Wireless Standards and Protocols IoT and LPWAN Informational

How does the duty cycle limitation in European ISM bands affect IoT device design?

How does the duty cycle limitation in European ISM bands affect IoT device design? In Europe, the ETSI EN 300 220 regulation imposes duty cycle limits on unlicensed ISM band devices, which fundamentally constrains how often an IoT device can transmit: (1) Duty cycle limits by sub-band: 868.0-868.6 MHz (g1 band): 1% duty cycle, 25 mW ERP (14 dBm). This is the primary LoRa/Sigfox band. 1% duty cycle = device can transmit for 36 seconds per hour. 868.7-869.2 MHz (g2 band): 0.1% duty cycle (3.6 seconds per hour), 25 mW ERP. 869.4-869.65 MHz (g3 band): 10% duty cycle (360 seconds per hour), 500 mW ERP (27 dBm). This is preferred for applications needing more frequent transmissions. 869.7-870.0 MHz (g4 band): 1% or LBT (listen-before-talk exempt from duty cycle), 25 mW ERP. (2) Impact on IoT device design: transmission frequency: at 1% duty cycle, the maximum transmission frequency depends on the packet airtime. For a LoRa SF12 packet (20 bytes, 1.5 s airtime): max 1 packet per 150 seconds (24 packets/hour). For a LoRa SF7 packet (20 bytes, 0.07 s airtime): max 1 packet per 7 seconds (514 packets/hour). SF7 allows 21× more transmissions than SF12 under the same duty cycle. This creates a direct trade-off between range (higher SF = longer range but fewer transmissions) and update rate (lower SF = shorter range but more frequent updates). Battery life: duty cycle limits inherently save battery (the device spends most of its time in sleep mode). However: if the application requires more frequent updates than the duty cycle allows, the designer must: use a sub-band with higher duty cycle (g3: 10%), use the FCC-regulated US band (no duty cycle; uses FHSS instead), or implement LBT (which exempts the device from duty cycle on some sub-bands). (3) LoRaWAN fair access policy: in addition to the ETSI duty cycle, the LoRa Alliance imposes a fair access policy: maximum 30 seconds of uplink airtime per device per day. This is more restrictive than the ETSI 1% duty cycle. At SF12: approximately 20 transmissions per day. At SF7: approximately 400+ transmissions per day. (4) Alternative: LBT (Listen Before Talk): some EU sub-bands allow LBT as an alternative to duty cycle. The device listens for 5 ms before transmitting; if the channel is clear, it transmits without duty cycle restriction. This is similar to Wi-Fi CSMA/CA and allows more frequent transmissions. However: LBT adds complexity (carrier sense circuitry) and variable latency (must wait if channel is busy).

Category: Wireless Standards and Protocols

Updated: April 2026

Product Tie-In: IoT Modules, Filters, Antennas

EU ISM Duty Cycle Limits

The duty cycle limitation is the most significant regulatory constraint for IoT devices in Europe, often more impactful than the transmit power limit.

US vs EU Regulatory Comparison

(1) US (FCC Part 15.247, 902-928 MHz): no duty cycle limit. Instead: frequency hopping spread spectrum (FHSS) with ≥ 50 channels or ≥ 500 kHz bandwidth. Maximum dwell time: 400 ms per channel. Maximum conducted power: 1W (30 dBm). This allows much more frequent transmissions than EU. A LoRa device at 915 MHz can transmit continuously (within the FHSS rules) with no duty cycle constraint. (2) The practical effect: a device designed for global deployment must respect the EU 1% duty cycle. This means: the firmware must track the cumulative airtime per sub-band per hour and refuse to transmit if the limit is reached. The application protocol must be designed around infrequent, small messages. For real-time monitoring: consider NB-IoT (licensed spectrum, no duty cycle) or LTE-M as an alternative to LoRa in Europe.

EU Duty Cycle Limits

g1 (868.0-868.6 MHz): 1% DC, 14 dBm
g3 (869.4-869.65 MHz): 10% DC, 27 dBm
1% DC = 36 seconds TX per hour
SF12 at 1%: ~24 packets/hour max
SF7 at 1%: ~514 packets/hour max

Common Questions

Frequently Asked Questions

What happens if I exceed the duty cycle?

Technically: the device is non-compliant with ETSI EN 300 220 and is operating illegally. Practically: there is no active enforcement mechanism in the ISM band (unlike licensed spectrum). However: exceeding the duty cycle causes increased interference for other ISM band users. If a certification body audits the device: it will fail compliance testing. For commercial products: the firmware MUST enforce the duty cycle. LoRaWAN stacks (e.g., LMIC, Semtech LoRa Basics Modem) include built-in duty cycle enforcement.

How do I maximize data throughput under duty cycle?

Use the lowest SF that provides reliable communication (SF7 allows 21× more packets than SF12). Use the g3 sub-band (869.4-869.65 MHz) with 10% duty cycle where available. Minimize payload size (fewer bytes = shorter airtime). Use data compression (delta encoding, bit-packing) to reduce payload. Aggregate multiple sensor readings into a single packet (send 10 readings in one packet instead of 10 separate packets). Consider LBT-enabled sub-bands (no duty cycle limit).

Do other countries have duty cycle limits?

Europe (ETSI): yes, as described above. US (FCC): no duty cycle, uses FHSS instead. Australia/NZ (ACMA): 1% duty cycle at 915-928 MHz (similar to EU). Japan (ARIB): duty cycle limits vary by band and power level. India: regulatory framework still being established. China: 470-510 MHz band with specific channel plans, no explicit duty cycle but power-limited. Most of Asia follows either FCC or ETSI models. For global products: design for the most restrictive regulation (EU 1% duty cycle) and unlock higher rates via firmware in less restrictive regions.

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