Flexible-Position MIMO for Wireless Communications: Fundamentals, Challenges, and Future Directions

The flexible-position multiple-input multiple-output (FLP-MIMO), such as fluid antennas and movable antennas, is a promising technology for future wireless communications. This is due to the fact that the positions of antennas at the transceiver and reflector can be dynamically optimized to achieve better channel conditions and, as such, can provide high spectral efficiency (SE) and energy efficiency (EE) gains with fewer antennas. In this article, we introduce the fundamentals of FLP-MIMO systems, including hardware design, structure design, and potential applications. We shall demonstrate that FLP-MIMO, using fewer flexible antennas, can match the channel hardening achieved by a large number of fixed antennas. We will then analyze the SE-EE relationship for FLP-MIMO and fixed-position MIMO. Furthermore, we will design the optimal trajectory of flexible antennas to maximize system sum SE or total EE at a fixed travel distance of each antenna. Finally, several important research directions regarding FLP-MIMO communications are presented to facilitate further investigation.Comment: 10 pages, 5 figures, 1 tables, accepted by IEEE Wireless Communications Magazin

Evolutionary Game of Digital-Driven Photovoltaic–Storage–Use Value Chain Collaboration: A Value Intelligence Creation Perspective

In the context of “carbon neutral”, distributed energy, including photovoltaic power generation and energy storage systems, is developing rapidly. Meanwhile, the new generation of information technology, such as “Cloud computing, Big data, the Internet of things, Mobile Internet, AI, Blockchain”, is driving the digital transformation of the energy industry. Under digital drive, how the agents in the photovoltaic–storage–use value chain collaborate and create value intelligently is a question worthy of deep consideration. Firstly, the value creation mechanism and collaborative process of the digital-driven photovoltaic–storage–use value chain are analyzed from a value intelligence creation perspective. Secondly, the tripartite evolutionary game model of photovoltaic power generator, energy storage provider and user is established. Finally, the influencing factors of digital- driven photovoltaic–storage–use value chain collaboration are explored through a numerical simulation, and management suggestions are put forward. The study finds the following: (1) The behavior choice of each agent in the value chain will affect the decision of other agents. In particular, the photovoltaic power generator has a great influence on the cooperative willingness of other agents. To promote value chain collaboration, the guiding role of the photovoltaic power generator should be fully realized. (2) Agents on the value chain can use a variety of digital technologies to improve enabling benefits, which is conducive to promoting value chain collaboration. (3) The driving costs and potential risks are obstacles for value chain collaboration. Cost reduction and risk prevention are effective ways to improve the willingness of collaboration. (4) Reasonable incentive compensation mechanisms and information asymmetry punishment measures are the keys to enhancing collective willingness. This research provides theoretical support for photovoltaic–storage–use value chain collaboration from a value intelligence creation perspective

Attention-Based LSTM Algorithm for Audio Replay Detection in Noisy Environments

Even though audio replay detection has improved in recent years, its performance is known to severely deteriorate with the existence of strong background noises. Given the fact that different frames of an utterance have different impacts on the performance of spoofing detection, this paper introduces attention-based long short-term memory (LSTM) to extract representative frames for spoofing detection in noisy environments. With this attention mechanism, the specific and representative frame-level features will be automatically selected by adjusting their weights in the framework of attention-based LSTM. The experiments, conducted using the ASVspoof 2017 dataset version 2.0, show that the equal error rate (EER) of the proposed approach was about 13% lower than the constant Q cepstral coefficients-Gaussian mixture model (CQCC-GMM) baseline in noisy environments with four different signal-to-noise ratios (SNR). Meanwhile, the proposed algorithm also improved the performance of traditional LSTM on audio replay detection systems in noisy environments. Experiments using bagging with different frame lengths were also conducted to further improve the proposed approach

Experimental Study on Low Alkalinity Ecotype Artificial Reef Materials

A new type of artificial reef with high strength was prepared by using slag-CaO-FGD gypsum as cementitious material and sea sand as aggregate. The effects of FGD gypsum on the compressive strength and hydration products of the new artificial reef materials were investigated by means of mechanical properties test, X-ray diffraction, thermogravimetric analysis and SEM. The results show that the addition of appropriate amount of desulfurized gypsum can significantly improve the cementitious strength of CaO activated slag cementitious materials, and promote the preferential formation of ettringite (AFt) in the hydration process. Under the optimal gypsum content, the 3 d strength can be increased by 51.4%, the 7 d strength by 35.7%, and the 28 d strength by 25.2%. The dissolution test results of heavy metal ions show that the seawater quality of the immersed samples conforms to the national first class sea water quality standard; pH detection of surface leaching solution showed that a small amount of OH- dissolved in the surface of the artificial reef material test block at the initial stage of seawater immersion, so that the pH value of immersion solution increased from 8.0 of fresh seawater to 8.5, but returned to the normal value after 60 days; in addition, the real sea area hanging board experiment showed that the reef had good marine compatibility and a large number of aquatic organisms attached. Low-alkalinity ecological artificial fish reefs can meet the basic performance requirements of fish reefs, have broad application prospects, and provide a new way for the comprehensive utilization of slag and sea sand

Optimization of secondary air operation parameters of waste incineration boiler based on response surface methodology

To reduce the NOx emission concentration of waste incineration boilers and improve the thermal efficiency of incinerators, the combustion process of a 600 t/d incineration boiler was numerically investigated. First, the influences of the secondary air injection angle, velocity and temperature on the NOx concentration at the waste incineration boiler outlet and the thermal efficiency of the incinerator were analyzed through a single factor simulation test. Then, coupling optimization of key operating parameters, including the secondary air injection angle, velocity and temperature, was conducted via the response surface design method to obtain the specific functional relationships between outlet NOx concentration, incinerator thermal efficiency, front wall secondary air injection angle, rear wall secondary air velocity and secondary air temperature, as well as the optimal operating parameters for the boiler. The results showed that when the secondary air injection angle of the front wall ranges from 68°∼80° and the secondary air injection angle of the back wall is 67°, the minimum NOx concentration is 142.23 mg/m3, and the maximum thermal efficiency of the incinerator reaches 85.51 %. When the secondary air velocity at the front wall is 42 m/s and the secondary air velocity at the back wall ranges from 42 ∼ 66 m/s, the NOx concentration at the outlet is the lowest at 140.05 mg/m3, and the thermal efficiency of the incinerator is the highest at 85.63 %. When the secondary air temperature ranges from 297.16 ∼ 309.16 K, the NOx concentration at the outlet is the lowest at 155.45 mg/m3, and the thermal efficiency of the incinerator is the highest at 84.64 %. The secondary air injection angle, velocity and temperature impose significant effects on the NOx concentration at the outlet and thermal efficiency of the incinerator. The optimal parameters, as determined in the multifactor simulation test, include a 77° secondary air injection angle of the front wall, 69 m/s secondary air velocity at the back wall, and 297.15 K secondary air temperature. Under these conditions, the NOx concentration at the outlet is 134.98 mg/m3, and the thermal efficiency of the incinerator reaches 86.11 %. This study has important guiding significance for reducing pollution and improving the efficiency of waste incineration boilers

Spectroscopic properties and diode end-pumped 2.79 μm laser performance of Er,Pr:GYSGG crystal

We demonstrate a 968 nm diode end-pumped Er,Pr:GYSGG (Gd₁.₁₇Y₁.₈₃Sc₂Ga₃O₁₂) laser at 2.79 μm operated in the pulse and continuous-wave (CW) modes. The lifetimes for the upper laser level ⁴I₁₁/ ₂ and lower level ⁴I₁₃/₂ are 0.52 and 0.60 ms, respectively. The laser produces 284 mW of power in the CW mode, corresponding to the optical-to-optical efficiency of 14.8% and slope efficiency of 17.4%. The maximum laser energy achieved is 2.4 mJ at a repetition rate of 50 Hz and pulse duration of 0.5 ms, corresponding to a peak power of 4.8 W and slope efficiency of 18.3%. These results suggest that doping deactivator Pr3+ ions can effectively decrease the lower-level lifetime and improve the laser efficiency

Performances of a diode end-pumped GYSGG/Er,Pr:GYSGG composite laser crystal operated at 2.79 μm

We demonstrate a comparative investigation on Er,Pr:GYSGG and GYSGG/Er,Pr:GYSGG composite crystals at 2.79 μm. Simulating results show the highest temperatures are 369 K and 318 K, respectively. A maximum output power of 825 mW with slope efficiency of 19.2% and maximum laser energy of 3.65 mJ with slope efficiency of 22.7% are obtained in the GYSGG/Er,Pr:GYSGG composite crystal, which have an obvious improvement than those of Er,Pr:GYSGG crystal. The thermal focal lengths are respectively 41 and 62 mm when the pump power is 2.5 W. All these results indicate that the GYSGG/Er,Pr:GYSGG composite crystal has great advantages in reducing the influence of thermal effects and improving laser performances