Performance Analysis of Free Space Optics Link Under the Effect of Rain Attenuation

Free space optical (FSO) networking has emerged as a promising technology for bridging the last mile gap in current high-rate fibre networks as well as for high-rate next-generation broadband wireless communication networks. This paper theoretically investigates the performance of the Free Space Optic system under rainy weather conditions using Optisystem software. Quality factor and eye-diagram analysis are used to analyse the FSO performance for several rain intensity and precipitation, following the Carbonneau model for rain attenuation. The results show that the link is completely lost when the distances are at 1.5 km, 1.2 km, and 0.8 km for light rain, moderate rain, and heavy rain, respectively. An optical amplifier is then introduced to improve the system performances and increase the signal intensity, which helps to mitigate the atmospheric effects easily. As a result, data transmission is sustained without interruptions, and overall connectivity is enhanced. Results show that the transmission range improves up to several meters, specifically under moderate rain weather condition when using the optical amplifier gain is applied

Experimental Investigation of All-Optical Relay-Assisted 10 Gb/s FSO Link Over the Atmospheric Turbulence Channel

This paper presents novel experimental results for a 10 Gb/s triple-hop relay-based all-optical free space optical (FSO) system by employing the amplify-and-forward relaying scheme. We provide a mathematical framework for the end-end signal-to-noise ratio (SNR) and the bit-error rate (BER) performance and confirm that the derived analytical results reasonably match experimental results especially at relatively high SNR. The evaluated BER performances under different atmospheric turbulence regimes (modeled by the Gamma-Gamma distribution) show that the considered relay-assisted FSO system offers a significant performance improvement for weak-to-strong turbulence regimes, even without knowledge of the channel state information. More precisely, at a target BER of 10-5, the proposed scheme offers ~5 and ~4 dB of SNR gains compared to the direct transmission for turbulence strengths Cn2 of 3.8 × 10-10 m-2/3 and 5.4 × 10-12 m-2/3, respectively

Performance Analysis of FSO Systems using Different Modulation Techniques under the Influence of Atmospheric Turbulence

Free Space Optics (FSO) communications is an emerging technology that offers high-speed data rate, highbandwidth, license-free and strong security against eavesdropping. However, the system performance mainly depends on the atmospheric phenomena, particularly atmospheric turbulence, as it can degrade and shut down the link. Modulation technique is the most affordable and simplest method to mitigate the turbulence problem without any additional devices, thus reducing the complexity and cost. This paper investigates the FSO performance under weak turbulence using Optisystem software based on various modulation schemes such as On-Off Keying Non-Return to Zero (OOKNRZ), Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and Eight-Quadrature Amplitude Modulation (8-QAM) to mitigate the turbulence effect and increase the FSO link performances. Bit Error Rate (BER), Quality factor (Q-factor), and eye diagram analysis are used to analyse the FSO performance. The results show that the 8-QAM modulation scheme gives the best performance, followed by QPSK, BPSK and OOK-NRZ with the Q-factor of 6.20, 6.06, 5.69, and 5.55, respectively

Study of All-Optical FSO Relay based Systems under the Influence of the Atmospheric Turbulence Channel

Free space optical (FSO) communications is an emerging high-speed data rate, high-bandwidth, and license-free access solution for a number of applications including the “last mile” access networks. However, the reliability and availability of FSO systems are affected by a number of atmospheric phenomena such as fog, rain, haze, smoke, and turbulence. Interestingly, the severity of such random degradations is highly related to the transmission distance, thus resulting in link deterioration and ultimately complete link failure. In this thesis, an all-optical FSO relay-assisted system technique is adopted to mitigate the destructive effects due to distance dependent atmospheric turbulence-induced fading. In this scheme, relays are incorporated to the direct link between the transmitter and the receiver nodes in order to reduce the turbulence induced path loss per link, thus extending the link span and ensuring higher link availability (i.e., 99.999%) as well as improving the overall system performance. Two all-optical relaying schemes are proposed and investigated, namely all-optical amplify-and-forward (AOAF) FSO relay and all-optical regenerate-and-forward (AORF) FSO relay assisted systems. In the AOAF FSO system, the performance analysis of triple-hop AOAF FSO communications system is investigated under the impact of non-homogeneous atmospheric turbulence condition. We present novel experimental results for the single, dual, and triple-hop AOAF FSO systems under several turbulence configurations and regimes. We also provide a mathematical framework for the end-to-end signal-to-noise ratio (SNR) and the bit error rate (BER) performance and confirm that the derived analytical results reasonably match with the experimental results especially at relatively high SNR. The evaluated BER performances under different turbulence regimes, modelled by the Gamma-Gamma distribution model show that the considered relay-assisted FSO system offers a significant performance improvement for weak to strong turbulence regimes, even without the knowledge of the channel state information. For instance, at a target BER of 10^-5 the proposed triple-hop FSO scheme offers ~5 dB and ~4 dB of SNR gains compared to direct transmission for turbulence strength

Performance analysis of a hybrid free space optics/ visible light communication systems

A hybrid free space optical (FSO)/visible light communication (VLC) system is a remarkable wireless technology for overcoming the last mile gap and for future broadband wireless communication. In detail, this research examines the hybrid FSO/VLC system performance using Optisystem 19 software. The system performance of the wireless hybrid FSO/VLC is evaluated using the bit error rate, quality factor, and eye diagram for weak and strong turbulence regimes referring to the Gamma-Gamma atmospheric turbulence channel. At BER of 10−9 the maximum attainable distances are 1.3 km and 1.8km for 0 dBm and 5 dBm transmitted power in clear weather, respectively. However, when the transmit power reduces to -5 dBm, the measured BER drops to 8×10-3 with a distance of 1 km link range. Moreover, when the power increases from 0 dBm to 5 dBm, the distance of the connection between Tx and Rx can be extended from 1.1 km and 1.9 km under weak turbulence conditions at the target BER of 10−9. Incontrast, at the same target of BER, only 5 dBm of transmitted power managed to capture the signal at a distance of 1.7 km for strong turbulence conditions. This result can be the benchmark research to investigate and identify the best strategies for validating future experimentation difficulties

Performance analysis of all-optical amplify-and-forward FSO relaying over atmospheric turbulence

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Experimental all-optical relay-assisted FSO link with regeneration and forward scheme for ultra-short pulse transmission

This paper presents experimental results for an all-optical free-space optical (FSO) relay-assisted system by employing an all-optical regenerate and forward (AORF) scheme in order to increase the transmission link span. The ultra-short pulse (i.e., 2 ps) regeneration technique based on Mamyshev method is adopted. We have developed a dedicated experimental test-bed composed of optical fiber components and FSO links to demonstrate the proposed scheme and evaluate its performance in terms of the Q-factor and bit error rate (BER) under turbulence regimes for both single and dual-hop network architectures. We show that, using the AORF a hundred times improvement in the BER performance is achieved compared to the amplify-and-forward scheme for a fixed signal-to-noise ratio under turbulence conditions

Analysis of the Effects of Environment on the Performance of Free Space Earth-to-Satellite Optical Link in Malaysia

Free Space Optics (FSO) is a promising optical technology that has a great chance to compliment the traditional wireless communications especially for applying this technology to satellite. It offers some inherent advantages compared to RF such as smaller telescopes, low power consumption, no frequency restrictions, no electromagnetic interference, and large increase in bandwidth. However, FSO is highly attenuated by weather because air is the medium of transmission channel. Moreover,recent studies mostly based on terrestrial link and focusing on temperate region which the attenuation is dominant by fog and snow. Therefore, this paper is aiming to provide FSO analysis of environmental effect for slant path that link from earth to Low Earth Orbit (LEO) satellite that occurs in tropical climate region where rain and haze are present throughout the year. The result of the analysis can provide more knowledge on the feasibility of performing FSO from earth-to-satellite under tropical region

Comparison of optical and electrical based amplify-and-forward relay-assisted FSO links over gamma-gamma channels

Relay-assisted or multi-hop free space optical communications is an efficient solution that offers diversity, which can significantly improve the link availability. Albeit this potential, the turbulence-induced fading can still impact the system performance. This paper investigates through numerical simulations the effect of turbulence by comparing the bit error rate (BER) performance for all-optical and conventional amplify-and-forward dual-hop relaying systems. For the latter case, two options of the erbium-doped fiber amplifier (EDFA) and the semiconductor optical amplifier (SOA) are studied, showing that the advantages of the EDFA solution where EDFA outperforms SOA by ~3 dB in term of signal to noise ratio (SNR) for Rytov variance σ2R = 1.6 at a target BER of 10-5. Under the same turbulence regime, we further investigate the effect of aperture averaging in relay-assisted links and show that a significant BER improvement can be achieved. The results show that SNR gain of ~5.5 dB is achieved when the receiver aperture size increases from 100 mm to 300 mm at a target BER of 10-5

Experimental validation of indoor relay-assisted visible light communications for a last-meter access network

This paper provides experimental results for a relay-assisted visible light communications (VLC) link using a white light-emitting diode (LED) for a last-meter access network. We demonstrate that a relay-based VLC scheme improves the system performance, especially for link spans longer than 5 meters, in the presence of blocking and shadowing by redirecting the transmitted signal. We also demonstrate a multiband carrier-less amplitude and phase modulation (m-CAP) VLC link where the decode-and-forward (DF) relay scheme offers improvement in the data rate by 25% and 60% when compared to the amplify-and-forward (AF) relay-based link and single VLC link over a 7 m transmission distance respectively