Why is my WiFi Slow?

Wi-FiOne of the universal complaints in the broadband world is that WiFi networks operate poorly. So today I thought I’d talk a bit about how WiFi functions. I think it’s probably different than what most people expect.

Most people know that there are two frequencies used for WiFi today – 2.4 GHz and 5 GHz. The 2.4 GHz band covers 80 megahertz of total bandwidth and is divided into 11 channels in the US. That may sound like a lot, but one 802.11 connection requires five consecutive channels. In practical terms this means that almost all WiFi gear in the US is preset to only offer channels 1, 6, and 11 and that means that only three non-overlapping transmissions can occur at the same time. The WiFi in Japan covers a wider spectrum footprint, up to channel 14, meaning they can use four non-overlapping signals simultaneously.

In practical use if you can see three or more WiFi networks you are experiencing interference, meaning that more than one network is trying to use the same channel at the same time. It is the nature of this interference that causes the most problems with WiFi performance. When two signals are both trying to use the same channel, the WiFi standard causes all competing devices to go quiet for a short period of time, and then both restart and try to grab an open channel. If the two signals continue to interfere with each other, the delay time between restarts increases exponentially in a phenomenon called backoff. As there are more and more collisions between competing networks, the backoff increases and the performance of all devices trying to use the spectrum decays. Your data is transmitted in short bursts each time you make a connection and before the restart cycle repeats.

If you’ve ever been in a hotel where you can see ten or more other WiFi signals, the reason for slow speeds is that there are huge conflicts between competing devices. People generally assume that the hotel has a poor Internet connection, but they could have a fast connection and the slo speeds are due to so many devices trying to connect simultaneously. Each WiFi device is rapidly turning on and off repeatedly trying to get open access to a channel. Your device will grab a channel for a short time and then get kicked off due to interference. Congestion has become so bad on the 2.4 GHz band that AT&T and Comcast no longer use 2.4 GHz for video or voice. Almost all smartphone makers no longer recommend using their smartphones at 2.4 GHz.

WiFi has improved dramatically with the introduction of the 5 GHz spectrum. In North America this spectrum swath has 24 non-overlapping channels. However, more than half of these channels are reserved for weather and military radar. However, this still provides a lot more potential paths to add to the three paths provided by the 2.4 GHz spectrum. Unfortunately the 5 GHz band shares the same WiFi characteristics as the 2.4 GHz spectrum and has the identical interference issues. But with more open channels there is still an increased chance of finding a free channel to use.

And interference between devices is not the only culprit of poor WiFi speeds. The network configuration can also contribute to poor performance. Some of the biggest sources of interference are range extenders or mesh networks that are used to try to get better signals. Range extenders listen to all WiFi transmissions and then retransmit them at a higher power level, and usually using a different channel. This creates even more WiFi signals in the intermediate environment competing for an open channel. When you can see your neighbor’s WiFi network, if they are using range extenders they might be always trying to use most of the available WiFi channels.

In a lot of the US we now also see a lot of public hotspots. For example, Comcast is in my neighborhood and I can walk and maintain a WiFi signal is most places from WiFi public signals that are transmitted from every Comcast home WiFi router. These public signals are always on, meaning that the WiFi router is using at least one channel at all times.

Probably the biggest new culprit for poor WiFi performance comes from our quest for greater speeds. The 802.11ac standard operates by merging together a lot of WiFi channels, and divides the whole WiFi spectrum into just two 160 MHz-wide channels. This means that only two devices using this 802.11ac can use up all of your home WiFi bandwidth. This standard was intended to be used to operate in short high-bandwidth bursts, but as people use this for gaming or watching 4K video the channels stay occupied all of the time.

Unfortunately the demands for WiFi are only increasing. The cellular carriers are still pestering the FCC to allow LTE-U, which would using WiFi to complete cellular calls. There are currently tests underway of the technology. We can also expect an increasing demand for WiFi from IoT devices. While most WiFi devices won’t use spectrum continuously, they still place demands on the channels and cause interference. There are also increasing use of devices that are always on, such as video surveillance cameras or smart home controllers like the Amazon Echo. A lot of experts look out five or ten years and expect WiFi to be unusable in a lot of places.

The Death of 2.4 GHz WiFi?

Wi-FiIt’s been apparent for a few years that the 2.4 GHz band of WiFi is getting more crowded. The very thing that has made the spectrum so useful – the fact that it allows multiple users to share the spectrum at the same time – is now starting to make the spectrum unusable in a lot of situations.

Earlier this year Apple and Cisco issued a joint paper on best network practices for enterprises and said that “the use of the 2.4 GHz band is not considered suitable for use for any business and/or mission critical enterprise applications.” They recommend that businesses avoid the spectrum and instead use the 5 GHz spectrum band.

There are a number of problems with the spectrum. In 2014 the Wi-Fi Alliance said there were over 10 billion WiFi-enabled devices in the world with 2.3 billion new devices shipping each year. And big plans to use WiFi to connect IoT devices means that the number of new devices is going to continue to grow rapidly.

And while most of the devices sold today can work with both the 2.4 GHz and the 5 GHz spectrum, a huge percentage of devices are set to default to several channels of the 2.4 GHz spectrum. This is done so that the devices will work with older WiFi routers, but it ends up creating a huge pile of demand in only part of the spectrum. Many devices can be reset to other channels or to 5 GHz, but the average user doesn’t know how to make the change.

There is no doubt that the spectrum can get full. I was in St. Petersburg, Florida this past weekend and at one point I saw over twenty WiFi networks, all contending for the spectrum. The standard allows that each user on each of these networks will get a little slice of available bandwidth, which leads to the degradation of everyone using it in a local neighborhood. And in addition to those many networks I am sure there were many other devices trying to use the spectrum. The WiFi spectrum band is also filled with uses by Bluetooth devices, signals from video cameras and is one of the primary bands of interference emitted by microwave ovens.

We are an increasingly wireless society. It was only a decade or so ago where people were still wiring new homes with Category 5 cable so that the whole house could get broadband. But we’ve basically dropped the wires in favor of connecting everything through a few channels of WiFi. For those that in crowded areas like apartments, dorms, or within businesses, the sheer number of WiFi devices within a small area can be overwhelming.

I’m not sure there is any really good long-term solution. Right now there is a lot less contention in the 5 GHz band, but one can imagine that in less than a decade that it will also be just as full as the 2.5 GHz spectrum today. We just started using the 5 GHz spectrum in our home network and saw a noticeable improvement. But soon everybody will be using it as much as the 2.4 GHz spectrum. Certainly the FCC can put bandaids on WiFi by opening up new swaths of spectrum for public use. But each new band of spectrum used is going to quickly get filled.

The FCC is very aware of the issues with 2.4 GHz spectrum and several of the Commissioners are pushing for the use of 5.9 GHz spectrum as a new option for public spectrum. But this spectrum which has been called dedicated short-range communications service (DSRC) was set aside in 1999 for use by smart vehicles to communicate with each other to avoid collisions. Until recently the spectrum has barely been used, but with the rapid growth of driverless cars we are finally going to see a big demand for the spectrum – and one that we don’t want to muck up with other devices. I, for one, do not want my self-driving car to have to be competing for spectrum with smartphones and IoT sensors in order to make sure I don’t hit another car.

The FCC has a big challenge in front of them now because as busy as WiFi is today it could be vastly more in demand decades from now. At some point we may have to face the fact that there is just not enough spectrum that can be used openly by everybody – but when that happens we could stop seeing the amazing growth of technologies and developments that have been enabled by free public spectrum.