Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted tremendous attention because of their unique electronic, optical and chemical properties. 2D TMDs, especially 2D MoS 2 , have been proved to show great potential in various applications such as sensing, hydrogen evolution and lithium ion batteries. Therefore, methods for the scalable preparation of 2D materials and 2D nanocomposites of high quality and low cost must be developed. Among the various synthesis methods, the hydrothermal synthesis method is simple and can meet the above requirements. In this review, the recent advances in the controllable hydrothermal synthesis of 2D MoS 2 and its nanocomposites by the hydrothermal synthesis method are highlighted. We provide insight into the growth mechanisms of few-layered 2D MoS 2 with different morphologies and the key technologies to realize wafer-scale growth of continuous and homogeneous 2D films which are important for practical applications. Further, the typical applications of TMDs in nonlinear optics as ultrafast optical modulation devices are presented based on work of our institute. For more clarity, we summarize the current challenges of the hydrothermal synthesis method encountering, and suggest solutions to these challenges concerning future developments in practical applications.
A novel modulation scheme termed orthogonal frequency-division multiplexing with subcarrier number modulation (OFDM-SNM) has been proposed and regarded as one of the promising candidate modulation schemes for next generation networks. Although OFDM-SNM is capable of having a higher spectral efficiency (SE) than OFDM with index modulation (OFDM-IM) and plain OFDM under certain conditions, its reliability is relatively inferior to these existing schemes, because the number of active subcarriers varies. In this regard, we propose an enhanced OFDM-SNM scheme in this paper, which utilizes the flexibility of placing subcarriers to harvest a coding gain in the high signal-to-noise ratio (SNR) region. In particular, we stipulate a methodology that optimizes the subcarrier activation pattern (SAP) by subcarrier assignment using instantaneous channel state information (CSI) and therefore the subcarriers with higher channel power gains will be granted the priority to be activated, given the number of subcarriers is fixed. We also analyze the proposed enhanced OFDM-SNM system in terms of outage and error performance. The average outage probability and block error rate (BLER) are derived and approximated in closed-form expressions, which are further verified by numerical results generated by Monte Carlo simulations. The high-reliability nature of the enhanced OFDM-SNM makes it a promising candidate for implementing in the Internet of Things (IoT) with stationary machine-type devices (MTDs), which are subject to slow fading and supported by proper power supply.Index Terms-Orthogonal frequency-division multiplexing with subcarrier number modulation (OFDM-SNM), subcarrier assignment, reliability enhancement, outage performance analysis, error performance analysis.
Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) has become a highprofile candidate for the modulation scheme in next generation networks, and many works have been published to analyze it in recent years. Error performance is one of the most important and interesting aspects of OFDM-IM, which has been analyzed in most works. However, most of them employ two key approximations to derive the closed-form expressions of block error rate (BLER) and/or average bit error rate (BER). The first one is to utilize the union bound assisted by the pairwise error probability (PEP) analysis, and the second one is to employ an exponential approximation of Q-function. In this letter, we apply Craig's formula to analyze the error performance for OFDM-IM in place of the exponential approximation. Because Craig's formula is the exact expression of Q-function, the accuracy of analytical results regarding error performance for OFDM-IM can be improved. We examine the proposed error performance analysis methodology based on Craig's formula by investigating both average BLER and BER. Index TermsOrthogonal frequency-division multiplexing with index modulation (OFDM-IM), error performance analysis, performance approximation, Q-function, Craig's formula.
To expedite research progress on terahertz (THz) communications, we analyze the outage performance of THz communication systems by a compound channel model in this paper. Different from existing models, the compound channel model incorporates the effects of spreading loss, molecular absorption loss, shadowing, and multi-path fading via a composite distribution. By using this model, we maintain an equilibrium of the outage performance analysis between mathematical tractability and the fidelity of realistic THz channels. Specifically, by utilizing the compound channel model, outage performance analysis can get rid of sophisticated case-specific channel modeling relying on field measurement and the ray-tracing assessment. To facilitate the application of the proposed channel model, we also design a maximum likelihood estimation (MLE) based channel parameter estimation approach for the compound channel model. The analytical results of outage performance by using the compound channel model are given in closed form and verified by numerical results.Index Terms-Outage performance analysis, terahertz communications, compound/composite channel model, channel parameter estimation, gaseous molecular absorption. I. INTRODUCTIONN OVEL wireless communication applications pose everincreasing requirements and challenges to the post fifth generation (post-5G) and sixth generation (6G) network design [1], among which the terabit-per-second (Tbps) wireless transmission is demanding and almost impossible by existing communication technologies. As foreseen in [2], both enhancing spectral efficiency (SE) and extending the available spectrum could be feasible solutions to the coming wireless capacity crisis with a set of preconditions. Different from non-orthogonal multiple access (NOMA) and index modulation (IM) that aim to enhance SE within a limited spectrum [3]-[6], terahertz (THz) communication technology focuses on expending the available spectrum to the frequency range between 0.1 THz and 10 THz [7]. In this way, a series of unprecedented wireless communication applications in the automotive industry, indoor
The smart building (SB), a promising solution to the fast-paced and continuous urbanization around the world, is an integration of a wide range of systems and services and involves a construction of multiple layers. The SB is capable of sensing, acquiring and processing a tremendous amount of data as well as performing proper action and adaptation accordingly. With rapid increases in the number of connected nodes and thereby the data transmission demand in SBs, conventional transmission and processing techniques are insufficient to provide satisfactory services. To enhance the intelligence of SBs and achieve efficient monitoring and control, both indoor visible light communications (VLC) and machine learning (ML) shall be applied jointly to construct a reliable data transmission network with powerful data processing and reasoning abilities. In this regard, we envision an SB framework enabled by indoor VLC and ML in this article. A&M University at Qatar, Education City, Doha, Qatar, before joining King Abdullah University of Science and Technology (KAUST), Thuwal, Makkah Province, Saudi Arabia as a professor of electrical engineering in 2009. At KAUST, he leads the Communication Theory Lab and his current research interests include the modeling, design, and performance analysis of wireless communication systems.
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