If you’re paying attention as you walk around a modern city, it won’t be long before you realise that, in terms of scale, range, and the number of devices per network, smart cities are among the largest Internet of Things (IoT) applications.
From lighting and traffic control to highly localised monitoring of temperature, humidity, and air pollution for smartphone apps, sensors are everywhere. When designing products for these scenarios, the proliferation and density of nodes mean that network reliability hinges on your chosen wireless protocol’s ability to meet these demands.
To this end, consider consider the Wireless Smart Ubiquitous Network (Wi-SUN), a sub-1 gigahertz (GHz), scalable, standards-based wireless mesh network that enables flexible device integration and responsive performance.
For smart city applications such as smart metering, public infrastructure, and environmental monitoring, this low-power, wide-area network (LPWAN) can support long-term deployments.
Why Wi-SUN for large-scale IoT?
Among the many wireless protocols I’ve encountered, Wi-SUN combines several features that align particularly well with smart city networking. First, it operates at sub-GHz frequencies, providing extended coverage and good penetration through building materials, enabling reliable communications in urban environments. This robustness in communication is further supported by Wi-SUN’s mesh networking capabilities.
Unlike the star topology used in Wi-Fi, mesh networking allows devices to relay data through neighbouring nodes. Gateway connections are established through self-organising, self-healing device chains. For widespread critical infrastructure applications, these rerouting mechanisms boost operational resilience when communication paths are disrupted.
Wi-SUN also offers low-latency communication for near-real-time device monitoring and control, along with power-efficient operation for multi-year battery life in duty-cycled sensor and metering applications. Furthermore, built-in security helps protect network access and data integrity through mutual authentication.
Still, Wi-SUN’s foundation in open standards is one of its advantages as smart city networks expand. Standards compliance reduces vendor lock-in and simplifies integration of devices from multiple manufacturers. With rapid IoT adoption and a competitive landscape driving innovation and ever-narrower time-to-market windows, developers need to simplify deployment and long-term network management.
Flexible, intelligent Wi-SUN solutions for long-term installations
For many years, Digi has provided XBee wireless modules for standard and emerging wireless protocols, so it was good to see that it also offers Wi-SUN variants of its XBee wireless modules. For example, the XB-WSB-RM-001 (Figure 1) micro-mount module (for North American markets) is designed for integration into smart city networks. A footprint of just 19 × 13 millimetres (mm) enables compact integration, and the XB-WSB-UM-001 alternative includes a surface-mounted U.FL port for direct connection with compatible antennas.
Figure 1: The XB-WSB-RM-001 Wi-SUN micro-mount module supports Wi-SUN connectivity in compact IoT devices, with integrated Edge intelligence and I/O to support smart IoT nodes. (Image source: Digi)
At the heart of Digi’s Wi-SUN modules is Silicon Labs’ EFR32FG25 system on chip (SoC), which supports custom MicroPython applications to enhance Edge intelligence and device autonomy. Event detection, data pre-processing, and local control workloads can run directly on the XBee module for sensing and control applications such as smart heating and lighting. Sensors and peripherals can connect via GPIO, I2C, SPI, and UART interfaces.
Digi’s Wi-SUN modules also support Bluetooth Low Energy (BLE) connections for remote provisioning and direct communication with nearby BLE sensors. Like many IoT devices, these modules offer an ultra-low-power sleep mode that draws as little as 1.5 microamperes (μA), supporting long battery life and reducing long-term maintenance requirements.
Nevertheless, smart city environments can strain device longevity. Accordingly, Digi specifies its Wi-SUN modules for operation over the temperature range of −40°C to 85°C. With a suitable enclosure, an XBee-based design can support smart city installations in both indoor and outdoor settings worldwide. The Wi-SUN modules feature regulatory approvals for the US, Canada, Europe, India, and Japan, which may simplify regulatory compliance and product development.
Setting up a Wi-SUN network with the Digi ecosystem
While mesh networking does most of the legwork for Wi-SUN data communications, you will still need a gateway to connect to wider networks and the cloud. Digi offers a few solutions for this, but the most versatile is the XH-WS0-CW1-101 XBee Hive Border Router for Wi-SUN (Figure 2).
Figure 2: The XBee Hive Border Router for Wi-SUN provides a bridge between Wi-SUN mesh networks and Cloud platforms for data and fleet orchestration. (Image source: Digi)
The XH-WS0-CW1-101 router supports up to 300 Wi-SUN devices per unit, making it suitable for scaling networks in applications such as smart metering in large buildings. It also provides Wi-Fi, Bluetooth, LTE Cat 1, Ethernet, and RS-232/485 connectivity for network redundancy and simplified, flexible integration with existing infrastructure.
Once your Wi-SUN network is in place, Digi Remote Manager provides an enterprise-grade software platform for securely deploying and managing your fleet. From a single desktop, tablet, or phone, you can:
- Schedule secure firmware updates, ensuring stable performance and network integrity
- Monitor equipment health to aid maintenance efforts and minimise downtime
- Create detailed reports on connection history, signal quality, latency, data usage, packet loss, and more to determine operational success and diagnose issues
- Provide real-time alerts based on raw data or patterns detected through on-module intelligence
Conclusion
Wi-SUN’s use of sub-GHz bands offers significant advantages for large-scale LPWANs, such as those used in smart cities. However, security, mesh networking, and Wi-SUN’s open nature are the defining characteristics for long-term deployment success. With XBee for Wi-SUN modules, the Hive Border Router, and the Digi Remote Manager platform, Digi provides a complete ecosystem for rapid Wi-SUN adoption, enabling engineers to build reliable smart city applications that can be easily scaled as needs evolve.
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