What is beamforming?

Beamforming is a telecommunications technology that enables the targeted delivery of larger and faster signals. The development of 5G relies in particular on beamforming. Florian Kaltenberger, researcher at EURECOM and 5G specialist, explains how this technology works.

What is beamforming?

Florian Kaltenberger: Beamforming consists of transmitting synchronized waves in the form of beams, from an antenna. This makes it possible to target a precise area, unlike conventional transmission systems that emit waves in all directions. This is not a new technology, it has been used for a long time in satellite communication and for radar. But it is entering mobile telecommunications for the first time with 5G.

Why is beamforming used in 5G?

FK: The principle of 5G is to direct the wave beams directly to the users. This allows a limited interference between the waves, having a more reliable signal, and saving energy. These three conditions are some of the demands that 5G must meet. Because the waves of 5G signals have high frequencies, they can carry more information, and do so faster. This system avoids congestion in hotspots, i.e. there will be no throughput problems in places where there are many connections simultaneously. Also, the network can be more locally diverse: there can be completely different services used on the same network at the same time.

How does network coverage work with this system?

FK: Numerous antennas are needed. There are several reasons for this. The size of the antennas is proportional to the length of the waves they generate. As the wavelength of 5G signals is smaller, so is the size of the antennas: they are only a few centimeters long. But the energy that the antennas are able to emit is also proportional to their size: a 5G antenna alone could only generate a signal with a range of about ten meters. In order to increase the range, multiple 5G antennas are assembled on base stations and positioned to target a user whenever they are in range. This allows a range of about 100 meters in all directions. So you still need many base stations to cover the network of a city. With beamforming it is possible to target multiple users in the same area at the same time, as each beam can be directed at a single user.

How are the beams targeted to users and how are they then tracked?

The user’s position signal is received by different parts of the 5G antennas. On each of these parts, there is a shift in the time of arrival of the signal, depending on the angle at which it hits the antenna. With mathematical models that incorporate these different time shifts, it is possible to locate the user and target the beam in their direction.

Then you have to track the users, and that’s more complicated. Base stations use sets of fixed beams that point at preset angles. There is a mechanism that allows the user’s device to measure the power of the received beam relative to adjacent beams. The device sends this information back to the base station, which is then able to choose the best beam.

What are the main difficulties when it comes to implementing beamforming?

FK: Today the 5G network still cannot work without the 4G network because of the short range of the beams, which makes its use only effective and useful in urban environments, and especially in hotspots. In more remote areas, 4G takes over. Beamforming cannot be used for a mobile user located several hundred meters from the antenna – let alone a few kilometers away in the countryside. Another difficulty encountered is the movement of users as they move from one base station to another. Algorithms are being developed to anticipate these movements, which is also what we are working on at EURECOM.

Should we expect the next generation of mobile communications, 6G, to go even further than beamforming?

FK: With every generation, there is a breakthrough. For example, 3G was initially designed as a voice communication network, then all the aspects related to internet data were implemented. For 4G it was the other way around: the network was designed to carry internet data, then voice communication was implemented. The operating principle of 6G has not yet been clearly defined. There’s roughly one new generation of cell phones every ten years, so it shouldn’t be long before the foundation for 6G is laid, and we’ll know more about the future of beamforming.

Interview by Antonin Counillon