Threshold optimization for modified switching scheme of hybrid FSO/RF system in the presence of strong atmospheric turbu
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ORIGINAL PAPER
Threshold optimization for modified switching scheme of hybrid FSO/ RF system in the presence of strong atmospheric turbulence Shreesh Kumar Shrivastava1 · Sujata Sengar1 · Shree Prakash Singh1 · Soyinka Nath1 Received: 24 September 2018 / Accepted: 22 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In hybrid free space optical/radio frequency (FSO/RF) systems, switching between the optical and RF links depends on the optical and RF signal to noise ratio (SNR) threshold levels; therefore, the correct choice of these threshold levels is essential to make best use of the complementary nature of optical and RF links. Optimal selection of these threshold levels is the prime objective of this paper. A hybrid FSO/RF system using modified switching scheme with two optical and one RF threshold is considered. Here, we propose an algorithm to obtain the optimized thresholds, which yield minimum bit error rate (BER) for a given outage probability under a constraint on maximum transmitted power. The optimized thresholds are dependent on the average optical and RF SNR. Hybrid FSO/RF system use both optical as well as RF power. The average system SNR is computed by considering the actual optical and RF power consumption. Also the performance of the hybrid FSO/RF system is studied with respect to average system SNR using optimized optical and RF thresholds. This analysis reveals the existence of a critical operating point of average optical SNR, beyond which the system should be preferably operated to ensure minimum BER. Keywords Threshold optimization · Negative exponential · Outage probability · Average system SNR · Modified switching scheme · Hybrid FSO/RF system
1 Introduction The hybrid FSO/RF system exploits the complementary features of FSO (Free Space Optical Communication) and RF (radio frequency) links to form a high speed and more reliable all-weather system as opposed to individual FSO or RF systems. As long as optical channel conditions are favorable, data are transmitted via the optical (FSO) link. In the event of optical link degradation, a ‘stand-by’ RF link is enabled, and data transmission is switched from the optical to the RF * Sujata Sengar [email protected] Shreesh Kumar Shrivastava [email protected] Shree Prakash Singh [email protected] Soyinka Nath [email protected] 1
Division of Electronics and Communication Engineering, Netaji Subhas Institute of Technology, Sector‑3, Dwarka, New Delhi 110078, India
link [1, 2]. This mode of switching, where, either the optical or the RF link is active is known as ‘hard switching’ [3]. In some variants of the hybrid FSO/RF system, both the optical and RF links may be active simultaneously, which is known as ‘soft switching’ [4]. Here, data rate of the FSO and RF links are adjusted according to channel conditions. A third variant of switching-‘hybrid switching’ [5] causes the data to be switched between two modes of transmission. In mode one, the data are transmitted through the optical link o
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