A comprehensive design is proposed for alternate mark inversion (AMI)-encoded free-space optical (FSO) communication system by hybridizing polarization division multiplexing (PDM) with wavelength division multiplexing (WDM) and its performance is investigated under diverse weather conditions. The WDM transmitter comprises eight channels transmitting 320 Gbps data over the atmospheric turbulent channel considering gamma–gamma (G–G) distribution for the FSO channel model. A PDM-WDM technique not only maximizes the link capacity of the FSO system but also enhances the spectral efficiency (SE) of the system. Besides, the proposed hybrid AMI-PDM-WDM FSO system performance is compared with the traditional AMI-WDM-PDM and AMI-WDM models to demonstrate the advantages of our proposed model for the design of FSO link. It is observed that our proposed hybrid system exhibits excellent performance under diverse weather conditions over the traditional models in terms of Q factor, received optical power, bit error rate (BER), eye diagrams and optical signal-to-noise ratio (OSNR).

A comprehensive design is proposed for the free-space optical (FSO) communication system by hybridizing circular polarization division multiplexing (CPDM) with coherent optical orthogonal frequency division multiplexing (CO-OFDM) and its performance is investigated realistically under diverse turbulent weather conditions of Bangladesh. Here, we consider Gamma–Gamma distribution for the turbulent FSO channel model. Moreover, the proposed scheme presents an excellent performance since the CPDM technique not only maximizes the link capacity of the FSO system but also enhances the spectral efficiency of the system. Besides, multipath fading, which is appeared during the FSO transmission, is significantly mitigated by OFDM modulation. The outcomes from the simulation confirm the advantages of the proposed hybrid scheme and also it can serve as a reference for the FSO application even in turbulent weather conditions. Performance analysis of the proposed model is described in terms of the optical power spectrum, optical signal-to-noise ratio, bit error rate, Q factor, constellation diagrams, and eye diagrams.

Free-space optical (FSO) communication system provides several advantages over radio frequency (RF) system offering high bandwidth, low cost, small space requirements and more secure transmission which is free from Electromagnetic Interference (EMI). However, when the transmitted light signal passes through the atmosphere it experiences attenuation and fluctuations due to atmospheric turbulence. This paper analyzes the bit error rate (BER) performance of FSO communication systems under strong atmospheric turbulence for on-off keying (OOK), binary phase-shift keying (BPSK), differential phase shift keying (DPSK), quadrature phase shift keying (QPSK) and 8-phase shift keying (8-PSK) for link distances of 500, 1,000, 1,500 and 2,000 m. The probability density function (pdf) of the received irradiance is modelled using the gamma-gamma distribution model. It is found that the system exhibits the best BER performance and compensates the lowest power penalty at BER of 10 - 9 for BPSK modulation compared with other modulation techniques which makes BPSK more appropriate to be used with FSO turbulent system.

A comprehensive design is proposed for free-space optical (FSO) communication system by hybridizing polarization division multiplexing (PDM) with wavelength division multiplexing (WDM) and its performance is investigated under diverse turbulent weather conditions of Bangladesh. Here we consider gamma–gamma (G–G) distribution for the turbulent FSO channel model. Moreover, a PDM-WDM technique not only maximizes the link capacity of FSO system but also enhances the spectral efficiency (SE) of the system. Besides, the performance of this hybrid PDM-WDM FSO system is compared with the traditional model and the proposed hybrid system exhibits excellent performance under diverse atmospheric conditions of Bangladesh. Performance analysis of the proposed model as well as the comparison with the traditional model is described in terms of optical power spectrum (OPS), optical signal to noise ratio (OSNR), bit error rate (BER), Q factor, constellation diagrams, and eye diagrams.

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