On closed loop transmit diversity for HSDPA - using an orthogonality matrix for system level evaluations

The paper studies closed loop (CL) transmit diversity in combination with high speed downlink packet access (HSDPA). A potential problem with this combination is the reduced interference predictability which affects scheduling and link adaptation. To study this, the orthogonality factor (OF), which is used to model the intra-cell interference for single antenna transmission and reception, is augmented by an orthogonality matrix (OM), which is used for dynamic system level evaluations. The results indicate that the reduced predictability may decrease system performance in terms of cell throughput by approximately one third for a system employing multiuser diversity in a dispersive environment. However, by scheduling multiple users in a certain proposed way, interference fluctuations may be reduced, and results show that the performance may be improved. A simple spatial channel model is used so that the impact of fading correlation is considered as well.