Wireless Standards and Protocols IoT and LPWAN Informational

What are the RF requirements for a LoRa device and how does the spreading factor affect range?

Q: Can different spreading factors coexist?

Yes. LoRa SFs are orthogonal: a receiver tuned to SF7 will not demodulate an SF12 signal, and vice versa. This means: a single gateway can receive multiple devices transmitting simultaneously on different SFs on the same channel. This is equivalent to a form of code-division multiple access (CDMA). A typical LoRaWAN gateway listens on 8 channels, each supporting SF7-SF12 simultaneously = up to 48 virtual channels.

Q: What limits LoRa range in practice?

In rural LOS: 10-15 km is routine (confirmed by many real-world deployments). In urban environments: 1-5 km due to building shadowing, multipath, and interference. In dense urban (city center): 500 m-2 km. In basements/underground: 100-500 m (severe penetration loss). The limiting factor is rarely the link budget (which is extreme at 161 dB) but rather the obstruction and multipath losses that can exceed 50 dB in dense environments.

What are the RF requirements for a LoRa device and how does the spreading factor affect range? LoRa is a proprietary spread-spectrum modulation using chirp spread spectrum (CSS) that enables communication over 2-15 km with power suitable for battery-operated IoT: (1) LoRa modulation: modulation type: CSS (Chirp Spread Spectrum), where the carrier frequency sweeps linearly across the bandwidth. Data is encoded in the timing of the chirp start frequency. Spreading factors (SF): SF7 to SF12. Higher SF = longer chirps, more spreading gain, longer range, but lower data rate. Bandwidth: 125 kHz, 250 kHz, or 500 kHz (most common: 125 kHz). (2) How spreading factor affects range: each increase in SF doubles the chirp duration, adding approximately 2.5 dB of processing gain: SF7: data rate 5.5 kbps, sensitivity -123 dBm. SF8: 3.1 kbps, -126 dBm. SF9: 1.8 kbps, -129 dBm. SF10: 980 bps, -132 dBm. SF11: 440 bps, -134.5 dBm. SF12: 250 bps, -137 dBm. From SF7 to SF12: sensitivity improves by 14 dB, which corresponds to approximately 4× the range (assuming free-space propagation). Trade-off: SF12 is 22× slower than SF7 (250 vs 5500 bps), and the airtime is 22× longer (impacts duty cycle compliance and battery life). (3) RF transceiver requirements: transceiver IC: Semtech SX1261/SX1262 (the standard LoRa chip). Output power: +22 dBm (SX1262 with integrated PA). Receiver sensitivity: -137 dBm at SF12, 125 kHz BW. Current consumption: TX at +14 dBm: 45 mA. TX at +22 dBm: 118 mA. RX: 4.6 mA. Sleep: 160 nA. Frequency bands: 868 MHz (Europe), 915 MHz (US), 433 MHz (Asia). (4) Link budget: TX power +22 dBm, antenna gain +2 dBi: EIRP = +24 dBm. RX sensitivity at SF12: -137 dBm. Link budget = 24 - (-137) = 161 dB. At 868 MHz: free-space path loss at 10 km = 111 dB. Margin: 161 - 111 = 50 dB (allows for building penetration, foliage, and fading). This extreme link budget enables LoRa communication over 10-15 km in rural areas. (5) Antenna: quarter-wave monopole at 868 MHz: 86 mm. For compact devices: helical (30-50 mm) or chip antenna (lower efficiency).

Category: Wireless Standards and Protocols

Updated: April 2026

Product Tie-In: IoT Modules, Filters, Antennas

LoRa RF and Spreading Factor

LoRa achieves its remarkable range by trading data rate for sensitivity, using chirp spread spectrum to demodulate signals well below the noise floor.

Below-the-Noise-Floor Reception

(1) At SF12 with 125 kHz bandwidth: thermal noise = -174 + 10 log(125000) = -123 dBm. With NF = 6 dB: noise floor = -117 dBm. Sensitivity = -137 dBm, which is 20 dB below the noise floor (SNR = -20 dB). This is possible because the chirp spreading provides approximately 20 dB of processing gain. Similar to GPS, which also operates below the noise floor. (2) The practical trade-off: SF12 at 250 bps: a 20-byte packet takes approximately 1.5 seconds to transmit. In Europe (868 MHz): 1% duty cycle limits one 1.5-second TX every 150 seconds. For applications sending one reading every 15 minutes: SF12 is acceptable. For more frequent reporting: use SF7-SF9 and deploy the gateway closer.

LoRa Spreading Factor Impact

SF7: 5.5 kbps, -123 dBm sensitivity
SF12: 250 bps, -137 dBm sensitivity
SF12 link budget: 161 dB (+22 dBm TX)
Range: 2‑5 km urban, 10‑15 km rural
SF7→SF12: +14 dB sensitivity, ÷22 data rate

Common Questions

Frequently Asked Questions

How do I choose the right spreading factor?

LoRaWAN ADR (Adaptive Data Rate) automatically selects the SF: devices close to the gateway use SF7 (fast, minimum airtime). Devices far from the gateway use SF12 (slow, maximum range). If you are designing a private LoRa network (not LoRaWAN): start with SF10 as a good balance. Test the actual link quality and adjust SF up (for range) or down (for throughput). Rule of thumb: use the lowest SF that gives reliable communication (< 5% packet loss).

Can different spreading factors coexist?

Yes. LoRa SFs are orthogonal: a receiver tuned to SF7 will not demodulate an SF12 signal, and vice versa. This means: a single gateway can receive multiple devices transmitting simultaneously on different SFs on the same channel. This is equivalent to a form of code-division multiple access (CDMA). A typical LoRaWAN gateway listens on 8 channels, each supporting SF7-SF12 simultaneously = up to 48 virtual channels.

What limits LoRa range in practice?

In rural LOS: 10-15 km is routine (confirmed by many real-world deployments). In urban environments: 1-5 km due to building shadowing, multipath, and interference. In dense urban (city center): 500 m-2 km. In basements/underground: 100-500 m (severe penetration loss). The limiting factor is rarely the link budget (which is extreme at 161 dB) but rather the obstruction and multipath losses that can exceed 50 dB in dense environments.

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