A prescription for decongesting Wi-Fi networks

The Wi-Fi Alliance’s release of Wi-Fi 6 and 6E are a major update to the most ubiquitous wireless technology used in IoT networks. The update delivers significant advancements in performance, efficiency, latency and other features – making this a major upgrade that will continue to make it a foundational technology for IoT. One of the most significant benefits of this new version of Wi-Fi is the impact it will have on eliminating congestion in high-density Wi-Fi networks.

Device density has exploded in recent years, pushing Wi-Fi-based device networks to their limit as more and more devices lean more heavily on those networks for a growing number of applications. These high-density environments include hospitals and clinics, factories, schools, arenas, airports, industrial facilities, warehouses and more. To illustrate this congestion, consider an emergency room bay at your local hospital. A single room in the ER can have dozens of wireless devices operating side-by-side in an area smaller than a residential bedroom. That is a lot of devices competing for connectivity in a complex RF environment. The same is true in those other environments above, where more and more sensors, robotic controls, smart machines, field worker tablets, consumer devices and other connected devices are asking more and more of Wi-Fi networks. The result is network congestion and significant performance issues for those connected devices.

Wi-Fi 6/6E was designed to address network congestion head-on with a number of features that dramatically increase the number of devices that can be supported in a physical space while also optimising performance for each. Below is a discussion of those key features that make this possible: MU-MIMO with Spatial Streams, OFDMA and BSS Colouring.

MIMO and spatial streams

One of the features that Wi-Fi 6/6E uses to reduce congestion utilises Multi-User Multiple-In Multiple-Out (MU-MIMO) to create spatial streams that focus RF activity in the physical direction of each device. This is achieved by using two antennas and creating an intentional interference pattern to focus signal toward the intended device or groups of devices.

As many as eight spatial streams are possible with this technology, which allows access points the flexibility to target many devices nearby with precision. In addition, the controlled directionality of the beam forming creates a cleaner RF environment and uses less power: a beamformed transmission within a spatial stream achieves a better link with less power. By focusing RF connections in this way, the RF environment is immediately cleaner, allowing more reliable connections that are more efficient. An added benefit is that neighboring access points have a lower concentration of competing RF activity, preventing an environment from becoming saturated with unintended signal – a symptom of overly-congested Wi-Fi networks that negatively impacts device performance.

Wi-Fi 6/6E bring bi-directional MU-MIMO to allow for more efficient use of the RF environment than previous generations had allowed. The beam forming can now be used by both the Access Point and the stations being talked to.

OFDMA with multi-channel communications

Another key feature that reduces network congestion is Orthogonal Frequency Division Multiple-Access (OFDMA), which allows multiple clients to talk to the access point at the same time. OFDMA uses different channels to allow more devices to send and receive data than the prior version of Wi-Fi. Rather than all devices waiting in line for their turn to send or receive, they do so simultaneously, but in non-interfering channel spaces, which means they all enjoy much more immediacy to their communications. In a given segment of time for a Wi-Fi link (a frame), OFDMA allows the access point to send and receive multiple messages across different channels (frequencies) to and from different devices. In the graphic below, you can see how this enables far more data transfer to happen in a dense environment, with faster throughput and lower latency.

In this way, OFDMA provides a multiplier effect on the benefits of MU-MIMO: MU-MIMO allows highly focused spatial streams to more devices, and OFDMA then allows that number of devices to expand even more by allowing devices to communicate with the access point on a number of channels simultaneously. This enables Wi-Fi to achieve a previously impossible level of bandwidth utilisation and potentially significantly lower latency for data delivery.

BSS Colouring with intelligent traffic management

BSS Colouring provides an additional layer of intelligence that alleviates congestion. BSS (Basic Service Set) refers to the basic network topology of a cluster of devices that are communicating with an access point. It is the fundamental unit of a Wi-Fi network. When multiple access points are located within RF range of each other, non-overlapping channels are used to avoid interference between access points across a given location. This previous architecture had its limits as device density increased because access points need to re-use channels as soon as more than three access points are in an environment – which is true for many healthcare, industrial and commercial Wi-Fi networks. That limitation of the prior version of Wi-Fi exacerbated network congestion because overlapping channels prompted devices to pause communications, check to make sure it is safe to proceed, and only proceed if there was no competing traffic. This leads to inefficient management of requests for connectivity.

BSS Colouring alleviates this issue by allowing the access point to intelligently manage traffic occurring on the same channel by adding a prepend to their broadcast identifier in the form of a colour. If a device hears a broadcast on its channel, but the broadcast is of a different colour, the device can determine that it’s for another service set and go ahead and broadcast without waiting. In doing this, we can categorise devices into association or affinity with a given access point with a high degree of likelihood that they will not interfere with each other, due to proximity. This will allow devices to talk to their nearest AP without fear of interrupting another service set.

With 63 available BSS colours and 88 non-overlapping 20 MHz channels, there are over 5500 unique combinations of channel and BSS colour alone. This means that BSS Colouring gives an exponentially greater way to prevent collocated service sets from slowing each other down. The result of BSS Colouring is that more devices can be placed within a smaller area and exist without being impacted by closely co-located AP’s utilising the same spectrum.

A prescription for decongestion

The combination of these three technologies – MU-MIMO with Spatial Streams, OFDMA with Multi-Channel Communications, and BSS Colouring – is significant for reducing network congestion. But Wi-Fi 6/6E integrates them in a way that enables them to have a combined effect that is even greater than the sum of the parts. Design engineers working on Wi-Fi based devices and IoT deployments have a powerful new tool for alleviating congestion in high-density environments.