Wi-Fi HaLow™—Worth the wait
April 15, 2021 by Kevin Walsh
You have probably heard it before: “Anything worth having is worth waiting for.”
It has certainly been a while since the IEEE balloted the 802.11ah specification—branded Wi-Fi HaLow™ by Wi-Fi Alliance®—so waiting has been the order of the day. But now we can see that Wi-Fi HaLow is finally at hand. No one imagined that when the IEEE definition process for 802.11ah started it would take nearly 10 years to get to this point, but new standards often take time to mature.
During this time, IoT use cases have solidified and many technologies have entered the arena to fulfill the need, including Bluetooth adding meshing for greater range, LoRa and SigFox for Low Power Wide Area (LPWA) IoT wireless options, and Wi-Fi 4, Wi-Fi 6, and Wi-Fi 6E for IoT in Local Area Networks (LANs).
So why Wi-Fi HaLow? What makes Wi-Fi HaLow worth the wait? In a simple sentence, Wi-Fi HaLow may just be the IoT wireless standard offering the best combination of range, throughput, density, low-power operation, and deployment costs. Not perfect, certainly, but pretty close.
First let’s discuss range. Wi-Fi HaLow uses a sub-gigahertz (S1G) wireless radio operating in a frequency range between 750 MHz and 928 MHz. Simply put, when talking range, “it’s the physics.” S1G transmissions travel farther. The lower the frequency, the less path loss, the farther the signal travels. Wi-Fi HaLow also uses narrowband channels, so although it uses low-power transmission, that transmission is focused, providing power exactly where needed. This means both a better link budget and better attenuation characteristics. Wi-Fi HaLow transmits farther and passes through materials better than higher frequency wireless transmissions. And of course, antenna and positioning options can improve the range as well. One additional benefit is that, because Wi-Fi HaLow uses the S1G spectrum, it frees up 2.4 GHz, 5 GHz and the new 6 GHz spectrum for high-efficiency applications. Fewer devices contend for valuable spectrum.
Now on to throughput. Wi-Fi HaLow supports a rich set of modulation and coding schemes (MCS), including binary phase shift keying (BPSK), quadrature phase shift keying (QPSK) and 16 to 256 quadrature amplitude modifications (QAM). From simple to sophisticated MCS 0-9, as well as the newly defined and simplest MCS 10, Wi-Fi HaLow provides scalable throughput options to meet the varied conditions found in “real-world” IoT networks. Wi-Fi HaLow provides a range of data rates depending on the MCS used, from 150 kbps using MCS 10 with BPSK modulation, to a top rate of 4 Mbps using MCS 9 at 256 QAM, with a single spatial stream at the narrowest bandwidth of 1 Mhz. Additionally, Wi-Fi HaLow supports both wider bandwidths and up to four spatial streams, further adding to the top data rate, which can support video applications at many hundreds of meters. The maximum data rate with four spatial streams using 4 MHz tops out at 80 Mbps.
So, what exactly is meant by density in the context of a “practically perfect” network IoT protocol? In the case of Wi-Fi HaLow, density, or network density, relates to the number of separate devices that a single access point (AP) can support. Wi-Fi HaLow expands the Association IDentifier (AID) parameter to 13 bits, allowing the AP to manage up to 8,191 devices. Wi-Fi HaLow uses a novel hierarchical structure made up of “pages,” “blocks,” “sub-blocks” and station (STA) “indexes,” currently unique in the Wi-Fi® world. This structure can be an effective way to categorize STAs with respect to their type of application, battery level or required Quality of Service (QoS) by limiting the number of STAs in a high-priority group. Although there are practical limits to managing any network, Wi-Fi HaLow allows an AP to approach those limits depending on the implementation and the nature of the network it supports.
Wi-Fi HaLow builds on the Power Saving Modes (PSM) of traditional Wi-Fi. For applications that are very low duty cycle, edge devices using Wi-Fi HaLow can remain in deep sleep, saving valuable battery power. A Max Idle setting determines when an edge device wakes up to listen. Wi-Fi HaLow devices can also use a feature called Target Wake Time (TWT), where the AP and the STA set specific times for the edge device to awaken and exchange data. The TWT feature has made its way into Wi-Fi 6, along with a feature first defined in 802.11ah called BSS Coloring. BSS Coloring allows devices to communicate more efficiently to their nearest AP, or associated AP, alone, reducing contention and eliminating the power consumed by redundant communication due to crowded spectrum. Wi-Fi HaLow also saves power by shortening the header sizes, thereby reducing the transmission overhead. The net result is that Wi-Fi HaLow can extend the lifetime operation of battery-operated edge devices, reducing overall operating costs. Power efficiency drives both better network utilization and lower cost.
Cost of deployment
Now let’s expand the discussion to one all-important metric: cost of deployment. From the beginning 802.11ah was specified to use a low-complexity radio, saving valuable silicon area. This simplifies both the packaging and test. Wi-Fi HaLow inherits these characteristics, and this results in lower cost silicon. Next, because Wi-Fi HaLow is an open standard, the expectation is that the ecosystem will grow, reducing the total cost of deploying and operating a network over time. Further, there are no data usage charges. Wi-Fi HaLow can be deployed alongside Wi-Fi 6. Large enterprises, service providers, Small Office/Home Office and individual households will have minimal buildout and operational costs. Simple arithmetic shows that a key objective of connecting billions of IoT devices is to address cost. Lowering the deployment and operational costs magnifies the return on investment and makes the cost-benefit analysis lean toward connecting everything where those benefits drive positive outcomes or usage enjoyment. Edge device silicon for Wi-Fi HaLow will become very cheap over time.
I hope you will agree Wi-Fi HaLow was worth the wait. Wi-Fi Alliance expects to begin device certification in Q4.
Kevin Walsh joined Palma Ceia SemiDesign in 2016 and has more than 25 years of experience in the Semiconductor, IP, and EDA industries. He has an extensive background in product marketing, including strategic and tactical marketing, both planning and operations, mergers and acquisitions, establishing distribution channels, and joint marketing partnerships. Most recently he worked for Faraday Technology as Vice President of Strategic Marketing. Other previous roles include serving as Vice President of Marketing and Director of Marketing at Gennum's Snowbush group, Semtech, and inSilicon, later acquired by Synopsys. His startup experience includes as a founder and Executive Vice President at Sapphire Design Automation, as well as Vice President of Marketing at Simplex Solutions. He holds a Bachelor of Science degree in Electrical Engineering and Computer Science from the University of California, Berkeley, and an MBA from Pepperdine University.