Gazing into a crystal ball can be a risky business, but amidst the haze, one thing seems clear about the future of wireless networks: The upcoming IEEE 802.11ax standard is right around the corner and it promises to increase data throughput per user by at least 4X even in dense user environments like sports arenas and airports.
But perhaps before we continue a little historical perspective is in order. The 802.11b Wi-Fi standard dating back to 1999 had a top link speed of 11 Mbps. Then, in 2003 the 802.11a/g revision increased speed to 54 Mbps with the introduction of Orthogonal Frequency Division Multiplexing (OFDM) technology. 802.11n launched in 2009 boosted speed with single stream links up to 150 Mbps and the most recent (2013) revision—802.11ac— broke through the Gbps barrier at 1.3 Gbps with wider channels and higher modulation (256-QAM; in quadrature amplitude modulation both the amplitude and phase of a high-frequency signal are modulated. In short, higher QAM levels deliver higher capacity).
To clarify the alphabet soup that is the 802.11 standard another flavor, IEEE 802.11ad, approved in late 2012, uses the 60GHz spectrum instead of the 5GHz and 2.4GHz used by most Wi-Fi connections and is aimed at providing data throughput speeds of up to 7 Gbps. vs 3.2Gbps for 802.11ac Wave 2.
Unfortunately using frequencies in the millimeter range 802.11ad Wi-Fi has a range of only a few meters. The aim is that it will be used for very short range (i.e. across a room) high volume data exchange such as HD video transfers. When longer ranges are needed 802.11ac is more applicable.
But back to 802.11ax, also known as “High-Efficiency Wireless” (why will become clear shortly). It is capable of using up to 160 MHz wide channels—double the current bandwidth—as well as faster modulation schemes such as 1024 QAM. Right now 802.11ax is projected to have a top speed of around 10 Gbps.
But speed alone isn’t its raison d'être. The biggest problem with Wi-Fi is congestion and how Wi-Fi is going to be able to handle IoT and lots of people and things trying to use wireless connections and overcrowding the network.
To solve these issues 802.11ax will utilize multi-user technology in the form of Multi-user MIMO (MU-MIMO), a set of multiple-input and multiple-output technologies for wireless communication employing antennas to send data streams to multiple devices simultaneously. 802.11ax devices also support MU-OFDMA multi-user orthogonal frequency division multiple access) the prevalent air interface for 4G and 5G broadband wireless communications.
At the risk of oversimplification, 802.11ax works like this: A major factor limiting current Wi-Fi is collisions: when multiple devices transmit at the same time they can interfere with each other. With 802.11ax each channel of spectrum is separated into dozens, or even hundreds, of smaller sub-channels, each with a slightly different frequency. The 802.11ax standard calls the smallest such subchannel a Resource Unit (RU), with a minimum size of 26 subcarriers. The subcarrier spacing has been reduced to one fourth the subcarriers spacing of previous 802.11 versions, preserving the existing channel bandwidths. It also allows routers to dynamically adjust signal strength in an effort to improve reception for devices further away from the router.
By turning these signals through right-angles (orthogonally), they can be stacked closer together. Rather than waiting in line for their turn to transmit across the whole frequency band, multiple devices will be able to share each channel simultaneously. In this way, multiple streams can be handled when they are free instead of having to take turns broadcasting and then listening. Previous versions of Wi-Fi held channels open until data transmission had finished. That’s because the 802.11 protocol uses a carrier sense multiple access (CSMA) method in which the wireless stations (STA) first sense the channel and attempt to avoid collisions by transmitting only when they sense the channel to be idle. Even using MU-MIMO where there can be multiple streams, each still had to wait for the transaction ahead of them to complete.
With 802.11ax this is no longer a speed bump. 802.11ax has the option of allocating the whole channel to only one user at a time, just as 802.11ac currently does, or partition it to serve multiple users simultaneously.
While the 802.11ax specification introduces significant changes to the physical layer of the standard it will operate in both the 2.4 GHz and 5 GHz bands and maintain backward compatibility with 802.11a/b/g/n/ac devices.
802.11ax also makes use of a Target Wake Time (TWT) function to define a specific time or set of times that individual stations can access the medium. Wireless stations and Access Points (APs) exchange information that includes expected activity duration. This way the AP controls how much contention and overlap there will be among STAs attempting access. 802.11ax STAs can use TWT to reduce energy consumption, remaining in a sleep state until their TWT arrives (maintaining Wi-Fi connections when a mobile device is inactive eats up a lot of battery life).
The Institute of Electrical and Electronics Engineers (IEEE) doesn't expect to ratify the new 802.11ax standard until later this year with product due on the market in the in the 2018-19 time frame. The market research firm IHS Markit earlier this year estimated that the total 802.11ax enabled device shipments will increase from 116,000 in 2019 to 58 million units in 2021.