[W-MBUS] Explain how interference occurs in the license free bands?

Radio regulations allow ALD in the same band as wMB at 169 MHz would use. It is typical for license free bands that applications share the same band. Interference may therefore occur.

As seen from ALD it would mean that they may be disturbed by meter transmissions, but as meters typically transmit for only 100 ms or so, it will not completely block the audio communication, but you will hear a “pop” or silence for a short moment. It can also be mitigated by forward error coding in the audio data stream.

As seen from the metering system, a strong ALD may block the communication for some time (as continuous audio transmission is allowed). This is mitigated in several ways:

-redundancy in the transmissions. Typically the same data packet is transmitted 2-4 times randomly during the day/night

-redundancy of meter data in each transmission. Typically the meter index from previous days (1-2) are sent together with the new index.

-finally, if any missed data (if the channel was blocked for a few days) it is also possible to ask for historical data that has been stored in the meter, when communication is established again.

Together these techniques will increase the likelihood of receiving the metering values at least once to a sufficient level (say 99%), even if several transmissions are blocked/lost.

Last Update: January 11, 2019  

January 11, 2019   724    Wireless M-Bus Q&A