IEEE 802.11ah also called Wi-Fi Halow

Introduction

This article gives a brief overview of the future  IEEE 802.11ah standard, which  is stamped by the Wi-Fi alliance as Wi-Fi Halow, there are many main features as  low energy consumption, the operation frequency in the 900MHz to reach more coverage range, the support of more than 8000 devices belonging to the same Access Point. Showing IEEE 802.11ah as one of the principal candidates to enable the   Internet of Things (IoT) communications.

Now we present the Development line in Table I.

Tabla I. Development line of IEEE 802.11ah

Status of the specification
Release Date
Percentage advance of the standard
Draft 1.02013-11-0473
Draft 2.02014-07-0583
Draft 3.02014-10-2590
Draft 4.02015-02-1493
Draft 5.02015-04-1693

Figure 1. Highlights the comparison in coverage range between distinct technologies

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Figure 1. Coverage range between multiple technologies in typical scenarios

Use cases.

The use cases mentioned by the  IEEE 802.11 ah Task Group are:

  1. Smart sensor and meters.
  2. Backhaul aggregation and extended range hotspot.
  3. Extended range hotspot and cellular offloading.

The most relevant changes of IEEE 802.11ah in respect to the legacy standards, as usual, are made in the PHY and MAC layers of the OSI (Open System Interconnection) model.

PHY layer features.

This near future standard operates at 900MHz frequency as an average data, is well know that each country has its own regulations in the frequency spectrum, Table II illustrate the specific operation frequency of IEEE 802.11ah in the world.

Tabla II. Operational frequency of IEEE 802.11ah around the world

Frequency (MHz)Country
614-787  & 779-787China
863-868,6Europe
915,9-929,7Japan
902-928United States

IEEE 802.11ah standard works with different channel bandwidth for transmissions as 1,2,4,8,16 MHz and similar as the frequency the number of channels are regulated by each country as show Table III.

Tabla III. Number of channels available in different countries for IEEE 802.11ah.

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MAC layer features.

The principal MAC layer features developed in IEEE 802.11ah are:

  • Increase on the supported number of devices linked to an access point, from 2007 to 8191 devices.
  • MAC headers reduction, from 30Bytes to 14Bytes
  • Frame control shortening.
  • The development of a new contention mechanism call Restricted Access Window (RAW).
  • The development of power saving mechanisms allowing an station stay in doze mode up to 7 days.

All of the above features are being developed focused on covering the IoT requirements, making probably to find in the market IEEE 802.11ah hardware in the end of the 2016 or in the start of the 2017.

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