Multiple antenna systems are known to provide spatial diversity and spatialrnmultiplexing advantages in constructing a reliable and spectrally efficientrncommunication link. In spatial diversity scheme the same message or replica ofrnthe same message is transmitted from the number of transmit antennas inrnsuch a way that at least one of transmitted messages reaches the receiver withrnout error. In this scheme the main objective is reduction in the probability ofrnerror. Unlike spatial diversity, in spatial multiplexing scheme differentrnmessages are transmitted from each of the transmit antennas so that the raternof data transfer between the transmitter and receiver is increased. As far asrnpractical system is concerned it needs to have both advantages in order to haverna high data rate link with low probability of error.rnIn this thesis by adaptively varying the modulation order of the spatial diversityrnand spatial multiplexing systems both advantages are obtained for anrnapplication with a certain error rate performance requirement. The simulationrnresult has shown that the spatial multiplexing system has a higher throughputrnat high SNR values as compared to the spatial diversity system. At low SNRrnvalues, it is the spatial diversity system that results in high throughput. The MLrndetection of spatial diversity system has less computational complexity asrncompared to ML detection spatial multiplexing scheme.rnKeywords: Spatial Diversity, Spatial Multiplexing, Maximum LikelihoodrnDetection, Space Time Coding, D-Blast and V-Blast