Date Added: Dec 2012
The authors investigate transmission protocols for relay-assisted Free-Space Optical (FSO) systems, when multiple parallel relays are employed and there is no direct link between the source and the destination. As alternatives to all-active FSO relaying, where all the available relays transmit concurrently, they propose schemes that select only a single relay to participate in the communication between the source and the destination in each transmission slot. The selection is based on the channel state information obtained either from all or from the last used FSO links. Thus, the need for synchronization of the relays' transmissions is avoided, while the slowly varying nature of the atmospheric channel is exploited.