This chapter explores the technical foundations of Sigfox, including Ultra-Narrow Band (UNB) modulation, radio parameters, network architecture, and how Sigfox compares with other LPWAN technologies from a technical perspective.
By the end of this chapter, you will be able to:
Sigfox uses ultra-narrowband radio to send tiny messages over long distances with extreme power efficiency. A Sigfox message is only 12 bytes – enough for a temperature reading or a door-open alert, but not a photo. This radical simplicity means devices can run on a coin cell battery for up to 10 years.
“Let us dig into how Sigfox really works!” Sammy the Sensor said. “The UNB modulation uses 100 Hz channels at 100 bits per second. That is incredibly slow compared to Wi-Fi, but it means my signal can travel 30 to 50 kilometers and penetrate deep inside buildings. For a sensor that only sends 12 bytes, slow speed is not a problem!”
“The software-defined approach is brilliant,” Lila the LED added. “In LoRaWAN, the gateway does some processing. In Sigfox, the base stations are as simple as possible – all the intelligence is in the cloud. This keeps infrastructure costs low and lets Sigfox update its network algorithms without touching any hardware.”
Max the Microcontroller said, “The architecture comparison with LoRaWAN is interesting. LoRaWAN gives you control – you own and operate your gateways. Sigfox gives you convenience – they own and operate everything. For a startup deploying 100 sensors, Sigfox’s zero-infrastructure approach can save months of setup time.”
“The cost crossover point matters,” Bella the Battery noted. “At small scale, Sigfox is cheaper because you avoid gateway costs. At large scale with thousands of devices in one area, LoRaWAN can be cheaper because you pay for gateways once instead of per-device subscriptions forever. Run the numbers for your specific deployment!”
Sigfox is a French company founded in 2009 with a vision to connect billions of IoT devices using a dedicated low-power wide-area network. Rather than selling equipment for customers to build their own networks, Sigfox operates as a network service provider—similar to how cellular carriers operate.
Key philosophy:
Table: Sigfox Technology Summary
| Property | Details |
|---|---|
| Name | Sigfox |
| Standard protocol is based on | Ultra Narrow Band (UNB) ISM radio band |
| Designed for | Uses Ultra Narrow Band (UNB) to transmit information between low power devices operating at 868 MHz frequency band, that divides the spectrum into 400 of 100 Hz channels |
| Connection range | 30-50 km for rural areas, and 3-10 km for urban areas |
| Data rate | 100bps, with a limit of 140 messages per day for each end device |
Sigfox uses Ultra Narrow Band (UNB) modulation, which is fundamentally different from spread spectrum techniques used by LoRa or frequency hopping used by Bluetooth.
UNB Characteristics:
This Gantt chart shows Sigfox’s transmission pattern: each message is sent 3 times on different frequencies over ~6 seconds, providing redundancy through time and frequency diversity.
Comparison with other modulation schemes:
| Technology | Bandwidth | Data Rate | Sensitivity |
|---|---|---|---|
| Sigfox (UNB) | 100 Hz | 100 bps | -142 dBm |
| LoRa (CSS) | 125-500 kHz | 250-5,470 bps | -148 dBm |
| FSK (Cellular) | 200 kHz | 1-100 kbps | -110 dBm |
| Wi-Fi (OFDM) | 20-40 MHz | 1-600 Mbps | -90 dBm |
Sigfox’s 100 Hz channel width is 1,250 times narrower than LoRa (125 kHz) and 200,000 times narrower than Wi-Fi (20 MHz). This extreme design choice has profound consequences that shape every aspect of the technology.
Narrower bandwidth concentrates power into a smaller frequency slice. Think of it like a garden hose: the same water pressure through a narrow nozzle produces a focused jet that reaches farther. A Sigfox device transmitting at +14 dBm (25 mW) into a 100 Hz channel has a power spectral density of -6 dBm/Hz. A LoRa device at the same +14 dBm spread across 125 kHz has a power spectral density of -37 dBm/Hz. That 31 dB difference in power concentration is why Sigfox base stations can decode signals at -142 dBm – far below the noise floor – using long integration times (2 seconds per message at 100 bps).
The trade-off is stark: range for data. Shannon’s theorem (C = B x log2(1 + SNR)) says channel capacity is proportional to bandwidth. At 100 Hz bandwidth with a practical SNR of 20 dB (typical for Sigfox’s operating conditions), the maximum theoretical data rate is about 665 bps (C = 100 x log2(1 + 100) = 665). Sigfox’s practical 100 bps uses just 15% of this theoretical maximum, leaving substantial margin for real-world impairments like fading and interference. This means a 12-byte payload takes 960 ms to transmit – nearly a full second for data that would take 0.05 ms on Wi-Fi.
Let’s calculate the power spectral density advantage and link budget that make Sigfox’s ultra-narrow band approach viable for IoT.
Power Spectral Density (PSD) Comparison:
For Sigfox transmitting at \(P_{TX} = +14\) dBm (25 mW) across \(BW = 100\) Hz:
\[\text{PSD}_{Sigfox} = P_{TX} - 10\log_{10}(BW) = 14 - 10\log_{10}(100) = 14 - 20 = -6 \text{ dBm/Hz}\]
For LoRa at same +14 dBm across 125 kHz:
\[\text{PSD}_{LoRa} = 14 - 10\log_{10}(125{,}000) = 14 - 51 = -37 \text{ dBm/Hz}\]
PSD Advantage: Sigfox has \(-6 - (-37) = 31\) dB higher power concentration per Hz!
Link Budget for 30 km Rural Deployment:
Using Friis equation with path loss:
\[L_{path} = 20\log_{10}(d) + 20\log_{10}(f) + 32.45\]
For \(d = 30\) km at \(f = 868\) MHz:
\[L_{path} = 20\log_{10}(30) + 20\log_{10}(868) + 32.45 = 29.5 + 59.0 + 32.45 = 121 \text{ dB}\]
Adding obstacle/foliage loss (+14 dB rural):
\[L_{total} = 121 + 14 = 135 \text{ dB}\]
Received power at base station:
\[P_{RX} = P_{TX} + G_{TX} - L_{total} + G_{RX}\] \[P_{RX} = 14 + (-2) - 135 + 10 = -113 \text{ dBm}\]
Sigfox base station sensitivity: \(-142\) dBm
\[\text{Link Margin} = P_{RX} - \text{Sensitivity} = -113 - (-142) = +29 \text{ dB}\]
This 29 dB margin accommodates: - Fading (10-15 dB) - Indoor penetration loss (10-20 dB) - Antenna misalignment (3-5 dB)
Result: 30 km range is achievable with sufficient margin for real-world conditions.
The 100 Hz width also explains the 140 message/day limit. In Europe (EU868), the duty cycle regulation is 1% – a device can transmit for at most 36 seconds per hour. Each Sigfox message (including 3 replicas) takes about 6 seconds of airtime. That gives 6 transmissions per hour x 24 hours = 144, rounded down to 140 for safety margin. This is not a Sigfox business decision to limit usage – it is a direct consequence of physics, regulation, and the triple-transmission redundancy scheme.
Frequency accuracy is the engineering challenge. A 100 Hz channel requires the transmitter’s frequency to be stable within +/-50 Hz. At 868 MHz, this is a relative accuracy of 0.06 ppm – far tighter than typical crystal oscillators (10-20 ppm). Sigfox solves this by having the base station, not the device, perform wideband scanning. The device transmits at an approximately correct frequency, and the base station’s SDR (software-defined radio) receiver scans the full 192 kHz band to find each 100 Hz signal. This pushes complexity (and cost) to the infrastructure side, keeping devices simple and cheap ($2-5 for the radio chip).
The technical specifications of Sigfox’s radio system define its unique operational characteristics and constraints:
Key Constraints to Remember:
Understanding the fundamental differences between Sigfox and LoRaWAN helps in making informed technology choices:
Decision Framework: When to Choose Each Technology
Choose Sigfox when:
Choose LoRaWAN when:
Crossover Point: Around 1,000-2,000 devices, LoRaWAN’s infrastructure cost becomes competitive with Sigfox’s cumulative subscription fees.
Use Sigfox when:
Use LoRaWAN when:
Use NB-IoT when:
| Criterion | Sigfox | LoRaWAN | NB-IoT |
|---|---|---|---|
| Range | 10-50 km rural, 3-10 km urban | 2-15 km rural, 1-5 km urban | 1-10 km (cellular coverage) |
| Payload | 12 bytes up, 8 bytes down | Up to 242 bytes | Up to 1600 bytes |
| Messages | 140 up/4 down per day | Unlimited (duty cycle limited) | Unlimited |
| Battery Life | 10-20 years | 5-15 years | 2-10 years |
| Device Cost | $5-15 | $10-25 | $15-30 |
| Connectivity | $1-2/device/year | $0 (own infrastructure) or $1-5/year (TTN) | $6-24/device/year |
| Infrastructure | $0 (operator-provided) | $200-1,500 per gateway | $0 (carrier-provided) |
| Coverage | 75+ countries, operator-dependent | Self-deployed or community (TTN) | 190+ countries (cellular) |
| Deployment | Easiest (plug-and-play) | Moderate (gateway setup) | Easy (SIM card) |
| Latency | 2-90 seconds | 1-5 seconds | 1-10 seconds |
100 DEVICES (5 years):
━━━━━━━━━━━━━━━━━━━━━━
Sigfox: $1,500 devices + $500 subscription = $2,000 ✓ CHEAPEST
LoRaWAN: $2,000 devices + $500 gateway + $0 subscription = $2,500
NB-IoT: $2,000 devices + $12,000 subscription = $14,000
1,000 DEVICES (5 years):
━━━━━━━━━━━━━━━━━━━━━━━━
Sigfox: $12,000 devices + $5,000 subscription = $17,000 ✓ WINNER
LoRaWAN: $20,000 devices + $5,000 gateways + $0 subscription = $25,000
NB-IoT: $25,000 devices + $120,000 subscription = $145,000
10,000 DEVICES (5 years):
━━━━━━━━━━━━━━━━━━━━━━━━━
Sigfox: $120,000 devices + $50,000 subscription = $170,000
LoRaWAN: $200,000 devices + $50,000 gateways + $0 subscription = $250,000 ✓ STARTS TO WIN
NB-IoT: $250,000 devices + $1,200,000 subscription = $1,450,000
50,000+ DEVICES: LoRaWAN becomes most economical (infrastructure amortized)Key Insight: Sigfox wins for small-to-medium deployments (<5,000 devices). LoRaWAN becomes cheaper at scale due to zero per-device fees. NB-IoT is premium option for specific use cases only.
Ultra-Narrow Band (UNB) Modulation Explained:
Sigfox uses DBPSK (Differential Binary Phase Shift Keying) for uplink and GFSK (Gaussian Frequency Shift Keying) for downlink, both squeezed into extremely narrow 100 Hz channels.
Why 100 Hz Channels?
Bandwidth vs Range Trade-off:
━━━━━━━━━━━━━━━━━━━━━━━━━━
Wide channel (Wi-Fi 20 MHz): High data rate, short range, high power
Medium channel (LoRa 125 kHz): Moderate data, long range, low power
Narrow channel (Sigfox 100 Hz): Tiny data, extreme range, minimal power
Shannon-Hartley Theorem: C = B × log₂(1 + SNR)
- Sigfox reduces bandwidth (B) dramatically
- Compensates by improving SNR through long transmission time
- Result: Same information, much lower power densityTechnical Specifications:
| Parameter | Uplink (DBPSK) | Downlink (GFSK) |
|---|---|---|
| Modulation | Differential BPSK | Gaussian FSK |
| Bandwidth | 100 Hz | 600 Hz |
| Data Rate | 100 bps | 600 bps |
| TX Power | 14-27 dBm (25-500 mW) | N/A (base station) |
| RX Sensitivity | -126 dBm typical, -142 dBm best | -142 dBm |
| Transmission Time | ~6 seconds per message | ~4 seconds |
| Frequency Hop | Random per message | Fixed during RX window |
Link Budget Calculation:
Sigfox Link Budget (Uplink):
━━━━━━━━━━━━━━━━━━━━━━━━━━━
TX Power: +14 dBm (device)
Antenna Gain (device): -2 dBi (PCB antenna)
Path Loss (10 km): -125 dB (free space + obstacles)
Antenna Gain (BS): +10 dBi (base station tower)
━━━━━━━━━━━━━━━━━━━━━━━━━━━
Received Signal: -103 dBm
RX Sensitivity: -126 dBm (typical)
Link Margin: 23 dB ✓ (good margin)
With 30 km range:
Path Loss: -135 dB
Received Signal: -113 dBm
Link Margin: 13 dB ✓ (still works)Why This Matters: The extreme sensitivity (-142 dBm) enables Sigfox to work in very challenging RF environments - underground pipes, inside metal containers, dense urban areas.
Three-Tier Architecture:
Spatial Diversity (Redundant Reception):
Sigfox base stations operate in “always listening” mode. When a device transmits, multiple base stations typically receive the same message, improving reliability:
Message Reception Example:
━━━━━━━━━━━━━━━━━━━━━━━━━━
Device sends 1 message
BS #1: RSSI -98 dBm, SNR 12 dB → ✓ Received
BS #2: RSSI -115 dBm, SNR 3 dB → ✓ Received
BS #3: RSSI -130 dBm, SNR -5 dB → ✗ Missed
Sigfox Cloud:
• Receives message from BS #1 and BS #2
• Deduplicates (keeps strongest signal)
• Uses triangulation for geolocation
• Result: 99%+ reliability even if one BS failsGeolocation Without GPS:
Sigfox can estimate device location using signal strength from multiple base stations:
RSSI-Based Geolocation:
━━━━━━━━━━━━━━━━━━━━━━
BS #1 (-98 dBm): Device ~5 km away
BS #2 (-110 dBm): Device ~15 km away
BS #3 (-105 dBm): Device ~10 km away
Triangulation Algorithm:
→ Calculates most likely position
→ Accuracy: 1-10 km (rural) to 100-500 m (urban)
→ No GPS needed (saves device cost + power)Use Cases: Asset tracking without GPS modules, emergency location for lone workers, wildlife monitoring.
Sigfox Atlas is a cloud-based service that provides device geolocation without requiring GPS hardware.
How It Works:
Accuracy Comparison:
| Environment | Atlas Accuracy | GPS Accuracy | Power/Cost Difference |
|---|---|---|---|
| Open rural | 1-5 km | 5-10 m | Atlas: 0 mW, $0 |
| Suburban | 500 m - 2 km | 5-10 m | GPS: +50 mW, +$5-15 |
| Dense urban | 100-500 m | 5-30 m | GPS battery: 2× drain |
| Indoor | Not available | Not available | Both fail indoors |
When to Use Atlas vs GPS:
This decision matrix provides an alternative comparison framework to help select between Sigfox and LoRaWAN based on deployment requirements:
Master Sigfox technical concepts through these progressive scenarios:
Example 1: Link Budget Calculation (Beginner) Calculate if a Sigfox device 15 km from a base station in suburban environment will connect:
Transmit Power: +14 dBm (25 mW, typical device)
Antenna Gain (device): -2 dBi (PCB trace antenna loss)
Path Loss (15 km suburban): -130 dB (from Hata model)
Antenna Gain (base station): +8 dBi (tower-mounted directional)
Received Signal: +14 - 2 - 130 + 8 = -110 dBm
Base Station Sensitivity: -126 dBm (typical)
Link Margin: -110 - (-126) = +16 dB ✓ Good!
Conclusion: Connection reliable with 16 dB margin (enough for fading)Example 2: UNB Capacity Analysis (Intermediate) How many devices can transmit simultaneously in a single Sigfox base station coverage area?
Available spectrum: 192 kHz (Europe 863-870 MHz ISM band)
Channel width: 100 Hz per transmission
Guard bands: 20 Hz between channels
Effective channels: 192,000 ÷ 120 = 1,600 channels
Triple transmission (3× redundancy on different frequencies):
Concurrent devices: 1,600 ÷ 3 ≈ 533 devices simultaneously
Message duration: 6 seconds (3 replicas × 2 sec each)
Base station hourly capacity: 533 × (3,600 sec ÷ 6 sec) = 319,800 messages/hour
Daily capacity: 7.67 million messages across all devices
Lesson: Sigfox scales through massive channel parallelism, not high data ratesExample 3: Cost Crossover Calculation (Advanced) At what deployment scale does LoRaWAN become cheaper than Sigfox?
Assumptions:
- Sigfox: $12/device + $6/year subscription
- LoRaWAN: $15/device + $500/gateway (covers 100 devices)
- Timeframe: 5 years
TCO equations:
Sigfox(N) = 12N + 6N×5 = 42N
LoRaWAN(N) = 15N + 500×(N/100) = 15N + 5N = 20N
Crossover point:
42N = 20N
22N = infrastructure difference
At N = 1,000: Sigfox = $42K, LoRaWAN = $20K + $5K gateways = $25K
At N = 2,000: Sigfox = $84K, LoRaWAN = $40K + $10K = $50K
Conclusion: LoRaWAN wins at >1,500 devices in one geographic area## Try It Yourself
Challenge: Design a Sigfox Payload for Multi-Sensor Deployment
You’re deploying 500 environmental sensors in a smart city. Each sensor must report: temperature (-40°C to +85°C), humidity (0-100%), air quality index (0-500), battery level (0-100%), and a status byte with 5 boolean flags (motion detected, tamper alert, low battery, calibration needed, sensor fault).
Your Task:
What to Observe:
Extension: Modify the design to add GPS coordinates (latitude/longitude). What trade-offs must you make to fit within 12 bytes?
Sigfox UNB Transmission: From Device to Cloud
When a Sigfox device sends a 12-byte message, the following sequence occurs over approximately 6 seconds:
Step 1: Frequency Selection (Device)
Step 2: Triple Transmission (Device)
Step 3: Spatial Diversity Reception (Base Stations)
Step 4: Cloud Processing (Sigfox Backend)
Step 5: Application Integration
Key Insight: The device has zero confirmation that the message was received. This fire-and-forget approach keeps device firmware ultra-simple (no ACK handling, no retransmission logic) but requires the network to provide reliability through redundancy (3 transmissions) and spatial diversity (multiple base stations).
| Core Concept | Builds On | Leads To | Contrasts With | Prerequisites |
|---|---|---|---|---|
| Ultra-Narrow Band (UNB) | Shannon-Hartley theorem, ISM band regulations | Extreme range (30-50 km), -142 dBm sensitivity | LoRa spread spectrum (125 kHz), Wi-Fi OFDM (20 MHz) | Basic RF modulation, frequency bands |
| DBPSK/GFSK Modulation | Phase-shift keying, frequency-shift keying | 100 bps uplink, 600 bps downlink data rates | LoRa chirp spread spectrum, NB-IoT OFDMA | Modulation fundamentals, duty cycle |
| Operator-Managed Model | Cellular network architecture | Zero infrastructure cost, global roaming | LoRaWAN user-deployable gateways | Network topologies, star topology |
| Sigfox Atlas | RSSI triangulation, propagation models | 1-10 km geolocation without GPS | GPS-based tracking (5-10 m accuracy) | Signal strength, path loss |
| Cost Crossover Analysis | TCO calculation, subscription vs. infrastructure | Sigfox optimal <5K devices, LoRaWAN >10K devices | NB-IoT carrier pricing ($6-24/year) | LPWAN economics, deployment scale |
This chapter covered the technical foundations of Sigfox:
Sigfox uses BPSK/DBPSK modulation on 100 Hz channels while LoRaWAN uses Chirp Spread Spectrum. Both achieve long range but through different mechanisms: Sigfox through ultra-narrowband filtering, LoRa through spread spectrum processing gain. Understanding the modulation difference explains their different interference characteristics.
Sigfox sends each message 3 times but uses very low data rates and short transmission windows. The 3x redundancy has a modest energy impact compared to the dominant sleep current for typical IoT reporting rates. Calculate actual energy budget rather than assuming 3x penalty.
Sigfox operates in the same ISM bands as LoRaWAN but uses different modulation and channel width. In regions with high LoRaWAN density, wideband LoRa transmissions overlap Sigfox’s 100 Hz channels and can cause interference despite different technologies.
Sigfox requires 3 base station receptions for reliable delivery (diversity combining). Single base station coverage is insufficient for production deployments. Verify that target locations have reception from at least 2–3 base stations before finalizing deployment plans.
| Chapter | Focus Area |
|---|---|
| Sigfox Introduction and Basics | Core concepts, business model, and positioning in the LPWAN landscape |
| Sigfox Scenarios and Common Mistakes | Real-world failure scenarios and deployment pitfalls to avoid |
| Sigfox Examples and Assessment | Worked examples, payload design exercises, and knowledge checks |
| LoRaWAN Architecture | User-deployable alternative with private network capability |
| NB-IoT Fundamentals | Cellular LPWAN alternative with higher data rates and global roaming |