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- 实验方案
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Turbulence-induced optical loss and cross-talk in spatial-mode multiplexed or single-mode free-space communication channels
摘要： Single-mode or mode multiplexed free-space atmospheric optical channels have drawn increasingly more attention in the past decade. The scope of their possible applications spans from the compatibility with the telecom WDM technology, fiber amplifiers, and modal multiplexing for increasing the channel throughput to various quantum communication related primitives such as entanglement distribution, high-dimensional spatially encoded quantum key distribution, and relativistic quantum cryptography. Many research papers discuss application of specific mode sets, such as optical angular momentum modes, for communication in the presence of atmospheric turbulence. At the same time some basic properties and key relations for such channels exposed to the atmospheric turbulence have not been derived yet. In the current paper we present simple analytic expressions and a general framework for assessing probability density functions of channel transmittance as well as modal cross-talk coefficients. Under some basic assumptions the presented results can be directly used for estimation of the Fried parameter of the turbulent channel based on the measured statistics of the fundamental mode transmittance coefficient.
关键词： free-space optical communication,single-mode channels,spatial-mode multiplexing,atmospheric turbulence,quantum communication
更新于2025-09-04 15:30:14
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Atmospheric turbulence mitigation using spatial mode multiplexing and modified pulse position modulation in hybrid RF/FSO orbital-angular-momentum multiplexed based on MIMO wireless communications system
摘要： In this paper, the capacity of a free-space optical (FSO) communication over radio frequency (RF) could potentially be increased by the simultaneous transmission of multiple orbital angular momentum (OAM) based on spatial mode multiplexing (SMM) as an additional effective degree of freedom (EDOF) and quadrature amplitude modulation (QAM). This paper describes using hybrid RF/FSO-OAM based on multiple-input multiple-output (MIMO)/SMM using M-ary modified pulse position modulation (MPPM) and spatial PPM (SPPM) for potentially enhancing capacity in wireless communication systems. We present an analytical system design concerning OAM multiplexing and MIMO/SMM processing in free space communications channel under atmospheric turbulence (AT). Here, we assume a new architecture that closes the gap in speeds between millimeter-wave (mm-wave) wireless and optical links. In this study, we highlight recent advances in the use of OAM multiplexing for high-capacity FSO and mm-wave communications. We have developed the MPPM in FSO communication over RF using the source Gaussian model and SMM by proposing a new version of hybrid SPPM and MPPM. The novelty approach presents performance enhancement of the acquisition, pointing, tracking position and AT mitigation of link. We propose to use SMM combined with OAM-QAM based MIMO communications system to mitigate both weak and strong turbulence distortions. Simulation results show that the capacity of OAM-based MIMO system outperforms the capacity of the conventional MIMO system when the propagation distance is larger than a specific threshold. The use of transmitter lenses could enhance the OAM beams with a larger mode spacing (MS) of 2 (OAM l +1, l +3, l +5, l +7 transmitted) shows a lower power penalty (PP) when the inter-channel crosstalk overwhelms a larger lateral displacement of about 2 mm. Using the lenses at the transmitter to focus OAM beams could reduce power loss and PP in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams and provide high power-efficiency. With a larger of the transmitter and receiver 8 cm, 10 cm aperture size respectively, the system with mode spacing of 2 (OAM l +1, l +3, l +5, l +7 transmitted) and mode spacing of 3 (OAM l +1, l +4, l +7, l +10 transmitted) of OAM beams based on MIMO should fulfill lower-power penalty of 2.2 dB, 3.4 dB, as respectively and could enhance system robustness under angular error but degrade tolerance of lateral displacement. The proposed system provides an excellent signal-to-noise ratio (SNR) for the capacity in the regime of strong atmospheric turbulence. In this way, the maximization of FSO communication and RF wide, the data capacity enhancement, and it is considered a massive solution in the bandwidth provision for future access networks. This work could be beneficial to the practical implementation of OAM-MIMO/SMM multiplexed RF/FSO links.
关键词： Multiple-input multiple-output,Spatial mode multiplexing,Orbital angular momentum,Free space optical communications,Millimeter-wave communications,Modified pulse position modulation
更新于2025-09-04 15:30:14