Publications

@article{chen_multi-policy_2025,

title = {Multi-policy reinforcement learning for network resource allocation with periodic behaviors},

author = {Zheyu Chen and Kin K. Leung and Shiqiang Wang and Leandros Tassiulas and Kevin Chan and Patrick J. Baker},

url = {https://www.sciencedirect.com/science/article/pii/S1389128625006127},

doi = {10.1016/j.comnet.2025.111645},

issn = {1389-1286},

year  = {2025},

date = {2025-11-01},

urldate = {2025-10-08},

journal = {Computer Networks},

volume = {272},

pages = {111645},

abstract = {Markov Decision Processes (MDPs) serve as the mathematical foundation of Reinforcement learning (RL), where a Markov process with defined states is used to model the system and the actions to be taken affect the state transitions and the corresponding rewards. The RL and deep RL (DRL) can produce the high-performing action policy to maximize the long-term reward. Although RL/DRL have been widely applied to communication and computer systems, a key limitation is that the system under consideration often does not satisfy the required mathematical properties, thus making the MDP inexact and the derived policy flawed. Therefore, we consider the periodic Markov Decision Process (pMDP), where the evolution of the underlying process and model parameters for the pMDP demonstrate some forms of periodic characteristics (e.g., periodic job arrivals and available resources) which violate the Markov property. To obtain the optimal policies for the pMDP, a policy gradient method with a multi-policy solution framework is proposed, and a deep-learning method is developed to improve the effectiveness and stability of the proposed solution. Furthermore, a layer-sharing strategy is proposed to reduce the storage complexity by reducing the number of parameters in the neural networks. The deep-learning method is applied to achieve the near-optimal allocation of resources to arriving computational tasks in a network setting corresponding to the software-defined network (SDN). Evaluation results reveal that the proposed technique is valid and capable of outperforming a baseline method that employs a single policy by 31% on average.},

keywords = {Deep reinforcement learning, Markov Decision Process, Network resource allocation, Reinforcement learning},

pubstate = {published},

tppubtype = {article}

}

@article{gong_rydberg_2025,

title = {Rydberg Atomic Quantum Receivers for Classical Wireless Communication and Sensing},

author = {Tierui Gong and Aveek Chandra and Chau Yuen and Yong Liang Guan and Rainer Dumke and Chong Meng Samson See and Mérouane Debbah and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10972179},

doi = {10.1109/MWC.015.2400381},

issn = {1558-0687},

year  = {2025},

date = {2025-10-01},

urldate = {2025-10-08},

journal = {IEEE Wireless Communications},

volume = {32},

number = {5},

pages = {90–100},

abstract = {Rydberg atomic quantum receivers (RAQRs) are emerging quantum precision sensing platforms designed for receiving radio frequency (RF) signals. It relies on the creation of Rydberg atoms from normal atoms by exciting one or more electrons to a very high energy level, thereby making the atom sensitive to RF signals. RAQRs realize RF-to-optical conversions based on atom-light interactions relying on the so-called electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS) so that the desired RF signal can be read out optically. The large dipole moments of Rydberg atoms associated with rich choices of Rydberg states facilitate an ultra-high sensitivity (textbackslashsimtextbackslashtextnv/textbackslashtextcm/textbackslashsqrttextbackslashtextHz) and an ultra-broadband tunability (direct-current to Terahertz). RAQRs also exhibit compelling scalability and lend themselves to the construction of innovative, compact receivers. Initial experimental studies have demonstrated their capabilities in classical wireless communications and sensing. To fully harness their potential in a wide variety of applications, we commence by outlining the underlying fundamentals of Rydberg atoms, followed by the principles and schemes of RAQRs. Then, we overview the state-of-the-art studies from both physics and communication societies. Furthermore, we conceive Rydberg atomic quantum single-input single-output (RAQ-SISO) and multiple-input multiple-output (RAQ-MIMO) schemes to facilitate the integration of RAQRs with classical wireless systems. Finally, we conclude with a set of potent research directions.},

keywords = {Atomic measurements, Electric fields, Electrons, Energy states, Laser beams, Quantum communication, Radio frequency, Receivers, RF signals, Rydberg atoms},

pubstate = {published},

tppubtype = {article}

}

@article{ihsan_energy-efficient_2025,

title = {Energy-Efficient TDMA-NOMA for RIS-Assisted Ultra-Dense VLC Networks},

author = {Asim Ihsan and Muhammad Asif and Wali Ullah Khan and Isaac N. O. Osahon and Sujan Rajbhandari},

doi = {10.1109/tgcn.2024.3511114},

issn = {2473-2400},

year  = {2025},

date = {2025-09-01},

journal = {IEEE Transactions on Green Communications and Networking},

volume = {9},

number = {3},

pages = {1239–1253},

abstract = {This paper proposes an energy-efficient optimization technique for downlink indoor visible light communication (VLC) systems using hybrid non-orthogonal multiple access (NOMA) and reconfigurable intelligent surfaces (RIS). The approach considers a hybrid time division multiple access-NOMA (TDMA-NOMA) to provide massive connectivity to multi-clusters. Clusters of users are formed using NOMA while TDMA is used to allocate a specific time slot within a communication frame. The proposed technique optimizes the precoding at the multi-LED transmitter, RIS tuning parameters, and time-slot allocation parameters for each cluster to maximize the system’s energy efficiency (EE). The EE optimization problem is solved through the block coordinate descent (BCD) framework, which splits the optimization problem into two blocks. An alternating optimization (AO) framework is used in the first block to optimize the transmit precoding through conic quadratic programming (CQP) and RIS tuning parameters through a semidefinite programming (SDP) technique based on the surrogate optimization method. The second block allocates energy-efficient time-slot for each cluster through linear programming (LP) approach to further improve the EE of the system. The simulation results indicate that the proposed BCD framework achieves fast convergence and excellent performance in terms of the EE of the system while maintaining low computational complexity.},

keywords = {energy efficiency, Hybrid TDMA-NOMA Systems, reconfigurable intelligent surfaces, Resource Allocations, Visible light communication},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@article{mehrotra_multi-dimensional_2025,

title = {Multi-Dimensional Sparse CSI Acquisition for Hybrid mmWave MIMO OTFS Systems},

author = {Anand Mehrotra and Jitendra Singh and Suraj Srivastava and Rahul Kumar Singh and Aditya K. Jagannatham and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10918701},

doi = {10.1109/TCOMM.2025.3549501},

issn = {1558-0857},

year  = {2025},

date = {2025-09-01},

urldate = {2025-10-08},

journal = {IEEE Transactions on Communications},

volume = {73},

number = {9},

pages = {8330–8344},

abstract = {Multi-dimensional sparse channel state information (CSI) acquisition is conceived for Orthogonal time frequency space (OTFS) modulation-based millimetre wave (mmWave) multiple input and multiple output (MIMO) systems. A comprehensive end-to-end relationship is derived in the delay-Doppler (DDA) domain by additionally considering the angular parameters and a hybrid beamforming (HB) architecture. A time-domain pilot model tailored for CSI estimation (CE) in the DDA-domain is proposed, which exploits the inherent multi-dimensional (4D) sparsity that emerges in the DDA-domain during the CE process. An efficient low-complexity Bayesian learning (LC-BL) technique is conceived to fulfil the objective of CSI estimation in such systems. Subsequently, a comprehensive examination of the complexity of the algorithm under consideration is also provided. It is worth noting that the complexity of the BL scheme designed is similar to that of popular orthogonal matching pursuit (OMP), but significantly lower than that of the traditional expectation-maximization (EM) based BL technique. Moreover, a single-stage transmit precoder (TPC) and receiver combiner (RC) design is proposed. This procedure aims for maximizing the directional gain of the RF TPC/RC pair by optimizing their weights. Additionally, a series of comprehensive simulations are conducted which incorporate the use of a practical channel model and fractional Doppler shifts. In light of the inherent trade-offs between complexity and estimation algorithm performance, our proposed scheme, LC-BL, appears suitable, especially considering the substantial enhancement in the performance of CE compared to the existing benchmarks.},

keywords = {Bayes methods, Channel estimation, Complexity theory, delay-Doppler-angular domain, Estimation, high-mobility, Hybrid precoding, Millimeter wave communication, MIMO, mmWave, Modulation, OFDM, OTFS, sparsity, Symbols, Training},

pubstate = {published},

tppubtype = {article}

}

@article{an_flexible_2025-1,

title = {Flexible Intelligent Metasurfaces for Enhancing MIMO Communications},

author = {Jiancheng An and Zhu Han and Dusit Niyato and Mérouane Debbah and Chau Yuen and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/abstract/document/10922153},

doi = {10.1109/TCOMM.2025.3550318},

issn = {1558-0857},

year  = {2025},

date = {2025-09-01},

urldate = {2025-10-08},

journal = {IEEE Transactions on Communications},

volume = {73},

number = {9},

pages = {7349–7365},

abstract = {Flexible intelligent metasurfaces (FIMs) show great potential for improving the wireless network capacity in an energy-efficient manner. An FIM is a soft array consisting of several low-cost radiating elements. Each element can independently emit electromagnetic signals, while flexibly adjusting its position even perpendicularly to the overall surface to ‘morph’ its 3D shape. More explicitly, compared to a conventional rigid antenna array, an FIM is capable of finding an optimal 3D surface shape that provides improved signal quality. In this paper, we study point-to-point multiple-input multiple-output (MIMO) communications between a pair of FIMs. In order to characterize the capacity limits of FIM-aided MIMO transmissions over frequency-flat fading channels, we formulate a transmit optimization problem for maximizing the MIMO channel capacity by jointly optimizing the 3D surface shapes of the transmitting and receiving FIMs as well as the MIMO transmit covariance matrix, subject to the total transmit power constraint and to the maximum perpendicular morphing range of the FIM. To solve this problem, we develop an efficient block coordinate descent (BCD) algorithm. The BCD algorithm iteratively updates the 3D surface shapes of the FIMs and the transmit covariance matrix, while keeping the other fixed, to find a locally optimal solution. Numerical results verify that FIMs can achieve higher MIMO capacity than that of the conventional rigid arrays. In particular, the MIMO channel capacity can be doubled by the proposed BCD algorithm under some setups.},

keywords = {Antenna arrays, capacity maximization, Directive antennas, Flexible intelligent metasurfaces (FIMs), Metasurfaces, MIMO, multiple-input multiple-output (MIMO), Receiving antennas, reconfigurable intelligent surfaces (RIS), Shape, Surface waves, surface-shape morphing, Three-dimensional displays, Transmitting antennas, Wireless networks},

pubstate = {published},

tppubtype = {article}

}

@article{tong_adaptive_2025,

title = {Adaptive FTN Signaling Over Rapidly-Fading Channels},

author = {Mingfei Tong and Xiaojing Huang and J. Andrew Zhang and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10902515},

doi = {10.1109/TCOMM.2025.3545655},

issn = {1558-0857},

year  = {2025},

date = {2025-09-01},

urldate = {2025-10-08},

journal = {IEEE Transactions on Communications},

volume = {73},

number = {9},

pages = {7166–7178},

abstract = {The research of faster-than-Nyquist (FTN) signaling has reached a state of maturity for considering practical multipath fading channels, rather than idealized additive white Gaussian noise channels only. To overcome fast-fading multipath propagations, conventional FTN systems tend to rely on channel coding techniques for cleaning up the residual errors, rather than harnessing Doppler effect mitigation. To circumvent this limitation, we propose an adaptive transmit precoding (ATPC) method associated with FTN signaling for applications in fast-fading multipath channels. Upon leveraging real-time channel state information fed back by the receiver, ATPC updates the modulation matrix to improve resilience against Doppler frequency shifts. To mitigate the inter-block interference and multipath effect, a cyclic prefix is inserted at the beginning of each transmission frame. In addition, we employ decision-directed successive interference cancellation for alleviating the inter-symbol interference stemming from FTN signaling and multipath effects. We also analyze the theoretical bit error rate (BER) performance and a pair of closed-form BER expressions are derived for extreme channel conditions, i.e., sufficiently large number of paths and sufficiently large Doppler frequency shift. Simulation results verify the effectiveness of the proposed ATPC method and demonstrate our performance improvements over conventional schemes.},

keywords = {ATPC, Complexity theory, delay-Doppler domain, diversity order, Diversity reception, Doppler effect, Frequency diversity, Frequency modulation, FTN signaling, inter-symbol interference, Interference cancellation, Multipath channels, multipath fast-fading channel, OFDM, Symbols, Time-frequency analysis},

pubstate = {published},

tppubtype = {article}

}

@article{wu_drl_2025,

title = {DRL for Network Slicing: IEEE International Conference on Computer Communications},

author = {Zhaozhou Wu and Anderson C Bravalheri and Juan Marcelo Parra Ullauri and Adrian-Cristian Nicolaescu and Yulei Wu and Dimitra Simeonidou},

url = {https://infocom2025.ieee-infocom.org/},

doi = {10.1109/INFOCOMWKSHPS65812.2025.11152844},

issn = {9798331543716},

year  = {2025},

date = {2025-09-01},

urldate = {2025-10-08},

journal = {IEEE INFOCOM 2025 - IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS)},

series = {IEEE Conference on Computer Communications Workshops, INFOCOM Wksps},

abstract = {Network Slicing (NS) can satisfy the differentiated service demands of vertical industries by tailoring a common infrastructure to multiple isolated logical networks. Such slices may need to be reconfigured given the varying traffic patterns, service requirements, device mobility and resource constraints. Frequent slice reconfigurations lead to service quality degradation for slice consumers. However, avoiding reconfigurations of existing slices leads to fewer deployed slices, in comparison to allowing reconfigurations. To mitigate this problem in the avoidance of reconfiguration, this paper proposes using Deep Reinforcement Learning (DRL) to optimise successful slice deployments over time, while avoiding reconfigurations. The DRL agent instructs a Linear Programming (LP) algorithm to deploy slices to maximise the chance of successful slice deployments over time. The results show that more slices are deployed compared to avoiding reconfiguration with LP-only algorithms. Our DRL-based slice orchestrator provides approximately 11% more slices, compared to existing slice orchestrations without such DRL guidance, demonstrating the potential advantage of DRL in NS applications.},

note = {Publisher: Institute of Electrical and Electronics Engineers (IEEE)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{chen_improved_2025,

title = {Improved Ultra-Dense Connection Provision Capability of Concurrent Upstream and Direct Inter-ONU Communication IMDD PONs by P2MP Flexible Optical Transceivers},

author = {Lin Chen and Han Yang and Shenming Jiang and Wei Jin and Jiaxiang He and Roger Philip Giddings and Yi Huang and Md Saifuddin Faruk and Xingwen Yi and Jianming Tang},

url = {https://www.mdpi.com/2304-6732/12/9/838},

doi = {10.3390/photonics12090838},

issn = {2304-6732},

year  = {2025},

date = {2025-09-01},

urldate = {2025-10-08},

journal = {Photonics},

volume = {12},

number = {9},

pages = {838},

abstract = {To cost-effectively meet 6G latency requirements, concurrent upstream and direct inter-optical network unit (ONU) communication passive optical networks (PONs) based on flexible point-to-multipoint (P2MP) optical transceivers and intensity modulation and direct detection (IMDD) have been reported to enable direct communications among different ONUs within the same PON without passing data to the optical line terminal (OLT). However, the previously reported P2MP transceivers suffer from high DSP complexity for establishing ultra-dense connections. For such application scenarios, the PON’s remote nodes also have high inter-ONU signal power losses. To effectively solve these technical challenges, this paper experimentally showcases (a) new P2MP transceivers by utilizing parallel multi-channel aggregation/de-aggregation and advanced extended Gaussian function (EGF)-based orthogonal digital filter banks, along with (b) low inter-ONU signal power loss-remote nodes. By introducing these two techniques into a 27 km, >54.31 Gbit/s concurrent upstream and direct inter-ONU communication IMDD PON, comprehensive experimental explorations of the PON’s performances were undertaken for the first time. The remote node is capable of supporting 128 ONUs. The results show that the new P2MP transceivers lead to >75% (>40%) reductions in overall transmitter (receiver multi-channel de-aggregation) DSP complexity, and they can also equip the PONs with an enhanced capability of providing ultra-dense connections. The experimental results also show that the PON allows each ONU to flexibly change its upstream and inter-ONU communication channel count without considerably compromising its performance. Therefore, the PON outperforms those of previously reported works in terms of ensuring low DSP complexity, highly robust transmission performance, and enhanced capabilities of flexibly accommodating numerous applications with diverse requirements regarding traffic characteristics, thus making it suitable for ultra-dense connection application scenarios.},

note = {Publisher: Multidisciplinary Digital Publishing Institute},

keywords = {intensity modulation and direct detection (IMDD), inter-ONU communications, multi-channel aggregation, passive optical networks, point-to-multipoint (P2MP) transceivers},

pubstate = {published},

tppubtype = {article}

}

@article{he_experimental_2025,

title = {Experimental Demonstrations of Chaotic Digital Filter-Based Physical Layer Security in Converged Fibre-mmWave Access Networks},

author = {Jiaxiang He and Luis Vallejo and Roger Philip Giddings and Wei Jin and Md Saifuddin Faruk and Xingwen Yi and Jianming Tang},

url = {https://opg.optica.org/jlt/abstract.cfm?uri=jlt-43-18-8839},

year  = {2025},

date = {2025-09-01},

urldate = {2025-10-08},

journal = {Journal of Lightwave Technology},

volume = {43},

number = {18},

pages = {8839–8848},

abstract = {Secure data transmission is experimentally demonstrated in a 1.67 Gb/s seamlessly converged fibre–millimeter wave (mmWave) network using the authors’ newly proposed chaotic digital filter (CDF)-based physical layer security (PLS) technique. The CDF-based encryption/decryption operates by introducing noise-like, key-dependent phase variations to conventional filter impulse responses. Validation is performed in a seamlessly converged network comprising a 25 km standard single-mode fibre (SSMF) link and a 5 m 36 GHz mmWave wireless link, utilizing cost-effective photonic-based mmWave generation and envelope detector-based reception. Experimental results show that the demonstrated PLS technique allows the encrypted signals to continuously flow between the fibre and radio frequency (RF) domains. The PLS technique also supports simultaneous optical and radio frequency access with almost identical BER transmission performances, and power penalties of <1 dB. To gain an in-depth understanding of the measured results, the CDFs’ characteristics, including their chaotic nature, sensitivity to security keys and optimum CDF design parameters, are explored both theoretically and experimentally in detail. The optimum security key properties and CDF's filter lengths are identified, which are independent of the transmission media and major characteristics of the encrypted signals. The CDF-based PLS technique offers salient advantages of ‘security-by-design’, ‘openness-by-design’, ‘dynamic security at the traffic level’, and ‘universal network compatibility’.},

note = {Publisher: IEEE},

keywords = {Bit error rate, Frequency division multiplexing, Optical signals, Phase noise, Quantum key distribution, Single mode fibers},

pubstate = {published},

tppubtype = {article}

}

@article{trinh_optical_2025,

title = {Optical RISs Improve the Secret Key Rate of Free-Space QKD in HAP-to-UAV Scenarios},

author = {Phuc V. Trinh and Shinya Sugiura and Chao Xu and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10993364},

doi = {10.1109/JSAC.2025.3568050},

issn = {1558-0008},

year  = {2025},

date = {2025-08-01},

urldate = {2025-10-08},

journal = {IEEE Journal on Selected Areas in Communications},

volume = {43},

number = {8},

pages = {2747–2764},

abstract = {Large optical reconfigurable intelligent surfaces (ORISs) are proposed for employment on building rooftops to facilitate free-space quantum key distribution (QKD) between high-altitude platforms (HAPs) and low-altitude platforms (LAPs). Due to practical constraints, the communication terminals can only be positioned beneath the LAPs, preventing direct upward links to HAPs. By deploying ORISs on rooftops to reflect the beam arriving from HAPs towards LAPs from below, reliable HAP-to-LAP links can be established. To accurately characterize the optical beam propagation, we develop an analytical channel model based on extended Huygens-Fresnel principles for representing both the atmospheric turbulence effects and the hovering fluctuations of LAPs. This model facilitates adaptive ORIS beam-width control through linear, quadratic, and focusing phase shifts, which are capable of effectively mitigating the detrimental effects of beam broadening and pointing errors (PE). Consequently, the information-theoretic bound of the secret key rate and the security performance of a decoy-state QKD protocol are analyzed. Our findings demonstrate that quadratic phase shifts enhance the SKR at high HAP-ORIS zenith angles or mild PE conditions by narrowing the beam to optimal sizes. By contrast, linear phase shifts are advantageous at low HAP-ORIS zenith angles or moderate-to-high PE by diverging the beam to mitigate LAP fluctuations.},

keywords = {Atmospheric modeling, Drones, Fluctuations, Free-space optics (FSO), Global Positioning System, high-altitude platforms (HAPs), Laser beams, low-altitude platforms (LAPs), Optical beams, Optical reflection, Power distribution, quantum key distribution (QKD), reconfigurable intelligent surface (RIS), reconfigurable intelligent surfaces, Satellites},

pubstate = {published},

tppubtype = {article}

}

@article{jafri_robust_2025,

title = {Robust Hybrid Beamforming in Cooperative Cell-Free mmWave MIMO Networks Relying on Imperfect CSI},

author = {Meesam Jafri and Pankaj Kumar and Suraj Srivastava and Aditya K. Jagannatham and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10945645},

doi = {10.1109/TVT.2025.3555484},

issn = {1939-9359},

year  = {2025},

date = {2025-08-01},

urldate = {2025-10-08},

journal = {IEEE Transactions on Vehicular Technology},

volume = {74},

number = {8},

pages = {12590–12602},

abstract = {A low-complexity robust cooperative hybrid beamformer is designed for both the downlink and uplink of cell-free millimeter wave (mmWave) multiple-input-multiple-output (MIMO) networks, while considering realistic imperfect channel state information (CSI). To begin with, a second-order cone program (SOCP)-based robust fully-digital beamformer (FDBF) is designed for minimizing the worst-case interference for the downlink of multiple-input-single-output (MISO) systems. Subsequently, we develop a Bayesian learning (BL) framework for determining both the analog and digital components of the hybrid transmit precoder (TPC) from the FDBF. The above designs are subsequently extended to employing eigenvector perturbation theory for constructing the robust TPC for the cell-free mmWave MIMO downlink, where the users have multiple receive antennas (RAs). Furthermore, the multi-dimensional covariance fitting (MCF) framework is harnessed for designing the robust TPC of the corresponding uplink. Finally, the efficiency of the proposed TPC designs is evaluated by simulation results both in terms of their ability to mitigate the multi-user interference (MUI), and improving the spectral efficiency achieved. Additionally, the proposed designs are shown to be computationally efficient and equivalent to a minimum variance hybrid beamformer.},

keywords = {Antenna arrays, Array signal processing, cell-free networks, Channel estimation, cooperative beamforming, CSI uncertainty, Downlink, Millimeter wave communication, MIMO, mmWave, Radio frequency, robust beamforming, Uncertainty, Uplink, Vectors},

pubstate = {published},

tppubtype = {article}

}

@article{liu_otfs-based_2025,

title = {OTFS-Based CV-QKD Systems for Doubly Selective THz Channels},

author = {Xin Liu and Chao Xu and Soon Xin Ng and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10857395},

doi = {10.1109/TCOMM.2025.3535889},

issn = {1558-0857},

year  = {2025},

date = {2025-08-01},

urldate = {2025-10-08},

journal = {IEEE Transactions on Communications},

volume = {73},

number = {8},

pages = {6274–6289},

abstract = {The feasibility of continuous variable quantum key distribution (CV-QKD) is considered in the Terahertz (THz) band, experiencing time-varying and frequency-selective fading. Advanced multi-carrier modulation is required for improving the secret key rate (SKR). However, the hostile quantum channel requires powerful classical channel coding schemes for maintaining an adequate reconciliation performance. Against this background, for the first time in the open literature, we propose a multi-carrier quantum transmission regime that incorporates both orthogonal frequency division multiplexing (OFDM) and orthogonal time frequency space (OTFS) transmission over doubly selective fading THz channels. Furthermore, we propose a modified multi-dimensional reconciliation algorithm for CV-QKD, facilitating the integration of OFDM/OTFS quantum transmission with low-density parity check (LDPC) coded key reconciliation. Moreover, we harness multiple-input multiple-output (MIMO) beamforming for mitigating the severe THz path loss. Our SKR analysis results demonstrate that the proposed OTFS-based and LDPC-assisted CV-QKD system is capable of outperforming its OFDM counterpart in mobile wireless scenarios. Moreover, we also demonstrate that increasing the MIMO dimension reduces the transmission power required for achieving the secure transmission distance target.},

keywords = {Array signal processing, continuous variable quantum key distribution (CV-QKD), Faces, Fading channels, low-density parity check (LDPC), multiple-input multiple-out (MIMO), OFDM, Orthogonal frequency division multiplexing (OFDM), Orthogonal Time Frequency Space (OTFS), Parity check codes, Random variables, secret key rate (SKR), Symbols, terahertz (THz), Terahertz communications, Time-frequency analysis, Vectors},

pubstate = {published},

tppubtype = {article}

}

@article{eldeeb_sub-centimeter_2025,

title = {Sub-Centimeter Indoor Optical Wireless Positioning Using An Optimized Machine Learning Technique},

author = {Hossien Eldeeb and Othman Younus and Sina Babadi and Isaac NO Osahon and Rizwana Ahmad and Iman Tavakkolnia and Harald Haas},

url = {https://www.repository.cam.ac.uk/handle/1810/387756},

doi = {10.17863/CAM.120417},

year  = {2025},

date = {2025-08-01},

urldate = {2025-10-08},

abstract = {This paper proposes a novel indoor optical wireless positioning (IOWP) framework that aims to enhance localization precision and robustness through an advanced machine learning (ML)-driven fusion technique. Unlike traditional single model approaches, the proposed framework uses received signal strength (RSS) data to intelligently combine multiple lightweight ML algorithms, including K-Nearest Neighbors (KNN), Random Forest (RF), and Gaussian Process Regression (GPR). In the training phase, our system utilizes a performance- optimized weight allocation strategy to identify the optimal weights, harnessing the complementary strengths of individual models while mitigating their limitations to achieve exceptional generalization in complex indoor environments. A comprehensive evaluation is conducted under a realistic ray-traced channel model that incorporates typical light distributions, high-order multipath reflections from walls and objects, and mixed diffuse-reflective surface interactions. Performance is assessed in terms of mean positioning error (MPE), 90th percentile (P90) error, and computational complexity. Results demonstrate that the proposed method achieves an MPE of 0.5 cm and a P90 error below 1 cm, offering a practical and scalable solution for next-generation IOWP applications in smart environments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}