Spectral Efficiency of Closed-Loop Transmit Diversity with Limited Feedback for UTRA Long Term Evolution

Performance evaluation of closed-loop transmit diversity (CETD) for 3GPP UTRA long term evolution (ETE) is addressed in this paper. To reduce the feedback and keep comparable performance with optimum weighting, we reduce the feedback by means of quantization and subcarrier grouping. Theoretical analysis on loss of different quantization resolution and size of groups shows the tradeoffs between signalling overhead and performance. Although CETD can bring array and diversity gain, the interaction of CETD with some of the essential features of UTRA ETE system like adaptive modulation coding (AMC)-based time domain link adaptation and hybrid ARQ may affect the attainable spectral efficiency gain from CETD. In this paper, detailed link level simulation is carried out to investigate this interaction with two transmit antennas assuming one or two receive antennas. Simulation results show that the cell level gain is quite limited for CETD, in which only 9.8% and 18% gain is observed in micro- and macro- cell respectively with two receive antennas and a grouping size of 25