Performance analysis of FSO/CDMA system based on binary symmetric wiretap channel

Transmission reliability, security, and efficiency are of great importance to free space optical (FSO) communication. For the first time, the authors obtain optimal parameters for the FSO/code division multiple access (CDMA) system taking into account the transmission reliability, security, and efficiency simultaneously. By establishing the eavesdropping model of the FSO/CDMA binary symmetric wiretap channel (BSWC), the performance of physical-layer security and reliability are evaluated simultaneously. Intercept probability is derived for FSO/CDMA BSWC, considering atmospheric attenuation, atmospheric turbulence, shot noise, thermal noise, background noise and multiple access interference (MAI). The effects of transmission distance, code length, transmission power and a number of interfering users on the physical-layer security and reliability are discussed. It is shown that, in order to meet the legitimate user's reliability and security simultaneously, the number of interfering users and code length must be in a certain interval. Furthermore, the maximum spectral efficiency can be obtained by selecting the transmission rate. These results open a new way of researching the FSO/CDMA system, where security, reliability, and spectral efficiency should be taken into account simultaneously.