Advanced Hybrid Analog-Digital Massive MIMO Techniques for Millimeter Wave and sub-Terahertz Wireless Systems (AdAMMM II)

• Applicant: Professor Dr.-Ing. Martin Haardt
• Subject Area: Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 402834619

Sixth Generation (6G) wireless networks envision the achievement of unprecedented data rates, transmission reliability, and link security. 6G will be the basis for sustainable economic growth in the next decade. It will open the way for new use cases such as massive machine connectivity, safe autonomous driving, holographic communications, extended reality, remote surgery, and many other applications to improve the life of modern society. In the second phase of this project, we consider the extension of the focus of the study to the sub-THz frequency range (100-300 GHz), which is considered as a favorable candidate for 6G. However, the higher bands entail additional difficulties due to the distinct propagation channel characteristics and the necessity to use wider operational bandwidths to meet the requirements for 6G. In particular, we need to mention the high variability and extreme sparsity of the sub-THz channels dominated by line-of-sight propagation conditions. Nevertheless, successful data transmission in the sub-THz frequency range is possible. One of the critical components to enable it will be large antenna arrays comprising hundreds or even thousands of elements. They will assure sufficient beamforming gain to compensate for the high propagation losses. Additionally, adaptive processing helps to handle the time-variable nature of the channel. However, the limitations of the current sub-THz technologies, the requirement of accurate CSI for successful data transmission, and the presence of impairments inherent to practical hardware give rise to new research questions to be explored before turning to the implementation stage. To this end, based on our knowledge and results obtained in phase I of the project, we want to develop novel concepts and algorithms for the new setting. In particular, we develop advanced power-efficient, low-complexity hybrid analog-digital techniques. Here, we will focus on novel hybrid analog-digital architectures with array-of-subarrays structures and dynamic array-of-subarrays. Moreover, we investigate novel high-resolution channel estimation algorithms by exploiting the sparse nature of sub-THz channels that will take into account wideband effects, molecular absorption, and beam squint. Furthermore, we study the near-field effects caused by the large dimensions of antenna arrays when the size of an array is comparable to the propagation distance. We also explore cutting-edge low-complexity methods for joint communications and sensing to improve the spectral efficiency and decrease the cost of transceivers in sub-THz scenarios. Additionally, we examine the influence of hardware impairments to develop appropriate techniques to combat them. Finally, we evaluate our sub-THz-band channel estimation and beamforming solutions with an analytical performance analysis and through numerical simulations.

• DFG Programme: Research Grants