Performance analysis of EDFA-based all-optical relaying FSO-CDMA wiretap channel

Free space optical (FSO) communication has many advantages and is widely used in communication scenarios such as regional communications, emergency communications, and ground-to-air communications. But atmospheric turbulence and attenuation will reduce the reliability of FSO communication system. At the same time, beam spreading and atmospheric scattering will make it possible for FSO communication link to be eavesdropped. In order to improve the reliability and physical layer security of FSO communication, in this paper, we establish an EDFA-based all-optical relaying FSO-CDMA wiretap channel model. Bit error rates (BERs) of the legitimate user and eavesdropper (Eve) are analyzed theoretically, and secrecy capacity is calculated by the binary symmetric channel model. BER of Bob in relay system is significantly lower than that in non-relay system under weak or moderate turbulence. In two different turbulence cases, with the increase of transmission distance, the secrecy capacity increases at first, then decreases gradually. When the transmission distance is short, the secrecy capacity of the moderate turbulence system is larger than that of the weak turbulence system, while when the transmission distance is long, the secrecy capacity of the weak turbulence system is larger than that of the moderate turbulence system.