Something not often brought up when discussing the Internet of Things (IoT) is Machine to Machine (M2M) communications. According to Gartner:

“Machine-to-Machine Communications is used for automated data transmission and measurement between mechanical or electronic devices. The key components of an M2M system are: Field-deployed wireless devices with embedded sensors or RFID-Wireless communication networks with complementary wire-line access.”

Why even mention M2M? That’s simple. M2M devices are expected to account for most of the digital traffic traversing the IoT.

Current methods of communicating

M2M devices are typically grouped into wireless sensor networks (WSNs) and communicate using Zigbee, 802.15.4, 6LoWPAN, Bluetooth, Wi-Fi, or proprietary radio solutions. If access to the internet is required that can be handled through the facility’s internet connection as Gartner alluded to, or if the WSN is in a remote location, mobile (GPRS/EDGE) or satellite networks can provide the internet gateway.

Current methods are lacking

The fact that several communication technologies are currently being used is indicative of a problem. Device manufacturers are trying to make do with existing communication protocols that do not meet the operational requirements of M2M. Having multiple protocols also hampers standardization.

As for internet gateways, mobile and satellite communications have node and bandwidth limitations that make them less than good choices for internet backhaul. There is some good news: The 3rd Generation Partnership Project (3GPP) is working towards supporting M2M applications on 4G broadband mobile networks, such as UMTS and LTE, with the goal of embedding M2M communications in the upcoming 5G systems.

What about 802.11?

Why not use Wi-Fi, in particular, 802.11ac? The authors of the paper IEEE 802.11ah: The Wi-Fi Approach for M2M Communications (PDF) have two good reasons why the present 802.11 technology is inadequate:

  • Absence of power-saving mechanisms: The energy constraints of sensor networks are not considered in the current IEEE 802.11 standard.
  • Unsuitable bands: Due to their short wireless range and high obstruction losses, existing Wi-Fi bands require the use of intermediate nodes, adding complexity to the network.

New 802.11 standard

In 2010, some forward-thinking people at the Institute of Electrical and Electronics Engineers (IEEE) decided to create the 802.11ah Task Group (TGah). The intent of the IEEE’s task group is to eliminate the capability and capacity gaps that now exist.

The 802.11ah research paper’s authors state, “TGah deals with the specification of an unlicensed sub-1GHz worldwide wireless local area network (WLAN) standard for future M2M communications supporting a wide set of scenarios based on a large number of devices, a long range and energy constraints.”

The requirements defined by IEEE 802.11ah to support M2M communications are as follows:

  • Up to 8,191 devices associated with an access point (AP) through a hierarchical identifier structure
  • Carrier frequencies of approximately 900 MHz (license-exempt) that are less congested and guarantee a long range
  • Transmission range up to 1 km in outdoor areas
  • Data rates of at least 100 kbps
  • One-hop network topologies
  • Short and infrequent data transmissions (data packet size approximately 100 bytes and packet inter-arrival time greater than 30 s)
  • Very low energy consumption by adopting power saving strategies
  • Cost-effective solution for network device manufacturers

Kevin Qian and Mingyan Wang of Keysight Technologies, in this EE Times article, write, “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.”

Increasing coverage to one kilometer is significant. That requirement will eliminate the need for mobile or satellite backhaul more often than any of the other WSN technologies.

It will be interesting

Wi-Fi’s current limitations take it out of consideration for M2M communications. IEEE’s 802.11ah and its improved energy-saving, better coverage, ability to simultaneously handle over 8,000 nodes make it a viable choice.

Qian and Wang note the standard is still in draft form, and the final version is expected in 2016. Even with the Wi-Fi Alliance already working on 802.11ah certification programs, the question becomes: Will that be soon enough to convince vendors to use Wi-Fi?

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