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

TL;DR

This work addresses the lack of accurate energy and timing models for LR-FHSS in direct-to-satellite IoT by conducting extensive measurements on LR1120-based devices across DR8/DR9, payloads, and transmit powers. It presents a measurement-backed ToA model with error below $0.3\%$ and introduces the first analytical current-consumption model for LR-FHSS, validated against data and capable of estimating battery lifetime. The results enable more precise simulations and energy budgeting for LR-FHSS devices, supporting feasibility assessments for satellite IoT deployments and informing future hardware variants. The models offer practical utility for simulators and network studies, with clear pathways to extend to new LR-FHSS devices and to compare against alternative IoT technologies.

Abstract

Long Range - Frequency Hopping Spread Spectrum (LR-FHSS) is an emerging and promising technology recently introduced into the LoRaWAN protocol specification for both terrestrial and non-terrestrial networks, notably satellites. The higher capacity, long-range and robustness to Doppler effect make LR-FHSS a primary candidate for direct-to-satellite (DtS) connectivity for enabling Internet-of-things (IoT) in remote areas. The LR-FHSS devices envisioned for DtS 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. This paper addresses this shortcoming through extensive field measurements and the development of analytical models. Specifically, we have measured the current consumption and ToA for variable transmit power, message payload, and two new LR-FHSS-based Data Rates (DR8 and DR9). We also develop current consumption and ToA analytical models demonstrating a strong correlation with the measurement results exhibiting a relative error of less than 0.3%. Thus, it confirms the validity of our models. Conversely, the existing analytical models exhibit a higher relative error rate of -9.2 to 3.4% compared to our measurement results. The presented in this paper results can be further used for simulators or in analytical studies to accurately model the on-air time and energy consumption of LR-FHSS devices.

Figures (12)

• Figure 1: The key components of the LR-FHSS packet structure.
• Figure 2: Illustrative frequency hopping profile of a single LR-FHSS packet of payload $L = 15$ bytes and DR8 featuring code rate =$\frac{1}{3}$ and $N_{H} = 3$
• Figure 3: LR1120 operational modes, where the states marked by filled green circles are not reported in the user manual USerManual. We identify these green states from experimental measurements and analyse the code of the transceiver's firmware, while the orange ones are irrelevant in this work. Notably, colour borders distinguish between the different states and build a relation with Fig. \ref{['fig7']}
• Figure 4: The structural diagram of the experimental setup for current consumption measurements of LR-FHSS transmissions.
• Figure 5: Frequency spectrum of LR-FHSS illustrating intra-packet frequency hopping profile of a single LR-FHSS packet of $L =$ 15-byte payload and DR8 featuring code rate =$\frac{1}{3}$ and $N_{H} = 3$.