Morötesi haberleşme için çeşitleme teknikleri

Strong molecular and aerosol scattering in ultraviolet (UV) wavelengths enable mechanisms where transmitter can communicate with the receiver in the absence of line of sight (LOS) link. Recent advances in solid state technologies have enabled the production of efficient semiconductor ultraviolet (UV) LED sources and detectors which led to a renewed interest in UV communication. Non-line-of-sight (NLOS) communication is particularly desirable to relax or eliminate pointing, acquisition and tracking requirements‎. ‎This thesis investigates spatial diversity techniques for NLOS UV communication systems‎. ‎Particularly‎, ‎we explore cooperative diversity in the form of relaying and multi-input multi-output (MIMO) communications to extract spatial diversity advantages.‎ ‎In the first chapter‎, ‎we provide an overview of NLOS UV communication discussing its advantages and applications and present a literature survey‎. ‎In the second chapter‎, ‎we present the NLOS UV channel model used in this thesis‎. ‎In third chapter‎, ‎we consider a cooperative UV system with orthogonal cooperation protocol and use DC biased optical orthogonal frequency division multiplexing (DCO-OFDM) as the underlying physical layer‎. ‎Under the assumption that turbulence can be ignored‎, ‎we study both amplify-and-forward (AF) and detect-and-forward (DF) relaying‎. ‎We analyze BER performance of the cooperative OFDM UV system under consideration and optimize the performance through optimal power allocation‎. ‎We also consider a variable-rate cooperative OFDM UV system and investigate bit loading (i.e.‎, ‎use of different modulation orders per subcarrier) in an effort to maximize the throughput.‎ ‎In the fourth chapter‎, ‎we further consider the effects of turbulence and investigate the performance of a multi-hop UV system with DF relaying‎. ‎Based on the asymptotic outage expressions‎, ‎we present a diversity gain analysis and obtain the diversity order as a function of link distance and system parameters‎. ‎In fifth chapter‎, ‎the performance of MIMO UV systems over turbulence channels is studied‎. ‎We derive BER expressions for MIMO UV systems over NLOS log-normal turbulence channels‎. ‎We also investigate the performance of single-input multiple-output (SIMO) and multiple-input single output (MISO) as special cases.‎