Abstract
In this paper, 10 Gb/s free space optical (FSO) wiretap channel using optical code division multiple access (OCDMA) time-diversity reception is designed and demonstrated for the first time. Reliability and security are investigated under weak and strong turbulence conditions. Two-dimensional optical encoder and decoder are constructed by wavelength selective switches and optical delay lines, and one-dimensional optical encoder and decoder are constructed by couplers and tunable optical delay lines. Experimental results show that reliability and security can be enhanced simultaneously using OCDMA time-diversity reception. At the received power of 2.58 dBm in strong turbulence, compared to non-diversity system, bit error rate (BER) of legitimate user in OCDMA time-diversity system is reduced from 3.9 × 10−7 to 6.73 × 10−8. Furthermore, the reliability improvement is more obvious when the correlation between the two signals of OCDMA time-diversity is smaller. The secrecy capacity can be increased from 0.546 bit/symbol to 0.665 bit/symbol in strong turbulence when received power is 2.28 dBm. On the other hand, the secrecy capacity of strong turbulence is about 15% higher than that of weak turbulence.
Highlights
Free space optical (FSO) communications are highly susceptible to atmospheric turbulence, which can cause fluctuations in both the intensity and the phase of the received signal [1], [2]
Two-dimensional optical encoder and decoder are constructed by wavelength selective switches and optical delay lines, and one-dimensional optical encoder and decoder are constructed by couplers and tunable optical delay lines
At the received power of 2.58 dBm in strong turbulence, compared to non-diversity system, bit error rate (BER) of legitimate user in optical code division multiple access (OCDMA) time-diversity system is reduced from 3.9 × 10−7 to 6.73 × 10−8
Summary
Free space optical (FSO) communications are highly susceptible to atmospheric turbulence, which can cause fluctuations in both the intensity and the phase of the received signal [1], [2]. By establishing the eavesdropping model of the FSO/CDMA wiretap channel, the performance of physical-layer security and reliability are evaluated simultaneously in [24]. OCDMA based hybrid FSO/fiber wiretap channel is proposed in [25], and the physical-layer security is analyzed theoretically, using the conditional secrecy outage probability as the performance metric. This paper only analyzes the performance of hybrid FSO/fiber wiretap channel, and does not study how to overcome the effect of atmospheric turbulence. Based on the binary asymmetric channel model, the physical-layer security performance of the time-diversity FSO/CDMA is analyzed theoretically in [27]. For the first time, we design and demonstrate a 10 Gb/s FSO wiretap channel using OCDMA time-diversity reception in weak and strong turbulence conditions.
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