Abstract
In hybrid FSO/RF systems, mostly a hard switching mechanism is preferred in case of the FSO signal level falls below to the predefined threshold. In this work, a computationally simple approach is proposed to increase the utilization of the FSO channels bandwidth advantage. For the channel, clear air conditions have been supposed with the atmospheric turbulence. In this approach, FSO bit rate is adaptively changed to achieve desired BER performance. An IM/DD modulation, OOK (NRZ format) has been used to show the benefit of the proposed method. Furthermore, to be more realistic with respect to the atmospheric turbulence variations within a day, some experimental observations have been followed up.
Highlights
Due to the high date rate capability of optical transmitters and the advances in laser and optical components technology, free-space optical (FSO) systems for wireless communication channels have attracted considerable attention recently for many different applications, such as ground-ground, ground-to-satellite and inter-satellite links
Despite the advantages that an FSO system holds over RF links, the signal intensity fluctuations caused by atmospheric turbulence can seriously degrade the system performance
The existing work related to high data rate applications has focused on hybrid FSO/RF and FSO communication systems using OOK modulation [6], [7], [8]
Summary
Due to the high date rate capability of optical transmitters and the advances in laser and optical components technology, free-space optical (FSO) systems for wireless communication channels have attracted considerable attention recently for many different applications, such as ground-ground, ground-to-satellite and inter-satellite links. In heavy attenuation conditions the operation of an FSO link cannot be always maintained, which reduces the availability. This paper investigates the possible use of varying bit rate control to reduce the turbulence effect on laser performance, for different scintillation levels. A practical lookup table based bit rate tune-up scheme is proposed to maintain FSO link. In this way, the FSO link can be used as long as its bit rate is acceptable to channel; it demands no switching to the RF link. The system switches to the RF link if the atmospheric turbulence level in clear air conditions prevents from maintaining the FSO link’s BER performance.
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