17-05-2023 | By Robin Mitchell
The 2.4GHz band has been a staple for tech devices ever since the first Wi-Fi networks were established back in 1997. While this frequency has been extremely helpful, thanks to its lack of licensing, the mass use of this band also comes with numerous drawbacks, including reliability and bandwidth challenges. Why has 2.4GHz been immensely popular amongst devices, what challenges does it face, and what technologies could engineers look towards?
The radio spectrum is full of frequency bands, ranging from long wavelength radio to the high-frequency sub-millimetre microwave, and yet, across this entire range, it is the 2.4GHz band that remains popular amongst engineers.
Contrary to popular belief, the choice of 2.4GHz for microwave ovens isn't due to water molecules resonating at this frequency. Dr. Christopher S. Baird, a known expert in the field, explains in an article titled "Why are the microwaves in a microwave oven tuned to water?" that microwaves generated inside an oven are not monochromatic, meaning they aren't tuned to a specific frequency. His work has been instrumental in debunking common misconceptions about microwave technology1. Instead, they are created by a device called a magnetron that emits a broad spectrum of frequencies, which vary depending on the specifics of the food being heated.
The microwaves heat food through dielectric heating. The electric field in the electromagnetic wave exerts a force on the molecules in the food, causing them to rotate, collide, and convert their somewhat ordered rotational motion into heat. This applies to many types of molecules in the food, not just water molecules1.
At the same time, the 2.4GHz band is unlicensed in almost all countries, meaning that anyone can use the frequency. Thus, when the development of Wi-Fi came about in 1997, it made sense for engineers to turn to an unlicensed frequency band. However, many unlicensed bands exist, with some example frequencies including 433MHz, 900MHz, 1890MHz, and 5.8GHz. So why did 2.4GHz persist over these other options?
For instance, take a look at the ubiquitous home router. Most routers from the early 2000s up until today default to this band because of its superior range and wall penetration. This band was a clear choice for manufacturers wanting to ensure their devices provided reliable internet access throughout a home.
Firstly, as Wi-Fi generally deals with large data transfers (megabytes per second), there is a significant requirement for bandwidth, which rules out many of the lower frequencies (sub 1GHz). Secondly, such a network needs to be able to operate over a wide area, and while lower frequencies have far better long-range capabilities, this comes at the cost of bandwidth. However, using very high frequencies (5GHz and over) not only struggles at a distance but also has poorer penetration capabilities through walls and corridors.
Thus, engineers came to the conclusion that 2.4GHz is the perfect frequency for Wi-Fi due to its long-range capabilities (up to 100 meters) while providing significant bandwidth and ability to propagate through indoor environments. Of course, barring all of this, the single most important reason for using 2.4GHz is that it’s free, and so is the Wi-Fi standard, meaning that anyone can develop their own Wi-Fi chipsets.
But it’s not just Wi-Fi that has benefitted from the 2.4GHz spectrum; many other protocols have utilised this band due to the lack of licensing and numerous capabilities offered. For example, Bluetooth is a low-energy radio technology that has taken advantage of this spectrum, and so has Thread and Zigbee. As a result, industries such as IoT have managed to see a massive acceleration in development and deployment, with almost all homes having some kind of IoT device.
For all of the advantages that 2.4GHz offers, the very aspects that make it an impressive band are also its Achilles heel. Because the band is unlicensed, almost anyone can make their own 2.4GHz devices, and this is starting to see issues with congestion. While this may not be a problem for the average home at the moment, the inclusion of more IoT devices over the next decade will quickly see networks begin to slow down. This is especially true for densely populated areas where multiple access points are often in close proximity, and the finite number of frequency channels fundamentally limits the maximum number of devices that can simultaneously connect and transfer data.
A real-world example of these challenges can be seen in densely populated apartment buildings. In such environments, the abundance of different Wi-Fi networks on the 2.4GHz band often leads to signal interference, reducing the quality of connections.
The 2.4GHz spectrum also faces challenges with modern applications and the need for increased bandwidth. For example, the shift towards 4K video has seen the amount of data being streamed from video services grow exponentially (4K require at least 4 x the amount of bandwidth compared to 1080), and the use of higher framerate video further increases this bandwidth requirement. A single device connected over a 2.4GHz network can stream such video, but when multiple clients are connected simultaneously, all requesting such video content, traditional 2.4GHz can start to struggle.
Overall, 2.4GHz has been great over the past few decades, but as the bandwidth requirements from devices increase combined with the increasing number of devices, it is clear that 2.4GHz is not up for the job, and new solutions are needed.
Thankfully, numerous governments around the world have already identified the ongoing issues with 2.4GHz, and have opened multiple frequencies. 5GHz is one such band that engineers can turn to for increased bandwidth and has existed for a number of years now. As there are few 5GHz IoT devices, the lack of congestion on this spectrum combined with its smaller range makes it ideal for localised networks inside rooms providing ultra-high-speed internet services. This low range also makes it a possibility for future short-range devices such as tags, identification chips, and even potentially a new version of Bluetooth.
According to a report by the Federal Communications Commission (FCC), the 6GHz band is expected to be the future of Wi-Fi technology due to its ability to support higher capacity operations and a wider range of applications. Their extensive research and ongoing studies on this topic make them a highly credible source in the field. While it is still in its infancy, 6GHz is able to offer devices with even greater bandwidth compared to 5GHz, supporting applications such as 8K VR. Devices that support these frequency bands are commonly labelled with Wi-Fi 6E, which is different to Wi-Fi 6, which operates at the traditional 2.4GHz and 5GHz bands.
Engineers that need to transmit small amounts of data could also consider the benefits of LoRa and 433MHz. Both of these bands are unlicensed, which reduces developmental costs, and their long-range nature allows for devices to consume little energy, transmit a few bytes, and do so over many kilometres.
Going forward, it is likely that 2.4GHz will become a network for slower devices, such as smart home sensors and interfaces that only occasionally send data. Devices needing greater bandwidths, such as smartphones and laptops, will need to shift towards different networks operating at much higher frequencies. Not only does this help to decongest the 2.4GHz band, but it also provides greater bandwidth to those devices, thereby allowing them to continue working with the latest features and services.
One successful example of transitioning away from the 2.4GHz band can be seen in the recent launch of the latest iPhone models. Apple has embraced the 5GHz and 6GHz bands, allowing for faster data transfer and less congestion. This has been positively received by users, with many reporting noticeably faster internet speeds.