Space Time Block Coding In Frequency Selective Fading Channel

Multiple-input-multiple-output (MIMO), employing multiple antennas on both transmitter and receiver, can improve the system capacity and performance without expanding the bandwidth or increasing transmit power. Space time coding (STC) is the coding scheme based on transmit diversity that can reach MIMO performance. Space time block coding, according to orthogonal design at the transmitter, can apply the maximum-likelihood decoding algorithm at the receiver. Because of its simple coding and decoding architectures and good performance, it has been used as the standard of W-CDMA and CDMA2000. The traditional space time block codes are used in frequency flat channels, but the practical channels are almost frequency selective fading channels. Applying STBC in frequency selective channels is an important topic.Orthogonal frequency division multiplexing (OFDM), transforming high rate data transmission into lower rate transmission with multiple orthogonal sub-carriers, can eliminate frequency selective fading. OFDM has been taken as the physical layer standard of 5GHz WLAN, its application in mobile communication is imperative under the situation. Single carrier frequency domain equalization (SC/FDE), by employing equalization at the receiver, compared with traditional time domain equalization, is less complicated and has the same complexity as OFDM, and can conquer the disadvantages of OFDM. SC/FDE, together with OFDM, has been used as the air-interface standard of the next generation WMAN. Combined with OFDM or SC/FDE, STBC can be used in frequency selective fading channels.In the paper, firstly the characters of wireless channel are discussed and the frequency selective channel model is given. Secondly the STBC is introduced and the performance of STBC in frequency flat channel is simulated. Then the theory of OFDM and SC/FDE are described, and also the key technologies, such as channel estimation and equalization algorithm. At last, the performance of STBC in frequency selective fading channels is discussed. Both OFDM-STBC and SC/FDE-STBC are given the system architecture and concrete expressions. Simulation results show that SC/FDE-STBC performs better than OFDM-STBC.