The coming Wi-Fi standard IEEE 802.11ax is an omnipresent subject at trade fairs and is equally gaining traction in the media. The tenor is always the same: In the world of Wireless LAN, ax is the next big thing. Many see this new standard as the answer for the overcrowded radio networks of the future.
The makers of the latest Wi-Fi standard aim to come to terms with the growing number of wireless applications that are driving today’s digitalization and interconnectivity on the Internet of Everything. If the marketing specialists from various network manufacturers are to be believed, we face the imminent arrival of the next generation of Wi-Fi. Woe betide anybody who misses the train.
Perhaps it is because of the many promises made by the industry that IEEE 802.11ax—also known as High Efficiency Wireless (HEW)—is such a hot topic. Ultimately the new standard aims not only to improve the user experience by a more stable connection, but to also offer higher bandwidth capacities than the preceding 802.11ac in high-density environments—i.e. in areas with very large numbers of Wi-Fi clients—by means of parallel data transmissions.
In Europe, at least, there is a decisive catch. But first, let’s take a closer look at the new features and enhancements that come with the sixth Wi-Fi standard.
Greater efficiency through smart features
One benefit is the improved utilization of the unlicensed spectrum available in the 2.4GHz and 5GHz bands (maybe even 6GHz in the near future) for high-bandwidth applications such as VoiP or video streaming. Performance gains also come with the increase in average throughput for each individual Wi-Fi client in high-density environments, as the available bandwidths are allocated more efficiently to the individual clients. Transmission is more stable and individual connections have a stronger signal.
The performance gain is achieved with parallel transmissions and not simply by higher transmission rates as such. A special role here is played by the parallel transmissions by multi-user MIMO—now for the uplink, too—and the introduction of OFDMA (Orthogonal Frequency Division Multiple Access).
So 11ax is less about an increase in absolute speed and more about the improved “simultaneity” of transmissions to and from multiple clients, i.e. an increase in efficiency. A look at the maximum single user transmission speeds reveals an increase of about 40 percent over current ac Wave 2 devices.
In addition to the improvements from parallel transmission, ax offers other advantages for users: An improved target wake-up time (TWT) increases the battery life of mobile clients. They “sleep” better or longer because they have to “wake up” less frequently in order to listen out for their access points. Completing the package are more robust transmissions outdoors, the indoor and outdoor application of frequencies between 1 and 6 GHz, enhanced coexistence with other wireless technologies and an expansion of the functions available under 802.11ac in the 2.4 GHz band.
Special case Europe
This all sounds very promising, so far. However, the whole story has one decisive catch—at least in Europe.
The devil is in the details, more precisely in the European norm EN 301 893 (LINK to PDF), currently of version V2.1.1. It regulates radio operations in the vital 5-GHz frequency band. All devices that transmit in the 5-GHz band, whichever radio technology they use, are obliged to comply with certain specifications. The reasons for this are plausible enough: On the one, hand they should ensure the efficient use of the limited frequencies that are available and, on the other hand, they enable a fair coexistence of different radio technologies.
However, Wi-Fi devices benefit from better performance as the EN 301 893 norm includes a number of exemptions for IEEE 802.11. These exemptions permit devices accessing Wi-Fi channels to use mechanisms that help achieve a better performance.
What is otherwise a good thing for the WLAN industry actually presents a problem for ax: The aforementioned EU norm only permits these exemptions in relation to the Wi-Fi standards 802.11b/g/a/n and ac—there is no mention of 802.11ax. The consequence of this is that ax devices in the EU currently cannot use their full performance.
Preamble and Energy Detection
Specifically, the exemptions in EN 301 893 relate to the mechanisms Energy Detection (ED) and Preamble Detection (PD). Whereas all other systems in the 5-GHz band are obliged to use Energy Detection to identify ongoing radio traffic and are prohibited from accessing channels over a threshold of -72 dBm, this requirement has been eased for Wi-Fi devices.
Instead of relying on Energy Detection alone, Wi-Fi devices up to 802.11ac may additionally use Preamble Detection in combination with a higher ED threshold. The advantage: For a Wi-Fi device, a channel is considered available while other systems would consider it to be occupied. As a result, Wi-Fi devices gain access sooner.
But how exactly do these mechanisms work?
With Energy Detection, the transmitter listens to the channel before each data transmission and compares the measured strengths of the noise and interference signals to a specified threshold, regardless of the wireless technology being used. If the signal exceeds the ED threshold, the transmitter classifies the channel as occupied and does not start a new transmission. In EN 301 893, this threshold was set to -72 dBm.
However, instead of Energy Detection, Wi-Fi devices operating the 802.11b/g/a/n or ac standards can use Preamble Detection (PD) up to -62dBm. This measures the signal strength (RSSI) of Wi-Fi packets on the channel and compares this to a certain threshold. If the RSSI is above the threshold, the medium is classified as occupied and no new data transmission is started.
The idea behind this is that any non-Wi-Fi device must go through the ED process at -72 dBm signal strength, unlike Wi-Fi with its -62 dBm threshold.
This gives Wi-Fi a 10 dB “advantage” over the other wireless technologies. In return, Wi-Fi is more sensitive to its own data packets and therefore has the PD threshold at -82 dBm, which is 10 dB lower than the ED value for other wireless technologies.
In short: Wi-Fi is less susceptible to interference (high
lower ED threshold) and therefore has an advantage over other radio signals, whereas it is more sensitive to other Wi-Fi signals (low PD threshold). There is one exception: 802.11ax.
Time for a common solution
In order to solve this European problem, ETSI has to revise EN 301 893 accordingly and permit the same exemptions for ax as for its predecessor standards. If this does not happen, IEEE 802.11ax would enter the EU market as a “mutilated” standard with a performance which, in the worst case—and as experts fear—could be worse than that of its predecessor, 11ac.
But the problems do not concern Europe alone: The ax standard itself is behind schedule.
The High Efficiency WLAN Study Group (HEW SG) started work in May 2013. Their goal then was to improve the spectrum utilization and data throughput in environments with high numbers of WLANs and sources of interference. The IEEE 802.11ax Task Group was born and immediately began developing a new Wi-Fi standard.
A look at the current timetable (Timeline of the Task Group) reveals that the standard itself is largely complete. However, its actual adoption is not expected until December 2019 at the earliest. We are optimistic that the problems will be solved and expect the first tested, market-ready enterprise products to appear in mid-2019. We are really looking forward to this next step in Wi-Fi and especially the more efficient usage of the available bandwidth.
Are enterprises getting their hopes up too early?
Despite the standard not being ready and the current restrictions in Europe, a number of network and chip manufacturers have nevertheless announced some early devices with 11ax. The first products for the European market are bound to appear soon. If we take a closer look at the problem of a non-adopted standard and an EU norm that lacks the exemptions required of this (unfinished) standard, it quickly becomes clear that the use of ax features (at least) in Europe currently doesn’t make sense for any user.
If things in Europe do not change in the near future, this could hinder, or even prevent, the next quantum leap in Wi-Fi domain. Initial proposals for a revision of EN 301 893 have already been presented to ETSI. It is vital for this to take place on the official agenda soon so that it is addressed in good time. Otherwise the launch of ax in Europe in 2019 is not going to happen.
Despite all this, the situation is not as dramatic as it may seem. Even today, the preceding standard IEEE 802.11ac is still not very widespread. According to IDC’s Enterprise Market Tracker from 2017, the share of ac access points sold in the business segment was 84.5% in Q2 2017, while in the consumer segment this was just 32.3%.
The potential of 11ac WAVE 2 is far from exhausted. So, there is still time for the standards officials to get their homework done.
The article was edited in October, 2020. Changes are marked.