This is an excerpt.
Read the full technical analysis:
https://www.vladavramut.com/articles/lora-spreading-factors-throughput.html
LoRa spreading factors (SFs) are often treated as magical settings that trade range for speed. But the real behavior of SFs in deployed networks is a function of physics, airtime limits, collision domains, and regulatory duty cycles — not just a knob you turn for “better range.”
Understanding SFs means understanding how LoRa modulation actually interacts with shared spectrum.
What Spreading Factors Actually Do
Each LoRa spreading factor increases:
• symbol duration
• processing gain
• airtime per packet
Higher SF values improve sensitivity — which can increase link margins — but they also inflate airtime dramatically.
This has three real consequences:
1) Longer on-air transmission time
2) Higher collision probability
3) Stricter duty-cycle impact
These physical effects dominate real throughput behavior, especially in mesh and multi-hop networks.
Airtime: The Real Cost of Higher SFs
A common misconception is that higher spreading factors boost throughput because they improve reception. In reality, they do:
• increase packet duration
• increase duty cycle occupation
• reduce usable channel capacity
• escalate collision domains
For a simple comparison:
- SF7 might occupy the channel for tens of milliseconds per packet
- SF12 can occupy the channel for multiple seconds per packet
This difference isn’t a tweak — it is a scaling effect that collapses usable capacity once traffic increases.
Collision Domains in Shared Spectrum
LoRa modulation uses a shared medium.
When one node transmits:
• everyone else on that channel cannot
• airtime reservation blocks other packets
• collision risk rises with high SF usage
In simple star networks, this is tolerable. In multi-hop meshes, it becomes a design constraint.
High SFs turn a low-traffic link into a throughput choke point, not a performance improvement.
Regulatory & Duty-Cycle Constraints
Across most jurisdictions, LoRa channels are limited by duty-cycle regulations.
In Europe (ETSI):
• duty limits restrict how long a radio can occupy a channel
• higher SF transmissions consume a disproportionate share
In the US (FCC):
• different constraints still bind cumulative airtime
• overlapping channels complicate spectrum occupancy
Designing for real networks means planning SF usage within these limits — not assuming free-range operation.
Continue reading the full technical analysis:
https://www.vladavramut.com/articles/lora-spreading-factors-throughput.html
Top comments (0)