What should the ED threshold be?

[jinpeng1989]

Is the CCA threshold exactly the same as the ED threshold? If so, then I have a question.

Suppose the LinkMargin of the two routers is 21 dB, the noise floor is set to the receive sensitivity -100 dBm, the RSSI is -79 dBm.
Since -79 is less than -75, it did not reach the ED threshold. Then, when router A is sending data, router B might determine that the channel is in an idle state, which implies that the transmissions of the two routers might cause a conflict.

[jinpeng1989]

The ED threshold for some products is -60 dBm. That is to say, the device will have transmission conflicts with neighboring devices whose RSSI is lower than -60dBm.

[abtink]

Is the capture effect you mentioned a widely applied technology? Does this technology have a specific name? I want to check whether the Thread chip we are using supports this technology.

It is not a technology; it is a physical phenomenon in RF signal demodulation. See https://en.wikipedia.org/wiki/Capture_effect.

[jwhui]

IEEE 802.15.4-2020 Section 12.3.4 specifies the receiver sensitivity for the O-QPSK PHY:

A compliant device shall be capable of achieving a receiver sensitivity of –85 dBm or better.

IEEE 802.15.4-2020 Section 22 specifies the LECIM DSSS PHYs and does not apply to Thread.

[jinpeng1989]

In our solution, all products adopt the CCA mode 1, so the ED threshold is the sole indicator for channel assessment.

• All the ED thresholds of SED are -75 dBm.
• All Thread routers (TBR & REED) will also be changed from -60dBm to -75dBm.
• I still have doubts as to whether the threshold of -75 dBm is applicable in actual situations.

As shown in the figure, TR-3, TR-4, and TR-5 are not within the blue area of TR-1. They may cause transmission conflicts with TR-1.

• If TR-1 and TR-3 simultaneously transmit data to TR-2, there are two possibilities. Both devices failed to transmit or one of the devices failed to transmit.
• If TR-1 and TR-4 simultaneously transmit data to TR-2, the most likely outcome is that TR-2 did not receive the data transmitted by TR-4.
• If TR-1 and TR-5 simultaneously transmit data to TR-3, there are also two possibilities. Both devices failed to transmit or one of the devices failed to transmit.
• If TR-1 and TR-3 simultaneously transmit data to each other, both transmissions will fail.

[jwhui]

RF communication characteristics have a lot of nuances. In many cases, simple models like what you're presenting do not accurately represent the behavior in practice.

What is needed here to meaningfully move this forward is a scientific study that presents data from real-world environments.

[jinpeng1989]

After changing the ED thresholds of TBR and TR from -60 dBm to -75 dBm, the communication reliability of multicast messages has significantly improved. The packet loss rate has decreased from a few percent to a few thousandths.