBm at 100m, -104 dBm at 500m, and -112 dBm at 1000m, with deviations of 2.42% at 50m, 2.22% at 100m, 0.029% at 500m, and 1.82% at 1000m. SNR also displayed a gradual decline as distance increased: 34 dB at 50m, 28 dB at 100m, 16 dB at 500m, and 8 dB at 1000m. These real-world results validate the reliability and consistency of the 915 MHz flat whip antenna for long-range, grid-based hiker tracking within decentralized LoRa network deployments.

Competition history

• CSEF 2026 Electronics & Electromagnetics (Senior Division) · Entry S-10-04

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