1073  LPWAN Assessment: Regulatory and Deployment

1073.1 Introduction

This chapter provides comprehensive assessment scenarios covering regulatory compliance, duty cycle calculations, scaling challenges, and operator risk mitigation for LPWAN deployments.

NoteLearning Objectives
  • Calculate duty cycle compliance for high-frequency LPWAN applications
  • Identify scaling challenges when expanding LPWAN deployments
  • Develop risk mitigation strategies for operator-dependent LPWAN networks
  • Apply regulatory knowledge to deployment planning

1073.2 Duty Cycle Compliance Quiz

Understanding regulatory constraints is critical for legal LPWAN operation.

Question: A LoRaWAN deployment in Europe (ETSI regulations) operates in the 868 MHz band with 1% duty cycle limitation. A device sends 20-byte messages at SF7 (airtime ~41ms per message). What is the maximum number of messages this device can send per hour while remaining compliant?

This demonstrates LPWAN duty cycle calculations and regulatory compliance:

Duty Cycle Definition:

Duty Cycle = (Transmission Time / Total Time) x 100%

1% duty cycle means: - Can transmit for 1% of time - Must be silent for 99% of time

In one hour (3600 seconds): - Allowed transmission: 3600 x 0.01 = 36 seconds - Required silence: 3600 x 0.99 = 3564 seconds

Complete Calculation (EU868, 1% Duty Cycle, SF7, 20-byte payload):

Step Calculation Result Notes
1. Allowed airtime 3600s x 1% 36 seconds/hour ETSI 1% limit
2. Convert to ms 36s x 1000 36,000 ms/hour -
3. Message airtime SF7, 20 bytes 41 ms/message From Semtech formula
4. Max messages 36,000 ms / 41 ms 878 messages/hour Floor(878.04)
5. Verify compliance 878 x 41 ms = 35,998 ms 0.9999% duty cycle Compliant
6. Optimal interval 3600s / 878 4.1 seconds Even distribution

Conclusion: With 1% duty cycle and SF7, a LoRaWAN device can send 878 messages/hour (one every 4.1 seconds) while remaining compliant.

Mathematical proof:

Given: - Duty cycle limit: 1% per hour - Hour duration: 3600 seconds = 3,600,000 milliseconds - Message airtime: 41 milliseconds - Payload: 20 bytes at SF7

Calculate maximum messages: 1. Allowed airtime = 3,600,000 ms x 1% = 36,000 ms 2. Messages per hour = 36,000 ms / 41 ms/message = 878.04 messages 3. Round down to integer: 878 messages 4. Remaining airtime = 36,000 - (878 x 41) = 2 ms (insufficient for another message)

Spreading Factor Impact on Capacity:

SF Airtime Max Msg/Hour Interval Range
7 41 ms 878 4.1s 2km
8 72 ms 500 7.2s 3km
9 144 ms 250 14.4s 5km
10 267 ms 134 26.7s 7km
11 524 ms 68 52.4s 11km
12 1024 ms 35 102.4s 15km

Trade-off: Lower SF = more messages but shorter range; Higher SF = fewer messages but longer range

Why other options are incorrect:

Option A: 36 messages/hour (WRONG) This confuses SECONDS of airtime with NUMBER of messages: - 36 seconds of transmission allowed per hour - Each message takes 41 milliseconds = 0.041 seconds - 36,000 ms / 41 ms = 878 messages

Option C: 1440 messages/hour (WRONG) - 1440 x 41 ms = 59,040 ms = 59.04 seconds - Duty cycle: 59.04 / 3600 = 1.64% - EXCEEDS LIMIT BY 64% - regulatory violation

Option D: 140 messages/hour (WRONG) This is Sigfox’s DAILY limit divided by 24 hours: - Sigfox: 140 messages per DAY - But this question is about LoRaWAN, not Sigfox

Summary: With 1% duty cycle (36 seconds/hour) and 41ms airtime per message: - Maximum messages = 36,000 ms / 41 ms = 878 messages/hour - The key insight is that duty cycle limits AIRTIME, not message count

1073.3 Scaling Challenge Scenario

Question: A university deploys 500 environmental sensors across campus (2 sq km) using LoRaWAN. After 2 years, they want to add building energy monitoring (1,500 sensors) requiring 10-second update intervals. What challenge will they face?

Option D is correct - Duty cycle is the critical constraint:

EU868 Duty Cycle Calculation:

Regulation: 1% duty cycle in 868 MHz ISM band = 36 seconds of transmission per hour per device.

Current deployment (environmental sensors): - Assume hourly updates: 24 messages/day - Airtime per message (SF7, 50 bytes): ~100 ms - Daily airtime: 24 x 0.1 sec = 2.4 seconds - Hourly airtime: 2.4 / 24 = 0.1 seconds - Duty cycle: 0.1 / 3600 = 0.0028% (well under 1%)

Proposed energy monitoring (10-second updates): - Messages per day: 86,400 sec/day / 10 sec = 8,640 messages/day - Messages per hour: 360 messages/hour - Airtime per message: 100 ms (SF7, assume 20-byte payload) - Hourly airtime: 360 x 0.1 = 36 seconds - Duty cycle: 36 / 3600 = 1.0% (exactly at limit!)

Problem: This assumes perfect conditions (SF7, minimum payload). Reality: - Varying SF (SF8-SF10 for indoor sensors): 200-400 ms airtime - With SF9 (200 ms): 360 x 0.2 = 72 seconds/hour = 2% duty cycle - VIOLATION - Penalties: 10,000-100,000 EUR fines, equipment confiscation, network shutdown

Solutions: 1. Reduce update rate: 60-second updates instead of 10-second 2. Use NB-IoT: Licensed spectrum has no duty cycle restrictions 3. Deploy Wi-Fi/Ethernet: Higher bandwidth, no duty cycle limits 4. Aggregate data: Send batched readings every 60 seconds

Why other options are wrong:

A - Capacity limit: LoRaWAN gateways support 10,000-100,000 devices; 2,000 is not a limit. The issue is duty cycle, not device count.

B - Battery life: While true that 10-second updates reduce battery life (from 10 years to 1-2 years), LoRaWAN can still support this. Building energy monitors are typically mains-powered anyway.

C - Range: LoRaWAN excels at indoor penetration (10-20 dB advantage). Indoor sensors easily reach outdoor gateways in a 2 sq km campus.

Key lesson: LPWAN is optimized for infrequent updates (minutes to hours). Sub-minute intervals violate regulatory duty cycles and battery/spectrum efficiency assumptions.

1073.4 Operator Risk Mitigation

Question: A logistics company tracks 50,000 shipping containers globally using Sigfox. After 3 years, Sigfox operator coverage disappears in a key region due to bankruptcy. What is their BEST mitigation strategy going forward?

Option C (NB-IoT/LTE-M) is the most pragmatic solution for global shipping logistics:

Analysis of each option:

Option A - LoRaWAN private network: - Pros: Full control, zero recurring costs after deployment - Cons: - Infeasible global coverage: 50,000 containers move globally - cannot deploy gateways at every port, warehouse, rail yard, and transit route worldwide - Mobility challenge: Containers move between ocean, rail, truck - LoRaWAN is designed for stationary sensors, not high mobility - Deployment complexity: Installing gateways in foreign countries involves permits, power, backhaul, maintenance - Cost: 1,000+ gateways x $1,500 = $1.5M upfront + ongoing maintenance - Verdict: Impractical for global mobile asset tracking

Option B - Alternative Sigfox operators: - Pros: Minimal device changes (same hardware/firmware) - Cons: - Same risk: Dependence on Sigfox ecosystem; if one operator failed, others may follow - Coverage gaps: Sigfox is unavailable or unreliable in many countries - No global roaming: Sigfox roaming is limited; containers crossing regions may lose connectivity - Technology lock-in: Sigfox ecosystem is declining; betting on recovery is risky - Verdict: Short-term fix but doesn’t address fundamental risk

Option C - NB-IoT/LTE-M cellular: - Pros: - Global coverage: Cellular networks in 190+ countries; containers stay connected worldwide - Carrier redundancy: Multi-IMSI SIMs connect to multiple carriers; if one fails, others provide coverage - Mobility support: LTE-M designed for mobile assets with full handover at vehicular speeds - No infrastructure: Leverages existing carrier networks; no gateway deployment needed - Future-proof: 4G/5G cellular is long-term bet; carriers won’t disappear like LPWAN startups - Cons: - Higher cost: $24-120/device/year subscription (50,000 devices x $50/year = $2.5M/year) - Device replacement: Must replace 50,000 Sigfox devices with cellular modules ($20 each = $1M hardware) - Higher power: Cellular consumes more power than Sigfox (but containers have rechargeable batteries/solar) - Total cost (10 years): $1M hardware + $25M subscriptions = $26M - Verdict: Most reliable solution for global logistics

Option D - Hybrid LoRaWAN + Satellite: - Pros: - LoRaWAN for controlled environments (ports/warehouses) - Satellite IoT (Iridium, Swarm) for oceanic/remote transit - Cons: - Complexity: Managing 3 technologies (LoRaWAN, satellite, transitional) - Satellite cost: $10-50/device/month = $500,000-$2.5M/month for 50,000 devices! - Power: Satellite transmission consumes 10x cellular (drains batteries on weeks-long ocean voyages) - Latency: Satellite IoT has minutes-to-hours latency - Verdict: Niche use case but very expensive and complex

Decision Matrix:

Option Coverage Reliability Cost (10yr) Complexity Mobility
LoRaWAN Regional Medium $2-5M High Poor
Alt. Sigfox Spotty Low $10M Low Poor
NB-IoT/LTE-M Global High $26M Low Excellent
Hybrid Global High $50M+ Very High Excellent

Recommended strategy: 1. Immediate: Activate NB-IoT/LTE-M fallback for affected regions (if devices have dual-mode radios) 2. 6-12 months: Gradual device replacement to NB-IoT/LTE-M modules 3. Risk mitigation: Use multi-IMSI SIMs to prevent single-carrier dependency 4. Cost optimization: Negotiate fleet discount with carrier (50,000 devices = bulk pricing power)

Key lesson: For mission-critical global deployments, cellular IoT’s reliability and ubiquity justify higher cost versus private LPWAN’s deployment complexity or operator LPWAN’s bankruptcy risk.

1073.5 Further Reading and Resources

LPWAN Comparisons: - “LPWAN Technologies for IoT and M2M Applications” by Bhaumik et al. - LoRa Alliance Technical Marketing Workgroup whitepapers - Sigfox technical documentation

Standards Bodies: - LoRa Alliance: www.lora-alliance.org - Weightless SIG: www.weightless.org - ETSI (European regulations) - FCC (US regulations)

Online Resources: - The Things Network: Community-driven LoRaWAN resources - TTN Mapper: Global LoRaWAN coverage maps - Sigfox coverage: www.sigfox.com/coverage

1073.6 Summary

This regulatory and deployment assessment covered:

  • Duty Cycle Compliance: Calculating maximum message rates within ETSI 1% limits
  • Scaling Challenges: Identifying when high-frequency updates violate regulatory constraints
  • Operator Risk Mitigation: Strategies for recovering from LPWAN operator failures
  • Global Deployment Trade-offs: Balancing cost, coverage, and reliability

Key Takeaways: - Duty cycle limits AIRTIME, not message count - SF7 allows 878 msg/hr while SF12 allows only 35 - High-frequency updates (sub-minute) often exceed regulatory limits and are unsuitable for LPWAN - Operator-dependent networks carry bankruptcy risk; cellular provides carrier redundancy - Global mobile asset tracking requires cellular IoT despite higher costs

1073.7 What’s Next

Continue your LPWAN learning with: