WiFi, or 802.11, is a wireless protocol that was built with the intent of replacing Ethernet using wireless communication over unlicensed bands. Its goal was to provide off-the-shelf, easy to implement, easy to use short-range wireless connectivity with cross-vendor interoperability. With zero spectrum cost, there was little focus on spectral efficiency and with expected use by desktop devices, power efficiency was not critical.
WiFi is an obvious choice for IoT connectivity because in-building WiFi coverage is now almost ubiquitous, however it is not always the appropriate choice.
The IEEE addressed these shortcomings by publishing specifications for 802.11ah and 802.11ax:
*WiFi HaLow (802.11ah): WiFi HaLow technology is based on the IEEE802.11ah standard ratified in October 2016. It was introduced specifically to address the range and power concerns of IoT. 802.11ah uses the 900 MHz ISM license-exempt band to provide extended range with low power requirements. Power use is further optimized by using predefined wake/doze periods and provides a reach of over a radius of one kilometer. It allows for station grouping to minimize contention and relay to extend the reach.
However, 802.11ah will require specialized wireless access points (or radios inside the APs) and client hardware. Even though the protocol was ratified in October 2016, there has been very little enthusiasm for WiFi HaLow from chip vendors.
*HEW (802.11ax). The upcoming High Efficiency Wireless (IEEE802.11ax) standard also adds a number of IoT friendly features. It retains the targeted wake time and station grouping features from 802.11ah to allow the clients to be power thrifty and avoid collisions. In addition, the uplink multi-user MIMO capabilities, coupled with the smaller (78.125 kHz) subcarrier spacing, allows up to 18 clients to send data simultaneously within a 40 MHz channel.