Search

In free-space optical communication (FSOC) systems, atmospheric turbulence can bring about power fluctuations in receiver ends, restricting channel capacity. Relay techniques can divide a long FSOC link into several short links to mitigate the fading events caused by atmospheric turbulence. This paper proposes a Reinforcement Learning-based Relay Selection (RLRS) method based on Deep Q-Network (DQN) in a FSOC system with multiple transceivers, whose aim is to enhance the average channel capacity of the system. Malaga turbulence is studied in this paper. The presence of handover loss is also considered. The relay nodes serve in decode-and-forward (DF). Simulation results demonstrate that the RLRS algorithm outperforms the conventional greedy algorithm, which implies that the RLRS algorithm may be utilized in practical FSOC systems. [ABSTRACT FROM AUTHOR]

In this paper, we analyze a combined terrestrial-underwater optical communication link for providing high-speed optical connectivity between onshore and submerge systems. For this purpose, different transmission signaling schemes were employed to obtain performance results in terms of average bit error rate (ABER). In this sense, from the starting point of a known conditional bit-error-rate (CBER) in the absence of turbulence, the behavior of the entire system is obtained by applying an amplify-and-forward (AF) based dual-hop system: The first link is a terrestrial free-space optical (FSO) system assuming a Málaga distributed turbulence and, the second one, is an underwater FSO system with a Weibull channel model. To obtain performance results, a semi-analytical simulation procedure is applied, using a hyper-exponential fitting technique previously proposed by the authors and leading to BER closed-form expressions and high-accuracy numerical results. [ABSTRACT FROM AUTHOR]

Abstract Space diversity of multiple-input multiple-output (MIMO) system combined with the adaptive subcarrier modulation technique can effectively reduce the atmospheric channel fading effects. Malaga turbulent probability density function is obtained based on the MeijerG function. The asymptotic expression of average bit error rate in non-adaptive and adaptive modulated MIMO wireless optical systems are derived respectively, and M-ary phase shift keying (MPSK) and M-ary differential phase shift keying (MDPSK) modulation are used in these two kinds of systems. Under moderate turbulence conditions, error performances are analyzed with numerical simulations between these two systems. The results show that the average bit error performance in the adaptive modulated system can be significantly better than the non-adaptive modulated system. But under the same conditions of modulation order and target bit error rate, error performance of non-adaptive modulation is easier to be affected by transmit and receive aperture number than adaptive modulation in MIMO system. [ABSTRACT FROM AUTHOR]

We investigate the influences of the phase noise induced by the demodulation module on the performance of subcarrier M-ary phase-shift keying (MPSK) optical communication system over turbulence channel. Novel asymptotic expression of average symbol error probability (SEP) is derived based on the Meijer's G function and Fourier series over Malaga turbulence. The Malaga channel model used in our study can be potentially applied to the performance analysis problems involving other turbulence channels. The influences of the phase noise and its truncation error on the SEP performance are analyzed under different turbulence conditions, phase noise deviation, and modulation order. It is illustrated that the phase noise significantly degrades the performance of the system over turbulence channel. The more truncated number of Fourier series is required to get the minimum truncation error when the phase noise is lower. Under turbulence conditions, the appearance of symbol error rate floor depends predominantly on the phase noise. [ABSTRACT FROM AUTHOR]