KEYWORDS: Matrices, Terahertz radiation, Antennas, Design and modelling, Analog electronics, Switches, Telecommunications, Power consumption, Phase shifts, Systems modeling
Terahertz (THz) communication is a key technology to 6G wireless communication systems. Due to the extremely short wavelength of THz wave, ultra-massive multiple-input multiple-output (UM-MIMO) systems can be realized. The high array gain generated by UM-MIMO systems can overcome the limitation of THz communication distance. In UM-MIMO systems architectures, dynamic array-of-subarrays (DAoSA) architecture can dynamically adjust the connections between radio frequency (RF) chains and subarrays according to the channel state. In this paper, a hybrid precoding scheme of DAoSA architecture with low complexity and good performance is proposed. Hybrid precoding of UM-MIMO systems is optimized with the spectral-energy efficiency rate (SEER) maximization as the objective function. To reduce the computation complexity of optimization problem, the intractable original problem is decoupled into two subproblems that can be solved easily. Then, element-by-element (EBE) algorithm is proposed to solve the DAoSA hybrid precoding subproblem. Furthermore, to determine the connections of the switch es, a logistic chaotic searching algorithm (LCS) is proposed, which can obtain the global optimal solution without traversing repeatedly all connections under a fixed search space. Simulation results showed that the proposed DAoSA hybrid precoding scheme can achieve higher SEER than the existing papers.
Aiming at the problem that the monolingual corpus (Chinese or English) is affected by the sentence structure in the sentiment analysis task, resulting in a large deviation of the extracted context information, and the traditional model does not consider the dependence between aspect words and context information words, which makes the sentiment classification inaccurate, a bilingual multi-feature sentiment analysis model with the degree of fusion relationship is proposed. Firstly, the attention mechanism is used to calculate the attention relationship degree of the aspect word in the sentence, and the Hadama product operation is performed with the context information to obtain the dependent information of the aspect word. Then, the Bidirectional Gated Recurrent Unit (BiGRU) is used to learn the global serialization information of the sentence to obtain the overall information characteristics of the sentence. Next, through the attention mechanism, the overall information characteristics and the aspect word-dependent features are integrated to obtain single-language information. Finally, through the attention mechanism, the overall information characteristics and the aspect word-dependent features are integrated to obtain single-language information. Experimental results on the public datasets Sem Eval2014 Task4 and AI Challenger 2018 show that the model can obtain sentiment information based on aspect words more comprehensively, and has higher accuracy of text sentiment polarity classification than the comparison model.
The deployment of sensors in Underwater Wireless Sensor Networks (UWSNs) is a fundamental issue in underwater wireless communications. Aiming at the problem of sensor nodes failure caused by the collection of information and too much data transformation in the deployment of sensor of UWSNs, the mobile sensor nodes scheduling algorithm based on grids competition in UWSNs is proposed. Firstly, a hexagonal grid partition model is designed to reduce the communication energy consumption combined with existing of grid computing. On the basis of the model, the energy consumption analysis and mathematical model of sensor node scheduling are given. Further, a length-search message exchange mechanism involved in the model is developed. Hence the scheduling plan among the grids can be computed therefore, the whole algorithm is proposed. Finally, simulation experiments illustrate the rationality and effectiveness of the proposed algorithm. The simulation results show that the proposed algorithm can significantly reduce the communication energy consumption and mobile consumption of sensor nodes. In a conclusion, the energy balance among sensor nodes can be guaranteed, and the network lifetime can be extended somewhat.
For the special meteorological condition of high altitude transmission,first,the influence of atmospheric turbulence on the Terahertz wireless communication is analyzed, and the atmospheric constants model with increase in height is given. On this basis, the relationship between the flicker index and the high altitude horizon transmission distance of the Terahertz wave is analyzed by simulation. Then, through the analysis of high altitude path loss and noise, the high altitude wireless link model is built. Finally, the link loss budget is given according to the current Terahertz device parameters, and bit error rate (BER) performance of on-off keyed modulation (OOK) and pulse position modulation (PPM) in four Terahertz frequency bands is compared and analyzed. All these above provided theoretical reference for high-altitude Terahertz wireless communication transmission.
Attenuation coefficient of seawater channel is not only related to the wavelength of optical, but also attenuation particle distribution, so the energy attenuation coefficient of the optical actual transmission changes with the attenuation particle distribution in the seawater, yet in the current underwater optical transmission simulation study, mostly adopts the method of selecting wavelength to determine the attenuation coefficient. Based on the existing of the Monte Carlo method, using the inverse function of modified Henyey Greenstein function to determine the optical scattering angle, and using photons weight change law to determine the photon annihilation. Respectively in the condition of a fixed seawater attenuation coefficient and attenuation coefficient changing with depth, this paper dynamically simulated the underwater optical slant path transmission of power attenuation and bit error rate, and analyzed the influence of the photons movement in power attenuation and bit error rate.
Most previous transmission characteristics analysis did not consider whole characteristic of the
atmospheric-seawater channel and model of underwater optical power attenuation was applied only to the horizontal
communication links. Optical power attenuation model in slant path is built based on seawater optical properties and idea
of seawater stratification. Power attenuation of downlink is analyzed with simulation in the conditions of pure
atmospheric and calm sea. The results show that, when communicating in the South China Sea and the receiver
sensitivity is -55.3dBm, the communication distance can reach underwater 54.4m to 66.5 m.
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