Listen Before Talk

The Listen Before Talk (LBT) protocol makes it possible for multiple users to share the same channel. When LBT is enabled, the device continuously monitors channels so as to transmit only when a channel is not in use.



Listen Before Talk Configuration

DOT Series devices automatically enable or disable Listen Before Talk depending on the regional requirements. The configuration can be set up through the global_conf.json file.

Command Definition
lbt_config LBT config collection name
enable false Disable LBT
enable true Enable LBT
rssi_target RSSI reading below which TX will be allowed
chan_config Set of channels to enforce LBT. Only channels in this list can be used for TX when LBT is enabled.
freq_hz Center frequency to track for LBT
scan_time_us Time in microseconds to track RSSI before TX (only values of 128 or 5000 are supported)
sx127x_rssi_offset Calibration value to apply to RSSI reading from the radio front end 


Following is a sample configuration for LBT enabled in AS923 plan.
Only frequencies above 915 MHz are supported by the v33 FPGA firmware.

"lbt_cfg": {
     "rssi_target":-80,/dBm */
     "chan_cfg":[/* channels maximum*

Updating MTAC FPGA firmware

MTAC-LORA-H-* or MTAC-LORA-HL-* hardware is needed to support LBT
Also v33 FPGA firware will need to be loaded on the card.

Check the currently loaded version when card is not being used
# mts-fpga-loader -i

To install the v33 FPGA image on Accessory Port 1
# mts-fpga-loader -i /usr/lib/mts-flash-binaries/mtcdt-fpga-v33.hex -p1

To install the v31 FPGA image on Accessory Port 1
# mts-fpga-loader -i /usr/lib/mts-flash-binaries/mtcdt-fpga-v31.hex -p1