  This paper is concerned with a wireless system operating in MIMO fading
channels with channel state information being known at both transmitter and
receiver. By spatiotemporal subchannel selection and power control, it aims to
minimize the average transmit power (ATP) of the MIMO system while achieving an
exponential type of average bit error rate (BER) for each data stream. Under
the constraints of a given fixed individual outage probability (OP) and average
BER for each subchannel, based on a traditional upper bound and a dynamic upper
bound of Q function, two closed-form ATP expressions are derived, respectively,
and they correspond to two different power allocation schemes. Numerical
results are provided to validate the theoretical analysis, and show that the
power allocation scheme with the dynamic upper bound can achieve more power
savings than the one with the traditional upper bound.
