As data transmission needs continue to grow, 5G and 6G networks have to meet increasingly demanding technical constraints: flexibility, miniaturization, energy optimization... Among the solutions explored by research: optimized radiation management, and the development of concrete applications for millimetre frequencies. Two projects, YACARI and PIIEC ME/CT, are tackling the technical hurdles of these approaches by combining various antenna technologies.
Millimetre frequencies, covering ranges from 30 to 300 GHz, represent promising innovation territory for 5G and 6G networks. The corresponding frequency bands, known as FR2, are distinct from the FR1 bands that largely dominate today's telecommunications, and use the ranges below 6 GHz. While these low frequencies are ideal for covering large areas with minimal infrastructure, particularly in rural or isolated areas, they do have limited data rates. Conversely, millimetre-wave frequencies enable ultra-fast communications over short distances, adapted to localized needs such as dense urban areas or industrial applications.
"The appeal of millimetre bands lies in their large useful bandwidth, which enables large amounts of data to be transmitted at high speeds and extremely low latencies," explains Christian Person, a researcher specialized in advanced telecommunications at IMT Atlantique.
"They open the way to localized spots of ultra-fast connectivity, at which it would be possible to download videos in a matter of seconds, for example, or deploy fully interactive augmented interfaces." On the other hand, these frequencies suffer from high spatial attenuation - making them less suitable for long distances - and from the less mature nature of dedicated microelectronics chains. Technological improvements are therefore needed to extend their range and exploit their full potential.
Beamforming to overcome signal attenuation
Among these improvements is the design of antennas in base stations to facilitate communication with terminals. This is one of the research focuses of the YACARI project, dedicated to the deployment of technical solutions for the use of millimetre bands as part of the "Networks of the Future" PEPR program. Project co-leader Christian Person is involved in the development of these adapted antennas, based on beamforming techniques or beam formation.
By concentrating an antenna's energy in a precise direction, beamforming maximizes directional gain, at the expense of coverage, and thus improves radio link quality. It complements beam steering, which consists in dynamically scanning the space to detect terminals, and adjusting the beams in real time, towards a moving user or in a changing environment for example. The equivalent of Sauron's eye searching for Frodo in Mordor for fantasy fans.
The researcher is therefore studying different approaches to manage antenna radiation. On the one hand, phased-array antennas: panels made up of several radiating elements whose waves interfere constructively to form a beam in a specific direction. This beam can be redirected by adjusting the phase and amplitude of each element in the array, enabling it to “scan” space without mechanical movement of the antenna. On the other hand, the application of holographic techniques, inspired by optics. "Using specially shaped antennas, it is possible to modulate radio waves on the same principle as holograms, and create precise directional beams," he explains. "The challenges lie in how to dynamically control these holographic interaction surfaces."
Miniaturization and smart surfaces: in the firing line
These approaches can be complemented by the use of Reconfigurable Intelligent Surfaces (RIS): devices that adapt to their environment to redirect signals. “A building facade equipped with RIS can, for example, pick up an incident signal and focus it on a moving car,” illustrates Christian Person. Today, many players are investigating these technologies, which promise to significantly improve connectivity, particularly in complex environments such as the connected city.
This is the case of another “Networks of the Future” PEPR project, PERSEUS, which focuses on the FR1 frequency bands at the other end of the spectrum. As a result, PERSEUS is concerned with imposing configurations: RIS in particular can be up to one square metre in size, and therefore very effective at re-routering signals in space. Conversely, in the YACARI project, the surfaces are designed for miniaturized integration - just a few square centimetres - on mobile devices or local Femtocells, elements designed to improve indoor network coverage.
For these controlled surfaces and antennas in the millimetre-wave range, miniaturization, in parallel with electromagnetic performance control, is a central challenge. At the moment, these devices are still bulky and expensive, which limits their adoption in consumer devices. "Our ambition is to experiment with new integration concepts and technologies, in order to provide antenna solutions that enable energy to be focused in an original direction in space: beamforming, multiple spot generation, mixed radiation beams, etc." develops Christian Person. All these solutions obviously involve the development of specific materials and components, which are being studied by other YACARI project partners.
Towards dynamic, adaptive network infrastructure management
The development of hardware solutions for the “head-end”, the part where signals are generated and transmitted to users, is also a central component of the IPCEI ME/CT project (Important Projects of Common Europeen Interest about MicroElectronics and Communication Technologies). Like the PERSEUS project, the IPCEI ME/CT targets conventional telecom bands up to 6 GHz to develop infrastructures adapted to specific use cases, including optimization of private corporate networks, vehicular applications and other scenarios requiring intelligent resource management.
Several IMT institutions are involved alongside companies such as Orange and Kalray, which develops specialized multi-core processors, in this large-scale project, covering a range of topics from coding to the security and network layers. Christian Person, who plays a key coordinating role for IMT, is also contributing as an expert to the development of “reconfigurable” multi-beam antenna solutions. "Unlike YACARI, these antennas allow simultaneous modes of operation, with several users, while probing the state of the network. This is what we call ISAC for Integrated Sensing And Communication", he explains. This is a crucial capability for base stations: "Most of the time, they send signals in all directions or sequentially by scanning the space. The aim is to adapt the flow and target only certain areas of the network according to user needs", adds the researcher.
Hybrid solutions combining beamforming, to track users, and channel probing, to locate them, are thus envisaged. They measure what is going on around the base station, and dynamically adjust the beams to distribute them according to identified priorities to specific areas of the network, such as a particular user. The aim of this adaptive management is to sectorize signals to avoid unnecessary broadcasting and concentrate energy where it is needed, thus reducing the network's energy footprint, while improving quality of service.
IPCEI ME/CT's ambition is also to anticipate the availability of the FR3 frequency bands around 7GHz (the “Golden Bands”), which will soon become available and provide new, relatively free spectrum. The YACARI and IPCEI ME/CT projects thus embody two complementary facets of the drive to make communications infrastructures more intelligent, efficient and adapted to the varied needs of users. Together, they pave the way for connectivity aligned with the challenges of tomorrow's networks, between performance and the minimization of energy resources.
More information
This article was republished from the I'MTech blog.
Read the original article: “5G, 6G : ces antennes qui façonnent les réseaux” (french).
by Pierre-Hervé VAILLANT
