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Changing LBT (Listen-Before-Talk) threshold in a PPW network

Some applications could benefit  from changing or disabling the LBT (Listen-before-talk). LBT is included in the PPW protocol to ensure that PPW does not jam other 2.4 GHz networks. It is also used in the decision-making regarding which RF-channels to use more frequently than others. The following is a short description on how LBT operates:


Prior to every master packet transmission the master spends a short time in RX on the channel to be used. It measures the energy on this channel, and if a interferer is currently using this frequency, the measured energy will be higher than “normal”, or at least higher than the threshold we have default set in the protocol (which is -65 dBm). In this case the master will refrain from sending its packet. If the energy is above the threshold in the next timeslot as well (the next time master will attempt to send a packet) the master will send the packet no matter what. In the situations where energy is above the threshold the PPW master will mark the channel as an interferer channel and try to avoid using it as much.

In some applications the PurePath Wireless network should have priority over other 2.4GHz devices and the LBT threshold can be disabled or altered. To change the LBT you have to open the master’s device configuration file (.ppwcfg) in a text editor. Search for “Normal LBT threshold” and find the following section:

<name>Normal LBT threshold</name>
<value>-65</value>

Change the value to the desirable setting. A threshold of 20 dBm (remember to remove the minus sign) is in practice the same as disabling the LBT altogether. Save the file and re-open the configurator (which will load the new and modified .ppwcfg file). Go to the flash programming panel and flash the master again.

Disabling or changing the LBT for a PPW network can give some reduction in throughput for other close-by 2.4GHz wireless networks like WiFi or Bluetooth. 

Regards, 
PPW team