Performance Improvement for Mixed RF–FSO Communication System by Adopting Hybrid Subcarrier Intensity Modulation

Jiang Jiang,Wei Wei,Luo Luo,Deng Deng,Liu Liu,Zhao Zhao,Yang Yang

doi:10.3390/app9183724

Jiang Jiang, Wei Wei + Show 5 more

Open Access

https://doi.org/10.3390/app9183724

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Journal: Applied sciences	Publication Date: Sep 6, 2019
Citations: 9	License type: CC BY 4.0

Affiliation: South China Normal University

Abstract

The improvement for hybrid radio frequency–free space optical (RF–FSO) communication system in wireless optical communications has acquired growing interests in recent years, but rarely improvement is based on hybrid modulation. Therefore, we conduct a research on end-to-end mixed RF–FSO system with the hybrid pulse position modulation–binary phase shift keying–subcarrier intensity modulation (PPM–BPSK–SIM) scheme. The RF link obeys Rayleigh distribution and the FSO link experiences Gamma–Gamma distribution. The average bit error rate (BER) for various PPM–BPSK–SIM schemes has been derived with consideration of atmospheric turbulence influence and pointing error condition. The outage probability and the average channel capacity of the system are discussed as well. Simulation results indicate that the pointing error aggravates the influence of atmospheric turbulence on the channel capacity, and the RF–FSO systematic performance is improved obviously while adopting PPM–BPSK–SIM under strong turbulence and severe pointing error conditions, especially, when the system average symbol length is greater than eight.

Highlights

In the past ten years, the hybrid radio frequency–free space optical (RF–FSO) communication system has attracted great interest due to its advantages compared with FSO system and RF system, respectively
There are many modulations that can be used in the hybrid RF–FSO system, they have a large difference in systematic performance due to their different characteristics, such as power efficiency, bandwidth efficiency, and simplicity, the most intuitive way to evaluate the quality of a modulation method is the bit error rate (BER) of the system
The performance of the mixed RF–FSO system with hybrid pulse position modulation (PPM)–binary phase shift keying (BPSK)–SIM is shown in figures below, including outage probability performance, average BER, and average channel capacity

Summary

Introduction

In the past ten years, the hybrid radio frequency–free space optical (RF–FSO) communication system has attracted great interest due to its advantages compared with FSO system and RF system, respectively. Considering impacts of atmosphere including turbulence, pointing error, and pass fading, many channel models have been used to describe the hybrid RF–FSO system. The RF link follows Rayleigh distribution, the FSO link obeys Gamma–Gamma distribution, atmospheric turbulence and pointing error is taken into consideration, and the system adopts various hybrid PPM–BPSK–SIM, the receiver employs intensity modulation/direct detection (IM/DD). The unconditional bit error rate (BER) of the PPM–BPSK–SIM is derived, it is noteworthy that the application of hybrid PPM–BPSK–SIM does bring optimization to the hybrid RF–FSO system performance from simulation results.

System and Channel Model

Outage Probability

Average Bit Error Rate

Average Capacity h i

Results and Discussion

Average

Conclusions