Transceiver architectures for cellular communications in the FR3 band

Over the last decades, communication networks have grown exponentially, starting with low-rate applications such as voice calls and now offering high-speed mobile internet based on 4G, 5G and soon 6G deployments. Over the generations, expanding networks have embraced new frequency bands in order to meet increasing user throughput demands.

In the cellular world, frequency ranges (FRx) have been defined, corresponding to different carrier frequencies. First applications used FR1 (up to 6 GHz), then FR2 was defined in the mm-wave frequencies (24 - 53 GHz). While mm-wave frequencies offer more bandwidth, some concerns on technology readiness and long-range path loss or indoor propagation are slowing down its adoption. Hence, the industry is now looking at intermediate frequencies in the so-called FR3 band (7 - 24 GHz) where new spectrum is made available.

This band offers a promising trade-off between additional capacity and sufficient coverage, but it also brings many research challenges, related to the following points:

• With a factor 3.5 between lowest and highest frequencies (24 vs. 7 GHz), the behavior is not uniform over the band. Channel propagation depends on the carrier frequency in terms of path loss and richness of channel multipath and diffraction components. As antenna dimensions scale with wavelength, the number or antennas and the way to integrate them in transceivers also differs a lot. This requires investigating the most appropriate multiple-antenna communication schemes and related architectures.
• Analog components also differ in performance over the FR3 band. For instance, different types of power amplifiers and related semiconductor technologies can be considered, in line with imec's advanced technology research.
• The whole FR3 band is fragmented into many different sub-bands and will require flexible systems that can reconfigure based on dynamic spectrum allocation between operators and changing propagation conditions. For instance, multiple-antenna systems can use all antennas together in the same band, achieving high-order MIMO or multi-user MIMO, but they can also be reconfigured to operate different antennas in different sub-bands, independently or aggregated as a wider compound band. Specific flexible architectures will be needed to support this in the most efficient way.
• Ultimately, deploying and optimizing different base stations types on different sites may require AI solutions to master the multi-dimensionality of related scenarios.

As a PhD student, you will seek fundamental understanding and propose novel solutions related to those challenges. You will understand the differences in channel propagation and hardware implementation constraints across the FR3 band. You will propose novel transceiver architectures and communication algorithms offering flexibility and the best power-performance trade-offs. You will also investigate how they could be developed to accommodate very different scenarios, either based on real-time reconfigurability or by developing a set of solutions tuned to different scenarios. AI tools may complement models to guide the selection and optimization of a different architectures at each specific site.

You will be part of a large imec community working on the research, implementation and prototyping of future communications systems with experts in wireless communication, signal processing, digital, analog and mm-wave design, and machine learning. This is a unique opportunity to develop innovative, multi-disciplinary technology and shape future wireless networks. You will publish your research in top-level journals and conferences.