arXiv subjects

A. Asadi

Publications and source records attributed to A. Asadi.

5 recordsLinked to original sources

arXiv2023

A Leakage-based Method for Mitigation of Faulty Reconfigurable Intelligent Surfaces

Reconfigurable Intelligent Surfaces (RISs) are expected to be massively deployed in future beyond-5th generation wireless networks, thanks to their ability to programmatically alter the propagation environment, inherent low-cost and low-maintenance nature. Indeed, they are envisioned to be implemented on the facades of buildings or on moving objects. However, such an innovative characteristic may potentially turn into an involuntary negative behavior that needs to be addressed: an undesired signal scattering. In particular, RIS elements may be prone to experience failures due to lack of proper maintenance or external environmental factors. While the resulting Signal-to-Noise-Ratio (SNR) at the intended User Equipment (UE) may not be significantly degraded, we demonstrate the potential risks in terms of unwanted spreading of the transmit signal to non-intended UE. In this regard, we consider the problem of mitigating such undesired effect by proposing two simple yet effective algorithms, which are based on maximizing the Signal-to-Leakage- and-Noise-Ratio (SLNR) over a predefined two-dimensional (2D) area and are applicable in the case of perfect channel-state-information (CSI) and partial CSI, respectively. Numerical and full-wave simulations demonstrate the added gains compared to leakage-unaware and reference schemes.

cs.IT↗

arXiv2022

RadiOrchestra: Proactive Management of Millimeter-wave Self-backhauled Small Cells via Joint Optimization of Beamforming, User Association, Rate Selection, and Admission Control

Millimeter-wave self-backhauled small cells are a key component of next-generation wireless networks. Their dense deployment will increase data rates, reduce latency, and enable efficient data transport between the access and backhaul networks, providing greater flexibility not previously possible with optical fiber. Despite their high potential, operating dense self-backhauled networks optimally is an open challenge, particularly for radio resource management (RRM). This paper presents, RadiOrchestra, a holistic RRM framework that models and optimizes beamforming, rate selection as well as user association and admission control for self-backhauled networks. The framework is designed to account for practical challenges such as hardware limitations of base stations (e.g., computational capacity, discrete rates), the need for adaptability of backhaul links, and the presence of interference. Our framework is formulated as a nonconvex mixed-integer nonlinear program, which is challenging to solve. To approach this problem, we propose three algorithms that provide a trade-off between complexity and optimality. Furthermore, we derive upper and lower bounds to characterize the performance limits of the system. We evaluate the developed strategies in various scenarios, showing the feasibility of deploying practical self-backhauling in future networks.

eess.SP↗

arXiv2021

Development and validation of an optimal GATE model for proton pencil-beam scanning delivery

Objective: To develop and validate an independent Monet Carlo dose calculation engine to support for software verification of treatment planning systems and quality assurance workflow. Method: GATE Monte Carlo toolkit was employed to simulate a fixed horizontal active scan-based proton beam delivery. Within the nozzle, two primary and secondary dose monitors have been designed allowing to compare the accuracy of dose estimation from MC simulation with respect to physical quality assurance measurements. The developed beam model was validated against a series of commissioning measurements using pinpoint chambers and 2D array ionization chambers in terms of lateral profiles and depth dose distributions. Furthermore, beam delivery module and treatment planning has been validated against the literature deploying various clinical test cases of AAPM TG-119 and a prostate patient. Result: MC simulation showed an excellent agreement with measurements in the lateral depth-dose parameters and SOBP characteristics within maximum relative error of 0.95% in range, 3.4% in entrance to peak ratio, 2.3% in mean point to point, and 0.852% in peak location. Mean relative absolute difference between MC simulation and the measurement in terms of absorbed dose in SOBP region was $0.93\% \pm 0.88\%$. Clinical phantom study showed a good agreement compared to a commercial treatment planning system (relative error for TG-119 PTV-D${}{95}$ $\mathrm{\sim}$ 1.8%; and for prostate PTV-D$_{95}$ $\mathrm{\sim}$ -0.6%). Conclusion: The results confirm the capability of GATE simulation as a reliable surrogate for verifying TPS dose maps prior to patient treatment.

physics.med-ph↗

arXiv2021

Dosimetric Comparison of Passive Scattering and Active Scanning Proton Therapy Techniques Using GATE Simulation

In this study, two proton beam delivery designs, passive scattering proton therapy (PSPT) and pencil beam scanning (PBS), were quantitatively compared in terms of dosimetric indices. The GATE Monte Carlo code was used to simulate the proton beam system; and the developed simulation engines were benchmarked with respect to the experimental measurements. A water phantom was used to simulate system energy parameters using a set of depth-dose data in the energy range of 120-235 MeV. To compare the performance of PSPT against PBS, multiple dosimetric parameters including FWHM, peak position, range, peak-to-entrance dose ratio, and dose volume histogram have been analyzed under the same conditions. Furthermore, the clinical test cases introduced by AAPM TG-119 were simulated in both beam delivery modes to compare the relevant clinical values obtained from DVH analysis. The parametric comparison in the water phantom between the two techniques revealed that the value of peak-to-entrance dose ratio in PSPT is considerably higher than that from PBS by a factor of 8%. In addition, the FWHM of the lateral beam profile in PSPT was increased by a factor of 7% compared to the corresponding value obtained from PBS model. TG-119 phantom simulations showed that the difference of PTV mean dose between PBS and PSPT techniques are up to 2.9% while the difference of max dose to organ at risks (OARs) exceeds 33%. The results demonstrated that the PBS proton therapy systems was superior in adapting to the target volume, better dose painting, and lower out-of-field dose compared to PSPT design.

physics.med-ph↗

arXiv2013

Thermodynamics of string black hole with hyperscaling violation

In this paper, we start with black brane and construct specific space-time which violates hyperscaling. In order to obtain the string solution we apply Null-Melvin-Twist and $KK$-reduction. By using the difference action method we study thermodynamics of system to obtain Hawking-Page phase transition. In order to have hyperscaling violation we need to consider $θ=\frac{d}{2}.$ In that case the free energy $F$ is always negative and our solution is thermal radiation without a black hole. Therefore we find that there is not any Hawking-Page transition. Also, we discuss the stability of system and all thermodynamical quantities.

hep-th↗