Abstract
This article investigates the performance of free-space optical (FSO) systems using sub-carrier quadrature amplitude modulation (SC-QAM) signaling for broadband terrestrial applications. While previous studies ignored the influence of phase noise, we theoretically analyze and derive closed-form expressions of the system's average bit error rate (ABER) considering the combined effect of pointing misalignment, turbulence-induced fading, and phase error. The log-normal distribution is used to model the atmospheric turbulence in the weak regime while the gamma-gamma distribution is applied for modeling the turbulent atmosphere in the moderate and strong regimes. The phase error, which becomes complicated under the effect of atmospheric turbulence, is modeled by Tikhonov distribution. The numerical results reveal that the influence of the phase error on the system performance is dominant in the weak turbulence and high order modulation while the fading becomes more severe in the moderate-to-strong turbulence regime. The accuracy of analytical results is also validated by Monte-Carlo simulations and a good match can be confirmed.
Highlights
Over the past decade, the ever-increasing demand for highspeed wireless applications has been resulting in the spectrum congestion problem in radio frequency (RF) communications [1]
In the case of weak turbulence modeled by log-normal distribution with Cn2 = 10 15, Fig. 8 compares performances of di↵erent quadrature-amplitude modulation (QAM) constellation sizes (e.g. 4 ⇥ 4 and 8 ⇥ 4 QAM) for di↵erent values of the average signal-to-noise ratio (SNR) per bit where the link length is set to 1000 m
Similar to phase-shift keying (PSK), it is evident that the performance loss due to phase error increases proportionally in accordance with an increase in the modulation order
Summary
The ever-increasing demand for highspeed wireless applications has been resulting in the spectrum congestion problem in radio frequency (RF) communications [1]. Nguyen et al.: Performance of Generalized QAM/FSO Systems with Pointing Misalignment and Phase Error over Atmospheric Turbulence Chann receiver. To the best of the authors’ knowledge, aside from the conference version of this paper [36], there has been no study on the performance analysis of SIM-QAM FSO systems considering the impact of phase errors in the literature. It has been shown in previous works that the influence of phase errors is proportional to the modulation order in the case of PSK. To facilitate the performance analysis of high-order modulation schemes like QAM, it is common to use the SNR per bit, which is b
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