FDM FSO communication system with coherent heterodyne optical receiver under strong turbulent condition
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RESEARCH ARTICLE
FDM FSO communication system with coherent heterodyne optical receiver under strong turbulent condition Bobby Barua1
•
S. P. Majumder2
Received: 29 July 2018 / Accepted: 19 July 2020 Ó The Optical Society of India 2020
Abstract We provide an analytical approach to analysis the performances of FDM FSO communication system with coherent heterodyne optical receiver under strong turbulent condition which is modeled as gamma–gamma distribution. Analysis is carried out to find the bit error rate and channel capacity with RF subcarrier modulation taking into consideration the effect of strong atmospheric turbulence. Results are evaluated numerically in terms of average CNR, BER, channel capacity and power penalty suffered by the system due to the effect of turbulence at a given BER for several system parameters like turbulence variance, link distance, local oscillator power, etc. It is observed that at a data rate of 10 Gbps with number of subcarrier 32, the power penalty at a BER of 10-9 is 12 dB for a link distance of 3.6 km and the performance improves gradually with increasing the number of RF subcarriers. It is also observed that, the overall performance improves with the improvement in both RF and optical local oscillator power. Keywords Coherent optical receiver Carrier to noise ratio (CNR) Free-space optical (FSO) communication Gamma–gamma distribution Subcarrier multiplexer
& Bobby Barua [email protected] 1
Ahsanullah University of Science and Technology, Dhaka, Bangladesh
2
Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
Introduction Free-space optical (FSO) communication system is the alternative solutions to fiber network where the light waves propagate through air [1, 2]. But the optical wave propagation through the air experiences fluctuation in amplitude and phase due to atmospheric turbulence [3]. A number of turbulence mitigation methods for FSO systems have been reported in the literature [4–10]. The technology that combines RF carrier modulation in FSO helps to improve the performance of FSO communication under turbulent condition. However, as the symbol duration reduces with the increase in data rate, the system using single carrier modulation suffers from more severe intersymbol interference (ISI) caused by the dispersive fading of FSO channels. So it is important to introduce multiple subcarrier modulation in FSO. However, the multiple subcarriers modulated (MSM) FSO system performance may be conspicuously degraded due to the LD nonlinearity that causes mixing of user signals, resulting in generation of harmonics and intermodulation distortions (IMD). Several research works on multiple subcarrier modulation have already been developed to reduce the atmospheric effect. Most of the research works are performed on direct detection optical receiver [4–9]. But in direct detection, the receiver photodetector directly detects changes in the light intensity without the need for a local oscillator [5]. Although coherent FSO communication systems offer sup
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