Optimization of MDM-FSO system with different encoding schemes
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ORIGINAL PAPER
Optimization of MDM-FSO system with different encoding schemes S Srivastava*, K K Upadhyay and N Singh Department of Electronics and Communication, University of Allahabad, Allahabad, UP, India Received: 12 January 2019 / Accepted: 09 September 2019
Abstract: Free space optical transmission has a wide area of applications in the field of digital services. It has special features such as low maintenance cost, licence-free and less deployment time. It is a solution to replace optical fiber cable for providing services in rural area. In this paper, the performance of the two independent channels LP01 and LP11 by mode-division multiplexing over free space optical (FSO) link is investigated. Each channel carries data at 10 Gbps data rate, and the data are transmitted over 8 km FSO link with NRZ/RZ encoding schemes. The performance of the MDM-FSO system is evaluated under atmospheric turbulences which gives better results in RZ encoding scheme as compared to NRZ scheme at acceptable level of SNR and BER. Keywords: Free space optics (FSO); Mode-division multiplexing (MDM); Linear polarization (LP); Signal-to-noise ratio (SNR) PACS Nos.: 42.30Lr; 42.50p; 42.64K; 42.79Sz; 42.82i
1. Introduction In the present era of information technology, free space optics (FSO) is a promising technology that can be used anywhere, anytime for transfer of information authentically and securely. FSO unified the features of optical and wireless communication technologies. In fiber optic communication, cost-effective optical network FSO consists of a high-speed optical carrier that stimulates transportation capacity [1]. FSO is the best option for the installation of new optical fiber network in rural areas. Transportation of signals via FSO link is highly secured [2]. There are many advantages of FSO communication systems in optical fiber network. There is no requirement of optical fiber; it is highly secured, consumes low power, has strong anti-jamming property, is less expensive and is costeffective [3]. FSO system requires no spectrum licencing; however, various atmospheric conditions in the tropospheric region affect the FSO links [4]. Transmission of modulated light through FSO link is influenced by numerous atmospheric parameters like scattering, absorption and non-selective scattering. Absorption occurs due to atmospheric gases and scattering and non-
selective scattering occur because of sizable raindrops [5]. Fog and heavy snow are the conspicuous weather condition to affect the FSO link in the temperate region [6, 7]. To increase the capacity of FSO system, mode-division multiplexing (MDM) is used [8–12]. MDM transmits a number of channels on different modes, and these modes are generated by different mechanisms such as spatial light modulators [13], optical signal processing [14, 15], few mode fiber [16–18], photonic crystal fiber and modal decomposition method [19]. The performance of MDM of two orbital angular momentum (OAM) modes generated by spatial laser modulators at 2 Tbps data rate are transmitted over 1
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