Choosing a Wireless Protocol for Home Automation

Which wireless protocol should you use when designing a home automation device?

As the Internet of Things begins to proliferate our personal and professional worlds, one of the first places it’s affected has been our homes. The ubiquity of wireless networks, smartphones and cloud connectivity has created rich opportunities for device makers to add value to our homes through smarter, connected home appliances.

With opportunity, however, comes competition, and there are a bewildering number of competing protocols in the wireless home automation space. Behind the confusion, there is method to the madness; no single protocol today is optimal for every use case but many of these protocols excel at certain applications in the IoT space. Let‘s take a look at the top wireless protocols in use for smart home automation today as well as a promising new standard hoping to unite them all.

Z-Wave

With over a thousand devices and well over a hundred companies making compatible products, Z-Wave is currently the most popular wireless protocol for home automation and sees no signs of slowing down. Z-Wave is a proprietary wireless protocol for home automation designed for the low power, low bandwidth requirements of the Internet of Things.
Z-Wave uses the IEEE 802.15.4 physical radio standard and uses mesh networking to increase operating range and increase network robustness. Unlike Bluetooth and ZigBee, which operate in the 2.4GHz range, Z-Wave operates at 868MHz in Europe and 915MHz in North America. Operating at sub-1GHz frequencies gives Z-Wave a signal impervious to Bluetooth or Wi-Fi networks. The lower frequency also gives Z-Wave superior range, letting it operate about three times further than ZigBee.
The topology of a Z-Wave network is a mesh, with each node acting as a repeater, increasing the operating range and allowing the network to keep on working in case one node fails. Each Z-Wave network has at least one controller, typically a Wi-Fi connected hub, which issues commands on the network and frequently also acts as a gateway to the Internet.
As a proprietary protocol, all Z-Wave device makers need to use one of the SoC chips licensed by Sigma Designs (PDF). The SoC approach allows most designs to be implemented on the radio chip without needing external MCUs, simplifying hardware development. Software development is done through a standard SDK available from Sigma. Newer, 500 series Z-Wave SoCs offer increased range up to 150m, 50% battery life, and 250% increased bandwidth, but maintain compatibility with all previous generation Z-Wave devices. After development, products must be certified before they can bear the Z-Wave logo.
The closed system means slightly higher prices, but it also means Z-Wave products are easily interoperable.
Z-Wave’s robust interference-free signaling and superior interoperability with over a thousand other Z-Wave products on the market make it a strong choice for IoT devices in the home automation space.

ZigBee

As an open standard created in 2005, using the IEEE 802.15.4 physical layer, ZigBee was the first major wireless protocol specifically designed for the IoT. Like Z-Wave, it features low power operation and mesh networking.
Though rated for up to 100m in open air, ZigBee devices often achieve much less than that as the radio is tuned for power efficiency instead of operating range. However, ZigBee’s mesh networking allows for large networks which can grow far beyond the range of an individual ZigBee device. Mesh networking enables the network to operate beyond the line of sight, around corners, past obstructions, or on different layers of a building.
The future of ZigBee is uncertain. Its power efficiency has been surpassed by Bluetooth Low Energy and several new or upcoming protocols which also feature mesh networking, including a new version of BLE.
The availability of cheap, well-qualified ZigBee modules have maintained its popularity until now and it makes it a reasonable choice for closed-network IoT projects, but its poor interoperability makes it hard to see it as a major home automation protocol in the future.

Thread

Released July 2015, Thread is a very promising new IP-based wireless home automation protocol created by Google Nest in collaboration with industry leaders including Samsung, Freescale, and ARM.
Thread aims to unite home automation products under one forward-looking protocol that can run on existing hardware. Unlike Z-Wave and ZigBee, Thread devices are inherently IP-addressable, using 6LowPAN at the network layer to give each Thread device its own IPv6 address. This makes it very easy to bridge Thread networks to the Internet and greatly simplifies integration with cloud applications.
Instead of introducing a new physical layer, Thread uses 802.15.4 just like ZigBee and Z-Wave. Thread radio modules (PDF) are already on the market and many existing ZigBee radio modules can also be updated to support Thread. Besides making it easy to build new Thread devices, this also means some current ZigBee products can add Thread support easily.
Thread supports very short messaging and “sleepy” devices to minimize power consumption. Like ZigBee and Z-Wave, Thread supports mesh networking for powerful network architectures.

Thread stack Courtesy of Thread Group

Importantly, the Thread stack defines the physical and network layers but leaves the application layer up in the air.
So far, only Nest Weave uses Thread as a native network layer. The ZigBee Cluster Library (ZCL) has also announced compatibility with the new protocol, meaning applications designed for ZCL can now run on Thread networks.
As a very new protocol, Thread hasn’t yet seen the widespread adoption of Z-Wave. But with a well-thought out, IP-addressable design, strong industry backing, and the ability to work on existing silicon, it has a lot going for it.
Thread is a protocol that today’s IoT device makers need to consider supporting.

Bluetooth Low Energy

Bluetooth Low Energy (BLE) burst onto the scene in 2010 as part of the Bluetooth 4.0 specification. With Bluetooth integrated into Android and iOS operating systems, BLE support is already built into today’s smartphones, making it an extremely attractive protocol for customer-facing devices including home automation.
Whereas devices using other IoT protocols (even Thread!) need to be accessed through a gateway, BLE devices can be accessed directly from a smartphone or tablet.
Unlike traditional Bluetooth, which was designed for streaming data, Bluetooth Low Energy is optimized for low bandwidth and infrequent, bursty communication. This makes it well-suited for transmitting sensing and control information. BLE can be very power efficient and BLE wireless sensors optimized for efficiency can achieve battery lives in the order of weeks, months, or even years.
Master-slave type connections are the most popular BLE topology. In a master-slave topology, one BLE master device can connect to multiple slaves, but a slave will connect to only one master. This topology is useful for small, asymmetric networks like a smartphone and its peripherals, a car and its electronic components, or an industrial computer and sensors on nearby equipment. On the other hand, master-slave topology is less suited for connecting large numbers of devices in a local area network.
Besides master-slave connections, Bluetooth Low Energy devices can also communicate by broadcasting data to devices nearby. In this mode, one BLE device broadcasts to an unlimited number of listening devices. A thermostat, for instance, could use this mode to broadcast temperature information at regular intervals.
As a very popular protocol, BLE chips have come down in price and are now very affordable. Many BLE chips come in an SoC design with an integrated application processor, allowing power-efficient IoT devices and sensors to be built easily at low cost.
Bluetooth Low Energy’s ubiquitousness in smartphones makes it perfect for home automation devices and its power efficiency makes it attractive for M2M communication, as well. It uses adaptive frequency hopping to avoid interference, so it can coexist with other wireless protocols such as Wi-Fi. However, it should be noted that BLE is not a mesh networking protocol, so BLE range is highly dependent on radio power and environmental obstacles.

Wi-Fi

Wi-Fi was never intended for home automation and is not power efficient for low-bandwidth applications compared to other protocols. Even so, it remains an immensely important home automation protocol because pretty much every home has a wireless network.
Wi-Fi devices can take advantage of existing networks instead of having to set up their own. This makes it an extremely attractive protocol for home automation devices that can simply connect to existing home networks.
On the downside, besides energy efficiency concerns, Wi-Fi also has a relatively large stack, requiring more memory and computing power than other protocols. For devices that have the resources for it, however, the ubiquitousness of wireless networks and their IP-based nature makes Wi-Fi support one of the best ways to ensure easy connectivity and interoperability to end users.

Protocol Considerations

As we’ve seen, each of the top wireless home automation protocols has its own strengths and weaknesses that make it more suited for certain applications than others.
If interoperability is important, Z-Wave should be considered. It currently has the largest ecosystem of interoperable devices. Z-wave boasts good power efficiency and mesh networking with better range than ZigBee and a more robust signal because it operates at sub-1GHz frequencies.
For cloud connectivity and “future-proofness”, the relatively new Thread protocol has a very well thought out, IP-addressable design and the backing of major industry players. It features low power, mesh networking, and IPv6 addressing for easy integration with cloud applications. Even  it’s a new protocol, it’s easy to support as it runs on existing 802.15.4 radios and can co-exist withthough ZigBee.
For utlra-low power applications, Bluetooth Low Energy is currently the lowest energy protocol on the market, as well as the one with the lightest stack. This makes it well-suited to small, cheap devices that need to last a long time without charging. In addition, users can directly access these devices with their smartphone or tablet, without having to go through an edge device or hub.

Finally, for ultimate ease of use, it’s hard to argue with Wi-Fi. This will be best for devices that can be connected to mains power, as Wi-Fi is not very energy efficient, but it makes up for that with speed. Wi-Fi excels at high bandwidth applications like security cameras. In addition, the ubiquity of Wi-Fi networks and its inherent IP addressability makes Wi-Fi an attractive protocol for any IoT device able to support it.