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Free-space optical communication (FSO) technology has wide prospects in deep space exploration, but it will encounter coronal turbulence during superior solar conjunction, and solar scintillation will seriously affect the communication quality. In this paper, we propose a terrestrial–deep space hybrid radio frequency (RF)/FSO system with the hybrid...
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... after the combination of PPM and BPSK, one bit of BPSK information is added to each frame, and the number of transmitted bits is increased, which improves the transmission efficiency. As present in Figure 4, the transmitter consists of an n-bit PPM encoder, a parallel serial converter and a transmitter filter with a rectangular pulse shape of duration. The PPM symbol is applied to the BPSK modulator on the radio frequency subcarrier. ...
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... Various vortex superpositions produce atmospheric turbulence, which greatly reduces the communication distance of free-space optical communication and damages the free-space optical communication link between the satellite and the ground, resulting in the attenuation of laser signals. Increasing the gain of the signal at this point does not necessarily improve the quality of the laser beam [15]. However, adaptive optics can effectively improve the effects of atmospheric turbulence or scattering and increase the speed of communication systems [16,17]. ...
Optical communication modulation technology and networking technology are two important technologies for constructing free-space optical (FSO) communication. In this paper, pulse width modulation (PWM) is used to realize free-space optical communication. The process of signal modulation and demodulation is implemented by means of a field programmable gate array (FPGA). An optical communication relay system is constructed to realize communication networking. The binary data bits in the communication process are converted into pulse signals of different widths, the data demodulation process is realized by sampling with a high-speed analog-to-digital converter (ADC), the data level is determined by counting the proportion of high and low voltages sampled in a pulse period. The relay system analyzes the routing target after receiving the pulse signal from the transmitter, and then sends the data to the target receiver. The experimental results show that the constructed system can achieve point-to-multipoint free-space optical communication. Additionally, using ADC to demodulate the received signal increases the stability of the free-space optical communication system. This system provides the design prototype system of FSO communication networking technology.
... Optical Communication [57], [90], [91], [92], [93], [94], [96], [97], [98], [99], [100], [101], [102], [103], [104], [105], [106] , [107], [108], [109], [110] THz Communication [111], [112], [113], [114], [115], [116], [117], [118], [119], [120], [121], [122], [123], [124] RIS [125], [126], [127], [128], [129], [130], [131] Multiple Spacecraft & Uplink per Antenna [132], [133], [134] Mars Planetary Network [57], [58], [135], [136], [137], [138], [139], [140], [141], [142] Cognitive Radio [143], [144], [145], [146], [147], [148], [149], [150], [151], [152], [153], [154], [155], [156], [157], [158], [159] Acquisition, Tracking, and Navigation [160], [161], [162], [163], [164], [165], [166], [167] Delay Tolerant Networking [5], [168], [169], [170], [171], [172], [173], [174], [175], [176], [177], [178], [179], [180], [181], [182] , [183], [184], [185], [186], [187], [188], [189], [190] Multiple Access Schemes [191], [192], [193], [194], [195], [196], [197], [198], [199], [200], [201], [202], [203], [204] Environment-Aware Communications [205], [206], [207], [208] Artificial Intelligence [209], [210], [211], [212], [213], [214], [215], [216], [217], [218], [219] User Modem and Amplifier Terminal (ILLUMA-T), which is expected to be released in 2023 and complete an end-to-end (E2E) optical communications relay system. High-resolution data is envisioned to be transmitted from the International Space Station (ISS) to the LCRD using 1.2 Gbps optical links. ...
... Early experiments of hybrid RF/optical interplanetary links are carried out by NASA in [105]. In [106], performance of a hybrid dual-hop RF/FSO deep space communication system is studied under the effect of solar scintillation. Results in the article are claimed to shown that the hybrid RF/FSO system enhances the BER performance in a deep space environment by a factor of 10 to 30. ...
Space exploration has been on the rise since the 1960s. Along with the other planets such as Mercury, Venus, Saturn, and Jupiter, Mars certainly plays a significant role in the history of space exploration and has the potential to be the first extraterrestrial planet to host human life. In this context, tremendous effort has been put into developing new technologies to photograph, measure, and analyze the red planet. As the amount of data collected from science instruments around and on Mars increased, the need for fast and reliable communication between Earth and space probes has emerged. However, communicating over deep space has always been a big challenge due to the propagation characteristics of radio waves. Nowadays, the collaboration of private companies like SpaceX with space agencies to make Mars colonization a reality, introduces even more challenges, such as providing high data rate, low latency, energy-efficient, reliable, and mobility-resistant communication infrastructures in the Martian environment. Propagation medium and wireless channel characteristics of Mars should be extensively studied to achieve these goals. This survey article presents a comprehensive overview of the Mars missions and channel modeling studies of the near-Earth, interstellar, and near-planet links. Studies featuring three-dimensional (3D) channel modeling simulations on the Martian surface are also reviewed. We have also presented our own computer simulations considering various scenarios based on realistic 3D Martian terrains using the Wireless Insite software. Path loss exponent, power delay profile, and root-mean-square delay spread for these scenarios are calculated and tabularized in this study. Furthermore, future insights on emerging communication technologies for Mars are given.
In optical communication systems, a laser is used as a light source to transmit information using optical signals. However, as the speed of data transmission and the distance between telecommunications stations increase, the possibility of errors in data transmission also increases. One of the main causes of errors in optical communication systems is the intensity of laser light output. Optical communication systems are a common means of transferring information from one place to another, often using lasers as strong light sources, such as in fiber optic communications and communication networks. However, the fluctuating power of laser output is a major issue when using lasers for data transmission. Therefore, stabilizing the laser output light intensity can greatly improve the quality of data transmission in optical communication systems, reducing the likelihood of errors in the light source. Various factors, such as temperature, voltage, and current, can cause fluctuations in the intensity of laser output. Changes in the intensity of laser output light can result in inaccuracies in data transmission, which can be avoided using laser output intensity stabilization techniques. These techniques reduce the intensity of light and source errors by continuously adjusting and correcting the amount of output light intensity over time. The manufacturing of semiconductor lasers and their continuous monitoring, including laser power and temperature regulation, are the most important components of these systems. Finally, with a comparison between the gain and the output waveform as a light source, for three bias currents of 0.85, the limit current at the modulation frequency of 109 GHz and the input power of – 40 dbm has been done. This paper presents a system that can adapt to 0–50 °C temperature fluctuations while stabilizing a semiconductor laser's operating parameters and power with an accuracy of 0.1%.
In the recent decades, free-space optical (FSO) communication technology has gained significant importance owing to its promising unique features: high user capacity, license-free spectrum, ease and quick deploy-ability. However, the performance of FSO communication systems depends on the uncontrollable terrestrial atmospheric effects. The second main challenge is that the FSO system performance degrades as a line-of-Sight (LoS) technology due to the misalignment transmitter and receiver. The third challenge is the consideration of time value of money, which is central to most engineering economic analyses in employing communication systems. The opportunity cost of making one choice over another must also be considered. This paper presents a proposed FSO system design model for mitigating the three performance challenges we mentioned. The results show an enhancement by 83.34% in system efficiency in case of moderate scintillation (using gamma-gamma model). This proposed hybrid model is proved to be applicable to any
atmospheric channel conditions.
In this paper, we derive accurate outage probability and bit error rate expressions for a high altitude platform station (HAPS) assisted terrestrial communication system. In particular, HAPS is deployed as a relay node to assist two ground stations for data transmission. Each ground station-to-HAPS communication link works on a hybrid radio frequency (RF) and free space optics (FSO) mode. Selection combining is performed at the HAPS and the destination ground station to select either RF or FSO link based on the instantaneous channel signal-to-noise ratio (SNR). The accuracy of the derived outage probability and bit error rate expressions are validated with extensive computer simulations. We further develop an optimal power allocation scheme that optimizes the transmit power of source-ground-station and HAPS while satisfying practical energy consumption constraints. The derived expressions provide more insights on system design and assist analyzing HAPS-terrestrial integrated network supported by hybrid RF/FSO system.
In this paper, we propose a mixed radio frequency (RF)/free space optical (FSO) unmanned aerial vehicle (UAV) communication system, based on modulating retro-reflector (MRR) and reconfigurable intelligent surface (RIS), which adopts the hybrid L-ary pulse position modulation-binary phase shift keying-subcarrier intensity modulation (L-PPM-BPSK-SIM). More specifically, the RF channel follows Rayleigh distribution, while the FSO channel obeys Gamma–Gamma distribution that considers atmospheric turbulence and pointing error. For decode-and-forward (DF) relay, the MRR is installed on the UAV to reduce its weight, size, and power consumption. In particular, the RIS is used as user terminal along with the RF signal generator to achieve signal enhancement. Based on this, closed expressions for the outage probability, average bit error rate (BER) and average channel capacity of the end-to-end uplink and downlink are derived. Numerical results confirm that while the relay limitation is solved by MRR, RIS significantly reduces the outage probability and average BER as well as obviously increases the average channel capacity. Furthermore, the hybrid L-PPM-BPSK-SIM with average symbol length greater than eight can effectively improve the average BER performance of the system.
