The orthogonal frequency division multiplexing (OFDM) modulation is a multicarrier transmission, which has received considerable attention due to its robustness against inter-symbol interference (ISI) and multipath distortion, low implementation complexity and high spectral efficiency. However, one of the main disadvantages of OFDM based systems is the sensitivity to synchronization errors, characterized mainly by frequency and timing offsets. Frequency offset causes a reduction of desired signal amplitude and introduces inter-carrier interference (ICI). The timing offset originates the rotation of the OFDM subcarrier signal constellation. This thesis presents a contribution in timing and frequency synchronization for OFDM based systems. The contribution consist on propose modified timing metrics based on preamble sequences in configurations of short and long preamble. The proposed timing metrics are the result of a review of the state of the art of methods, and the corresponding analysis by simulation of timing and frequency synchronization errors. The new proposed timing and frequency synchronization methods are based on weighted preambles; these preambles are designed applying Golay-Rudin-Shapiro (GRS) sequences. GRS sequence exhibits good autocorrelation properties and reduced peak to average power ratio (PAPR), being useful characteristics to obtain algorithms with reduced mean square error (MSE) and improved response of the bit error rate (BER) in OFDM based systems.