Intermodulation Distortion
What is it?
Intermodulation distortion (IMD) is a phenomenon that occurs when multiple signals are mixed in a non-linear device, like a radio frequency amplifier or power amplifier. These signals generate additional unwanted signals at frequencies that are the sum and difference of the original signals. These other signals can interfere with the desired ones and degrade the system’s overall performance.
In the context of the LoRaWAN® protocol, IMD is particularly relevant. The reason is LoRaWAN® operates in the sub-GHz frequency band, typically around 868 MHz or 915 MHz. There are various sources of interference in this frequency range, including other wireless systems and harmonics from nearby electronic IoT devices. Intermodulation distortion can amplify these interfering signals, increasing the possibility of collisions and reducing the range and capacity of the LoRaWAN® network.
How does it work?
IMD occurs because of the non-linear behaviour of the amplifiers used in a communication system. When two or more signals with different frequencies pass through a non-linear device, their interactions cause new signals to be generated at frequencies not part of the original ones. We call them intermodulation products.
In LoRaWAN®, the intermodulation products can appear within the bandwidth of the desired signal, leading to interference. This interference can disrupt the reliable reception of data by the LoRaWAN® gateway. It results in packet loss and reduced network performance.
How to solve it?
To mitigate intermodulation distortion in LoRaWAN® networks, several solutions can be implemented:
- Filter Design: Appropriate filters allow for attenuating or eliminating unwanted signals and intermodulation products. Filters can block out interfering signals while allowing the desired LoRaWAN® sensor signals to pass through.
- Frequency Planning: Careful frequency planning can help avoid interference from other wireless systems operating in the same frequency spectrum. You can reduce the impact of intermodulation distortion by selecting frequencies with minimal interference and avoiding harmonic frequencies of nearby electronic devices.
- Power Control: Controlling the transmit power of LoRaWAN® devices can prevent non-linear behaviour in the amplifiers, reducing the generation of intermodulation products. By carefully managing the transmit power levels, you can minimize the impact of intermodulation distortion.
- Antenna Placement: Proper antenna placement can help reduce the effects of intermodulation distortion. You can reduce the likelihood of IMD by placing antennas away from other sources of interference. They include, for example, nearby electronic devices or high-power transmitters.
By implementing these solutions, you can improve the performance of LoRaWAN® networks, signal quality, range, and data rates.
