Listen Before Talk Feature (LBT)

1. Introduction

Dragino Gateways are able to support the Listen Before Talk (LBT) feature when used with the LA66 USB LoRaWAN Adapter. LBT is a channel access mechanism that allows the gateway to detect whether the LoRa channel is occupied before initiating a downlink transmission, thereby reducing signal collisions and improving the reliability of data delivery in congested environments.

The following products support the LBT feature:

Model	LBT Enable Method
LPS8N,DLOS8N,LG308N	Requires firmware upgrade to LBT version
LPS8v2	Enable via configuration file only

For LPS8v2 users: The LBT feature can be enabled simply by adding a few lines of configuration to the /usr/local/dragino/generate-config.sh script. No firmware upgrade is needed. Please refer to section 2.4 Configuration LBT for LPS8v2 for detailed instructions. For other models (e.g., LPS8N,DLOS8N,LG308N), please upgrade to the LBT firmware version first:

• Firmware version: LBT--build-v5.4.1658454438

LA66 LBT firmware: USB LoRaWAN Adapter LBT

2. How to use

Connect the LA66 module to the USB port on the side of the gateway.

2.1 Configuration LBT for (LPS8N,DLOS8N,LG308N)

Upgrade the gateway firmware to the LBT version for specific device Firmware download. This LBT version firmware support LBT by default, users just need to plug in the LA66 USB LoRaWAN Adapter.

2.2 Debug

Apply and save on the web after the above configure has been made

Run logread -f in Linux to check the LBT running status.

If LA66 module returned the value FREE, indicating that can be downlinked normally.

If LA66 module returned the value BUSY, indicates that the downlink can be disturbed.

Received signals greater than -85dBm return BUSY, less than return FREE

2.3 Trouble Shootings

2.3.1 How to debug if LBT does not work

Make sure that the gateway is connected to the LA66 module, Can check by command or via the Web UI.

Access LA66 module log will show CP210X Converter Now Attached to ttyUSBX

LPS8 Requires firmware upgrade to LBT version

2.4 Configuration LBT for LPS8v2

For LPS8v2 models, the LBT feature is supported without firmware upgrade. It is enabled by adding configuration entries to the /usr/local/dragino/generate-config.sh script.

Hardware setup: Connect the LA66 USB LoRaWAN Adapter to the USB port on the gateway.

Configuration to add (the exact location inside the script is typically within the gateway configuration function):

json_add_boolean "lbt_enable" 1
json_add_boolean "lbt_isftdi" 1
json_add_boolean "lbt_tty_enabled" 1
json_add_string "lbt_tty_path" "/dev/ttyUSB0"
json_add_int "lbt_tty_baude" "9600"
json_add_int "lbt_rssi_target" "-70"
json_add_int "lbt_scan_time_ms" "6"

After adding these lines, apply the configuration via the Web UI: go to LoRa-->LoRa, select any frequency band, and click Save&&Applay. Then reboot the gateway for the changes to take effect.

If it is necessary to check the LBT log, the log_mask parameter needs to be modified to debug mode

json_add_string "log_mask" "111111"

Verification: After reboot, run journalctl -u draginofwd -f and check the LBT status:

• FREE – channel clear, downlink allowed.
• BUSY – channel occupied (RSSI > -85 dBm typically triggers BUSY).

Parameter reference:

Parameter	Type	Value	Description
lbt_enable	boolean	1	Enable LBT
lbt_isftdi	boolean	1	FTDI interface mode
lbt_tty_enabled	boolean	1	Enable TTY serial
lbt_tty_path	string	/dev/ttyUSB0	Serial device path
lbt_tty_baude	integer	9600	Baud rate
lbt_rssi_target	integer	-70	RSSI threshold (dBm)
lbt_scan_time_ms	integer	6	Scan time (ms)

Troubleshooting if LBT does not work:

• Verify the LA66 module is detected: dmesg | grep tty should show CP210X Converter Now Attached to ttyUSBX.
• Ensure lbt_tty_path matches the actual device (e.g., /dev/ttyUSB0, /dev/ttyUSB1).
• Confirm the seven lines were added correctly and the Web UI save was performed.
• Check logs with journalctl -u draginofwd -f for any LBT-related errors during startup or downlink attempts.