22 Jul 2013 04:58 PM

The arrival of 1Gigabit Wi-Fi

In June, the Wi-Fi Alliance certified the 802.11ac standard, which will offer three times the speed of current Wi-Fi. Wi-Fi expert Matthew Gast explains to James Atkinson why wireless is becoming the primary access layer for data transmission

The arrival of 1Gigabit Wi-Fi

Wi-Fi customers will soon be able to take advantage of much faster Wi-Fi speeds as equipment and devices supporting the latest 802.11ac standard begin to come on the market. 802.11ac operates in the 5GHz unlicensed band, unlike all previous standards, including the current 802.11n, which use the more crowded 2.4GHz band.

However, the transition to 802.11ac will not happen overnight, according to Matthew Gast, chair of the Wi-Fi Alliance Security Task Group and of the IEEE 802.11 revision task group, and Director of Product Management at Wi-Fi equipment provider Aerohive.

Gast says: ‘802.11ac is an evolution, unlike the current standard 802.11n, which completely upended everything that had come before, so it won’t create an earthquake or change the basic structure of the industry, but it will change the way people design Wi-Fi networks.’

The new standard has four broad features that enable it to deliver more data at a faster throughput: more spatial streams; wider channels; 256 QAM; and beamforming. The caveat with more spatial streams is that they require a new chip to support them, which means many existing Wi-Fi deployments will need new hardware.

Efficiency gains

Wi-Fi started out with 20MHz channels and went up to 40MHz with 802.11n. ‘When you double the width of a channel you double the throughput and 802.11ac adds 80MHz and 160MHz channels, which has exactly the effects you would expect,’ notes Gast.

The 802.11ac standard has 256 QAM (quadrature amplitude modulation). QAM is a way of taking a phase shift and amplitude change in a transmission and combining them into a point on a graph. The number of points helps you determine the number of bits you are transmitting. 256 QAM is therefore better than 802.11n’s 64 QAM, because you have more points and therefore you can transmit more data.

Gast describes beamforming as the ‘big wild card’. ‘Beamforming is the ability to steer or direct energy in a particular direction,’ he explains. ‘But it really doesn’t hit its stride until you have multi-user MIMO (multiple in-multiple out). We’ve had single MIMO since 802.11n, where you use multiple antennas to transmit and to get a bit of redundancy. It’s easier to see and hear if you have multiple eyes and ears, so in the same way it is easier to transmit and receive if you have multiple antennas.

‘Multi-user MIMO is the next wave of that,’ he continues. ‘Everything on the market is single user MIMO at the moment. If I want to transmit to a receiver, rather than send the energy out in all directions, I focus it on one direction, so the receiver in a Wi-Fi hotspot gets it. With multi-user MIMO, you can transmit to multiple receivers at the send time providing the signals do not overlap.’

The first wave of 802.11ac products coming out this quarter includes 256QAM, 80MHz channels and three spatial streams. The second wave, which Gast guesses will probably come out next year, may add 160MHz channels (or it may not, as it is hard to use channels that wide in an already crowded radio space).

Density challenge

‘You will also get a fourth spatial stream and it will bring multi-user MIMO, which is the big driver for that wave,’ says Gast. Where all of those spatial streams have a big potential impact is with multi-user MIMO, as it means you can serve multiple devices at the same time.

The challenge for the Wi-Fi equipment vendors and network architects is to deal with high densities of users, all with large bandwidth demands. Gast cites the example of a primary school, which wants one AP for every two classrooms of 30 students, all of whom have an iPad.

‘You need an AP that can handle 60 devices all day long,’ says Gast, ‘and to make it work at that kind of scale takes us longer to do. We [Wi-Fi vendors] are all at various stages of handling that, but this quarter will see products coming to market.’

Gast argues that Wi-Fi is now at the point where everyone accepts it is the way you connect to networks. More and more devices are Wi-Fi enabled, including TVs, which receive services such as Netflix via built in Wi-Fi. Building automation is another area where Wi-Fi is being used to control ventilation or energy usage.

‘All that can be done on Wi-Fi now, and there is a huge amount of innovation going on with Wi-Fi as the base protocol everyone is adding on to,’ says Gast. However, he warns: ‘Preparing for a world where even more things use Wi-Fi is not a problem we solve just by changing the radio link with 802.11ac. It is about changing the way we build networks, so that we can support high densities without being crushed by the complexity of that.’



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