1.
Li, Qingchao; El-Hajjar, Mohammed; Xu, Chao; An, Jiancheng; Yuen, Chau; Hanzo, Lajos
Stacked Intelligent Metasurface-Based Transceiver Design for Near-Field Wideband Systems Journal Article
In: IEEE Transactions on Communications, vol. 73, no. 9, pp. 8125–8139, 2025, ISSN: 1558-0857.
Abstract | Links | BibTeX | Tags: Array signal processing, Channel models, Hardware, holographic beamforming architecture, Low earth orbit satellites, Metamaterials, Metasurfaces, near-field channel model, phase tuning error, Stacked intelligent metasurface, Transceivers, Tuning, Vectors, Wideband, wideband system
@article{li_stacked_2025,
title = {Stacked Intelligent Metasurface-Based Transceiver Design for Near-Field Wideband Systems},
author = {Qingchao Li and Mohammed El-Hajjar and Chao Xu and Jiancheng An and Chau Yuen and Lajos Hanzo},
url = {https://ieeexplore.ieee.org/document/10900449},
doi = {10.1109/TCOMM.2025.3544929},
issn = {1558-0857},
year = {2025},
date = {2025-09-01},
urldate = {2025-10-08},
journal = {IEEE Transactions on Communications},
volume = {73},
number = {9},
pages = {8125–8139},
abstract = {Intelligent metasurfaces may be harnessed for realizing efficient holographic multiple-input and multiple-output (MIMO) systems, at a low hardware-cost and high energy-efficiency. As part of this family, we propose a hybrid beamforming design for stacked intelligent metasurfaces (SIM) aided wideband wireless systems relying on the near-field channel model. Specifically, the holographic beamformer is designed based on configuring the phase shifts in each layer of the SIM for maximizing the sum of the baseband eigen-channel gains of all users. To optimize the SIM phase shifts, we propose a layer-by-layer iterative algorithm for optimizing the phase shifts in each layer alternately. Then, the minimum mean square error (MMSE) transmit precoding method is employed for the digital beamformer to support multi-user access. Furthermore, the mitigation of the SIM phase tuning error is also taken into account in the digital beamformer by exploiting its statistics. The power sharing ratio of each user is designed based on the iterative waterfilling power allocation algorithm. Additionally, our analytical results indicate that the spectral efficiency attained saturates in the high signal-to-noise ratio (SNR) region due to the phase tuning error resulting from the imperfect SIM hardware quality. The simulation results show that the SIM-aided holographic MIMO outperforms the state-of-the-art (SoA) single-layer holographic MIMO in terms of its achievable rate. We further demonstrate that the near-field channel model allows the SIM-based transceiver design to support multiple users, since the spatial resources represented both by the angle domain and the distance domain can be exploited.},
keywords = {Array signal processing, Channel models, Hardware, holographic beamforming architecture, Low earth orbit satellites, Metamaterials, Metasurfaces, near-field channel model, phase tuning error, Stacked intelligent metasurface, Transceivers, Tuning, Vectors, Wideband, wideband system},
pubstate = {published},
tppubtype = {article}
}
Intelligent metasurfaces may be harnessed for realizing efficient holographic multiple-input and multiple-output (MIMO) systems, at a low hardware-cost and high energy-efficiency. As part of this family, we propose a hybrid beamforming design for stacked intelligent metasurfaces (SIM) aided wideband wireless systems relying on the near-field channel model. Specifically, the holographic beamformer is designed based on configuring the phase shifts in each layer of the SIM for maximizing the sum of the baseband eigen-channel gains of all users. To optimize the SIM phase shifts, we propose a layer-by-layer iterative algorithm for optimizing the phase shifts in each layer alternately. Then, the minimum mean square error (MMSE) transmit precoding method is employed for the digital beamformer to support multi-user access. Furthermore, the mitigation of the SIM phase tuning error is also taken into account in the digital beamformer by exploiting its statistics. The power sharing ratio of each user is designed based on the iterative waterfilling power allocation algorithm. Additionally, our analytical results indicate that the spectral efficiency attained saturates in the high signal-to-noise ratio (SNR) region due to the phase tuning error resulting from the imperfect SIM hardware quality. The simulation results show that the SIM-aided holographic MIMO outperforms the state-of-the-art (SoA) single-layer holographic MIMO in terms of its achievable rate. We further demonstrate that the near-field channel model allows the SIM-based transceiver design to support multiple users, since the spatial resources represented both by the angle domain and the distance domain can be exploited.
2.
Yu, Quantao; Mishra, Deepak; Wang, Hua; He, Dongxuan; Yuan, Jinhong; Matthaiou, Michail
Toward LoRa-Based LEO Satellite IoT: A Stochastic Geometry Perspective Journal Article
In: IEEE Internet of Things Journal, vol. 12, no. 15, pp. 30725–30738, 2025, ISSN: 2327-4662.
Abstract | Links | BibTeX | Tags: Access probability, Analytical models, Interference, Internet of Things, Long-Range (LoRa), LoRa, Low earth orbit satellites, Performance analysis, Rayleigh channels, Satellite broadcasting, satellite Internet of Things (IoT), Satellites, stochastic geometry (SG), Uplink
@article{yu_toward_2025,
title = {Toward LoRa-Based LEO Satellite IoT: A Stochastic Geometry Perspective},
author = {Quantao Yu and Deepak Mishra and Hua Wang and Dongxuan He and Jinhong Yuan and Michail Matthaiou},
url = {https://ieeexplore.ieee.org/document/11007561},
doi = {10.1109/JIOT.2025.3571928},
issn = {2327-4662},
year = {2025},
date = {2025-08-01},
urldate = {2025-10-08},
journal = {IEEE Internet of Things Journal},
volume = {12},
number = {15},
pages = {30725–30738},
abstract = {Recently, Long-Range (LoRa)-based low-Earth orbit (LEO) satellite Internet of Things (IoT) has garnered growing interest from both academia and industry, since it can guarantee pervasive connectivity in an energy-efficient and cost-effective manner. In this article, we provide a novel spherical stochastic geometry (SG)-based analytical framework for characterizing the uplink access probability of LoRa-based LEO satellite IoT system. Specifically, multiple classes of LoRa end-devices (EDs) are taken into consideration, where each class of LoRa EDs is modeled by an independent Poisson point process (PPP). Both the channel characteristics of the satellite-to-Earth communications and the unique features of the LoRa network are considered to derive closed-form analytical expressions for the uplink access probability of such a new paradigm. Moreover, the nontrivial impact of the spreading factor, the ED’s density, the orbit altitude, and the satellite effective beamwidth on the system performance is thoroughly investigated. Extensive numerical simulations are conducted, which not only validate the accuracy of our theoretical analysis but also provide useful insights into the practical design and implementation of LoRa-based LEO satellite IoT system.},
keywords = {Access probability, Analytical models, Interference, Internet of Things, Long-Range (LoRa), LoRa, Low earth orbit satellites, Performance analysis, Rayleigh channels, Satellite broadcasting, satellite Internet of Things (IoT), Satellites, stochastic geometry (SG), Uplink},
pubstate = {published},
tppubtype = {article}
}
Recently, Long-Range (LoRa)-based low-Earth orbit (LEO) satellite Internet of Things (IoT) has garnered growing interest from both academia and industry, since it can guarantee pervasive connectivity in an energy-efficient and cost-effective manner. In this article, we provide a novel spherical stochastic geometry (SG)-based analytical framework for characterizing the uplink access probability of LoRa-based LEO satellite IoT system. Specifically, multiple classes of LoRa end-devices (EDs) are taken into consideration, where each class of LoRa EDs is modeled by an independent Poisson point process (PPP). Both the channel characteristics of the satellite-to-Earth communications and the unique features of the LoRa network are considered to derive closed-form analytical expressions for the uplink access probability of such a new paradigm. Moreover, the nontrivial impact of the spreading factor, the ED’s density, the orbit altitude, and the satellite effective beamwidth on the system performance is thoroughly investigated. Extensive numerical simulations are conducted, which not only validate the accuracy of our theoretical analysis but also provide useful insights into the practical design and implementation of LoRa-based LEO satellite IoT system.
3.
Majumder, Debparna; Bottrill, Kyle R. H.; Petropoulos, Periklis
Fibre-Based Dynamic Speckle Generation for Emulation of Atmospheric Turbulence Proceedings Article
In: 2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), pp. 1–1, 2025, ISSN: 2833-1052, (ISSN: 2833-1052).
Abstract | Links | BibTeX | Tags: Emulation, Europe, Free-space optical communication, Generators, Low earth orbit satellites, Optical fibers, Phase modulation, Satellites, Speckle, System performance
@inproceedings{majumder_fibre-based_2025,
title = {Fibre-Based Dynamic Speckle Generation for Emulation of Atmospheric Turbulence},
author = {Debparna Majumder and Kyle R. H. Bottrill and Periklis Petropoulos},
url = {https://ieeexplore.ieee.org/abstract/document/11110258},
doi = {10.1109/CLEO/Europe-EQEC65582.2025.11110258},
issn = {2833-1052},
year = {2025},
date = {2025-06-01},
urldate = {2025-10-08},
booktitle = {2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)},
pages = {1–1},
abstract = {Mitigating the impact of atmospheric turbulence induced speckle is a major challenge for free-space optical communications (FSOC). Such turbulence results in a multimodal, speckled beam which can be challenging to couple into the small active-area photoreceivers needed for high-bandwidth detection. Naturally, lab-based turbulence emulators are needed to benchmark FSOC system performance and develop turbulence mitigating subsystems. Common approaches to turbulence emulation include: rotating phase plates (PPs) [1], spatial light modulators (SLMs) [2] and turbulent-air generators [3]. In this work, we present a fibre-based, dynamic speckle generator, notable for its simplicity, cost-effectiveness (especially compared to SLMs and PPs), and unobtrusive in-lab use (compared to turbulent-air approaches). Unlike today's SLMs, which currently struggle to replicate the fast-changing distortion caused by high slew-rate Low-Earth-Orbit (LEO) satellite tracking, our all-fibre speckle generator can be easily scaled to faster modulation speeds (demonstrated here with a modest 230RPM).},
note = {ISSN: 2833-1052},
keywords = {Emulation, Europe, Free-space optical communication, Generators, Low earth orbit satellites, Optical fibers, Phase modulation, Satellites, Speckle, System performance},
pubstate = {published},
tppubtype = {inproceedings}
}
Mitigating the impact of atmospheric turbulence induced speckle is a major challenge for free-space optical communications (FSOC). Such turbulence results in a multimodal, speckled beam which can be challenging to couple into the small active-area photoreceivers needed for high-bandwidth detection. Naturally, lab-based turbulence emulators are needed to benchmark FSOC system performance and develop turbulence mitigating subsystems. Common approaches to turbulence emulation include: rotating phase plates (PPs) [1], spatial light modulators (SLMs) [2] and turbulent-air generators [3]. In this work, we present a fibre-based, dynamic speckle generator, notable for its simplicity, cost-effectiveness (especially compared to SLMs and PPs), and unobtrusive in-lab use (compared to turbulent-air approaches). Unlike today's SLMs, which currently struggle to replicate the fast-changing distortion caused by high slew-rate Low-Earth-Orbit (LEO) satellite tracking, our all-fibre speckle generator can be easily scaled to faster modulation speeds (demonstrated here with a modest 230RPM).
4.
Trinh, Phuc V.; Sugiura, Shinya; Xu, Chao; Hanzo, Lajos
Toward Quantum SAGINs Harnessing Optical RISs: Applications, Advances, and the Road Ahead Journal Article
In: IEEE Network, vol. 39, no. 3, pp. 215–222, 2025, ISSN: 1558-156X.
Abstract | Links | BibTeX | Tags: Airplanes, Buildings, Drones, free-space optics, Low earth orbit satellites, next-generation network, Optical beams, Optical fiber networks, Optical fibers, optical reconfigurable intelligent surface, Quantum entanglement, quantum Internet, Relays, Satellites, Space-air-ground integrated network, Space-air-ground integrated networks
@article{trinh_toward_2025,
title = {Toward Quantum SAGINs Harnessing Optical RISs: Applications, Advances, and the Road Ahead},
author = {Phuc V. Trinh and Shinya Sugiura and Chao Xu and Lajos Hanzo},
url = {https://ieeexplore.ieee.org/document/10858146},
doi = {10.1109/MNET.2025.3536848},
issn = {1558-156X},
year = {2025},
date = {2025-05-01},
urldate = {2025-10-08},
journal = {IEEE Network},
volume = {39},
number = {3},
pages = {215–222},
abstract = {The space-air-ground integrated network (SAGIN) concept is vital for the development of seamless next-generation (NG) wireless coverage, integrating satellites, unmanned aerial vehicles, and manned aircraft along with the terrestrial infrastructure to provide resilient ubiquitous communications. By incorporating quantum communications using optical wireless signals, SAGIN is expected to support a synergistic global quantum Internet alongside classical networks. However, long-distance optical beam propagation requires line-of-sight (LOS) connections in the face of beam broadening and LoS blockages. To overcome blockages among SAGIN nodes, we propose deploying optical reconfigurable intelligent surfaces (ORISs) on building rooftops. They can also adaptively control optical beam diameters for reducing losses. This article first introduces the applications of ORISs in SAGINs, then examines their advances in quantum communications for typical SAGIN scenarios. Finally, the road ahead towards the practical realization of ORIS-aided NG quantum SAGINs is outlined.},
keywords = {Airplanes, Buildings, Drones, free-space optics, Low earth orbit satellites, next-generation network, Optical beams, Optical fiber networks, Optical fibers, optical reconfigurable intelligent surface, Quantum entanglement, quantum Internet, Relays, Satellites, Space-air-ground integrated network, Space-air-ground integrated networks},
pubstate = {published},
tppubtype = {article}
}
The space-air-ground integrated network (SAGIN) concept is vital for the development of seamless next-generation (NG) wireless coverage, integrating satellites, unmanned aerial vehicles, and manned aircraft along with the terrestrial infrastructure to provide resilient ubiquitous communications. By incorporating quantum communications using optical wireless signals, SAGIN is expected to support a synergistic global quantum Internet alongside classical networks. However, long-distance optical beam propagation requires line-of-sight (LOS) connections in the face of beam broadening and LoS blockages. To overcome blockages among SAGIN nodes, we propose deploying optical reconfigurable intelligent surfaces (ORISs) on building rooftops. They can also adaptively control optical beam diameters for reducing losses. This article first introduces the applications of ORISs in SAGINs, then examines their advances in quantum communications for typical SAGIN scenarios. Finally, the road ahead towards the practical realization of ORIS-aided NG quantum SAGINs is outlined.
5.
Li, Qingchao; El-Hajjar, Mohammed; Cao, Kaijun; Xu, Chao; Haas, Harald; Hanzo, Lajos
Holographic Metasurface-Based Beamforming for Multi-Altitude LEO Satellite Networks Journal Article
In: IEEE Transactions on Wireless Communications, pp. 1–1, 2025, ISSN: 1558-2248, (arXiv:2501.04164 [cs]).
Abstract | Links | BibTeX | Tags: Array signal processing, Computer architecture, Downlink, holographic metasurface, hybrid beamforming, inter-satellite interference, Low Earth Orbit (LEO) satellite communication, Low earth orbit satellites, Metasurfaces, Precoding, Satellite broadcasting, Satellite communications, Satellites, stochastic geometry, Throughput
@article{li_holographic_2025,
title = {Holographic Metasurface-Based Beamforming for Multi-Altitude LEO Satellite Networks},
author = {Qingchao Li and Mohammed El-Hajjar and Kaijun Cao and Chao Xu and Harald Haas and Lajos Hanzo},
url = {https://ieeexplore.ieee.org/abstract/document/10844052/?casa_token=5kb4rgy_qqAAAAAA:Qy4zV9IQ3FSfC6Cy7it5EvcxjQM2a675RSsbRiRKNPsADHjWFXZ0VHem5zJ_dVf5IBDhE6R2sg},
doi = {10.1109/TWC.2025.3527962},
issn = {1558-2248},
year = {2025},
date = {2025-01-01},
urldate = {2025-02-24},
journal = {IEEE Transactions on Wireless Communications},
pages = {1–1},
publisher = {arXiv},
abstract = {Low Earth Orbit (LEO) satellite networks are capable of improving the global Internet service coverage. In this context, we propose a hybrid beamforming design for holographic metasurface based terrestrial users in multi-altitude LEO satellite networks. Firstly, the holographic beamformer is optimized by maximizing the downlink channel gain from the serving satellite to the terrestrial user. Then, the digital beamformer is designed by conceiving a minimum mean square error (MMSE) based detection algorithm for mitigating the interference arriving from other satellites. To dispense with excessive overhead of full channel state information (CSI) acquisition of all satellites, we propose a low-complexity MMSE beamforming algorithm that only relies on the distribution of the LEO satellite constellation harnessing stochastic geometry, which can achieve comparable throughput to that of the algorithm based on the full CSI in the case of a dense LEO satellite deployment. Furthermore, it outperforms the maximum ratio combining (MRC) algorithm, thanks to its inter-satellite interference mitigation capacity. The simulation results show that our proposed holographic metasurface based hybrid beamforming architecture is capable of outperforming the state-of-the-art antenna array architecture in terms of its throughput, given the same physical size of the transceivers. Moreover, we demonstrate that the beamforming performance attained can be substantially improved by taking into account the mutual coupling effect, imposed by the dense placement of the holographic metasurface elements.},
note = {arXiv:2501.04164 [cs]},
keywords = {Array signal processing, Computer architecture, Downlink, holographic metasurface, hybrid beamforming, inter-satellite interference, Low Earth Orbit (LEO) satellite communication, Low earth orbit satellites, Metasurfaces, Precoding, Satellite broadcasting, Satellite communications, Satellites, stochastic geometry, Throughput},
pubstate = {published},
tppubtype = {article}
}
Low Earth Orbit (LEO) satellite networks are capable of improving the global Internet service coverage. In this context, we propose a hybrid beamforming design for holographic metasurface based terrestrial users in multi-altitude LEO satellite networks. Firstly, the holographic beamformer is optimized by maximizing the downlink channel gain from the serving satellite to the terrestrial user. Then, the digital beamformer is designed by conceiving a minimum mean square error (MMSE) based detection algorithm for mitigating the interference arriving from other satellites. To dispense with excessive overhead of full channel state information (CSI) acquisition of all satellites, we propose a low-complexity MMSE beamforming algorithm that only relies on the distribution of the LEO satellite constellation harnessing stochastic geometry, which can achieve comparable throughput to that of the algorithm based on the full CSI in the case of a dense LEO satellite deployment. Furthermore, it outperforms the maximum ratio combining (MRC) algorithm, thanks to its inter-satellite interference mitigation capacity. The simulation results show that our proposed holographic metasurface based hybrid beamforming architecture is capable of outperforming the state-of-the-art antenna array architecture in terms of its throughput, given the same physical size of the transceivers. Moreover, we demonstrate that the beamforming performance attained can be substantially improved by taking into account the mutual coupling effect, imposed by the dense placement of the holographic metasurface elements.