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Spreading Factor & ADR

What Are LoRa Spreading Factors?​

Imagine you're trying to talk to someone across a wide, open field.

  • If you shout quickly (short, fast messages), your voice may not travel as far—but you can share more in less time.
  • If you speak slowly and clearly (drawing out each word), your voice carries farther—but it takes longer to say the same thing.

This is exactly how Spreading Factors (SF) work in LoRa communication.

Understanding Spreading Factors​

In LoRa, the spreading factor controls how fast data (also called “chirps”) is sent:

Choosing the right spreading factor is a balance between range, power efficiency, and data speed—just like choosing how loudly or slowly to speak depending on how far away your listener is.

Spreading FactorDescriptionData RateRange
SF7 (Lower SF)Talking fast – sends more data quickly but covers shorter distances 🐇 HighShort
SF12 (Higher SF)Speaking slowly – data travels farther but takes more time 🐢LowLong

The Influence of Spreading Factors in LoRa​

LoRa technology uses Spreading Factors (SF) ranging from SF7 to SF12, which determine how data is transmitted over long distances. These spreading factors influence several critical aspects of LoRa communication and play a key role in optimizing network performance based on your application needs.

Data Rate​

Using a lower spreading factor like SF7 allows devices to send more information quickly, increasing the data rate but reducing the communication range.

  • Example: At SF7 and 125 kHz bandwidth, the bit rate is 5.5 kbit/s. Increasing the bandwidth to 500 kHz boosts it to 21.9 kbit/s.
  • Analogy: It's like using a wider pipe to send water faster—higher bandwidth sends more data in less time, but range drops.

Distance​

Higher spreading factors, like SF12, allow signals to travel longer distances but at slower speeds.

  • Analogy: It's like speaking slowly and clearly across a canyon—your voice travels farther, but it takes more time to deliver the message.

Time-on-Air​

A higher spreading factor means the message takes longer to transmit, which increases time-on-air.

  • Longer time-on-air consumes more energy, affecting battery life.
  • You can use tools like The Things Network’s LoRaWAN airtime calculator to estimate airtime based on SF, payload size, and bandwidth.

Receiver Sensitivity​

Higher spreading factors improve receiver sensitivity, enabling the device to pick up weaker signals from far away.

  • Example: At SF12, sensitivity can reach -137 dBm, which is excellent for long-range applications.
  • Analogy: Like hearing a slow, loud shout from a distance.

Battery Life​

Using a higher spreading factor drains the battery faster because the radio stays on longer.

  • Tip: For battery-powered sensors, choosing the right SF is essential to balance longevity and performance.

Why It Matters​

Spreading factors allow LoRaWAN networks to balance data speed, range, and power consumption, ensuring reliable communication across urban, rural, and remote environments. Selecting the correct SF is crucial for IoT deployments like smart agriculture, asset tracking, and environmental monitoring.

How Adaptive Data Rate (ADR) Works in LoRaWAN​

Adaptive Data Rate (ADR) is a key feature of LoRaWAN that helps optimize network performance by automatically adjusting a device’s communication settings for better efficiency.

Key Parameters Managed by ADR​

ADR intelligently manages the following transmission parameters:

  • Spreading Factor (SF):
    Determines how “loud” your message is and how far it can travel. A higher SF increases range but reduces data rate.

  • Bandwidth:
    Think of this as the size of the road your message travels on — wider bandwidth allows more data to flow faster.

  • Transmission Power:
    Refers to the signal strength. Higher power means the signal can reach farther, but it consumes more battery.

The Balancing Act of ADR​

ADR dynamically adjusts settings based on the device’s distance from the gateway:

  • Close to Gateway:
    The device can communicate quickly using lower spreading factor and higher data rate, saving energy.

  • Far from Gateway:
    It will use higher spreading factor and transmission power to ensure reliable communication over long distances.

When to Enable ADR​

ADR is best used when radio frequency (RF) conditions are stable, making it ideal for:

  • Static devices like parking sensors
  • Environmental monitors placed in fixed locations

ADR & Mobile Devices​

Mobile LoRaWAN devices can benefit too:

  • If a device detects that it has remained stationary for a period, it can enable ADR to conserve energy while maintaining optimal performance.

Scheduling ADR Requests in LoRaWAN​

Adaptive Data Rate (ADR) in LoRaWAN is not a one-time setup — it involves continuous monitoring and scheduling. Here's how ADR requests are managed over time:

Initial ADR Request​

  • Triggered right after a device joins the network.
  • Helps initiate the communication configuration.
  • This initial setup may not be accurate due to limited signal measurements, so some flexibility is applied during early transmissions.

Regular ADR Requests​

  • Once the network collects enough signal and quality data, it schedules periodic ADR requests.
  • These requests are typically attached to uplink messages, minimizing overhead.

Trigger-Based Requests​

  • ADR requests are also sent when:
    • A device is stuck at the lowest data rate (DR0).
    • The device hasn’t received any downlink messages for a while.
  • These help ensure the device adjusts to changing network conditions.

Refusal to Adjust​

  • If a device repeatedly ignores ADR requests, it may signal:
    • A misconfiguration on the device
    • Incompatibility with the LoRaWAN Network Server
    • Or firmware limitations preventing ADR compliance

By managing ADR requests intelligently, LoRaWAN networks can ensure that devices maintain optimal performance, coverage, and battery life — even in changing environments.

RSSI (Received Signal Strength Indicator)​

Think of RSSI as how loud someone sounds at a noisy party.

  • A strong signal (closer to 0 dBm) is like someone shouting — easy to hear.
  • A weak signal (very negative dBm, e.g., -120 dBm) is like someone whispering from across the room — hard to understand.

In LoRaWAN:

  • RSSI measures signal strength between a transmitter (end device) and a receiver (gateway).
  • It’s affected by:
    • Distance (path loss)
    • Antenna gain (how strong the device can “speak”)
    • Obstacles (walls, cables, connectors)

Higher RSSI = better signal clarity, but it's only part of the story.

SNR (Signal-to-Noise Ratio)​

Now imagine trying to talk in a noisy room. SNR measures how well your voice stands out from the background noise.

📐 Formula:​

SNR (dB) = P_received_signal (dBm) - P_noise (dBm)