WiFi 6 – a revolution in the wireless space

The last two decades have seen many WiFi versions come into the market and most targeting performance and throughput improvements over their predecessors. WiFi 6 is no exception, however, it attempts to tackle a bunch of other common issues of recent times, whilst keeping tabs on performance and throughput improvements. With the exponential growth of connected clients leading to increased network traffic and use-cases such as WiFi Calling and live streaming calls, WiFi 6 seems to be the best bet around.

WiFi 101

To fully appreciate and comprehend the capabilities of WiFi 6, let’s take a little history lesson here and see how WiFi has evolved. Below table provides a chronological snapshot of different WiFi standards, their data rate and bands utilized, etc.

WiFi version	Year released	Frequency Band	Max Data Rate	Notes
WiFi 1 – 802.11a	1999	5 Ghz	54 Mbps
WiFi 2 – 802.11b	1999	2.4 Ghz	11 Mbps	First commercially used standard
WiFi 3 – 802.11g	2003	2.4 Ghz	54 Mbps
WiFi 4 – 802.11n	2009	2.4 Ghz and 5 Ghz	600 Mbps	First dual band standard
WiFi 5 – 802.11ac	2013	5 Ghz	3.47 Gbps	Includes 2.4GHz radio (802.11n)
WiFi 6 – 802.11ax	2019	2.4 Ghz and 5 Ghz	14 Gbps

WiFi 6 was built for high efficiency, capacity improvement, increased coverage, and most importantly better user experience. In simple terms, its bringing great Wi-Fi experience to the real world.

Why WiFi 6?

Businesses are allowing employees to bring their own devices such as smartphones, tablets, etc that need to be secured without compromising the performance. Houses/apartments are deploying a variety of Wireless-connected clients that require both high and low data transfer. These would be smart cameras (eg: Nest cameras, IP cameras, etc), voice-activated devices (eg: Amazon echo, Google assistant, Apple home, etc), smart doorbells (eg: Ring doorbell, August locks, etc), Smart garage openers, smart automation hubs, etc. As smart devices are growing day by day and network density increasing, demand for performance is inevitable. Power consumption of each client devices raises even when they are idle, as they need to content for the channel availability to pass traffic. Moreover, the resolution of video streaming is increasing consistently from 2K to 4K to 8K to which the wireless environment should adopt. WiFi 6 promises to resolve a lot of these issues.

How does WiFi 6 solve it?

WiFi 6 is designed to solve the aforementioned problems by utilizing a number of technologies as below:

• Orthogonal Frequency Division Multiple Access (OFDMA) Uplink/Downlink
• Multi-user Multiple Input Multiple Output (Mu-MIMO) Uplink/Downlink
• BSS Coloring (Spatial Reuse)
• Target Wake-up Time (TWT)
• New PHY Headers
• Support for both 5 GHz and 2.4 GHz
• Enhanced outdoor robustness

Here, I will explain about OFDMA, MU-MIMO, BSS Coloring, TWT, New PHY headers that address the use cases of Dense network environment (performance is key), video/game streaming (that needs low latency), saving power for clients.

OFDMA

Orthogonal Frequency Division Multiple Access (OFDMA) is an extension to Orthogonal Frequency Division Multiplexing (OFDM) which is in effect from 802.11g to 802.11 ac. In Orthogonal Frequency Division Multiple Access (OFDMA), the access points (AP) divide a 20 MHz channel into 256 sub-carriers where each sub-carrier is 78.125 KHz width. These sub-carriers can be Data sub-carriers (those that carry modulated date), Pilot sub-carriers (those that help in synchronization between client and AP), Unused sub-carriers (used as guard carriers to avoid interference from others). These sub-carriers are further grouped into sub-channels called Resource Units (RU)

When data (traffic) has to be passed, OFDMA can either allocate the whole sub-channels of a channel to a user or allocate specific sub-channels to individual users. By this way, the channel is being optimally used thus having faster responses to end devices and increasing throughput. Think of a taxi serving one customer at a time compared to a carpool service where multiple users are being served at the same time.

Above figure 1 explains how OFDMA works and how OFDMA differs from OFDM. For simple understanding, I have chosen 2.4 GHz radio which has 11 channels each of 20 MHz widths. Here, channel 6 operates at 2.437 GHz.

In OFDM, channel 6 is divided into 64 sub-carriers. A data that needs to be transmitted to iPhone, Tablet, Chromecast will be sent sequentially on first come basis. Data for iPhone will be sent first followed by Tablet and Chromecast. In OFDMA, channel 6 is divided into 256 sub-carriers. The sub-carriers are grouped together as Resource Units (RU) and data are sent parallelly as and when they are ready to be transmitted. So, multiple clients (Tablets, chromecast) receive their respective data simultaneously. This will increase the performance tremendously especially for devices (such as IoT) that requires low-bandwidth.

MU-MIMO

Multi-User – Multiple Input Multiple Output (MU-MIMO) is a mechanism to improve overall performance. Here, multiple frames can be transmitted to different receivers at the same time on a single channel using multiple spatial streams. In Wi-Fi 6, APs can transmit data to a maximum of 8 users simultaneously (downlink traffic) and receive data from a maximum of 8 users simultaneously (uplink traffic). In WiFi 5 (802.11ac – wave 2), only downlink MU-MIMO was supported which means the data from wireless access points to clients can utilize the MU-MIMO. In the real world, a lot of uplink traffic (uploading photos to google drive, uploading videos in Instagram and Facebook, tweets, etc) happens due to the increased use of social networking sites which can be benefitted from WiFi 6. In addition, MU-MIMO can be used for high traffic use-cases such as HD streaming, online games, live video streaming, etc that require high bandwidth.

MU-OFDMA allows multi-user access by dividing a channel into sub-carriers. MU-OFDMA is mostly used for Increased efficiency, reduced latency, applications with low-bandwidth and with small packets 

MU-MIMO allows multi-user access by using same channel on different spatial streams. MU-MIMO is mostly used for Increased capacity, high data rates per user, applications with high-bandwidth and with large packets

BSS Coloring (Spatial Reuse)

In a wireless RF medium, only one radio can transmit/receive on a frequency domain or a channel. An 802.11 radio will defer from transmitting if it hears the physical (PHY) preamble transmitted by any other 802.11 radio (maybe from a neighbour’s wireless router) at a signal detect (SD) threshold of four decibels (dB) or greater. This congestion and channel contention issues are solved by BSS Coloring mechanism.

A number between 0 and 7 is added on the PHY header of WiFi 6 frame to each BSS (Basic Service Set) in an environment. When a listening radio sees a PHY preamble, it checks for the BSS ‘color’ bit (the number assigned between 0 and 7) of the transmitted radio and does either of the below:

• If the BSS ‘Color’ bit is the same as its own: it considers the channel is busy on its own BSS which is intra-BSS. In this case, the radio defers from the transmission
• If the BSS ‘Color’ bit is different from its own: it considers the channel is not in its own BSS which is inter-BSS. The radio then transmits the data.

Target Wake-up Time

TWT is a power-saving mechanism that helps wireless clients to save their battery power. AP schedules/negotiates a time frame with each of the client devices as a ‘wake-up’ time. Only during the scheduled wake up interval time, the client devices wake up to transmit/receive data. This will tremendously increase the battery life of the client devices as they are not awake the whole time. In this technique, clients need not contend for the time to transmit. Instead, the clients can sleep (low power mode) until it is their turn to send traffic (wake up). AP and clients can negotiate up to 8 separate ‘wake-up’ time based on the application traffic running on the clients. This is a big win for battery operated devices for achieving longer battery life. The biggest benefit will be for IoT devices.

New PHY Headers

In general, all 802.11 frames are prefixed with PHY headers which contains a preamble and other pieces of information that are used for initial setup and communication between AP and wireless clients. Given all the new technologies added to WiFi 6, the PHY headers are enhanced with newer fields to achieve the desired communication. Therefore, WiFi 6 introduces 4 new PHY headers in the physical layer to support High Efficiency (HE) radio transmission.

• HE SU – High-Efficiency Single-User header is used for single user communication
• HE MU – High-Efficiency Multi-User header is used for multiple user communication like OFDMA, MU-MIMO, RU allocation
• HE ER SU – High-Efficiency Extended-Range Single-User is used mostly for outdoor communications and range
• HE TB – High-Efficiency Trigger-based is used as a response to the trigger frame

Below figure provides a high-level idea of how the preamble information is present.

Other key factors to know about WiFi 6

In addition to the above mentioned important technologies/features, WiFi 6 also includes:

• WiFi Protected Access version 3 (WPA3) which has lots of security enhancements
• Support of 2.4GHz as many existing wireless clients and mesh environment requires it
• 802.3at/802.3bt PoE might be required based on the features included in WiFi 6
• Multigig ethernet ports with 2.5 Gbps, 5 Gbps speed to truly experience performance

Do you need to upgrade your Wireless router from WiFi 5 to WiFi 6?

The answer depends on the way you use your wireless clients. For users who don’t have to upgrade their wireless clients to be WiFi 6 compatible or who do not need a lot of IoT devices at home, WiFi 5 should be good enough for a while. Also, since WiFi 6 is relatively new, some users might not feel comfortable adapting to the first version of WiFi 6 wireless routers. For users who do not stream 4K or 8K videos might not benefit from WiFi 6. But eventually, adapting to the newer technology will have its own benefits. A lot of wireless mesh systems utilize 2.4GHz which might benefit from WiFI 6. Also, to keep in mind that true WiFi 6 compatible wireless clients are yet to come to market to truly experience end-end WiFi 6 solution. Below table provides differences between WiFi 5 and WiFi 6.

Features	WiFi 5 (802.11ac)	WiFi 6 (802.11ax)
Band	5 GHz only (supports 2.4GHz of 802.11n)	2.4GHz and 5 GHz
Channel Bandwidth	20 MHz,40 MHz,80 MHz,80+80 MHz,160 MHz	20 MHz,40 MHz,80 MHz,80+80 MHz,160 MHz
Modulation max	256-QAM	1024-QAM
Sub-carrier spacing	312.5 KHz	78.125 KHz
MU-MIMO	Downlink only (4×4)	Downlink and uplink (8×8)
OFDMA	N/A	Yes

WiFi 6 routers currently available in market

The WiFi 6 routers need to be certified by WiFi Alliance to meet the IEEE 802.11ax standards. Below lists provide the currently available WiFi 6 routers for both home/apartment and enterprise purposes.

Summary

WiFi 6 is loaded with rich new feature sets that are going to improve the user experience multi-folds. As it is very common for any new technology to get stabilized, there will be few initial hiccups which might be unnoticeable to end users. When new WiFi 6 clients are introduced to the market, the true potential of WiFi 6 can be experienced by end users. Nevertheless, WiFi 6 is here to stay and revolutionize the wireless industry.