Table 1 Literature summary.

From: Robust high-capacity free-space optical communication using OAM-based structured light and intelligent adaptive signal processing

Ref

Objectives

Model/techniques used

Key limitations

19

Explore OAM waveform generation and communication performance.

Comparative analysis of OAM generation, energy efficiency, BER, and fiber-to-atmosphere transition.

Lacks experimental validation; focused on short-range systems.

20

Develop simplified detection for OAM states using weak optical differentiation.

Differential measurements on LG beams with topological charges (l=5, l=8).

Limited real-time differentiation of vortex modes; small-scale detection only.

21

Improve distorted vortex beam recognition using CNN transfer learning.

Transfer learning-based CNN for OAM mode classification under turbulence.

Accuracy drops with stronger turbulence/distance; limited hardware testing.

22

Introduce modulation using the phase-difference degree of freedom.

Phase-interference encoding with NN-based decoding.

Requires precise phase control; complexity grows with more modes.

23

Enhance OAM state separation under turbulence.

CNN-based vortex modulation and image classification.

Fractional OAM recognition is still weak; noise-sensitive.

24

Implement co-scale reception with Airy compensation.

Experimental setup with an adjustable ring-shaped Airy wavefront.

Mode power fluctuation reversal under strong V-AT isn’t resolved.

25

Maximize diversity gain and minimize fading in OAM multiplexed links.

Diversity gains modeling, channel assignment, and fiber delay line.

Synchronization complexity; optical-domain combination needed.

26

Evaluate MIMO-DWDM-FSO under turbulence with coding.

MIMO, MMSE, STC, STBC, QO-STBC.

Ignores pointing error turbulence; limited FEC flexibility.

27

Distribute multiple OAM channels using precoding.

Grid array antennas with OAM precoding, interference mitigation.

Limited scalability; large arrays required.

28

Propose an OCDMA-OAM hybrid for high-speed FSO.

FRS coding with LG modes for multi-channel allocation.

High turbulence sensitivity; lacks AI/ML compensation.

29

Reduce BER in FSO using spatial diversity + beamforming.

Spatial diversity and beamforming under turbulence.

Range reduced in fog/dust; weak environmental robustness.

30

Demonstrate real-time spatiotemporal acoustic OAM.

Single-sensor Doppler detection of harmonic OAM waveforms.

Needs high spatial resolution and synchronization; hardware limits.

31

Study OAM multiplexing in terrestrial FSO under weather effects.

Simulations with AMI, RZ, and NRZ at 40 Gb/s.

Simulation only; no experimental results.

32

Mitigate noise in OAM mode extraction.

FBDMD matrix synthesis to reduce crosstalk.

Computationally heavy; limited real-time scalability.

33

Enable UAV-to-ground OAM-FSO with 4-OAM-OFDM.

4-OAM-OFDM integration in dynamic UAV-ground topology.

OFDM complexity under mobility isn’t fully addressed.

34

Design a robust OAM pointing error model for short-range FSO.

Crosstalk-optimized BER model vs modulation/mode count.

Short-range only; lacks multi-user/multi-beam validation.

35

Assess vortex beam propagation in nonlinear Kerr turbulence channels.

Nonlinear Schrödinger equation with turbulence index model.

Energy alignment isn’t addressed.

36

Assess the resilience of Airy beams against incident turbulence.

Exhaust-flow turbulence tracking with beam modulation.

Limited generalization to other turbulence types.

37

Reduce crosstalk in OAM transmission under turbulence.

CLA-DV.

Signal quality still degrades at longer distances.

38

Strengthen BER performance in MDM-FSO systems using Hermite–Gaussian channels.

PTFB with MMSE optimization across Hermite–Gaussian channels.

Effectiveness decreases under strong turbulence.

39

Extract phase information from distorted Hermite–Gaussian modes.

Deep-learning model using GDL(VggNet).

High computational cost limits real-time applicability.

40

Achieve liquid data-rate inter-satellite communications.

MDM with potential WDM integration.

System complexity and synchronization remain challenging.

41

Compact multi-dimentional demultiplexing (wavelength, SAM, OAM)

Single layer dielectric metasurfaces

Practical integration of nanophotonic components remains challenging.

42

To reduce signal degradation and BER caused by atmospheric turbulence.

N-encoded SM with L-ary PPM in a DWDM-MIMO FSO

High system complexity

43

To mitigate atmospheric turbulence and alignment-related signal degradation.

Multi-hop MIMO with SM and M-ary PPM

The Practical deployment may be constrained by hardware and relay station requirements.

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