Link to this headingLORA

  • Long Range of up to 13.6 miles, 1300km
  • Uses 902-928 MHz in US
  • Uses 863-870 MHz in Europe
  • Uses 433 MHz in Asia
  • Between 0.3 kbps to 5.5 kbps.

LoRa: Physical Layer
LoRaWAN: MAC, Network, and app built on LoRa.

Source

Building a private LoRa network
GNU Radio implementation of a LoRa transceiver

Link to this headingRF

Uses Modulation in the form of Chirp Spread Spectrum. This means that the frequency will either grow or decrease at a constant rate with a wrap around.
- Upchirp is for increasing frequency
- Downchirp is for decreasing frequency

Resilient against multi-path and Doppler effects. This is also used in radar.

Link to this headingDemodulation

  • 2.25 Downchirps seems to be the Start of Frame Delimiter (SFD)
  • Then the data is encoded using modulation using Frequency modulation

Bandwidth: The Spectrum occupied by the chirp.
- uses 125 kHz, 250 kHz, or 500 kHz
Spreading Factor: Number of bits encoded in each state
- Uses 7-12 bits per symbol
Chirp Rate: The rate at which it changes in frequency because of the chirp
- is bandwidth/(2^spreadingFactor)

Link to this headingDechirping

When adding and upchirp and downchirp together you get a constant frequency if there is no data.
When there is data using a FFT with the number of bins for the spreading factor allows the highest bin to be the correct state.

Link to this headingFinding the Preamble

After dechirping you have two signals the upchirped and downchirped. Finding the constant bin for some time in the upchirp. then finding the same for the downchirp.

Link to this headingEncoding

  • Adds Error tolerance
  • Induces randomness
  • Scrambles bits with in the frame
  • Adds correcting parity bits

Whitening:

  • XOR pseudo random sequence

  • Make it better for synchronization

  • Interleaves the first 2 bits

Link to this headingPacket structure

Implicit mode: knows the length of the data being transmitted and does not include the header
Explicit mode: has a header that has information about the length of the packet.

There are different whitening on each of the modes

  • First 8 symbols
    • Spreading factor is two less then the actual packet spreading factor.
    • Code rate is 4/8

Link to this headingLORAWan

Internet protocols over LORA

Link to this headingMeshtastic

An open source, off-grid, decentralized, mesh network built to run on affordable, low-power devices

Meshtastic Website

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