Abstract: Wireless designers constantly seek to improve the data rate, spectral efficiency, coverage of wireless networks and link reliability. Orthogonal Frequency Division Multiplexing (OFDM) technique has been widely accepted for the transmission of high rate data. Multiple Input Multiple Output (MIMO) techniques provide strong diversity gain and can increase the link throughput with the use of Adaptive Modulation and Coding (AMC). The idea behind AMC is to dynamically adapt the modulation and coding scheme to the channel conditions so as to achieve the highest spectral efficiency at all times. Further MIMO schemes can be combined with OFDM as STBC-OFDM or SFBC-OFDM. Combining the advantages of space-time coding and OFDM is attractive in wireless system designs. However, one of the main drawbacks is its high sensitivity to frequency offsets since the orthogonality between sub carriers is destroyed thus leading to considerable system performance degradation. The Carrier Frequency Offset (CFO) arises mainly due to the Doppler shift and/or oscillator mismatch. Hence, the effect, estimation and correction of frequency offsets have been subject of intensive research in the decade. Performance of various MIMO techniques is evaluated with combination of OFDM. The objective is optimum combination of MIMO-OFDM in presence of CFO. This system is also implemented as per WiMAX standard. The performance is also observed with different modulation techniques and multiple antenna system for multi-users.
Keywords: Carrier frequency offset (CFO); Orthogonal Frequency Division Multiplexing OFDM; Multiple Input Multiple Output (MIMO); Space Time Block Code-OFDM (STBC-OFDM); Space Frequency Block Code-OFDM (SFBC-OFDM)