| The MIMO (Multiple-Input Multiple-Output) system can be utilized to transmit data as well as to increase spectral utilization ratio without increasing the system bandwidth. Space-time code based on multiple antennas is an effective way to approach the MIMO channel capacity. Beamforming technology which comes of smart antenna is used to enhance the anticipant signal and restrain the interferential signal virtually by weighted processing on matrix datas. Enhancing the anticipant signal and restraining the interferential signal is its typical advantage, also is the base of implementing space division multiple access. OFDM technology converted high-rate data stream into the low-rate through serial-parallel transformation, and distributed it to many orthogonal subcarriers to transform so that the data bandwidth was reduced and frequency selective fading channel can be transformed into flat fading channel and the multi-path-fading can be resisted efficiently.Firstly, the essential theory of the MIMO system, capability of the system, multi-antenna diversity and transmit beamforming technology. Then space-time code and OFDM is introduced. Emphatically , the technology which combines beamforming used for restraining interference STC and OFDM is reached. And in MIMO-OFDM system, on the basis of existing space-time block coding ,a new space-time-frequency coding is designed for frequency-selective fading channels whose OFDM subcarriers'frequency response is repeat periodly. With data simulation, this code scheme has lager diversity gain and low BER . |
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