Pseudo-orthogonal multibeam-time transmit diversity for OFDM-CDMA

This paper proposes using a quasi-orthogonal (QO) full-rate space-time block code (STBC) and a fixed multibeam transmit array with low sidelobes for orthogonal frequency-division multiplexing code-division multiple access (OFDM-CDMA) downlink transmission. The proposed beam-time transmit diversity orthogonalizes signals between adjoining beams with a QO-STBC and suppresses unorthogonalized signals between separated beams with beam forming. Simulation results demonstrate that the proposed scheme retains orthogonality in narrow angular spread environments and provides two-beam diversity combining when a user is located between beams. In addition, the proposed scheme can alleviate multiuser interference (MUI) by allocating several users into different symbols in a QO-STBC matrix while assigning them all to the same spreading code