Abstract

Present wireless communication systems uses FDMA, TDMA and CDMA techniques and are facing various issues like multipath fading, time dispersion which leads to inter symbol interference (ISI), lower bit rate capacity and less spectral efficiency. In a conventional terrestrial broadcasting, the transmitted signal arrives at the receiver through various paths of different lengths. Hence multiple versions of the signal interfere with each other and it becomes difficult to extract the original information. The use of Space Time Block Coded (STBC) Orthogonal Frequency Division Multiplexing (OFDM) technique provides better solution for the above issues. In this paper, we study the Bit Error Rate (BER) performance of STBC OFDM system employing BPSK, QPSK and QAM modulations. As STBCs have been derived from Generalized Complex Orthogonal Designs (GCOD), the norms of the column vectors are the same (e.g., Alamouti Code). We present an analysis of how multiple transmitting antennas and one receiving antenna produces reduced BER at lower value of SNR. From the simulation results, we observed that the BPSK allows improved BER performance over a noisy channel at the cost of maximum data transmission capacity. But the use of QPSK and QAM allows higher transmission capacity at the cost of slight increase in the probability of error.