TERRAMETA
Reconfigurable Metasurfaces for Ultra-high-rate Wireless Communications Communications
Description
TERRAMETA is a Horizon Europe project in the scope of the Smart Networks and Services Joint Undertaking (SNS-JU) that started on January 2023 and aims to investigate revolutionary technologies for 6G and demonstrate the feasibility of Terahertz (THz) Reconfigurable Intelligent Surface (RIS) assisted ultra-high data rate wireless communications networks. Novel high-performance hardware including the THz RIS and THz transmitter/receiver will be developed and advanced network analysis/optimizations techniques will be developed using these real THz components. The proposed TERRAMETA THz network will be driven by 6G usage scenario requirements and indoor, outdoor, and indoor-to-outdoor scenarios will be demonstrated in real factory setting and telecom testing field.
Scientific Advances
TERRAMETA will focus on the development of reconfigurable intelligent surfaces at 140 GHz and 300 GHz, innovating beyond the state of the art in the following ways:
• Reconfigurable hardware: RF-SOI CMOS, SiGe BiCMOS, memristor and microfluidics based switches, potentially achieving extremely low power consumption.
• Hardware implementation of a RIS’s sensing capability considering both reflective and transmissive RIS architectures.
• Scalability of RIS design method to realize RISs with a reduced number of elements compared to the conventional RISs.
• Demonstration of a direct carrier modulator at 300 GHz with a power level of 50 mW.
• New channel models based on measurements in non-static radio channels containing fabricated THz RIS devices.
• RIS-aided THz ultra massive MIMO architectures, for both co-located and distributed (i.e. cell-free) scenarios.
• Models and tools developed for the simulation of propagation- link- and system-level behavior.
• Signal processing algorithms for channel modelling and estimation, beam management, ultra-massive MIMO and localisation and sensing.
• Baseband processing unit with compensation of THz front-end impairments.
• One of the first industry THz communication system demonstrators supporting ultra-high data rate transmission leveraging THz RISs.
Impact
Considerable hardware developments have been made along the following three main lines: 1) novel RF switch technology assessment, 2) high power THz transmitter and receiver development, and 3) electrically large Reconfigurable Intelligent Surface (RIS) design.
Switch level reconfigurable technologies being investigated at D-band (140 GHz):
i) Memristors
• The work has been focused on the optimization of the structure and active layer of the memristor devices for the target requirements of the project. A first batch of devices has been fabricated and characterized at DC. RF test-fixtures have been designed to allow for the RF characterization.
• Preliminary tests at a lower band (around 30 GHz) are being prepared for testing the integration of this technology in a Reflective-RIS unit cell.
• There was a patent application submitted in M12 (Application in Portugal) entitled "Cell for transmit array or reflect array, transmit array or reflect array, and system", PT119158, which protects the concept of using memristors for controlling unit-cells from transmit and reflect array antennas.
ii) Gallium Nitride (GaN)
• The evaluation of the CEA GaN-on-Silicon technology for RF switch application has been approached with a design-of-experiment technique to implement a switch specific layout of test. The first fabricated wafer was received in Q4 2023 and measurements confirmed the devices to be fully functional and the series-shunt structures to be measurable.
iii) Phase Change Materials (PCM)
• Although not initially planned, a PCM based RF switch has been identified as a relevant option. The switch has been experimentally characterized and integrated into a T-RIS unit cell design.
• There were 2 patent applications in year 1 (Application in France) protecting the concept of a RF switch based on a phase change material, as well as a unit cell design using this switch:
• “Commutateur à base d'un matériau à changement de phase,” 2023, FR2210292.
• “Cellule d’antenne à réseau transmetteur,” 2023, FR2313128.
iv) Microfluidics
• Several conductive liquid materials and microfluidic structures have been fabricated and tested. A RIS prototype with 32 independently controlled sub-array lines has been manufactured and its radiation pattern has been experimentally measured. This represents a world first result, and therefore constitutes a great achievement of the project. Next steps to be carried out in Year 2 include the integration of automatic actuation in an operational unit cell.
High power THz transmitter and receiver development
• A high-power THz transmitter with ASK modulation has been designed using an amplitude modulator based on Schottky-diodes, and initial results were achieved in simulation. Design optimizations of this modulator will be conducted and integrated with a 300 GHz source, to be followed by fabrication and experimental characterization.
Electrically large RIS design
• A set of unit cells have been developed at 300 GHz for implementing the same R-RIS design with different phase quantization steps (1,2 and 3 bits). A total of 30 metasurfaces (with a size of 5x5 cm2, 10000 unit cells) have been manufactured and used in an channel measurement campaign in Q1 2024.
• A D-band proof-of-concept of a 1-bit wideband RIS comprising planar tightly coupled dipoles was designed and manufactured. In this initial result fixed connections were used instead of real RF switches, although the design is compatible with the future integration of RF switches. The passive prototypes with fixed beams were fabricated and measured, with good agreement on the main beams for the simulated and measured results. A second version of this prototype using RF switches will be developed during Year 2.
Considerable progress towards the development of signal processing techniques for THz communications, localisation, and sensing with various forms of reconfigurable metasurfaces have been made as follows:
- Measurement Campaign: Characterisation of the channel and the impact of reflective RIS and transmissive RIS using a 300 GHz channel sounder.
• Measurements have been carried out during March 2024 at TUBS premises, including assessment of near- and far-field regimes, diffraction properties, and effect of misalignment.
- RIS-parametrised channel modelling and unit-cell modelling:
• A novel multi-user near-field channel model with holographic MIMO transceivers (e.g., metasurface-based antenna panels) and triple polarisation using the dyadic Green’s function has been developed.
• Ongoing work for unit-cell wideband frequency response modelling, parametrised in terms of Q-factors and circuital hardware, extending the coupled mode theory.
• Electromagnetic consistent modelling based on S-parameters to model mutual coupling is being investigated.
• Literature review of physics-inspired RIS-parametrized channel models has been conducted including: scattering parameter analysis, mutual impedance modelling, and coupled dipole formalism (PhysFad channel model).
• Capacity characterization and optimization for various fading channels has been conducted.
- Channel Estimation Algorithms:
• A time-domain channel estimation approach has been developed for umMIMO THz systems considering a spatial representation of the wideband channel and the beam-squint effect.
- Beamforming Codebooks:
• A near-field dynamic codebook for directional beamforming has been investigated and implemented for a tracking scenario considering metasurface-based transceivers.
• A low-complexity neural-network-based beam training for THz beamforming has been studied considering an umMIMO system operating in the far-field,. Hierarchical codebook search assisted by a neural network to establish the relationship between the codewords in the angle domain to speed up the beam search was designed.
- Beamforming Strategies:
• An optimal design of RISs to increase the rank of the channel matrix in umMIMO systems was proposed.
• A multi-user downlink beamforming scheme with leaky waveguide antennas for wideband THz systems, exploiting the THz rainbow effect, was devised [GSR24].
• A low complexity fully digital beamforming transceivers aided by stacked transmissive RISs that realise wave-based analog beamforming were designed.
• An optimal receiving design, that maximizes capacity, for metasurface-based receivers with 1-bit Analog-to-Digital-Converters (ADCs) to assist multi-user uplink communications was designed.
- Localisation and Sensing:
• Proposed a RIS-enabled and access-point-free simultaneous radio localization and mapping method.
• Evaluated a joint 3D user and 6D hybrid RIS localization.
• Proposed a method based on full-duplex metasurface-based transceivers for integrated sensing and communication.
• Evaluated near-field localization with metasurface-based receivers with 1-bit ADCs to reduce power consumption.
• Reviewed and compared different positioning schemes along with algorithm evaluation.
Scientific Advances
TERRAMETA will focus on the development of reconfigurable intelligent surfaces at 140 GHz and 300 GHz, innovating beyond the state of the art in the following ways:
• Reconfigurable hardware: RF-SOI CMOS, SiGe BiCMOS, memristor and microfluidics based switches, potentially achieving extremely low power consumption.
• Hardware implementation of a RIS’s sensing capability considering both reflective and transmissive RIS architectures.
• Scalability of RIS design method to realize RISs with a reduced number of elements compared to the conventional RISs.
• Demonstration of a direct carrier modulator at 300 GHz with a power level of 50 mW.
• New channel models based on measurements in non-static radio channels containing fabricated THz RIS devices.
• RIS-aided THz ultra massive MIMO architectures, for both co-located and distributed (i.e. cell-free) scenarios.
• Models and tools developed for the simulation of propagation- link- and system-level behavior.
• Signal processing algorithms for channel modelling and estimation, beam management, ultra-massive MIMO and localisation and sensing.
• Baseband processing unit with compensation of THz front-end impairments.
• One of the first industry THz communication system demonstrators supporting ultra-high data rate transmission leveraging THz RISs.
Impact
Considerable hardware developments have been made along the following three main lines: 1) novel RF switch technology assessment, 2) high power THz transmitter and receiver development, and 3) electrically large Reconfigurable Intelligent Surface (RIS) design.
Switch level reconfigurable technologies being investigated at D-band (140 GHz):
i) Memristors
• The work has been focused on the optimization of the structure and active layer of the memristor devices for the target requirements of the project. A first batch of devices has been fabricated and characterized at DC. RF test-fixtures have been designed to allow for the RF characterization.
• Preliminary tests at a lower band (around 30 GHz) are being prepared for testing the integration of this technology in a Reflective-RIS unit cell.
• There was a patent application submitted in M12 (Application in Portugal) entitled "Cell for transmit array or reflect array, transmit array or reflect array, and system", PT119158, which protects the concept of using memristors for controlling unit-cells from transmit and reflect array antennas.
ii) Gallium Nitride (GaN)
• The evaluation of the CEA GaN-on-Silicon technology for RF switch application has been approached with a design-of-experiment technique to implement a switch specific layout of test. The first fabricated wafer was received in Q4 2023 and measurements confirmed the devices to be fully functional and the series-shunt structures to be measurable.
iii) Phase Change Materials (PCM)
• Although not initially planned, a PCM based RF switch has been identified as a relevant option. The switch has been experimentally characterized and integrated into a T-RIS unit cell design.
• There were 2 patent applications in year 1 (Application in France) protecting the concept of a RF switch based on a phase change material, as well as a unit cell design using this switch:
• “Commutateur à base d'un matériau à changement de phase,” 2023, FR2210292.
• “Cellule d’antenne à réseau transmetteur,” 2023, FR2313128.
iv) Microfluidics
• Several conductive liquid materials and microfluidic structures have been fabricated and tested. A RIS prototype with 32 independently controlled sub-array lines has been manufactured and its radiation pattern has been experimentally measured. This represents a world first result, and therefore constitutes a great achievement of the project. Next steps to be carried out in Year 2 include the integration of automatic actuation in an operational unit cell.
High power THz transmitter and receiver development
• A high-power THz transmitter with ASK modulation has been designed using an amplitude modulator based on Schottky-diodes, and initial results were achieved in simulation. Design optimizations of this modulator will be conducted and integrated with a 300 GHz source, to be followed by fabrication and experimental characterization.
Electrically large RIS design
• A set of unit cells have been developed at 300 GHz for implementing the same R-RIS design with different phase quantization steps (1,2 and 3 bits). A total of 30 metasurfaces (with a size of 5x5 cm2, 10000 unit cells) have been manufactured and used in an channel measurement campaign in Q1 2024.
• A D-band proof-of-concept of a 1-bit wideband RIS comprising planar tightly coupled dipoles was designed and manufactured. In this initial result fixed connections were used instead of real RF switches, although the design is compatible with the future integration of RF switches. The passive prototypes with fixed beams were fabricated and measured, with good agreement on the main beams for the simulated and measured results. A second version of this prototype using RF switches will be developed during Year 2.
Considerable progress towards the development of signal processing techniques for THz communications, localisation, and sensing with various forms of reconfigurable metasurfaces have been made as follows:
- Measurement Campaign: Characterisation of the channel and the impact of reflective RIS and transmissive RIS using a 300 GHz channel sounder.
• Measurements have been carried out during March 2024 at TUBS premises, including assessment of near- and far-field regimes, diffraction properties, and effect of misalignment.
- RIS-parametrised channel modelling and unit-cell modelling:
• A novel multi-user near-field channel model with holographic MIMO transceivers (e.g., metasurface-based antenna panels) and triple polarisation using the dyadic Green’s function has been developed.
• Ongoing work for unit-cell wideband frequency response modelling, parametrised in terms of Q-factors and circuital hardware, extending the coupled mode theory.
• Electromagnetic consistent modelling based on S-parameters to model mutual coupling is being investigated.
• Literature review of physics-inspired RIS-parametrized channel models has been conducted including: scattering parameter analysis, mutual impedance modelling, and coupled dipole formalism (PhysFad channel model).
• Capacity characterization and optimization for various fading channels has been conducted.
- Channel Estimation Algorithms:
• A time-domain channel estimation approach has been developed for umMIMO THz systems considering a spatial representation of the wideband channel and the beam-squint effect.
- Beamforming Codebooks:
• A near-field dynamic codebook for directional beamforming has been investigated and implemented for a tracking scenario considering metasurface-based transceivers.
• A low-complexity neural-network-based beam training for THz beamforming has been studied considering an umMIMO system operating in the far-field,. Hierarchical codebook search assisted by a neural network to establish the relationship between the codewords in the angle domain to speed up the beam search was designed.
- Beamforming Strategies:
• An optimal design of RISs to increase the rank of the channel matrix in umMIMO systems was proposed.
• A multi-user downlink beamforming scheme with leaky waveguide antennas for wideband THz systems, exploiting the THz rainbow effect, was devised [GSR24].
• A low complexity fully digital beamforming transceivers aided by stacked transmissive RISs that realise wave-based analog beamforming were designed.
• An optimal receiving design, that maximizes capacity, for metasurface-based receivers with 1-bit Analog-to-Digital-Converters (ADCs) to assist multi-user uplink communications was designed.
- Localisation and Sensing:
• Proposed a RIS-enabled and access-point-free simultaneous radio localization and mapping method.
• Evaluated a joint 3D user and 6D hybrid RIS localization.
• Proposed a method based on full-duplex metasurface-based transceivers for integrated sensing and communication.
• Evaluated near-field localization with metasurface-based receivers with 1-bit ADCs to reduce power consumption.
• Reviewed and compared different positioning schemes along with algorithm evaluation.