LoRa & LPWAN
Long-range, low-power wide-area networks — LoRa, Sigfox, NB-IoT, and LoRaWAN enable IoT sensors to communicate across cities and farmland on coin-cell
What is LPWAN?
Low-Power Wide-Area Networks (LPWAN) are a class of wireless technologies designed for IoT applications that need to send small amounts of data over long distances while consuming minimal power. A typical LPWAN sensor can operate on a coin-cell battery for 5–10 years, communicating over distances of 2–15 kmin urban areas and up to 50+ km in rural line-of-sight conditions.
LPWAN fills the gap between short-range protocols (Bluetooth, Zigbee, Wi-Fi) and cellular networks. Where Wi-Fi covers ~50 m and cellular covers a city but drains batteries in hours, LPWAN covers kilometers on microwatts. This makes it ideal for smart agriculture, asset tracking, environmental monitoring, smart meters, and building automation.
LoRa: Chirp Spread Spectrum
LoRa (Long Range) is a proprietary modulation technique developed by Cycleo (France) and acquired by Semtech in 2009. It uses chirp spread spectrum (CSS) modulation — the same family as chirp radar and some military communications. A chirp is a signal whose frequency sweeps linearly across a bandwidth over time. LoRa encodes data by varying the starting phase and direction (up-chirp vs. down-chirp) of these frequency sweeps.
LoRa operates in unlicensed ISM bands: 868 MHz (Europe),915 MHz (North America), 433 MHz (Asia), and2.4 GHz (global). Key parameters:
- Bandwidth: 125 kHz, 250 kHz, or 500 kHz
- Spreading Factor (SF): 7–12 (higher SF = longer range, lower data rate)
- Coding Rate: 4/5 to 4/8 (forward error correction)
- Data Rate: 0.3–50 kbps (SF12 to SF7 at 125/250/500 kHz BW)
- Sensitivity: down to −148 dBm (SF12, 125 kHz BW)
- Link Budget: up to 157 dB (highest of any commercial LPWAN)
The spreading factor determines how many chirps per second are transmitted. At SF12, each symbol spans 4096 chirps over ~4096/125 kHz ≈ 32.8 ms, providing extreme processing gain at the cost of throughput. At SF7, each symbol is ~128 chirps over ~1.024 ms, offering faster data rates but shorter range.
LoRaWAN: The MAC Layer
LoRaWAN is the open MAC layer protocol built on top of LoRa modulation. Developed by the LoRa Alliance (founded 2012 by Semtech, Actility, IBM, and Microchip), it defines the network architecture, device classes, security, and data formats.
LoRaWAN uses a star-of-stars topology: end devices communicate with gateways, which forward data to a network server, which routes it to an application server. Gateways are simple packet forwarders — they receive LoRa packets on multiple channels simultaneously and forward them over IP (Ethernet, cellular, or satellite) to the network server.
Device Classes
- Class A (Alliance): Bi-directional with receive windows. Device transmits, then opens two short receive windows (RX1 at 1s, RX2 at 2s after TX). Lowest power — device sleeps between transmissions. Best for battery-powered sensors.
- Class B (Beacon): Scheduled receive windows. Gateway sends beacons; device opens receive windows at predictable intervals. Lower latency than Class A, higher power consumption.
- Class C (Continuous): Always listening (except when transmitting). Lowest latency, highest power — suitable for mains-powered devices like streetlights.
Sigfox: Ultra-Narrowband
Sigfox (founded 2009, France) takes a different approach to LPWAN. Instead of spread spectrum, Sigfox uses ultra-narrowband (UNB) modulation — each transmission occupies a 100 Hz channel within the ISM band. By concentrating all energy into such a narrow bandwidth, Sigfox achieves excellent sensitivity with very low transmit power.
Sigfox transmits at up to +14 dBm (25 mW) with data rates of100 bps (uplink) and 600 bps (downlink). Messages are limited to 12 bytes uplink (4 messages/day) and 8 bytes downlink (1 message/day). Sigfox operates a network-as-a-servicemodel — device manufacturers pay per device per year, and Sigfox operates the base stations. Coverage exists in 72+ countries.
NB-IoT: Cellular LPWAN
Narrowband IoT (NB-IoT) is a 3GPP standard (Release 13, 2016) that repurposes a single 180 kHz LTE resource block for IoT communication. Unlike LoRa and Sigfox, NB-IoT operates in licensed spectrum, using existing cellular base stations and infrastructure. Three deployment modes:
- In-band: Uses LTE resource blocks within the carrier bandwidth
- Guard-band: Uses the guard band between LTE carriers
- Standalone: Uses re-farmed GSM spectrum (200 kHz channels)
NB-IoT achieves a link budget of ~164 dB, enabling coverage in basements, underground parking, and deep indoor locations where LoRa struggles. It supportsQoS, authentication (SIM-based), and handover — features absent from unlicensed LPWAN. Power-saving modes (PSM and eDRX) enable multi-year battery life. NB-IoT is deployed by major carriers worldwide, particularly in China (China Mobile, China Unicom, China Telecom).
LPWAN Comparison
| Feature | LoRa | Sigfox | NB-IoT |
|---|---|---|---|
| Modulation | CSS (chirp spread spectrum) | UNB (ultra-narrowband) | SC-FDMA (licensed LTE) |
| Bandwidth | 125–500 kHz | 100 Hz | 180 kHz |
| Max Range (urban) | 2–5 km | 3–10 km | 1–10 km |
| Uplink Data Rate | 0.3–50 kbps | 100 bps | ~20 kbps |
| Max Payload | 242 bytes | 12 bytes | 1600 bytes |
| Spectrum | Unlicensed ISM | Unlicensed ISM | Licensed cellular |
| QoS | No (best-effort) | No (best-effort) | Yes (SIM-based) |
Other LPWAN Technologies
- Zigbee (IEEE 802.15.4): Short-range (10–100 m), mesh networking, 250 kbps at 2.4 GHz. Used in smart home (Matter) and building automation.
- Wi-SUN: Field area networks for smart grid, mesh topology, 50–300 kbps. Used by utilities for smart meter rollouts.
- Weightless: Open standard LPWAN (Weightless-N, -P, -W), never achieved significant deployment.
- Mioty: ETSI TS 103 357 — telegram splitting protocol, designed for massive IoT deployments.