  We consider a multiple-input multiple-output (MIMO) relaying boardcast
channel in downlink cellular networks, where the base station and the relay
stations are both equipped with multiple antennas, and each user terminal has
only a single antenna. In practical scenarios, channel estimation is imperfect
at the receivers. Aiming at maximizing the SINR at each user, we develop two
robust linear beamforming schemes respectively for the single relay case and
the multi-relay case. The two proposed schemes are based on sigular value
decomposition (SVD), minimum mean square error (MMSE) and regularized
zero-forcing (RZF). Simulation results show that the proposed scheme
outperforms the conventional schemes with imperfect channel estimation.
