Wi-Fi HaLow

In recent years, Internet of Things (IoT) technologies have been rapidly developing, and along with them, the demands on the wireless communication technologies they use have increased: thousands of “smart” devices—from industrial sensors to urban monitoring devices—must exchange data over both short and long distances quickly, reliably, and energy-efficiently. To address these challenges, a new Wi-Fi standard was introduced in 2016: IEEE 802.11ah, known as Wi-Fi HaLow. To meet the requirements of IoT applications, Wi-Fi HaLow operates in the sub-gigahertz frequency band (~900 MHz), which allows the coverage radius to extend up to several kilometers, supports simultaneous connections for more than eight thousand devices, and introduces new mechanisms for fast, reliable, and energy-efficient data transmission.

The Wireless Networks Laboratory actively studies the key mechanisms of Wi-Fi HaLow—Restricted Access Window (RAW), Target Wake Time (TWT), and fast association mechanisms (Distributed Authentication Control, DAC, and Centralized Authentication Control, CAC). Using the RAW mechanism, sensors can transmit data within specially allocated time intervals that are inaccessible to other devices. This isolation helps sensors transmit data more quickly and reliably. Using TWT, sensors can enter “sleep mode” outside these intervals to save energy. Optimizing the schedules and durations of these intervals, as well as grouping sensors, is a non-trivial task. Laboratory researchers addressed this challenge using mathematical modeling methods and identified optimal parameters for the RAW and TWT mechanisms, achieving the best metrics—for example, average latency, energy consumption, or their percentiles—under a given constraint on the proportion of channel time used. These results can be used by manufacturers as practical guidelines for deploying Wi-Fi HaLow networks and configuring TWT and RAW mechanisms.

A separate challenge concerns network association. Although IoT networks often include a large number of devices, an access point can manage data transmissions in the network using an efficient schedule through TWT and RAW mechanisms. However, a problem arises, for example, if the access point is rebooted and all devices must attempt to associate with the network simultaneously. In such a scenario, the access point initially has no information about the stations and cannot generate a proper transmission schedule. To address this, Wi-Fi HaLow includes CAC and DAC mechanisms, but the standard does not specify how to use these mechanisms or which parameters to select depending on the scenario. To solve this problem, Laboratory researchers studied these mechanisms and their applicable scenarios, and for the CAC mechanism, they also developed an adaptive algorithm for managing the association process, capable of efficiently servicing any number of associating devices.

It should be noted that solutions developed based on mathematical modeling require validation on real hardware before implementation in user devices. Currently, Laboratory staff are engaged in the practical implementation and optimization of the RAW mechanism on real devices and are working on synthesizing the theoretical and practical knowledge obtained.

List of relevant papers: