A look at IEEE 802.11ah: Wi-Fi below 1 GHz

August 26, 2015 //By Kevin Qian and Mingyan Wang
A look at IEEE 802.11ah: Wi-Fi below 1 GHz
Kevin Qian and Mingyan Wang examine the key issues of the IEEE 802.11ah standard

The IEEE 802.11 working group is defining a new standard called 802.11ah. It operates in sub 1 GHz license-exempt bands, providing a much improved transmission range and can also be used for large scale sensor networks with low power consumption targeting for billions of IoT (Internet of Things) or M2M (Machine-to-Machine) device connections. 802.11ah is based on down-clocking of the 802.11ac standard and adds some enhancements in PHY and MAC layers such as power saving, large number of station support, better coverage, and mobile reception. This standard is still in the draft status, with a final version expected in 2016. The Wi-Fi Alliance has also begun to define certification programs based on 802.11ah.

IEEE 802.11 Wireless Local Area Network (WLAN) is mainly operated in the 2.4 GHz and 5 GHz frequency bands. However, these high-frequency bands limit the transmission range of 802.11n and 802.11ac for outdoor environments. Learn the basics of 802.11ah and about some of the test challenges.

Use Cases

In general, there are three use case categories for 802.11ah: sensor networks, backhaul networks for sensors and meter data, and Wi-Fi extended range networks. Large coverage, low power consumption, native IP support and large numbers of device support are the main advantages for 802.11ah. It's characteristics include:

  1. 802.11ah can extend the range with 1 MHz and 2 MHz mandatory modes;
  2. There are some enhancements in 802.11ah PHY and MAC layers designed to achieve ultra-low power consumption and multi-year battery life for large scale sensor networks, optimized for small packet size and long sleep time;
  3. 802.11ah sensor is native IP support;
  4. Up to 8,191 devices associated with an AP (access point) through a hierarchical identifier structure.

Figure 1 shows an example of sensor networks in a future smart home. In this application, an AP (access point) with 802.11ah technology is placed indoors. A large number of devices such as temperature sensors, light sensors, and smart meters are deployed throughout the home, enabling home devices and appliance to be "smart."

Figure 1: 802.11ah will cover a greater distance than 801.11ac in smart home environment.

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