MRF24J40 - Errata - Messages Received on Different Channels with Low RSSI

Why do high probability of messages being received in a different channel (that were transmitted on a different channel, e.g., transmitted on 11 but received on 15) have low received signal strength indicator (RSSI) value?

Please read Errata 3 for more information. Below are a few recommendations to workaround this problem:

  • The errata specifies couples of ways to only receive the data related to the current network:
    • Reduce transmission power on the nearby devices
    • Increase the spacing between devices
    • Add channel number information to the packet etc..)
  • Frequency Agility - We have an option in the MiWi™ Stack to periodically scan the available channels and move the entire network to the channel with the lowest energy. For more details, read the application note AN1371.
  • Define COMM_RSSI_THRESHOLD (RSSI communication threshold) appropriately, or implement a feature similar to it in the application layer. Drop the received packets which have an RSSI value lower than the value defined in COMM_RSSI_THRESHOLD.

You can hear packets that are in a different channel (which is approximately 20 MHz away) because of the close proximity of those devices and the transmit power on those devices. We recommend reducing transmit power or increasing distance between such interfering modules.

If the RSSI for these packets are close to zero, the channel scan for noise might not detect these. MRF24J40 use channels 11 - 26, using both the ends of the spectrum can also reduce the interference.

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