  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.
