WiGig: IEEE 802.11ad 60GHz Microwave Wi-Fi

IEEE 802.11ad also known as WiGig or 60GHz WiFi is a microwave form of Wi-Fi that can provide data transfer of up to 7 Gbps at frequencies around 60GHz.


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Wi-Fi tends to be used for short distances, typically across a room, and increasingly very high volumes of data need to be transferred very quickly. IEEE 802.11ad, WiGig is able to provide a solution, giving very high throughput rates and using frequencies in the microwave section of the spectrum at frequencies around 60GHz.

As a result it is sometimes called 60GHz Wi-Fi or Microwave Wi-Fi.

The microwave section of the radio spectrum has a number of major advantages. It is possible to use a very wide bandwidth to enable high throughput data, and also good re-use of the spectrum is possible. As signals do not travel over such great distances and are absorbed by buildings, etc, high levels of re-use can be obtained without users on the same channel experiencing interference.

As part of the marketing, the scheme will be known by the name WiGig after the Wireless Gigabit Alliance that endorses the system, but it is also sometimes referred to as 60GHz WiFi.

Wireless Gigabit Alliance

To promote and advance the use of microwave Wi-Fi an alliance called the Wireless Gigabit Alliance was set up. Working with the IEEE, both organisations are committed to the advancement of the standard. It has been standardised as IEEE802.11ad, but its marketing name is WiGig.

Accordingly, the WiGig MAC/PHY specification aligns exactly with the 802.11ad standard. This provides industry standardisation, industry recognition, input from industry to ensure that the standard is realisable and also meets the industry needs, and it also provides an easy marketing name.

The Wireless Gigabit Alliance was formed to provide a single multi-gigabit wireless communications standard among consumer electronics, handheld devices and PCs, and drives industry convergence using unlicensed ISM (industrial, scientific and medical) 60 GHz spectrum.

It is anticipated that as microwave technology becomes cheaper and the requirement for spectrum increases, WiGig technology will become widespread in its use.

WiGig 802.11ad salient features

The table below gives a summary of the salient features of 802.11ad - 60GHz Wi-Fi.


WiGig 802.11ad
Characteristic
Description
Operating frequency range 60 GHz ISM band
Maximum data rate 7 Gbps
Typical distances 1 - 10 m
Antenna technology Uses beamforming
Modulation formats Various: single carrier and OFDM

In addition to the tabulated details, the system uses a MAC layer standard that is shared with current 802.11 standards to enable session switching between 802.11 Wi-Fi networks operating in the 2.4 GHz, and 5 GHz bands with those using the 60 GHz WiGig bands. In this way, seamless transition can occur between the systems.

However the 802.11ad MAC layer has been updated to address aspects of channel access, synchronization, association, and authentication required for the 60 GHz operation.

WiGig physical layer

The WLAN system uses frequencies in the 60GHz unlicensed spectrum. Dependent upon geography these are located between 57 GHz and 66GHz.

60 GHz Global Allocations
Region Allocation (GHz)
Australia 59.4 - 62.90
European Union 57.00 - 66.00
Japan 59.00 - 66.00
South Korea 57.00 - 64.00
USA & Canada 57.05 - 64.00
The ITU-R then recommends the use of four channels, each 2.16 GHz wide with centre frequencies of 58,32, 60.48, 62.64, and 64.80 GHz. It can therefore be seen that only channel 2 with its centre frequency of 60.48 GHz is globally available. This is recommended to be the default channel. The fact that only four channels are available is not seen as a problem because signal absorption is high in this region and even with high re-use, signals are unlikely to interfere.

One of the main forms of modulation used is OFDM. This is a key element of the overall modulation and RF signal format, providing the capability for high data rates while supplying good resilience against multiple paths.

Note on OFDM:

Orthogonal Frequency Division Multiplex, OFDM is a form of signal format that uses a large number of close spaced carriers that are each modulated with low rate data stream. The close spaced signals would normally be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is shared across all the carriers and this provides resilience against selective fading from multi-path effects.

Read more about OFDM, Orthogonal Frequency Division Multiplexing.

The WiGig 802.11ad PHY supports three main signals with different modulation.

  • Control PHY, CPHY:   Providing control, this signal has high levels of error correction and detection. Accordingly it has a relatively low throughput. As it does not carry the main payload, this is not an issue. It exclusively carriers control channel messages.

    The CPHY uses differential encoding, code spreading and BPSK modulation.
  • Single Carrier PHY:   The SCPHY employs single carrier modulation techniques: BPSK, QPSK or 16-QAM on a suppressed carrier located on the channel centre frequency. This single has a fixed symbol rate of 1.76 Gsym/sec. A variety of error coding and error coding modes are available according to the requirements.
  • Orthogonal Frequency Division Multiplex PHY, OFDMPHY:   As with any OFDM scheme, the OFDMPHY uses multicarrier modulation to provide high modulation densities and higher data throughput levels than the single carrier modes.

    The modulation format SQPSK is Spread QPSK and involves using paired OFDM carriers onto which the data is modulated. The two carriers are maximally separated to improve the robustness of the signal in the presence of frequency selective fading.
  • Low Power Single Carrier PHY, LPSCPHY:   This 802.11ad signal uses a single carrier as the name implies, and this is to minimise the power consumption. It is intended for small battery devices that may not be able to support the processing required for the OFDM format.

802.11ad Modulation and Coding Summary
 
 
Control PHY
Coding Modulation Ideal RAW bit rate
1/2 LDPC 32X Spreading Π/2 DBPSK 27.5 Mbps
 
 
Single Carrier PHY
Coding Modulation Ideal RAW bit rate
1/2 LDPC, 2X repetition
1/2 LDPC
5/8 LDPC, 3/4 LDPC
13/16 LDPC
Π/2 BPSK
Π/2 QPSK
Π/2 16-QAM
385 Mpbs
to
4620 Mbps
 
 
OFDM PHY
Coding Modulation Ideal RAW bit rate
1/2 LDPC
5/8 LDPC, 3/4 LDPC
13/16 LDPC-
OFDM-SQPSK
OFDM-QPSK
OFDM-16-QAM
OFDM-64-QAM
693 Mpbs
to
6756.75 Mbps
 
 
Low Power Single Carrier PHY
Coding Modulation Ideal RAW bit rate
RS(224,208) + Block Code (16/12/9/8.8) Π/2 BPSK
Π/2 QPSK
625.6 Mpbs
to
2503 Mbps

WiGig 802.11ad beam management

One of the features of WiGig microwave Wi-Fi is the aspect of antenna beam management. The very high frequencies used means that the antennas are very small and this makes the development, manufacture and use of the phased arrays required for this a feasible proposition.

The beam-forming is accomplished using a bi-directional training sequence that is appended to each transmission. This enables the system to shape the transmit and / or the receive beams to achieve the optimum link properties. This enables the system to overcome any movement of the transmitter, receiver, or objects between them that might alter the path characteristics.



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