Unused Wi-Fi reserves

In countries and cities with a developed telecommunications infrastructure, users are increasingly having complaints about Wi-Fi. In an urban environment densely saturated with client devices using Wi-Fi, the average quality of communication worsens from year to year. Is it possible to somehow reverse this trend?

Now there are more than 6.5 billion devices connected to the network through this wireless standard in the world, and by 2020 their number will reach almost 21 billion. This is about 2.8 devices per person on the planet. So the lack of bandwidth wireless channels will only worsen. However, to solve this problem, it is not enough just to install more powerful routers. The cause of “virtual traffic jams” is not only the “narrowness of the roads”, but also a number of other factors.

Today, in every home and many apartments there is a Wi-Fi router, and in some of them there are several. Increasing the connection speed is usually associated with a more dense use of bandwidth. In addition, mobile operators are encroaching on the Wi-Fi range, packing some traffic into it, and with the advent of 5G, the situation can be even more aggravated.
')
That is, Wi-Fi actually became a victim of its own success. What can be done to solve this problem, or at least to mitigate it?

Crowd on the air

Although regulators in different countries may impose certain requirements on licensing the frequency spectrum of Wi-Fi, in general, this range remains more or less open. Users must comply with technical requirements, including transmission power limitations, but for this they do not need to obtain any special permits. Today, almost all public Wi-Fi networks, including home networks, operate in the 2.4 and 5 GHz bands. At the same time, 2.4-gigahertz waves penetrate better through walls and furniture, and generally transmitted further compared to 5-gigahertz, with the same transmit power.

For example, in the USA, the regulator has allocated a 84.5 MHz wide band for Wi-Fi. Within the 802.11b / g / n standard, the channel width is 20 or 22 MHz, so that only three channels can fit into the total band without overlapping: 1, 6 and 11. In Europe, the situation is almost the same: 13 channels , of which simultaneously You can use only three without overlapping. In Japan, a little easier: 14 channels and 4 simultaneous non-overlapping.



So if you see more than three 2.4-gigahertz routers in the list of Wi-Fi networks, or if there are three of them, but one uses a channel other than 1, 6, and 11, then the channels overlap.

The situation is different in 5 GHz Wi-Fi: 38 non-overlapping channels of 10 MHz and 20 MHz width are laid in the range from 5170 to 5905 GHz (in the USA - 5180-5825 and 24 channels of 20 MHz width, in Europe and Japan the channels are even smaller ). It would seem that several times more channels that do not interfere with each other should improve the quality of communication in the 5-gigahertz range. But regional specifics interfere here: in different countries, some of the channels may not be available for public use, since military and meteorological radars and satellite television operate on these frequencies. Therefore, due to the complexity of “fitting” traffic into the “problem” frequencies, the vast majority of routers simply ignore them.

So, in each of the two ranges, we have a series of non-overlapping channels. But due to the abundance of routers and client devices, the overlap has become a normal situation. When a collision occurs - two Wi-Fi broadcasts intersect - all participants temporarily fall silent, and after some pause they return to the air again. The duration of pauses increases exponentially as the number of collisions increases, as a result, the speed and reliability of Wi-Fi connections decrease.

In densely populated areas, the load of the ether may be such that the connection in the 2.4-gigahertz range barely creeps. This has led to the fact that in some countries providers have started to close this range for video or voice transmission, and most smartphone manufacturers do not recommend using 2.4 GHz Wi-Fi at all. The IEEE 802.11ac standard generally implies operation only in the 5 GHz range, although it is backward compatible with the older IEEE 802.11n.

Modern Wi-Fi-air can be compared with busy highway at rush hour. But, as mentioned above, it’s not just the number of client connections. The transition from 2.4 to 5 GHz was intended to solve the problem of channel congestion, but it had to sacrifice coverage. This led many users to use hardware amplifiers and build mesh networks in order to achieve a decent signal level in each room. Amplifiers listen to the broadcast, receive a signal from the router and duplicate it with a higher power, sometimes on a different channel. This leads to an increase in the number of overlaps of Wi-Fi transmissions in the same frequency bands.

Providers and operators

From this point of view, public Wi-Fi access points have become a real evil. In 2005, the Spanish provider Fon Wireless first introduced the concept of community access points (community hotspots), which are based on private routers, and today this phenomenon is gaining popularity in the world. Some Internet providers began to rapidly deploy such points for subscribers, using their clients' routers for this. According to Juniper Research, in 2017, one third of home routers in the world will be able to work as a community access point. Part of the Wi-Fi spectrum will be allocated for these needs, and the owners of the routers themselves will not even be warned about this.

But that is not all. The rapid growth in the livestock of smartphones has led to the fact that the spectrum bands allocated for mobile communication have been practically exhausted. In the coming years, telecom operators are planning to transfer a significant part of the mobile data traffic load to unlicensed Wi-Fi bands. Such technologies are called LTE-U (LTE-Unlicensed) and LAA (Licensed Assisted Access). They imply the use of 4G LTE and routers for data transmission in the same 5 GHz band as Wi-Fi. And although telecom operators claim that this will have a weak effect on Wi-Fi users, a number of large companies , including Google and Microsoft, believe that LTE-U and LAA will definitely exacerbate the workload of Wi-Fi channels and reduce the quality of communication.

Do you want to check or go?

Go ahead: in the most recent IEEE 802.11ac standard, the number of channels has been reduced in favor of increased speed in order to broadcast streaming video in high resolution and save mobile device batteries that will transmit data at high frequencies only for a limited time. The maximum bandwidth was raised to 1.3 Gb / s. compared to 450 MB / s. in 802.11n. But this was achieved including by combining channels. In IEEE 802.11ac Wave 3, the entire available Wi-Fi spectrum is generally divided into only two channels at 160 MHz, that is, in this mode only two pairs of devices can operate simultaneously without overlapping. If, for example, your neighbor uses one of these two channels to watch a movie, and the other neighbor has occupied the second channel, then you will have nothing left.

Somehow, the main advantage of the 5-gigahertz range to the 2.4-gigahertz range suddenly disappeared - a large number of non-overlapping channels.

Given all the above, in the coming years, Wi-Fi in big cities risks turning from a fast alternative to mobile Internet to annoyingly slow. Alas, the widespread use of the 802.11ac standard, which offers wider and faster, but fewer channels, will only worsen the situation. By the way, the telecommunications agency Ofcom, back in 2013, published a study predicting that the critical level of congestion of the Wi-Fi spectrum would be reached by 2020.

DFS as a temporary measure

Remember about radars that have priority right to use part of the 5 GHz range? Today, these channels are ignored by consumer devices, but if you start using them massively, this can completely change the picture.

As Captain suggests, military and meteorological radars are not found at every corner in large cities, many of which, moreover, do not work around the clock. Therefore, this part of the spectrum can be used by consumer devices subject to the mass introduction of the DFS ( Dynamic Frequency Selection ) mechanism: the router constantly monitors the activity of priority signal sources, and as soon as the radar starts working, switching to another channel or reducing the transmit power occurs. DFS implies releasing a channel for 10 seconds for the next half hour, even if a 1-millisecond pulse is detected from a priority source.



Most consumer devices launched in the last 3-4 years - first of all, smartphones, tablets and laptops - can understand DFS commands, but for this, routers must be DFS masters. That is, it is the responsibility of the routers to monitor the spectrum and free the channels of adjacent use.

But it’s not so easy to integrate the DFS master function into a router: radar pulses can be very difficult to detect due to their transience (0.5 ms) and extremely low energy level (-62 ..- 64 dB per mlW). Moreover, the tools for detecting radar pulses eat up part of the bandwidth of the router, because it is forced to listen to it for 60 seconds before using the channel, before deciding that it is free, and also to listen between data exchange sessions.

Today, the DFS wizard feature is found only in expensive routers that are commonly used in large companies. But gradually DFS penetrates into lower price segments. True, this is also not a panacea: after all, when a signal is detected from a priority source, the router is forced to switch to one of the default channels, to the non-DFS-part of the 5 GHz spectrum, and there it is rather “cramped”. Moreover, modern routers usually do not return to DFS channels until they are rebooted. In corporate systems this is done daily, and home routers can work without rebooting for weeks and months, until the owners realize that the Wi-Fi speed is too low and it's time to reboot.

The fact is that in modern implementations of DFS, the radio module only listens to one channel at a time. And when the DFS master monitors the channel, its radio module should not transfer anything to other channels for 60 seconds in order not to interfere with the current listening. To avoid such situations, most DFS implementations require a reboot of the router to return to the open DFS channel.

But if you create a more efficient technology for detecting priority sources, the channels that are actually idle today would help to unload the 5 GHz Wi-Fi spectrum. For example, you can equip a router with a detector system — an additional radio module for scanning the spectrum and a separate processor for detecting radar pulses and controlling channels. At the same time, the detector system should be completely separated from the Wi-Fi receiving / transmitting system, which will solve most of the problems inherent in modern DFS implementations, when one processor is responsible for transmitting data and searching for priority signal sources. A separate radio module will allow regular scanning of all channels, and when a priority source appears in the current channel, the router will know if there is another DFS channel currently open, transferring the connection there, and not to the default public channel. Similarly, the router can automatically return to the previous DFS channel after a half-hour limit without interrupting the connection.

At the same time, an additional processor will help minimize the number of false detections, thereby increasing the duration of work in DFS channels. Given the increase in the load on the processors of modern routers, the second processor does not look like an excess.

In principle, all this is also a temporary measure: the more routers the idle channels use today, the faster they will be overloaded too. But by that time can be agreed for use by Wi-Fi-networks and other bands. Or we will just have to accept the fact that in a few years Wi-Fi in metropolitan areas will not work quickly, to put it mildly.