IEEE 802.11ax Will Save Wi-Fi from Itself

If the success of a technology is judged by how many people use it, Wi-Fi surely ranks high on the list of the most successful technologies of all time. It’s so successful, in fact, that the airwaves have become massively populated with Wi-Fi signals in many places to the point that establishing or maintaining a Wi-Fi connection is sometimes impossible. And it’s not just in stadiums and airports where many people congregate but in homes packed with Wi-Fi-enabled devices.

Fortunately, the next Wi-Fi standard—IEEE 802.11ax—promotes a leap forward for increasing Wi-Fi efficiency (and thus, capacity) in areas of high congestion. The need for a new standard is clear, and although the standard will not be formally released until 2019, manufacturers are expected to introduce 802.11ax-enabled routers in 2018. It’s also possible we’ll see chip sets released in advance of the new standard, which aims to improve efficiency, capacity, and performance. This article explores key improvements that reach beyond the IEEE 802.11ac standard: These include multiple access modulation, multi-user Multiple Input Multiple Output (MU-MIMO), Basic Service Set (BSS) coloring, multi-frequency accommodation, and Target Wake Time (TWT).

The Need for 802.11ax

For an example of just how crowded the Wi-Fi spectrum can be, consider last year’s Super Bowl LI, which set records for Wi-Fi usage. More than 27,000 fans used Wi-Fi simultaneously in Houston’s NRG Stadium, and 35,430 fans (or 49 percent) were on the network sometime during the game. A mind-numbing 11.8TB of data was transferred during the day, and while this is an extreme case, it’s not unique: In April 2016, WrestleMania 32 at AT&T Stadium in Arlington, TX, generated 6.77TB of Wi-Fi data.

However, many homes have something akin to this in miniature form. According to various reports, an “average” home typically has about 10 devices connected to the Internet; those same reports also project that this number may reach about 50 by 2022. The big increase will come from so-called “smart” devices within the realm of the Internet of Things (IoT), such as door locks, surveillance cameras and security systems, HVAC, and indoor/outdoor lighting. While these devices communicate with each other using short-range standards, such as Bluetooth and ZigBee, they need a way to reach the Internet. Because Wi-Fi is the only standard that has direct Internet access, it acts as a gateway through which data passes on its way to the outside world.

Of course, IoT devices typically don’t generate much data and intermittently transmit and receive, so they’re not much of a problem. But when combined with HD streaming devices, like Roku- or Wi-Fi-enabled TVs (which generate gigabytes of data) along with the smartphones, laptops, and tablets in most homes, a typical Wi-Fi access point can’t serve them all and maintain respectable performance ( Figure 1 ). IEEE 802.11ax should go a long way toward solving this problem.

Figure 1: Streaming of entertainment transfers huge amounts of data from the Internet, and Wi-Fi is how it gets to the end user.

IEEE 8021.11ax in a Nutshell

Beginning with IEEE 802.11n, previous Wi-Fi standards began to make progress in better serving dense signal environments, but only the current standard, 802.11ac, really delivered significant improvements. 802.11ax enhances its predecessor’s capabilities while adding new ones. As speed alone isn’t a panacea, 802.11ax focuses instead on other technologies, such as MU-MIMO, beamforming, a higher-order modulation scheme, more effective scheduling between devices, and several others ( Table 1 ).

Table 1 : An IEEE 802.11ac and IEEE 802.11ax comparison.

Key Improvements Increase Efficiency, Capacity, and Performance

IEEE 802.11ax does promise a higher maximum speed of nearly 10Gbps, but that’s only 38 percent higher than 802.11ac. The real measure is in the increase of throughput, which is what a given user will actually experience, and achieving a higher throughput is the result of many factors, not just speed. For example, 802.11ax incorporates many changes to the physical layer of the standard, which should allow it to achieve a four-times increase in throughput “on the ground,” even in dense signal environments. Several improvements contribute to increased efficiency, capacity, and performance, including:

• Multiple access modulation that increases efficiency and capacity
• MU-MIMO that increases capacity and improves performance
• BSS coloring that reduces co-channel interference
• Multiple frequencies (i.e., 2.4GHz and 5GHz) that provide greater versatility and capacity
• TWT that increases battery life

Multiple Access Modulation

One of the most important improvements is Orthogonal Frequency Division Multiple Access (OFDMA) modulation, an enhanced version of Orthogonal Frequency-Division Multiplexing (OFDM) used in Wi-Fi, beginning with IEEE 802.11g. OFDMA increases capacity and efficiency by allowing several devices to occupy the same channel bandwidth to help maintain multiple data streams. It splits the frequencies used by Wi-Fi into something called time-frequency resource units (RUs), and by carefully scheduling the use of the RUs, contention between devices can be avoided.

Multi-user MIMO

Multiple Input Multiple Output (MIMO) technology has been an extremely important feature of Wi-Fi, since 802.11n. It increases capacity and overall performance by exploiting a propagation phenomenon called multipath distortion along with spatial diversity—the use of multiple antennas spaced some distance from each other. Multipath distortion has a decidedly negative connotation for good reason: It can single-handedly degrade or make useless a communications path, because it is the result of signals bouncing off various things in the environment, creating multiple paths that arrive at the receiver at different times.

It was once the bane of vehicle FM radios, because it causes an annoying, reception-destroying effect, called picket fencing, when signal characteristics change as the vehicle moves through its environment. The auto industry solved the problem by using more than one antenna, creating spatial diversity, in which the radio rapidly assesses signal conditions at each antenna, selects the “best” choice, and switches back and forth between them at high speed.

MIMO puts multipath into good use, using different signal arrival times to increase received signal strength by employing multiple antennas at both ends of the communication path. It augments this by sending and receiving multiple data streams over a single channel, splitting the data into the multiple streams at the transmitter and recombining them at the receiver. It can do this even when there’s no clear line-of-sight transmission path, which is a huge benefit for Wi-Fi, as non-line-of-sight paths are a common scenario.

A single-user MIMO antenna system directs its signals to a single device, but multi-user MIMO (MU-MIMO) used in a downlink path in 802.11ac and uplink/downlink paths in 802.11ax makes it possible to serve multiple devices through beamforming. This technique, which is a key ingredient in modern phased-array radars, can rapidly change the radiation pattern of a radar or MIMO system for various purposes. In a MIMO-enabled Wi-Fi access point, beamforming increases the power radiated in directions where devices need it most and reduces it in others. The result is the user experience is enhanced and interference is reduced.

In a downlink path, a MU-MIMO device can simultaneously transmit to multiple receivers, and in an uplink path MU-MIMO can receive from multiple transmitters ( Figure 2 ). In 802.11ax, MU-MIMO and OFDMA work collaboratively to increase the capacity of an access point, reduce interference, and provide an overall better performance in places where many people are using Wi-Fi at the same time.

Figure 2: Single-user MIMO can serve only a single device at a time, while multi-user MIMO can serve several. (source: Author)

BSS Coloring

A complete Wi-Fi “signal ecosystem” consists of an access point and devices connected to it that forms a Basic Service Set (BSS). A new feature in 802.11ax can reduce co-channel interference caused by BSSs, in a specific area, that are inefficiently reusing channels. It accomplishes this by Carrier Sense Multiple Access (CSMA), a “listen-before talk” approach where an access point “sniffs” its electromagnetic environment; if another Wi-Fi client is detected, it waits until the environment is silent. All of this takes place in near real time, but its effectiveness decreases in dense signal environments, resulting in interference between users.

To remedy this, 802.11ax uses BSS coloring that inserts an identifier within the first bits of data in a transmitted Wi-Fi signal. All devices receiving this “colored” signal will now know which BSS is sending it and its signal strength, and a new logic sequence used in 802.11ax optimizes the process of determining when and when not to transmit. Although variants of this approach are already used in some access points, they’re typically proprietary and usable only by access points and not by user devices. As a single BSS coloring approach is baked into the 802.11ax standard that is usable by both the access point and client device, it’s likely that the new standard should effectively reduce co-channel interference.

Multiple Frequencies: 2.4 and 5GHz

The enhancements described so far are some of the most wide-reaching within 802.11ax. However, they’re not the only ones, as a variety of others are being employed to help accomplish its goals. For example, 802.11ac is the most capable Wi-Fi standard by far, but it only operates in the 5GHz band, which is far less populated (so far), because the 2.4GHz band, used by Wi-Fi since Day One, has reached the saturation point.

This isn’t surprising as there are still many access points in service that use IEEE 802.11g and even IEEE 802.11b—all of which operate in this band. 802.11ax also operates at both frequencies, which when combined with its other benefits provides greater versatility. 802.11ax also adds 1024-state Quadrature Amplitude Modulation (1024QAM) to the existing modulation schemes used by 802.11ac, which increases capacity by about 33 percent versus 256QAM, the highest modulation rate used by 802.11ac.

TWT Increases Battery Life

Finally, another feature within IEEE 802.11ax is the Target Wake Time (TWT), which improves the battery life of smartphones and other mobile devices, by ensuring, through precise synchronization, that they remain in a state of full power only when necessary to communicate with the access point.

Conclusion

IEEE 802.11ax is a very comprehensive step forward for Wi-fi, especially in solving its congestion problems in situations where technology has reached or soon will reach its limits of achievement without fundamental changes in how it operates. Key improvements, including multiple access modulation MU-MIMO, BSS coloring, multi-frequency accommodation, and TWT, contribute to user experiences of increased efficiency, capacity, and performance.

Most manufacturers will introduce the first 802.11ax-enabled routers in 2018, though the standard itself is not set for release until 2019.

This might appear to be jumping the gun, but it’s not unusual for Wi-Fi: 802.11n chip sets were available, followed by the routers that use them, long before the standard was released. That said, it’s important remember that even though a router may boast of this new technology, the devices that will use this technology at the other end of the link, including smartphones to TVs and other streaming devices, will take longer to enter the market.

It’s likely that the next generation of smartphones from Samsung and Apple, for example, may include 802.11ax, as both companies will announce new products in the fall. The standard will take even longer to reach many places that need it most, such as stadiums, airports, and convention centers, because the replacement of dozens to, perhaps, hundreds of access points is expensive and time-consuming. Nonetheless, it should be worth the wait.