Unwrapping WiFi 6: Getting out of the traffic jam
Previous generations of WiFi focused on increasing data rates and speed. WiFi 6 (also known as 802.11ax) is the new generation of WiFi technology with a focus on efficiency and performance.
WiFi 6 technology is all about better and more efficient use of the existing radio frequency medium. WiFi 6 handles client density more efficiently through a new channel-sharing capability that promises true multi-user communications on both the downlink and uplink. WiFi 6 also uses a new client power-saving mechanism that schedules wake-times to improve client battery life.
There is a big misconception that data rates are the same as actual throughput. Furthermore, speed can be overrated. What good is a Ferrari that can travel at 300km/h if the Ferrari is stuck in traffic gridlock?
Historically, previous 802.11 amendments defined technologies that gave us higher data rates and wider channels but did not address efficiency. WiFi operates at both layer one and layer two of the OSI model and the inefficiency exists at both layers. An often-used analogy is that faster cars and bigger highways have been built, but traffic jams still exist. Despite the higher data rates and 40/80/160MHz channels used by 802.11n/ac radios, multiple factors contribute to the WiFi traffic congestion, which do not provide for an efficient use of the medium.
Speed can be overrated. What good is a Ferrari that can travel at 300km/h if the Ferrari is stuck in traffic gridlock?
In laboratory conditions, TCP throughput of 60% to 70% of the operational data rate can be achieved using 802.11n/ac communication between one access point (AP) and one client. The aggregate throughput numbers are considerably less in real-world environments with active participation of multiple WiFi clients communicating through an AP. As more clients contend for the medium, the medium contention overhead increases significantly, and efficiency drops.
Therefore, the aggregate throughput is usually at best 50% of the advertised 802.11 data rate. Not very efficient. In addition, because legacy WiFi clients often still participate in enterprise, RTS/CTS protection mechanisms are needed, which contributes to the inefficiency.
As shown in Figure 1, about 60% of all WiFi traffic is 802.11 control frames, and 15% is 802.11 management frames.
Control and management frames consume 75% of the usable airtime, and only 25% of WiFi traffic is used for 802.11 data frames. Additionally, layer two retransmissions as a result of either RF interference or a poorly designed WLAN, can also contribute to 802.11 inefficiency.
Despite the higher data rates and wide channels that can be used by 802.11n/ac radios, the result is WiFi traffic congestion. Automobile traffic congestion can result in drivers becoming frustrated and thereby engaging in road rage. WiFi 6 (802.11ax) technology is all about better 802.11 traffic management and hopefully eliminating WiFi radio rage.
WiFi 6 (802.11ax) technology focuses on better and more efficient use of the existing radio frequency medium. Higher data rates and wider channels are not the goals of WiFi 6. Most of the WiFi 6 enhancements are at the PHY layer and involve a new multi-user version of OFDM technology, as opposed to the single-user OFDM technology already used by 802.11a/g/n/ac radios. Another significant WiFi 6 change is that an access point (AP) can actually supervise both downlink and uplink transmissions to multiple client radios while the AP has control of the medium.
In addition to these multi-user efficiency enhancements, WiFi 6 (802.11ax) radios will be backward-compatible with 802.11/a/b/g/n/ac radios. Table 1 shows a high-level comparison of 802.11n, 802.11ac, and 802.11ax capabilities.
Note that unlike 802.11ac radios, which can transmit only on the 5GHz frequency band, 802.11ax radios can operate on both the 2.4GHz and 5GHz frequency bands.
In a nutshell, the key benefits of WiFi 6 will be a result of the partitioning of a 20MHz channel into smaller sub-channels using a multi-user version of OFDM called orthogonal frequency division multiple access (OFDMA). WiFi 6 makes use of both multi-user technologies, OFDMA and multi-user, multiple input, multiple output (MU-MIMO).
OFDMA allows for multiple-user access by subdividing a channel. MU-MIMO allows for multiple-user access by using different spatial streams. Using the car and road analogy I mentioned earlier, OFDMA uses a single road subdivided into multiple lanes for use by different cars at the same time, whereas MU-MIMO uses different single lane roads to arrive at the same destination.