Çok röleli serbest uzay optik haberleşme sistemlerinin başarım analizi

Free space optical (FSO) communication has attracted a great attention in recent years because of their high bandwidth capacity in unregulated spectrum which makes them a cost-effective and easy-to-install alternative to fiber optics. Moreover they provide high immunity to interference and jamming due to directional and narrow beams. FSO systems are appealing for number of applications including last-mile access, fiber back-up, back-haul for wireless cellular networks, and disaster recovery among others. The major degrading factor in these systems is atmospheric turbulence induced fading particularly for long range links. Relay-assisted FSO systems provide significant performance gains by using the advantage of shorter hops and the fact that fading variance is distance dependent in FSO channels. In this thesis, we investigate the performance of multi-relay FSO systems in various settings. In the first part of thesis, we consider an all-optical relaying system to remove the need for optical -electrical- optical conversions. We explore the benefits of relay selection and investigate its outage performance over Gamma-Gamma distributed turbulence channels. In the second part of thesis, we assume that source is equipped with multiple transmit apertures employing the so-called spatial pulse position amplitude modulation (SPPAM). We investigate an upper bound for bit error rate of this system with multiple parallel relays over log-normal distributed channels.