Meshtastic
What is meshtastic?¶
Meshtastic is a decentralized wireless off-grid mesh networking LoRa protocol. The main goal of the project is enabling low-power, long-range communication over unlicensed radio bands.
What are unlicensed radio bands?¶
Unlicensed radio bands are portions of the radio spectrum that can be used by anyone without needing a specific license from a regulatory authority. These bands encourage innovation and are commonly used for technologies like Wi-Fi, Bluetooth but also Microwave and Citizens Band (27MC), but they can also experience interference due to multiple users sharing the same frequencies.
What is LoRa (Long Range)¶
LoRa is a wireless modulation technique derived from Chirp Spread Spectrum (CSS) technology. It encodes information on radio waves using chirp pulses - similar to the way dolphins and bats communicate! LoRa modulated transmission is robust against disturbances and can be received across great distances.
Don’t be alarmed about the complex terms; LoRa modulation and Chirp Spread Spectrum technology are simple to understand in practice. In case you are curious, in this video, Richard Wenner explains how Chirp Spread Spectrum technology works: https://youtu.be/dxYY097QNs0
Advantages of LoRa¶
- Excellent long-range functionality: LoRa is exceptional for long-range communications, allowing data to pass through structures, and cover significant areas with minimal infrastructure.
- Energy efficiency: LoRa benefits from low power usage, which extends battery life for IoT devices. This feature is crucial for devices deployed in remote or hard-to-access locations where frequent battery replacements are impractical.
- Cost efficiency: LoRa generally operates within unlicensed frequency bands, reducing the costs associated with spectrum licensing and maintaining a network.
- Flexibility: LoRa can be leveraged in various point-to-point, mesh, and point-to- multipoint configurations, making it suitable for various communication needs.
Disadvantages of LoRa¶
- Data rate limitations: LoRa can have a lower data rate than some other wireless technologies. This limitation can be a drawback for applications requiring high-bandwidth data transmission.
- Network management: By itself, LoRa doesn’t include network management, routing, or device coordination features. It only handles the physical layer of communications.
- Interference: Operating in unlicensed bands can mean LoRa networks occasionally suffer from interference from other devices using the same spectrum.
meshtastic¶
Meshtastic® is a project that enables you to use inexpensive LoRa radios as a long range off-grid communication platform in areas without existing or reliable communications infrastructure. This project is 100% community driven and open source!
So what is meshtastic:¶
Meshtastic® is a project that enables you to use inexpensive LoRa radios as a long range off-grid communication platform in areas without existing or reliable communications infrastructure. This project is 100% community driven and open source!
Features:¶
- Long range (331km record by MartinR7 & alleg)
- (No) phone required for mesh communication
- Decentralized communication - no dedicated router required
- Encrypted communication - AES256-CTR
- Excellent battery life
- Send and receive text messages between members of the mesh
- Optional GPS based location features
- And more!
How it works¶
When you send a message on your Meshtastic companion app, it is relayed to the radio using Bluetooth, Wi-Fi/Ethernet or serial connection. That message is then broadcasted bythe radio. If it hasn’t received a confirmation from any other device after a certain timeout, it will retransmit the message up to three times.
When a receiving radio captures a packet, it checks to see if it has heard that message before. If it has it ignores the message. If it hasn’t heard the message, it will rebroadcast it. For each message a radio rebroadcasts, it marks the “hop limit” down by one. When a radio receives a packet with a hop limit of zero, it will not rebroadcast the message. The radio will store a small amount of packets (around 30) in its memory for when it’s not connected to a client app. If it’s full, it will replace the oldest packets with newly incoming text messages only.
Europe Frequency Bands¶
EU countries will generally be covered by the Radio Equipment Directive (2014/53/EU) and subsequent amendments, which is then enacted in local laws. Useful information on this is located here. The bands below were selected based on the maximum power and the duty cycle available. It may be possible to use other frequency bands for specific applications, but these are not currently supported “out of the box”.
433 MHz¶
The maximum power allowed for Europe is +10 dBm ERP (Effective Radiated Power). The band range is from 433 to 434 MHz.
There are four frequency slots defined with the standard radio preset LongFast . After factory reset the radio will be set to frequency slot 4 with a center frequency of 433.875 MHz.
868 MHz¶
The maximum power allowed for Europe is +27 dBm ERP (Effective Radiated Power). The band range is from 869.40 to 869.65 MHz. This is less than the 863–870 MHz range defined as SRD (Short Range Devices) Band, but allows for a higher ERP and a duty cycle of 10%.
There is one frequency slot defined with the standard radio preset LongFast . After factory reset the radio will be set to frequency slot 1 with a center frequency of 869.525 MHz. It is worth noting that 868 MHz is generally the most popular frequency band for Meshtastic in Europe.
Data Rates¶
Considerations¶
- Various data-rate options are available when configuring a frequency slot and are inversely proportional to the theoretical range of the devices.
- Spreading Factor (SF) - How much we “spread” our data over time.
- Each step up in Spreading Factor doubles the airtime to transmit.
- Each step up in Spreading Factor adds about 2.5db extra link budget.
- Bandwidth - How big of a slice of the spectrum we use.
- Each doubling of the bandwidth is almost 3db less link budget.
- Bandwidths less than 31 may be unstable unless you have a high quality Crystal Oscillator.
- Coding Rate - How much redundancy we encode to resist noise.
- Increasing coding rate increases reliability while decreasing data-rate.
4/5 - 1.25x overhead¶
4/6 - 1.5x overhead¶
4/7 - 1.75x overhead¶
4/8 - 2x overhead¶
Presets¶
We have eight LoRa radio presets. These are the most common settings and have been proven to work well:
| Channel setting | Alt Channel Name | Data-Rate | SF/Symbols | Coding Rate | Bandwidth | Link Budget |
|---|---|---|---|---|---|---|
| Short Range Turbo | Short Turbo | 21.88kbps | 7/128 | 4/5 | 500 kHz | 140dB |
| Short Range | Short | 10.94kbps | 7/128 | 4/5 | 250 kHz | 143dB |
| Short Range | Short | 6.25kbps | 8/256 | 4/5 | 250 kHz | 145.5dB |
| Medium Range | Medium | 3.52kbps | 9/512 | 4/5 | 250 kHz | 148dB |
| Medium Range | Medium | 1.95kbps | 10/1024 | 4/5 | 250 kHz | 150.5dB |
| Long Range | Long | 1.07kbps | 11/2048 | 4/5 | 250 kHz | 153dB |
| Long Range | Long | 0.34kbps | 11/2048 | 4/6 | 125 kHz | 156dB |
| Long Range | Long | 0.18kbps | 12/4096 | 4/6 | 125 kHz | 158.5dB |
| Very Long Range | Very Long | 0.09kbps | 12/4096 | 4/7 | 62.5 kHz | 161.5dB |
Note
The link budget used by these calculations assumes a transmit power of 22dBm and an antenna with 0dB gain. Adjust your link budget assumptions based on your actual devices. Data-rate in this table is the theoretical max but doesn’t account for packet headers, hops and re-transmissions. Calculations based on data from the official Semtech LoRa calculator.
MQTT Server¶
The Meshtastic project provides a public MQTT service that users can connect to, with certain restrictions in place to ensure network stability. This service allows Meshtastic devices to bridge over the internet, providing global connectivity for remote networks. For instructions on connecting to the public MQTT server, please refer to Connect to the Default Public Server.