LoRaWAN Reference

Class A is the default, lowest-power mode: the device transmits an uplink, then opens two short receive windows (RX1 after 1 second, RX2 after 2 seconds). Downlinks can only be sent during these windows. Class B adds beacon-synchronized scheduled receive slots (ping slots), allowing the server to send downlinks at predictable times -- useful for actuator control. Class C keeps the receive window open whenever not transmitting, giving the lowest downlink latency but highest power consumption -- suitable for mains-powered devices like streetlights.

OTAA (Over-The-Air Activation) is the recommended method. The device uses DevEUI (unique device ID), AppEUI/JoinEUI (application ID), and AppKey (root key) to perform a JoinRequest/JoinAccept handshake with the network server, which dynamically derives session keys (NwkSKey, AppSKey) and assigns a DevAddr. ABP (Activation By Personalization) pre-provisions DevAddr, NwkSKey, and AppSKey directly on the device, skipping the join procedure. ABP is simpler but less secure because keys never rotate, and frame counter resets after power loss can cause packet rejection.

LoRaWAN uses license-free ISM bands that vary by region: EU868 (868 MHz, Europe), US915 (915 MHz, North America), KR920 (920 MHz, South Korea), AS923 (923 MHz, Asia-Pacific), and AU915 (915 MHz, Australia). Each region has specific channel plans, data rate ranges, TX power limits, and duty cycle regulations. For example, KR920 uses channels at 922.1, 922.3, and 922.5 MHz with data rates from DR0 (SF12/125kHz, 250 bps) to DR5 (SF7/125kHz, 5470 bps).

Spreading Factor (SF) ranges from SF7 to SF12. Lower SF (SF7) gives faster transmission, shorter range, and lower power consumption. Higher SF (SF12) gives slower transmission, longer range, and higher power consumption. Each SF increase roughly doubles the airtime and range. SF12 achieves receiver sensitivity of -137 dBm, enabling multi-kilometer range, while SF7 achieves -123 dBm for shorter distances but 5470 bps throughput. ADR (Adaptive Data Rate) automatically selects the optimal SF based on link quality.

LoRaWAN uses two session keys: NwkSKey (Network Session Key) for MAC command encryption and MIC (Message Integrity Code) calculation, and AppSKey (Application Session Key) for payload encryption. Encryption uses AES-128 in CTR mode: the device generates A_i blocks from direction, DevAddr, frame counter, and block number, then encrypts them with AppSKey to produce an S_i keystream XORed with the plaintext. MIC is a 4-byte AES-128 CMAC calculated with NwkSKey. Frame counters (FCntUp, FCntDown) prevent replay attacks.

ADR (Adaptive Data Rate) is a mechanism where the network server automatically adjusts the device's spreading factor (SF) and TX power based on received signal quality. When ADR is enabled, the server analyzes uplink SNR/RSSI over multiple packets, then sends a LinkADRReq MAC command to change the data rate and TX power. This optimizes both battery life (by using the lowest necessary SF and TX power) and network capacity (by reducing airtime). ADR should be enabled for stationary devices but disabled for mobile ones.

A LoRaWAN gateway consists of: 1) A concentrator chip (Semtech SX1301 or SX1302) that can simultaneously receive on 8+ channels with different spreading factors. 2) GPS module for Class B beacon timing synchronization. 3) Backhaul connection (Ethernet, 4G/LTE, or Wi-Fi) to forward packets to the network server. 4) Packet forwarder software -- either the legacy Semtech UDP Packet Forwarder (PUSH_DATA, PULL_RESP, TX_ACK messages) or the newer WebSocket-based BasicStation protocol. The network server (e.g., ChirpStack, TTN) handles device authentication, deduplication, ADR, and application routing.

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