Modeling and investigation on the performance enhancement of hovering UAV-based FSO relay optical wireless communication systems under pointing errors and atmospheric turbulence effects

Abstract

This paper investigates and enhances unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) optical wireless communication (OWC) systems under the effects of pointing errors (PEs) and atmospheric turbulences (ATs). The incorporation of UAVs as buffer-aided moving relays in the conventional FSO (CFSO) relay-assisted systems is proposed for enhancing the performance of PEs through AT. Using M-PSK (phase shift keying) and M-QAM (quadrature amplitude modulation), the impact of PEs on transmission quality is evaluated in this work. We evaluate and optimize the symbol error rate, outage probability (OP), and signal-to-noise ratio (SNR) for the UAV-to-ground station-based FSO communications systems. The spatial diversity-based relay-assisted CFSO systems can enhance the performance of the UAV-UAV FSO links. In this paper, a new FSO (NFSO) channel model for the hovering UAV-FSO OWC fluctuations under the PEs, AT effects, jitter, deviation, receiving an error, and wind resistance effects are established. To improve the performance of hovering UAV-based FSO relay OWC systems. We reduce the influence of UAV-FSO OWC fluctuations under PEs and AT effects. By receiving incoherent signals at various locations, the spatial diversity-based relay-assisted NFSO systems can significantly increase the system's redundancy and enhance connection stability. Numerical results show that to achieve a bit-error-rate (BER) of $$\le 10^{ - 5}$$ ≤ 10 - 5 , the required SNR is ≥ 23 dB when the wind variance of the UAVs $$\sigma_{\alpha }^{2}$$ σ α 2 increases from 0 to 7 mrad with FSO link distance L = 2000 m. The required SNR is ≥ 25 dB when the wind variance $$\sigma_{\alpha }^{2}$$ σ α 2 is 1 mrad at an OP of $$10^{ - 6}$$ 10 - 6 . To obtain an average BER of $$10^{ - 6}$$ 10 - 6 , the SNR should be 16.23 dB, 17.64 dB, and 21.45 dB when $$\sigma_{\alpha }^{2}$$ σ α 2 is 0 mrad, 1 mrad, and 2 mrad, respectively. Using 8-PSK modulation without PEs requires 23.5 dB at BER of $$10^{ - 8}$$ 10 - 8 while 16-QAM without PEs requires 26.5 dB to maintain the same BER of $$10^{ - 8}$$ 10 - 8 . Compared with 16-QAM without PEs, the SNR gain of 8-PSK without PEs is 3 dB. The results show the relay-assisted UAV-FSO system with five stationary relays can achieve BER $$10^{ - 8}$$ 10 - 8 at 25 dB SNR in the ideal case and $$10^{ - 5}$$ 10 - 5 at 27 dB SNR with AT and PE at FSO length 1000 m. The results show the relay UAV-FSO system outperforms the CFSO at the BER and SNR performance. The effects of UAV’FSO s fluctuation increase when the UAV-FSO link length, $${\text{L}}_{{{\text{fso}}}}$$ L fso increases. The results of the weak turbulence achieve better SER compared with MT and ST. The obtained results show that decreasing $${\text{L}}_{{{\text{fso}}}}$$ L fso can compensate for the effects of UAV-FSO link fluctuation on the proposed system. Finally, we investigated the CFSO relay-assisted UAV-FSO system with aided NFSO-UAVs spatial diversity-based relay-based on NFSO OWC and revealed the benefits of the resulting hybrid architecture.

Coding techniques for diversity enhancement of dense wavelength division multiplexing MIMO‐FSO fault protection protocols systems over atmospheric turbulence channels

“…In the proposed system, 8 channels are utilised with wavelengths starting from 1550 nm with 100 GHz channel spacing (0.8 nm) in the C-band over a wavelength-division multiplexing MIMO-FSO system for a maximum FSO link distance of 1500 m. Table 1 shows the simulation parameter values used in the calculations [11,44,45]. The results showcase a transmission distance of 1500 m with a promising performance at 20 Gbit/s (8 channels � 2.5 GHz data rate) [12][13][14][15][16].…”

“…In these calculations, Channel 1 (1550 nm) was the benchmark, and the wavelengths of other channels were computed using the expression c = λf, where c is the speed of light (299,792,458 m/s), λ denotes the wavelength, and f refers the frequency. [11,44,45]. Figure 3 shows the bit error rate (BER) against the signal-to-noise ratio (SNR) for different MIMO schemes when compared to a Single-Input, Single-Output (SISO) setup.…”

“…The power gain of the QO-STBC MMSE is 3 dB compared with OSTBC. With achieving the MIMO and diversity system can overcome the obstruction of FSO which suffer from the inter-channel crosstalk, atmospheric turbulence and pointing errors [45]. In Figure 4, the space-time block code techniques can be used to reduce the OP of a system, without losing of data rate.…”

“…For indoor usages, the receiver radius of the small FSO nodes is 1-6 cm and for outdoor usages, the receiver radius is 10-25 cm is used for larger FSO nodes. We use the receiver aperture radius of 6 cm for the proposed system in DWDM-MIMO for the FSO communications system as shown in Table 1 [11,44,45].…”

“…where the parameters μ and σ 2 denote mean and variance respectively [40][41][42][43][44][45][46][47][48][49]. The relation μ = −σ 2 mean path intensity E[A 2 ] = 1, the scintillation index (S.I) ranges between 0.4 and 1.…”