Both Zigbee® and Bluetooth® wireless protocols are widely used for local communications in Internet of Things (IoT) applications, and there are some trade-offs to review in choosing the right one for your application. Each protocol has unique strengths that guide which solution to implement when designing a new network.
In certain situations, one protocol will be a better fit than the other, though sometimes the right solution is to implement both together to take advantage of their combined strengths, as we will discuss in this article.
To better understand these IoT protocol options, let's take a look at the advantages and limitations of Zigbee, followed by the same for three different "flavors" of Bluetooth: Classic, BLE, and BT Mesh. This will help explain the trade-offs and show some use cases for each, so that you can choose the optimal protocol for your IoT application - be it a smart city, industrial IoT, digital signage or other connected technology use case.
Zigbee Technology in IoT Applications
Zigbee is an open global standard for cost-effective low-power, low-bandwith wireless mesh networking, developed by a consortium of companies in the Zigbee Alliance. The Zigbee protocol allows the transmission of data over long distances by passing information through a mesh network of intermediate nodes to reach distant ones. Messages "hop" through intermediary radio nodes on the way to their destination. Zigbee's 2.4 GHz frequency range can be implemented globally, license-free. There are approximately 300 million Zigbee nodes currently deployed.
Advantages of the Zigbee Protocol
Substantial mesh networks can be created with Zigbee that are much larger than the reach of any one radio. The Zigbee mesh configures itself automatically (self-forming) and will reconfigure dynamically to repair itself if nodes are disabled or removed (self-healing). As an interoperable standard, devices from many different manufacturers can communicate seamlessly, helping to create Zigbee's broad acceptance in both home automation and industrial IoT. Costs are modest, with lots of OEM equipment options on the open market.
Documentation is widely available and covers many different use cases. Routing tables, address resolution, security, retries and acknowledgements are built right in to the protocol, saving considerable engineering time. Zigbee supports multiple network topologies such as point-to-point, point-to-multipoint, star, and mesh networks, and allows over 65,000 nodes per network and up to two miles (3.2 km) of ideal line-of-sight outdoor range.
Limitations of the Zigbee Protocol
Like most mesh networks Zigbee nodes that route or "hop" messages must be powered on at all times. End devices that can sleep to extend battery life can participate in the mesh, but not extend it.
Note: See DigiMesh®, Digi's mesh networking technology, for applications that require the entire mesh network to sleep. DigiMesh provides an alternative to Zigbee mesh networking with some features that support application requirements such as network-wide sleep. Digi provides both Zigbee and DigiMesh solutions to support the full range of mesh application needs.
Zigbee does not use IP addressing. Therefore, gateways must be installed to communicate with the Internet and cloud services. Because most phones, tablets and computers do not include Zigbee, gateways are required to communicate with them as well. Provisioning must be carried out deliberately to ensure that nodes join the correct network and communicate with the proper gateway. Latency is greater with mesh than with simpler point-to-point protocols, though this must be considered in the context of the mesh's far greater effective range and reliability.
Zigbee Use Cases in Smart Cities, Agriculture and More
Home automation was the birthplace of Zigbee, but commercial and industrial use cases have become equally prominent including smart energy, lighting, medical device systems, factory automation, municipal street lighting and retail monitoring systems.
Smart city street lighting is an excellent example of a growing trend in mesh networking that Zigbee is well-suited for, as it enables key functionality such as remote management of a large network of devices. See the CIMCON customer story on Digi.com for an example of this use case.
Agricultural applications are also taking advantage of mesh network technology, for example to manage devices that connect smart watering systems
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Bluetooth Technology in IoT Applications
Bluetooth is a personal area wireless networking protocol designed for communicating over short distances. It was originally created to replace the wiring needed to connect devices like computers and cell phones to their peripherals, such as headphones, keyboards and mice. Like Wi-Fi and Zigbee, it operates in the 2.4GHz frequency range, which is license-free globally.
The Bluetooth standard is developed and administered by the Bluetooth Special Interest Group (SIG), which coordinates interoperability between device manufacturers. The Bluetooth branding covers several rather different protocols. While there is some interoperability between these protocols, it's easiest to consider them separately from each other, so we will cover Bluetooth: Classic, Bluetooth Low Energy and Bluetooth Mesh in their own sections. About 4 billion Bluetooth devices ship every year.
Bluetooth "Classic"
Bluetooth Classic is designed to steam high-throughput data at up to 2.1 Mbps over short distances where long battery life is not a major concern. It is an excellent solution for audio and video devices that require high-bandwidth and that can be recharged on a daily basis. Classic devices include mobile headsets, earphones, keyboards, mice, printers and other peripherals typically connected to a computer, vehicle entertainment system or mobile phone. Bluetooth uses a master/client architecture. One master may communicate with up to seven client devices in a small personal-area network.
Advantages of Bluetooth Classic
If your project needs to send or receive a lot of data, Bluetooth Classic's high throughput will serve it well. There are many devices that implement Classic. For audio and video feeds it's easy to pair with a phone, tablet or laptop to begin receiving information, and serial streams can be supported as well. Classic is a highly mature protocol and documentation is widely available in books, online and of course in the official standards documentation.
Limitations of Bluetooth Classic
Bluetooth Classic can be complex to implement, with pairing required along with a user interface for managing that process. Its high bandwidth also means that it is relatively power-hungry. The protocol is designed for devices that are easily recharged on a daily or perhaps weekly basis, making it unsuitable for many IoT applications. Networks are quite limited in size since the protocol was designed for short-range peripheral cable replacement and not for scaleable sensor networks hosting hundreds of devices.
Bluetooth Classic Use Cases
The Classic version of Bluetooth is wildly popular in audio headsets, smartphone-vehicle pairing and home entertainment. Its high bandwidth and industry-standard acceptance will continue to drive its use in these types of applications for some time to come. For most IoT applications, the next two versions of Bluetooth are likely to be a better fit.
Bluetooth Low Energy (BLE)
Bluetooth Low Energy supports low-bandwidth connections over short distances with excellent power management. It is used in situations where a personal-area network does not need to handle large data streams, and where batteries need to last months or even years. BLE devices include location beacons, digital scales, temperature monitors, lighting controllers, smart watches, cook pots and thousands of other low-bandwidth battery-operated use cases.
BLE implements a client/server architecture that allows hardware to implement only the communication features needed, saving money, battery and bandwidth. BLE networks can theoretically contain a huge number of devices, though bandwidth, physical space and most importantly range limits the size of a single BLE personal-area network to nodes in the low hundreds.
Advantages of BLE
It's right there in the name, Bluetooth Low Energy doesn't use a lot of power. Devices can be run off coin cells for extended periods, making it the Bluetooth protocol of choice for data skinny devices that need to run unattended for months at a time. Its simpler protocol comes with other advantages. Less complex hardware means that BLE chips and devices can be quite low cost.
The client-server model makes communications simpler to implement, lowering engineering and development time. It also means that devices don't have to be paired to communicate, but can read and send data asynchronously and instantaneously whenever needed. The protocol is widely accepted and implemented across billions of devices worldwide with lots of documentation, OEM equipment and trained development staff at the ready.
Limitations of BLE
BLE is a point-to-point protocol. Therefore, radios cannot communicate beyond their individual range. This limits the physical size of networks to BLE's typical 10-meter range, fine for home offices, but not so great for agricultural monitoring applications or municipal street lighting control. IP addressing is not implemented, therefore gateways must be used to pass information to the Internet and to cloud solutions.
Many BLE applications are designed to use smartphones as their gateway; however, this only works when a smartphone is present. For wearables like smartwatches or fitness bands, that's fine, however the sensors used in commercial and industrial applications are typically unattended, making smartphone gateways impractical or impossible to implement. BLE is much lower bandwidth than Bluetooth Classic, and cannot effectively be used for media streaming.
Bluetooth Low Energy Use Cases
Personal-area networks are a prime use case for BLE including home appliances, fitness monitors and vehicle networks. Beaconing in BLE is designed to support indoor positioning systems that can determine your location in a retail store or inside a factory.
Home automation is a key market, but also any small commercial system can leverage Bluetooth Low Energy to communicate inside a home-sized space. So while BLE might not be great for large scale farming, it's perfectly suited to monitoring small commercial greenhouses. It can also provide local communications for installers who are configuring IoT devices that will normally talk via a longer-range protocol, such as Zigbee mesh or cellular mobile data.
Bluetooth Mesh
Bluetooth Mesh (BT Mesh) is a very new protocol. It extends simple point-to-point BLE using additional routing and network formation standards to create mesh networks where nodes can act as relays to extend the network beyond the range of any one device. BT Mesh is broadly similar to Zigbee in overall function and architecture, but with several very important differences. A BT Mesh network can theoretically support over 32 thousand nodes, however like other protocols, the practical limitations of bandwidth and physical space generally keep individual networks to the low hundreds of devices.
Advantages of Bluetooth Mesh
Networks formed as a mesh are not limited by any individual radio node's reach. Instead each node can forward and route messages to destinations well beyond their nominal range, forming very large physical networks. Because Bluetooth Mesh is based in BLE, it carries over many of that protocol's advantages including low energy use, good security, beaconing support and pervasive underlying documentation. BT Mesh networks are self-forming and self-healing, with sleep support for end devices in a store-and-forward parent/child relationship similar to those in Zigbee.
Limitations of Bluetooth Mesh
Bluetooth Mesh is still a new protocol, and it is still undergoing enhancements and revisions. It is not yet widely supported, meaning OEM equipment, gateways and handheld devices are not yet likely to be fully compliant. This will likely improve as the protocol gains traction; however, it's certainly a concern for applications being designed today.
The "managed flood" protocol makes network design simpler, but is a trade-off in efficiency and power use compared to a fully routed mesh protocol like Zigbee. Any device that routes must be mains powered rather than running on a battery, because like Zigbee nodes, BT Mesh routers are not allowed to sleep. They do not use IP addressing, therefore interactions with the Internet and cloud servers must be passed through fixed gateways or border routers that translate between BLE and the regular protocol of the Internet. Mesh networks always have higher latency since messages need to "hop" through multiple nodes on their way to their destination, so applications must be able to tolerate slower response times in trade-off for the larger mesh network scale.
Bluetooth Mesh Use Cases
Bluetooth Mesh was initially designed with the lighting market in mind. Because router nodes need to be powered continuously, lighting is an excellent application since most devices will have ample access to full-time mains power. There is also an application layer implemented by Bluetooth Mesh specifically for cross-manufacturer interoperability in lighting, so switches from one vendor can control lighting devices created by other vendors. Sensor networks can be supported easily by BT Mesh, although since routing nodes in the mesh cannot be battery powered, sensors themselves are best implemented in situations where a mains-powered network is available, for example in a building with BT Mesh lighting already in place.
Combined Zigbee BLE
Digi XBee 3 Zigbee RF modules also support Bluetooth Low Energy as a single hardware solution. BLE can be used alongside Zigbee to support easy smartphone-based module configuration using the Digi XBee Mobile App. Beaconing applications can be developed with the Digi XBee Mobile SDK (Software Development Kit).
The SDK includes a set of libraries, code examples and documentation designed to simplify the process of creating iOS and Android mobile apps to interact with Digi XBee 3 modules. The SDK can support beaconing applications and will also be useful for communicating with local BLE sensors in future applications combining Bluetooth and Zigbee devices to form large and fully interoperable multivendor networks.
Zigbee and Bluetooth are each useful in different types of IoT solutions. Most importantly, they can work together to create dramatically flexible applications that combine the strengths of each well-established and interoperable protocol. Understanding the strengths and weaknesses of each, including the many versions of Bluetooth, should help developers create the most efficient communication system — one that balances power use, bandwidth, and device costs to create powerful wireless IoT networks.
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