Out of Band Rejection

What is out-of-band rejection?

Out-of-band rejection is the system’s ability to filter and ignore signals that fall outside the frequency range allocated for communication. In other words, LoRaWAN® IoT devices reject any signals that attempt to access the network outside the predefined frequencies. Consequently, it enhances the network’s overall security.

How does out-of-band rejection work?

Understanding out-of-band rejection comes with comprehending the underlying structure of a LoRaWAN® low-power wide-area network. The LoRaWAN® protocol involves using a star-of-stars architecture. This is where numerous end devices, such as LoRaWAN® sensors or actuators, transmit data to a central gateway.

When an end device wishes to communicate with the LoRaWAN® gateway, it first scans frequencies within the authorized range. The LoRaWAN® specification defines frequency bands that LoRaWAN® devices can use for communication. Regulatory bodies license these frequency bands to ensure interference-free transmission.

In the case of LoRaWAN®, out-of-band rejection works as follows:

  • Receiving Signals: When an end device receives a signal, it checks if it falls within the predefined frequency bands. If the signal is within the authorized range, it processes it as a legitimate communication. However, if it is outside the frequency spectrum, the device immediately recognizes it as an out-of-band one.
  • Filtering and Ignoring: After identifying an out-of-band signal, the device applies a filter to remove it. The filter blocks the out-of-band signal. This also prevents the unwanted signal from disturbing the regular communication between the end device and the gateway.
  • Enhanced Security: Out-of-band rejection significantly improves the protection of the LoRaWAN® network. Ignoring signals outside the allowed frequency range makes the network robust against interference from nearby devices operating in different frequency bands. It also offers a defence against potential attacks known as “jamming” attempts. This is where malicious individuals deliberately flood the network with unauthorized signals to disrupt or disable communication.
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