Most telecommunications systems now utilize Fiber To The Home (FTTH) networks based on Gigabit Passive Optical Network (GPON) due to its flexibility in managing technologies and services for future expansion. Within this FTTH network, significant challenges are encountered in deployment within inaccessible areas or maintenance within construction sites. Therefore, this article aims to develop a proactive technique for deploying and maintaining the FTTH network in inaccessible areas or construction sites such as the Bus Rapid Transit (BRT) projects in Dakar, Senegal. The approach involves replacing severed wired sections with Free Space Optical (FSO) communication. The integration of a hybrid FTTH-FSO system is considered one of the most significant technologies to meet these requirements. This study first models the FTTH network using OptiSystem software before replacing the affected wired sections with a minimum of free-space optical connections. The study evaluates the network's performance from Optical Network Terminals (ONTs). The results obtained demonstrate the feasibility of replacing a 144-fiber optical cable with 12 FSO links (12FO/FSO Antenna) over a distance of 680 meters with a Bit Error Rate (BER) of 7.85837 x 10-10. Furthermore, for shorter distances up to 480 meters, 4 FSO links (36FO/FSO Antenna) suffice to replace the cable with a BER of 2.90502 x 10-10. Finally, this study also reveals that, for distances up to 1200 meters, a single optical fiber can be employed per wireless optical link, necessitating 144 antennas to replace the 144-fiber optical cable.
The deployment of future access networks is motivated by the necessity to increase data volumes for triple play services (Internet, Voice, and Video) and to cater to both mass market customers and business applications. Hence, fiber-optic based infrastructures such as Fiber To The Building (FTTB) and Fiber To The Home (FTTH) offer commercial solutions based on passive optical networks, for example XGPON, GPON, and EPON (Ethernet PON), to provide progressively closer communication services to the end-user 1. For GPON technology, a maximum of 128 uses can be included in a network with a maximum range of 60 km in 2, while in 3, the FTTH network implemented can serve 1000 users. However, deployment in inaccessible areas or maintenance in construction sites leads to repeated or prolonged service disruptions, thereby increasing installation and maintenance costs.
Free Space Optical (FSO) communication serves as an alternative to optical fibers when they are not performing optimally or when their propagation is challenging. It has emerged as one of the most important technologies to address the exponentially growing user demands, especially in the last mile, as it can overcome bottlenecks with its high transmission capacity. This type of wireless optical communication stands out due to its unlicensed transmission spectrum, high transfer rates, ease of deployment, and low cost compared to radiofrequency methods 4. The performance of the hybrid GPON-FSO network is evaluated in 1 based on packet losses. Furthermore, these results indicate that integrating the FSO link into the GPON system does not introduce additional effects and does not compromise the quality of GPON signals, except for losses that can be compensated for through amplification. An indoor 6-meter FSO link was applied to the PON system, resulting in a penalty of less than 1 dB. The signal qualities of 16 QAM OFDM modulated channels in baseband and Radio Over Fiber (ROF) were successfully demonstrated through measurements of Error Vector Magnitude (EVM) and Bit Error Rate (BER) 5. By taking link length of 500 m with attenuation factor of 100 dB/Km, simulation results in 6 show that Q-factor of 9.17 is achieved at BER value of 2.28 10-20 FSO can be considered one of the key technologies to address the recurring or prolonged disruptions in FTTH caused by construction work. This study involves replacing the severed wired sections with Free Space Optical communication.
The remainder of this article is structured as follows: Section 2 initially describes the network modeling, including the FTTH network, presentation of FSO network parameters, and the integration of the hybrid FTTH-FSO network in the area affected by construction work. Subsequently, Section 3 presents the simulation results of the FTTH and hybrid FTTH-FSO networks. Finally, Section 4 provides the conclusion and outlines future work.
Telecommunications companies are constantly looking for technological advances in their operations and maintenance (O&M) management methods, which are still struggling to move towards innovation and process simplification 7. In this sense, FTTH-FSO hybrid technology as a solution for deployment and maintenance in inaccessible areas or Construction Civil Engineering Sites.
2.1. Presentation of the FTTH Network ModelFTTH (Fiber To The Home) is an optical signal transmission format that extends from the service provider's center to the user's location using optical fibers as the transmission medium. The construction of an FTTH network employs GPON (Gigabit Passive Optical Network) technology to support data, voice, and video services across an infrared wavelength range of 800 nm to 1555 nm 8. In this study, we have modeled a portion of the network belonging to the Société Nationale de Télécommunication du Sénégal (Sonatel). The downstream and upstream GPON wavelengths are 1490 nm and 1310 nm, respectively, both utilizing the Non-Return to Zero (NRZ) format. The Optical Line Terminal (OLT) and Optical Network Terminals (ONTs) support a downstream rate of 2.5 Gbps and an upstream rate of 1.25 Gbps. The network is distributed using passive splitters: C0 (2 input and 2 outputs). One of the inputs is used for maintenance to initiate measurements in the event of a malfunction. The two outputs of C0 feeds 2C1 (1 input and 8 outputs), and each C1 output feeds into a C2 input (1 input and 4 outputs). Figure 1 depicts a 10 km transport deployment leading to passive splitters C1 in Zone B01.
These splitters allow feeding 32 users from a single port of the OLT, grouped at an Optical Branching Point (PBO) of 6 or 12 connections per pole or on building facades. For instance, the SONATEL PBO 1-2A shown in Figure 1 consists of 6 optical fibers, including the 4 outputs from the first C2 coupler (F1 red, F2 blue, F3 green, and F4 yellow) and the first 2 outputs from the second C2 coupler (F5 violet and F6 white).
Upon reception, an Avalanche Photodetector (APD) detects the optical signal and converts it into an electrical signal. The signal is then transmitted through a Bessel low-pass filter. A 3R regenerator with a Bit Error Rate (BER) analyzer is used to measure the Quality Factor (Q) and the Bit Error Rate.
The Quality Factor (Q) is a function of the Optical Signal-to-Noise Ratio (OSNR) and is closely related to the BER through this relationship:
 | (1) |
Thus, the Quality Factor (Q) can be calculated using the following equation:
 | (2) |
In this equation, I1 and σ1 are the mean and variance values generated by the Gaussian pulse I, while I0 and σ0 are the mean and variance values generated by the Gaussian pulse 0 9. Additionally, apart from the long-distance installation costs, the recurrent or prolonged disruptions in Fiber To The Home (FTTH) networks necessitate an alternative technique to meet customer demands. As a result, the description of the components used in the simulation is provided in Table 1.
2.2. Study of FSO System ParametersThe solution to FTTH disruptions is provided by the integration of Free Space Optical (FSO) communication, which offers an added degree of mobility and an effective response to rapid backup connections for FTTH network link recovery. The FSO system relies on laser signal propagation through the atmosphere for data transmission. As such, FSO technology offers advantages like license-free operation, high traffic rates, robust security, full-duplex communication, protocol transparency, infrastructure flexibility, and cost-effectiveness 10.
Transmission occurs using 5 cm diameter lenses for transmitting the light signal and 25 cm lenses for receiving. The FSO communication is exposed to varying weather conditions, such as clear and rainy conditions in Dakar, Senegal. Consequently, visibility decreases under adverse conditions, leading to a reduction in system performance. Based on the attenuation coefficients in Table 2, our study focuses on an attenuation of 10 dB/km under rainy weath conditions for our FSO channel link in Dakar, Senegal.
The integration of a hybrid FTTH-FSO system is regarded as one of the most crucial technologies to address recurrent or prolonged network outages.
2.3. Study of the Hybrid FTTH-FSO Network IntegrationThe focus of this article is to replace the disrupted wired portion of the FTTH network, which occurs during construction or in inaccessible areas, with Free Space Optical (FSO) communication. In this study, the OptiSystem software is utilized to model the hybrid FTTH FSO network in order to assess its performance. Figure 2 depicts the deployment of several areas labeled as B01, B31, B32, and B33 at SONATEL, affected by the Bus Rapid Transit (BRT) project in Dakar, Senegal. Indeed, these areas are connected to the central hub via a transport cable containing approximately 144 optical fibers. This cable is impacted by the BRT construction work at a distance of around 600 meters.
The performance of the Free Space Optical (FSO) communication link is validated by comparing the proposed design results with the measurement standards from the Kim model 4. According to the Kim model standard, the acceptable lowest binary error rate in telecommunications is 10-9, and the Quality Factor Q is approximately 6 11. Indeed, replacing this large cable with FSO antennas introduces new challenges related to replacing multiple optical fibers with a single FSO antenna or one fiber per antenna depending on the affected distance.
The simulation is conducted using practical cable types such as a 36-fiber cable, a 12-fiber cable, or one fiber per antenna. Figure 3 illustrates the simulation of the hybrid FTTH-FSO network. This deployment involves a portion of the FTTH network and an FSO link to replace the disrupted wired section, approximately 600 meters long, under predefined atmospheric conditions. A power splitter with an input and a number of outputs equal to the number of optical fibers to be replaced by an FSO link is used, depending on the cable type (1FO, 12FO, or 36FO). The signal quality of the network is assessed at the ONT level.
The designs of the FTTH and hybrid FTTH-FSO networks were implemented using version 17 of the OptiSystem software to evaluate their performances.
3.1. Study on the FTTH NetworkThe design of the FTTH network depicted in Figure 1 accurately reflects the practical deployment of the network while adhering to power margins and signal quality. The photometric measurements at various output points, C2, C1, and OLT, are -21.696 dBm, -14.675 dBm, and -3.645 dBm, respectively. The quality of the received signal from an Optical Network Terminal (ONT) is evaluated through an eye diagram and in relation to the transmission threshold Bit Error Rate (BER) of 10-9, as illustrated in Figure 4.
This eye diagram enables experimental verification of the bandwidth limitation effect. Moreover, it serves as a general measurement of the received signal quality. Similarly, in a digital transmission system, the Bit Error Rate (BER) represents the ratio of incorrectly received bits to the transmitted bits. BER is a critical parameter as it provides a measure of the overall communication system quality. In this study, a very open eye diagram is observed with a BER of 4.8732 x 10-15 and a Quality Factor (Q) of 7.7414, as shown in Figure 4. These results indicate excellent signal quality and are consistent with measurements obtained from OLTs, C1, and C2 at SONATEL in Dakar, Senegal.
Our deployment model can serve up to 2048 users within a distribution area spanning up to 20 km. This stands in comparison to the model proposed by Abdellaoui 2, where a maximum of 128 users can be included in a network, with a maximum range of 60 km. Similarly, in the work of Al-Quzwini 3, the implemented FTTH network can accommodate 1000 users.
In Abdellaoui's work 2, where a linear attenuation of 0.25 dB/km is observed over a distance of 60 km in optical fiber, this corresponds to the insertion of an 8-way splitter (C1: 1 input and 8 outputs) in our short-range distribution area. Nonetheless, the quality of the FTTH network, while commendable, is often marred by recurrent and prolonged disruptions caused by civil engineering projects. This necessitates a preventive technique for the deployment and maintenance of the FTTH network.
As a result, the proposed technique involves replacing the wired segment affected by construction-related disruptions with Free Space Optical (FSO) communication. This approach aims to mitigate the impact of disruptions and ensure continuous and reliable connectivity for users.
3.2. Study of the Hybrid FTTH-FSO NetworkThis section verifies the feasibility of replacing a wired segment of the FTTH network with Free Space Optical (FSO) communication in a construction area of the BRT spanning 600 meters, as depicted in Figure 2 and designed as shown in Figure 3. The objective is to replace a cable containing 144 optical fibers with a minimal number of FSO antennas over a distance of 600 meters. To achieve this, an attenuation of 10 dB/km under rainy conditions is employed as the meteorological setting in Dakar.
Simulation results, following photometric measurements, demonstrate that the signal powers passing through the wireless zone and at the C1 and C2 outputs are -4.550 dBm, -13.781 dBm, and -20.001 dBm, respectively. Notably, these power values fall within the acceptable power margin of SONATEL FTTH network (greater than -24 dBm).
The assessment of signal quality in the hybrid FTTH-FSO link, aiming to replace 12 optical fibers with a single FSO link, is illustrated through the eye diagram in Figure 5(a). Under these meteorological conditions and at this distance of 680 meters, the Hybrid FTTH-FSO link performs effectively, resembling the FTTH network, with a Bit Error Rate (BER) of 7.85837 x 10-10 and a Quality Factor (Q) of 6.0059.
However, a cable containing 36 optical fibers can be replaced by a single FSO antenna for a maximum distance of 490 meters, ensuring good signal quality as depicted in Figure 5(b). This configuration achieves an excellent signal quality, yielding a Bit Error Rate (BER) of 2.90502 x 10-10 and a Quality Factor (Q) of 6.17288. This corresponds to signal powers traversing the wireless zone of -4.779 dBm, C1 output: -14.010 dBm, and C2 output: -20.231 dBm.
In contrast, for significantly greater distances, a single transported fiber can be replaced by Free Space Optical (FSO) communication up to 1200 meters. This achieves a BER of 3.66964 x 10-10 and a Quality Factor (Q) of 6.12007. Notably, this outcome corresponds to an open eye diagram, as illustrated in Figure 5(c).
The three types of FTTH-FSO deployments studied are depicted in Figure 6, illustrating the number of optical fibers to be replaced by an FSO link (36FO/FSO Antennas, 12FO/FSO Antennas, or 1FO/FSO Antennas). Figure 6 displays the BER (Bit Error Rate) signal quality for these three FTTH-FSO deployment types based on the FSO link distance. An abrupt increase in BER is observed for the 36FO/FSO Antennas and 12FO/FSO Antennas deployments at respective distances of 490 meters and 680 meters before reaching the BER threshold.
Based on the telecommunication BER threshold of 10-9, the 36FO/Antenna link can extend up to a distance of 490 meters with a BER of 2.90502 x 10-10 and a Quality Factor (Q) of 6.17288. On the other hand, the 12FO/FSO Antenna link can reach a distance of 680 meters with a BER of 7.85837 x 10-10 and a Quality Factor (Q) of 6.0059. This distinction is attributed to the use of a distributor with 36 outputs integrated at the end of the wireless link to replace the 36FO cable or a distributor with 12 outputs for the 12FO cable. The attenuation of these power splitters increases as the number of outputs rises.
In our case study, 12 FSO links are sufficient to replace the 144-fiber optical cable with Free Space Optical (FSO) communication throughout the BRT construction area. However, for much larger spaces, the 1FO/FSO Antenna link in Figure 6 can extend up to 1200 meters. Under the same rainy conditions, the signal quality is dependent on the FSO link distance. As the FSO link distance increases, the signal quality deteriorates, as previously demonstrated in the work of Alnajjar 4. This degradation is attributed to the absorption and refraction of optical signals by rainwater droplets, leading to intersymbol interference and consequently an increase in the bit error rate.
In the case of our point-to-multipoint distribution model, signal quality deteriorates when the network distribution becomes extensive. The deployment of 1FO/FSO Antenna serves 32 ONTs, while 12FO/FSO Antenna serves 384 ONTs, and 36FO/FSO Antenna serves 1152 ONTs.
Compared to the point-to-point FSO deployment model with a distance of 1.728 km in the work by Hameed 6, our point-to-multipoint model serving 32 ONTs can achieve an FSO distance of 1.2 km with a Bit Error Rate (BER) of 3.66964 x 10-10.
In this article, the performance of hybrid FTTH-FSO systems has been evaluated in terms of Bit Error Rate (BER) and Quality Factor (Q) using simulation with the Optisystem software. This study contributes to the development of a preventive technique for deploying and maintaining FTTH networks in inaccessible areas or construction sites.
Initially, the design of the FTTH network was carried out to locate the construction site of the BRT in order to determine the distance and the number of optical fibers to be replaced by an FSO link. Furthermore, for the practical distance affected by the extended construction works spanning a length of 600 meters, under rainy conditions, simulation results demonstrated the feasibility of deploying a 12FO/FSO Antenna link with a BER of 7.85837 x 10-10. Moreover, this allows us to replace a 144FO cable with 12 FSO antennas for a distance of 650 meters, or 4 FSO antennas for a distance of 450 meters. On the other hand, for longer distances of up to 1400 meters, a single fiber can be replaced by an FSO antenna.
However, to expand upon these findings, a multi-beam system could be considered for improved availability of hybrid FTTH-FSO links. Such a system could potentially increase the distance and the number of optical fibers that can be replaced by antennas.
Massaer Marone head of the fixed infrastructure curative maintenance service (MCIF) at SONATEL has read and accepted the published version of the manuscript.
The authors declare no conflicts of interest regarding the publication of this paper.
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| In article | View Article | ||
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| In article | View Article | ||
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| [9] | Huszaník, T., Turán, J., & Ovseník, Ľuboš. (2018). Simulation of Downlink of 10G-PON FTTH in the city of Košice. Carpathian Journal of Electronic and Computer Engineering, 11(1), 33-39. | ||
| In article | View Article | ||
| [10] | Hemanth, C., Sangeetha, R. G., & Jaiswal, I. (2023). Performance of orthogonal frequency division multiplexing based M‐ary quadrature amplitude modulation in asymmetrical dual‐hop mixed RF‐FSO transmission system. International Journal of Communication Systems, e5497. | ||
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Published with license by Science and Education Publishing, Copyright © 2023 Mamadou Sarr, Dialo Diop, Abel Sambou, Massaer Marone, Ndolane Diouf, Kharouna Talla and Aboubaker Chèdikh Beye
This work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit
https://creativecommons.org/licenses/by/4.0/
| [1] | Parca, G., Tavares, A., Shahpari, A., Teixeira, A., Carrozzo, V., & Beleffi, G. T. (2013, October). FSO for broadband multi service delivery in future networks. In 2013 2nd International Workshop on Optical Wireless Communications (IWOW) (pp. 67-70). IEEE. | ||
| In article | View Article | ||
| [2] | Abdellaoui, Z., Dieudonne, Y., & Aleya, A. (2021). Design, implementation and evaluation of a Fiber To The Home (FTTH) access network based on a Giga Passive Optical Network GPON. Array, 10, 100058. | ||
| In article | View Article | ||
| [3] | Al-Quzwini, M. M. (2014). Design and Implementation of a Fiber to the Home FTTH Access Network based on GPON. International Journal of Computer Applications, 92(6). | ||
| In article | View Article | ||
| [4] | Alnajjar, S. H., & Arif, F. A. R. (2021, February). Performance Optimization of Hybrid ROFSO Link Using Hybrid Optical Amplifiers (RAMAN\EDFA) for Long-Haul Transmission with the C-band and L-band Comparison. In IOP Conference Series: Materials Science and Engineering (Vol. 1094, No. 1, p. 012061). IOP Publishing. | ||
| In article | View Article | ||
| [5] | Shahpari, A., Abdalla, A., Ferreira, R., Parca, G., Reis, J. D., Lima, M., ... & Teixeira, A. (2014). Ultra-high-capacity passive optical network systems with free-space optical communications. Fiber and Integrated optics, 33(3), 149-162. | ||
| In article | View Article | ||
| [6] | Hameed, N., Mehmood, T., & Manzoor, H. U. (2017). Effect of Weather Conditions on FSO link based in Islamabad. arXiv preprint arXiv:1711.10869. | ||
| In article | |||
| [7] | Mazzei, C., Crescitelli, M., Fioramanti, D., Quagliarini, A., Reale, A., & Brunetti, F. (2023). Technical–economic analysis to identify the acceptable maximum attenuation on PON FTTH lines for wholesale network operators. Scientific Reports, 13(1), 12327. | ||
| In article | View Article PubMed | ||
| [8] | Fauzi, A. (2022). Perancangan Konfigurasi FTTH Jaringan Akses Fiber Optik Dengan Optisystem Dalam Modul Praktikum Komunikasi Optik. IJAI (Indonesian Journal of Applied Informatics), 5(2), 146-154. | ||
| In article | View Article | ||
| [9] | Huszaník, T., Turán, J., & Ovseník, Ľuboš. (2018). Simulation of Downlink of 10G-PON FTTH in the city of Košice. Carpathian Journal of Electronic and Computer Engineering, 11(1), 33-39. | ||
| In article | View Article | ||
| [10] | Hemanth, C., Sangeetha, R. G., & Jaiswal, I. (2023). Performance of orthogonal frequency division multiplexing based M‐ary quadrature amplitude modulation in asymmetrical dual‐hop mixed RF‐FSO transmission system. International Journal of Communication Systems, e5497. | ||
| In article | View Article | ||
| [11] | Wandernoth, B. (1994). 5 photon/bit low complexity 2 Mbit/s PSK transmission breadboard experiment with homodyne receiver applying synchronization bits and convolutional coding. In Proceedings (Vol. 1, pp. 59-62). | ||
| In article | |||
