In this book, first OFDM systems and related structures are elaborated; then multi-antenna systems namely MIMO are explained. Indeed Blind estimation CFO for MIMO-OFDM systems is analyzed. Since calculating the exact value of CFO in an OFDM modulation-based system is significant, proposing an exact method for evaluation of CFO shows its importance. Thus, in this book some methods with the least complications are studied in which their semi-optimized algorithms are mostly optimized. Results indicate that selected methods enjoy less complexities compared with current methods. It is concluded that simulated methods can be proper substitute for optimized method due to its complexity and delay, and not suitability for real time systems. Because of low level of calculations and simple equipment of detection, these algorithm semi-optimized can be implemented practically in real time systems.