Abstract
In this paper, we derive the average bit error rate (BER) of subcarrier multiplexing (SCM)-based free space optics (FSO) systems using a dual-drive Mach-Zehnder modulator (DD-MZM) for optical single-sideband (OSSB) signals under atmospheric turbulence channels. In particular, we consider the third-order intermodulation (IM3), a significant performance degradation factor, in the case of high input signal power systems. The derived average BER, as a function of the input signal power and the scintillation index, is employed to determine the optimum number of SCM users upon the designing FSO systems. For instance, when the user number doubles, the input signal power decreases by almost 2 dBm under the log-normal and exponential turbulence channels at a given average BER.
Highlights
Nowadays, as Internet is widely spread, a volume of multimedia traffic is streamed into networks and the number of users is ever increasing
We focus our investigation on the worst performances among the subcarrier multiplexing (SCM) group due to the IM3 components, since the worst performance may limit the whole system
Since signal-to-noise-and-distortion ratio (SNDR) is sensitive to the input signal power and the total number of users (M), as shown in (14), in Fig. 2(a) we present the average bit error rate (BER) as a function of the input signal power according to the total number of users under the log-normal and the exponential channels
Summary
As Internet is widely spread, a volume of multimedia traffic is streamed into networks and the number of users is ever increasing. The primary methods for enhancing the performance of the SCM based FSO systems has been to increase the signal power to ensure a high signal-to-noise ratio (SNR). This increase in power results in problems that degrade system performance, such as an increase of laser relative intensity noise (RIN), and harmonic distortion from the Mach-Zehnder modulator (MZM) and other devices in FSO systems. Among these degradation factors, intermodulation distortion can significantly degrade the system performance because intermodulation power is typically higher than noise power in systems with high input power [3]. Numerical results are provided to illustrate the degradation of performance according to the input signal power and the scintillation index
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