Since a deep and long-term fading in optical intensity results in considerable burst errors in the data, a terrestrial free-space optical (FSO) system has to be designed with consideration of a frequency characteristic of optical scintillation to achieve high quality wireless services over the link. In designing a terrestrial FSO link, we had better design the system considering variations caused by some slow time-varying parameters. This paper proposes a Butterworth-type spectral model of optical scintillation to design a terrestrial FSO link, which enables us to estimate the power spectral density of optical scintillation in a current optical wireless channel when time zone and weather parameters, such as temperature and rainfall intensity, are given. The spectral parameters of optical scintillation, cut-off frequency, and spectral slope are estimated from the data obtained in the experiment, and then their dependencies on time zone, temperature, and rainfall intensity are examined.
Proc. SPIE. 7620, Broadband Access Communication Technologies IV
KEYWORDS: Statistical analysis, Data modeling, Signal attenuation, Radio over Fiber, Free space, Free space optics, Scintillation, Atmospheric propagation, Atmospheric optics, Channel projecting optics
This paper presents empirical probability density functions (p.d.fs) of variance and fluctuation speed of scintillation,
through analyzing a number of experimental data measured in Japan by a statistical model. The model enables us to treat
scintillation speed by one parameter of cut-off frequency in the power spectral density (PDS). By using the model and
based on the two p.d.fs, we also present simulation results on the level crossing rate (LCR) and average fade duration
(AFD). Combined the two results, an outage probabilities corresponding to a threshold optical intensity can be derived.
This paper firstly derives a new model of RoFSO (Radio on Free Space Optics) channel considering fluctuation speed of
the scintillation and the probability density function (p.d.f) of the random and time-correlated optical intensity disturbed
by scintillation. The relationships among frequency characteristic of RoFSO channel, variance of received optical
intensity and atmospheric conditions (temperature and insolation) are statistically analyzed by the proposed model. By
using the proposed model and the relationships, the throughput performance of WLAN (802.11a) over RoFSO link is
evaluated with computer simulations. For two cases of without-shadowing and with-shadowing in the radio propagation
channel, evaluations of degradation due to scintillation are conducted. As a result, it is found that the degradation due to
scintillation is much smaller than that due to shadowing in the throughput performance for WLAN.