Measurement-Based Analysis of LoRaWAN Parameter Effects on Communication Performance and Uplink-Downlink Imbalance

Abstract

LoRaWAN is a low-power wide-area network (LPWAN) protocol widely used in IoT applications for its long-range communication and energy efficiency. However, downlink limitations and link asymmetry, exacerbated by duty cycle restrictions and physical layer parameter settings, can cause communication failures such as Join request losses and reduced packet delivery performance. This study empirically investigates the effects of the Spreading Factor (SF) and Coding Rate (CR) on communication performance and uplink–downlink imbalance. Two experimental environments were constructed to evaluate the impact of key parameters. In a LoRa point-to-point (P2P) setup using STM32WL-based modules, 72 combinations of SF, Bandwidth (BW), and CR were tested to measure RSSI, SNR, and Packet Delivery Ratio (PDR). Additionally, a full LoRaWAN network was implemented—including end devices, a gateway, and a network server—to analyze performance variations across different SF and CR settings. Results show that RSSI remained largely unaffected, whereas SNR and PDR were significantly influenced by SF and CR. Specifically, downlink SNR at the end device decreased by up to 7.75 dB as SF increased, while uplink SNR measured at the network server remained stable or slightly improved. Moreover, higher CR values led to increased packet loss, with CR 4/8 showing a notable drop in PDR. These findings confirm the presence of uplink–downlink performance asymmetry and suggest that using lower SF and CR values can improve downlink reliability in constrained LoRaWAN environments.