Calculating Low Power Wide Area Network End Node Battery Longevity
LPWAN end node longevity relies on dynamic state-machine energy integration multiplied by chemical passivation and thermal capacity derating factors.
LoRaWAN Spreading Factor Energy
Meaning
Total power consumed during the transmission of a single packet at a specific modulation rate represents the largest variable in the energy budget of a long-range node. In these low-power networks, the LoRaWAN spreading factor energy increases as the data rate decreases, because a higher spreading factor requires the radio to transmit for a longer period. This relationship forces a design trade-off between the communication range and the operational lifespan of the device.
Airtime Coefficient
Operating at a higher spreading factor increases the duration of the packet on the air, which directly scales the active current consumption of the transmitter. For example, changing from spreading factor seven to twelve increases the packet duration by a factor of nearly sixty. This extended duration means that the LoRaWAN spreading factor energy rises dramatically, requiring the battery to sustain high-current transmission for seconds rather than milliseconds.
Understanding this scale is essential for defining the battery requirements of remote sensors.
Receiver Window
Downlink listening windows also demand more energy when higher spreading factors are used. After transmitting, the device must open its receiver at a precise time, and the duration of this listening window is proportional to the symbol length. This means that the energy cost of receiving is closely tied to the transmission settings.
Battery Resource
Selecting a lower spreading factor reduces the total energy per packet, but it requires the device to be closer to a gateway to maintain a reliable link. In sparse networks where only high spreading factors can reach the gateway, the accumulated LoRaWAN spreading factor energy dictates a larger battery capacity or more frequent battery replacements. Designers must evaluate the target network density during the planning phase to ensure the system meets its lifespan goals.