1. LoRa: What It Is and What It Isn't
What It Is
LoRa (Long Range) is a proprietary physical-layer radio frequency modulation technology based on Chirp Spread Spectrum (CSS). In the United States (ITU Region 2), it operates within the unlicensed 902–928 MHz ISM (Industrial, Scientific, and Medical) band under FCC Part 15 regulations.
LoRa transmits tiny packets of data across vast geographic distances with extreme energy efficiency by spreading narrowband signals across a wider RF bandwidth. This spread-spectrum technique enables receivers to demodulate and decode signals even when the received signal power drops significantly below the local thermal noise floor (down to -20 dB SNR).
Unlike conventional narrowband FM or FSK, LoRa does not require the signal to be stronger than background atmospheric and thermal noise. It correlates chirps across time, pulling readable data out of pure static.
What It Isn't
- Not Wi-Fi or Cellular: LoRa cannot stream video, carry high-fidelity voice, load standard web pages, or transfer megabyte-sized files.
- Not an Internet Replacement: Throughput ranges from 0.3 kbps to 22 kbps. It is an ultra-low-bandwidth physical layer engineered specifically for short text payloads, telemetry packets, sensor beacons, and geographic coordinates.
How It Works: Chirp Spread Spectrum & Spreading Factors
CSS encodes digital bits into continuously rising and falling frequency sweeps ("chirps"). By selecting a Spreading Factor (SF)—ranging from SF7 to SF12—the radio trades raw bit-rate throughput for receiver sensitivity and link budget:
| Spreading Factor | Raw Bitrate | Time on Air (20B) | Receiver Sensitivity | Ideal Operating Condition |
|---|---|---|---|---|
| SF7 | ~5.47 kbps | ~41 ms | -123 dBm | High density, urban line-of-sight |
| SF8 | ~3.12 kbps | ~72 ms | -126 dBm | Balanced mobile mesh |
| SF9 | ~1.76 kbps | ~144 ms | -129 dBm | Regional coverage |
| SF10 | ~0.98 kbps | ~288 ms | -132 dBm | Suburban ridge links |
| SF11 | ~0.54 kbps | ~575 ms | -134 dBm | Extreme mountain-to-valley (LongFast) |
| SF12 | ~0.29 kbps | ~1,150 ms | -137 dBm | Maximum penetration, high latency |
2. Meshtastic: What It Is and What It Isn't
What It Is
Meshtastic is an open-source, decentralized, off-grid Mobile Ad-Hoc Network (MANET) protocol built on top of LoRa packet radios. It transforms individual LoRa transceivers into nodes of a self-healing, peer-to-peer mesh network.
Any packet transmitted by an originating node can be repeated and forwarded across intermediate relay nodes until it reaches its intended destination or exhausts its hop counter. Meshtastic operates with:
- Zero cellular towers
- Zero satellite uplinks
- Zero centralized internet infrastructure
What It Isn't
- Not a Full-Duplex Chat Room: Because all nodes in a geographic region share the same simplex 915 MHz frequency channel, only one radio can transmit at any given instant. High transmission volume leads to packet collisions and network congestion.
- Not a Guaranteed Delivery Protocol (No TCP Handshakes): Broadcast packets are sent over the air without end-to-end receipt confirmations. Delivery relies on spatial diversity and probability.
How It Works: Managed Flood Routing
Meshtastic implements a managed flood routing algorithm designed to minimize channel congestion while maximizing packet reach:
- Packet Identification: Every packet includes a unique 32-bit packet hash. When a node hears a packet, it checks its local circular cache. If the packet has already been heard, it is dropped immediately.
- Hop Counter: If the packet is new and
hop_limit > 0, the node decrements the counter by 1. - Randomized Backoff: To prevent multiple relay nodes from keying their transmitters simultaneously and jamming the channel, each node calculates a randomized Contention Window backoff delay before rebroadcasting.
- Channel Utilization Awareness: If a node hears another node rebroadcast the same packet during its backoff window, it cancels its own retransmission to save airtime.