A Multi-Dimensional Matrix Pencil-Based Channel Prediction Method for Massive MIMO with Mobility

This paper addresses the mobility problem in massive multiple-input multiple-output systems, which leads to significant performance losses in the practical deployment of the fifth generation mobile communication networks. We propose a novel channel prediction method based on multi-dimensional matrix pencil (MDMP), which estimates the path parameters by exploiting the angular-frequency-domain and angular-time-domain structures of the wideband channel. The MDMP method also entails a novel path pairing scheme to pair the delay and Doppler, based on the super-resolution property of the angle estimation. Our method is able to deal with the realistic constraint of time-varying path delays introduced by user movements, which has not been considered so far in the literature. We prove theoretically that in the scenario with time-varying path delays, the prediction error converges to zero with the increasing number of the base station (BS) antennas, providing that only two arbitrary channel samples are known. We also derive a lower-bound of the number of the BS antennas to achieve a satisfactory performance. Simulation results under the industrial channel model of 3GPP demonstrate that our proposed MDMP method approaches the performance of the stationary scenario even when the users' velocity reaches 120 km/h and the latency of the channel state information is as large as 16 ms

Synthesis of N/Fe Comodified TiO 2

To improve the efficiency of TiO2 as a photocatalyst for contaminant degradation, a novel nanocomposite catalyst of (N, Fe) modified TiO2 nanoparticles loaded on bentonite (B-N/Fe-TiO2) was successfully prepared for the first time by sol-gel method. The synthesized B-N/Fe-TiO2 catalyst composites were characterized by multiple techniques, including scanning electron microscope (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), X-ray fluorescence (XRF), nitrogen adsorption/desorption, UV-Vis diffuse reflectance spectra (DRS), and electron paramagnetic resonance (EPR). The results showed that bentonite significantly enhanced the dispersion of TiO2 nanoparticles and increased the specific surface area of the catalysts. Compared with nondoped TiO2, single element doped TiO2, or unloaded TiO2 nanoparticles, B-N/Fe-TiO2 had the highest absorption in UV-visible region. The photocatalytic activity of B-N/Fe-TiO2 was also the highest, based on the degradation of methyl blue (MB) at room temperature under UV and visible light irradiation. In particular, the synthesized B-N/Fe-TiO2 showed much greater photocatalytic efficiency than N/Fe-TiO2 under visible light, the newly synthesized B-N/Fe-TiO2 is going to significantly increase the photocatalytic efficiency of the catalyst using sun light

A Partial Reciprocity-based Channel Prediction Framework for FDD Massive MIMO with High Mobility

Massive multiple-input multiple-output (MIMO) is believed to deliver unrepresented spectral efficiency gains for 5G and beyond. However, a practical challenge arises during its commercial deployment, which is known as the ``curse of mobility''. The performance of massive MIMO drops alarmingly when the velocity level of user increases. In this paper, we tackle the problem in frequency division duplex (FDD) massive MIMO with a novel Channel State Information (CSI) acquisition framework. A joint angle-delay-Doppler (JADD) wideband precoder is proposed for channel training. Our idea consists in the exploitation of the partial channel reciprocity of FDD and the angle-delay-Doppler channel structure. More precisely, the base station (BS) estimates the angle-delay-Doppler information of the UL channel based on UL pilots using Matrix Pencil (MP) method. It then computes the wideband JADD precoders according to the extracted parameters. Afterwards, the user estimates and feeds back some scalar coefficients for the BS to reconstruct the predicted DL channel. Asymptotic analysis shows that the CSI prediction error converges to zero when the number of BS antennas and the bandwidth increases. Numerical results with industrial channel model demonstrate that our framework can well adapt to high speed (350 km/h), large CSI delay (10 ms) and channel sample noise.Comment: 9 figures, 15 pages, to appear in IEEE Transactions on Wireless Communication

Effects of ferrihydrite nanoparticle incorporation in cementitious materials on radioactive waste immobilization.

To enhance the long-term immobilization of radioactive wastes, ferrihydrite nanoparticles were incorporated into cementitious materials. The effects of ferrihydrite nanoparticles on the physicochemical and mechanical properties of cementitious materials and the immobilization of uranium (U), strontium (Sr) and cesium (Cs) were investigated. Adding ferrihydrite nanoparticles at 0.65%, 1.30%, 3.90% and 6.50% of cement weight slightly improved compressive strength by 5-11%, but dramatically reduced U leaching by 50-57%. The enhanced U immobilization was attributed to the strong adsorption of U by ferrihydrite nanoparticles, and the structural incorporation of U into hematite formed during ferrihydrite recrystallization. Although ferrihydrite nanoparticles had weaker effect than hematite nanoparticles on improving cement hydration and reducing permeability, they exhibit stronger U immobilization capacity. In contrast, incorporating ferrihydrite nanoparticles into cementitious materials had no significant effects on Cs and Sr leaching and no detectable adsorption of Sr and Cs. This study elucidated the fundamental differences in the interactions between ferrihydrite nanoparticles and U, Sr or Cs within cementitious systems that led to the distinctive immobilization mechanisms for these radionuclides. It generated new mechanistic understandings of U, Sr and Cs leaching from cementitious barriers modified by Fe-based nanoparticles, and proposed a new approach for enhancing long-term immobilization of U

Homogeneous and Heterogeneous (Fe_<i>x</i>, Cr_1–<i>x</i>)(OH)₃ Precipitation: Implications for Cr Sequestration

The formation of (Fe, Cr)­(OH)₃ nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small-angle X-ray scattering, precipitation rates of (Fe, Cr)­(OH)₃ nanoparticles in solution and on quartz were quantified from 0.1 mM Fe­(III) solutions containing 0–0.25 mM Cr­(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr­(III)/Fe­(III) controlled the chemical composition (<i>x</i>) of (Fe_<i>x</i>, Cr_1–<i>x</i>)­(OH)₃ precipitates, solutions’ supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, the aqueous Cr­(III)/Fe­(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fe_<i>x</i>, Cr_1–<i>x</i>)­(OH)₃ through different mechanisms. The sequestration mechanisms of Cr­(III) in precipitates were also investigated. In solutions with high aqueous Cr­(III)/Fe­(III) ratios, surface enrichment of Cr­(III) on the precipitates occurred, resulting in slower particle growth in solutions. From solutions with 0–0.1 mM Cr­(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr­(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fe_<i>x</i>, Cr_1–<i>x</i>)­(OH)₃ nanoparticles, which can help determine the fate of Cr in aquatic environments

Interaction of Organic Cation with Water Molecule in Perovskite MAPbI₃: From Dynamic Orientational Disorder to Hydrogen Bonding

Microscopic understanding of interaction between H₂O and MAPbI₃ (CH₃NH₃PbI₃) is essential to further improve efficiency and stability of perovskite solar cells. A complete picture of perovskite from initial physical uptake of water molecules to final chemical transition to its monohydrate MAPbI₃·H₂O is obtained with in situ infrared spectroscopy, mass monitoring, and X-ray diffraction. Despite strong affinity of MA to water, MAPbI₃ absorbs almost no water from ambient air. Water molecules penetrate the perovskite lattice and share the space with MA up to one H₂O per MA at high-humidity levels. However, the interaction between MA and H₂O through hydrogen bonding is not established until the phase transition to monohydrate where H₂O and MA are locked to each other. This lack of interaction in water-infiltrated perovskite is a result of dynamic orientational disorder imposed by tetragonal lattice symmetry. The apparent inertness of H₂O along with high stability of perovskite in an ambient environment provides a solid foundation for its long-term application in solar cells and optoelectronic devices