  Multiple-input multiple-output (MIMO) systems greatly increase the overall
throughput of wireless systems since they are capable of transmitting multiple
streams employing the same time-frequency resources. However, this gain
requires an appropriate precoder design and a power allocation technique. In
general, precoders and power allocation schemes are designed assuming perfect
channel estate information (CSI). Nonetheless, this is an optimistic assumption
since real systems only possess partial or imperfect CSI at the transmitter
(CSIT). The imperfect CSIT originates residual inter-user interference, which
is detrimental for wireless systems. In this paper, two adaptive power
allocation algorithms are proposed, which are more robust against CSIT
imperfections than conventional techniques. Both techniques employ the mean
square error as the objective function. Simulation results show that the
proposed techniques obtain a higher performance in terms of sum-rate than
conventional approaches.
