Interference Measurements in European 868 MHz ISM bands
A recent wireless signal measurement study shows as high as 33.7% chance of interference in the European ISM bands. (study)
Specifically aimed towards evaluating the signal quality of LPWAN technologies such as LoRa and Sigfox, the recent publication by the Dept. of Electronic Systems, Aalborg University, Denmark measured signal activity in fives distinct types of settings: a shopping area, a business park, a hospital complex, an industrial and residential area.
The two hour collection of data at each site yielded as high as 33.7% interference probability in the downtown shopping area and 22.8% in a business park.
What does this mean for IoT LPWAN technologies?
Interference in the “real world” is going to limit a LPWAN technology’s range and reliability. There are some key features/workarounds that will drastically improve performance. Here are two…
1. Ultra Narrowband
With increasing technologies using the unlicensed ISM band frequencies, the real estate is becoming precious. Using a narrowband technology increases your probability of finding a clean frequency to use. So think twice when evaluating LoRa using 125MHz per channel over a Sigfox technology using just 200 Hz per channel.
2. Bi-directional Communication
If you can confirm a message sent in the network is successful (ACK) then you don’t need to fret about packet loss. Weightless-P is the LPWAN technology that has been capitalising on this feature that is growing in demand; this Sigfox and LoRa cannot support.
This void has also led a number of variations of LoRa. Companies using the LoRa PHY and developing their own protocol stack on top it but the “125MHz per channel” is still inherent.
pictured – Aalborg University , Denmark