Over the past two decades, Zigbee has established itself as one of the main communication protocols in the home automation market. As a result, the open-source standard is used by a wide array of vendors in the automation market. It's a good idea to familiarize yourself with it if you are looking to get into the home automation game!
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What Is Zigbee?
Zigbee is a communication standard used for low-power, close-proximity devices. Zigbee specifications, a set of standards devices need to comply with, were ratified by the Institute of Electrical & Electronics Engineers (IEEE) in 2003 and have been widely used ever since. Because of its low power consumption and relatively higher speeds, Zigbee is consistently used in smart home networks.
The Zigbee Alliance, an organization of manufacturers and scientists, is responsible for developing and maintaining standards. Zigbee-certified devices can communicate with each other and seamlessly connect in any Zigbee mesh network.
Zigbee Frequencies per Geographical Area
The frequencies used by Zigbee devices lie in the radio frequency range, which is also used by most computers, mobile phones, radios, and television transmissions. Hence it is essential to specify frequency limits for devices to not interfere with other communication frequencies. By working closely with the Zigbee Alliance and Communication Standards Institutes of each country/region, Zigbee frequencies are defined for each area.
The standard allows operation in 2.4GHz–2.4835GHz worldwide. Some devices also use 902MHz to 908MHz in the Americas and Australia and 868MHz to 868.8MHz in Europe. The data transmission rates are 250kbps per channel in the 2.4GHz range, 40kbpc in the 915MHz spectrum, and 20kbps in the 868MHz field.
Working within these ranges, manufacturers usually decide on a particular frequency by studying the environment where their device will be installed. For example, for smart home devices, the obstruction to these frequencies are walls and windows, which will be easier to penetrate, unlike an industrial space where the communication signals might have to penetrate electronic panels or steel used in heavy machinery.
What Is Zigbee Plus?
Since its ratification in 2003, Zigbee has been improving quickly, with manufacturers and researchers continuously adding to its libraries and hardware standards. At its inception, Zigbee communicated between sensors and remotes only, and connecting to complex user interfaces was next to impossible. The latest standard, Zigbee 3.0, can integrate with a variety of user interfaces and devices.
This integration is possible because of an application layer, like a mesh placed over all the devices. As a result, Zigbee protocols can even be installed in some smart home devices if they are not already there, adding them to the Networking Mesh. This is what the market refers to as Zigbee Plus.
How Does Zigbee Work?
You can think of a Zigbee network as an interconnected low-power Wi-Fi network. Everybody has a Wi-Fi router in their home which connects to their phones, computers, and other gadgets. The router is connected to the Internet. This allows your devices to access the world wide web via your router.
A Zigbee network works similarly, except the devices are connected with the hub and each other. All communication occurs via radio frequencies, so all your devices will have a Zigbee antenna in them.
A Zigbee network usually consists of a coordinator, a router, and multiple smart home devices. The coordinator sits on top of the network, acting as the brain; it can connect with the Internet, with your phones/computers, or with other coordinators in separate networks. The coordinator sends signals to individual devices, which are first stored in the router.
As the device becomes ready to receive instruction, the router sends the information from the coordinator to the device. Essentially, all devices are connected to the router (the gateway) and coordinator (the processing brain), giving you one point of access for your entire home.
For example, if you only want a bulb to turn on if another light is off, you can connect them with the coordinator, and it will decide based on the logic the manufacturer has provided when to turn on a light.
What Does a Zigbee Hub Controller Do?
A Zigbee Hub Controller is the coordinator in a network (refer to the previous text). It sits on top of the Zigbee Network Mesh, sending and receiving instructions from each device via a router. Most Hub Controllers nowadays have a user interface.
For example, if you want to turn off a bulb, use the Controller's UI to send this instruction; the controller sends this instruction via RF waves to the router, which then routes these instructions to your bulb (via a small Zigbee device). The controller is simultaneously connected to every device in your house, giving you complete access via one interface.
Types of Zigbee Devices
Depending on their functionality, Zigbee devices can be divided into three categories.
The Zigbee coordinator is the brain of the network. It has the most processing and storage capabilities of any device in the network. It stores crucial instructions such as passkeys, organizational hierarchies, etc., and processes any new information it receives from the connected devices.
Modern coordinators use an application layer to connect every device via the same mesh, operable through a user interface. So the homeowner deals with the coordinator, and the coordinator deals with the entire house.
A router sits between your devices and the coordinator, receiving information from the coordinator and transmitting it when appropriate. All appliances are connected to the router, which then connects to the coordinator. Routers can also connect with other routers providing additional functionality and security to your smart home network.
The End Device
This is the simplest device in this network, capable of rudimentary communication and functionality. These devices, essentially, consist of Zigbee antennas and a low-power electronic circuit for encoding/decoding.
End Devices do not relay data to other devices, and hence are simpler in construction and cheaper to replace. Your home utilities connect directly to these devices. Some researchers consider the utility and end device to be one whole unit.
Are All Zigbee Devices Repeaters?
Strictly speaking, no. Repeaters are Zigbee devices that are always powered on to act as a messenger between the router/hub and an end device. Repeaters can receive information and transmit it to other devices. They are usually placed at the periphery of the network.
So if an end device is out of a router's range, the repeater can relay the message from the hub to that end device. When you install an end device, it will either connect to the hub or a repeater, depending on which signal is stronger and will remain connected to that particular option.
How Secure Is Zigbee?
Zigbee's security is three-fold: authentication, encryption, and integrity checks. At the heart of network security are cryptographic keys. The network uses these keys to access different nodes. Every node key can be stored independently at the corresponding access points or cumulatively in additional encryption at the hub or router. If the keys are spread out, nodes will require extra storage and processing capabilities, making your network expensive.
Zigbee's security protocols are incorporated into the IEEE 802.15.4 standard. The consensus in the market right now is that is very secure from hackers targeting its wireless capabilities; however, if an intruder physically interacts with any of the nodes, they might be able to access your network. For this reason, additional microcontrollers are recommended for nodes that contain security information or access.
How Far Can Zigbee Transmit?
Zigbee devices can usually transmit within a radius of 80m (uninterrupted). Smaller devices that consume less power can transmit anywhere between 10-40m. Beyond these ranges, repeaters can be used to relay data and communication signals.
However, there is a catch. Adding repeaters enhances the processing, storage, and power needs of a network, making it more expensive. The range is not as big an issue in smart homes as industrial or corporate setups, where Zigbee networks might spread to kilometers.
How Do I Extend My Zigbee Network?
There are two problems here—extending the range and using the complete range you currently have. Let's tackle the latter first. Zigbee signals usually work in 2.4GHz frequency ranges, which means other devices in this range will produce noise for your network, reducing its efficiency and range.
So try to isolate devices such as Wi-Fi routers, cell phones, baby monitors, microwave ovens, and wireless game controllers. You can change the frequency settings on these devices or buy variants that do not interfere with Zigbee devices.
As for extending the range, devices called repeaters are used. Repeaters are Zigbee devices that do not power off. They can act as relays between your hub and other Zigbee devices, transmitting messages between them and the hub and them and the devices out of the hub's range. Any device that does not turn off can pretty much be used as a repeater.
If you're looking to add smart home devices to your humble abode, it's hard to go wrong with Zigbee. Zigbee specifications have been improving for the past two decades. Major smart home manufacturers such as Amazon, Samsung, Xiaomi, and Google not only use Zigbee but are actively dedicating resources for its development.
Zigbee devices are efficient, have a decent range, and are relatively secure, making them the first choice for most smart home consumers today.