Noise threshold for forming a network

The ZigBee PRO stack provides a mechanism for forming a new network in the quietest IEEE802.15.4 radio channel. The Coordinator (centralized network) or Router (distributed network) that forms the network performs a channel scan to listen for activity from other local networks.

During the channel scan, the activity in each channel is assigned a noise level in the range 0 to 254. This result is compared with a noise level threshold, which is defined by the NIB value u8VsFormEdThreshold (which is part of the structure ZPS_tsNwkNibInitialValues). If the measured noise level for a channel is above this threshold, the channel is excluded from further consideration. Therefore, if all the channels in the scan are noisier than the threshold allows, no network is formed.

The stack then re-scans the channels that passed the noise threshold test (if any) and selects the one with the lowest beacon count in which to form the network.

Note:

  • This assessment takes into account IEEE802.15.4 beacons only and no activity from networks based on other systems, such as Wi-Fi.

  • The assessment is based on beacons only and does not consider the noise levels of the shortlisted channels.

Default Behavior

To avoid the situation in which no network is formed, the default value of u8VsFormEdThresholdis 0xFF, which is a special value and not a noise threshold. In this case, the network is always formed in the channel with the lowest IEEE802.15.4 beacon activity (no noise level assessment is performed).

Parent topic:Noise threshold for forming a network

Customizing the scan

You can implement network formation based on the noise level threshold, as described above, by setting u8VsFormEdThresholdto an appropriate value in the range 0 to 254. In the following code fragment, a noise level threshold of 100 is set:

ZPS_psNwkNibGetHandle(ZPS_pvAplZdoGetNwkHandle())->u8VsFormEdThreshold = 100

Thus, in the above case, all channels with a noise level above 100 will be rejected.

If no suitable channel is found and no network formed, the application can dynamically increase the value of u8VsFormEdThresholdand initiate another scan.

Parent topic:Noise threshold for forming a network

Parent topic:Appendix B: Application design notes