Last updated on July 8th, 2021
WiFi 6 technology has been introduced with a sole motive of making WiFi communications highly efficient and effective for Enterprise as well as home use. By borrowing key features from well established cellular phone and IoT industries, WiFi 6 technology aims to provide vastly improved performance to end users and peace of mind to service providers.
In this Article
- Introduction of the standard
- Top 7 Features the standard
WiFi 6 technology introduction
Access points that operate as per 802.11ax standards are expected to grow exponentially in the coming months. In the 1st quarter of 2020 (Jan-Mar), access points with WiFi 6 technology made up almost 12% of global enterprise access point shipments, which is still dominated by the previous 802.11ac standard at 80%. The 802.11 ax standard can operate from 1 GHz up to 6 GHz. This means the standard can operate in both 2.4 GHz and 5 GHz WiFi bands unlike its predecessor 802.11ac, which operates only in 5 GHz band.
802.11ax standard is technically called High Efficiency(HE). It is called as high efficiency because the goal of this new standard is not higher data throughput but better utilization of available resources to operate a more efficient WLAN. The standard does introduce 1024-QAM, which means higher throughputs, but major feature launches and upgrades of 802.11ax are targeted towards efficient utilization of scarce resources.
802.11 ax is certified by WiFi Alliance as WiFi 6 as per their branding initiative, where WiFi 5 will now denote 802.11 ac and WiFi 4 will denote 802.11 n . The WiFi 6 standard for 6 GHz frequency bands is called WiFi 6E.
As per usual norm, client stations using previous standards of 802.11 a/b/g/n/ac can communicate with WiFi 6 access points, as it is fully backwards compatible with older client stations.
But an 802.11 ax WLAN having only older clients will not see any great performance improvements as advertised for WiFi 6. Only 802.11ax clients can take advantage of newer features offered by the standard. But when more and more 802.11ax clients stations are added to the 802.11 ax WLAN, it will result in performance improvements for older clients as well. This is because more airtime will be available for them due to more efficient communications between 802.11ax access points and 802.11ax clients stations.
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Top 7 features of WiFi 6 Technology
The advantages provided by WiFi 6 can be summarized as per below figure.
Fig 1: WiFi 6 / 802.11 ax summary.
A. More Clients per Access Point
OFDMA (Orthogonal Frequency Division Multiple Access)
WiFi 6 access points will use OFDMA technique for efficient usage of channels. OFDMA is the technology used currently in 4G LTE networks. OFDMA is the multi-user version of the OFDM (Orthogonal Frequency Division Multiplexing) technique used by the previous WiFi standards for communicating with users. In both cases the channel is divided into smaller sub-channel units called tones or sub-carriers.
In OFDM, a whole channel is dedicated to a single user station irrespective of data transmission requirements. WiFi stations get access to the medium based on a contention mechanism: the stations wait to take turns. Every station is treated equally.
In OFDMA, the whole channel bandwidth is not dedicated to a single station. Here a channel’s sub-carriers are grouped together as Resource Units (RU) of various sizes. In a 20 MHz channel width, a maximum of 9 users can be accommodated, each with 26 RUs (~2 MHz). OFDMA divides a 20 MHz channel into 26(~2 MHz), 52(~4 MHz), 106(~8 MHz) or 242(~20 MHz) RUs, as per requirement.
Based on data transmission requirements, the AP decides the size of resource unit allocation. If a station has a large amount of data to transmit, the AP may decide to dedicate all 20 MHz to the single station. In the subsequent TXOP (Transmit Opportunity), the requesting station can use all 20 MHz bandwidth to send its data packets.
If there are multiple stations requesting bandwidth to send smaller chunks of data, the AP may decide to allocate the bandwidth equally among the users. In the next TXOP, the stations will transmit their data as per allocated RUs. This is a quantum improvement from earlier OFDM technology, where the whole channel got allocated only to a single user, irrespective of data size. Also OFDMA technology results in scheduling of air medium access for the stations, instead of their self contention. For the 1st time in WiFi history, client up-link can be controlled by the access point.
However contention is not replaced entirely. Empty resource units can still be contented for by the stations and utilized. But this is a huge improvement over stations contending for the whole channel, unable to send any data without winning the contention game first.
During down-link, a similar process is followed. If the AP is having data that needs to be sent to multiple clients, it packs the data into a single packet and sends it to clients. Before sending the data packet, a trigger frame is sent to client stations. The trigger frame contains information about RUs that contain data. The receiving stations will use this information to look into the respective RUs for their data. In OFDM present in previous standards, the AP had to content for medium everytime after using the full channel to send data packets to each client.
OFDMA also helps to reduce the airtime usage by reducing the number of packets utilizing the air media. In the contention mechanism, all stations and AP had to wait to take turns and get involved in collisions while trying to send data packets at the same time. This whole process generates lot of avoidable packets in the air. OFDMA not only speeds up the whole communication process, but also clears up WiFi communications quickly from the air medium.
MU-MIMO technology, which was introduced in 802.11 ac standard, has been increased in scope in 802.11 ax. In 802.11 ac, MU-MIMO can be applied only on downlinks with upto 4 streams in 5 GHz band. But in 802.11 ax, MU-MIMO can be applied to both uplink and downlinks between the AP and client stations, with upto 8 streams in either direction. And this is applicable to both 2.4 GHz and 5 GHz bands.
MU-MIMO, combining with beamforming, makes it possible to communicate with multiple client stations concurrently using multiple beams without interference between the beams. This process uses complex channel sounding techniques to locate a station for beamforming purposes. On the downside, this locating process generates lots of transmission overheads, making MU-MIMO less efficient for transmissions having thin data. The overheads may take more time to communicate than the data itself. This makes MU-MIMO useful in conditions only where heavy data transmissions are required. This proves especially useful in outdoor use cases where there is larger distance between clients and access points. Comparing to MU-MIMO, OFDMA does not require a sounding mechanism, making it effective in managing smaller data units that need to be sent quickly. Hereby 802.11 ax gives options to manage different data transmission scenarios using different technologies.
Also 802.11 ax standard provides the option to use a combination of MU-MIMO and OFDMA in the same transmission. But this feature is expected to be taken up by vendors only after 802. 11 ax becomes more evolved in the market.
B. More AP’s per site
Another important feature update that can be expected in WiFi 6 technology is called BSS coloring. This feature has been inspired from the BSS coloring scheme used in 11ah standard. In 802.11ax each AP is identified individually with an identifier called color and all client stations communicating with that AP are associated with that color. Now when a station wants to communicate and looks at the medium and sees another transmission with the same color in the same channel, it stops transmitting. If the transmission is found to be coming from another station with a different color, and if it is below a preset signal level , the competing signal will be ignored and the station will begin its own communication.
This can be very helpful in high density environments with closely packed access points. The stations can ignore communications from other nearby stations using the same channels, thereby avoiding agressive co-channel transmission limitations present in earlier standards. BSS color information is included in the preamble frames of the WiFi and can have 63 different values. This can potentially identify 62 different neighbouring stations/networks. ‘Color’ is chosen by an AP, which can also adjust its color if it is found overlapping with any neighbouring APs. Clients stations will have the capability to alert APs with duplicate color.
In the above figure, a sample scenario is showcased to describe BSS coloring principle and its advantages. Here AP1 and AP2 are operating in the same channel 44. The access point AP1 and station STA2 are above preamble detect(PD) threshold of -82 dBm. Similarly, AP2 and STAT1 are outside PD. But stations STA1 and STA2 and below the PD threshold.
In a pre-WiFi 6 world, since the 2 client stations are within the PD threshold of -82 dBm, they will contend for the medium. They will patiently wait for the other station to finish its communication to get a free channel. This will happen even when AP2 cannot hear STA1 and AP1 cannot hear STA2. This is a handicap which was unnecessarily slowing down WiFi communications.
But with WiFi 6 technology, the BSS coloring is available to address above such issues. As per this, each BSS will have its own color. Color is actually a value set in the PHY header of the frames. In the above figure, the right side image has BSS colors yellow and orange.
In this BSS color applied scenario, the client station STA1 will look at header frames from STA2. If it notes it has a different color it will start its transmission even if PD from STA2 is stronger than -82 dBm, unlike earlier times when it begin the contention process. This simultaneous transmission will greatly improve the actual speed of communications as unnecessary wait times are eliminated for stations.
Here PD values can only be between -82 dBm and -62 dBm, which is the ED of WiFi transmissions. ED is for Energy Detect. In WiFi, a channel is marked as busy if any energy in the channel, including non-WiFi interference is noted to be above this ED value. Non-WiFi interference includes microwave ovens, blue tooth, wireless CCTV signals etc and these can be easily found using WiFi spectrum analyzers.
802.11 ax standard gives the option to transmit at 1024 QAM data rates, which is 10 bits per symbol. The 802.11 ac standard allowed 256 QAM at 8 bits per symbol. 802.11 ax thereby offers a 25% increase in throughput. But transmissions at 1024 QAM are going to need a very clear spectrum and close proximity of client stations to the 802.11 ax access points.
802.11 ax gives a concept called preamble puncturing, which can help client stations to transmit using wider channels. In the 802.11 ac, when using wider channels with channel bonding, any interference happening in any of the channels will make the client station to fall back to reduced channel width, which is usually the primary 20 MHz channel.
But 802.11 ax gives an option to still transmit under such conditions using a wider channel. When any interference is detected in any of the channels used in channel bonding, the station will ignore the particular channel and transmit using other channels without falling back to truncated channel widths.
This feature is expected to help stations transmit at higher channel widths and thereby improve the speed of transmissions in dense environments like corporate offices.
6 GHz Operations
On April 23, 2020 USA’s FCC opened up the entire 6 GHz of spectrum for unlicensed use. This historic decision enables 802.11 ax operations in 1200 MHz of previously unused WiFi spectrum. This spectrum ranges from 5925 MHz to 7125 MHz. So far WiFi was operating in about 240 MHz of total non-overlapping bandwidth in 2.4 GHz and 5 GHz bands.
As the 5 GHz spectrum is also quickly getting congested in all dense areas, this additional spectrum is expected to help smooth WiFi operations. Usage of wider channel widths may be possible for some time till 6 GHz bandwidths also get congested. Also a larger pool of available channels will make interference management less tiresome than presently possible in 2.4 GHz and 5 GHz bands.
6 GHz operations, when combined with the additional new features in the WiFi 6 technology is expected to make WiFi operations more tolerant to interference when accessed with compatible client stations.
D. More Power Savings with WiFi 6 Technology
Target Wake Time
Target Wake Time is a feature that has been developed from 802.11ah “Ha-Low” standard. This feature helps APs and client stations to negotiate optimal time periods for their communication. After successful negotiation, the clients are woken up by the AP only at the agreed times using a trigger for the specific client. At other times, the clients can sleep. They can hereby conserve battery without constantly being awakened by triggers not meant for them, as per existing WiFi standards.
This feature is expected to greatly help IOT clients that have minuscule data communication requirements. They need not be awakened periodically by triggers not meant for them and can continuously sleep for long periods of time.
As can be seen, 802.11 ax is a standard targeted towards improving the overall efficiency of WLAN networks. Many of the features introduced or improved upon in WiFi 6 were considered as critical handicaps of the technology for a long time. When WiFi was originally introduced, the engineers certainly did not imagine the huge popularity it would attain globally and the millions of devices it would end up supporting. After such explosion in popularity, what WiFi needed was features and improvements that would accommodate such scale of usage by its design. By targeting such improvements, the 802.11 workgroup has set the platform for WiFi to be the bedrock of information access in the coming decades by both enterprise and non-enterprise users. Once widespread usage of WiFi 6 access points begins, it is going to improve the whole experience of wireless communications for all the stake holders.