Advantages of Adding LFN Nodes to Wi-SUN Networks: A Smart Solution for Smart Cities

Wi-SUN is a wireless communication standard that enables interoperable, secure, and scalable networks for smart city applications. It supports various services such as smart metering, smart lighting, smart parking, smart waste management, and more. Wi-SUN networks are composed of different types of nodes that have different roles and capabilities. In this blog, we will focus on one specific type of node: the limited function node (LFN).

What is the Current Market Challenge?

Network operators are looking for ways to add additional functionality to their networks to expand use cases and increase the return on investment to deploy those networks. In the case of Wi-SUN deployments, the easiest way to do this is by adding additional nodes and functionality to the network allowing for the expansion of use cases beyond line-powered devices. Devices like gas or water meters, parking meters, or sensors are typically battery powered and create a logical extension of networks that are being created using streetlights and electric meters. These battery-powered devices create synergies for utility companies, municipalities, or other network owners but the initial roll out of the Wi-SUN FAN did not have any mechanism to support these types of devices.

What is a Low Energy Node?

A low-energy node, or LFN is a device that has limited functionality and resources compared to a full function node (FFN). An FFN is a device that can act as a router, relay, or coordinator in a Wi-SUN network. An LFN, on the other hand, is a device that can only act as an end device or a leaf node in a Wi-SUN network. An LFN cannot route or relay packets for other nodes. An LFN can only communicate with its parent node, which is usually an FFN.

Why Use a Limited Function Node or LFN?

LFN devices are designed to be low cost, low power, and long -lasting. They are ideal for applications that require simple and secure reliable data transmission over long distances and harsh environments. Some examples of LFN devices are:

• Smart meters: These devices measure and report the consumption of gas, water, or other utilities, but unlike electric meters are typically battery powered and expected to last 10-20 years without a battery change.
• Smart sensors: These devices monitor and report various environmental parameters such as temperature, humidity, air quality, noise level, etc. Typically installed in hard-to-reach locations, these sensors need to operate reliably with minimal maintenance or interaction.
• Smart actuators: These devices control and operate various devices such as valves, switches, motors, etc. Things like irrigation systems or solar panel arrays can take advantage of already deployed networks to add control and monitoring without any additional infrastructure cost.

Features for Wi-SUN FAN 1.1 and LE Nodes

Wi-SUN FAN 1.1 brings many changes to the Wi-SUN standard meant to improve performance and reliability while also adding support for LE Nodes. Some of the major changes include:

• OFDM Modulation: The addition of OFDM support to Wi-SUN networks allows for increased data rates for support of things like over-the-air update while also improving overall network performance and lowering network congestion.
• Multicast Support: This allows for devices on the network to send messages to, or receive messages from, multiple nodes at the same time. This further reduces network congestion and lowers overall latency by allowing for a single transmission rather than multiple.
• Backward Compatibility: Newly deployed FAN 1.1 devices will be able to communicate and operate on already established FAN 1.0 networks. This ensures that older devices can remain in the field and operational while newer devices are added to the infrastructure.

LFN devices have several features that enable them to work efficiently and reliably in Wi-SUN networks. Some of these features are:

• Low power consumption: LFN devices use batteries or energy harvesting techniques to power themselves. They also use low-power radio modules that consume less energy than conventional ones.
• Long battery life: LFN devices can last for years without requiring battery replacement or recharging. They achieve this by using sampled listening techniques that reduce their radio activity and power consumption.
• Sampled listening: LFN devices listen to the channel periodically instead of continuously. They synchronize their listening intervals with their parent node using beacon frames. This way, they can save energy and avoid collisions with other nodes.
• RPL Unaware Leaf (RUL) mode: LFN devices can operate in RUL mode, which means they are unaware of the routing protocol used by the Wi-SUN network. RUL mode simplifies the implementation and configuration of LFN devices. It also reduces the overhead and complexity of the network.

What are the Benefits of Using a Limited Function Node or LFN?

LFN devices offer several benefits for end users, network operators, and device manufacturers. Some of these benefits are:

• For end users: LFN devices provide reliable and secure data transmission for various smart city services. They also reduce the operational and maintenance costs of these services by extending the battery life and reducing the need for human intervention.
• For network operators: LFN devices increase the scalability and robustness of Wi-SUN networks by adding more nodes without affecting the performance or quality of service. They also improve the network efficiency and coverage by using OFDM modulation and multicast support.
• For device manufacturers: LFN devices lower the production and development costs by using standardized and interoperable components and protocols. They also increase the market potential and customer satisfaction by offering compatible and flexible products.

What are the Challenges and Solutions of Using an LFN?

LFN devices face some challenges that will be addressed by the Wi-SUN FAN 1.1 specification. Some of these challenges are:

• Scalability: LFN devices need to be able to join or leave the network dynamically without affecting the network stability or performance. They also need to be able to handle large volumes of data from multiple sources or destinations.
• Interoperability: LFN devices need to be able to communicate with different types of nodes from different vendors or manufacturers. They also need to be able to support different applications and services with different requirements and preferences.
• Backward compatibility: LFN devices need to be able to work with existing or legacy nodes that use previous versions of Wi-SUN standards or protocols. They also need to be able to upgrade or update their firmware or software without disrupting their functionality or connectivity.

Silicon Labs Wi-SUN Portfolio

Silicon Labs has been developing solutions for industrial and commercial applications for more than a decade and has a long track record of leading the development of the Wi-SUN standard. Silicon Labs offers a portfolio of Wi-SUN certified ICs that support both FSK and OFDM modulations, as well as a full range of reference designs and development tools.

One of the products that supports Wi-SUN is the EFR32FG25 sub-GHz wireless SoC, which is a Series 2 SoC that integrates a high-performance radio, an ARM Cortex-M33 core, and a 1920 KB flash memory. It supports Wi-SUN FAN 1.1 specification and RPL Unaware Leaf (RUL) mode for Limited Function Nodes (LFN) devices. With support for OFDM, FSK, and O-QPSK PHYs, the FG25 is optimized for routing and line powered nodes.

Another product that supports Wi-SUN is the EFR32FG28 sub-GHz wireless + 2.4 GHz BLE SoC, which is a Series 2 SoC that combines a 2.4 GHz transceiver, an ARM Cortex-M33 core, and a 1024 KB flash memory. It also supports Wi-SUN FAN 1.1 specification and RUL mode for LFN devices. The FG28 is ideal for low power LFN applications due to its low active and sleep currents and superior RF performance.

Silicon Labs’ Wi-SUN portfolio enables mixed network implementations with both EFR32FG25 and EFR32FG28 devices, as they are compatible and interoperable with each other and with other Wi-SUN certified nodes. This allows network operators to deploy flexible and robust networks that can support various smart city services such as smart metering, smart lighting, smart parking, smart waste management, and more.

Living Lab: Real-world Implementation of the Wi-SUN Network

Silicon Labs is the first corporate founding partner for IIIT Hyderabad’s Smart City Living Lab, which provides an R&D ecosystem for next-generation technologies designed to improve safety, sustainability, energy efficiency, and overall quality of life in densifying cities. The Living Lab is a project that aims to demonstrate the benefits of Wi-SUN technology in a real-world environment. LFN nodes will be deployed in the test network by the end of the year and Silicon Labs’ active role in the Smart City Living Lab will witness next-generation technologies – being designed in India for the world – to improve safety, sustainability, energy efficiency, and overall quality of life in densifying cities.

Wi-SUN LFN nodes are smart devices that have limited functionality and resources compared to FFN nodes. They are designed to be low-cost, low-power, and long-lasting. They are ideal for smart city applications that require simple and reliable data transmission over long distances and harsh environments.

Wi-SUN LFN nodes have several features that enable them to work efficiently and reliably in Wi-SUN networks, such as low power consumption, long battery life, sampled listening, and RPL Unaware Leaf mode. They also offer several benefits for end users, network operators, and device manufacturers, such as reliable and secure data transmission, reduced operational and maintenance costs, increased scalability and robustness, improved network efficiency and coverage, lower production and development costs, increased market potential and customer satisfaction.

The latest Wi-SUN FAN 1.1 standard will improve LFN nodes by enabling multicast, OFDM, and FAN 1.0 backward compatibility. Silicon Labs’ EFR32FG25 and EFR32FG28 devices support the latest Wi-SUN FAN 1.1 specifications. With proven reference designs, certified stack and PHYs, and a flexible wireless MCU portfolio, Silicon Labs gives designers a single platform to meet the needs of any Wi-SUN device.