807  Quiz: Cellular & LoRaWAN Regulations

807.1 Introduction

This chapter covers regulatory compliance and spectrum selection for cellular IoT and LoRaWAN deployments. You’ll work through scenarios involving duty cycle calculations, ETSI compliance, and technology selection for campus and wide-area deployments.

NoteLearning Objectives

By completing this chapter, you will be able to:

  • Calculate duty cycle limits and time-on-air for LoRaWAN deployments
  • Analyze spreading factor trade-offs for capacity vs range
  • Evaluate licensed vs unlicensed spectrum options
  • Design compliant LPWAN deployments under ETSI regulations

807.2 Prerequisites

Before attempting these assessments, you should have completed:

807.3 Knowledge Check: 2.4 GHz Channel Selection

Question 1: The 2.4 GHz ISM band has 14 channels (numbered 1-14), but only channels 1, 6, and 11 are non-overlapping. Why is channel overlap problematic for Wi-Fi networks?

Explanation: Each 2.4 GHz Wi-Fi channel occupies 22 MHz of bandwidth, but channels are only 5 MHz apart. Channels 1, 6, and 11 are spaced 25 MHz apart, providing non-overlapping operation. When neighboring access points use overlapping channels (e.g., channels 1 and 3), their transmissions interfere with each other even though they’re on different “channels.” This causes:

Performance impacts: - Collision domain expansion: Devices must wait for both channels to be clear - Hidden node problem: Devices on channel 1 can’t sense channel 3 transmissions - Increased retransmissions: Corrupted frames require resending - Reduced effective throughput: Can drop from 50-70% to 20-30% utilization

Best practice for multi-AP deployments: - Use only channels 1, 6, 11 in dense deployments - Adjacent APs should use different non-overlapping channels - Modern Wi-Fi uses 5 GHz with 23 non-overlapping channels to avoid this issue - Tools like Wi-Fi Analyzer can help identify the least congested channel

807.4 Knowledge Check: Radio Frequency Selection

Question 2: In the electromagnetic spectrum, why do IoT devices primarily use radio frequencies (3 kHz - 300 GHz) rather than visible light or infrared for wireless communication?

Explanation: Radio frequencies are ideal for IoT because they can penetrate walls, reflect around obstacles, and provide omnidirectional coverage without line-of-sight requirements.

Comparison across spectrum:

Radio (3 kHz - 300 GHz): - Penetrates walls, furniture, vegetation - Reflects/diffracts around obstacles - Works through weather (rain, fog) - Omnidirectional antennas possible - Regulated spectrum requires compliance

Infrared (300 GHz - 430 THz): - Line-of-sight only - Blocked by walls, even thin paper - Used for TV remotes, IrDA (obsolete) - Very short range (1-5 meters)

Visible Light (430-750 THz): - Line-of-sight only - Li-Fi uses LED flicker for data - Blocked by any opacity - Extreme directional requirements

Why B is wrong: Radio waves actually have LESS energy per photon than visible light (E = h × f, so lower frequency = lower energy), but this is irrelevant for communication - what matters is propagation characteristics, not photon energy.

Real-world example: A Wi-Fi router in one room can serve devices throughout a house because 2.4 GHz radio penetrates walls. A Li-Fi system would require line-of-sight to every device and fails if you walk between the transmitter and receiver.

807.5 Scenario-Based Assessment: Campus LoRaWAN Deployment

Scenario: A European university is deploying a campus-wide environmental monitoring system using LoRaWAN on the 868 MHz ISM band. The system must comply with ETSI regulations requiring 1% duty cycle on the g1 sub-band (868.0-868.6 MHz).

System Requirements: - 500 outdoor sensors (air quality, weather, noise) - 8 LoRaWAN gateways covering 2 km² campus - Sensors use SF7 (fastest spreading factor) at 5.47 kbps - Each sensor sends: 50-byte payload + 13-byte overhead = 63 bytes total - Required reporting intervals: Environmental (every 10 min), Alerts (immediate)

Regulatory Constraints: - ETSI EN300.220: 1% duty cycle on 868.0-868.6 MHz (g1 sub-band) - Alternative: 10% duty cycle on 869.4-869.65 MHz (g3 sub-band, but only 3 channels) - Violation penalties: EUR 10,000-50,000 fines, equipment confiscation

Analysis Questions:

  1. Duty Cycle Calculation: For a 63-byte packet at 5.47 kbps, calculate:

    • Time-on-air per transmission
    • Maximum packets per hour (1% duty cycle)
    • Minimum interval between packets

  2. Scalability Analysis: With 500 sensors sending every 10 minutes:

    • Total packets per hour across all sensors
    • Average channel utilization
    • Is the system compliant?

  3. Trade-off Decision: Compare operating strategies:

    • Strategy A: Use SF7 (5.47 kbps) on 1% duty cycle g1 band
    • Strategy B: Use SF12 (250 bps, 20× longer ToA) on 10% duty cycle g3 band
    • Which provides better network capacity?

  4. Alert Handling: If 10% of sensors need to send emergency alerts (30 seconds response time), how does this impact normal operation?

  5. Alternative Solutions: If duty cycle limits are exceeded, evaluate:

    • Deploy private LTE-M network (licensed spectrum, no duty cycle)
    • Switch to NB-IoT (licensed, higher cost)
    • Implement adaptive sampling (reduce reporting during low activity)

1. Duty Cycle Calculation:

Time-on-Air (ToA) Calculation: - Packet size: 63 bytes = 504 bits - Data rate: 5.47 kbps = 5470 bits/second - ToA: 504 bits / 5470 bps = 0.092 seconds = 92 milliseconds

1% Duty Cycle Limits: - 1 hour = 3600 seconds - 1% transmission budget: 3600 × 0.01 = 36 seconds per hour - Maximum packets: 36 seconds / 0.092 seconds = 391 packets per hour - Minimum interval: 3600s / 391 = 9.2 seconds between packets

2. Scalability Analysis:

System Load Calculation: - 500 sensors × 6 transmissions/hour (every 10 min) = 3,000 packets/hour - Each packet: 92 ms ToA - Total airtime: 3000 × 0.092s = 276 seconds/hour = 7.67% utilization

Per-Sensor Compliance Check: - Each sensor: 6 packets/hour × 92 ms = 0.552 seconds/hour - Duty cycle: 0.552 / 3600 = 0.015% per sensor ✓ Compliant (well under 1%)

Channel Capacity: - 3 channels available in g1 band (868.1, 868.3, 868.5 MHz) - With 8 gateways, effective channel capacity increases - Verdict: System is compliant but approaching saturation (7.67% vs theoretical 30% max)

3. Trade-off Analysis:

Strategy A: SF7 on 1% Duty Cycle (g1 band) - ToA: 92 ms per packet - Packets/hour per sensor: 391 maximum (using 6 = 1.5% of limit) - Range: ~2 km (urban), ~5 km (rural) - Channels: 3 available - Network capacity: ~1,173 packets/hour (3 channels × 391)

Strategy B: SF12 on 10% Duty Cycle (g3 band) - ToA: 1.81 seconds per packet (20× longer due to slower data rate) - 10% duty cycle: 360 seconds/hour available - Packets/hour per sensor: 360 / 1.81 = 199 maximum - Range: ~10 km (urban), ~20 km (rural) - Channels: 3 available (g3: 869.4-869.65 MHz) - Network capacity: ~597 packets/hour (3 channels × 199)

Comparison Table:

Metric SF7 (1% DC) SF12 (10% DC) Winner
Packets/hour (3 ch) 1,173 597 SF7
Range 2-5 km 10-20 km SF12
ToA 92 ms 1.81 s SF7
Battery life 100% 95% SF7
Collision risk Lower Higher SF7

Recommendation for campus scenario: Use SF7 on g1 band because: - Campus is only 2 km² (SF7 range sufficient) - 2× higher capacity needed for 500 sensors - 20× faster ToA reduces collision probability - Better battery life (shorter transmissions)

4. Alert Handling:

Emergency Alert Impact: - 10% of sensors = 50 sensors - Alert requirement: 30-second response time - Normal 10-minute reporting: 6 packets/hour - Alert rate: 120 packets/hour per sensor (every 30 sec)

Duty Cycle Check: - 120 packets × 92 ms = 11 seconds/hour = 0.3% ✓ Still compliant

Network Load During Alert: - Normal sensors: 450 × 6 pkts = 2,700 pkts/hour - Alert sensors: 50 × 120 pkts = 6,000 pkts/hour - Total: 8,700 packets/hour

Channel capacity check: - 3 channels × 391 max pkts/hour = 1,173 total capacity - 8,700 packets EXCEEDS capacity by 7.4× System FAILS under alert load

Solution: Implement priority classes: - Normal: SF7, 10-minute intervals - Alerts: Guaranteed delivery via confirmed uplinks or licensed spectrum backup

5. Alternative Solutions:

Option A: Private LTE-M Network - Pros: No duty cycle, guaranteed QoS, higher data rates (375 kbps) - Cons: Requires spectrum license (EUR 50K-500K/year), infrastructure ($100K+) - Use case: Mission-critical systems (safety, security)

Option B: NB-IoT (Cellular) - Pros: No duty cycle, wide coverage, carrier-managed - Cons: $2-5 per device/year subscription, 10-year cost = $25,000 - Use case: Long-term deployments without infrastructure investment

Option C: Adaptive Sampling - Pros: Stays within duty cycle, no additional cost - Cons: Reduced data granularity during high-activity periods - Implementation: - Normal: 10-minute intervals - Low activity (night): 30-minute intervals - Alert mode: 30-second intervals for affected sensors only - Result: Reduces baseline load to 2.5% utilization, leaving 5% headroom for alerts

Recommended Hybrid Approach: 1. Primary: LoRaWAN SF7 on g1 band (1% DC) for 95% of time 2. Backup: 10 LTE-M modems ($20 each) for critical alert beacons 3. Adaptive: Reduce sampling frequency during low-activity hours 4. Total cost: $200 for LTE-M backup vs $25K for full NB-IoT

Key Engineering Insight: Duty cycle regulations exist to prevent “tragedy of the commons” in unlicensed spectrum. The 1% limit means 100 devices can coexist per channel if all transmit continuously. Smart systems use adaptive rates, sleep cycles, and hybrid solutions to stay compliant while meeting performance requirements.

Verification Questions: 1. If packet size doubles to 126 bytes, how does this affect capacity? (Calculate new ToA and limits) 2. What spreading factor balances range and capacity for 1,000 sensors? (Hint: SF9 gives 5 km range with 500 ms ToA) 3. Could you use listen-before-talk (LBT) to exceed 1% duty cycle safely? (Research ETSI LBT exemptions)

807.6 Summary

This quiz covered regulatory compliance and spectrum selection for LPWAN:

  1. Duty Cycle Compliance: 1% duty cycle limits LoRaWAN to ~391 packets/hour per channel on EU868 g1 band
  2. Spreading Factor Trade-offs: SF7 provides 2× capacity vs SF12, but SF12 offers 5× range
  3. Alert Handling: Emergency alerts can easily exceed duty cycle limits; hybrid solutions are often necessary
  4. Licensed vs Unlicensed: Licensed spectrum (LTE-M, NB-IoT) avoids duty cycle limits but increases cost

Key Takeaways:

  • Always calculate time-on-air before deploying LPWAN systems
  • Per-sensor duty cycle compliance doesn’t guarantee system-wide compliance
  • Hybrid approaches (LoRaWAN + cellular backup) often provide best cost/performance balance
  • ETSI regulations carry significant penalties for non-compliance

807.7 What’s Next

Continue testing your wireless knowledge:

Related Chapters: - LoRaWAN Overview - LoRaWAN protocol details - Cellular IoT Fundamentals - LTE-M, NB-IoT comparison