Wireless communication in internet infrastructure

Electromagnetic radiation is all around us. It literally surrounds us, whether it is natural or created by human activity. Everything happens thanks to electromagnetic waves of various wavelengths. But telling the whole story would take several chapters of serialised reading, starting in 1832 with Michael Faraday and ending with nanoelectronics, which is used for communication between nanorobots employed in diagnostic medicine.

So let us come back down to earth and take a look at the telecommunications universe closest to us.

TIP: You may also like our article What is Wi-Fi, after all? Wireless network options.  

Try it without wires, dear Marconi

The classic quip does not adequately describe the huge progress humanity has made thanks to the simple transmission of impulses from radio stations on the ocean coast, and the possibility of two-way communication between ships at sea. Back then, low frequencies and enormous power supplied to antenna systems were used. Range was what mattered. Communication was slower than spoken words, but it could be picked up on the other side of the planet. The curvature of the Earth was not a problem, as the waves were reflected from the layers of the stratosphere.

Over time, the need to transmit more data began to grow. As usual, the driving force of progress was the military. Transmitting higher capacities requires a higher carrier frequency. Generating centimetre waves with magnetrons in turn made it possible to detect objects using radio waves, and the invention of radar completely changed the balance of power at the start of the Second World War. After the war, it enabled the development of civil aviation. And in telecommunications, a fundamental novelty appeared for humanity: the radio data link. Using directional antennas, it became possible to transmit information about the combat situation over long distances, to manage the logistics of supplying moving armies, and to replace damaged telecommunications infrastructure in liberated countries. That was when the world discovered the true magic of wireless communication.

As time went on and the development of electronic communications far outpaced the possibilities of expensive buried metallic cables, a large part of ordinary civil communication began to rely on radio links. Do you remember those huge parabolic antennas on the transmitters of České radiokomunikace? Czechoslovak Television used antennas like these to broadcast from the very beginning.

Options for data links have grown considerably

Transmitted capacities have grown, the need for long-distance radio links has almost disappeared, and the transmission power of such equipment has fallen to a fraction of Marconi's original values. In 1945, the US Army worked with an analogue transmission system that carried several parallel telephone calls. In 1950, a period of massive use of radio links in the telephone network began in North America, but the Soviet bloc did not lag behind for very long. In Czechoslovakia, TESLA manufactured top-quality equipment that was exported not only to COMECON countries but all over the world. In the competitive struggle with Western companies, the Eastern bloc began to fall behind only when it moved to digital transmission systems.

From the 1990s onwards, digital communication has been experiencing an incredible acceleration. The transition from two-state frequency modulation schemes to modulation using 1024 states, with several times the bandwidth, did not take even 20 years. Thanks to advances in semiconductor technology, the integration of previously large blocks into miniature integrated circuits and the use of the enormous computing power of signal processors, today's radio links can easily transmit 10 Gbps per second.

Radio links themselves are most often divided according to the frequency bands used and the way they are used. The most basic division is equipment for connecting two points in a network. For the average internet user at home, it is easier to understand communication between one base station and many participants. A typical example of such point-to-multipoint radio transmission is the connection of a mobile phone to a base station. Or a home Wi-Fi router. We will look at the principle of such multiple communication in another article.

Point-to-point links are relied upon by all base stations of a mobile network and by the access points of internet providers. For high-speed internet to work reliably and for phone calls not to drop when you are on the move, a high density of access points is needed. One day, perhaps in several decades, all such points in the countryside will be connected by an optical network. With a sarcastic smile, I would like to write at length about the bureaucratic trap of building anything in this country, where we do not talk but get things done, but that would deprive you of a description of the frequency bands used.

Radio communication in infrastructure uses frequencies from 4 GHz to 80 GHz. The lower the frequency of a radio link, the lower the loss of radiated energy in rain and in the environment. On the other hand, with a higher frequency the gain of antennas increases, because a high frequency is directed more efficiently by a parabolic antenna into the energy beam. The gain of an antenna 60 cm in diameter is 29.5 dBi in the 6 GHz band in use, while an equally sized dish in the 80 GHz millimetre band has a gain of 51 dBi. Such a number does not impress laypeople, but anyone who still remembers their secondary school physics can see an improvement of several orders of magnitude.

The low communication bands are quite crowded, due to their historical load, technical development and the laws of physics. Regulatory bodies, such as CEPT at European level and the Czech Telecommunication Office (CTU) at national level, set binding rules for the operation of such networks. Regulators must ensure undisturbed operation not only for telecommunications purposes, but also for the military and civil radars mentioned above, satellite operations and traffic control. Anything capable of transmitting is subject to regulation, including RC toys or the key fobs for car central locking. In the higher bands, which we have only recently learned to use, there is plenty of room. There is enough space for high data transfer capacities without radio lines interfering with each other. Limiting distances for building such a link is also an advantage. For example, in the 60 GHz band the energy disappears completely after a few hundred metres. Radio operations therefore cannot affect each other. During operational tests of the connection between the Újezd.Net network and the company Eurosignal, we achieved a connection with a capacity of 2.5 Gbps, at the same quality as would be achievable with optical fibre, over a distance of around 2 km. We used a CERAGON IP20E link for the 80 GHz band.

Another, non-technical division of radio links is based on the type of permit needed to use these frequency bands. The Czech Telecommunication Office (CTU) issues licences for the use of the bands. Some of them carry quite high fees and must be carefully coordinated with each other, and the mutual interference during operation in the spectrum must be calculated in a complicated way. This is a logical measure, especially if you want to link distant locations by radio. Links in other bands, in turn, are required to use low power, and no payment for mutual coordination is required. As I mentioned, with increasing frequency there is no need to worry about mutual interference, and at the same time a telecommunications operator can transmit multiples of its transmission capacity. Comparing such professional links with an optical line does not come off badly at all. Such links use full-duplex operation and two pairs of frequencies for communication, one for each direction of transmission.

You can see the dependence on the frequency used, the capacity used for data transfer and the licensing conditions in Table 1. I am not describing all the bands.

The entire telecommunications industry uses radio links. At the end of every optical fibre there is probably some such radio connected, which transports data to other network customers. People often ask me about the reliability of such a link in rain or fog. Calculating a radio route and its reliability is something any electrical engineering school student can do these days. Manufacturers supply route design tools, and according to the ITU-R P.530 standard, statistics on rainfall in the area where the link is deployed are also taken into account. Calculations for a specific device will reliably determine whether the connection will still work even during an apocalyptic cloudburst. Do you remember the last time you made a phone call from your mobile in the rain?

Did you like the article? Are you about to sort out a new connection? Have a look at the article Looking for a suitable internet connection but don't know your way around the plans? 

Author: Jakub Moník

Updated 16 February 2024