Zigbee vs. Bluetooth: choosing the ideal edge device mesh protocol

I. Introduction

Most IoT applications are grouped around four functions: sensing, communication, computing, and actuation. The internet of things (IoT) uses these applications to connect companies' assets to their operating systems. However, it is impossible for a single device to support all four capabilities. Older systems thus used end devices for environmental sensing, gateways for communication and network needs, and the centralised cloud-like server did the computation. The system then sent the generated information to selected devices that acted as executors. However, such a centralised computing system failed to satisfy the exacting needs of time-critical and compute-intensive applications. The shortcomings of the centralised computing system have led to edge devices adopting new management systems. These systems enable real-time response and management of critical assets in highly distributed environments.

Edge device mesh networking involves connecting multiple edge devices to create a mesh network that provides high reliability, flexibility, and scalability. However, a key challenge is to choose the correct protocol when setting up an edge device mesh network. It is vital to select one that fits your specific needs. Two popular protocols for edge device mesh networking are zigbee and bluetooth. Each protocol has its advantages and disadvantages. Ultimately, the choice between zigbee and bluetooth will depend upon the specific application needs and the devices used. The correct protocol enables the network to run smoothly and achieve the desired outcome. This article will explain why choosing the proper edge device mesh networking protocol is crucial.

II. Zigbee

Zigbee is a globally accepted open standard that allows low-power, low-bandwidth wireless mesh networking at an affordable cost. The zigbee protocol facilitates data transmission over extremely long distances. These messages reach their destination by hopping through the intermediary radio nodes. The 2.4 GHz frequency range allows license-free communication up to a range of 100 meters.

3 Zigbee mesh kit
Digi XBee

ONsemi Strata enabled
Zigbee green power kit

Digi Xbee 2.4GHz

USB dongle
OM15080-K32W

Advantages of the zigbee protocol

Zigbee can help to create substantial mesh networks that can exceed the reach of a single radio. The mesh network can configure itself automatically (self-forming) and is self-healing. By self-healing, zigbee can dynamically reconfigure itself to restore functionality if any nodes are removed or disabled. The interoperable standard of zigbee allows seamless communication amongst devices from various manufacturers, leading to its widespread adoption in home automation and industrial IoT.

Zigbee comes with tough security measures, such as support for AES-128 encryption that safeguards the data when it is exchanged amongst devices. Zigbee provides superior scalability and can accommodate up to 65,000 devices in a single network.

Limitations of the zigbee protocol

The zigbee nodes that "hop" or route messages inside the zigbee mesh network must have power. This is typical with most mesh networks. Although end devices can participate inside the mesh, they cannot extend it. These devices conserve battery life through intermittent sleep. The zigbee nodes do not favour the IP addressing method. Instead, the nodes install gateway devices to establish connectivity with cloud and internet services. Platforms such as Android, iOS, and Windows do not currently support zigbee. An additional gateway is required to connect them to zigbee, making it a complex process. The higher latency of the mesh network must be considered in light of the mesh's noticeably greater reliability and effective range.

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III. Bluetooth

Bluetooth is used in personal area networks (PAN). Bluetooth special interest group (SIG) develops and manages this wireless networking protocol. The bluetooth protocol implements a master/client architecture where, in a small personal-area network, a master device can connect up to seven client devices. The specially designed bluetooth classic can transmit high-throughput data at 2 Mbps and maintain long battery life. The SIG ensures compatibility amongst various device manufacturers.

Bluetooth mesh is a recent protocol that includes routing and network formation standards to extend simple point-to-point BLE and establish mesh networks. Such networks can use nodes as relays to expand beyond the range possible by a single device. Despite being similar in architecture and function to zigbee, bluetooth Mesh has many differences. Although a bluetooth network can theoretically accommodate over 32,000 nodes, practical considerations such as bandwidth restrict it to a few hundred devices.

Advantages of using bluetooth

Bluetooth can transfer streaming audio or video content or large files due to its high data transfer speeds, reaching 2 Mbps. In addition, bluetooth has AES-128 encryption support and other excellent security features.

Mesh networks enabled through bluetooth technology are not restricted by the range of a single radio node. This is possible as a single node can route and forward messages to destinations beyond their nominal range, creating extensive physical networks. Since bluetooth Mesh is built on BLE, it inherits the many advantages of that protocol, like low energy use, beaconing support, and good security. BT Mesh networks are self-repairing and autonomous, and like zigbee, with sleep support for end devices engaged in a store-and-forward parent/child relationship.

Limitations of the bluetooth protocol

Bluetooth mesh is a new protocol with ongoing modification and improvements. Support for this protocol is limited, and original equipment manufacturers (OEMs), handheld devices, and gateways may not be completely compliant. When compared with zigbee, bluetooth Mesh has a lower level of scalability. Bluetooth mesh can support a maximum of 32,000 devices per single network.

Bluetooth mesh follows the "managed flood" protocol in network design. This protocol simplifies network design, but there are trade-offs: power usage and efficiency are sacrificed. Devices routed in bluetooth mesh must be mains powered as routers cannot sleep like zigbee nodes. Interactions of BT mesh routers with the Internet and cloud servers must pass via border routers or fixed gateways, as IP addressing is not used. Mesh networks must have higher latency since messages must "hop" through several nodes to reach their destination. Applications thus must tolerate slower response times. This slowness is a trade-off for the bigger mesh network scale.

IV. Comparison between zigbee and bluetooth

- Range, scalability & mesh network size

Bluetooth mesh and zigbee do not need a license to work in the 2.4GHz spectrum. However, many devices have BLE and, by extension, bluetooth mesh capability. Conversely, a Zigbee mesh network requires a communication gateway with smartphones and other devices.

Bluetooth Mesh and zigbee networks share similar conditional range limits between nodes — 10 meters to 100 meters. Zigbee can support a higher number of nodes in a mesh. The theoretical limit of bluetooth Mesh is 32,000 nodes, whilst it is 65,000 nodes for zigbee. This implies that a zigbee mesh network-theoretically- can cover twice the area of bluetooth mesh. In practice, the network size will be limited by other concerns.

- Power consumption and sleep modes

Engineers must consider power consumption. This is specifically applicable to battery-powered nodes. The bluetooth mesh and zigbee nodes that act as routers must be active if these nodes transfer data across the mesh. End devices in both protocols can sleep when they are non-participants in the mesh. Bluetooth Mesh nodes need less power than zigbee nodes when active.

Figure 1: End devices can sleep without participating in the mesh. (Source: STMicroelectronics)

- Data rates

Bluetooth mesh, at first glance, seems to have an advantage over zigbee when it comes to the data rate of each network. BT Mesh has an air data rate of 1Mbps, and zigbee's is 250Kbps. However, making decisions solely on the basis of air data rate is not recommended as data is relayed between many nodes, and the efficiency of data transfer depends upon the path it takes through the mesh network.

The architecture of a mesh network can vary even if the same protocol is used. The architecture depends on various factors such as the nodes' physical location and the network's configurable logical structure. For example, if the end devices have to sleep, a zigbee network can use many router nodes close to the end device nodes' clusters. There can be fewer router nodes if power consumption is a negligible concern.

- Security

Both zigbee and bluetooth offers support for AES-128 encryption. With this, they have robust security features. However, zigbee has a higher level of security compared to Bluetooth.

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V. Use cases

Zigbee finds use in various industries:

1. Home automation: Smart homes use zigbee control security systems, lighting, thermostats, and security systems.
2. Industrial automation: Manufacturing plants use zigbee in industrial automation for monitoring and controlling processes.
3. Healthcare: Healthcare applications, including remote patient monitoring, medical adherence, and tracking medical equipment, uses zigbee.

Bluetooth finds use in many industries.

1. Healthcare: Many healthcare applications that monitor vital signs, track medical equipment, and monitor remote patients use bluetooth.
2. Consumer electronics: Wireless headphones, speakers, and other audio devices generally use bluetooth.
3. Retail: Bluetooth is used in retail applications that use indoor location-based services, and proximity marketing use bluetooth.
4. Automotive: Cars that offer hands-free calling, audio streaming, and other features use bluetooth.

VI. Conclusion

Bluetooth mesh and zigbee networks share more similarities than distinctions. Both are excellent options; you do not have to choose between them. Modern hardware, such as STMicroelectronics' STMWB55 series of SoCs, supports zigbee and bluetooth mesh networks.

Several factors must be considered when comparing bluetooth and zigbee for mesh networking on edge devices. Zigbee is better suited for larger networks and low-power applications. It offers better scalability and security but with trade-offs such as limited range and slower data transfer rate. Conversely, bluetooth is suitable for smaller networks and high-speed data transfers. It provides lower scalability, with a shorter range and high-power consumption. The choice between zigbee and bluetooth for edge device mesh networking requires consideration of power consumption, scalability, range, and security. The protocol must also be compatible with the devices to be used in the network.

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