Space-Time Block Coding Technology And Simulation Research In OFDM System

In the third-generation mobile communication system, Space-time coding technology is a new coding method to combat channel fading and improve system capability. It can obtain more coding gain and diversity gain when not to sacrifice the bandwidth. It improves the capability of the system and the performance of combating multipath fading. An new STBC technology and NSTBC-OFDM system combined with NSTBC technology and OFDM technology are studied in the thesis.There are six chapters in the thesis.Chapter 1 The background of the thesis and development of Space-Time Coding technology ,OFDM technology and MIMO technology are introduced.Chapter 2 The transmitting characteristic of mobile wireless channel is studied. The fading characteristic of multipath time-varying channel is analyzed. The system model of MIMO space-time channel is introduced and the capacity of MIMO system is studied.Chapter 3 OFDM system is studied.The basic theory of OFDM system is introduced. Application of IFFT/FFT in OFDM system and choice of cyclic prefix are analyzed.And the correlative technologies to OFDM system are introduced.Chapter 4 The encoding and decoding theories and performance of STBC are studied. Simulation results suggest Alamouti transmit diversity project and MRRC receive diversity project can obtain the same diversity gain. But when the whole power is same, the performance of Alamouti transmit diversity is worse than MRRC receive diversity project, which because compared with MRRC receive diversity project, the power from each antenna of Alamouti transmit diversity project is only a half. At the same time, simulation results indicate when the receive antenna numbers are same, diversity gain of STBC increase with the transmit antenna numbers increasing, when the transmit antenna numbers are same, the performance of STBC using complex orthogonal design is better than the real one, the performance of STBC with one-half transmit rate is better than the one with three-quarter transmit rate. An new STBC is studied. Simulation results indicate its performance is similar with STBC by BPSK modulate and better than STBC by QPSK modulate.Then the new STBC is generalized to multiple transmit antennas, and the coding matrix and simulation result are gained.Chapter 5 NSTBC-OFDM system scheme is proposed, and the system is studied. NSTBC has good performance in the plat fading channels and the spectral efficiency is high, but the actual wireless channels are frequency-selective fading channels, in this condition, design of NSTBC become complex. OFDM can convert a frequency-selective channel into a parallel collection of frequency-flat subchannels which are orthogonal, So NSTBC is studied in OFDM system in this chapter. The principle and performance of NSTBC-OFDM system is studied. It is proved that the performance of NSTBC-OFDM system is influenced by the product of the number of transmit antennas, the number of receive antennas and the number of multipath. Simulation results indicate that the performance of NSTBC-OFDM system is better than OFDM system which doesn't use NSTBC technology and the performance of NSTBC-OFDM system will be better with the number of receive antennas increasing.Chapter 6 The thesis is summarized and the work to do next is suggested.