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WiFi has a few notable differences from other wireless technologies. For example, WiFi transmits at frequencies of 2.4 GHz or 5 GHz. These frequencies are much higher than the frequencies used for cellular transmission. Higher frequency means that signals can carry more data.
However, as you now know well, all forms of wireless communication represent a tradeoff between power consumption, range, and bandwidth. So in exchange for high data rates, WiFi consumes a lot of power and doesn’t have a lot of range.
In fact, the longest range WiFi has ever transmitted data is 260 miles. The Swedish Space Agency transmitted data to an overhead stratospheric balloon 260 miles away, but they used non-standard WiFi equipment and 6 watt amplifiers to achieve this.
For your average WiFi router, ranges are much, much shorter and depend on a number of factors. Range can depend on the antenna, reflection and refraction, and radio power output. A range of about 100 ft is common, so if you have thousand of sensors out in a field, WiFi isn’t a great option.
WiFi can be good for IoT applications that don’t have to worry about power drain (e.g. devices that are plugged into an outlet), that need to send a lot of data (e.g. video), and that don’t need high range. A good example would be a home security system.
Like LPWANs and cellular connectivity, there are several versions of WiFi including, 802.11a, 802.11b, 802.11g, 802.11n, and 802.11ac.
Each of these standards comes with various pros/cons related to data speed, signal interference from outside sources, and cost. Cost is a factor because different hardware is needed for different standards, though newer versions are made to be backwards compatible with older versions.
So, while WiFi currently isn’t great for many IoT applications, there are two WiFi standards that have been developed, or are being developed, specifically for IoT; WiFi HaLow (802.11ah) and HEW (802.11ax).
WiFi HaLow was ratified in 2016 and aimed at addressing range and power concerns for IoT applications. HEW (High Efficiency Wireless) is an upcoming standard that builds on HaLow to add additional IoT-friendly features.
As always, it all comes down to your specific application. One of the advantages of WiFi is that it’s a proven and standardized technology that’s already present in many buildings and public areas. However, current instantiations of WiFi lack the necessary range and consume too much power for many IoT applications.