IEEE802.11ah, better known as Wi-Fi HaLow, is a wireless communication standard designed specifically to address the requirements of Internet of Things (IoT) devices. Introduced in 2016, it remained relatively obscure for years. However, the continuously growing market for smart devices has led to a resurgence of interest in this IoT-centric wireless technology.
Of course, it’s easy to say that Wi-Fi HaLow is “designed for IoT requirements.” What we really need to know is how, and how well, it addresses these requirements. In this article, we’ll go over the basics of Wi-Fi HaLow and how it compares to other wireless options. At the end, we’ll review some real-world applications for which Wi-Fi HaLow is potentially a good fit.
To start us off, Figure 1 provides a quick list of Wi-Fi HaLow’s features and benefits.
Figure 1. Overview of Wi-Fi HaLow and its benefits. Image used courtesy of Wi-Fi Alliance
In addition to the features listed above, it’s worth noting that up to 8,191 devices can be connected at a time to a single Wi-Fi HaLow access point. As for items that are on the list, a few of them—using Wi-Fi security, for example—can apply to any Wi-Fi certified product. We’ll pass over these in favor of discussing what makes Wi-Fi HaLow distinctive, starting with its frequency of operation.
Wi-Fi HaLow vs. Traditional Wi-Fi: Operating Frequency
Depending on the specific standard, traditional Wi-Fi operates at frequencies ranging from 2 GHz and 6 GHz. By contrast, Wi-Fi HaLow operates in the sub-1GHz frequency band. The exact frequency range varies by country—in the United States, it’s between 902 MHz and 928 MHz.
When compared to higher-frequency operation, operating below 1 GHz grants the following advantages:
- A less crowded spectrum.
- Greater maximum transmission distance.
- Better signal penetration.
- Lower power consumption.
The disadvantage of this frequency band is that it limits bandwidth, which also translates to a limited data rate. Wi-Fi HaLow does have a higher data throughput than LoRaWan, as we’ll see in the next section. Still, it may work better as a complement to traditional Wi-Fi networks than as a replacement. The frequency difference between Wi-Fi HaLow and other Wi-Fi types reduces the risk of interference if they’re used side-by-side.
Wi-Fi HaLow vs. LoRaWAN: Range and Data Rate
In theory, LoRaWan can cover distances of hundreds of kilometers. In practice, it’s used to cover distances of about 5 km. Wi-Fi HaLow is designed to work in a range of 1 km, though it’s possible to extend the area of coverage further by deploying the network in a mesh configuration. Even with that taken into account, LoRaWAN still has the greater range.
On the other hand, Wi-Fi HaLow represents a large increase in speed. LoRaWAN works from 250 bps to 22 Kbps. As Figure 2 illustrates, Wi-Fi HaLow’s data throughput ranges from 150 Kbps over long distances to 78 Mbps at short range. Note that these numbers assume a single spatial stream—Wi-Fi HaLow can use up to four.
Figure 2. Data rate vs. distance for Wi-Fi HaLow and other IoT communication standards. Image used courtesy of Wi-Fi Alliance (pdf, sign-in required)
This difference in data rates makes a difference to potential applications: unlike LoRaWAN, Wi-Fi HaLow can be used to transmit video. It’s often discussed in the context of wireless security cameras.
Data Rates and Modulation
The two preceding sections compared Wi-Fi HaLow with other wireless technologies. Now let’s examine it on its own merits, starting with a slightly more detailed look at data throughput.
Wi-Fi HaLow uses the following types of data modulation:
- Binary and Quadrature Phase Shift Keying (BPSK and QPSK).
- 16, 64, and 256 Quadrature Amplitude Modulation (QAM).
The modulation and coding scheme (MCS) index for Wi-Fi HaLow includes 11 total options. Of these, MCS 0 through MCS 8 can use 1 MHz, 2 MHz, 4 MHz, 8 MHz or 16 MHz channels. MCS 9, which gives us the highest data rate, works on any of these bandwidths except for the 2 MHz channel. Finally, MCS 10 (which represents the minimum data rate and maximum transmission range) runs only on the 1 MHz channel.
If you’re interested in learning more, the full MCS index for Wi-Fi HaLow is included in a 2021 Wi-Fi Alliance white paper titled “Wi-Fi CERTIFIED HaLow™ Technology Overview.” Note that you’ll have to either sign into their website or create a guest account to view this. For the dedicated, the signup-averse, and people who really like spreadsheets, MCSindex.net provides a more extensive version of the index that includes numbers for multiple (up to four) spatial streams.
The key thing to understand is that there’s a trade-off between data rate and maximum transmission distance, and another between data rate and power consumption. Wi-Fi HaLow’s wide range of data rates and modulation options—and the ability to tune them—allows the user to customize these trade-offs to meet the requirements of different applications.
Power Consumption
For battery-powered IoT devices, power consumption is a major consideration. The more power is consumed by the device’s wireless connection, the more often its battery needs to be replaced. This is both a cost and a reliability issue—if the battery is dead, the device can’t transmit, and data is lost. Plus, having to constantly trek out to the location of a sensor and replace its battery is no fun at all.
Wi-Fi HaLow is intended for use with exactly those kinds of devices, so it tries to keep power consumption down. It does this quite well. We mentioned one reason—its low frequency of operation—near the beginning of the article.
It’s not just the frequency band that makes a difference, however. Figure 3 compares device battery life for five different sub-1-GHz wireless technologies, including Wi-Fi HaLow (IEEE802.11ah). This figure comes from an IMEC research presentation on the topic, the slides of which are available here.
Figure 3. Battery lifetime comparison for different sub-1-GHz wireless technologies. Image used courtesy of Jeroen Famaey
As you can see, Wi-Fi HaLow provides the best battery life of the five options.
Contributing to this performance are Wi-Fi HaLow’s multiple power-saving modes. These reduce the amount of time that devices must spend awake in order to not be dropped by the access point and require re-authentication. For the specifics of Wi-Fi HaLow’s energy saving features, please refer to the Wi-Fi Alliance white paper linked to in the previous section.
Wi-Fi HaLow: What Is It Good For?
At this point, we should have a pretty good idea of Wi-Fi HaLow’s strengths. To recap, it offers:
- Low power consumption; extended battery life for connected devices.
- Mid-to-long range data transmission.
- High enough data throughput to transmit video over relatively long distances.
- Options for adjusting the data rate based on application requirements.
- Simultaneous connection from one access point to many devices with differing requirements.
- High signal penetration, useful for networks with no direct line of sight between nodes.
- An operating frequency that won’t interfere with higher-speed Wi-Fi networks in the same vicinity.
So, how does this translate to real-world applications? We mentioned remote security cameras earlier in the article, but Wi-Fi HaLow also has potential for use in smart buildings and smart agriculture.
Both industrial buildings and agricultural facilities use extensive networks of remote sensors and actuators. Wi-Fi HaLow provides good scalability, and the sensors and actuators benefit from its energy efficiency. Meanwhile, long range and high signal penetration means better connection with nodes that are not only far away but also separated from the access point by walls or dense vegetation.
For more details about Wi-Fi HaLow applications, I suggest the following white paper from the Wireless Broadband Alliance: “Wi-Fi HaLow for IoT: Field Trials Report.” Published in July 2024, it’s a great deal more recent than the Wi-Fi Alliance technology overview. However, as with the Wi-Fi Alliance paper, you will have to sign in or create a free account to access it. Whether you choose to look further into Wi-Fi HaLow or not, I hope you’ve found this article informative.
Featured image used courtesy of Adobe Stock
