How to prevent dropped communication in critical IoT applications
Jason Tollefson, Microchip Technology
We’ve all had it happen: one minute we are talking on a mobile phone, and the next minute our call dropped, and we are disconnected. We feel inconvenienced when this happens. Perhaps we were in the middle of an important conversation, or worse, we were on a critical call with the police or the fire department.
This experience that we have all shared also applies to the IoT products we design. Whether you are designing a home automation leak sensor, a wireless security system or an industrial process controller, the specter of lost communication will wreak havoc on the user experience and reliability of your application.
Fortunately, there are wireless IoT solutions built for maximum durability, reliability and longevity in the market today. These solutions feature robust meshing technology, low power consumption and sub-GHz frequencies, making them the ideal technology to fight dropped communication.
IEEE 802.15.4 Technology’s Self-Healing Capability
You may know of wireless technologies such as Zigbee, WirelessHART, 6LoWPAN and MiWi. These are all based on the IEEE 802.15.4 standard. A key characteristic of this standard is the ability to form mesh networks that include nodes with separate roles. In these networks there are reduced function devices (RFD), full function devices (FFD) and coordinators. The RFD and FFD devices connect to each other, while the final connection is made with the coordinator or gateway.
Mesh networks have several important attributes for reliable communication; specifically range extension, re-routing and persistence. The reach of an individual radio is extended in mesh networks by enabling node to node communication. In figure 1, each node has a working range of 10 meters, but with meshing, the reach of the network is extended to 30 meters.This ability to extend range increases communication reliability by ensuring that nodes are “in-range” and networks are preserved.
Figure 1 – Range Extension in Mesh Networks
A second key attribute of mesh networks includes re-routing, or self-healing. Many of you have experienced an unexpected event while driving a car - perhaps a highway exit is closed for repairs, or an unfamiliar street takes you in the wrong direction. In these situations, we usually turn to our mobile phone’s mapping app, which typically offers an alternative route. That is the idea behind 802.15.4 mesh network re-routing.
In wireless networks, there are many issues that arise, such as dead batteries, temporary interference caused by human movement, permanent interference caused by changes in the environment, new nodes being introduced into the network and more.When these disturbances occur, mesh networks based on the 802.15.4 standard can self-heal. In other words, the connection from the node to the coordinator can be re-routed through a different FFD that offers a more optimal path. This feature dramatically improves the strength of the network and therefore the reliability of the communication.
A third benefit of nodes in 802.15.4 mesh networks is persistence. Unlike network technologies such as Ethernet or Wi-Fi which “age-out” uncommunicative nodes within the network, 802.15.4 networks feature permanent membership, allowing nodes to stop communicating for extended periods of time. A node may sleep for a week, then wake, immediately join the network and transmit data - in as little as 30 milliseconds. This is a tremendous advantage for power consumption. Transmitting and listening functions consume most of the power in IoT devices, therefore this feature greatly reduces the ratio of radio-to-sleep activity.
Frequency Matters for Reliability
There is an inverse relationship between radio carrier frequency and its ability to penetrate solid objects in the immediate environment. The most highly used frequency today is 2,4 GHz. This is the frequency used throughout our homes for Wi-Fi, Bluetooth and microwave ovens. This frequency band is known for its high data rate transmission, but due to the relatively poor penetration that 2,4 GHz offers over lower frequency bands, it’s also likely to run into coverage issues throughout the home. However, the unlicensed 800/900 MHz bands offer superior penetration ability, at lower data rates, when used in environments with solid objects such as walls, trees, furniture and doors.Therefore, sub-GHz frequencies offer superior performance when looking to build a network that can perform well in harsh or confined environments.
Figure 2 illustrates the powerful combination of sub-GHz frequencies with mesh networking technology.
OK, I Hear You Now
By combining the excellent penetration of sub-GHzs with 802.15.4 mesh networking, the communication network is loud and clear. The signal is routed to the coordinator through the best path, infiltrating barriers, recovering from changes in the environment and preserving its power until it needs to send data. This combination results in a robust, reliable and long-life communication network.
Deploying Robust IoT
Today, most 802.15.4 radios are based on 2,4 GHz and only take advantage of a few benefits we previously discussed. Products, like Microchip’s ATSAMR30 family of microcontroller units (MCUs), are integrated with IEEE 802.15.4 compliant radio for the sub-1 GHz frequency bands. There is a small module that can be easily implemented into applications offering regulatory certification for North America, Europe and China. With 256 KB of flash, the ATSAMR30 devices can easily run mesh stacks such as MiWi, while still accommodating application code for security, home automation, lighting and metering applications.
Staying in Touch
It’s important to communicate clearly and reliably, especially when the information can be life-changing. By using mesh networks based on 802.15.4 and sub-GHz frequencies, nodes will stay reliably connected within the IoT network. Networks like those offered in the ATSAMR30 family of MCUs with sub-GHz radio help ensure critical pieces are in place for information to be reliably transferred in changing environments when needed, all while sustaining long battery life.
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