Digitally Mitigating Doppler Shift in High-Capacity Coherent FSO LEO-to-Earth Links

Fernandes, Marco A.; Loureiro, Pedro A.; Fernandes, Gil M.; Monteiro, Paulo P.; Guiomar, Fernando P.

doi:10.1109/jlt.2023.3281082

Cited by 10 publications

(2 citation statements)

References 35 publications

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“…They also examined Doppler shifts for different connection scenarios and proposed a new method for all-digital Doppler shift compensation, when the traditional methods are insufficient. Fernandes et al in [110] addressed challenges in Earth-satellite and inter-satellite coherent FSO links for LEO constellations, aiming to provide ultra-high capacity and reliability. They proposed a technique for mitigating the Doppler effect using Probabilistic Constellation Shaping (PCS) and adapted the system symbol-rate, while keeping the bit-rate fixed.…”

Section: Physical Layer Designmentioning

confidence: 99%

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Free Space Optical Communication: An Enabling Backhaul Technology for 6G Non-Terrestrial Networks

Elamassie,

Uysal

2023

Photonics

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The deployment of non-terrestrial networks (NTNs) is envisioned to achieve global coverage for 6G and beyond. In addition to space nodes, aerial NTN nodes such as high-altitude platform stations (HAPSs) and rotary-wing unmanned aerial vehicles (UAVs) could be deployed, based on the intended coverage and operational altitude requirements. NTN nodes have the potential to support both wireless access and backhauling. While the onboard base station provides wireless access for the end users, the backhauling link connects the airborne/space-borne base station to the core network. With its high data transmission capability comparable to fiber optics and its ability to operate in the interference-free optical spectrum, free space optical (FSO) communication is ideally suited to backhauling requirements in NTNs. In this paper, we present a comprehensive tutorial on airborne FSO backhauling. We first delve into the fundamentals of FSO signal transmission and discuss aspects such as geometrical loss, atmospheric attenuation, turbulence-induced fading, and pointing errors, all of which are critical for determining received signal levels and related link budget calculations. Then, we discuss the requirements of airborne backhaul system architectures, based on use cases. While single-layer backhaul systems are sufficient for providing coverage in rural areas, multi-layer designs are typically required to establish connectivity in urban areas, where line of sight (LoS) links are harder to maintain. We review physical layer design principles for FSO-based airborne links, discussing both intensity modulation/direct detection (IM/DD) and coherent modulation/coherent demodulation (CM/CD). Another critical design criteria for airborne backhauling is self-sustainability, which is further discussed in our paper. We conclude the paper by discussing current challenges and future research directions. In this context, we discuss reconfigurable intelligent surfaces (RIS) and spatial division multiplexing (SDM), for improved performance and an extended transmission range. We emphasize the importance of advanced handover techniques and scalability issues for practical implementation. We also highlight the growing role of artificial intelligence/machine learning (AI/ML) and their potential applications in the design and optimization of future FSO-based NTNs.

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Section: Physical Layer Designmentioning

confidence: 99%

“…In order to enhance the transmission range and link stability, researchers further explored the concept of using FSO-based airborne nodes as relays [109,110,118,119]. For example, Fawaz et al [118] explored the concept of utilizing UAVs as moving relays equipped with buffers to enhance the performance of terrestrial links.…”

Section: Physical Layer Designmentioning

confidence: 99%