How Much Better is 802.11ax?

The new WiFi standard 802.11ax is expected to be ratified and released as a standard sometime next year. In the new industry nomenclature this now be called WiFi-6. A lot of the woes we have today with bandwidth in our home is due to the current 802.11ac standard that this will be replacing. 802.11ax will introduce a number of significant improvements that ought to improve home WiFi performance.

To understand why these improvements are important we need to first understand the shortcomings of the current WiFi protocols. The industry groups that developed the current WiFi standards had no idea that WiFi would become so prevalent and that the average home might have dozens of WiFi capable devices. The current problems all arise from a WiFi router trying to satisfy multiple demands for a data stream from multiple devices. Unlike cellular technologies, WiFi has no central traffic cop and every device in the environment can make an equal claim for connectivity. When a WiFi router has more demands for usage than it has available channels it pauses and interrupts all data streams until it chooses how to reallocate bandwidth. In a busy environment these stops and restarts can be nearly continuous.

The improvements from 802.11ax will all come from smarter ways to handle requests for connectivity from multiple devices. There is only a small improvement in overall bandwidth with a raw physical data rate of 500 Mbps compared to 422 for 802.11ac. Here are the major new innovations:

Orthogonal Frequency-Division Multiple Access (OFDMA). This improvement will likely have the biggest impact in a home. OFDMA can slice the few big existing WiFi channels into smaller channels, being called resource units. A router will be able to make multiple smaller bandwidth connections using resource units and avoid packet collision and the start/stop cycle of each device asking for primary connectivity.

Bi-Directional Multi-User MIMO. In the last few years we’ve seen home WiFi routers introduce MIMO, which uses multiple antennas to make connections to different devices. This solves one of the problems of WiFi by allowing multiple devices to download separate data streams at the same time without interference. But today’s WiFi MIMO still has one big problem in that the MIMO only work for downloading. Whenever there is a request for any device to use a channel for uploading, today’s MIMO pauses all the downloading streams. Bi-Directional MIMO will allow for 2-way data streams meaning that a request to upload won’t kill downstream transmissions.

Spatial Frequency Reuse. This will have the most benefit in apartments or in homes that have networked multiple WiFi routers. Today a WiFi transmission will pause for any request for connection, even for connections made to a neighbor’s router from the neighbor’s devices. Spatial Frequency Reuse doesn’t fix that problem, but it allows neighboring routers to coordinate and to adjust the power of transmission requests to increase the chance that a device can connect to and maintain a connection to the proper router.

Target Wake Time. This will allow small devices to remain silent most of the time and only communicate at specific and pre-set times. Today a WiFi router can’t distinguish between a request from a smart blender and a smart TV, and requests from multiple small devices can badly interfere with the streams we care about to big devices. This feature will reduce, and distribute over time the requests for connectivity from the ever-growing horde of small devices we all have.

There’s no rush to go out and buy and 802.11ax router, although tech stores will soon be pushing them. Like all generations of WiFi they will be backwards compatible with earlier WiFi standards, but for a few years they won’t do anything differently than your current router. This is because all of the above features require updated WiFi edge devices that also contain the new 802.11ax standard. There won’t be many devices manufactured with the new standard even in 2019. Even after we introduce 802.11ax devices into our home we’ll continue to be frustrated since our older WiFi edge devices will continue to communicate in the same inefficient way as today.

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New and Better WiFi

Wi-Fi Signal logo (Photo credit: Wikipedia)

There are two new standards for WiFi that will be hitting the market in the next few years. The standards are 802.11ac and 802.11ad. The two new standards use different spectrum with 802.11ac at 5 GHz and 802.11ad at 60 GHz. Both new Wifi standards will be able to deliver up to 7 gigabits per second, compared to today’s WiFi that tops out at 600 megabits per second.

Looking at basic spectrum characteristics there are four major differences in the way these two standards will use the spectrum:  bandwidth available, propagation characteristics, antenna size and interference.

The maximum data speed that can be delivered by any radio spectrum is limited by the amount of spectrum used and the signal-to-noise ratio. This limit is defined by the Shannon-Hartley Theorem. The 802.11ac at 5 GHz can use about 0.55 GHz of spectrum. The 802.11ad at 60 GHz can use up to 7 GHz. 802.11ac has channels that are 160 MHz wide while 802.11 will have channels that are 2,160 MHz wide. But the channels in 802.11ac can be bonded which will allow it to deliver almost as much bandwidth as 802.11ad.

802.11ac will use the same 5 GHz spectrum that is used by today’s Wifi and will have similar propagation characteristics. But the 802.11ad spectrum at 60 GHz will not travel through bricks, wood or paint and thus this technology will be most useful as an in-room technology.

For these spectrums to achieve full potential they need to be able to transmit multiple signals, meaning that they need multiple antennas. Antenna size is proportional to the wavelength being transmitted. A 5 GHz antenna has to be about an inch long and spaced at least an inch apart to be effective. But 60 GHz antennae only need to be 1/10 inch long and apart. This is going to make it easier to put 802.11ad into handsets or into any small device.

Finally is the issue of interference. There is already a lot of usage in the 5 GHz band today. In addition to being used for WiFi the spectrum is used for weather Doppler radar. There are also a few other channels in the band that have been allowed for other uses. And so 802.11ac will have to work around the other uses in the spectrum. The 60 GHz spectrum range is mostly bare today, and since this will go such short distances there should be very few cases of interference. However, multiple 801.11d devices in the same room will interfere with each other to some extent.

The standard is pretty much set but won’t be fully certified until 2014. However, there are already devices being shipped that include some of the features of the standard. For example, it’s included in the Samsung Galaxy S4 and MacBooks. But today’s version uses beamforming to send the signal to one device at a time. Beamforming means that the signal is sent to one device from each separate antenna in an array, but at slightly different times.

Still to come is the best feature of, which is to support separate sessions with different devices, different priorities and different power needs. This feature is called multi-user MIMO and it will revolutionize the way that WiFi is used. For example, you will be able to make a WiFi voice call while simultaneously downloading a video from another device. Your WiFi chip will determine the location of each device you will be talking to and will initiate a prioritized session with each. In this example it can give priority to the voice call.

The fully deployed will be the first generation wireless that is getting ready for the Internet of Things. It will be able to communicate with multiple devices in the environment at the same time. It will turn smartphones and tablets into workhorses able to gather data from sensors in the environment.

802.11ad is going to be far more limited due to its inability to pass through barriers. The most likely use for the spectrum will be to create very high-speed wireless data paths between devices, such as connecting a PC or laptop to a wireless network. It should be able to achieve speeds approaching 7 Gbps with only one device and one path in play.

One would expect by 2016 or 2017 for devices using these two technologies will become widespread. Certain in the telecom industry an upgrade to 802.11ac will allow carriers to deliver more bandwidth around a home or office and be able to handle multiple sessions with wireless devices. This new technology is a fork-lift upgrade and is not backwards compatible with earlier WiFi devices. This means it will take some time to break into the environment since all of the local wireless devices will need to be upgraded to the new standard. One would expect first generation 802.11ac routers to still include 802.11n capabilities.

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