Cost-Effective Bidirectional SMF-FSO-5G NR Wireless System Employing FBG Sensors

This paper presents a cost-effective bidirectional communication system that integrates single-mode fiber (SMF), free-space optical (FSO) link, and a 5G new radio (NR) wireless links, employing FBG sensors. The sensors serve as wavelength selectors, reducing signal loss and system costs. This approach is simpler and more affordable than advanced filtering techniques, wavelength demultiplexers, and multiple distributed feedback laser diode sources. The system supports a downstream data rate of 120-Gb/s (3 × 40-Gb/s/100-GHz) using wavelength division multiplexing, while the upstream transmission supports 60-Gb/s (3 × 20-Gb/s/60-GHz). These data rates are transmitted over a 32 km SMF, a 1.6 km FSO, and a 25 m 5G NR wireless link. Experimental results show that removing the FBG sensor from the downstream receiver setup leads to significant signal degradation. Specifically, the bit error rate (BER) increases from 2.04×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>) to 4.68×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub>) and 2.29×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub>) to 5.75×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>). Similarly, the error vector magnitude (EVM) rises from 10.53% (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>) to 11.57% (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub>) and 10.70% (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub>) to 11.70% (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>). Moreover, the constellation patterns become less defined. Under foggy conditions, these issues become more severe, with BER and EVM increasing significantly. Thus, the presence of the FBG sensor in the downstream receiver setup improved system performance. This approach offers a cost effective solution for expanding 5G NR coverage.