10,153 research outputs found
Relay-Assisted Free-Space Optical Communications
The atmospheric lightwave propagation is considerably influenced by
the random variations in the refractive index of air pockets due to
turbulence. This undesired effect significantly degrades the
performance of free-space optical (FSO) communication systems.
Interestingly, the severity of such random degradations is highly
related to the range of atmospheric propagation. In this thesis, we
introduce relay-assisted FSO communications as a very promising
technique to combat the degradation effects of atmospheric
turbulence. Considering different configurations of the relays, we
quantify the outage behavior of the relay-assisted system and
identify the optimum relaying scheme. We further optimize the
performance of the relay-assisted FSO system subject to some power
constraints and provide optimal power control strategies for
different scenarios under consideration. Moreover, an application of
FSO relaying technique in quantum communications is investigated.
The results demonstrate impressive performance improvements for the
proposed relay-assisted FSO systems with respect to the conventional
direct transmission whether applied in a classical or a quantum communication channel
Game-Theoretic Spectrum Trading in RF Relay-Assisted Free-Space Optical Communications
This work proposes a novel hybrid RF/FSO system based on a game theoretic
spectrum trading process. It is assumed that no RF spectrum is preallocated to
the FSO link and only when the link availability is severely impaired by the
infrequent adverse weather conditions, i.e. fog, etc., the source can borrow a
portion of licensed RF spectrum from one of the surrounding RF nodes. Using the
leased spectrum, the source establishes a dual-hop RF/FSO hybrid link to
maintain its throughout to the destination. The proposed system is considered
to be both spectrum- and power-efficient. A market-equilibrium-based pricing
process is proposed for the spectrum trading between the source and RF nodes.
Through extensive performance analysis, it is demonstrated that the proposed
scheme can significantly improve the average capacity of the system, especially
when the surrounding RF nodes are with low traffic loads. In addition, the
system benefits from involving more RF nodes into the spectrum trading process
by means of diversity, particularly when the surrounding RF nodes have high
probability of being in heavy traffic loads. Furthermore, the application of
the proposed system in a realistic scenario is presented based on the weather
statistics in the city of Edinburgh, UK. It is demonstrated that the proposed
system can substantially enhance the link availability towards the
carrier-class requirement
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