# IEEE 802.11ad

## Summary


In scenarios where we desire throughput in excess of 1 Gbps and low latency, such as in home or office environments, we still use wires. At least, there wasn't a suitable Wi-Fi protocol to cater to these scenarios until IEEE 802.11ad was conceived.

IEEE 802.11ad is a protocol for very high data rates (about 8 Gbps) for short range communication (about 1-10 meters) at the 60 GHz unlicensed band. Because of its 60 GHz operation band, 802.11ad complements but does not interoperate at the PHY layer with 802.11ac at 5 GHz band. This standard is also called **Directional Multi-Gigabit (DMG)**. Commercially, the term **WiGig (Wireless Gigabit)** is common. 

Vendor support for IEEE 802.11ad has been growing since 2016. This standard has an evolution path towards IEEE 802.11ay, which also operates in the 60 GHz band.

## Discussion

### What are the typical use cases for 802.11ad?

We are surrounded by gadgets at home, office and even in our daily commutes. Content is also media rich and there's a need to stream HD videos or play interactive games. Wires are one option but going wireless would be lot more convenient. Think about connecting your laptop to a projector; or connecting Blu-ray player to HDTV; or sharing content from one phone to another; or playing a virtual reality game with wireless controls. 

IEEE 802.11ad enables us to get rid of wires in homes and offices. It can be used for wireless docking, display, entertainment, instant file transfers, HD media streaming, AR/VR apps, and more. In general, applications that require high bandwidth (> 1 Gbps) and low latency (~ 10 us) can benefit from 802.11ad. With 802.11ad, it becomes possible to connect without wires consumer electronics devices, handheld devices and personal computers. 

This standard is ideal for short range line-of-sight (LOS) connections, although non-LOS is possible due to multiple antennas. It could also see usage in public Wi-Fi infrastructure and small cells backhaul.  


### What frequency bands are used by 802.11ad?

Previously, in the 802.11-2016 standard, 802.11ad had four channels in the range 57-66 GHz. Today, IEEE 802.11ad operates in the 57-70 GHz frequency range. Six channels are available with each having a nominal channel bandwidth of 2.16 GHz. Channel 2 (59.40-61.56 GHz) is available in all regions and is considered as the default channel. 

Channel bandwidth of 2.16 GHz is a lot of spectrum, thus allowing 802.11ad to offer multi-gigabit speeds. Comparatively, the most that 802.11ac Wave2 can offer is 160 MHz via channel bonding. 


### What are some technical details or parameters of 802.11ad?

At the PHY layer, 802.11ad has three modes: Control, Single Carrier (SC), and OFDM. Later, OFDM mode was made obsolete. There's also the optional Low-power Single Carrier mode for mobile devices. 

802.11ad does not support spatial multiplexing such as MIMO. It supports a single spatial stream on a single channel. However, it supports **beamforming** for spatial separation and directional operation. Up to 32 antennas are possible. 2 Gbps at 100 feet LOS is possible. 

A variety of modulation and coding schemes (MCS) are available. MCS0 is for Control. MCS1-12 with extensions are for SC mode. MCS25-31 are for Low-power SC mode. MCS13-24 are for OFDM mode. Data rates vary from 385 Mbps to 8085 Mbps. The maximum rate is achieved in MCS12.6 using π/2-64QAM and Low Density Parity Code (LDPC) at rate 7/8. Maximum rate for Low-power SC is at MCS31 giving 2503 Mbps. 

Compared to 802.11ac, 802.11ad is more power efficient. It has five times lower power consumption per bit. 

The MAC frame consists of preamble, header, data, and optional training for beamforming. **Golay Sequences** are extensively used in the preamble. 


### Could you explain Fast Session Transfer?

**Fast Session Transfer (FST)** is a MAC layer feature of 802.11ad that allows for multiband operation. While 802.11ad is incompatible with older standards at the PHY layer due to operation in 60 GHz, interoperability is possible at the MAC layer. FST is managed by a Common Upper MAC sublayer that sits on top of Lower MAC sublayer containing band-specific implementation. 

With FST, we can have seamless transfer of sessions from 60 GHz band to other bands, and vice versa. For example, if a better range is desired then the session may be transferred from 60 GHz to 5 GHz while sacrificing throughput. A session transfer that involves a different MAC address may be slower than when same MAC client and address is used for all bands. Some devices may be capable of supporting multiple bands at the same time. TP-Link's AD7200 offers such a multiband operation. 

A related concept is called **band steering** where an access point presents a single SSID for clients across all bands. This is supported by some D-Link routers but not by TP-Link's AD7200. 


### Who are currently supplying 802.11ad chipsets?

Chipsets are available from Broadcom, Intel, Qualcomm Atheros, Wilocity, Tensorcom, Peraso, Lattice Semiconductor, MediaTek, Nitero, and others. Wikipedia gives a list of specific chips from these vendors.

At CES 2013, Wilocity was one of the first to give a prototype demo of the technology based on its chips. The Wilocity chip was also used in the Dell Latitude 6430u Ultrabook. In July 2014, Wilocity was acquired by Qualcomm. Qualcomm stated that their future chips will be tri-band: 2.4 GHz, 5 GHz and 60 GHz. 


### Commercially, what 802.11ad products are currently available?

Wireless routers and access points are available from Netgear, Acelink, TP-Link, IgniteNet and Asus. In January 2016, Acer released TravelMate P648 notebook with 802.11ad support. Asus announced a 802.11ad smartphone back in September 2017. 

TP-Link's Talon AD7200 claims a theoretical speed of 7200 Mbps via multiband operation but a speed test over a distance of couple of meters gave 868 Mbps downlink and 280 Mbps uplink. 


### What are the alternatives to 802.11ad?

IEEE 802.11ad is not the only protocol for multi-gigabit wireless.

There's SiBeam's **WirelessHD** (aka **UltraGig**), also operating in the 60 GHz band. Back in 2010 when 802.11ad was being standardized, SiBeam was already shipping its chips for integration into consumer products. WirelessHD is designed for video, as high as 28 Gbps. This means that uncompressed 1080p FullHD video can be transmitted. WirelessHD specs were released in January 2008. However, WirelessHD website shows no news after 2013.

There's also **Wireless Home Digital Interface (WHDI)**, which operates in the 5 GHz band. It's purpose is to deliver interactive HD video from any device to any display, with quality equivalent to wired HDMI cable. 

Let's not forget **Miracast**, which runs over 802.11n or 802.11ac in the 5 GHz band. With Miracast, for example, we can stream content from a smartphone to a TV. 


### How is 802.11ad related to Media Agnostic USB?

In September 2013, Wi-Fi Alliance transferred its work on "WiGig Serial Extension Specification" to USB-IF (USB Implementers Forum). USB-IF will use this as a starting point for standardising **Media Agnostic USB (MA-USB)**. An alternative standard called **Wireless USB** operates in the range 3.1-10.6 GHz. MA-USB is agnostic of the underlying technology. Data could be transferred on Wi-Fi 2.4/5 GHz or WiGig 60 GHz. 

## Milestones

Jan  
2009

At the IEEE, the VHT Study Group starts looking into **Very High Throughput (VHT)** at 60 GHz. Both 802.11ac and 802.11ad come under the scope of VHT. 

May  
2009

About 15 technology companies come together to form **Wireless Gigabit (WiGig) Alliance**, an organization tasked with defining a wireless specification at the 60 GHz band. 

Dec  
2009

Version 1.0 of the WiGig specification is released. It supports data rates up to 7 Gbps. WiGig 1.0 announced

May  
2010

Wi-Fi Alliance and WiGig Alliance enter into a partnership. This enables Wi-Fi products in the 60 GHz band. Wi-Fi Alliance commits to studying the WiGig specs and perhaps certify for it. 

Dec  
2012

As an amendment to the overall IEEE 802.11, **IEEE 802.11ad-2012** is published with the title "Enhancements for Very High Throughput in the 60 GHz Band". It contains changes to both PHY and MAC layers. This is subsequently amended in March 2014. 

Mar  
2013

After two years of collaboration, Wi-Fi Alliance and Wireless Gigabit Alliance merge. Further work on WiGig, including product certification, will be taken up by Wi-Fi Alliance. 

Jan  
2016

At CES 2016, TP-Link demos its WiGig router, Talon AD7200. At 60 GHz, it claims 4.6 Gbps raw data rate. It also supports a/b/g/n/ac standards where 802.11ad is not available. It has eight antennas for beamforming. Inside, it uses two Qualcomm Atheros chips, one for older standards and another for 802.11ad. Also at CES 2016, Acer shows off its TravelMate P648 with 802.11ad support. 

Mar  
2016

OFDM mode has interoperability issues with Single Carrier (SC) mode. As a result, OFDM mode is made obsolete. In future, 802.11ay may design a proper OFDM PHY at 60 GHz. This change goes into IEEE 802.11-2016 standard, released in December 2016. 

Sep  
2017

Asus ZenFone 4 Pro becomes the world's first smartphone to support WiGig. It's not clear if the device is certified by the Wi-Fi Alliance. It uses Snapdragon 835 Mobile Platform.