The right network components
When planning your smarthome, it is important to choose the right network components. I always try to achieve everything primarily by cable and only in exceptional cases by radio. And I do not want to have an ideological discussion about radio radiation here. The principle with me is therefore. Where it is easy, a cable is taken, otherwise just a wireless solution.
Therefore, a GBit Ethernet network was installed throughout the house and every single network socket was realized as a double connection. Each floor has its own power-saving GBit switch which are connected by a cable. Thus, the network traffic is separated within one floor and does not affect the other floor. Whereby this effect has already been largely eliminated by the use of switches.
In addition, there is a AVM Fritzbox 7590 in the hall which provides a wireless in the 5 / 2.4GHz range.