More than thirty years ago when Wi-Fi was still a nascent technology, a limited amount of mid-band radio spectrum was available for unlicensed use. While this spectrum has only seen minor additions since then, the number of wireless devices bustling around in this limited part of the radio spectrum has skyrocketed – but the part of the spectrum used by wireless technologies has not grown to match this development.
Today, half of the global population lives in urban areas with increasing numbers of Wi-Fi connections—the quality of which is steadily getting worse. For obvious reasons: There is an ever growing number of people—and devices—using wireless technologies and clients, with no end in sight. Depending on which forecast you are looking at, predictions vary between 12 and 20 billion devices being around by 2020.
The reason we are in this position is the technological advance in the wireless industry, with theoretical Wi-Fi speeds reaching Gbits per second. But with all the tweaks and features, we tend to forget that the portion of the radio spectrum available to wireless networks has its limits. If nothing changes, our already dense wireless networks will continue to become even more crowded.
There is no Such Thing as Free Lunch in Physics
Wi-Fi makes use of a specific part of the unlicensed spectrum. It allows users to access the radio spectrum for free. The downside is that this spectrum is shared with many other radio technologies that consume bandwidth and that cause interference.
There are numerous unlicensed bands in various parts of the radio spectrum; some of them are referred to as ISM bands – Industrial, Scientific and Medical – going back to their initial area of application. They carry everything from microwave ovens to radio communications. Many of them, including the 2.4- and 5-GHz bands used for Wi-Fi, have been allocated globally, while local restrictions may apply.
A Victim of Its Own Success
Congestion of these frequency bands is the most imminent threat in the near future. There is a limited number of lanes in which Wi-Fi signals can travel without slowing down the overall traffic. It is not just the number of devices that contributes to the congestion; other factors are the wireless networks themselves, the available lanes (channels), and how wide they are.
For example, in the United States the FCC has authorized roughly 80 megahertz of the unlicensed spectrum for the usage of Wi-Fi – in the 2.4-GHz band. The channels operating under the IEEE 802.11n standard are 20 MHz wide. This allows for just three non-overlapping channels with 80 MHz in total. In Europe, the situation is only slightly different: There are 13 channels which again allows only for three non-overlapping channels at a time. Japan allows 14 channels, which provides four non-overlapping ones.
The maximum bit-rate of a wireless channel is limited by its bandwidth, expressed in the amount (usually in Hz) of the (unlicensed) spectrum allocated. The limit is provided by the Shannon-Hartley Theorem. This physical law, named after its inventors Claude Shannon and Ralph Hartley, states that if you want to increase the speed you either have to allocate more spectrum or improve the signal-to-noise ratio.
At Stake From Various Sides
It is also the technological advance of Wi-Fi itself that worsens congestion: In its highest-performance configuration, IEEE 802.11ac Wave 2 wireless LAN combines the entire available Wi-Fi spectrum into two 160-MHz-wide channels in the 5-GHz band. This means that only two pairs of devices can simultaneously communicate on the widest of channels without interfering—the reason being the limited amount of frequencies available between 5.150 and 5.725 GHz.
Furthermore, Wi-Fi congestion in the 5-GHz band will soon get even worse as mobile-phone carriers, who have exhausted much of their expensive licensed spectrum, are planning to off-load a great deal of their mobile data transmissions onto the unlicensed spectrum. The hot debate about new mobile data standards like LTE-U and LTE-LAA and their battle with Wi-Fi for spectrum has already been covered in our blog and also by the IEEE.
Wireless Traffic Jams Ahead
Every day, Wi-Fi users around the world depend on the availability of the given spectrum for content and services. Analysts and industry experts around the globe agree on the fact that, soon, demands on Wi-Fi will exceed the capacity of the limited amount of unlicensed spectrum available. But what can we do about it?
The Wi-Fi Alliance recently commissioned the Wi-Fi Spectrum Needs Study to assess whether available spectrum resources are sufficient to support Wi-Fi connectivity in the future. The findings indicate that by 2020, Wi-Fi networks around the world will need significantly more mid-band spectrum than is currently available in the 5-GHz range to satisfy expected growth.
The study claims that between 500 MHz and 1 GHz of additional spectrum will be required by 2020 to support the predicted growth of Wi-Fi. In case traffic increases even faster than expected, another 1.3 GHz to 1.8 GHz of spectrum may be required by 2025.
In addition, analysts say that Wi-Fi spectrum needs to be contiguous to enable 160 MHz wide channels. These broad channels are required to support a growing number of bandwidth-intensive applications and to allow maximum data rates for the increasing number of devices using 802.11ac Wave 2 Wi-Fi.
Spectrum on the Move – But Not Everywhere
Driven by the exhaustion of the 2.4-GHz band, current debates about extending the spectrum for Wi-Fi target the 5- and parts of the 6-GHz band. This is because current Wi-Fi standards like 802.11ac (and 11ax to be standardized by 2019) rely exclusively on 5 GHz as this offers a combination of range and rate that is unmatched by 2.4 GHz. Theoretically, the 5-GHz band has more than 500 MHz to offer for Wi-Fi usage. But various restrictions and regulations mean that there are still gaps in this part of the spectrum where Wi-Fi use is not allowed, and this makes a contiguous use very difficult.
In 2005, the European Commission allocated a total of 455 MHz (5.120-5.350 and 5.470-5.725 MHz) for use by Wi-Fi in the 5-GHz band, which restricts the accommodation of 160-MHz wide channels. Similar parts of the wireless spectrum have been allocated for wireless use around the globe. As a result of these restrictions, there has been some movement recently in the United States and also in Europe, to extend the bandwidth available at 5 GHz. In particular, filling the gap between 5.350-5.470 MHz and allocating the top end of the 5-GHz band from 5.725 to 5.850 MHz, which has been available for wireless usage in the U.S. for quite some time now.
Earlier this year a new law in the United States requires the FCC and the National Telecommunications and Information Administration (NTIA) to look into the possibility of operating wireless devices in the 5.350-5.470 and 5.850-5.925 MHz. One major problem in Europe is that at the top end of the 5-GHz band the challenge comes from co-existence with radar systems and lower power limits.
In the U.K. radio spectrum regulator Ofcom has decided to allow Wi-Fi in the 5725-5850 MHz band. With this decision, Ofcom has officially recognized and acted upon the need for additional Wi-Fi spectrum, making the U.K. the first country in Europe to open 5.8 GHz for Wi-Fi operations and 80-MHz channels.
In Europe the European Electronic Communications Committee (EECC) took up the advice by the Wi-Fi Alliance to allow Radio Local Area Networks (RLANs) deployments in the 5925-6.425 MHz band – extending the wireless spectrum all the way into the 6 GHz frequency band. At the moment they are still waiting for the first results of ongoing frequency sharing studies supported by the Wi-Fi Alliance. After positive results, the frequency range may be extended to 6.725 MHz.
We Need More Spectrum!
Wi-Fi is certainly one of the most successful radio technologies around the globe. Many households in the developed world, and just about every business, are today running their own private radio network. If governments and regulators around the globe are to avoid putting these networks at stake – without even allowing for further technological advances – they will have to tackle the spectrum issue, soon.
With the next World Radiocommunication Conference (WRC) organized by the International Telecommunication Union (ITU) coming up in 2019 in Geneva, regulators will have a unique chance to set the path for the future of unlicensed spectrum on a global scale, with the current strong growth of Wi-Fi in mind. The need is imminent: We need a greater portion of unlicensed spectrum – sooner rather than later!