The Application Of Space-Time Coding In OFDM System

Space-time coding (STC) based on MIMO (multi-input and multi-output) can increase the wireless communication system capacity and the data rate without additional system bandwidth and transmitting power. The application of STC in an OFDM system is studied in this dissertation.Three of the STC have been introduced. Space-time block coding (STBC) is one of the STC which is easy to decode. The performance of the STBC is analyzed and verified with different number of transmitting and receiving antennas by simulation, when the maximum likelihood decoding at the receiver is applied. It is shown that the space diversity can be acquired by increasing the number of transmitting and receiving antennas. But it has a limited range.To improve the performance of STC in a frequency-selective fading channel, the combination of STBC and orthogonal frequency division multiplexing (OFDM) technique is investigated, where the frequency diversity can be acquired. It is shown by the simulation that the signal to noise ratio (SNR) can drop about 3.5dB by the applying of STBC in an OFDM system provided the bit error of 10^-2.At last, in order to improve the coding gain, an STBC-OFDM system cascading the Low Density Parity Check (LDPC) coding is studied. It is shown by the simulation that the signal to noise ratio (SNR) can drop about 3dB by the applying of LDPC coding in a STBC-OFDM system provided the bit error of 10^-2.Both the frequency diversity and the space diversity have been acquired by the applying the MIMO-OFDM, LDPC can be used to get the coding diversity. All the techniques have been studied in this paper to get the good performance for the given system.