It may also help to understand a little more about the difference in design philosophy between Wi-Fi devices and Zwave devices.
WiFi depends on the signal strength from the access point being strong enough to reach each individual device on the network
Wi-Fi uses a “star” topology, with each device is connected directly to the router or an access point. There is a fixed route for messages to that device. The broadcast signal is pretty strong. Each individual device uses a lot of power, which is why typical battery life is about 10 hours. The messages that are sent are strong and relatively fast. Also, because of that fixed route, there is a built in serial nature to the messages. All of this is why Wi-Fi is so good for streaming music or video.
Zwave uses a lot less Power, and depends on a relay system to pass messages around until they reach their destination.
Z wave uses a “mesh” topology. Instead of a fixed route for messages, each message gets passed around from device to device until it gets to its final destination. There can be many different paths that the message can take. Each individual device is designed to be as low power as possible, in part to make the batteries last as long as they can, and in part to reduce the cost of each individual device. The messages are low power, fairly slow, short range, usually tiny, and do not have enforced sequencing, meaning if you send out two messages at once you can’t guarantee what order they will arrive in.
You definitely don’t want to do streaming video over a mesh network. But mesh can be a great match for home automation, particularly for battery-powered sensors, because you can get battery life of a year or more and each individual device can be very inexpensive.
You will often hear people talk about creating “a strong mesh.” This is a network that offers many different pathways for each possible message. Usually with Wi-Fi, the more devices you add, the slower the network runs. But with a mesh topology, the more devices there are, quite often the more quickly messages will get through, because there are more pathways to choose from. And again, the design intent is that each individual message is tiny.
A “hop” is just any message being passed along from one device to another device. It’s a big relay system. The devices are allowed to talk directly to each other without going back to the hub each time if they’re just passing messages along. (The devices are also smart enough to go as far as they can each time, so you don’t use up hops just because there are more devices in the room.)
However, battery-powered devices are not part of the relay transmitter system. They can only be recipients. That’s because relaying messages for other nodes would use too much battery life. So only the mains-powered devices are an active part of the relay. Typically light switches, wall receptacles, and micro relays.
Two ways to plan a Zwave network
So with Wi-Fi, you get full house coverage by making sure there is a strong signal from each access point to anywhere in their zone. Every device in that zone will talk directly to that access point each time.
With Z wave, The most comprehensive way to make sure you get a strong mesh is by installing mains-powered Zwave plus devices every 40 to 60 feet (depending on the local architecture), and ideally two of these per room so that there are more choices for relaying messages. Again, most typically this is done just by putting in light switches, plug in pocket sockets, in wall micros, and in wall receptacles.
Of course, that might be more devices than you want to pay for. The alternative is to actually decide where your battery-powered devices will be, and then plan a “backbone” of repeating devices that will reach those specific battery powered devices in the fewest number of hops. In this kind of approach, it’s pretty common for people to just run repeaters, for example, down a central hallway rather than putting them into every individual room. You might even skip areas where you know you don’t plan to have any battery-powered devices.
With either method, you can always add more repeaters later if you find that you need them, as long as you don’t exceed that maximum of four hops to get to the intended recipient device.
Zwave networks typically use about 25% of the energy draw of a Wi-Fi network that accomplishes the same thing. They also usually require much less human maintenance, both because of longer battery life for the individual devices and because the network does its own routing.
Because the primary goals are low energy use and low device cost, the relay method is used to extend the coverage area, rather than just boosting the signal from the central hub.
So you plan a mesh network by thinking about where the individual relay devices will go, and you strengthen the mesh by adding more of those relay participants, rather than a stronger broadcast signal from a central router.