Introduction
We all know what WiFi is for – fast wireless connections between computers/phones or other devices and the internet. And what we expect from a WiFi upgrade is more of the same – faster speed. This is what the progression from WiFi 3 to 4 to 5, has offered – speed upgrades around an order of magnitude.
WiFi 6, however, is focused on something different. Whilst theoretically there is some speed increase possible, the main purpose of the new capabilities is to offer “WiFi for IOT”, via support for more connections and low power operations. This article will explore the key changes in WiFi 6 and what they offer.
Orthogonal Frequency Division Multiple Access (ODFMA)
The first change is the introduction of Orthogonal Frequency Division Multiple Access (ODFMA). This is a technology “borrowed” from cellular technology and allows the available bandwidth to be split up into multiple “resource units”. Earlier versions of WiFi required a channel solely to communicate with a single device at a time, with the only flexibility being the width of the channel (20, 40, 60, 80 and 160Mhz). A wider channel theoretically allows a higher bandwidth but increases the risk of interference and limits the number of concurrent devices. In practice, most routers will use 20 or 40 Mhz channels.
Under ODFMA, a channel can be split into subcarriers (in frequency and versus allocated Resource Units in the time domain), so multiple devices can connect to a single router. The division into subcarriers can be carried out flexibly, so individual users can be allocated bandwidth dynamically dependent on need. This uses the available bandwidth efficiently. It also offers lower latency, as a device doesn’t have to wait until the entire channel is available.
Multiple device connections
In practice, this means that a single 20Mhz channel can be used to connect to up to 9 devices simultaneously or share bandwidth flexibly between a smaller number. A further change in the standard allows an end device to only support 20Mhz channels (previously, they were required to support up to 80Mhz channels), allowing for simpler end device chipsets with potentially lower power consumption.
What does all this add up to? Taken together, these changes permit a larger number of simpler devices with lower data requirements to share the network efficiently and with low latency. This is where WiFi traditionally hasn’t performed well and is a typical scenario for Internet of Things applications.
Scenarios such as a smart home with many connected devices or an industrial production line with many connected machines might previously have struggled to work efficiently, as they battled for access to the network. The new WiFi 6 standard allow a much more flexible use of contested spectrum.
Lower power capability
A further feature that enhances WiFi’s suitability for Internet of Things applications is Target Wait Time (TWT). Older WiFi standards required a continuous connection between router and device without devices having to re-authenticate and rejoin the network. The time out delay was a single number for all devices. Target Wake Time lets each device negotiate a wait time with the router, enabling devices to sleep for longer intervals between active radio transmissions. In turn this allows much lower power applications, especially in the case of devices requiring lower data rates and less frequent connections. It can also further liberate spectrum by not requiring devices to transmit unless they need to.
WiFi 6 and BLE – competing now?
These features – lower power devices, and support for dense networks – of WiFi 6 seem like those of Bluetooth Low Energy (BLE). There is some convergence, with the introduction of low power features and better support for multiple devices. However, there is still a big gap in terms of data rate and power consumption. Even at the lowest data rate, with for example a 20Mhz channel being shared between multiple devices, one could expect a data rate an order of magnitude of throughput above the BLE limit of 2Mbps. In addition, WiFi 6 can utilise the less congested 5Ghz band, and in certain territories, the 6Ghz band (WiFi6E).
Conversely, on the power consumption side, a BLE device will still offer far better low power performance. The relative simplicity of BLE means it can run on much smaller processors, which in turn consume less power, and the lower bandwidth radio signal can be transmitted more efficiently. Or in other words, you don’t get something for nothing, and so there are still trade offs to be made.
The trend of multiple radios
To put this in more concrete terms, a suitably designed BLE device could run off a coin cell battery, whereas a WiFi 6 based object more realistically needs an AA type battery. BLE also doesn’t rely on having an access point. You can establish local connections between devices easily and securely.
What the next generation of IOT devices is likely to offer is multiple radio access for different functions. For instance, BLE’s easy ad-hoc connections could be used for commissioning and maintenance, with the WiFi established for ongoing standard usage. This is the type of scenario the Matter protocol envisages. Many products provide combined BLE and WiFi capability. For example, Insight SiP’s ISP5261 RF module includes WiFi6 and the latest generation of BLE in a single module with integrated antennas.
There are further enhancements contained within the WiFi 6 upgrade. Network “colouring” permits different access points to distinguish themselves and allow an end device to not be blocked by a low power signal creeping over from a neighbouring Access Point. This adds additional support for dense networks. The network “colour” is an arbitrary designation. You can’t make blue or red radio waves!
Additional modulation options also offer the possibility of higher speeds, albeit only in very high-quality signal situations with a limited number of devices.
Conclusion
The next generation of WiFi, WiFi 6, has taken the standard in a different direction to previous upgrades. There is a relatively modest upgrade in speed, but the key changes are to allow dense networks and lower power devices. It is therefore reasonable to describe this as “WiFi for IOT”. The previous generations of WiFi were mostly aimed at devices with a person using them at the end point. A dense network of low power devices, with modest data communication needs, is, by contrast, exactly the situation in many IOT applications and use-cases.
Author: Dr Nick Wood, Director, Sales & Marketing, Insight SiP
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