An average bit error ratio (ABER) performance model for multiple phase shift keying (MPSK) based on a balanced detector with a fiber is presented in the free-space link for the first time. The Johnson S B probability distribution function (pdf), to the best of our knowledge, is first experimentally explored, which can be used to describe the fading characteristics of an optical signal coupled into a single-mode fiber (SMF) in an atmospheric turbulence channel. Subsequently, an ABER expression is established by combining the photon characteristics of the balanced detector with the fiber. The numerical results show that the system has the most superior ABER performance when the splitting ratio is 0.5 and the quantum efficiency of the two photodetectors is equal. Moreover, the communication performances can be optimized by adjusting parameters, such as increasing the system bandwidth, selecting the appropriate modulation order, and improving the received optical power. Finally, the MPSK-signal-to-noise-ratio (SNR) model is also studied to evaluate system communication performance. Through our asymptotic analysis, if the required ABER falls below the 7% forward error correction (FEC) limit of 3.8 × 10 −3 , the SNR should maintain at least 38 dB or more, while the normalized fluctuation variance deteriorates to 5.2441. This paper provides a parameter reference for designing the MPSK free-space optical (FSO) communication system, especially the fiber-coupling receiver.
We characterize the performance of the optical signal propagation model of multi-level pulse amplitude modulation (M-PAM) based on avalanche photodiode (APD) detector in the free-space link for the first time. When the number of photons absorbed by the active surface of the APD is large enough, the bit error rate (BER) performance relationship of the systems based on the signal intensity and the photon characteristics are depicted. We use the Gamma-Gamma (G-G) channel model to analysis the communication systems with joint parameter constraints, and demonstrate the atmospheric turbulence intensity, link lengths, optical wavelength, symbol transmission rate, temperature of APD and pointing errors (PEs) impact on the system average bit error rate (ABER) performance. Moreover, the relationship between signal-to-noise-ratio (SNR) and ABER rate is given. The numerical results show that the 4-PAM free-space optical (FSO) communication is suitable for medium-to-weak turbulence, and the high gain of APD can mitigate the influence of ABER. The best detection condition of the 4-PAM optical signal is at least 20 dB SNR, when the ABER is under the 7% forward error correction (FEC) limit of 3.8 × 10. This work provides a reference for parameter designing and evaluating in M-PAM FSO communication systems.
The data transmission between 5G floating base stations will be an important application area of the free space optical (FSO) link, but the problem of atmospheric disturbance will directly affect the application effect. An atmospheric turbulence suppression algorithm based on avalanche photodiode adaptive gain control (APDAGC) for the laser transmission terminal was proposed to suppress atmospheric turbulence. The given design mechanism and experimental results demonstrate its function to improve the performance of FSO. When APDAGC is over 1 km FSO, the variance of intensity fluctuation is lowered from 0.046 to 0.009, with the bit error rate reduced from 4.82E-6 to 1E-12. Comparatively, as APDAGC is over 6.5 km FSO, the variance of intensity fluctuation is decreased from 1.767 to 0.376, with the bit error rate varying from 4.6E-2 to 2.4E-4. Moreover, it was used for the first FSO transmission of 5G floating base station signals on an airship platform.
We report on a communication link demonstration in a 1 km simulated atmospheric turbulent channel with a wide-spectral mode-locking fiber laser. Wide-spectral beams are part of the supercontinuum, which is generated from pumping a dispersion-shifted fiber by an active mode-locked fiber laser. In addition, the propagation effects of wide-spectral beams were investigated experimentally in a simulated atmosphere channel. The characteristics of bit error rate and eye pattern before and after turbulence were analyzed, respectively. The experimental results showed that the sensitivity of the whole link reaches -40 dBm. The scintillation index of free-space optical communication between wide-spectral partially coherent and narrow-spectral coherent beams was compared, which indicates that the wide-spectral partially coherent optical communication link is more resistant to atmospheric turbulence. We experimentally verified that the scintillation index of wide-spectral carriers is dependent on coherent degree rather than spectral width.
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