Capacity Analysis In MIMO-OFDM System Based On STBC

With the development of mobile communication development and increasementof the mobile users, spectrum resource is more and more limited, which make itdifficult to realize high speed data transmission. MIMO-OFDM technology is raisedon this background. A system will have a spatial diversity and frequency diversity if itcombines MIMO technology with OFDM technology, and it will combat multi-patheffect, and the noise interference.The MIMO-OFDM system will improvestransmission rate and communication capacity. The transmitting terminal in MIMOsystem can be process the signal with space time block coding, which increase systemreliability by using the time diversity. Therefore, combination of the space-time blockcoding and MIMO-OFDM technology can realize high speed data rate and reliabilityof the system.In order to realize transmission reliability and high data rate in wirelesscommunication system, this paper analyzes the MIMO-OFDM technology and putsforward the MIMO-OFDM system model. In communication system, whenorthogonal code is used the transmit antenna number can not more than two, or thetransmission rate will be less than one. When quasi-orthogonal code is used, it isimpossible to achieve full diversity gain.So a new kind of space-time block codingwhich with four transmit antennas is put forward to solve the above problem.Compared with existing code, the improved coding can realize full rate transmissionand full diversity gain, so the transmission performance is improved. Then, the newcoding method is applied in the MIMO-OFDM system, the system signal model andcapacity is analyzed.In the MIMO-OFDM system，the improved space-time blockcoding,the classic quasi-orthogonal coding and orthogonal coding capacity iscompared. The result shows that by using the improved space time block coding inMIMO-OFDM system,the capacity is bigger than the Alamouti code, which with twoantennas, and space-time block code. It also found that the capacity will improve withthe improvement of number of receiving antennas.