Paris (AFP)
Announced as the big bang of telecoms, 5G must offer innovative services while relying on the same public resource that previous generations of mobile telephony: electromagnetic waves. Limited, they must be divided according to their physical characteristics to be able to answer all the uses.
Frequencies, the nerve of war
Light, from infra-red to ultraviolet, through colors, microwave oven, radio or mobile phone pass through electromagnetic waves, all measurable via their wavelength but also by their frequency. hertz, which is why we talk about hertzian waves.
The majority of the waves used for human technological activities (television, radio, telephone, but also satellites, walkie-talkie, wifi, radar ...) are between 3 kilohertz (KHz) and 300 gigahertz (GHz).
For each use, we reserve a part of the spectrum, delimited by two precise wavelengths: these are called frequency bands, which can be of very different sizes, depending on the needs and possibilities.
Mobile telephony uses only a very small part of all these frequency bands: at most six, taking into account the one about to be allocated, improperly called the 3.5 GHz band (but actually between 3 , 4GHz and 3.8GHz).
Various physical properties
Depending on their position on the electromagnetic spectrum, the bands do not have the same physical qualities.
In particular, the lower they are, the more important they are to reach with better penetration into buildings - important elements for telecoms. This is the reason why the 700MHz band, the lowest used for mobile telephony, is nicknamed the "golden frequency".
But these lower bands are also the most loaded. Telecom operators use the bands 700 to 900 MHz for 2G and 3G networks, still active, the 4G of course, but also a number of uses for connected objects or RFID, radio-identification.
Above all, these tapes are stuck between those used for television and those of aeronautical systems. The telecom operators can not therefore have a large bandwidth. At the time of the provision of the band 700MHz, they were in fact received each between 5MHz and 10MHz.
The higher you get in the frequencies, the less they are used, because of a reduced range. This lower usage makes it possible to unblock 300MHz to the operators between the frequencies 3.4 and 3.8GHz. The remaining 100MHz are already used by telecoms, for WiMax, a communication standard aimed at bringing fixed internet.
From 25 Ghz, we speak of millimeter waves because of their very reduced wavelength: the diffusion capacity is limited by all kinds of obstacles, even the rain.
Different uses according to the frequencies
3G and more 4G have taken off the use of mobile internet and significantly increase data traffic. The explosion of video on smartphone contributes particularly, with the risk of saturating networks. Because so far, the allocation of frequency bands was thought according to the needs of the moment. But if a frequency band is not very wide, it can quickly be saturated. To circumvent this difficulty, operators begin to aggregate frequency bands, that is to say to associate them in order to indirectly create a wider communication channel.
As the 5G had to speed up this movement even more, it was necessary to find wider and available bands. This is the case of the 3.5GHz band.
Eventually, the other bands currently used by operators will switch to 5G. The lower bands (700-800-900 MHz) will be used for coverage, the middle bands (1.8 GHz, 2.4 GHz, 3.5 GHz) to strengthen it in the densest areas, absorb the traffic and speed up the connection speed, the high bands (26 GHz) to offer a very high speed with little latency. But these, still poorly known, are just beginning their test phase.
© 2019 AFP