Design and performance analysis of a 56 Gb/s DSP-enabled integrated SMF-FSO transmission link using IQ-modulated 16-QAM signals under diverse Indian climatic conditions

Abstract The design, analysis of performance of a 56 Gb/s integrated 50 km single mode fiber (SMF)-free space optics (FSO) link with 16-quadrature amplitude modulated (16-QAM) in-phase quadrature signals is presented. For the mitigation of SMF and FSO induced impairments, a receiver-side digital signal processing (DSP) chain is used, which consists of an adaptive equalizer, a frequency-offset estimation, and a carrier-phase estimation. The link is evaluated in four climatically different Indian cities of coastal-tropical (Chennai, 1.13 dB/km), semi-arid (Jodhpur, 4.696 dB/km), humid-coastal (Mumbai, 4.974 dB/km), and Himalayan-foggy (Srinagar, 13.59 dB/km). The performance is evaluated using the logarithmic bit-error-rate (log(BER)), error vector magnitude (EVM%), and received optical power (ROP) as a function of the FSO range, for receiver aperture diameters of 10, 15, and 20 cm. The maximum FEC-limited ranges for the 20 cm aperture are 9, 3.75, 3.5, and 1.65 km for Chennai, Jodhpur, Mumbai, and Srinagar, respectively. Smaller apertures will have shorter ranges because the collected power is lower.