In this paper, a mitigation method for minimizing the distortion caused by frequency selective fast fading is illustrated. The proposed system combines between two types of diversity schemes; frequency diversity represented by the orthogonal frequency division multiplexing (OFDM) scheme and antenna diversity represented by space time block coding (STBC) scheme these are for mitigating the distortion caused by frequency selective fading. The multiplexing technique proposed here is the code division multiple access (CDMA) scheme which is considered the solution for eliminating the distortion caused by fast fading. The main problem of the OFDM system is the high peak-to-average power ratio (PAR). In the proposed system, three techniques used for reducing the PAR are applied together. And in order to reduce the bit error rate caused by intersymbol interference (ISI) or multiple access interference (MAI) channel coding is applied which can make error detection and correction at the receiver and simulation results have shown that by applying any of channel coding techniques, the bit error rate (BER) has reached a satisfying level at a low signal-to-noise ratio (SNR).