Comparing LoRaWAN Spreading Factor Airtime Costs against Cellular Repetition Overhead
SF12 airtime expands energy consumption by sixty-four times over SF7 while NB-IoT repetitions multiply battery drain linearly per transport block transmission.
ETSI Duty Cycle Limit
Meaning
Airtime usage ceilings imposed on unlicensed radio transmitters in European frequency bands prevent mutual interference among uncoordinated wireless devices. The ETSI duty cycle limit restricts the percentage of time a device may actively transmit within a designated observation window, typically evaluated over a one-hour period. Sub-gigahertz bands enforce strict maximum transmission limits ranging from 0.1% to 10% depending on the specific frequency sub-band.
The restriction applies to all end devices and gateways operating within European Telecommunications Standards Institute jurisdictions.
Regulatory Framework
European Harmonised Standards define maximum transmission allocations across non-specific short range device allocations. Compliance with the ETSI duty cycle limit forms a mandatory requirement for CE marking under the Radio Equipment Directive 2014/53/EU. Standard EN 300 220 establishes sub-band boundaries and output power limits across the 868 MHz spectrum.
Manufacturers testing radio equipment must prove compliance across all environmental operating temperatures and supply voltage extremes.
Airtime Calculation
Transmit duration includes preamble symbols, frame headers, payload data, and forward error correction overhead. Calculating cumulative airtime against the ETSI duty cycle limit requires multiplying individual frame time-on-air by the total number of transmissions within the observation hour. A module transmitting a 100-millisecond frame in a 1% sub-band gets thirty-six seconds of total allowed airtime per hour, limiting transmission to three hundred sixty frames.
Exceeding this calculated budget violates regional spectrum access conditions and risks regulatory non-compliance fines.
Compliance Mitigation
Software transmission queues block packet requests when airtime quotas deplete. Protocol stacks track cumulative millisecond usage inside non-volatile memory to prevent illegal transmissions following system reboots. Frequency hopping across compliant sub-bands expands available duty cycle budgets across multiple channels.