Preliminary WMBUS network planning

How to plan radio network to gather measurements from WMBUS sensors

Radio network planning shall be done thoroughly before installation.

In fact, there is (and cannot be) any precise or unambiguous definition of "distance" or "reliable coverage" in radio technology. It all depends on the transmitting power, the transmitting and receiving antenna, interference, the quality of the obstacle, other radio equipment, the state of the air, and so on.

WMBUS operates at 869MHz and such radio waves propagate quite well even inside houses, but thick concrete (and especially reinforced concrete) walls strongly inhibit transmission and coverage. WMBUS sensors transmit short and rather weak radio messages to save battery power, therefore a careful radio network plan is necessary for high performance and long sensors lifespan. Sometimes the signal is fine at around 200m, sometimes at 20m the signal is too weak for the receiver.

Each house is unique and because the walls and materials of the house cannot be modelled, no calculation will give clear results. Probably the best method would be the following:

1. take 1 piece of sensor, 1 piece of FXAirReceiver, 1 piece of 230VAC Repeater
2. configure all of them in the office, make sure that the sensor data is transferred to the PLC.

3. Install the sensor in the farest possible location in the planned building with maximum obstruction (walls, doors, etc.).

4. Install the FXAirReceiver in a location that is between all sensors (same distance up to each planned sensor, e.g., in the lobby of a stairwell, on the second or third floor).

5. If the test sensor data does not come to the PLC, add a repeater halfway between the FXAirReceiver and the sensor.

6. If the test probe data comes through without the repeater, move the probe to the other side of the building and repeat the test.

7. This will help understand if a repeater(s) is needed and where to install the FXAirReceiver/repeater.

If your house is about 30 -50 m long and 3/4 floors, it can be said that you need 1-3 repeaters in different staircases and their configuration to transfer only the messages from the house sensors from one to the other and finally to the FXAirReceiver.

Please note that FXAirReceiver can handle max 256 registers (2 registers per measurement, total 128 measurement data) i.e. about 64 sensors (e.g. temperature + humidity)