In this paper, the authors propose and analyses an efficient wireless telecommunication system with multiple antennas to the emission and reception MIMO (Multiple Input Multiple Output) with space diversity in an OFDM (Orthogonal Frequency Di vision Multiplex). The proposed system consists to add modified Alamouti encoder to the system OFDM to improve the performance of the destination by intimately collaborating with the antennas system. They analyze the performance of a DTT (Digital Terrestrial Television) broadcasting system that includes MIMO encoder, associate with OFDM techniques, which can improve the appreciation of the quality of transmission Bit Error Rate (BER) in terms of (C/N) Carrier-to-Noise ratio.