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The main characteristic of wireless communication is the randomness that can be seenboth in users transmission channels and in users geographical locations. These uncertaintieslead to random signal attenuation independently across users and across transmission chan-nels of individual users. This randomness can be used as a tool to enhance performancethrough diversity. We broadly define diversity as the method of conveying informationthrough multiple independent instantiations of these random attenuations. In wireless com-munication systems to increase system reliability various diversity techniques have beenproposed which can be collected under three domains, namely, temporal diversity, frequencydiversity and spatial diversity domains. Due to its efficiency in terms of system resourceusage, the diversity tool we utilize in the whole dissertation is spatial diversity which isattained through multiple spatially separate antennas and multiple geographically separate(independent) users.It has been shown that diversity techniques, when properly administered, may providetremendous gains to the performance of wireless systems. In this thesis, using tools providedby information theory, we propose a comparative study of the gains obtained by variousspatial diversity techniques. Under different channel condition and power allocation schemesthese diversity techniques will be compared and ones that give best results under differentconstraints will be clearly specified. Furthermore, impact of simultaneous use of multiplediversity techniques will be investigated.