810  Quiz: Smart City & Multi-Technology Deployments

810.1 Introduction

This chapter covers complex multi-technology deployment decisions for smart city and agricultural IoT scenarios. You’ll work through total cost of ownership analysis, technology comparison matrices, and risk assessment for large-scale deployments.

NoteLearning Objectives

By completing this chapter, you will be able to:

  • Calculate 10-year total cost of ownership for competing technologies
  • Evaluate risk factors including vendor lock-in and technology obsolescence
  • Create weighted decision matrices for technology selection
  • Design robust deployments with redundancy and failover strategies

810.2 Prerequisites

Before attempting these assessments, you should have completed:

810.3 Scenario-Based Assessment: Smart City Parking System

Scenario: A smart city is deploying an intelligent parking management system across a downtown area spanning 15 km². The system will monitor 10,000 parking spaces using wireless sensors that detect vehicle presence and transmit occupancy status.

System Requirements: - 10,000 parking sensors (surface lots, garages, street parking) - Expected operational lifetime: 10 years minimum - Reporting frequency: Status change (vehicle arrives/leaves) + hourly heartbeat - Average parking duration: 2.5 hours (~ 4 events per space per day) - Peak usage: 80% occupancy during business hours - Uptime requirement: 99% (not mission-critical) - Battery: Must last 5-10 years (no access for maintenance)

Technology Options:

Option A: Licensed Cellular (NB-IoT) - Spectrum: Licensed LTE bands (carrier-operated) - Coverage: Pre-existing citywide coverage - Subscription cost: $3 per device per year - Module cost: $8 per device - Data plan: 10 MB/month included - Infrastructure: None required (uses carrier towers) - QoS: 99.9% uptime guaranteed, interference-protected

Option B: Unlicensed LoRaWAN (868/915 MHz ISM) - Spectrum: Unlicensed ISM band (no fees) - Coverage: Must deploy gateways - Gateway cost: $1,200 per gateway (20 needed for 15 km²) - Module cost: $6 per device - Infrastructure: 20 gateways + backhaul (fiber/4G) @ $100/month each - QoS: Best-effort, shared spectrum with interference risk - Duty cycle: 1% limit (EU) or unlimited (US)

Option C: Licensed Private LTE-M Network - Spectrum: Leased LTE-M spectrum - License cost: EUR 150,000/year - Module cost: $10 per device - Infrastructure: 15 base stations @ $8,000 each - QoS: Full control, carrier-grade reliability - Maintenance: $50,000/year for network operations

Analysis Questions:

  1. Total Cost of Ownership (TCO): Calculate 10-year TCO for each option including:
    • Device modules
    • Infrastructure (initial + maintenance)
    • Spectrum/subscription fees
    • Operational costs
  2. Coverage Analysis: For 15 km² urban area:
    • How many gateways does LoRaWAN need? (Assume 1 km² coverage per gateway)
    • What’s the LoRaWAN infrastructure cost vs NB-IoT?
  3. Traffic Analysis: Verify LoRaWAN duty cycle compliance:
    • Calculate daily transmissions per sensor (events + heartbeats)
    • Estimate time-on-air per transmission (20 bytes @ 5 kbps)
    • Check if 1% duty cycle is sufficient
  4. Risk Assessment: Compare failure modes:
    • What happens if NB-IoT carrier raises prices to $8/device/year?
    • What if LoRaWAN gateway fails? (affects ~500 sensors)
    • What if interference degrades LoRaWAN performance by 20%?
  5. Decision Matrix: Create weighted scoring (scale 1-10) across:
    • Cost (40% weight)
    • Reliability (30% weight)
    • Control/flexibility (20% weight)
    • Deployment speed (10% weight)

1. Total Cost of Ownership (10-Year TCO):

Option A: NB-IoT (Licensed Cellular)

Initial Costs: - Device modules: 10,000 × $8 = $80,000 - Infrastructure: $0 (carrier-provided) - Initial Total: $80,000

Recurring Costs (10 years): - Subscriptions: 10,000 × $3/year × 10 years = $300,000 - Maintenance: $0 (carrier-managed) - Recurring Total: $300,000

10-Year TCO: $380,000

Option B: LoRaWAN (Unlicensed ISM)

Initial Costs: - Device modules: 10,000 × $6 = $60,000 - Gateways: 20 × $1,200 = $24,000 - Installation/commissioning: $10,000 - Initial Total: $94,000

Recurring Costs (10 years): - Gateway backhaul: 20 × $100/month × 120 months = $240,000 - Maintenance/replacements: $20,000 - Recurring Total: $260,000

10-Year TCO: $354,000

Option C: Private LTE-M (Licensed)

Initial Costs: - Device modules: 10,000 × $10 = $100,000 - Base stations: 15 × $8,000 = $120,000 - Installation: $30,000 - Initial Total: $250,000

Recurring Costs (10 years): - Spectrum license: EUR 150,000 × 10 = EUR 1,500,000 (~$1,650,000) - Network ops: $50,000 × 10 = $500,000 - Recurring Total: $2,150,000

10-Year TCO: $2,400,000

Cost Winner: LoRaWAN saves $26,000 vs NB-IoT (7% savings)

2. Coverage Analysis:

LoRaWAN Gateway Planning:

Urban coverage parameters: - LoRaWAN range (urban): 1-2 km radius - Coverage area per gateway: π × (1.5 km)² ≈ 7 km² - Gateways needed: 15 km² / 7 km² ≈ 3 gateways minimum

But for redundancy and reliability: - 2× redundancy for critical areas: 6 gateways - Indoor/underground garage coverage: +4 dedicated gateways - Recommended deployment: 10 gateways (not 20)

Revised LoRaWAN Infrastructure: - Gateways: 10 × $1,200 = $12,000 (not $24,000) - Backhaul: 10 × $100/month × 120 months = $120,000 (not $240,000)

Revised LoRaWAN 10-Year TCO: $206,000 (saves $174,000 vs NB-IoT!)

NB-IoT Coverage: - Pre-existing carrier towers: 0 additional infrastructure - Coverage verified via carrier: Immediate deployment

3. Traffic & Duty Cycle Analysis:

Daily Transmission Calculation: - Parking events: 4 per day (vehicle arrive/leave) - Hourly heartbeat: 24 per day - Total: 28 transmissions per day

Time-on-Air (ToA): - Packet size: 20 bytes = 160 bits - LoRaWAN data rate (SF7): 5.47 kbps - ToA: 160 / 5470 = 29 milliseconds

Daily Duty Cycle Check: - Daily airtime: 28 × 0.029s = 0.812 seconds per day - Percentage: 0.812 / 86,400 seconds = 0.00094% per day - Hourly: 0.0011% (well under 1% limit) ✓ Fully compliant

Channel Capacity: - 1% duty cycle allows: 3600s × 0.01 / 0.029s = 1,241 sensors per gateway per hour - 10 gateways × 1,241 = 12,410 sensor capacity - Verdict: LoRaWAN easily supports 10,000 sensors with headroom

4. Risk Assessment:

Scenario A: NB-IoT Price Increase ($3 → $8/year) - New 10-year subscription cost: 10,000 × $8 × 10 = $800,000 - New TCO: $880,000 (2.3× original estimate) - Risk impact: HIGH - No control over carrier pricing - Mitigation: None - locked into carrier terms

Scenario B: LoRaWAN Gateway Failure - Affected sensors: 10,000 / 10 gateways = 1,000 sensors down - Affected parking spaces: 10% of system - MTTR (mean time to repair): 4-24 hours - Risk impact: MEDIUM - localized outage - Mitigation: - Hot spare gateways ($1,200 × 2 = $2,400) - Overlapping coverage reduces impact to 5% - Remote diagnostics and auto-failover

Scenario C: 20% LoRaWAN Interference Degradation - Packet delivery rate: 95% → 76% - Lost transmissions: 24% - Parking system impact: - Heartbeats: Tolerable (next hour compensates) - Events: Concerning (missed arrive/leave events) - Risk impact: MEDIUM-HIGH - Mitigation: - Adaptive data rate (switch to SF9/SF12 in high-interference areas) - Increase transmission frequency (send twice) - Use confirmed uplinks for critical events - Added cost: $0 (software update)

Scenario D: Carrier Discontinues NB-IoT Service (Year 7) - Must migrate to alternative: LoRaWAN or LTE-M - Migration cost: $60,000 (new modules) + $12,000 (gateways) = $72,000 - Risk impact: HIGH - forced technology change - Precedent: Real risk (e.g., 2G/3G sunset forcing device replacements)

5. Decision Matrix (Weighted Scoring):

Criterion Weight NB-IoT Score LoRaWAN Score LTE-M Score
Cost (10-yr TCO) 40% 6 ($380K) 9 ($206K) 2 ($2.4M)
Reliability (Uptime) 30% 9 (99.9%) 7 (99%) 10 (99.99%)
Control/Flexibility 20% 3 (Carrier-dependent) 9 (Full control) 10 (Full control)
Deployment Speed 10% 10 (Immediate) 6 (2-3 months) 4 (6+ months)

Weighted Scores: - NB-IoT: (6×0.4) + (9×0.3) + (3×0.2) + (10×0.1) = 2.4 + 2.7 + 0.6 + 1.0 = 6.7/10 - LoRaWAN: (9×0.4) + (7×0.3) + (9×0.2) + (6×0.1) = 3.6 + 2.1 + 1.8 + 0.6 = 8.1/10 - LTE-M: (2×0.4) + (10×0.3) + (10×0.2) + (4×0.1) = 0.8 + 3.0 + 2.0 + 0.4 = 6.2/10

Winner: LoRaWAN (8.1/10)

Final Recommendation: Deploy LoRaWAN with Risk Mitigation

Rationale: 1. Cost savings: $174,000 over 10 years (46% lower than NB-IoT) 2. Full control: No carrier dependency, pricing lock-in, or service sunset risk 3. Sufficient reliability: 99% uptime acceptable for non-critical parking 4. Scalability: Can add 2,410 more sensors without infrastructure changes 5. Future-proof: Infrastructure owned, can upgrade/modify without carrier approval

Risk Mitigation Plan: - Deploy 12 gateways (2 extra for redundancy): +$2,400 - Use confirmed uplinks for critical events: $0 (built-in) - Adaptive data rate for interference: $0 (software) - Annual interference monitoring: $2,000/year - Total mitigation cost: $22,400 over 10 years

Adjusted LoRaWAN TCO: $228,400 (still $151,600 cheaper than NB-IoT)

When to Choose NB-IoT Instead: - Cannot deploy/maintain gateway infrastructure - Need immediate deployment (< 1 month) - Coverage area exceeds 50 km² (gateway cost becomes prohibitive) - Mission-critical application requiring 99.9% uptime SLA

Key Engineering Insight: The “licensed vs unlicensed” decision is fundamentally a trade-off between OPEX and CAPEX. Licensed spectrum (NB-IoT) trades higher ongoing costs for zero infrastructure burden. Unlicensed (LoRaWAN) requires upfront investment but offers long-term cost savings and control. For 10,000+ devices over 10 years, the break-even point is ~2 years, after which LoRaWAN’s savings compound significantly.

Verification Questions: 1. At what subscription price does NB-IoT become more expensive than Private LTE-M? (Hint: Calculate break-even per-device cost) 2. If parking turnover increases to 10 events/day, does LoRaWAN still comply with duty cycle? (Recalculate ToA budget) 3. What TCO change occurs if LoRaWAN gateways need replacement every 5 years at $800 each? (Add replacement costs)

810.4 Knowledge Check: Wi-Fi Channel Selection

Question 1: A Wi-Fi network scan reveals 15 access points on channel 6, 8 on channel 1, and 12 on channel 11. When deploying a new access point for IoT devices, which channel should you select and why?

Explanation: Channel selection should minimize co-channel interference by choosing the least congested non-overlapping channel.

Why Channel 1 is correct: - Channels 1, 6, 11 are the only non-overlapping channels in 2.4 GHz - Channel 1 has only 8 networks (vs 15 on ch6, 12 on ch11) - Lower congestion = less competition for airtime - Fewer collisions and retransmissions

Why other options are wrong:

Channel 6 (most congested): - 15 networks means high competition - Every transmission must wait for all 15 networks to be idle (CSMA/CA) - Results in poor throughput and high latency

Channel 3 (overlapping): - Overlaps with both channel 1 and channel 6 - Receives interference from neighboring channels - Creates interference for channels 1 and 6 - Worst possible choice - avoid at all costs!

Channel 14: - Illegal in most countries (only allowed in Japan) - Not supported by most devices - Would cause regulatory violations

Advanced consideration - Signal strength matters too: If channel 1 has 8 strong signals (-40 dBm each) but channel 6 has 15 weak signals (-80 dBm each), channel 6 might actually perform better because strong signals dominate airtime more than numerous weak ones. Use Wi-Fi analyzer tools to measure both count AND strength!

Pro tip: Many “smart” home routers auto-select channel 6 by default, causing artificial congestion. Manually selecting channel 1 or 11 often dramatically improves performance.

810.5 Knowledge Check: Multipath Propagation

Question 2: You measure RSSI values of -45 dBm at 5 meters and -65 dBm at 50 meters from a 2.4 GHz access point. The theoretical free space path loss predicts a 20 dB increase (from 20log10 of the 10x distance increase). Why is the observed loss (20 dB) close to theoretical despite being indoors?

Explanation: This scenario demonstrates the complex nature of indoor RF propagation where multipath effects can sometimes improve signal strength.

Why observed loss matches theoretical:

Free space path loss calculation: - Path loss ratio: 20log10(50/5) = 20log10(10) = 20 dB - Predicted RSSI at 50m: -45 dBm - 20 dB = -65 dBm - Observed RSSI at 50m: -65 dBm ✓ Perfect match!

But wait - what about walls and obstacles?

Indoor environments create multipath propagation: 1. Direct path: Line-of-sight signal (if available) 2. Reflected paths: Signals bouncing off walls, ceilings, furniture 3. Diffracted paths: Signals bending around obstacles

Constructive interference scenario: - Multiple reflected paths arrive at the receiver - If path lengths differ by integer multiples of wavelength, signals add constructively - Combined signal strength can exceed direct path alone - This can compensate for attenuation through obstacles

Real-world variation: - Move receiver 1 meter and RSSI might drop to -75 dBm (destructive interference) - Indoor propagation creates standing wave patterns with “hot spots” and “dead zones” - This is why walking around with a phone shows fluctuating signal bars

Path loss models for indoor: - Free space: FSPL = 20log10(d) + 20log10(f) + 32.45 (baseline) - Indoor: FSPL_indoor = FSPL + n × wall_loss + floor_loss (typically adds 10-30 dB) - But multipath can reduce actual loss by -10 to +10 dB locally

Practical implications: - Never rely on single-point measurements - Take measurements at multiple locations - Expect ±10 dB variation due to multipath - Design systems with fade margin to handle variations

810.6 Knowledge Check: Zigbee/Wi-Fi Coexistence

Question 3: A Zigbee mesh network operates on 2.4 GHz channel 15 (2.425 GHz center frequency). A nearby Wi-Fi network on channel 3 (2.422 GHz center frequency) is causing interference. Why does this occur when they’re on different channel numbers?

Explanation: This illustrates a critical coexistence challenge in the 2.4 GHz ISM band where different technologies have different channel bandwidths.

Channel bandwidth comparison:

Wi-Fi (802.11b/g/n): - Each channel occupies 22 MHz bandwidth - Channel 3 centers at 2.422 GHz - Spans from 2.411 GHz to 2.433 GHz

Zigbee (802.15.4): - 16 channels numbered 11-26 in 2.4 GHz band - Each channel occupies only 2 MHz bandwidth - Channel 15 centers at 2.425 GHz - Spans from 2.424 GHz to 2.426 GHz

Overlap calculation: - Wi-Fi channel 3: 2.411-2.433 GHz - Zigbee channel 15: 2.424-2.426 GHz - Complete overlap! Zigbee ch15 falls entirely within Wi-Fi ch3 bandwidth

Interference mechanism: 1. Wi-Fi transmits high-power bursts (100-1000 mW) 2. Zigbee transmits low-power signals (1-10 mW) 3. Wi-Fi signal “drowns out” Zigbee during transmission 4. Zigbee must wait or retransmit, reducing throughput

Coexistence strategies:

Option 1: Frequency separation - Use Wi-Fi channel 1 (2.412 GHz) or 11 (2.462 GHz) - Use Zigbee channels 25-26 (2.475-2.480 GHz) - Provides ~60 MHz separation, minimal interference

Option 2: Migrate to 5 GHz - Move Wi-Fi to 5 GHz band - Leave 2.4 GHz for Zigbee, Bluetooth, Thread - 5 GHz has 23 non-overlapping channels

Option 3: Thread with channel hopping - Thread protocol includes frequency hopping - Automatically avoids interfering channels - More resilient than static Zigbee channels

Real-world example: A smart home with Zigbee sensors on channel 15 experiences 30-50% packet loss when streaming 4K video on nearby Wi-Fi. Moving Wi-Fi to channel 11 or 5 GHz band eliminates the issue entirely.

810.7 Scenario-Based Assessment: Agricultural IoT Deployment

Scenario: A precision agriculture company is deploying a soil monitoring system across a 2 km² farm (approximately 500 acres) for optimal irrigation management. The system will measure soil moisture, temperature, and electrical conductivity at multiple depths to optimize water usage and crop yields.

Farm Characteristics: - Area: 2 km² (1.4 km × 1.4 km rectangular field) - Terrain: Flat farmland with no obstructions - Crops: Corn and soybeans (1-2 meter height at maturity) - Power: No electrical infrastructure in fields - Connectivity: Nearest Wi-Fi/4G is at farmhouse (corner of property) - Climate: Temperate (rain, snow, -20C to +40C temperature range)

System Requirements: - 200 sensor nodes distributed across 2 km² (10,000 m² per sensor) - Each node: 3 soil sensors at different depths - Reporting frequency: 10 readings per day (every 2.4 hours) - Data per reading: 50 bytes (moisture %, temperature, EC, battery status) - Battery life: 10 years minimum (no maintenance access) - Network reliability: 95%+ (occasional packet loss acceptable) - Installation: Solar panel not preferred (adds cost/maintenance)

Technology Options:

Option A: Wi-Fi 5 GHz (802.11ac) - Range: 50-100 meters outdoor - Power consumption: 300-500 mW transmit, 50 mW idle - Module cost: $5 - Bandwidth: Up to 867 Mbps - Battery life estimate: 3-6 months per 5,000 mAh battery

Option B: Zigbee 2.4 GHz (802.15.4) - Range: 10-100 meters (mesh extends this) - Power consumption: 30-50 mW transmit, 3 mW idle - Module cost: $3 - Bandwidth: 250 kbps - Battery life estimate: 1-2 years per 5,000 mAh battery - Mesh networking: Nodes relay for others

Option C: Bluetooth Low Energy 5.0 (Long Range) - Range: 200-400 meters (long range mode) - Power consumption: 10-15 mW transmit, 1 mW idle - Module cost: $4 - Bandwidth: 125 kbps (long range) to 2 Mbps (normal) - Battery life estimate: 3-5 years per 5,000 mAh battery

Option D: LoRaWAN 868/915 MHz (Sub-GHz) - Range: 2-5 km rural (line of sight), 1-2 km with crops - Power consumption: 20-30 mW transmit (short burst), <1 uA sleep - Module cost: $8 - Bandwidth: 250 bps - 50 kbps (adaptive) - Battery life estimate: 10+ years per 5,000 mAh battery - Gateway: $600-1,200 (1-2 needed)

Analysis Questions:

  1. Range & Coverage: For 200 sensors across 2 km²:
    • Calculate maximum sensor-to-gateway distance
    • How many gateways/access points does each option need?
    • Total infrastructure cost?
  2. Power Budget Analysis: Calculate 10-year battery feasibility:
    • Daily energy consumption per sensor (10 transmissions)
    • Sleep mode energy (remaining time)
    • Total energy needed for 10 years
    • Battery capacity required (typical: 5,000-10,000 mAh @ 3.6V)
  3. Link Budget: For 1 km transmission:
    • Calculate path loss at 915 MHz vs 2.4 GHz
    • Account for crop attenuation (1-2 dB/meter for 2.4 GHz in corn)
    • Determine if link closes with typical transmit powers
  4. Cost Analysis: Total 10-year deployment cost:
    • Sensor modules (200 units)
    • Gateways/infrastructure
    • Battery replacements (if needed)
    • Installation labor (@$50/hour)
  5. Trade-off Decision: Rank technologies by:
    • Battery life feasibility (can it reach 10 years?)
    • Coverage (infrastructure needed)
    • Total cost
    • Reliability in agricultural environment

1. Range & Coverage Analysis:

Maximum Sensor Distance: - Field dimensions: 1.4 km × 1.4 km - Gateway at center: Maximum distance = 0.7 × sqrt(2) ≈ 1 km to corners - Average distance: 500-700 meters

Infrastructure Requirements:

Option A: Wi-Fi 5 GHz - Range: 100 meters max - Coverage radius: 50 m (accounting for crops, weather) - Area per AP: π × 50² = 7,850 m² - APs needed: 2,000,000 / 7,850 ≈ 255 access points Not feasible - Cost: 255 × $150 = $38,250 (plus power/backhaul)

Option B: Zigbee 2.4 GHz Mesh - Range per hop: 75 meters (through crops) - Mesh topology: Sensors relay for each other - Gateway needed: 1 at farmhouse - Average hops: 1000m / 75m = 13-14 hops - Infrastructure cost: $200 (1 gateway) - Concern: Long multi-hop delays and reliability degradation

Option C: BLE 5.0 Long Range - Range: 300 meters (realistic through crops) - Gateways needed: 2,000,000 / (π × 300²) ≈ 8 gateways - Infrastructure cost: 8 × $300 = $2,400 - Concern: Marginally adequate coverage

Option D: LoRaWAN 915 MHz - Range: 2 km (rural, through crops) - Coverage: π × 2000² = 12.6 km² - Gateways needed: 1 (covers entire 2 km²) - Infrastructure cost: 1 × $800 = $800 - Optimal: Single gateway covers entire farm with margin

2. Power Budget Analysis (10-Year Battery Life):

Daily Energy Consumption:

Transmission Energy (10 readings/day):

Wi-Fi 5 GHz: - Tx power: 400 mW, Time: 5 ms per transmission - Energy: 10 × 400 mW × 0.005s = 20 mWh/day

Zigbee 2.4 GHz: - Tx power: 40 mW, Time: 20 ms per transmission - Mesh overhead: 2× (relaying for others) - Energy: 10 × 40 mW × 0.02s × 2 = 16 mWh/day

BLE 5.0 Long Range: - Tx power: 12 mW, Time: 10 ms per transmission - Energy: 10 × 12 mW × 0.01s = 1.2 mWh/day

LoRaWAN 915 MHz: - Tx power: 25 mW, Time: 200 ms per transmission (SF9) - Energy: 10 × 25 mW × 0.2s = 0.5 mWh/day

Sleep Mode Energy (23.8 hours/day):

Wi-Fi: 50 mW × 23.8 hr = 1,190 mWh/day Zigbee: 3 mW × 23.8 hr = 71.4 mWh/day BLE: 1 mW × 23.8 hr = 23.8 mWh/day LoRaWAN: 0.001 mW × 23.8 hr = 0.024 mWh/day

Total Daily Energy: - Wi-Fi: 20 + 1,190 = 1,210 mWh/day - Zigbee: 16 + 71.4 = 87.4 mWh/day - BLE: 1.2 + 23.8 = 25 mWh/day - LoRaWAN: 0.5 + 0.024 = 0.524 mWh/day

10-Year Energy Requirement: - Wi-Fi: 1,210 × 3,650 days = 4,417 Wh (requires massive battery or solar) - Zigbee: 87.4 × 3,650 = 319 Wh (needs battery replacement or solar) - BLE: 25 × 3,650 = 91 Wh (borderline, may need 1 battery replacement) - LoRaWAN: 0.524 × 3,650 = 1.9 Wh ✓ Easily achievable

Battery Capacity Check (3.6V Li-SOCI2 battery):

Standard 5,000 mAh battery @ 3.6V = 18 Wh - Wi-Fi: Needs 245× batteries (completely infeasible) - Zigbee: Needs 18× batteries (1 change every 7 months) - BLE: Needs 5× batteries (1 change every 2 years) - LoRaWAN: Needs 0.1× battery (10-year battery life with margin) ✓

Winner: Only LoRaWAN meets 10-year battery requirement

3. Link Budget Analysis (1 km Range):

Free Space Path Loss: - 915 MHz: FSPL = 20log(1) + 20log(915) + 32.45 = 91.7 dB - 2.4 GHz: FSPL = 20log(1) + 20log(2400) + 32.45 = 100.5 dB

Crop Attenuation (1.5m tall corn at maturity): - 915 MHz: ~0.5 dB/meter × 1000m = 5 dB (low attenuation) - 2.4 GHz: ~1.5 dB/meter × 1000m = 15 dB (significant attenuation)

Total Path Loss: - 915 MHz: 91.7 + 5 = 96.7 dB - 2.4 GHz: 100.5 + 15 = 115.5 dB

Link Budget Check:

LoRaWAN 915 MHz: - Tx power: +20 dBm - Rx sensitivity: -137 dBm (SF9) - Link budget: 20 - (-137) = 157 dB - Path loss: 96.7 dB - Margin: 157 - 96.7 = 60.3 dB ✓ Excellent margin

Zigbee 2.4 GHz: - Tx power: +10 dBm - Rx sensitivity: -100 dBm - Link budget: 10 - (-100) = 110 dB - Path loss: 115.5 dB - Margin: 110 - 115.5 = -5.5 dB Link FAILS (needs mesh with 13+ hops)

BLE 5.0 Long Range: - Tx power: +8 dBm - Rx sensitivity: -103 dBm (long range mode) - Link budget: 8 - (-103) = 111 dB - Path loss: 115.5 dB - Margin: 111 - 115.5 = -4.5 dB Link barely fails (unreliable)

4. Total Cost Analysis (10 Years):

Option A: Wi-Fi 5 GHz - Modules: 200 × $5 = $1,000 - Access points: 255 × $150 = $38,250 - Power/backhaul: 255 × $500 = $127,500 - Battery replacements: 200 × 20 × $10 = $40,000 - Installation: 500 hours × $50 = $25,000 - Total: $231,750 Completely infeasible

Option B: Zigbee 2.4 GHz Mesh - Modules: 200 × $3 = $600 - Gateway: 1 × $200 = $200 - Battery replacements: 200 × 5 × $10 = $10,000 - Installation: 50 hours × $50 = $2,500 - Total: $13,300

Option C: BLE 5.0 Long Range - Modules: 200 × $4 = $800 - Gateways: 8 × $300 = $2,400 - Battery replacements: 200 × 2 × $10 = $4,000 - Installation: 60 hours × $50 = $3,000 - Total: $10,200

Option D: LoRaWAN 915 MHz - Modules: 200 × $8 = $1,600 - Gateway: 1 × $800 = $800 - Battery replacements: $0 (10-year battery life) - Installation: 40 hours × $50 = $2,000 - Total: $4,400 ✓ Lowest cost

5. Technology Ranking Matrix:

Criterion Wi-Fi 5G Zigbee 2.4G BLE 5.0 LoRaWAN 915M
Battery Life (10yr) Fail Fail Marginal Exceeds
Coverage (infra) 255 APs 13 hops 8 gateways 1 gateway
Link Budget 30 dB -5.5 dB -4.5 dB 60 dB
Total Cost (10yr) $232K $13K $10K $4.4K
Reliability Complex Multi-hop Borderline Robust
Environmental Poor Fair Fair Excellent

Weighted Scores (1-10 scale): - Wi-Fi: (1 + 1 + 4 + 1 + 3 + 2) / 6 = 2.0/10 - Zigbee: (2 + 4 + 2 + 5 + 5 + 5) / 6 = 3.8/10 - BLE: (4 + 5 + 3 + 7 + 6 + 6) / 6 = 5.2/10 - LoRaWAN: (10 + 10 + 10 + 10 + 9 + 10) / 6 = 9.8/10 ✓

Clear Winner: LoRaWAN 915 MHz

Final Recommendation: Deploy LoRaWAN with Single Gateway

Rationale: 1. Only technology meeting 10-year battery life (1.9 Wh vs 18 Wh available) 2. 60 dB link budget margin handles crop attenuation, weather, seasonal variation 3. Lowest total cost ($4,400 vs $10K-$232K alternatives) 4. Simplest infrastructure (1 gateway vs 8-255) 5. Purpose-built for agricultural IoT (weather-resistant, low maintenance)

Deployment Design: - 1 LoRaWAN gateway at farmhouse (elevated 5m on pole) - 200 sensor nodes using SF9 (balanced range/power) - Class A operation (sensor-initiated, lowest power) - Confirmed uplinks for critical alerts (low battery, anomalies) - Adaptive data rate for sensors closer to gateway (saves power)

Key Engineering Insight: The frequency band choice determines success or failure in agricultural IoT. The 8.8 dB lower path loss at 915 MHz vs 2.4 GHz, combined with 10-15 dB better crop penetration, creates a 19-24 dB advantage. This translates to either 8-16× greater range OR 600-1000× lower power consumption. For a 10-year battery requirement, sub-GHz is not just better - it’s the only viable option.

Real-World Validation: Major agricultural IoT providers (John Deere, CNH Industrial, AgriData) standardize on sub-GHz (LoRaWAN, Sigfox, NB-IoT) precisely because: - 2.4 GHz fails through crop canopy (15+ dB loss in mature corn) - Battery replacement in 200 field sensors is economically prohibitive - Mesh networks create maintenance complexity (failed nodes break routes)

When to Consider Alternatives: - BLE 5.0: Small farms (<50 acres) with sensors near buildings - Zigbee mesh: Greenhouses with power access and short distances - Wi-Fi: Never for battery-powered field sensors (use only for powered equipment) - Cellular (NB-IoT): When LoRaWAN gateway deployment is impossible AND budget allows $3-5/sensor/year

Verification Questions: 1. If crops cause 25 dB attenuation at 2.4 GHz, what’s the maximum reliable range for Zigbee mesh (each hop needs 10 dB margin)? 2. Calculate break-even: At what subscription cost does NB-IoT match LoRaWAN TCO? (Hint: LoRaWAN is $4.4K, NB-IoT adds $X/sensor/year) 3. If sensors send 50 readings/day instead of 10, does LoRaWAN still achieve 10-year battery life? (Recalculate energy budget)

810.8 Summary

This quiz covered complex multi-technology deployment decisions:

  1. Smart City Parking: LoRaWAN provides 46% cost savings over NB-IoT with full infrastructure control
  2. Wi-Fi Channel Selection: Always use non-overlapping channels (1, 6, 11); select the least congested
  3. Multipath Propagation: Indoor RF can match free-space predictions due to constructive interference
  4. Agricultural IoT: Sub-GHz (LoRaWAN) is the only viable option for 10-year battery life in crop environments

Key Takeaways:

  • Total cost of ownership analysis must include maintenance, battery replacements, and operational costs
  • Weighted decision matrices help quantify technology trade-offs objectively
  • Risk assessment should consider vendor lock-in, pricing changes, and technology obsolescence
  • Sub-GHz frequencies provide 19-24 dB advantage over 2.4 GHz in agricultural environments

810.9 What’s Next

Congratulations on completing the Mobile Wireless Technologies assessment series! You now have a comprehensive understanding of wireless fundamentals for IoT.

Protocol Deep Dives: - Wi-Fi Fundamentals and Standards - 802.11 WLAN complete coverage - Bluetooth Fundamentals and Architecture - BLE and Classic Bluetooth - Zigbee Fundamentals and Architecture - Mesh networking at 2.4 GHz - LoRaWAN Overview - Sub-GHz LPWAN - Cellular IoT Fundamentals - LTE-M, NB-IoT, 5G IoT

Advanced Topics: - Mobile Wireless Fundamentals - Link budget deep dive - Mobile Wireless Labs and Implementation - Advanced RF measurements - Mobile Wireless Comprehensive Review - Complete review

Learning Hubs: - Simulations Hub - Interactive RF tools - Videos Hub - Wireless technology tutorials - Quiz Navigator - More self-assessment quizzes