KEYWORDS: Telecommunications, Modulation, Wireless communications, Transceivers, Signal generators, Reliability, LabVIEW, Internet of things, Eye, Digital modulation
With the rapid advancement of the Internet of Things, terahertz band has emerged as a prominent area of research for high-speed wireless communication over the past decade to satisfy the growing demand for network traffic and is extensively employed in indoor wireless communication systems. This study experimentally examines the transmission efficacy of MSK signals in terahertz channels via upconversion. In the LabVIEW development environment, the PN sequence serves as the baseband signal. The MSK signal, with a bandwidth of 1GHz and a transmission rate of 1Gbit/s, is modulated and output using the high-speed vector signal transceiver platform, PXIe-5841. This signal is then upconverted to 230~300GHz for wireless transmission. The findings from the constellation and grid diagrams reveal the stable and reliable transmission of the MSK signal in the terahertz communication system, underscoring its viability and potential for future research and application.
With the advancement of terahertz technology, there is growing anticipation for 6G communication in the international community, and terahertz communication is gaining increasing attention. Nonetheless, terahertz waves possess strong directionality, leading to the obstruction of transmission signals. Consequently, achieving largeangle, directed transmission poses a technical obstacle for terahertz communication. Metasurfaces technology has great potential to improve the coverage performance of 6G networks, making it one of the most promising technologies in this field. This paper designed a terahertz directional reflector that is insensitive to polarization in the terahertz communication band (0.25 THz). The unit structure is selected using the resonant phase modulation principle, utilizing a metal-insulator-metal structure. Following the phase compensation principle, the structure of the unit is arranged and simulation experiments are conducted to achieve a 30-degree abnormal deflection of the reflected beam. This scheme will hold some application value for terahertz 6G channel control in future research.
Recently, research on 6G wireless communication technology has become a hot topic. In 6G technology, terahertz communication is considered the most promising part. The research and application of the terahertz communication frequency range (0.1-10 THz) will bring revolutionary changes to the field of communication. It has the potential to bridge the transmission gap between the infrared and microwave bands, and offers highspeed data transmission, low latency, and high-capacity communication. Therefore, the development of terahertz communication is highly anticipated as a significant driving force for 6G technology. At present, research on outdoor terahertz channels is far less extensive compared to indoor channels, requiring more efforts to explore the characteristics of outdoor terahertz channels. In this paper, we focus on the three-dimensional scenario of street canyon and model the terahertz channel using ray tracing. The carrier frequencies used for simulation range from 220 to 330 GHz. By calculating the power loss and required time for each path from the transmitter to the receiver, we obtain parameters such as power delay spectrum and power angle spectrum. Next, we analyze the relationships between path loss, delay spread, angle spread, and distance, gaining further understanding of the outdoor terahertz multipath channel characteristics.
In this thesis, firstly, based on the MATLAB/Simulink platform, the simulation channel module for terahertz wave (300GHz) communication is established based on the MPM modeled clear sky atmospheric channel,and Hamming (7,4) and RS (188,204) channel compilation code and 2FSK, QPSK, 16QAM signal modulation and demodulation, which are commonly used in the traditional frequency bands, are selected to form a simulation model of terahertz communication system. By comparing the BER analysis, it is found that Hamming (7,4) coding and QPSK modulation technology can achieve relatively low BER, but the traditional modulation and coding method has poor performance in terahertz communication at low SNR.Then,the experiments conducted on the wireless communication system controlled by LabVIEW on the PXIe platform confirmed and validated the conclusions derived from the simulations.
Terahertz (THz) waves have great potential applications in communication, imaging, and spectroscopy fields. Effective THz modulators are highly desired to realize those functionalities. Wherein, as a kind of artificial composite material, THz metamaterials can achieve extraordinary responses to the electromagnetic wave through the geometric structure design. Nevertheless, normal metamaterials have no tunability once they have been designed and fabricated. To overcome this issue, active medias have been explored to enable the expected modulation of metamaterials under the external stimuli. Among them, phase transition materials are often used in dynamically tunable THz devices due to their intriguing properties. Particularly, vanadium dioxide (VO2) has attracted attention owing to the reversible physical properties and can exhibit insulator-to-metal transition (IMT) behavior at near room temperature. Here, we explore the strength of the resonance response and the change of spectral lineshape caused by the size variation in the metamaterial unit cell. On this basis, adding VO2 thin film can realize broadband modulation during the IMT process. Furthermore, by incorporating the VO2 patches in the gold microstructure can further achieve the dual modulation of amplitude and frequency simultaneously. The design of VO2 hybrid metamaterial can break the single function limitation of traditional metamaterial modulators, reduce material loss, and open up a new path for the development of multifunctional THz modulators.
Metamaterial induced transparency (MIT) has great potential in photonic device applications. Here, we design a metastructure with MIT effect generated by destructive interference of bright-dark-dark three modes. Therein, the cross resonator formed by the combination of the cut-wire resonator and the long vertical metal bar (LVMB) act as the bright mode, and two pairs of split ring resonators of different lengths are distributed around the cross resonator as two dark modes, realizing significant multi-band MIT effect. Furthermore, the embedded photosensitive Si island in the broken LVMB can be used to tune the effective length by changing the conductivity, thereby actively controlling the conversion from multi-band behaviors into triple MITs. Our results could achieve the dynamic multi-band switching, which has broad application prospects for optical information processing and communication.
Metamaterial induced transparency (MIT) has shown great application potential in terahertz regime, which is of great significance in constructing photonic components such as slow light systems and tunable filters. The single or multiple transparent windows can be induced through near-field coupling via two or more resonant modes. Compared with the single MIT, multi-MIT effect can realize multiband sensing, communication, and storage applications. Here, we design a dual-MIT metastructure composed of three bright resonators including a cut-wire resonator (CWR), a pair of large toroidal split ring resonators (LTSRRs), and a pair of small toroidal split ring resonators (STSRRs). Dual-MIT windows can be induced through coupling between the electric dipole resonance and two inductance capacitance (LC) resonances. By optimizing and adjusting the geometric parameters of the metasurface, the resonant strength could be suppressed or enhanced. Thus, we can passively manipulate the frequency and amplitude of the dual-MIT windows and realize the switching between the two windows and single MIT. In addition, by actively tuning the conductivity of photosensitive Si introduced in the gap of the LTSRRs and STSRRs, we observe the LC resonance can be weakened to quench the dual-MIT windows. Our research provides an approach to explore the miniaturized, multi-functional, and switching components in terahertz regime.
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