Space-time and space frequency diversity methods for mimo OFDM systems

Multipath fading affects the mobile wireless systems destructively. Diversity is a powerful tool to combat multipath fading. Diversity allows using less redundant data for forward error correcting codes and allows reducing complexity of the decoding algorithm.The transmitted signal arrives the receiver through many different channels by means of diversity. Diversity allows the total signal to noise ratio to stay at an acceptable level even if some of the channels have deep fading.Diversity can be applied at tranmitter, receiver or both side. Receiver diversity is not suitable for the mobile stations because of size and power limits. In this study we proposed new transmit diversity methods that allow utilizing four, eight or more transmit diversity order without reducing transmission rate. We also proposed the applications of the proposed methods for OFDM systems such as DVB-H and IEEE 802.20. We obtained and compared BER performances of the proposed methods and the other methods for the different applications and the parameters by computer simulations.Having systematicallay designable coding matrices is one of the advantages of the proposed techniques. On the other hand the proposed techniques can have lower detection complexity than OSTBC, QOSTBC and spreading diversity techniques. According to simulation results the proposed technique can perform better than the other techniques. The propsoed techniques can provide 11dB or more gain than compared transmitter techniques under some conditons.