LAUSR

In this letter, a new diagonal and Alamouti space-frequency coded quadrature index modulation (DASFC-QIM) scheme for MIMO-OFDM systems is proposed to achieve higher transmit diversity. In the proposed DASFC-QIM scheme, firstly two modulated symbols are associated through a Hadamard matrix and a rotation matrix to construct a diagonal code. Next, by independently selecting the indices of the space-frequency units in each resource block (RB) twice, the in-phase and the quadrature components of the diagonal code are put into each RB. Finally, the signal in each RB is divided into two parts which are used to construct an Alamouti space-frequency code fitting for four transmit antennas. It can be proved that the DASFC-QIM scheme achieves the fourth order transmit diversity so that it achieves better bit error rate (BER) performance than some existing typical IM schemes. Simulation results show that DASFC-QIM exhibits superior BER performance over both the independent and correlated Rayleigh fading channels.