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graph TB
subgraph "Capital Expenses (CapEx)"
C1["Infrastructure<br/>(Gateways, base stations)"]
C2["Device Hardware<br/>(Radio modules, sensors)"]
C3["Installation<br/>(Labor, equipment)"]
C4["Spectrum License<br/>(One-time or annual)"]
end
subgraph "Operating Expenses (OpEx)"
O1["Connectivity<br/>(Subscriptions, backhaul)"]
O2["Power<br/>(Electricity, battery replacement)"]
O3["Maintenance<br/>(Repairs, updates)"]
O4["Support<br/>(Monitoring, troubleshooting)"]
end
TCO["Total Cost of<br/>Ownership (TCO)"]
C1 --> TCO
C2 --> TCO
C3 --> TCO
C4 --> TCO
O1 --> TCO
O2 --> TCO
O3 --> TCO
O4 --> TCO
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style C2 fill:#E67E22,stroke:#2C3E50,color:#fff
style C3 fill:#E67E22,stroke:#2C3E50,color:#fff
style C4 fill:#E67E22,stroke:#2C3E50,color:#fff
style O1 fill:#16A085,stroke:#2C3E50,color:#fff
style O2 fill:#16A085,stroke:#2C3E50,color:#fff
style O3 fill:#16A085,stroke:#2C3E50,color:#fff
style O4 fill:#16A085,stroke:#2C3E50,color:#fff
style TCO fill:#2C3E50,stroke:#16A085,color:#fff
787 IoT Network Design: Protocol Selection Worked Examples
NoteLearning Objectives
By the end of this section, you will be able to:
- Analyze spectrum allocation for multi-technology IoT deployments
- Evaluate trade-offs between licensed and unlicensed spectrum
- Calculate total cost of ownership for different connectivity options
- Apply interference mitigation strategies for coexisting wireless technologies
787.1 Prerequisites
Before studying this chapter, review:
- IoT Network Design: Reference Model Framework: Understanding the 7-Level IoT Reference Model and protocol selection criteria
- IoT Protocols Fundamentals: Knowledge of different protocol characteristics and trade-offs
787.2 Worked Example: Spectrum Allocation for Multi-Technology Deployment
Scenario: A smart campus is deploying three IoT systems simultaneously: Wi-Fi-based security cameras (50 devices), Zigbee building automation sensors (200 devices), and BLE asset trackers (100 beacons). All systems share the 2.4 GHz ISM band. Design a spectrum allocation plan to minimize interference.
Given: - Available spectrum: 2.4 GHz ISM band (2400-2483.5 MHz) - Wi-Fi: Uses 20 MHz or 40 MHz channels - Zigbee (802.15.4): Uses 2 MHz channels, 16 channels available (11-26) - BLE: Uses 2 MHz channels, 40 channels with adaptive frequency hopping - Campus layout: 3 buildings (A, B, C) with 100m separation
Steps:
- Analyze spectrum overlap:
- Wi-Fi Channel 1: 2401-2423 MHz (overlaps Zigbee 11-14)
- Wi-Fi Channel 6: 2426-2448 MHz (overlaps Zigbee 15-20)
- Wi-Fi Channel 11: 2451-2473 MHz (overlaps Zigbee 21-26)
- BLE: Hops across entire band, but avoids busy frequencies adaptively
- Allocate Wi-Fi channels by building:
- Building A: Wi-Fi Channel 1 (2412 MHz center)
- Building B: Wi-Fi Channel 6 (2437 MHz center)
- Building C: Wi-Fi Channel 11 (2462 MHz center)
- 100m separation ensures minimal adjacent-building interference
- Allocate Zigbee channels to avoid Wi-Fi:
- Building A (Wi-Fi Ch 1): Use Zigbee Ch 25-26 (2475-2480 MHz) - outside Wi-Fi Ch 1
- Building B (Wi-Fi Ch 6): Use Zigbee Ch 15-16 (2425-2430 MHz) - in Wi-Fi null between Ch 1 and Ch 6
- Building C (Wi-Fi Ch 11): Use Zigbee Ch 11-12 (2405-2410 MHz) - below Wi-Fi Ch 11
- Each Zigbee deployment avoids its co-located Wi-Fi channel
- Configure BLE for coexistence:
- Enable Adaptive Frequency Hopping (AFH) on all BLE beacons
- BLE automatically detects and avoids Wi-Fi energy
- Channel classification: Mark channels 0-12 (2402-2426 MHz) as “bad” in Building A
- BLE hops across remaining 28+ good channels
- Validate with interference analysis:
- Wi-Fi Ch 1 signal at Zigbee Ch 25: -60 dBm Wi-Fi, -20 dBm Zigbee = 40 dB SIR (good)
- Wi-Fi Ch 6 signal at Zigbee Ch 16: -55 dBm Wi-Fi, -25 dBm Zigbee = 30 dB SIR (acceptable)
- BLE RSSI through AFH: Maintains -70 dBm average (reliable tracking)
Result: All three systems operate simultaneously with minimal interference: - Wi-Fi cameras: 50 Mbps throughput (sufficient for 720p video) - Zigbee sensors: 0.1% packet loss (within 802.15.4 spec) - BLE beacons: 95% detection rate at 5m range
Key Insight: The 2.4 GHz ISM band is only 83.5 MHz wide, but careful channel planning allows Wi-Fi (20 MHz), Zigbee (2 MHz), and BLE (frequency hopping) to coexist. The key is spatial separation (different buildings use different Wi-Fi channels) and spectral separation (Zigbee uses frequencies NOT overlapped by local Wi-Fi). Never deploy Zigbee on channels 15-20 if Wi-Fi Channel 6 is active nearby.
787.3 Worked Example: Licensed vs Unlicensed Spectrum for Smart Metering
Scenario: A utility company must choose between LoRaWAN (unlicensed 915 MHz), NB-IoT (licensed LTE Band 8), or private LTE (licensed 3.5 GHz CBRS) for 50,000 smart electric meters across a 500 km² service area. Deployment must last 15 years with 99.9% reliability.
Given: - Meters transmit 100 bytes every 15 minutes (96 messages/day) - Required battery life: 10+ years - Environment: Mixed urban/suburban/rural - Budget constraint: $10M over 15 years - Regulatory region: United States (FCC rules apply)
Steps:
787.3.1 Step 1: Analyze Spectrum Characteristics
| Aspect | LoRaWAN (915 MHz) | NB-IoT (LTE Band 8) | Private LTE (CBRS 3.5 GHz) |
|---|---|---|---|
| Spectrum type | Unlicensed ISM | Licensed (carrier) | Shared licensed (PAL/GAA) |
| Access cost | Free | $0.50-2/device/month | $100K-500K spectrum lease |
| Interference risk | Medium (shared) | Very Low (exclusive) | Low (priority access) |
| Range (rural) | 10-15 km | 15-35 km | 5-10 km |
| Range (urban) | 2-5 km | 5-10 km | 1-3 km |
787.3.2 Step 2: Calculate Infrastructure Requirements
LoRaWAN: - Rural coverage: 15 km radius = 707 km² per gateway - Urban coverage: 3 km radius = 28 km² per gateway - Required gateways: 500 km² / (0.4 x 707 + 0.6 x 28) = ~25 gateways - Gateway cost: 25 x $2,000 = $50,000 - Backhaul: 25 x $50/month x 180 months = $225,000
NB-IoT: - Uses existing cellular infrastructure (no new towers) - Module cost premium: $5/meter more than LoRa = $250,000 - Subscription: 50,000 x $1/month x 180 months = $9,000,000
Private LTE (CBRS): - Requires new base stations (shorter range than NB-IoT) - Required sites: ~100 (at $50,000 each) = $5,000,000 - Spectrum lease (PAL): $200,000/year x 15 = $3,000,000 - Backhaul: 100 x $100/month x 180 = $1,800,000
787.3.3 Step 3: Calculate 15-Year Total Cost of Ownership
| Cost Item | LoRaWAN | NB-IoT | Private LTE |
|---|---|---|---|
| Infrastructure | $50K | $0 | $5,000K |
| Spectrum/License | $0 | $0 | $3,000K |
| Backhaul | $225K | $0 | $1,800K |
| Device premium | $0 | $250K | $500K |
| Subscription | $0 | $9,000K | $0 |
| Maintenance | $300K | $100K | $1,500K |
| Total | $575K | $9,350K | $11,800K |
787.3.4 Step 4: Evaluate Reliability Requirements
- LoRaWAN on unlicensed spectrum: Risk of interference from other users
- Mitigation: Deploy redundant gateways (add $50K)
- Achievable reliability: 99.7-99.9%
- NB-IoT on licensed spectrum: Carrier-grade reliability
- Achievable reliability: 99.95%
- Private LTE: Full control over spectrum
- Achievable reliability: 99.99% (but at 20x cost)
787.3.5 Step 5: Make Recommendation Based on Constraints
- Budget constraint: $10M eliminates Private LTE ($11.8M)
- Reliability constraint: 99.9% achievable by both LoRaWAN and NB-IoT
- Battery life: LoRaWAN (15+ years) > NB-IoT (10-12 years) at this duty cycle
- Winner: LoRaWAN - meets all requirements at 1/16th the cost
Result: Deploy LoRaWAN with 30 gateways (20% redundancy) for total 15-year cost of $625K. The unlicensed spectrum risk is mitigated by: - Using spreading factor SF10 (16 dB processing gain against interference) - 20% gateway redundancy ensures coverage if one gateway experiences interference - Firmware capability to shift to backup channels if primary congested
Key Insight: Licensed spectrum guarantees exclusive access but at premium cost ($180/meter over 15 years for NB-IoT vs $12.50/meter for LoRaWAN). For applications tolerating occasional retransmissions (utility metering is not life-safety), unlicensed spectrum with proper interference mitigation delivers equivalent reliability at fraction of cost. Reserve licensed spectrum for mission-critical applications (healthcare, autonomous vehicles) where interference cannot be tolerated.
787.4 Cost-Benefit Analysis Framework
When evaluating protocol options, consider these cost categories:
{fig-alt=“Total Cost of Ownership breakdown showing Capital Expenses (infrastructure, device hardware, installation, spectrum license in orange) and Operating Expenses (connectivity subscriptions, power costs, maintenance, support in teal) all contributing to TCO calculation (navy). Helps visualize full cost picture beyond initial purchase price.”}
787.4.1 Key Cost Considerations by Protocol Type
| Protocol | Low CapEx | Low OpEx | Best For |
|---|---|---|---|
| LoRaWAN | Moderate (gateways) | Very Low (no subscription) | Large private deployments |
| NB-IoT | Low (no infrastructure) | High (subscriptions) | Small deployments, urban areas |
| Wi-Fi | High (many APs) | Moderate (power, backhaul) | High-bandwidth, indoor |
| Zigbee | Low (coordinators) | Low (self-powered mesh) | Building automation |
787.5 Knowledge Check
NoteRelated Chapters
Protocol Fundamentals: - IoT Protocols Fundamentals - Protocol stack overview - LPWAN Fundamentals - Wide-area connectivity - LoRaWAN - LoRaWAN deep dive
Design Considerations: - Five Key Design Considerations - Device, data, and infrastructure planning - Scenarios and Labs - Case studies and hands-on exercises
787.6 Summary
Protocol selection involves complex trade-offs between technical capabilities, cost, and operational requirements:
- Spectrum allocation requires careful planning when multiple technologies share the same band
- Licensed vs unlicensed spectrum decisions balance guaranteed access against subscription costs
- Total Cost of Ownership must consider infrastructure, subscriptions, power, and maintenance over the deployment lifetime
- Interference mitigation strategies (channel planning, redundancy, adaptive hopping) can make unlicensed spectrum viable for most applications
787.7 What’s Next?
Continue to Five Key Design Considerations to explore how device characteristics, data requirements, addressing schemes, and topology decisions shape IoT network architecture.