---
tags:
  - radio
  - LoRa
---

# LoRa radio

LoRa (which stands for "long range") is a proprietary method of radio
communication.

It operates within the unlicenced ISM (Industrial, Scientific and Medical)
bands. In Europe, the center frequency within the ISM for LoRa is 868MHz.

It uses a specialised and characteristic technique to avoid interference in
communication: **chirp-spread-spectrum modulation**. With this technique, radios
"chirp", meaning they sweep over a range of frequencies over time. This is
similar to a voice getting higher in pitch.

This technique gives LoRa several beneficial properties.

We know that in general, radio signals get weaker with distance. The weaker they
become, the more susceptable they are to background noise. When a signal falls
below the noise floor it is lost.

Noise is noise, because it is random, without uniformity. A chirping signal
however, has a clear pattern - it rises through both the frequency and time
domain (it traverses different frequencies over a duration of time). This rising
pattern can be explicitly filtered for which makes it detectable even amidst
noise. This means even though a signal may be weak and far away, it can still be
detected because of it's sweeping pattern, thus making LoRa long range.

Moreover, a higher spreading rate results in a longer range of transmission and
reception.

Thus the key properties of LoRa are:

- The signal is long range, travelling from 2-15km in urban areas and up to 50Km
  in rural areas

- Receivers can pick up very weak signals

- There is good resistance to noise interference since the receiver is trained
  to look for a pattern amidst the noise. Also, if there is interference at one
  frequency this is discounted once the data moves to the next frequency in the
  sweep.

There are some trade-offs though.

- A higher spreading rate results in a longer range but slower data transfer
  since each bit takes longer to transmit because it is spread accross more
  chirps.

- A lower spreading rate results in faster data transfer (increased bandwidth)
  but reduced range
