Experiment-Based Models for Air Time and Current Consumption of LoRaWAN LR-FHSS

The higher capacity, long-range and robustness to Doppler effect make Long Range - Frequency Hopping Spread Spectrum (LR-FHSS) a primary candidate for direct-to-satellite (DtS) connectivity. The LR-FHSS devices envisioned for DtS Internet-of-things (IoT) will be primarily battery-powered. Therefore, it is crucial to investigate the current consumption characteristics and Time-on-Air (ToA) of LR-FHSS technology. However, to our knowledge, no prior research has presented the accurate ToA and current consumption models for this newly introduced scheme while accounting for a broad range of parameters covering the allowed transmit power values for European Telecommunications Standards Institute and Federal Communications Commission regions. This paper addresses this shortcoming through extensive laboratory measurements and the development of analytical models. Specifically, we conducted measurements for variable transmit power from 0 dBm to +22 dBm, message payload from 10 bytes to 65 bytes, and two LR-FHSS-based data rates (DR8 and DR9). We also developed current consumption and ToA analytical models demonstrating a strong correlation with the measurement results, exhibiting a relative error of less than 0.3%, thus confirming the validity of our models. Compared to our measurement results, the existing two ToA analytical models exhibited a higher relative error rate of -9.2% and 3.4%, respectively. Additionally, we investigated the energy per packet to evaluate whether LR-FHSS offers better energy efficiency compared to legacy LoRa modulation. The results presented in this paper can be further used for simulators or in analytical studies to accurately model the ToA and energy consumption of LR-FHSS devices.