KEYWORDS: Turbulence, Signal to noise ratio, Free space optics, Receivers, Telecommunications, Monte Carlo methods, Systems modeling, Statistical analysis, Free space optical communications, Satellites
In this letter, we study the average bit-error-rate (BER) performance of coherent free space optical communication systems with selection combining (SC) receive diversity over correlated Gamma-Gamma channels under non-Kolmogorov turbulence. Novel and computationally efficient analytical expressions over correlated and independent Gamma-Gamma channels of the average BER are derived. Then using these analytical expressions, we analyze the effects of the spectral power law and the channel correlation coefficient on the average BER performance. The correctness of the analytical results is verified by Monte Carlo simulation. This work will help with the further investigation of the fading correlation in the spatial diversity systems.
Chaotic optical communication is a secure communication method which uses synchronous chaotic carrier to realize encryption and decryption. With the demand for information security increasing, chaotic encryption has been applied to space optical communication experimentally. However, due to the complexity of chaotic system design, the bit error rate (BER) of space chaotic optical communication system is much higher than that of traditional one. High BER limits the bitrate of space chaotic optical communication while bitrate is quite important since a large amount of information needs to be transmitted in space downlink. According to our previous work, introducing two diffractive optical elements (DOEs) into optical subsystem can improve transmission efficiency, which equals to increasing transmission power. In this manuscript, we further investigate the effect of DOEs on BER and propose some suggestions on BER enhancement of space downlink chaotic optical communication.
When optical chaos communication system is applied to space optical communication, some necessary structural modifications are needed, and atmospheric effects are required to be considered. As one of these effects, beam spreading can affect the bit error rate (BER) of space optical chaos communication system under nonzero detector mismatch. To study the specific effect of beam spreading on the system BER, we make a formula modification including this effect. And based on the derived formula, we conduct a numerical simulation of the system BER under different detector mismatches. In our numerical simulation, we select the five typical system parameters of such system, which are synchronization error, zenith angle, transmitting power, divergence angle, and receiving diameter, and obtain their relationships with the BER. Corresponding discussions are made according to our results, which are beneficial to practical application of space optical chaos communication system.
Numerous communication techniques and optical devices successfully applied in space optical communication system indicates a good portability of it. With this good portability, typical coherent demodulation technique of Costas loop can be easily adopted in space optical communication system. As one of the components of pointing error, the effect of jitter plays an important role in the communication quality of such system. Here, we obtain the probability density functions (PDF) of different jitter degrees and explain their essential effect on the bit error rate (BER) space optical communication system. Also, under the effect of jitter, we research the bit error rate of space coherent optical communication system using Costas loop with different system parameters of transmission power, divergence angle, receiving diameter, avalanche photodiode (APD) gain, and phase deviation caused by Costas loop. Through a numerical simulation of this kind of communication system, we demonstrate the relationship between the BER and these system parameters, and some corresponding methods of system optimization are presented to enhance the communication quality.
CMOS is a good candidate tracking detector for satellite optical communications systems with outstanding feature of
sub-window for the development of APS (Active Pixel Sensor) technology. For inter-satellite optical communications
it is critical to estimate the direction of incident laser beam precisely by measuring the centroid position of incident beam
spot. The presence of detector noise results in measurement error, which degrades the tracking performance of systems.
In this research, the measurement error of CMOS is derived taking consideration of detector noise. It is shown that the
measurement error depends on pixel noise, size of the tracking sub-window (pixels number), intensity of incident laser
beam, relative size of beam spot. The influences of these factors are analyzed by numerical simulation. We hope the
results obtained in this research will be helpful in the design of CMOS detector satellite optical communications systems.
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