55 lines
2 KiB
Markdown
55 lines
2 KiB
Markdown
---
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tags:
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- radio
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- LoRa
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---
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# LoRa radio
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LoRa (which stands for "long range") is a proprietary method of radio
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communication.
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It operates within the unlicenced ISM (Industrial, Scientific and Medical)
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bands. In Europe, the center frequency within the ISM for LoRa is 868MHz.
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It uses a specialised and characteristic technique to avoid interference in
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communication: **chirp-spread-spectrum modulation**. With this technique, radios
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"chirp", meaning they sweep over a range of frequencies over time. This is
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similar to a voice getting higher in pitch.
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This technique gives LoRa several beneficial properties.
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We know that in general, radio signals get weaker with distance. The weaker they
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become, the more susceptable they are to background noise. When a signal falls
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below the noise floor it is lost.
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Noise is noise, because it is random, without uniformity. A chirping signal
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however, has a clear pattern - it rises through both the frequency and time
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domain (it traverses different frequencies over a duration of time). This rising
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pattern can be explicitly filtered for which makes it detectable even amidst
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noise. This means even though a signal may be weak and far away, it can still be
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detected because of it's sweeping pattern, thus making LoRa long range.
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Moreover, a higher spreading rate results in a longer range of transmission and
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reception.
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Thus the key properties of LoRa are:
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- The signal is long range, travelling from 2-15km in urban areas and up to 50Km
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in rural areas
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- Receivers can pick up very weak signals
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- There is good resistance to noise interference since the receiver is trained
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to look for a pattern amidst the noise. Also, if there is interference at one
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frequency this is discounted once the data moves to the next frequency in the
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sweep.
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There are some trade-offs though.
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- A higher spreading rate results in a longer range but slower data transfer
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since each bit takes longer to transmit because it is spread accross more
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chirps.
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- A lower spreading rate results in faster data transfer (increased bandwidth)
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but reduced range
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