1.
Gadamsetty, Pavan Kumar; Hari, K. V. S.; Hanzo, Lajos
Sum-Rate Maximization of RIS-Aided Digital and Holographic Beamformers in MU-MISO Systems Journal Article
In: IEEE Transactions on Communications, vol. 73, no. 5, pp. 3106–3118, 2025, ISSN: 1558-0857.
Abstract | Links | BibTeX | Tags: alternating maximization (AM), Array signal processing, Arrays, Beamforming, Millimeter wave communication, MISO communication, Programming, Radio frequency, Reconfigurable holographic surfaces (RHS), reconfigurable intelligent surfaces (RIS), Signal to noise ratio, sum-rate, Transceivers, Vectors, Wireless communication
@article{kumar_gadamsetty_sum-rate_2025,
title = {Sum-Rate Maximization of RIS-Aided Digital and Holographic Beamformers in MU-MISO Systems},
author = {Pavan Kumar Gadamsetty and K. V. S. Hari and Lajos Hanzo},
url = {https://ieeexplore.ieee.org/document/10737121},
doi = {10.1109/TCOMM.2024.3487305},
issn = {1558-0857},
year = {2025},
date = {2025-05-01},
urldate = {2025-10-08},
journal = {IEEE Transactions on Communications},
volume = {73},
number = {5},
pages = {3106–3118},
abstract = {Reconfigurable holographic surfaces (RHS) are intrinsically amalgamated with reconfigurable intelligent surfaces (RIS), for beneficially ameliorating the signal propagation environment. This potent architecture significantly improves the system performance in non-line-of-sight scenarios at a low power consumption. Briefly, the RHS technology integrates ultra-thin, lightweight antennas onto the transceiver, for creating sharp, high-gain directional beams. We formulate a user sum-rate maximization problem for our RHS-RIS-based hybrid beamformer. Explicitly, we jointly design the digital, holographic, and passive beamformers for maximizing the sum-rate of all user equipment (UE). To tackle the resultant nonconvex optimization problem, we propose an alternating maximization (AM) framework for decoupling and iteratively solving the subproblems involved. Specifically, we employ the zero-forcing criterion for the digital beamformer, leverage fractional programming to determine the radiation amplitudes of the RHS and utilize the Riemannian conjugate gradient algorithm for optimizing the RIS phase shift matrix of the passive beamformer. Our simulation results demonstrate that the proposed RHS-RIS-based hybrid beamformer outperforms its conventional counterpart operating without an RIS in multi-UE scenarios. The sum-rate improvement attained ranges from 8 bps/Hz to 13 bps/Hz for various transmit powers at the base station (BS) and at the UEs, which is significant.},
keywords = {alternating maximization (AM), Array signal processing, Arrays, Beamforming, Millimeter wave communication, MISO communication, Programming, Radio frequency, Reconfigurable holographic surfaces (RHS), reconfigurable intelligent surfaces (RIS), Signal to noise ratio, sum-rate, Transceivers, Vectors, Wireless communication},
pubstate = {published},
tppubtype = {article}
}
Reconfigurable holographic surfaces (RHS) are intrinsically amalgamated with reconfigurable intelligent surfaces (RIS), for beneficially ameliorating the signal propagation environment. This potent architecture significantly improves the system performance in non-line-of-sight scenarios at a low power consumption. Briefly, the RHS technology integrates ultra-thin, lightweight antennas onto the transceiver, for creating sharp, high-gain directional beams. We formulate a user sum-rate maximization problem for our RHS-RIS-based hybrid beamformer. Explicitly, we jointly design the digital, holographic, and passive beamformers for maximizing the sum-rate of all user equipment (UE). To tackle the resultant nonconvex optimization problem, we propose an alternating maximization (AM) framework for decoupling and iteratively solving the subproblems involved. Specifically, we employ the zero-forcing criterion for the digital beamformer, leverage fractional programming to determine the radiation amplitudes of the RHS and utilize the Riemannian conjugate gradient algorithm for optimizing the RIS phase shift matrix of the passive beamformer. Our simulation results demonstrate that the proposed RHS-RIS-based hybrid beamformer outperforms its conventional counterpart operating without an RIS in multi-UE scenarios. The sum-rate improvement attained ranges from 8 bps/Hz to 13 bps/Hz for various transmit powers at the base station (BS) and at the UEs, which is significant.
2.
Liu, Yi; Ali, Wajahat; Chen, Rui; Bamiedakis, Nikolaos; White, Ian H.; Haas, Harald; Crisp, Michael; Penty, Richard V.
A Scalable VCSEL-Array Optical Wireless Transmitter With Experimental Multi-Beam Prototype Journal Article
In: Journal of Lightwave Technology, pp. 1–7, 2025, ISSN: 1558-2213.
Abstract | Links | BibTeX | Tags: Arrays, Free-space optical communication, Interference, Lenses, LRDC, Microoptics, Optical arrays, optical communication equipment, Optical fibers, Optical receivers, Optical transmitters, Vertical cavity surface emitting lasers, verticalcavity surface-emitting lasers, Wireless communication
@article{liu_scalable_2025,
title = {A Scalable VCSEL-Array Optical Wireless Transmitter With Experimental Multi-Beam Prototype},
author = {Yi Liu and Wajahat Ali and Rui Chen and Nikolaos Bamiedakis and Ian H. White and Harald Haas and Michael Crisp and Richard V. Penty},
url = {https://ieeexplore.ieee.org/document/11189981},
doi = {10.1109/JLT.2025.3617131},
issn = {1558-2213},
year = {2025},
date = {2025-01-01},
urldate = {2025-10-17},
journal = {Journal of Lightwave Technology},
pages = {1–7},
abstract = {A 5×5 VCSEL array-based optical wireless communication multi-beam transmitter is designed and simulated. Each element of the array addresses a separate spatial attocell. A microlens-array based homogenizer achieves uniform coverage at the receiver plane from each multi-mode VCSEL output. 1 m2 total coverage is achieved with each attocell covering an area of 400 cm2 at a range of 3 m. For a proof-of-concept demonstration a 1×3 channel VCSEL array-based transmitter prototype is experimentally tested. The performance is verified by demonstrating three channels achieving ∼ 0.12 mW/m2 uniform power with negligible optical interference to adjacent attocells (<-14 dB). With a simple receiver design using low cost, off-the-shelf components, each channel of the transmitter achieves ∼10 Gb/s throughput using OFDM within 7 cm lateral range and > 4 Gb/s within 12 cm lateral range at 3 m. The transmitter meets eye-safety restrictions and could be scaled to 250 Gb/s aggregate data rate by employing all 25 VCSELs with independent OFDM modulation.},
keywords = {Arrays, Free-space optical communication, Interference, Lenses, LRDC, Microoptics, Optical arrays, optical communication equipment, Optical fibers, Optical receivers, Optical transmitters, Vertical cavity surface emitting lasers, verticalcavity surface-emitting lasers, Wireless communication},
pubstate = {published},
tppubtype = {article}
}
A 5×5 VCSEL array-based optical wireless communication multi-beam transmitter is designed and simulated. Each element of the array addresses a separate spatial attocell. A microlens-array based homogenizer achieves uniform coverage at the receiver plane from each multi-mode VCSEL output. 1 m2 total coverage is achieved with each attocell covering an area of 400 cm2 at a range of 3 m. For a proof-of-concept demonstration a 1×3 channel VCSEL array-based transmitter prototype is experimentally tested. The performance is verified by demonstrating three channels achieving ∼ 0.12 mW/m2 uniform power with negligible optical interference to adjacent attocells (<-14 dB). With a simple receiver design using low cost, off-the-shelf components, each channel of the transmitter achieves ∼10 Gb/s throughput using OFDM within 7 cm lateral range and > 4 Gb/s within 12 cm lateral range at 3 m. The transmitter meets eye-safety restrictions and could be scaled to 250 Gb/s aggregate data rate by employing all 25 VCSELs with independent OFDM modulation.