802.11ad Wifi – Whitepapers on 60 GHz Wifi

Wifi in the 60 GHz band has been specified since 2012 in the 802.11ad extension of the IEEE WLAN standard. It has taken a number of years but it seems that products are slowly becoming available now. Heise and Anandtech have been reviewing the Netgear X10 access point here (in German) and here and the Wi-Fi Alliance has begun certifying products. So it’s about time to have a closer look at the technology.

There are three interesting whitepapers I can recommend on the topic. On the physical (PHY) layer, have a look at this R&S whitepaper and a similar one by Agilent. After those whitepapers you probably wonder how things are working on the MAC layer which is answered by this great paper by Hany Assasa and Joerg Widmer. Here’s the ultra short summary:

  • On the PHY, a single carrier data stream with 16-QAM modulation at the high end is used for raw data speeds of around 4 GBit/s. For higher speeds up to 7 Gbit/s, Orthogonal Frequency Division Multiple Access (OFDM) with 355 sub-carriers and 64-QAM modulation at the high end are used. Speeds on layer 3 are, as in the other PHYs, significantly slower!
  • Both PHYs use a bandwidth of 2 GHz. Yes, that’s enormous, that’s 100 times more bandwidth for a single channel than the 20 MHz and 12 times more than the 8 channels 802.11ac wave 2 devices use in the 5 GHz band for a combined 160 MHz channel.
  • At 60 GHz data transmissions must be directional, so beamforming is part of the specification an even part of the PHY name: ‘Directional Multi-Gigabit’ DMB PHY.
  • Signals can’t penetrate walls and must be directional, i.e. they have ‘near-optical’ qualities.
  • In-room coverage over a distance of 10 meters is the main usage scenario.
  • On the MAC layer, things work a bit differently compared to previous PHYs for the 2.4 and 5 GHz band. Transmissions are separated into beacon intervals and each interval has zones which are exclusively used for sending beacons in different directions (due to the directional nature of signals at 60 GHz), for beamforming preparation and for sending data packets.
  • In addition a fast transfer function is part of the standard to continue data transmission in the 2.4 / 5 GHz band when the 60 GHz link suddenly fails. The same functionality can also be used to transfer and ongoing data stream back to 60 GHz when a signal can be detected again.

As noted above, there are only few products supporting 802.11ad so far. However, with 2 access points now available and some client implementations in notebooks as noted in the references above, more might become available soon.