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News about emerging Wi-Fi standards usually focuses on how rapidly a user can download a movie, but Wi-Fi is equally beneficial when throughput isn't the only consideration. Consider IoT, where Wi-Fi signal range -- and not transfer rates -- is most important.
IoT presents a particular opportunity for low-power Wi-Fi. Devices can be scattered across large areas, such as factories or warehouse complexes, with some placed a kilometer or more away from the nearest access point (AP). Managing the devices' power consumption is another issue, as most IoT components are powered by batteries. Because the Wi-Fi technology commonly used in offices and homes is limited to approximately 100 meters, longer-range alternatives are needed.
Lower frequencies permit longer ranges and, equally important, enable signals to penetrate walls and other barriers. While office and home Wi-Fi operates at either 2.4 GHz or 5 GHz, three other protocols -- IEEE-approved 802.11af, 802.11ah and the soon-to-be-approved 802.11ba -- operate in frequencies below 1 GHz. 802.11ah -- also known as Wi-Fi HaLow -- and .11ba have ranges of up to 1 km, while .11af can support the transmission of signals up to 3 km.
802.11af operates in frequencies spaced between TV channels. These frequencies are located between 54 MHz and 590 MHz, which gives .11af a boost over .11ah and .11ba, which operate between 900 MHz and 1 GHz, respectively. The clearest parts of this range will vary by locality, since occupied spectrum is determined by which TV channels are in use and by any other users of these frequencies. 802.11af devices search for the clearest part of the spectrum and configure themselves to operate there.
802.11ah and .11ba can support a data rate of 230 Mbps, depending on channel width and coding scheme, while .11af provides up to 35 Kbps, also based on channel width and coding scheme.
IoT devices don't typically exchange data frequently. The devices may be sensors that track temperature or pressure or devices that report the location of mobile equipment. Keeping radios on consumes power, so both .11ah and .11ba have the means to switch them off when not needed.
802.11ah adds Target Wake Time (TWT), a feature that enables APs to negotiate a transmission time with each device, thus limiting contention. The device's radio stays off until the scheduled time, activates to exchange data and shuts off after the transmission is completed.
Along with supporting TWT, .11ba introduces another power-saving feature, called Wake Up Radio (WUR). TWT schedules transmissions, but in some cases, an AP needs to transmit to a station outside of the allotted time. With WUR, IoT devices use an auxiliary, exceedingly low-power radio to communicate with APs. The radio then listens for a request from the AP to turn on the primary radio for longer, higher-rate transmissions.
Markets and devices
While IoT is the primary market for these low-power Wi-Fi protocols, other uses are possible, including wireless backhaul. In this scenario, phones within range use Wi-Fi instead of the cellular network to make the necessary wired network connections needed to place calls on the internet.
Devices that support .11af and .11ah are now available, and .11ba devices will be finalized in early 2021. As more devices and types of IoT equipment are developed, expect the use of low-power Wi-Fi protocols to undoubtedly increase.