In this paper, we enhance the performance efficiency of the free-space optical (FSO) communication link using the hybrid on-off keying (OOK) modulation, M-ary digital pulse position modulation (M-ary DPPM), and M-pulse amplitude and position modulation (M-PAPM). This work analyzes and enhances the bit error rate (BER) performance of the moment generating function, modified Chernoff bound, and Gaussian approximation techniques. In the existence of both an amplified spontaneous emission (ASE) noise, atmospheric turbulence (AT) channels, and interchannel crosstalk (ICC), we propose a system model of the passive optical network (PON) wavelength division multiplexing (WDM) technique for a dense WDM (DWDM) based on the hybrid fiber FSO (HFFSO) link. We use eight wavelength channels that have been transmitted at a data rate of 2.5 Gbps over a turbulent HFFSO-DWDM system and PON-FSO optical fiber start from 1550 nm channel spacing in the C-band of 100 GHz. The results demonstrate (2.5 Gbps × 8 channels) 20 Gbit/s-4000 m transmission with favorable performance. In this design, M-ary DPPM-M-PAPM modulation is used to provide extra information bits to increase performance. We also propose to incorporate adaptive optics to mitigate the AT effect and improve the modulation efficiency. We investigate the impact of the turbulence effect on the proposed system performance based on OOK-M ary- PAPM-DPPM modulation as a function of M-ary DPPM-PAPM and other atmospheric parameters. The proposed M-ary hybrid DPPM-M-PAPM solution increases the receiver sensitivity compared to OOK, improves the reliability and achieves a lower power penalty of 0.2–3.0 dB at low coding level (M) 2 in the WDM-FSO systems for the weak turbulence. The OOK/M-ary hybrid DPPM-M-PAPM provides an optical signal-to-noise ratio of about 4–8 dB of the DWDM-HFFSO link for the strong turbulence at a target BER of 10−12. The numerical results indicate that the proposed design can be enhanced with the hybrid OOK/M-DPPM and M-PAPM for DWDM-HFFSO systems. The calculation results show that PAPM-DPPM has increased about 10–11 dB at BER of 10−12 more than the OOK-NRZ approach. The simulation results show that the proposed hybrid optical modulation technique can be used in the DWDM-FSO hybrid links for optical-wireless and fiber-optic communication systems, significantly increasing their efficiency. Finally, the use of the hybrid OOK/M-ary DPPM-M-PAPM modulation schemes is a new technique to reduce the AT, ICC, ASE noise for the DWDM-FSO optical fiber communication systems.

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.

Green and smart buildings (SBs) are promising solutions to the fast-growing and ongoing urbanization around the globe and are the composition of huge services. The SB can acquire a tremendous amount of information and perform proper handling of many broadcasting residents accordingly. With the abrupt increase in the high-quality data transmission demands over long reach for the large number of connected residents in SBs, conventional data transmission techniques are inadequate to provide adequate services. Thus, in this paper, to improve the intelligence and reliability of SBs with high overall efficiency, cost-effectiveness, and security, a hybrid passive optical network (PON) and visible light communication (VLC) indoor broadcasting system is proposed. The bidirectional hybrid PON-VLC consists of integrated time and wavelength division multiplexing (TWDM) and wavelength division multiplexing (WDM) with optical code division multiplexing (OCDMA) PON with red green blue employed light emitting diodes (RGB LEDs) based VLC system. Seven OCDMA codes are utilized in the proposed work at a 10/2.5Gbps per channel transmission rate over hybrid fiber-VLC channels to strengthen the system performance. The simulation results show that the modified new zero cross-correlation (MNZCC) code outperforms other codes and provides a faithful 100km fiber length and 5m VLC range for 200 active residents. Moreover, VLC distance can be incremented up to 10m wireless range by increasing the received aperture diameter of 25cm. Also, the numerical analysis, as well as comparative performance, depicts the superiority of PON-VLC under the impact of impairments and noise in fiber-VLC link-based SBs.

This paper investigates and enhances unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) communication systems under the effects of pointing errors (PEs) and atmospheric turbulences. 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 examine and enhance the symbol error rate, outage probability (OP), and signal-to-noise ratio (SNR) for the UAV-to-ground stationbased FSO communications systems. The spatial diversity-based relay-assisted CFSO systems can enhance the performance of the UAV-UAV FSO links. Numerical results show that to achieve a bit-error-rate (BER) of ≤ 10-5 , the required SNR is ≥ 23 dB when the wind variance of the UAVs 𝜎𝛼2 increases from 0 to 7 mrad with FSO link distance L = 2000 m. The required SNR is ≥ 25 dB when the wind variance 𝜎𝛼2 is 1 mrad at a OP of 10-6 . To obtain an average BER of 10−6 , the SNR should be 16.23 dB, 17.64 dB, and 21.45 dB when 𝜎𝛼2 is 0 mrad, 1 mrad, and 2 mrad, respectively. Using 8-PSK modulation without PEs requires 23.5 dB at BER of 10-8 while 16-QAM without PEs requires 26.5 dB to maintain the same BER of 10-8 . Compared with 16-QAM without PEs, the SNR gain of 8-PSK without PEs is 3 dB.

This paper investigates and optimizes unmanned aerial vehicle (UAV) relay-assisted free-space optics (FSO) communication systems under the effects of pointing errors (PEs) and atmospheric turbulences. 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 enhance 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. Numerical results show that to achieve a bit-error-rate (BER) of \(\le {\text{10}}^{\text{-5}}\), the required SNR is ≥ 23 dB when the wind variance of the UAVs \({\sigma }_{\alpha }^{2}\) increases from 0 to 7 mrad with FSO link distance L = 2000 m. The required SNR is ≥ 25 dB when the wind variance \({\sigma }_{\alpha }^{2}\) is 1 mrad at a OP of \({\text{10}}^{\text{-}\text{6}}\). To obtain an average BER of \({10}^{-6}\), the SNR should be 16.23 dB, 17.64 dB, and 21.45 dB when \({\sigma }_{\alpha }^{2}\) is 0 mrad, 1 mrad, and 2 mrad, respectively. Using 8-PSK modulation without PEs requires 23.5 dB at BER of \({\text{10}}^{\text{-8}}\) while 16-QAM without PEs requires 26.5 dB to maintain the same BER of \({\text{10}}^{\text{-8}}\). Compared with 16-QAM without PEs, the SNR gain of 8-PSK without PEs is 3 dB.