Semi-blind channel estimation and PAR reduction for MIMO-OFDM system with multiple antennas

A combining of MIMO signal processing with OFDM is regarded as a promising solution of enhancing the performance of next generation wireless system. Therefore, in this paper, an OFDM-based wireless system employing layered space-time architecture is considered for a high-rate transmission. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation based on the time-domain windowing and its imperfectness in MIMO-OFDM system. By properly designing each preamble for multiple antennas to be orthogonal in the time domain, the channel estimation can be executed based on semi-blind processing in the case of more than two transmitting antennas. And also we evaluate the PAR performance in the MIMO-OFDM system using the SLM and PTS approaches. The investigated SLM and PTS schemes for MIMO-OFDM signals select the transmitted sequence with lowest average PAR over all transmitting antennas and retrieve the side information very accurately at the expense of a slight degradation of the PAR performance. The low probability of false side information can improve the overall detection performance of the MIMO-OFDM system with erroneous side information compared to the ordinary SLM and PTS approaches, respectively. Also, we provide closed form of the average BER performance in MIMO-OFDM system using analytic approach.     

Least squares decoding in binomial frequency division multiplexing

This paper proposes a method that can reduce the complexity of a system matrix by analyzing the characteristics of a pseudoinverse matrix to receive a binomial frequency division multiplexing (BFDM) signal and decode it using the least squares (LS) method. The system matrix of BFDM can be expressed as a band matrix, and as this matrix contains many zeros, its amount of calculation when generating a transmission signal is quite small. The LS solution can be obtained by multiplying the received signal by the pseudoinverse matrix of the system matrix. The singular value decomposition of the system matrix indicates that the pseudoinverse matrix is a band matrix. The signal-to-interference ratio is obtained from their eigenvalues. Meanwhile, entries that do not contribute to signal generation are erased to enhance calculation efficiency. We decode the received signal using the pseudoinverse matrix and the removed pseudoinverse matrix to obtain the bit error rate performance and to analyze the difference.     

Unraveling the Significance of Li+/e−/O2 Phase Boundaries with a 3D-Patterned Cu Electrode for Li–O2 Batteries

The reaction kinetics at a triple-phase boundary (TPB) involving Li⁺, e⁻, and O₂ dominate their electrochemical performances in Li–O₂ batteries. Early studies on catalytic activities at Li⁺/e⁻/O₂ interfaces have enabled great progress in energy efficiency; however, localized TPBs within the cathode hamper innovations in battery performance toward commercialization. Here, the effects of homogenized TPBs on the reaction kinetics in air cathodes with structurally designed pore networks in terms of pore size, interconnectivity, and orderliness are explored. The diffusion fluxes of reactants are visualized by modeling, and the simulated map reveals evenly distributed reaction areas within the periodic open structure. The 3D air cathode provides highly active, homogeneous TPBs over a real electrode scale, thus simultaneously achieving large discharge capacity, unprecedented energy efficiency, and long cyclability via mechanical/electrochemical stress relaxation. Homogeneous TPBs by cathode structural engineering provide a new strategy for improving the reaction kinetics beyond controlling the intrinsic properties of the materials.     

Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics

Stretchable conductive fibers have received significant attention due to their possibility of being utilized in wearable and foldable electronics. Here, highly stretchable conductive fiber composed of silver nanowires (AgNWs) and silver nanoparticles (AgNPs) embedded in a styrene–butadiene–styrene (SBS) elastomeric matrix is fabricated. An AgNW‐embedded SBS fiber is fabricated by a simple wet spinning method. Then, the AgNPs are formed on both the surface and inner region of the AgNW‐embedded fiber via repeated cycles of silver precursor absorption and reduction processes. The AgNW‐embedded conductive fiber exhibits superior initial electrical conductivity (σ₀ = 2450 S cm^?1) and elongation at break (900% strain) due to the high weight percentage of the conductive fillers and the use of a highly stretchable SBS elastomer matrix. During the stretching, the embedded AgNWs act as conducting bridges between AgNPs, resulting in the preservation of electrical conductivity under high strain (the rate of conductivity degradation, σ/σ₀ = 4.4% at 100% strain). The AgNW‐embedded conductive fibers show the strain‐sensing behavior with a broad range of applied tensile strain. The AgNW reinforced highly stretchable conductive fibers can be embedded into a smart glove for detecting sign language by integrating five composite fibers in the glove, which can successfully perceive human motions.     

Room‐Temperature Metallic Fusion‐Induced Layer‐by‐Layer Assembly for Highly Flexible Electrode Applications

To fabricate flexible electrodes, conventional silver (Ag) nanomaterials have been deposited onto flexible substrates, but the formed electrodes display limited electrical conductivity due to residual bulky organic ligands, and thus postsintering processes are required to improve the electrical conductivity. Herein, an entirely different approach is introduced to produce highly flexible electrodes with bulk metal–like electrical conductivity: the room‐temperature metallic fusion of multilayered silver nanoparticles (NPs). Synthesized tetraoctylammonium thiosulfate (TOAS)‐stabilized Ag NPs are deposited onto flexible substrates by layer‐by‐layer assembly involving a perfect ligand‐exchange reaction between bulky TOAS ligands and small tris(2‐aminoethyl)amine linkers. The introduced small linkers substantially reduce the separation distance between neighboring Ag NPs. This shortened interparticle distance, combined with the low cohesive energy of Ag NPs, strongly induces metallic fusion between the close‐packed Ag NPs at room temperature without additional treatments, resulting in a high electrical conductivity of ≈1.60 × 10⁵ S cm^?1 (bulk Ag: ≈6.30 × 10⁵ S cm^?1). Furthermore, depositing the TOAS–Ag NPs onto cellulose papers through this approach can convert the insulating substrates into highly flexible and conductive papers that can be used as 3D current collectors for energy‐storage devices.     

Chiroptical‐Conjugated Polymer/Chiral Small Molecule Hybrid Thin Films for Circularly Polarized Light‐Detecting Heterojunction Devices

Herein, a simple and facile strategy is described to obtain chiroptically active semiconductor thin films by blending of poly(3‐alkylthiophene)s, which are conventional achiral polymer semiconductors, and 1,1′‐binaphthyl (BN), a versatile chiral molecule. As expected, the intermolecular interaction between the two materials is important to extend the chirality of the binaphthyl molecules to the hybrid films. The controlled phase separation and crystallization of poly[3‐(6‐carboxyhexyl)thiophene‐2,5‐diyl] (P3CT) and binaphthyl hybrid films result in unique heterojunction bilayer thin‐film structures that consisted of BN microcrystals at the top and a P3CT/BN mixed layer at the bottom. Such heterojunction bilayer films exhibit significantly amplified chiroptical response with weak broadened tails, which is due to the enhanced crystallization of the chiral BN molecules and formation of heteroaggregates in the hybrid films. Based on the characterization of crystalline structure and photoluminescence analysis, it is found that new electronic energy states are formed in the conduction band region of P3CTs in the P3CT/BN heteroaggregates, which contribute to chirality transfer from BN to the hybrid films. As a proof of concept, a photodiode capable of distinguishably sensing the left‐ and right‐handed circularly polarized light is successfully fabricated by using the hybrid films with the heterojunction bilayer structure.     

A new hybrid active power filter (APF) topology

In this paper, a new hybrid active power filter topology is presented. A higher-voltage, low-switching frequency insulated gate bipolar transistor (IGBT) inverter and a lower-voltage high-switching frequency metal oxide semiconductor field effect transistor (MOSFET) inverter are used in combination to achieve harmonic current compensation. The function of the IGBT inverter is to support utility fundamental voltage and to compensate for the fundamental reactive power. The MOSFET inverter fulfills the function of harmonic current compensation. To further reduce cost and to simplify control, the IGBT and MOSFET inverters share the same DC-link via a split capacitor bank. With this approach harmonics can be cancelled over a wide frequency range. Compared to the conventional APF topology, the proposed approach employs lower dc-link voltage and generates less noise. Simulation and experimental results show that the proposed active power filter topology is capable of compensating for the load harmonics     

A new measurement technique for obtaining the complex relativepermittivity of terrain surfaces

A new method for measuring the effective complex relative permittivity of a reflecting surface is presented. The approach is based on the two-ray model. We derive an equation of a circle representing the complex reflection coefficient which relates the incidence angle, frequency, and received power from the path gain using the two-ray model. The intersection point of three such circles at different heights, while maintaining the same incidence angle, yields the correct complex reflection coefficient value. By measuring the received power for both the vertical and horizontal polarizations, the relative permittivity of the surface can be determined. The technique is validated using computer simulation, as well as field measurements of typical terrain surfaces, such as asphalt, grass, and bare soil. A major advantage of this method is that it obviates the need to use antennas with a narrow beam pattern     

Long-wavelength GaInNAs(Sb) lasers on GaAs

The boom in fiber-optic communications has caused a high demand for GaAs-based lasers in the 1.3-1.6-μm range. This has led to the introduction of small amounts of nitrogen into InGaAs to reduce the bandgap sufficiently, resulting in a new material that is lattice matched to GaAs. More recently, the addition of Sb has allowed further reduction of the bandgap, leading to the first demonstration of 1.5-μm GaAs-based lasers by the authors. Additional work has focused on the use of GaAs, GaNAs, and now GaNAsSb barriers as cladding for GaInNAsSb quantum wells. We present the results of photoluminescence, as well as in-plane lasers studies, made with these combinations of materials. With GaNAs or GaNAsSb barriers, the blue shift due to post-growth annealing is suppressed, and longer wavelength laser emission is achieved. Long wavelength luminescence out to 1.6 μm from GaInNAsSb quantum wells, with GaNAsSb barriers, was observed. In-plane lasers from these samples yielded lasers operating out to 1.49 μm, a minimum threshold current density of 500 A/cm² per quantum well, a maximum differential quantum efficiency of 75%, and pulsed power up to 350 mW at room temperature     

A Thermoelectric Generator Using Engine Coolant for Light-Duty Internal Combustion Engine-Powered Vehicles

We proposed and fabricated a thermoelectric generator (TEG) using the engine water coolant of passenger vehicles. The experimental results revealed that the maximum output power from the proposed thermoelectric generator was ~75 W, the calculated thermoelectric module efficiency of the TEG was ~2.1%, and the overall efficiency of electric power generation from the waste heat of the engine coolant was ~0.3% in the driving mode at 80 km/h. The conventional radiator can thus be replaced by the proposed TEG without additional devices or redesign of the engine water cooling system of the existing radiator.