Performance study of multi-hop coherent OFDM FSO system over M distribution model

Wu Hao; Wang Yi

doi:10.12086/oee.2020.190337

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Wu H, Wang Y. Performance study of multi-hop coherent OFDM FSO system over M distribution model[J]. Opto-Electron Eng, 2020, 47(1): 190337. doi: 10.12086/oee.2020.190337

Citation:

Wu H, Wang Y. Performance study of multi-hop coherent OFDM FSO system over M distribution model[J]. Opto-Electron Eng, 2020, 47(1): 190337. doi: 10.12086/oee.2020.190337

Performance study of multi-hop coherent OFDM FSO system over M distribution model

Wu Hao^1,,
Wang Yi^1,2,3, ,

1.
Key Laboratory of Electromagnetic Wave Information Technology and Metrology of Zhejiang Province, College of Information Engineering, China Jiliang University, Hangzhou, Zhejiang 310018, China
2.
State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, Guangdong 510641, China
3.
State Key Laboratory of Deep Sea Manned Vehicles, Wuxi, Jiangsu 214082, China

Fund Project: Supported by National Natural Science Foundation of China (51704267), Open Fund of State Key Laboratory of Luminescent Materials and Devices (South China University of Technology) (2019-skllmd-13), and the State Key Laboratory of Deep Sea Manned Vehicles (702SKL201702)

More Information

^*Corresponding author: Wang Yi, E-mail:wcy16@cjlu.edu.cn

Received Date 19 June 2019

Revised Date 30 September 2019

Published Date 01 January 2020

Abstract

Abstract

The performance of multi-hop coherent orthogonal frequency division multiplexing (OFDM) free space optical (FSO) system is studied by using quadrature phase shift keying (QPSK) modulation in this paper. A generalized model called M distribution is selected, which is suitable for all categories of turbulence ranging from weak to strong and characterizes other existing statistical models of atmospheric turbulence induced fading as its special case. The system uses decode and forward (DF) relay protocol between the transmitter and receiver of the relay auxiliary link. Considering the joint attenuation effects of atmospheric turbulence, path loss and pointing error on the atmospheric channel fading model, we derive the Meijer G closed-form expressions of outage probability and symbol error rate (SER). Furthermore, the effects of key factors, such as relay link length, the number of relay nodes and subcarriers on the outage and SER performance of OFDM FSO system are analyzed through simulations. This work lays a theoretical foundation for the practical application of the relay system.
- free space optical /
- orthogonal frequency division multiplexing /
- multi-hop /
- M distribution model /
- quadrature phase shift keying

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References

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Overview

Overview

Overview: Free space optical (FSO) communication is a bidirectional communication system which is realized by laser signal propagating in atmospheric channel without optical fiber. It can quickly establish communication links in special complex terrain, which is considered as a practical solution to the "last mile problem." Nevertheless, the performance of FSO system is seriously limited by the combined effects of the atmospheric turbulence, atmospheric attenuation, and pointing error. In order to solve this problem, the addition of serial relay technology can effectively alleviate the deterioration of the performance of FSO system. In this paper, we investigate the performance of multi-hop coherent orthogonal frequency division multiplexing (OFDM) FSO system by using quadrature phase shift keying (QPSK) modulation. A generalized model called M distribution is selected, which is suitable for all categories of turbulence ranging from weak to strong and characterizes other existing statistical models of atmospheric turbulence induced fading as its special case. The system uses decode and forward (DF) relay protocol between the transmitter and receiver of the relay auxiliary link. Considering the joint attenuation effects of atmospheric turbulence, path loss and pointing error on the atmospheric channel fading model, we derive the Meijer G closed-form expressions of outage probability and symbol error rate. Furthermore, the effects of key factors, such as relay link length, the number of relay nodes and subcarriers on the outage and SER performance of OFDM FSO system are analyzed through simulations. It can be concluded from the simulation results that increasing the number of relay nodes and subcarriers, longer relay link, and higher atmosphere turbulence intensity will increase the outage probability and SER of the system. According to the analysis, it is suitable that the number of subcarriers and the relay link length are 256 and 1000 m, respectively. In addition, reducing the normalized threshold can reduce the outage probability of the system. Therefore, controlling the appropriate normalized threshold can improve the stability of communication system. At the same time, increasing the average signal-to-noise ratio can improve the system's symbol error performance. It is also known that when a relay node is added to the communication link, the outage probability and SER of OFDM FSO system increase obviously. With the relay node continuing to join, the downward trend of the outage and symbol error performance is getting smaller. Although the outage and symbol error performance is sacrificed with the increase of relay nodes, it solves the design problems of system links, such as making the transmitter and receiver unable to communicate when there are buildings blocking.