Due to the limited space in the tunnel environment, multiple-input multiple-output (MIMO) systems with double-port fed leaky coaxial cables (LCXs) can not only reduce the number of LCXs, but also improve the channel capacity. Based on the geometry based on single bonce (GBSB) and electromagnetic field radiation theory of LCX, a MIMO channel model with double-port fed LCX in a tunnel scenario is proposed in this paper. The channel impulse response (CIR) is derived, and verified with measurement results in terms of channel capacity. The distribution of channel capacity of single double-port fed LCX under different LCX lengths in the tunnel scenarios has also been analyzed in this work, and the distribution of channel capacity for the LCX-MIMO system with long LCX is predicted. The results show that the single double-port fed LCX-MIMO system outperforms the dipole antenna MIMO system with respect to channel capacity in the considered tunnel scenarios.
Sub-terahertz (sub-THz) communications have promising prospects for future beyond-5G or 6G applications due to the sufficient spectrum resources. However, the bit-error-rate (BER) performance of sub-THz is seriously deteriorated by phase noise because of the defective high-frequency oscillators. In this paper, a novel modulation and demodulation method with low peak-to-average power ratio (PAPR) is proposed to resist phase noise, where the signal waveform is generated in the form of Gray-mapping amplitude and differential phase shift keying (Gray-ADPSK). As phase noise varies slowly in time, the amplitude and differential phase between adjacent symbols almost remain after transmission with Gray-ADPSK, and hence the BER performance is barely affected by phase noise. In order to support decoding effectively, a soft-decision demodulation method with low complexity is also put forward. Numerical simulations demonstrate that the proposed Gray-ADPSK can resist phase noise significantly, and the high-spectral-efficiency transmission even in the order of 4096 is feasible under high-intensity phase noise.
The morphology evolution of carbide precipitated on grain boundary nearby different triple junctions in grain boundary engineering (GBE) treated nickel-based Inconel Alloy 690 aged at 715°C for different time was investigated by scanning electron microscopy and electron backscatter diffraction. The results show that, the diversity of triple junction types was increased by GBE significantly. The size and morphology of grain boundary carbide were not only affected by the grain boundary character, but also the nearby grain boundary character at the triple junction. The higher Σ values of the nearby grain boundaries, the larger carbide precipitated on the other grain boundary. Based on the experimental results, the effects of grain boundary characters and triple junction types on the carbide precipitation behaviours are discussed.
In this paper, we present a new secrecy-enhancing scheme for the spatial modulation (SM) system, by considering imperfect channel state information (CSI). In the proposed scheme, two antennas are activated at the same time. One of the activated antennas transmits information symbols along with artificial noise (AN) optimized under the imperfect CSI condition. On the other hand, the other activated antenna transmits another AN sequence. Because the AN are generated by exploiting the imperfect CSI of the legitimate channel, they can only be canceled at the legitimate receiver, while the passive eavesdropper will suffer from interference. We derive the secrecy rate of the proposed scheme in order to estimate the performance. The numerical results demonstrated in this paper verify that the proposed scheme can achieve a better secrecy rate compared to the conventional scheme at the same effective data rate.
The rapid development of high-speed train and Metro communications has provided new challenges for the application of MIMO technologies. Therefore, we propose a three-dimensional (3D) multiple-input multiple-output (MIMO) channel model using leaky coaxial cable (LCX) in a rectangular tunnel. The channel model is based on geometry-based single-bounce (GBSB) channel model and the electric field distribution of LCX in the tunnel environment. The theoretical expressions of channel impulse response (CIR) and space-time correlation function (CF) are also derived and analyzed. The CFs for different model parameters (moving velocity and moving time) and different regions of the tunnel are simulated by Monte Carlo method to verify the theoretical derivation at 1.8 GHz. In the same parametric configuration of nonstationary tunnel scenarios, the time delay of the first minimum value of CFs for LCX-MIMO is 1/5 of the time delay of the minimum value of CFs for dipole antennas MIMO when the train moving velocity is 360 km/h. It is shown that, for MIMO system, the performance of using LCXs is better than using dipole antennas.
Non-orthogonal multiple access (NOMA) is an emerging multiple access technique and enjoys the benefits by enabling multiple users to multiplex in power domain. More recently, NOMA has been discussed in visible light communications (VLC) but less in underwater wireless optical communications (UWOC). In this paper, we evaluate the average channel capacity and outage probability of NOMA UWOC systems in the presence of turbulence. We consider the impacts of power or bandwidth allocation coefficient and oceanic turbulence fading coefficient on the performance of the designed system. Numerical results suggest that NOMA has higher data rate while orthogonal multiple access (OMA) such as orthogonal frequency division multiple access (OFDMA) has better coverage performance. As expected, turbulence degrades both the capacity and coverage performance.
The Industrial Internet of Things (IIoT) is a typical future application for the mobile networks. Unmanned aerial vehicle (UAV) has attracted a great deal of interest in relay assisted wireless communication systems due to its benefits of high mobility, rapid deployment and high probability of line-of-sight (LoS) transmissions. This paper proposes the three-dimensional (3-D) geometry-based non-stationary channel models for wireless communication underlaying UAV-based relay assisted industrial internet of things (IIoT) networks in the sub-terahertz (sub-THz) band. In order to accurately describe the propagation characteristics of the UAV-based wireless channels in the sub-THz band, the propagation gain and atmospheric absorption gain in free space, LoS path, single UAV-based relay and double UAVbased relay propagation paths are considered in the proposed channel models. The channel impulse response (CIR) expressions of different propagation paths are derived respectively. The statistical properties of the channel models including path loss, channel capacity, temporal auto-correlation function (T-ACF), and Doppler power spectral density (DPSD) at 140 GHz band are investigated and analysed, with a performance comparison at 60 GHz band.
In the field of laser applications, it needs to know the optical characters of sea's atmosphere. By referring, measuring and theoretically studying, the optical characters of atmosphere of China's sea are studied herein. These optical characters are mainly about Cn2, and visibility, and so on. And the differences between sea and earth are compared with their optical characters. Then, some basic and important conclusions are made.
Vacancies, as well as their derivatives, usually play a crucial role in many essential properties of materials. However, they always behave erratically, especially under universal thermal vibration, and are therefore difficult to accurately locate. Until now, the lack of an accurate and flexible method for locating and identifying vacancies has hampered the development of relative fields. In this paper, we present a new method to solve this problem. The strategy is to target the atomic cage enwrapping vacancies instead of the vacancies themselves. The core of the method is a time-averaged atomic volume spectrum (TAVS). The key to this method is to identify atoms using time-averaged rather than transient atomic volume, thereby simultaneously denoising intrinsic thermal vibration and avoiding vacancy migration jump. Using this method, we have succeeded for the first time in obtaining the panoramic maps of spontaneously trapped defects in quenched and annealed face-centered cubic aluminum and even the instantaneous images of a steady trapping process. All characteristics of each trapped vacancy, including location, dimension, volume and morphology, as well as aggregate statistical data such as vacancy amount and concentration, can be completely and accurately obtained. Furthermore, these first maps of defects (vacancies) revealed some surprising and interesting phenomena for future exploration. In conclusion, this method provides not only a means of locating and catching vacancies, but also a strategy for identifying and characterizing vacancies. On the basis of its successful application in FCC Al, the TAVS method can be easily extended to other systems as well.
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