@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}

}

@article{liu_near-field_2025,

title = {Near-field Communications: What Will Be Different?},

author = {Yuanwei Liu and Jiaqi Xu and Zhaolin Wang and Xidong Mu and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/10944643},

doi = {10.1109/MWC.001.2300588},

issn = {1558-0687},

year  = {2025},

date = {2025-04-01},

urldate = {2025-10-08},

journal = {IEEE Wireless Communications},

volume = {32},

number = {2},

pages = {262–270},

abstract = {The design dilemma of “What will be different between near-field communications (NFC) and far-field communications (FFC)?” is addressed from four perspectives. First, from the channel modelling perspective, the differences between near-field and far-field channel models are discussed. A novel Green's function-based channel model is proposed for continuous-aperture antennas, which is contrasted to conventional channel models tailored for spatially-discrete antennas. Second, from the performance analysis per-spective, analytical results for characterizing the degrees of freedom and the power scaling laws in the near-field region are provided for both spatially-discrete and continuous-aperture antennas. Third, from the beamforming perspective, far-field beamforming is analogous to a “flashlight” that enables beamsteering, while near-field beamforming can be likened to a “spotlight” that facilitates beamfocusing. As a further advance, a couple of new beamforming structures are proposed for exploiting the new characteristics of NFC. Fourth, from the application perspective, new designs are discussed in the context of promising next-generation technologies in NFC, where our preliminary numerical results demonstrate that distance-aware target sensing and enhanced physical layer security can be realized in NFC. Finally, several future research directions of NFC are discussed.},

keywords = {Antennas, Array signal processing, Channel models, Green's function methods, Next generation networking, Performance analysis, Physical layer security, Sensors},

pubstate = {published},

tppubtype = {article}

}

@article{sui_performance_2025,

title = {Performance analysis and optimization of STAR-RIS-aided cell-free massive MIMO systems relying on imperfect hardware},

author = {Zeping Sui and Hien Quoc Ngo and Michail Matthaiou and Lajos Hanzo},

url = {https://www.scopus.com/pages/publications/105002491232},

doi = {10.1109/TWC.2025.3526563},

issn = {1558-2248},

year  = {2025},

date = {2025-04-01},

urldate = {2025-10-08},

journal = {IEEE Transactions on Wireless Communications},

volume = {24},

number = {4},

pages = {2925–2939},

abstract = {Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided cell-free massive multiple-input multiple-output (CF-mMIMO) systems are investigated under spatially correlated fading channels using realistic imperfect hardware. Specifically, the transceiver distortions, time-varying phase noise, and RIS phase shift errors are considered. Upon considering imperfect hardware and pilot contamination, we derive a linear minimum mean-square error (MMSE) criterion-based cascaded channel estimator. Moreover, a closed-form expression of the downlink ergodic spectral efficiency (SE) is derived based on maximum ratio (MR) based transmit precoding and channel statistics, where both a finite number of access points (APs) and STAR-RIS elements as well as imperfect hardware are considered. Furthermore, by exploiting the ergodic signal-to-interference-plus-noise ratios (SINRs) among user equipment (UE), a max-min fairness problem is formulated for the joint optimization of the passive transmitting and reflecting beamforming (BF) at the STAR-RIS as well as of the power control coefficients. An alternating optimization (AO) algorithm is proposed for solving the resultant problems, where iterative adaptive particle swarm optimization (APSO) and bisection methods are proposed for circumventing the non-convexity of the RIS passive BF and the quasi-concave power control sub-problems, respectively. Our simulation results illustrate that the STAR-RIS-aided CF-mMIMO system attains higher SE than its RIS-aided counterpart. The performance of different hardware parameters is also evaluated. Additionally, it is demonstrated that the SE of the worst UE can be significantly improved by exploiting the proposed AO-based algorithm compared to conventional solutions associated with random passive BF and equal-power scenarios.},

keywords = {imperfect hardware, massive MIMO systems, Performance analysis, STAR-RIS},

pubstate = {published},

tppubtype = {article}

}

@article{zhang_space-air-ground_2025,

title = {Space-Air-Ground Integrated Networks: Their Channel Model and Performance Analysis},

author = {Chao Zhang and Qingchao Li and Chao Xu and Lie-Liang Yang and Lajos Hanzo},

url = {https://ieeexplore.ieee.org/document/11018358},

doi = {10.1109/OJVT.2025.3575360},

issn = {2644-1330},

year  = {2025},

date = {2025-01-01},

urldate = {2025-10-08},

journal = {IEEE Open Journal of Vehicular Technology},

volume = {6},

pages = {1501–1523},

abstract = {Given their extensive geographic coverage, low Earth orbit (LEO) satellites are envisioned to find their way into next-generation (6G) wireless communications. This paper explores space-air-ground integrated networks (SAGINs) leveraging LEOs to support terrestrial and non-terrestrial users. We first propose a practical satellite-ground channel model that incorporates five key aspects: 1) the small-scale fading characterized by the Shadowed-Rician distribution in terms of the Rician factor K, 2) the path loss effect of bending rays due to atmospheric refraction, 3) the molecular absorption modelled by the Beer-Lambert law, 4) the Doppler effects including the Earth's rotation, and 5) the impact of weather conditions according to the International Telecommunication Union Recommendations (ITU-R). Harnessing the proposed model, we analyze the long-term performance of the SAGIN considered. Explicitly, the closed-form expressions of both the outage probability and of the ergodic rates are derived. Additionally, the upper bounds of bit-error rates and of the Goodput are investigated. The numerical results yield the following insights: 1) The shadowing effect and the ratio between the line-of-sight and scattering components can be conveniently modelled by the factors of K and m in the proposed Shadowed-Rician small-scale fading model. 2) The atmospheric refraction has a modest effect on the path loss. 3) When calculating the transmission distance of waves, Earth's curvature and its geometric relationship with the satellites must be considered, particularly at small elevation angles. 3) High-frequency carriers suffer from substantial path loss, and 4) the Goodput metric is eminently suitable for characterizing the performance of different coding as well as modulation methods and of the estimation error of the Doppler effects.},

keywords = {Absorption, Atmospheric modeling, Attenuation, Bending, Channel model, Channel models, Doppler effect, Earth, Fading channels, goodput, Meteorology, Performance analysis, Rician channels, Space-air-ground integrated networks},

pubstate = {published},

tppubtype = {article}

}