Tag: OFDMA

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Introducing 6 GHz into WiFi

WiFi is already the most successful deployment of spectrum ever. In the recent Annual Internet Report, Cisco predicted that by 2022 that WiFi will cross the threshold and will carry more than 50% of global IP traffic. Cisco predicts by 2023 that there will be 628 million WiFi hotspots – most used for home broadband.

These are amazing statistics when you consider that WiFi has been limited to using 70 MHz of spectrum in the 2.4 GHz spectrum band and 500 MHz in the 5 GHz spectrum band. That’s all about to change as two major upgrades are being made to WiFi – the upgrade to WiFi 6 and the integration 6 GHz spectrum into WiFi.

The Impact of WiFi 6. WiFi 6 is the new consumer-friendly name given to the next generation of WiFi technology (replaces the term 802.11ax). Even without the introduction of new spectrum WiFi 6 will significantly improve performance over WiFi 5 (802.11ac).

The problem with current WiFi is congestion. Congestion comes in two ways – from multiple devices trying to use the same router, and from multiple routers trying to use the same channels. My house is probably typical, and we have a few dozen devices that can use the WiFi router. My wife’s Subaru even connects to our network to check for updates every time she pulls into the driveway. With only two of us in the house, we don’t overtax our router – but we can when my daughter is home from college.

Channel congestion is the real culprit in our neighborhood. We live in a moderately dense neighborhood of single-family homes and we can all see multiple WiFi networks. I just looked at my computer and I see 24 other WiFi networks, including the delightfully named ‘More Cowbell’ and ‘Very Secret CIA Network’. All of these networks are using the same small number of channels, and WiFi pauses whenever it sees a demand for bandwidth from any of these networks.

Both kinds of congestion slow down throughput due to the nature of the WiFi specification. The demands for routers and for channels are queued and each device has to wait its turn to transmit or receive data. Theoretically, a WiFi network can transmit data quickly by grabbing a full channel – but that rarely happens. The existing 5 GHz band has six 80-MHz and two 160-MHz channels available. A download of a big file could go quickly if a full channel could be used for the purpose. However, if there are overlapping demands for even a portion of a channel then the whole channel is not assigned for a specific task.

Wi-Fi 6 introduces a few major upgrades in the way that WiFi works to decrease congestion. The first is the introduction of orthogonal frequency-division multiple access (OFDMA). This technology allows devices to transmit simultaneously rather than wait for a turn in the queue. OFDMA divides channels into smaller sub-channels called resource units. The analogy used in the industry is that this will open WiFi from a single-lane technology to a multi-lane freeway. WiFi 6 also uses other techniques like improved beamforming to make a focused connection to a specific device, which lowers the chances of interference from other devices.

The Impact of 6 GHz. WiFi performance was already getting a lot better due to WiFi 6 technology. Adding the 6 GHz spectrum will drive performance to yet another level. The 6GHz spectrum adds seven 160 MHz channels to the WiFi environment (or alternately adds fifty-nine 20 MHz channels. For the typical WiFi environment, such as a home in an urban setting, this is enough new channels that a big bandwidth demand ought to be able to grab a full 160 MHz channel. This is going to increase the perceived speeds of WiFi routers significantly.

When the extra bandwidth is paired with OFDMA technology, interference ought to be a thing of the past, except perhaps in super-busy environments like a business hotel or a stadium. Undoubtedly, we’ll find ways over the next decade to fill up WiFi 6 routers and we’ll eventually be begging the FCC for even more WiFi spectrum. But for now, this should solve WiFi interference in all but the toughest WiFi environments.

It’s worth a word of caution that this improvement isn’t going to happen overnight. You need both a WiFi 6 router and WiFi-capable devices to take advantage of the new WiFi 6 technology. You’ll also need devices capable of using the 6 GHz spectrum. Unless you’re willing to throw away every WiFi device in your home and start over, it’s going to take most homes years to migrate into the combined benefits of WiFi 6 and 6 GHz spectrum.

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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 802.11.ax 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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A New WiFi Standard

There is a new version of WiFi coming soon that ought to solve some of the major problems with using WiFi in the home and in busy environments. The new standard has been labeled as 802.11ax and should start shipping in new routers by the end of this year and start appearing in devices in early 2018.

It’s the expected time for a new standard since there has been a new one every four or five years. 802.11a hit the market in 1999, 802.11g in 2003, 802.11n in 2009 and 802.11ac in 2013.

One of the most interesting thing about this new standard is that it’s a hardware upgrade and not a real change in the standards. It will be backwards compatible with earlier versions of 802.11, but both the router and the end devices must be upgraded to use the new standard. This means that business travelers are going to get frustrated when visiting hotels without the new routers.

One improvement is that the new routers will treat the 2.4 GHz and 5 GHz spectrums as one big block of spectrum, making it more likely to find an open channel. Most of today’s routers make you pick one band or the other.

Another improvement in 801.11ax is that the routers will have more antennas in the array, making it possible to connect with more devices at the same time. It’s also going to use MIMO (multiple input, multiple output) antenna arrays, allowing it to identify individual users and to establish fixed links to them. A lot of the problems in current WiFi routers come when routers get overwhelmed with more requests for service than the number of antennas that are available.

In addition to more signal paths the biggest improvement will be that the new 801.22ax routers will be able to better handle simultaneous requests for use of a single channel. The existing 802.11 standards are designed to share spectrum and when a second request is made to use a busy channel, the first transmission is stopped while the router decides which stream to satisfy – and this keep repeating as the router bounces back and forth between the two users. This is not a problem when there are only a few requests for simultaneous use, but in a crowded environment the constant stopping and starting of the router results in a lot of the available spectrum going unused and in nobody receiving a sustained signal.

The new 802.11ax routers will use OFDMA (orthogonal frequency division multiplying) to allow multiple users to simultaneously use the same channel without the constant stopping and starting at each new request for service. A hotel with a 100 Mbps backbone might theoretically be able to allow 20 users to each receive a 5 Mbps stream from a single WiFi channel. No wireless system will be quite that efficient, but you get the idea. A router with 802.11ax can still get overwhelmed, but it takes a lot more users to get to that condition.

We’ll have to wait and see how that works in practice. Today, if you visit a busy business hotel where there might be dozens of devices trying to use the bandwidth, the constant stopping and starting of the WiFi signal usually results in a large percentage of the bandwidth not being given to any user – it’s lost during the on/off sequences. But the new standard will give everybody an equal share of the bandwidth until all of the bandwidth is used or until it runs out of transmitter antennas.

The new standard also allows for scheduling connections between the router and client devices. This means more efficient use of spectrum since the devices will be ready to burst data when scheduled. This will allow devices like cellphones to save battery power by ‘resting’ when not transmitting since they save on making unneeded requests for connection.

All these various changes also mean that the new routers will use only about one-third the energy of current routers. Because the router can establish fixed streams with a given user it can avoid the constant off/off sequences.

The most interesting downside to the new devices will be that their biggest benefits only kick in when most of the connected devices are using the new standard. This means that the benefits on public networks might not be noticeable for the first few years until a significant percentage of cellphones, tablets, and laptops have been upgraded to the new standard.

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