Abstract: The era of entirely wireless, mobile communication is rapidly approaching.Increasingly; users are demanding versatile and convenient modes of communication along with high-speed broadband and technology in the premise of guaranteeing certain quality of communication without losing performance and efficiency. The challenges are to give users high-speed, high-performance in different channel conditions. So, Orthogonal Frequency Division multiplexing (OFDM) has been recognized as one of the most promising techniques to meet these challenges. Space Time block Coding (STBC) has drawn much attention in 4G wireless technologies just because of its decoding simplicity. This paper presents the performance evaluation of STBC-OFDM systems covering channel model and coding scheme, it includes Rayleigh fading channels by which it is observed that Bit Error Rate(BER) is reduced to achieve the high data rate.In this work, a performance criterion such as bit error rates for low SNR is analyzed. The BER for OFDM system over Rician fading channel is observed to be 0.1273.It has been reduced to 0.03919 over Rayleigh fading channel with Line of Sight (LOS) for the same Signal to noise ratio (SNR).

Keyword: Wireless Systems, OFDM, BER, STBC, MIMO, SNR.