Effect of Imperfect Channel Estimation on Multi-User Beamforming in LTE-Advanced System

LTE-Advanced extends the number of transmit antennas of evolved NodeB (eNB) up to 8, which will provide substantial spatial degrees of freedom. However, the user is usually equipped with a small number of antennas due to space constraints. Thus, multi-user beamforming (MU-BF) was proposed to dramatically boost the spectrum efficiency by transmitting multiple users´ data on the same time-frequency resource. The co-channel interference (CCI) among users scheduled on the same resource can be eliminated by block diagonalization (BD); however, the performance of downlink MU-BF with BD relies on the accuracy of channel estimation to a great extent. Therefore, the effect of imperfect channel estimation on MU-BF for the downlink of LTE-Advanced system is studied in this paper. The reference signal targeting data demodulation (DM-RS) and uplink sounding reference signal (SRS) for deriving the downlink channel in TDD system are considered with different error models respectively. The estimation errors are modeled through link level simulations. It is shown that the imperfect SRS and DM-RS channels degrade the system performance in different degree through system level simulation.