Adaptive PSD-Guided Filtering for Interference Mitigation in LoRa–Wi-Fi Coexistence at 2.4 GHz

Abstract

Long Range (LoRa) technology is one of the most promising Low-Power Wide-Area Network (LPWAN) technologies that has attracted much attention from research and academia owing to its wide area coverage, robustness to the Doppler effect and low energy consumption. The main purpose for moving from Sub-GHz to 2.4 GHz was to take advantage of the globally available 2.4 GHz ISM band. The major challenge of LoRa 2.4 GHz is the coexistence with other various technologies that currently utilize the 2.4 GHz ISM band such as Wi-Fi. This paper investigates the impact of Wi-Fi interference on LoRa communication in the 2.4 GHz band and presents an effective approach to mitigate the interference of Wi-Fi on LoRa and enable the coexistence between technologies in the 2.4 GHz Unlicensed Band. In this approach, frequency domain tracking and adaptive filtering are utilized. Thus, the interference from the OFDM subcarriers that interfere with LoRa’s transmissions is identified and tracked via the power spectral density (PSD). The paper employs a simulation framework to assess the effectiveness of an Infinite Impulse Response (IIR) Butterworth adaptive filtering to mitigate the interference. This method dynamically adjusts to interference to ensure efficient LoRa communication despite Wi-Fi interference. Simulation results demonstrate that an adaptive filter targeting the primary OFDM subcarrier frequencies can improve Bit Error Rate (BER) performance of LoRa system. With Butterworth filtering (order = 4, 4 bands), the LoRa BER under Wi-Fi interference is reduced (from $\approx 3\times 10^{-1}$ to $\approx 10^{-4}$ at $\mathrm {SNR}=8$ dB), enabling near-unity packet success probability (normalized throughput) and a near-zero packet loss rate (PLR) in the 2.4 GHz ISM coexistence scenario.