Home Automation

Short-range wireless

Problems using domestic Wi-Fi.

Domestic Wi-Fi isn’t a suitable technology for home automation. It might require setting up, or the password for each switch which would be a chore, especially if passwords change. Some parts of the building might be out of the range of Wi-Fi, and the power consumption used makes it unsuitable, in a device for example where batteries are meant to last for years. Our scales at home require connection to our Wi-Fi network and Wi-Fi password, for example, to send data to the Fitbit application. When we change the service provider or change our Wi-Fi password, we also need to reset the scales and enter the new (rather long) password. This would not be ideal if this was the case for all IoT applications such as lightbulbs!

Short-range, low-power, low-throughput network for controlling domestic appliances.

Examples are ZigBee, Z-wave, 6LoWPAN, Thread, Bluetooth Low Energy (BLE) and Wifi HaLow (the current version of Wi-Fi adapted for IoT applications, and officially known as 802.11ah. Often these standards are used in conjunction because they deal with different sorts of processes. Some might specify the format of instructions and acknowledgements, others might concern the details of radio transmission.

Thread uses 6LowPan, which itself uses a communication standard known as 802.15.4 (as do several others) which deals with the basic radio communication protocol. The standard 802.15.4 was produced by the Us-based Institute of Electrical and Electronics Engineers (IEEE), which also produces the 802.11 series of standards for Wi-Fi.

Mesh Networks

Another recurring feature of networks for home automation is the use of mesh networking, to get around the problem caused by hub-and-spoke configuration of conventional Wi-Fi (also called infrastructure mode).

Hub-and-spoke conventional wi-fi – Conventional wifi uses a system, where the hub (router) connects directly to each spoke (wifi disc). While some spokes may have a good connection with the hub, others may have walls or other obstacles blocking the signal, and the signal will be much weaker.

Mesh network – in a mesh network, the communication between nodes might go between other nodes in a process known as hopping. In mesh networks, any device with a message to send addresses the message to the neighbouring device that is on route to the destination, and that forwards it to its best-placed neighbour (this is similar to how the Internet Protocol uses routing devices to forward IP packets on the internet)

Numerous routing procedures exist. They differ in such things as whether each node has full routing information or whether that information is restricted to certain nodes. Routing is complex which always means power consumption and delay.

An alternative to routing is flooding. In flooding, data sent by a device reaches all nodes within range and is retransmitted by those nodes. Flooding is a much simpler process than routing but is inefficient as it involves many more devices and packets to carry the data to its destination.

Whether routing or flooding is used, mesh networks can cover more distance than the hub-and-spoke network, and the more networked devices there are in a building, the better the coverage is.

Licence-free spectrum.

ZigBee, Z-wave and other domestic systems operate in the licence free spectrum, but this might or might not be the same unlicensed frequency bands used for Bluetooth and Wi-Fi. Z-wave uses 868.42 MHz in Europe and 908.42 MHz in the USA, which are not used for Wi-Fi or Bluetooth. Frequencies such as these are below 1 GHz, and propagate around buildings much better than the 2.4 and 5 GHz bands used for Wi-Fi.

Given the transmission power, frequencies below 1 GHz travel further than those above 1 GHz. Usually, above 1GHz, higher frequencies propagate less well than lower frequencies.

Whatever band is used,  non-Wifi systems require a separate hub or gateway from that used for Wi-Fi. Devices are controlled by the hub, either from a remote connected device or from a wifi-enabled controller in the same location. The hub or gateway is then connected to a domestic broadband router by either wired connection or wirelessly.

This hub is also called the ‘protocol translation gateway’ This is because instructions need to be translated and conveyed to the broadband route, and then any response sent back is also translated by the hub before it reaches the device.

In mesh networks with nodes of devices designed for battery operation, it is common for the device to go into standby or low energy mode. They need to be woken from this mode to send data or act on instructions. Because waking up takes time, standby mode contributes to the relatively long latency of low energy mesh networks compared with high power hub and spoke networks such as Wi-Fi.

A delay of a second or two would not be critical for most devices, although I can imagine in our society lots of humans would find it irritating if light didn’t come on immediately when entering a room. A more crucial issue might be a stove that didn’t turn off immediately when requested if it became a potential hazard because of its hot surface.