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": {
"enable":tru,
"rssi_target":-80,/dBm */
"chan_cfg":[/* channels maximum*
{freq_hz":923000000,"scan_time_us":5000},
{freq_hz":923200000,"scan_time_us":5000},
{freq_hz":923400000,"scan_time_us":5000},
{freq_hz":923800000,"scan_time_us":5000},
{freq_hz":924000000,"scan_time_us":5000},
{freq_hz":924200000,"scan_time_us":5000},
{freq_hz":924400000,"scan_time_us":5000},
{freq_hz":924600000,"scan_time_us":5000}
],
"sx127x_rssi_offset":-165/*dB*/
},
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