High spectral efficiency and high transmission data rate are the challenging requirements of wireless broadband communications. The MIMO technology has rapidly gained in popularity due to its powerful performance-enhancing capabilities. Spatial diversity can be obtained by using multiple antennas and space-time codes. For future wireless broadband systems, OFDM is discussed as access scheme. OFDM provides an essentially flat fading channel for each subcarrier by insertion of a cyclic guard interval at each antenna. Therefore, space-time block codes are well suited to be applied in OFDM. We investigate SFBC for OFDM systems with multiple transmit antennas, where coding is applied in the frequency domain rather than in the time domain. In this thesis, performance of two coding techniques STBC and SFBC is analyzed in OFDM. In order to appreciate the performances offered by coding through space and frequency, different simulation scenarios have been proposed where variation of the modulation order , channel fading, antenna selection technique, receiver diversity and effect of power conditions have been considered.